We include information here that is relevant to ecosystem considerations of fisheries managers, but does not fit our typical indicator format. Information included here is often new, a one-time event, or a deeper discussion on a topic of interest.
Gulf of Alaska Pacific cod (2017–2023)
The Gulf of Alaska stock of Pacific cod Gadus macrocephalus Tilesius experienced a 70% decline in population abundance in 2017, and has remained at reduced levels through 2023 (although the population is showing signs of growth in 2023). The commercial fishery was dramatically reduced from 2017–2019, closed in 2020, and has been opened to a very small harvest since 2021 (Barbeaux et al., 2020b; Hulson et al., 2022). The initial decline in cod abundance was attributed to the marine heatwave (MHW) from 2014–2016. The ocean temperatures at depth on the shelf exceeded the optimal thermal window for Pacific cod egg survival (3–6°C; Laurel and Rogers 2020). During the same period, adult cod increased their metabolic rate when nutritional quality and availability were reduced (Barbeaux et al., 2020b; Arimitsu et al., 2021). Since the 2014–2016 heatwave, the GOA remained relatively warm and experienced another MHW event in 2019. The GOA Pacific cod stock has not returned to pre-2014 levels, raising questions as to its productive capacity with continued and future warming.
Fluctuations in early year class strength of GOA Pacific cod may offer clues to future recruitment potential. Coastal monitoring of age-0 and age-1 year classes in Kodiak since 2006 (and expanded across the central and western GOA since 2018) indicated very low abundance during 2013–2016 and 2019 (MHW years). Age-0 year classes from 2017 and 2018 were strong, but did not reappear as age-1’s in the following year’s survey. Strong year classes reappeared in 2020 and 2022, and were observed as age-1’s the following year in the beach seine survey. The 2020 year class appears to be recruiting to the fishery this year (Hulson et al., 2023) and the success of the very strong 2022 year class remains to be seen.
Remarkable year class variation in the age-0 cohort has been coupled with equally remarkable changes in size-structure. Since 2006, there has been an ∼ 200% increase in average individual mass of age-0 juveniles observed in August (Laurel et al., 2023). While these changes adhere to the ‘temperature size rule’ for fish, the mechanisms contributing to these size shifts are not entirely growth-related. New daily increment analyses on larval and juvenile otoliths indicate a consistent shift in hatch phenology, with hatch dates occurring an average of 19 days earlier for both larvae and juveniles since recent MHWs began. At the larval stage, observed increases in body size-at-capture could be wholly explained by their earlier hatch dates, and hence older ages. However, the increased body size-at-capture for juveniles could only partially be explained by their older age and modestly faster growth rates (Almeida et al., In Press). Rather, size-selection was enhanced during MHWs, contributing to the observed increases in body size. Overall, warmer temperatures account for some, but not all, of the observed changes in phenology and growth. Factors such as parental effects, epigenetics, and selection have also likely contributed. Therefore, these new otolith analyses challenge assumptions about how warming influences growth during early life history, which can inform future forecasting efforts.
Contributed by Ben Laurel1, Jessica Miller2, Hillary Thalmann2, Zoe Almeida2, and Lauren Rogers3
1Hatfield Marine Science Center, Alaska Fisheries Science Center, NOAA Fisheries
2Hatfield Marine Science Center, Department of Fisheries and Wildlife, and Conservations Sciences, Oregon State University
3EcoFOCI, Resource Assessment and Conservation Engineering Division, Alaska Fisheries Science Center, NOAA Fisheries