Catch quotas for walleye pollock Gadus chalcogrammus, the dominant<br />species in the groundfish fishery off Alaska, are set by applying<br />harvest control rules to annual estimates of spawning stock biomass<br />(SSB) from age-structured stock assessments. Adult walleye pollock<br />abundance and maturity status have been monitored in early spring in<br />Shelikof Strait in the Gulf of Alaska for almost three decades. The<br />sampling strategy for maturity status is largely characterized as<br />targeted, albeit opportunistic, sampling of trawl tows made during<br />hydroacoustic surveys. Trawl sampling during pre-spawning biomass<br />surveys, which do not adequately account for spatial patterns in the<br />distribution of immature and mature fish, can bias estimated maturity<br />ogives from which SSB is calculated. Utilizing these maturity data, we<br />developed mixed-effects generalized additive models to examine spatial<br />and temporal patterns in walleye pollock maturity and the influence of<br />these patterns on estimates of SSB. Current stock assessment practice is<br />to estimate SSB as the product of annual estimates of numbers at age,<br />weight at age, and mean maturity at age for 1983-present. In practice,<br />we found this strategy to be conservative for a time period from<br />2003-2013 as, on average, it underestimates SSB by a 4.7 to 11.9%<br />difference when compared to our estimates of SSB that account for<br />spatial structure or both temporal and spatial structure. Inclusion of<br />spatially explicit information for walleye pollock maturity has<br />implications for understanding stock reproductive biology and thus the<br />setting of sustainable harvest rates used to manage this valuable<br />fishery.
Williams, B. C., Kruse, G. H., & Dorn, M. W. (2016). Interannual and spatial variability in maturity of walleye pollock Gadus chalcogrammus and implications for spawning stock biomass estimates in the Gulf of Alaska. PLoS ONE, 11(10). https://doi.org/10.1371/journal.pone.0164797