Patchy distribution fields: an interleaved survey design and reconstruction adequacy.

A mathematical model was used to compare the effects of a regular (one-pass) or interleaved (two-pass) acoustic survey on the adequacy of reconstructing patchy distribution fields. The model simulates fish or plankton patches of different shapes and spatial orientations, and a set of parallel or zigzag transects forming a regular or interleaved acoustic survey. The efficiency of a survey is determined by the adequacy of a reconstructed field to that originally generated, which is evaluated by calculating their correlations. Regarding the immovable fields, the efficiency of a regular or interleaved acoustic survey was tested with the following two alternative assumptions: (1) the entire survey was completed; (2) the survey was interrupted for some reason at the moment when one transect remained non-accomplished. In the former case, the efficiencies of both acoustic surveys were nearly the same; in the latter case, the efficiency of an interleaved survey was superior to that of a regular one. With respect to movable fields, the efficiency of the completed interleaved surveys was even higher than that of the regular ones. Thus, the results obtained allow us to conclude that an interleaved survey is expedient in cases where there is no preference regarding the position of a vessel for further work.