Estimating biomass, fishing mortality, and "total allowable discards" for surveyed non-target fish

Shephard, S.
Reid, D. G.
Gerritsen, H. D.
Farnsworth, K. D.
Shephard, S. Reid, D. G.; Gerritsen, H. D.; Farnsworth, K. D. (2014). Estimating biomass, fishing mortality, and "total allowable discards" for surveyed non-target fish. ICES Journal of Marine Science 72 (2), 458-466
Demersal fisheries targeting a few high-value species often catch and discard other "non-target" species. It is difficult to quantify the impact of this incidental mortality when population biomass of a non-target species is unknown. We calculate biomass for 14 demersal fish species in ICES Area VIIg (Celtic Sea) by applying species-and length-based catchability corrections to catch records from the Irish Groundfish Survey (IGFS). We then combine these biomass estimates with records of commercial discards (and landings for marketable non-target species) to calculate annual harvesting rates (HR) for each study species. Uncertainty is incorporated into estimates of both biomass andHR. Our survey-based HR estimates for cod and whiting compared well with HR-converted fishing mortality (F) estimates from analytical assessments for these two stocks. Of the non-target species tested, red gurnard (Chelidonichthys cuculus) recorded some annual HRs greater than those for cod or whiting; challenging "Pope's postulate" that F on non-target stocks in an assemblage will not exceed that on target stocks. We relate HR for each species to two corresponding maximum sustainable yield (MSY) reference levels; six non-target species (including three ray species) show annual HRs >= HRMSY. This result suggests that it may not be possible to conserve vulnerable non-target species when F is coupled to that of target species. Based on biomass, HR, and HRMSY, we estimate "total allowable catch" for each non-target species.
Oxford University Press (OUP)
Publisher DOI
Attribution-NonCommercial-NoDerivs 3.0 Ireland