Economic expenditures by recreational anglers in a recovering atlantic bluefin tuna fishery.

The recent return of Atlantic bluefin tuna to northern Europe following the recovery of the east Atlantic stock has sparked substantial public and scientific interest. This is particularly true for recreational anglers in Denmark, who often consider Atlantic bluefin tuna to be the catch of a lifetime. This attitude has previously sustained a substantial recreational fishery for bluefin tuna with annual tournaments in Denmark, which peaked in the 1950s before the subsequent collapse of the stock during the 1960s. Several scientific tagging programs have recruited recreational anglers in recent years to help catch and release tagged bluefin tuna. The anglers' investment of time and money in the scientific tagging projects indicate that the recreational fishery could recover in the future. However, the economic aspects of a potential future recreational bluefin tuna fishery remain unknown. We surveyed anglers participating in a scientific catch and release bluefin tuna fishery in Denmark across three years (2018-2020) and calculated the total annual expenditures associated with the activities. Additionally, we estimated the magnitude of the negative impact (i.e., incidental mortalities) on the bluefin tuna stock. Our results show that total annual expenditures by the recreational anglers approached 1,439,540€, totaling 4,318,620€ between 2018 and 2020. We found that recreational bluefin tuna anglers had mean annual expenditures directly related to the bluefin tuna fishing between 7,047€ and 2,176€ with an associated mortality impact on the stock of less than 1 tonne annually. By comparing the mortality impact to the expenditures, we estimate that each dead Atlantic bluefin tuna during the three study years generated 398,163€ in mean annual expenditures, equivalent to approximately 1636€ kg-1. Our study demonstrates significant economic expenditures among recreational anglers who target Atlantic bluefin tuna. This provides a clear example of how a recovery of marine natural capital and related ecosystem services can support development in the blue economy.

Introduction

The Atlantic bluefin tuna (Thunnus thynnus; ABFT) is an iconic and highly migratory species, which is among the most valuable fish in both commercial and recreational fisheries [1]. ABFT supported seasonal commercial and recreational fisheries near Denmark and in other parts of Scandinavia in the 1940s and 1950s, but by the first half of the 1960s, these fisheries collapsed, [2, 3]. Furthermore, the increasing global market demand for ABFT and resulting exploitation during the 1990s to early 2000s reduced ABFT biomass in the entire stock area (northeast Atlantic and Mediterranean) and raised concerns that the stock could collapse if exploitation was not reduced [4, 5]. The ABFT fishery is currently managed through the International Commission for the Conservation of Atlantic Tunas (ICCAT). To allow the stock to recover, ICCAT introduced a 15-year recovery plan in 2007 with reduced quotas for Contracting Parties [6]. Subsequent stock assessments have indicated a recovery of the stock with associated increases in quotas for the ICCAT member states [3]. In 2018, ICCAT adopted a management plan replacing the recovery plan [7], signifying a change in management strategy for the stock from recovery to sustainable exploitation. The recovery of ABFT has also been officially recognized by The International Union for Conservation of Nature (IUCN), which changed the status of ABFT from “Endangered” to “Least Concern” in September 2021 [8]. Following the recovery, ABFT has become more common in the northern part of its range, and, in 2016 and all subsequent years, several sightings of ABFT have been reported in Denmark [9] following more than 50 years when the species was seldom observed. In spite of considerable commercial and recreational fisheries for ABFT in Denmark up until 1950s [10], the fisheries had collapsed by the time the first quotas were allocated through ICCAT in 1992. Denmark and some neighboring countries (e. g., Sweden) therefore presently lack an annual quota allocation for either commercial or recreational fishing.

Nevertheless, the return of ABFT to Danish waters has sparked significant scientific and public interest. Similarly, the commercial fishing sector in Denmark has indicated an interest [11] in developing a consumption ABFT fishery if an adequate quota can be obtained in the future.

The importance of ABFT for the commercial fisheries sector is well established [e.g. 1], as also evidenced by global export-import arrangements for trade in the species. However, from an economic perspective there are indications that recreational fishing may provide larger economic benefits if ABFT are exploited by recreational anglers as a cultural ecosystem service rather than as for food (i.e. a provisioning ecosystem service) [12]. In Canada for example, recreational charter industry based on catch and release angling for ABFT was estimated to generate six times more revenue per tonne (t) compared to harvest based commercial fishing [13]. The global recovery of the stock has also coincided with a decrease in the commercial price at the final point of sale of ABFT, which has decreased by 47% from $67 kg-1 in 2012 to $37 kg-1 in 2018 [1]. While the recovery has resulted in increased quotas and tripled the total reported landings from 13,000 t in 2012 to 30,000 t in 2018, the end value of the commercial ABFT fishing sector has only grown from $870 million to $1.1 billion [1].

The scientific tag and release program (T&R program)

To understand the biological background for the recovery of ABFT in Scandinavia, a research project was carried out with tagging of tuna in the Skagerrak between 2017 and 2021. The project adopted a method for tagging ABFT involving rod and reel capture, similar to methods used by catch and release fisheries in the United States of America and Canada [14]. Voluntary anglers with adequate boats, gear and experience were recruited for the T&R program to catch ABFT, using conventional rod and reel tackle. More anglers than needed for the T&R program volunteered highlighting the high motivation in the angling community to fish for ABFT. The aim of the scientific T&R program was to gather data on the biology and migratory behavior of ABFT passing through Scandinavian waters.

From the anglers’ perspective, the fishing activities within the T&R program mimic catch and release fishing for ABFT in e.g. Croatia, the U.S.A, or Canada. This non-consumptive orientation is characteristic of ABFT anglers, and the more central ABFT fishing is to their lifestyle, the more likely they are to have a positive attitude towards catch and release fishing for ABFT [15]. Catch and release fishing for ABFT relies on the experience of catching ABFT as the primary source of interest and associated monetary spending, and mortality of ABFT is incidental rather than intentional. Incidental mortality of catch and release ABFT angling using rod and reel has been found to be low, typically ranging from 0% to 5% (Table 1), enabling recreational catch and release to have a minimal impact on the ABFT population.

Table 1

Mortalities of ABFT caught and released using rod and reel.

[14, 16–22]. Mortality in % is calculated based on the number of ABFT tagged minus the number of nonreports divided by the number of mortalities. Mortality categories include mortalities immediate (e.g. at-vessel), post-release mortality, both or none if no mortalities were observed. Both immediate and post-release mortality were counted when calculating the mortality percentages.

	ABFT tagged (#)	ABFT without non-report	Mortalities (#)	Mortality (%)	Mortality category	Non-report (fate unknown)
Block et al. (1998)	37	35	0	0	None	2
Lutcavage et al. (1999)	20	17	0	0	None	3
Stokesbury et al. (2004)	35	32	1	3.1	Immediate	3
Wilson et al. (2005)	68	60	1	1.7	Immediate	8
Stokesbury et al. (2007)	6	3	0	0	None	3
Galuardi et al. (2010)	41	36	0	0	None	5
Stokesbury et al. (2011)	60	56	3	5.4	Both	4
Marcek & Graves (2014)	20	20	0	0	Post release	0

Similar to the assessment of many other marine cultural ecosystem services [23], the economic impacts related to ABFT angling in Scandinavia is presently unknown, but could be important for the region’s economy, comparable to the situations in North America [24, 25]. To estimate the economic potential of a future recreational ABFT fishery in Scandinavia, we therefore studied angler behavior and expenditures associated with the recreational fishing involved in the Scandinavian T&R program across three years (2018–2020). Specifically, the aim of this study was to determine the economic potential in the recovering recreational ABFT fishery in Scandinavia by evaluating the expenditures of recreational ABFT anglers associated with the T&R program. To this end, the Scandinavian T&R program was studied as a proxy for a future catch and release program.

Methods

“Ethics statement

The study involved interviews with volunteers and gathered information was kept confidentially. No medical records or archived samples were used in our study. All data was anonymized. Our study included no patients. No animals were used in our study as our study was concerned with economic expenditures of people involved in recreational activities. No anesthesia, euthanasia or any kind of animal sacrifice was covered by our study. Given this set-up for the research, we decided that committee approval for our study was not necessary.”

Recreational angling is in this context defined as a form of recreational fishing in which participants, known as anglers, use fishing rod, reels, hook and line to catch fish. Catch and release also known as live release angling is a mode of recreational angling where some or all of the fish caught are released alive and the aim of the activity is partly or exclusively experiential rather than consumptive. Motivations for recreational angling includes challenge, achievement, sport, recreation, relaxation, social activity etc. [26].

Angler participation in the T&R program

The Scandinavian fishing for ABFT took place exclusively as part of a T&R program which aimed to capture, tag and release ABFT [27]. The fishery was organized by a research team from the Technical University of Denmark who directed the fishing activities, including the timing and duration of each season (defined as the time from August-September in each year in which ABFT could take place), the fishing area, minimum gear and vessel requirements and number of participants. The ABFT fishery was therefore confined to a specific group of official participants, with no other ABFT fishing allowed in Denmark. Formal permission for the fishery was obtained from ICCAT and relevant national authorities in Denmark; the latter were also responsible for ensuring compliance with the fishing regulations. The framework adopted to manage the fishery in the context of the T&R program was largely based on the recreational fishing regulations for catch and release fishing for ABFT in Canada [28] and included the exclusive use of circle hooks, and appropriately sized fishing gear. The fishing tackle used for ABFT fishing, including rods, reels, line, hooks etc. are highly specialized. Anglers were recruited for the T&R program based on their previous experience fishing for ABFT or other large game fish species (e. g., yellowfin tuna (Thunnus albacares), and billfish (Istiophoridae)) in other parts of the world. Only anglers adhering to minimum gear requirements (e.g. the use of circle hooks and 130 lbs. test line), and with appropriate vessels for the type of fishing were allowed to participate. Participating anglers were responsible for their own expenses related to their participation in the ABFT fishery. Anglers decided themselves how much time and money they wished to allocate to fishing for ABFT as long as the minimum gear requirements were met. There are no other recreational fisheries in Denmark which rely on the specialized equipment and fishing methods used to fish for ABFT. For this reason, anglers cannot reuse equipment they already own and use for e.g. salmon fishing. The anglers would thus have to invest in specialized tuna fishing gear to participate in the fishery even if no minimum gear requirements were enforced by the tagging project. Therefore, we assume that the expenditures related to ABFT fishing within the T&R program reflect expenditures that would have occurred if there had been an open recreational ABFT catch and release fishery of comparable size and format as those in other regions (e.g. Canada, U.S.A or Croatia).

The COVID-19 pandemic was ongoing during the ABFT fishing activities under the T&R program in Denmark in 2020. The fishing took place in August-September at a time with only few restrictions on the free movement and behavior of residents in Denmark, and no restrictions related to the pandemic applied specifically to the ABFT anglers or the fishery.

Survey

The expenditure survey (See S1 File) was designed based on the Recreational Fisheries Economic Impact Assessment Manual published by the Food and Agriculture Organization of the United Nations [29]. We developed the methodology and survey based on previous expenditure surveys applied to recreational fisheries [30-33]. Questions addressed individual recreational anglers’ monetary expenditures specifically related to the ABFT angling including travel, accommodation and investments in angling equipment. Additional questions addressed personal characteristics and behavior of the respondents, including age, time spent angling for ABFT, travel, and gross annual income. The survey targeted all ABFT anglers with permits to fish for ABFT from 2018–2020, which amounted to 302, 500 and 600 ABFT anglers (sampling units) in 2018, 2019 and 2020 respectively. Previous studies [30, 31, 34, 35] have highlighted that this type of survey represents an effective method of obtaining economic data in similar contexts.

To administer the survey via email to ABFT anglers in Denmark, it was necessary to establish contact with them individually. To obtain their email addresses we attempted to contact anglers in three different ways. 1) Face-to-face at the point of access during the fishing (harbor), 2) via telephone numbers provided by the T&R program, and 3) via an open call in a Facebook group for Scandinavian ABFT anglers. We were only able to perform face-to-face contact at the point of access in 2018 due to logistical limitations in 2019 and 2020. Upon contact, ABFT anglers were asked if they were willing to participate in the survey and, if they were, we asked an email address to which we subsequently sent the survey. There was full and unconditional consent from all interviewees and all contributions were delivered voluntarily. There was no reward for the participation in our study. Information was gathered both verbally and in written form. No minors were included in any parts of the study, including the interviews. In 2018, 2019 and 2020 the questionnaire was sent out immediately after the angling ended (September-October) to reduce recall bias [29]. Two weeks after administering the surveys, a SMS reminder to fill out the survey was sent to the participants. Partial survey responses were discarded. Respondents reported expenditures in Danish kr. (DKR) and an exchange rate of 7.45 DKR €-1 was used to convert the expenditures to euros (€).

Angler categories

Our approach corresponds to the approach used by Morales-Nin et al. [33], and we separated respondents into two groups, as anglers owning or co-owning boats and anglers having no ownership in the boats (hereafter “regular” anglers) have significantly different costs related to angling. The total number of anglers owning boats and regular anglers in each year was provided through the registration to the T&R project, and therefore the relative proportion of regular anglers to anglers owning boats could be determined for each year.

Behavior

Mean values of time spent ABFT fishing, mean distance travelled related to ABFT fishing, annual income and similar metrics available via the survey were used to reveal demographic and behavioral characteristics.

Expenditures

The expenditures reported by the survey respondents were raised to the total number of permit holders in the recreational fishery for ABFT by multiplying the annual mean expenditures of regular anglers and anglers owning boats separately with the total number of regular anglers and anglers owning boats participating in the recreational tuna fishery in each year (2018–2020).

Impact on the stock

The ICCAT management plan [3] for ABFT regulates the total allowable catch in tonnes and includes estimates of the entire biomass in the stock area (northeast Atlantic Ocean and Mediterranean Sea). The biomass of ABFT due to incidental mortality from a recreational catch and release fishery will give an indication of its impact on the stock. Researchers from the T&R program recorded immediate (observed) mortalities during the fishing activities as well as known and presumed post-release mortalities (based on tagging data and individual condition upon release). We calculated a relative mortality rate of recreationally caught ABFT by dividing the total number of immediate and post-release ABFT mortalities in the T&R fishery by the total number of ABFT caught each year. We derived upper and lower confidence limits (Cl) of the mortality estimates in each year using the Clopper-Pearson binomial proportion method [37]. The resulting mortality of ABFT in the recreational fishery applied in our calculations was 4.35% (95% CL: 2.54, 6.97). We multiplied the mortality estimates with the total number of ABFT caught in each year to estimate the number of ABFT that may have died incidentally in each year as a direct result of the recreational angling and scientific tagging activity. The estimated absolute number of ABFT lost due to incidental mortality was multiplied with the mean weight of ABFT caught in each respective year to estimate the mortality impact on stock biomass. All tunas were length measured on a platform on the stern of a tagging vessel by researchers from the T&R program: lengths of tunas caught were measured as curved fork length (CFL). We converted measures of individual curved fork length (to nearest 1 cm) to straight fork length (SFL) using SFL = 1.7959 + 0.9517 x CFL and estimated individual body mass in kg (W) using W = 0.0000350801 x SFL2.878501 [38]. The status and condition of the tunas during measuring and tagging were closely monitored by the tagging crew and health indicators including bleeding, inactivity or injury were recorded. These observations were subsequently used to evaluate the likelihood of post release mortality caused by the catching and subsequent release of the tunas. Tunas with significant bleeding, injury or inactivity upon release were presumed dead. The results were used to estimate the total mass of the tunas that died incidentally as a consequence of the recreational angling on an annual basis. Expenditures tuna-1 and kg-1 of tuna due to mortality were calculated by dividing total expenditures in each year with the estimated total number and total biomass of ABFT, respectively, due to incidental mortality within the same year. The annual values of expenditures tuna-1 and kg-1 were then averaged across years to derive an estimate for the 3-year period. In addition, we summarized the literature for reported mortalities of ABFT caught using recreational fishing methods (Table 1).

Results

Expenditures

A total of 302, 500 and 600 ABFT anglers were registered as participants in the fishery in 2018, 2019 and 2020 respectively. Of these a total of 219 agreed to participate in the expenditure survey. The survey yielded a total of 131 valid survey responses with a response rate of 57%, 47% and 72% in 2018, 2019 and 2020, respectively (Table 2). The total estimated expenditures of ABFT anglers in Denmark from 2018–2020 was 4,318,620€, resulting in total average annual expenditures of 1,439,540€. Individual anglers owning boats spent an annual average of 7,047€ on ABFT fishing, which is substantially more than individual regular anglers not owning boats, who spent an average of 2,176€ annually. Due to the higher total number of regular anglers, the total annual spending was higher for regular anglers at 779,974€ than anglers owning boats who had total annual spending of 659,567€. The largest categories of spending was fishing gear, boat expenses and fuel accounting for 27%, 13% and 12% of total expenditures, respectively (Table 3).

Table 2

Key results of the from the survey of ABFT anglers from 2018–2020 including total numbers of participants in the ABFT fishery in the categories of regular anglers and anglers owning boats.

Mean and total annual expenditures in Euro for regular anglers and anglers owning boats with lower and upper [L U] 95% Confidence limits (Cl) for expenditures based on the mortality estimates derived according to Clopper and Pearson (1934) [36]. Mortality includes both immediate and post-release mortality.

	2018	Cl 95% [L U]	2019	Cl 95% [L U]	2020	Cl 95% [L U]		Cl 95% [L U]
Total number of participants	302	-	500	-	600	-		-
Regular anglers	227	-	400	-	475	-		-
Anglers owning boats	75	-	100	-	125	-	Total	-
Participants interviewed	53	-	83	-	83	-	219	-
Survey responses regular anglers	12	-	11	-	21	-	44	-
Survey responses anglers owning boats	18	-	30	-	39	-	87	-
Survey responses (total)	30	-	41	-	60	-	131	-
Response rate	57%	-	49%	-	72%	-
							Mean
Number of tuna caught	104	-	56	-	116	-	92	-
Mean individual weight of tunas caught (kg)	234	-	240	-	260	-	245	-
Mortality total (%)	2.88	[0.75, 6.96]	5.36	[1.66, 14.78]	5.17	[2.28, 9.95]	4.35	[2.54, 6.97]
Mortalities (# of deceased tuna)	4.5	[2.64, 7.25]	2.4	[1.42, 3.90]	5.1	[2.95, 9.09]	4	[2.34, 6.41]
Incidental mortality (t)	1.1	[0.6, 1.7]	0.6	[0.3, 1.0]	1.3	0.8, 2.1	1.0	[0.6, 1.6]
Mean expenditures (€) regular anglers	2,356	-	2,355	-	1,817	-	2,176	-
Mean expenditures (€) anglers owning boats	10,734	-	5,085	-	5,321	-	7,047	-
Expenditures (€) kg-1	1,263	[788, 2,163,]	2,481	[1,549, 4,249]	1,080	[727, 1,995]	1,636	[949, 2,516]
Expenditures (€) dead tuna-1	296,173	[184,843, 507,226]	595,465	[371,631, 1,19,792]	302,850	[189,10, 518,661]	398,163	[224,493, 616,31]

Table 3

Total annual expenditures in EUR by category for regular anglers and anglers owning boats exclusively related to recreational fishing for ABFT as part of the T&R program.

	2018		2019		2020
Category	Anglers owning boats	Regular anglers	Anglers owning boats	Regular anglers	Anglers owning boats	Regular anglers
Angling gear	192,796	125,757	141,119	365,324	176,774	155,026
Tackle	66,421	133,557	52,421	70,861	79,533	86,934
Bait	6,946	19,501	1,790	6,935	1,874	7,661
Boat expenses	212,763	6,925	60,913	91,107	106,199	91,539
Boat equipment	166,672	1,108	89,485	65,884	59,033	58,546
Harbor costs	8,781	19,667	17,173	24,279	34,291	25,154
Other equipment	6,890	16,897	9,253	22,707	17,192	50,976
Fuel	77,297	95,538	53,505	120,176	75,459	111,929
Accommodation	31,482	27,700	25,378	36,353	35,470	75,609
Transport	12,930	20,775	11,329	32,550	27,121	33,907
Public transport	1,398	2,770	0	5,034	172	6,376
Souvenirs	979	3,739	3,284	8,166	3,599	3,289
Food and drink	15,296	53,184	25,982	80,397	31,109	116,556
Additional	4,362	7,756	16,911	12,237	17,318	39,533
Total expenditures	1,339,887		1,450,552		1,528,182

Demographics

The mean age of all respondents was 51, 51 and 52 years of age in 2018, 2019 and 2020, respectively. The anglers were predominantly male with 97%, 93% and 93% of respondents identifying as male in 2018, 2019 and 2020, respectively. Anglers owning boats and regular anglers had mean annual income before taxes of 85,748€ and 84,064€; consequently, anglers owning boats spent on average 8.2% of their annual pre-tax income on recreational ABFT fishing while regular anglers spent 2.6%. The mean value of the individual boats participating in the fishery was 73,467€. Anglers with and without boats were predominantly (92%) non-local residents, here defined as those living outside the postal zip code of the point of access (Skagen) or a neighboring zip code to the point of access for the fishing. This pattern is also reflected in the mean distance travelled by each angler related to the fishery reaching 1,213 km annually.

Angler behavior

In 2018 and 2019, the recreational angling year for ABFT was limited to a 14-day period, whereas in 2020, the angling year was limited to a 16-day period. Weather conditions restricted the fishing within these periods with anglers being prevented from fishing due to weather an average of three days in 2018, and seven days in both 2019 and 2020. Anglers reported fishing for ABFT an average of six days in 2018 and 2019 and an average of five days in 2020, spending an average 9.9 hours fishing pr. fishing day. Anglers reported sailing an average of 340 nautical miles pr. year during the ABFT fishing. Anglers predominantly chose to stay in the Skagen area on bad weather days, spending an average of nine days in Skagen (entry point to the fishery) pr. season in all three years. In addition, anglers spent 70, 75 and 52 hours on preparation before the fishing activities in 2018, 2019 and 2020, respectively. No respondents reported any time spent targeting other species of fish during the period apart from catching baitfish intended for ABFT fishing. The average number of anglers on board each boat was three in 2018 and four in 2019 and 2020. In total, 73% of anglers reported experiencing catching ABFT personally, or as part of a team effort, in 2018 and 2019 whereas 77% did so in 2020. The corresponding number of ABFT caught pr. angler pr. season was 1.9, 1.5 and 2.1 in 2018, 2019 and 2020 respectively. However, multiple anglers usually take part in catching each ABFT, and so more than one angler experienced catching the same ABFT (although the ABFT was only caught once).

Impact on the stock

A total of 12 ABFT were lost due to incidental mortality caused by the recreational fishery. The total number of ABFT caught from 2018–2020 was 276 fish, giving a mortality of 4.35% (95% CI = 2.54, 6.97%, corresponding to a range of 7–19 individuals). Of the 276 ABFT caught, 104, 56 and 116 were caught in 2018, 2019 and 2020, respectively, giving an average annual catch of 92 ABFT. The mean size of ABFT caught in each year was 245 cm, 247 cm and 254 cm (CFL) corresponding to weights of 234 kg, 240 kg and 260 kg in 2018, 2019 and 2020, respectively. The resulting biomass of ABFT attributed to incidental mortality related to the recreational fishery and associated tagging efforts from 2018–2020 is 1 tonne annually (95% CL = 0.6, 1.6).

Discussion

We surveyed recreational anglers participating in a scientific ABFT fishery and analyzed their expenditures in the period from 2018–2020. Our survey design was based on previous studies of economic expenditures in recreational fishing and we applied it to a substantial recreational ABFT fishing sector which has supported the T&R program in Denmark. The first ABFT was caught in Denmark in 2017 after nearly 60 years of absence, and our results indicate that the angling sector has responded with a dramatic increase in number of ABFT anglers and spending associated to the fishery during the subsequent years. Over a period of three years we contacted 219 ABFT anglers and received 131 expenditure survey responses from both regular anglers and anglers who owned or part-owned the boats from which the fishing was performed.

Our survey revealed an annual average of 1,439,540€ of expenditures associated with ABFT angling during the period. In comparison the entire Danish angling sector without ABFT fishing totals 387€ million annually but the average angler only spends 336€ annually [39] which is six times less than the amount spent on ABFT angling by regular anglers and 20 times less by anglers owning boats. This indicates that fishing recreationally for ABFT has much higher associated costs than the average type of recreational fishing activities in Denmark.

Our study indicates that Danish ABFT anglers spent an average of 2.5–8.2% of their annual pre-tax income on recreational ABFT fishing and allocated an average of 10 days per year in order to participate in the fishery. Both numbers suggest strong motivation among participating anglers for ABFT fishing. Expenditures in ABFT fishing are even higher than boat fishing for Atlantic salmon (Salmo salar) and sea run brown trout (Salmo trutta) which has traditionally had the highest levels of expenditures by anglers in Denmark [39]. Anglers participating in salmon and sea run sea trout fishing had annual expenditures of 2826€ angler-1 equivalent to 6.2% of their annual income [39] which is slightly more than the 2,176€ spent annually on ABFT by regular anglers, but less than half of the amount spent on ABFT by anglers owning boats. This makes ABFT the type of fishing in Denmark with the highest associated annual expenditures by anglers.

When sending out the questionnaire we had no knowledge whether the anglers had ownership in a boat or were regular anglers. Unfortunately, we received a lower number of responses from regular anglers than anglers owning boats and the sample size for the regular anglers is lower than we hoped, totaling 44 responses and with 2018 having the lowest number of 11 responses. We attempted to recruit more regular anglers to respond to the survey through the open Facebook call but received only four responses. One explanation for the bias in number of responses towards boat owners is that they are more interested in ABFT fishing in general and, as a consequence, were more likely to respond to the survey. As we separate the groups of regular anglers and anglers owning boats in our analysis, we therefore see higher confidence in the expenditures for boat owners compared to regular anglers. As the sample size for regular anglers is small, there is a possibility that the actual total expenditures in the group of regular anglers could be lower or higher than those we found.

Rather than relying on ABFT as a consumable commodity, a recreational catch and release fishery is based on the value anglers are willing to attribute to the activity. This attributable value is experiential rather than consumptive, and likely has both an individual as well as a social character for the involved recreational fishers, given that multiple anglers typically participated on the same boat in catching the same individual ABFT during the effort to get the tuna to the boat. Similarly this indicates that most or all the expenditures paid by multiple anglers is derived from the experience of catching relatively few ABFT. As a result, it is relevant to scale the economic impact of the fishery with the number of participants acquiring an experience of fishing for and catching an ABFT rather than the number of tunas caught. In the commercial fishery for Eastern Atlantic BFT higher landings does not necessarily mean higher revenue as a rapid increase in total allowable catch resulting in an increase in supply will negatively affect the price of ABFT as a market commodity [40].

The mortality resulting from recreational catch and release fishing for ABFT was 4.35%, which is comparable to mortalities reported in the literature for this type of fishing activity. By comparing the mortality and the expenditures, each deceased ABFT was on average associated with 398,163€ in expenditures equivalent to 1,636€ kg-1. Expenditures kg-1 of deceased ABFT is four times higher than trout and salmon which are the most popular target species of recreational angling in Denmark constituting 47% of the Danish angling sector [39], which generate expenditures of 353€ kg-1 [41].

The recovery of ABFT in Scandinavian waters represents a similar economic opportunity as the recreational ABFT fishery which developed near Hatteras, North Carolina in the 1990s. In 1996, this newly emerged fishery had 2,900 boat trips targeting ABFT where there had been none just a few years before [25]. In 1997, just three years after the fishery emerged near Hatteras, expenditures by ABFT anglers resulted in a total impact of $4,627,108 and $5,032,870 on the Hatteras-area economy and North Carolina economy, respectively, resulting in 126 full and part-time jobs attributed to this fishery in 1997 [25]. The expenditures we present here are directly related to the activity of fishing recreationally for ABFT. As this activity has not previously been possible in Denmark for several decades due to the long period of rarity of ABFT and lack of quota, it follows that the related expenditures represent mainly new economic activity.

Anglers were not limited by restrictions due to COVID-19 during their participation in ABFT fishing in the 2020 season and it is likely that their related expenditures where not inhibited during the period. On the contrary, the lack of available options for recreation in the time up to the ABFT season e.g. travelling abroad for holidays, may have restricted spending on other goods and services, allowing savings to be spent on ABFT fishing instead, resulting in higher spending than under normal conditions.

We assumed an averaged overall mortality of 4.35% for the captured and released tunas to derive an estimate of the expenditure per deceased tuna, and to enable comparison of this indicator with those in other regions where ABFT is exploited in catch and release or tag and release fisheries. The fish caught in the Danish tagging project were captured, tagged, sampled and released. It is possible that mortalities in such a fishery could be higher than in a catch-release fishery without tagging. However, most rod-reel based estimates of ABFT mortality have been obtained in catch-tag-release fisheries. In such fisheries, ABFT are often handled more after capture e.g. mounting tags, taking tissue and blood samples etc. [14, 21, 42] than would be common in a catch and release recreational fishery without tagging. ABFT mortalities may depend on the angling method. In particular, the use of circle hooks lowers the mortality [43]. If the anglers follow proper handling practices, it is therefore likely that incidental mortality in a catch and release recreational fishery could be lower than the numbers reported in scientific tagging studies (Table 1).

Assuming a 4.35% mortality, the total estimated loss of ABFT due to incidental mortality during the study period of three years was 3t, (i.e. one t per year 95% CL = 0.6, 1.6). When comparing the annual mortalities here, including the upper 95% CI estimate, with the total allowable catch of ABFT in the northeast Atlantic of 36,000t in 2020–2022 [10], it is evident that a substantial recreational sector could develop in Denmark and likely other parts of Scandinavia if a small quota was allocated for this purpose.

In support of previous studies [25, 44], the study indicates that recreational angling for ABFT presents an emerging opportunity for economic development in the areas where tuna populations have recovered. We expect that the future potential for economic activity in a recreational ABFT fishery will likely be much higher if the sector can develop beyond the scope of scientific tagging projects. There are multiple restrictions enforced by the tagging projects which likely decrease the level of expenditures and participation associated with recreational ABFT fishing. 1) The number of anglers is limited by the tagging project operations, and in all years, several anglers were not able to participate even though they indicated their interest by applying for the tagging projects. 2) The fishing season is restricted by the tagging projects, and in this case, anglers were only allowed to fish for ABFT a maximum of 14 days in 2018–2019 and 21 days in 2020. Even though anglers may prioritize their participation in the fishery within this period, many anglers indicated that they would fish for ABFT beyond the timeframe of the tagging projects if allowed to do so. 3) The tagging projects restricted the possibility for charter operations to offer ABFT fishing as a service. Charter fishing for ABFT could likely develop into a significant sector if allowed to do so. 4) The tagging projects recruit almost exclusively local anglers. This, in addition to the lack of a charter fleet, effectively inhibits the development of a tourism sector based on recreational ABFT fishing. Big game fishing including fishing for ABFT is an important sector of tourism demonstrated by the fishery in North Carolina (U.S.A.) where just 15.6% of anglers where local residents, and charter trips outnumbered private trips by nearly a factor of three [25]. A selection criteria for participating in the ABFT fishery was experience in ABFT or similar big game fishing which means that the Danish anglers themselves have previously traveled abroad for this activity. In addition to increasing economic activity by attracting non-local anglers and thus increasing the total number of participants in the fishery, non-locals also generate more new revenue in the local economy as opposed to locals who to a greater degree could be expected to shift their expenditures from one sector (or fish species) to another. From a policy perspective, the present study provides a successful example of how marine conservation actions aimed at restoring lost or reduced biodiversity (e. g., the ICCAT recovery plan), could support economic development, which is a combined policy target in several European strategies related to the Blue Economy and biodiversity protection [45, 46]. Additionally the economic estimates suggests that utilization of ABFT as provider of primarily cultural ecosystem services (recreational experiences) rather than provisioning service (commercial harvest of food), may be preferable from an economic development perspective, which resonates with policy goals related to decoupling economic growth from biodiversity exploitation and loss, as highlighted by e.g. the European Green Deal [46]. The substantial spending by ABFT anglers across a variety of goods and services combined with low mortality associated with recreational catch and release methods allows economic activity with a low impact on the ABFT stock in the form of incidental mortality. The present study showcases the potential economic benefits associated with recovering iconic marine fish stocks by providing the basis for low impact recreational angling.

Conclusions

This study indicates that recreational catch and release angling for ABFT in Northern Europe presents an attractive economic opportunity with low associated mortality and impact on the stock. The high level of effort and expenditures required to participate in the fishery under the management of the T&R program demonstrate a basis for the potential development of a considerable recreational ABFT fishing sector, assuming quotas are available. These data provide a new scientific and economic basis for policy makers and managers seeking to manage the different options for exploiting ABFT fisheries in Northern Europe sustainably. Presently the case of ABFT recovery provide an example of likely economic benefits from successful restoration of marine biodiversity and its related ecosystem services.

(DOCX)

Click here for additional data file.

(XLSX)

Click here for additional data file.

3 Feb 2022

2 Jun 2022

PONE-D-21-36689

Economic expenditures by recreational anglers in a recovering Atlantic bluefin tuna fishery

Response to Editor

Dear Editor,

We would like to thank you and the reviewers for your highly constructive comments. We have found them very useful and they have helped to improve clarity and transparency of our methods, interpretations and conclusions. We have made several changes to the text and calculations to address these comments and issues. We believe that the manuscript is now sharper and easier for readers to understand and follow. Below we present detailed responses to the general and specific comments.

We hope that our manuscript may be suitable for publication in PLOS One and look forward to your decision regarding publication at earliest convenience.

Sincerely

Kristian Maar (on behalf of the co-authors)

#1

From the economics perspective, there is confusion between economic value and economic expenditure. Other technical problems concerning fisheries economics have been reported by one reviewer.

Response:

We have considered the comments about economic value and economic expenditure/impact and have changed the manuscript accordingly. In order to clarify we have changed the phrasing or removed the mentions of economic value. Following the comments of reviewer #2, we have changed the comparisons between value and impact. The technical problems concerning fisheries economics have also been addressed – see specific replies in the individual responses below.

#2

Another reviewer has raised several issues about the estimation of mortality rates and its use, and recommends clarification about mortality (e.g., types and sources of mortality). The paper could be improved by including a statistical framework.

Response:

We fully agree that the estimation of mortality was not presented clearly. To address this issue, we have changed the sections regarding mortality estimation and clarified how we estimate it and how it is used. See specifics below. We have also followed the recommendations to regarding estimation of uncertainties by deriving 95% upper and lower confidence limits for the mortality rates, and subsequently used these to derive the likely range of economic expenses and impact on the tuna population. Details of the method and results are provided in the manuscript, and in the individual responses below.

#3

The manuscript needs a number of additional minor revisions and a careful revision of the English language.

Response:

We have carefully read and addressed all the comments from the reviewers. For each minor revision and language/grammar suggestion, we have followed the reviewers’ suggestions and provide a detailed account of the resulting changes in the manuscript below. We have had the revised manuscript proof-read by a native English speaker to improve the language.

Additional requirements

When submitting your revision, we need you to address these additional requirements.

1. Please ensure that your manuscript meets PLOS ONE's style requirements, including those for file naming. The PLOS ONE style templates can be found at

https://journals.plos.org/plosone/s/file?id=wjVg/PLOSOne_formatting_sample_main_body.pdf and

https://journals.plos.org/plosone/s/file?id=ba62/PLOSOne_formatting_sample_title_authors_affiliations.pdf

Response:

The file names in the resubmission now follow the PLOS ONE style requirements.

2. We note that the grant information you provided in the ‘Funding Information’ and ‘Financial Disclosure’ sections do not match.

When you resubmit, please ensure that you provide the correct grant numbers for the awards you received for your study in the ‘Funding Information’ section.

Response:

The funding information in the manuscript L470-472 has been updated to include the sentence “The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.” It now matches the ‘Financial Disclosure’.

3. We note that Figure 1 in your submission contain map images which may be copyrighted. All PLOS content is published under the Creative Commons Attribution License (CC BY 4.0), which means that the manuscript, images, and Supporting Information files will be freely available online, and any third party is permitted to access, download, copy, distribute, and use these materials in any way, even commercially, with proper attribution. For these reasons, we cannot publish previously copyrighted maps or satellite images created using proprietary data, such as Google software (Google Maps, Street View, and Earth). For more information, see our copyright guidelines: http://journals.plos.org/plosone/s/licenses-and-copyright.

Response:

The map figure has been removed from the submission.

4. Please review your reference list to ensure that it is complete and correct. If you have cited papers that have been retracted, please include the rationale for doing so in the manuscript text, or remove these references and replace them with relevant current references. Any changes to the reference list should be mentioned in the rebuttal letter that accompanies your revised manuscript. If you need to cite a retracted article, indicate the article’s retracted status in the References list and also include a citation and full reference for the retraction notice.

Response:

The reference list has been reviewed and is now correct.

Reviewers’ comments

Reviewer #1: General comments

The document presents an estimation of the potential expenditures of a recreational catch and release fishery for Atlantic bluefin tuna and the amount of bluefin tuna mortality it would imply.

The procedure is simple (an estimation of the average expense multiplied by the number of anglers and relate it to the number and weight of tuna estimated to die in the catch, tagging and release operations) and the conclusions are clear. I am not familiar with this type of studies but, in spite of its simplicity, it provides a clear an interesting message: catch and release fisheries can be a source of income more profitable than extraction fisheries by providing an alternative type (non-lethal) of ecosystem services.

In general, there are only a couple of moderately important issues that need further explanation and exploration:

Reviewer 1:

- Mortality: There are usually two types of mortality in tag and release studies: an immediate mortality (the fish is dead, or almost dead when hauled on-board) and a post-release mortality (that takes place when a fish is released seemingly in good conditions but ends up dying). It is not clear the rates the authors have used. Furthermore, in L. 233 the authors indicate they used a 5% mortality based on previous studies, but the numbers shown in table 2 are not in agreement with these percentages and, in L. 305 the authors mentions they obtain an estimate of mortality of 4.5%. It is confusing throughout the document how mortality has been computed and the values that have been used in the different calculations.

Response:

This point has been carefully evaluated as there are multiple points of confusion about the mortality estimates in the manuscript. The reason for the confusion is in part rounding errors and a poor explanation as the reviewer mentions. The manuscript has now been corrected and the correct mortality of 4.35% is used consistently throughout. For clarification we have added a paragraph explaining the mortality observations (243-248). We have also clarified how the mortality is used for the different calculations (L251-258). We believe that these changes have improved how we estimate and use the mortality rates

Reviewer 1:

It is important to describe the sources of mortality and clarify if the values in tables 1 and 2 correspond to at-vessel, post-release or total mortality. In my opinion, a good estimate of total mortality should include the number of tuna dead during the hauling plus the number of tuna released alive multiplied by a literature-based estimate of post-release mortality.

Response:

Agree that this needs to be more clearly described. We have made changes to the text to address this point. Please see also our reply to the previous comment.

Reviewer 1:

Also, as will be explained further below, I was not able to reproduce the expenditure estimates shown in table 2.

Response:

The values presented in table 2 have been corrected. For further details see replies to specific comments below

Reviewer 1:

- Further recognition and exploration of potential biases:

It is true that a priori there is no reason for considering the surveys can be biased. On the other hand, the surveys themselves could serve to check this point, by comparing the interaction rate of interviewed anglers with the total interactions and number of participants.

As an example, the authors indicate in L295-299 that the average number of anglers onboard was 4 people, and that the number of ABFT caught per angler and season was two… Since there were, as an example, 500 anglers in 2019, on average in groups of 4 people and each group interacted on average with 2 ABFT, it would result in a total catch of 250 ABFT (assuming that each tuna is caught by a team and the four people in the team would report it as a catch). However, the total catch for that year is only of 50 fish. Even in the unlikely case two boats participate on average in the catch of a fish, it would also yield a figure well above the actual levels. It could be hypothesized that fishermen more active in the fishery, investing more time and resources are more prone to provide a response to the surveys. It that is the case, the total expenditure would be an overestimate.

Response:

This is a very good point which has multiple explanations. The first is a rounding issue – the average catch angler-1 in 2019 was in fact 1.5 ABFT, with the numbers being 1.9 in 2018 and 2.1 in 2020. This has been corrected in the text (L333-334). Another reason is that compared to the relative proportion of boat-owners to non-owners in the fishery, there is an overrepresentation of boat-owners in our survey response group. As the reviewer correctly predicts – the boat-owners participate more in the fishery (they stay with the boat throughout the season) while non-owners participate less in the fishing activities. Therefore, the average boatowner will report a higher average number of tunas caught compared to the average in the total population of anglers. This is however not as big of a problem as the reviewer may think as we split the group into boat-owners and non-owners for our calculations. And therefore, higher participation and related expenditures by boat owners are not extrapolated to cover all 500 participants but only the 100 boatowners and part owners participating in 2019 while the lower expenditures of non-boat owners is used for the 400 remaining participants. This will protect against overestimation based on the responses of the most active anglers (boat owners).

Reviewer 1:

- Estimates on variabiliy (e.g., sd) throughout the document would be welcome (particularly table 2). Ideally, a statistical procedure (bootstrapping, montecarlo simulations… on expenditures, post-release mortality estimates, etc.) would provide confidence intervals for the estimates.

Response:

Agree. We have now derived 95% upper and lower confidence limits for the mortality rates, and subsequently used these to derive the likely range of economic expenses and impact on the tuna population. Details of the method and results are provided in the manuscript.

Specific comments

Reviewer 1:

L26 “northern” should be in lower case.

Response:

We have modified the manuscript in accordance with the suggestion of the reviewer (L26)

Reviewer 1:

L28 […] in Denmark, who often consider

Response:

We have modified the manuscript in accordance with the suggestion of the reviewer (L28)

Reviewer 1:

L30 […] in Denmark, which peaked

Response:

We have modified the manuscript in accordance with the suggestion of the reviewer (L30)

Reviewer 1:

L41-42 Fragmented, rephrase

Response:

We have modified the manuscript in accordance with the suggestion of the reviewer (L41-45)

Reviewer 1:

L54-55 I am not very familiar with those fisheries, but I seem to remember there was a fishery for ABFT in Scandinavia with significant catches in the 1940’s. Please double-check

Response:

That is correct – changed to 1940s and 1950s (L55)

Reviewer 1:

L61 Conservation of Atlantic Tunas

Response:

We have modified the manuscript in accordance with the suggestion of the reviewer (L61)

Reviewer 1:

L62 Consider changing member states by Contracting Parties (it is the regular nomenclature. The EU, as an example is a party, not a MS).

Response:

We have modified the manuscript in accordance with the suggestion of the reviewer (L63)

Reviewer 1:

L70 […] and, in 2006 and all subsequent years, […]

Response:

We have modified the manuscript in accordance with the suggestion of the reviewer (L70)

Reviewer 1:

L73 Do not understand very well the sense of “as late as” in this context. Does it mean “as early as”?.

Response:

Changed from ‘as late as’ to ‘up until’

Reviewer 1:

L78-79 The fact that Denmark and Sweden lack quotas is mentioned just two lines above.

Response:

Second mentioning removed

Reviewer 1:

L82 Consider removing “landing based” since it is implicit in the term commercial. To my knowledge, there are no commercial non-landing based ABFT fisheries.

Response:

We have modified the manuscript in accordance with the suggestion of the reviewer (L81)

Reviewer 1:

L96 Some inconsistency with the lines above : 10,000 t x 69 €/kg = 0.69 billion €, but in L96 in the value is 0.9 billion €

Response:

The report in which the numbers are found used rounded numbers which is the reason for the inconsistency. The more accurate numbers are: an average end value of ABFT in 2012 = 66.9 USD kg-1 x 13,000 metric tons = 870 million USD. This is corrected in the manuscript (L95-98)

Reviewer 1:

L97 Add abbreviation (T&R program), since it is used later throughout the document

Response:

We have modified the manuscript in accordance with the suggestion of the reviewer (L99)

Reviewer 1:

L108-110: Is this all mentioned in ref [16] or is this a conclusion of the current study?. If the latter, consider moving to the discussion section.

Response:

These findings are mentioned and summarized from the statement in reference [16] (Sutton & Ditton, 2001): “Specifically, anglers for whom fishing was more central to their lifestyle and anglers who placed lower importance on keeping fish were more likely to have a positive attitude toward catch-and-release for the Hatteras fishery and were more likely to release all bluefin tuna caught during their 1-day fishing trip.” Additionally in Table 2 in Sutton & Ditton, 2001 it is reported that the statement “I want to keep all the fish I catch” only scores 1.8 on the Likert 5 point scale.

Reviewer 1:

L118 (Table 1) Tags not reporting are, IMHO, more likely to be mortalities than the average. In any instance, the estimate of % mortality should at least be done removing them from the calculation (e.g., for Wilson et al, 2015 the calculation should be 1/(68-8)=0.7%. It should be indicated in the legend or in the main text.

Furthermore, it must be indicated (in the legend if it applies to all the studies or in an additional column if not) if the mortality is at-vessel, post-release or both.

Response:

We thank the reviewer for pointing out this point of clarification. We have added two additional columns in table 1 indicating whether the mortalities were immediate, post-release or both. We have also recalculated the mortality percentages excluding the non-reports from the samples as suggested by the reviewer. We also added a full explanation in the table legend (L122-126) in order to clarify the issue.

Reviewer 1:

L142 […] the fishing activities, including […]

Response:

We have modified the manuscript in accordance with the suggestion of the reviewer (L144)

Reviewer 1:

L152 yellowfin tuna (lower case). Consider changing marlin by billfish. To my knowledge, the former does not include all the species in the family (sailfish and spearfish), although I am not sure if they are important in terms of recreational fisheries, please check.

Response:

We have modified the manuscript in accordance with the suggestion of the reviewer (L154)

Reviewer 1:

L152-153 In other parts of the world {remove e.g.}. Only anglers adhering to minimum gear requirements (e.g. use of the circle hooks and 130 lbs test line), and with […]

Response:

We have modified the manuscript in accordance with the suggestion of the reviewer (L155-156)

Reviewer 1:

L158-159 Consider rephrasing: The anglers would have had to invest […] even if no minimum gear requirements had been enforced by the tagging project, as there are

Response:

We have modified the manuscript in accordance with the suggestion of the reviewer (L160-166)

Reviewer 1:

L160 […] there are no other significant recreational fisheries in Denmark which [..]

Response:

See response above.

Reviewer 1:

L163 […] an open recreational […]

Response:

We have modified the manuscript in accordance with the suggestion of the reviewer (L168)

Reviewer 1:

L184 [..] contact with them

Response:

We have modified the manuscript in accordance with the suggestion of the reviewer (L190)

Reviewer 1:

L185 […] we attempted to contact anglers…

Response:

We have modified the manuscript in accordance with the suggestion of the reviewer (L191)

Reviewer 1:

L189 […] in the survey and, if they were,…

Response:

We have modified the manuscript in accordance with the suggestion of the reviewer (L196)

Reviewer 1:

L195 was sent

Response:

We have modified the manuscript in accordance with the suggestion of the reviewer (L201)

Reviewer 1:

L200 euros (lower case)

Response:

We have modified the manuscript in accordance with the suggestion of the reviewer (L206)

Reviewer 1:

L207-2021 Consider moving to the following section on expenditures

Response:

We have modified the manuscript in accordance with the suggestion of the reviewer (L228-232)

Reviewer 1:

L212-213 Merge with first sentence in the section (L202)

Response:

We have modified the manuscript in accordance with the suggestion of the reviewer (L208)

Reviewer 1:

L226 Consider using biomass instead of weight and “ABFT mortalities due to” instead of “ABFT lost to” throughout the document.

Response:

Weight changed to biomass in lines 236, 247, 255 and 319. ‘lost to’ changed to ‘due to’ in lines 236, 246, 254, 256 and 313.

Reviewer 1:

L227 […] will give an indication of its impact on the stock.

Response:

We have modified the manuscript in accordance with the suggestion of the reviewer (L237)

Reviewer 1:

L228-231 This part is very confusing. I first understood the authors estimated mortality rate from the literatures and applied it to the total catches, then it seemed they calculated a relative mortality rate by dividing the number of mortalities in the T&R program by the total number of tunas caught, but now they mention they calculate a relative mortality rate based on the total number of mortalities and catches in the fishery and apply it again to the total number of ABFT caught each year (does it mean there are catches and mortalities out of the T&R program). This is a central point to clarify: how mortality rate is estimated, if it includes at-vessel and post-release mortality and if the observation rate in the T&R program is not 100% and the values observed are extrapolated to the global catches.

Response:

The confusion about the mortality estimate and related calculations is valid as we have not explained it adequately in the manuscript. We have edited the whole section about mortality (L239-275) in order to clarify this point and address all the questions raised here.

Reviewer 1:

L231-236 On top of the above, provide a rationale for the selection of 5% (it is not straightforward from the values in table 1).

Response:

See reply to comments above. The text has been corrected for clarification.

Reviewer 1:

L237 […] multiplied by the mean weight of ABFT caught in each respective year…

Response:

We have modified the manuscript in accordance with the suggestion of the reviewer (L247)

Reviewer 1:

L238-239 It might be beneficial to indicate how fish measures, fish status, mortalities… were taken and recorded.

Response:

We agree. Additional paragraphs explaining the details have been added (lines 248 to 250 and 253 to 258)

Reviewer 1:

L240 SFL/CFL relationship. Use same number of decimals. If it is derived from row 2 in table 2 of Rodriguez-Marin et al (CFL=-1.887+1.0507SFL) and I am not mistaken it should yield SFL = 1.7959+0.9517CFL

Response:

Yes, the equation is from row 2 in Table 2 of Rodriguez-Marin et al. Yes, the slope coefficient for CFL should be 0.9517 instead of 0.9518 as indicated in our text. However the difference has no effect on our findings. Nevertheless, we thank the reviewer for drawing our attention to this inconsistency and have edited the text accordingly. Regarding a difference in number of decimal places in the slope and intercept terms of the equation, this is also the case in the original equation, so we have retained the same number of decimal places here.

Reviewer 1:

L254 4,318,620€, resulting in average annual…

Response:

We have modified the manuscript in accordance with the suggestion of the reviewer (L271)

Reviewer 1:

L256 […] not owning boats, who spent…

Response:

We have modified the manuscript in accordance with the suggestion of the reviewer (L273)

Reviewer 1:

L264 A couple of significant issues (e.g., year 2018): (i) If the number of fish was 109 and a mortality rate of 5% was assumed, if would result in 5.45 tuna dead, not 3 (therefore, it seems they are not using a 5% mortality rate in the estimation, as stated in L 232). (ii) The total expenditures would be (227x2,356)+(75*10,734)= 1,339,862. This value, divided by the number of fish indicated in the table would be 1,339,862/3=446,620, but in the table 2 it estimates 257,671€ /tuna.

The total expenditure should also be included in the table.

Again, the value of fish dead is an actual observation (fish already dead when hauled onboard), an estimate of post-release mortality or a combination of both?.

Response:

We thank the reviewer for spotting this error in the calculations. The actual number of tuna in 2018 was 4.52 and the resulting value is: 1,339,862/4.52 = 296,173. Table 2 has now been edited to reflect the correct values.

The total expenditures have been added to Table 3

Clarification about the mortality has been added to the table legend (Table 2) see comments of mortality above.

Reviewer 1:

L269 (table 3) My understanding is that these expenses are only related to the ABFT T&R activity, i.e., they would not have taken place in the absence of the T&R program. If that is the case, please note in the legend.

Response:

We have modified the manuscript in accordance with the suggestion of the reviewer (L287-288)

Reviewer 1:

L274-276 I think splitting and showing the information for boat owners and non-owners was very useful. Consider doing it when mentioning incomes as well.

Response:

Good point, we have included the information for boat owners and non-owners in lines 292-295.

Reviewer 1:

L304 How many fish in total, 275 (table 2) or 276?. Also, 12/275=4.4 and 12/276=4.3, not 4.5%

Response:

We thank the reviewer for noticing this error. The numbers are 109, 50 and 116. In 2018, 2019 and 2020 respectively. Table 2 has been corrected.

Reviewer 1:

L305 Of the 276 ABFT, 104, 56 and 106 were caught in 2018, 2019 and 2020. Note in table 2 they are 109, 50 and 116.

Response:

Once again we thank the reviewer for noticing this inconsistency – corrected according to response above.

Reviewer 1:

L307 Indicate it is CFL

Response:

We have modified the manuscript in accordance with the suggestion of the reviewer (L326)

Reviewer 1:

L312 At this stage, if the fishery has taken place using ICCAT research mortality allowance (BTW, it might be good to mention it in the MS) and there is not allocated quota, it should not be treated as an emerging fishery (it is not emerging, but only the result of a specific, discrete scientific action)

Response:

The point is relevant and the text has now been edited so it reads “anglers participating in a scientific ABFT fishery” rather than “emerging ABFT fishery”.

Reviewer 1:

L315 Same as above.

Response:

The text has been edited so it is now clear that the fishery is part of the scientific T&R program, and is not an independently emerging fishery.

Reviewer 1:

L348 interested instead of invested?

Response:

Interested is probably a better term than invested. Corrected according to the reviewers suggestion (L368)

Reviewer 1:

L348 […] fishing in genera and, as a consequence, were more likely…

Response:

We have modified the manuscript in accordance with the suggestion of the reviewer (L368-369)

Reviewer 1:

L350 […] in our analysis?

Response:

We have modified the manuscript in accordance with the suggestion of the reviewer (L370)

Reviewer 1:

L358-359. Beginning with “multiple anglers”. As it is now, it seems all the experiential value is related to the team work and that is not possibly the case. Consider merging this statement with the following paragraph, were there is a clear link with the economic implications of the experience at the group, rather than the individual, level.

Response:

We have now merged the two paragraphs, to make it clear that both the experience related to the activity likely both has an individual as well as a social character for the participating recreational fishers.

Reviewer 1:

L368 Remove “entire”, since it is not comparing total incomes, but the average of the whole commercial fishery.

Response:

We have removed this phrase from the manuscript based on the comments from reviewer # 2. See clarification in the response to reviewer 2 below.

Reviewer 1:

L370 […] trout and salmon, which are…

Response:

We have modified the manuscript in accordance with the suggestion of the reviewer (L370)

Reviewer 1:

L383-384 Please, see note about L269 (table 3). It means the expenditures in table 3, including angling gear, boat expenses and equipment (which account for around half of the total in 2018) would not have taken place in the absence of the T&R program. Is that correct?

Response:

Yes, that is correct. We have modified the legend in Table 3 to agree with this point and modified the text from line 160 to 170. As there are simply no other opportunities to use the highly specialized fishing equipment for other types of fishing – the expenses would not have taken place outside the T&R program, or a similar fishery for ABFT. Additionally, we specifically ask survey respondents to only report expenses ‘directly related to tuna fishing’ in each question in the survey (see survey in supplementary materials).

Reviewer 1:

L384-387. Not sure about the inference: With few exceptions, the different expenditures would have been additional inputs to the local economy regardless of the origin of the anglers. In fact, some of them (angling equipment, boat equipment…) are likely to take place elsewhere when the anglers are foreigners…

Response:

We agree with the point raised by the reviewer here and have removed the section (L425-428) from the text.

Reviewer 1:

L409 Again, not sure if it is assuming a 5% mortality rate or using the observed data. Moreover, a 5% mortality would imply 3.4t fish and the 3t seems to correspond to the observed values…

Response:

The value has been corrected to 4.35. For clarification on mortality see responses to comments above.

Reviewer 1:

A good reference for the discussion could be: Sun et al. 2019. More landings for higher profit? Inverse demand analysis of the bluefin tuna auction price in Japan and economic incentives in global bluefin tuna fisheries management. PLoS ONE 14(8): e0221147 DOI: 10.1371/journal.pone.0221147

Response:

We thank the reviewer for this suggestion and have included a paragraph discussing the findings in lines 404-407.

Reviewer #2:

This manuscript is an investigation of the potential economic benefits of a restored recreational bluefin tuna fishery in Denmark, especially in the Skagen peninsula. Bluefin tuna have begun reappearing off the Danish coast in the past decade and a small catch and release recreational fishery has followed. Following the collapse of bluefin in the 1960s, Denmark lost its allocation of the ICCAT Atlantic bluefin harvest, so the reemergence will remain catch and release for the foreseeable future. The authors of the manuscript surveyed Danish anglers for three years (including during the pandemic) and engaged a portion of them to engage in an unpaid recreational tag and release program, then calculated associated expenditures. The authors then project those expenditures to estimate the full value of a catch and release program to the Danish economy as well as the potential impacts on the bluefin stock from discard mortality.

Reviewer #2:

The article sometimes confused economic value and economic expenditure. The economic expenditures of a recreationally landed or caught species is not directly comparable to the commercial value of a landed fish. The first is how much was spent catching the fish (a comparable commercial number would be how much was spent by a commercial fisherman doing the same) but that is not in line with the authors’ intent. In fisheries economics, we would compare consumer and producer surpluses, but that is outside the scope of this paper. There are many problems with using only expenditures–for one, it implies that the value of the fishing goes up when trip costs become more expensive (for example, if fuel prices rise), which is quite the opposite of the way an angler would perceive it. The Canadian report that the authors cite (13) is looking at charter sales (a commercial enterprise), not the recreational fishing expenditures of private anglers. They later cite Goldsmith, Scheld, and Graves (2018), who did generate consumer surplus estimates and hence economic value. The Bohnsack et al (2002) paper is more similar to what they do here, which looked at economic expenditures and economic impact. Lines 86-96, 360-372 and elsewhere that attempt to directly compare whether a fish should be allocated to the commercial or recreational sectors should be discarded or at least scaled back. Recreational fishing may well be a better use of BFT than commercial fishing, but this paper cannot show that with the data provided.

Response:

We thank the reviewer for this important clarification, and we have modified the text for clarity according to the suggestion. Lines 86-96 have been condensed, rewritten and now avoid direct comparisons. Likewise, lines 360-372 have been reduced and only comparison with comparable data sets (i.e. economic impact data) is included. Other mentions of value has been removed or replaced with ‘impact’ see lines 356, 364 and 380.

Reviewer #2:

I see no issues with the biological sampling or impacts sections, with the caveat that I am an economist and not a biologist. The sampling frame looks fine and the authors did a commendable job with pushing through during the pandemic.

Less important notes:

Reviewer #2:

Section on “Angler participation in the T & R program” beginning line 138–was Danish bluefin angling exclusively limited to these participants? The paper was somewhat unclear on this. Clarify. I assume that anglers can catch and release whatever they want, but I may be wrong. Lines 283-284 seem to suggest that there is a pre-existing season for BFT angling, then lines 411-412 indicate that “ a substantial recreational sector could develop in Denmark.”

Response:

To account for this lack of clarity a new paragraph has now been added to clarify that the participants in the research project are the only recreational anglers allowed to catch ABFT in Denmark within the study period.

Reviewer #2:

Lines 171-172 –the FAO manual is on fisheries economic impacts, which is how much money is being spent in the area, make sure to use that language throughout the manuscript.

Response:

We have modified the manuscript using the term ‘impact’ throughout in accordance with the suggestion by the reviewer, e.g. lines 356, 364 and 380.

Submitted filename: Response to Reviewers.docx

Click here for additional data file.

8 Jul 2022

Economic expenditures by recreational anglers in a recovering Atlantic bluefin tuna fishery

PONE-D-21-36689R1

Dear Dr. Maar,

We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements.

Within one week, you’ll receive an e-mail detailing the required amendments. When these have been addressed, you’ll receive a formal acceptance letter and your manuscript will be scheduled for publication.

An invoice for payment will follow shortly after the formal acceptance. To ensure an efficient process, please log into Editorial Manager at http://www.editorialmanager.com/pone/, click the 'Update My Information' link at the top of the page, and double check that your user information is up-to-date. If you have any billing related questions, please contact our Author Billing department directly at authorbilling@plos.org.

If your institution or institutions have a press office, please notify them about your upcoming paper to help maximize its impact. If they’ll be preparing press materials, please inform our press team as soon as possible -- no later than 48 hours after receiving the formal acceptance. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information, please contact onepress@plos.org.

Kind regards,

Antonio Medina Guerrero, Ph.D.

Academic Editor

PLOS ONE

Additional Editor Comments (optional):

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.

Reviewer #1: All comments have been addressed

Reviewer #2: All comments have been addressed

**********

2. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Yes

Reviewer #2: Yes

**********

3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Reviewer #2: Yes

**********

4. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: Yes

Reviewer #2: Yes

**********

5. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

Reviewer #2: Yes

**********

6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: (No Response)

Reviewer #2: (No Response)

**********

7. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy.

Reviewer #1: Yes: Francisco J. Abascal

Reviewer #2: No

**********

14 Jul 2022

PONE-D-21-36689R1

Economic expenditures by recreational anglers in a recovering Atlantic bluefin tuna fishery

Dear Dr. Maar:

I'm pleased to inform you that your manuscript has been deemed suitable for publication in PLOS ONE. Congratulations! Your manuscript is now with our production department.

If your institution or institutions have a press office, please let them know about your upcoming paper now to help maximize its impact. If they'll be preparing press materials, please inform our press team within the next 48 hours. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information please contact onepress@plos.org.

If we can help with anything else, please email us at plosone@plos.org.

Thank you for submitting your work to PLOS ONE and supporting open access.

Kind regards,

PLOS ONE Editorial Office Staff

on behalf of

Dr. Antonio Medina Guerrero

Academic Editor

PLOS ONE