Herring catch per unit effort in the Magdalens trap fishery and implications for gulf herring stock assessment / H. Powles, J. Boulva, P. Spenard.: Fs70-8/79-29E-PDF

"It has been suggested, based on a consideration of schooling behaviour and on data from North Sea herring fisheries, that catchability in mobile gear fisheries on schooling pelagic fish stocks increases with decreasing stock size, and therefore that fishing mortality is not proportional to fishing effort in such fisheries (Pope, 1978 MS, most recently). Under this hypothesis, CPUE in mobile gear fisheries would vary little with stock size above a critical lower limit of stock size (Fig. 1). Although not stated by Pope (1978, MS), it appears intuitively reasonable that below a critical stock size both catchability and catch per unit effort would fall off rapidly (Fig. 1). In inshore fixed gear fisheries, on the other hand, CPUE should change in proportion to stock size (Pope, MS, 1978) (Fig. 1). If Pope's hypothesis is correct, FT (terminal fishing mortality) values for cohort analyses calculated from mobile gear effort and fishing mortality may be too low and biomass estimates from the analyses too high"--Introduction.

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