Gulf of Alaska | Fishes and Fish Habitats
Thermal effects on early life stages of Gulf of Alaska Pacific cod: Shifts in reproductive phenology, size, and growth
Presenter: Jessica Miller , jessica.miller@oregonstate.edu, Oregon State University Hillary Thalmann , hillary.thalmann@oregonstate.edu, Oregon State University L. Zoe Almeida , almeidle@oregonstate.edu, Oregon State University Laura Rogers , lauren.rogers@noaa.gov, NOAA Fisheries, Alaska Fisheries Science Center Taylor Brooks , taylor.j.brooks@okstate.edu, Oregon State University Rebecca Forney , Rebecca.Forney@humboldt.edu, Oregon State University Ben Laurel , ben.laurel@noaa.gov, NOAA Alaska Fisheries Science Center
A dramatic reduction in the abundance of adult Pacific Cod in the Gulf of Alaska (GOA) occurred after marine heatwaves (MHWs) in 2014-2016 and 2019, leading to an unprecedented fishery closure. To better understand the effects of MHWs on early stages of Pacific Cod, we combined structural analysis of otoliths with field and laboratory data to estimate spawn timing and reconstruct size and growth for pelagic larvae collected in May and juveniles collected in coastal nurseries in July. In addition to the MHWs, water temperatures in the GOA were relatively warm in 2017 and 2018. Therefore, we compared early life attributes before (2006-2014) and during and after MHWs (2015-2019). For both larvae and juveniles, hatch dates were notably earlier during and after MHWs, with mean hatch dates 19-21 days earlier since 2015. Based on lab-derived temperature-specific development rates, we determined that differences in water temperature during incubation could account for only 15% of the shift in hatch dates for larvae and 31% for juveniles. Therefore, other factors, such as changes in spawn timing and/or selective mortality, also contributed to these observed shifts. Additionally, within years, the mean hatch dates for larvae collected in May were nearly a month later than for juveniles collected in coastal nurseries in July. Differences in hatch timing between life stages could be due to temporal bias in the larval collections, different source populations, or selective mortality associated with hatch date. We used mixed models to examine the effects of temperature, hatch date, and age on size and growth and to evaluate if, and how, those relationships changed since the MHWs. The effect of MHWs on size and growth varied with age. For both larvae and juveniles, size and growth early in life (<14 d) were greater at similar temperatures prior to the MHWs. However, at intermediate ages (>14 to 50 d), growth rates were greater during and after MHWs, which contributed to substantially larger size-at-age observed in juveniles by ~110 days old. These results highlight how relatively large shifts in hatch timing combined with modest differences in growth rates can amplify differences in size-at-age of juveniles at settlement, which can have cascading effects on older age classes. Understanding how ocean warming affects reproductive timing and early growth will be integral to predicting population-level responses to climate variation.
Alaska Marine Science Symposium 2023 15
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