Patchy distribution fields: a zigzag survey design and reconstruction adequacy.

A mathematical model was used to examine the effects of a zigzag survey design on the adequacy of reconstructing patchy distribution fields. The model simulates fish or plankton patches (or gaps) of different shapes and spatial orientations, and an acoustic survey by a set of transects forming a zigzag. Adequacy of the reconstructed fields to those originally generated was evaluated by calculating their correlations (r). A priori information on the autocorrelation radius for the field in the direction of a survey (R) allows optimization of survey design and the algorithm of data analysis. A patchy field can be reconstructed properly (r > 0.80) if the distance between transects D < (1.0-1.5)R. If a priori information on the field is not available, the autocorrelation radius should be determined when reconstructing the field, i.e. a posteriori. In cases of field movement, the criterion for choosing a survey direction is based on the relationship between the dimension of moving patches in the direction of movement and that of the surveyed area. The results obtained indicate that, for a fixed transect spacing, zigzag pattern allow less adequate reconstruction of an original distribution field (in cases of both immovable and movable fields) than corresponding parallel pattern.