Interannual variation in the coastal distribution of a juvenile gadid in the northeast Pacific Ocean: The relevance of wind and effect on recruitment

Abstract

Drift of propagules occurs within many populations inhabiting flow fields. This affects the number of propagules that rejoin their source population (recruitment) and plays a role in adaptive spatial redistribution. We focus on the cause and consequence of interannual variation in geographic distribution of population density among five cohorts of young-of-the-year (age-0) juvenile walleye pollock Gadus chalcogrammus in the western Gulf of Alaska (GOA). The coastal GOA is a wind-driven advective system. Walleye pollock spawn during spring and their eggs and larvae drift southwestward; by late summer, age-0 juveniles are variously distributed over the shelf. We found that high population densities of age-0 juveniles (ca. 6 months old) near the southwestward exit of the Alaska Coastal Current from the GOA corresponded with high abundance of larvae from the major spawning area upstream, but did not translate into high abundance at older ages. Further, offshore and upwelling-favorable winds were associated with the high downstream abundance and presumed export. In contrast, downwelling-favorable (northeasterly) wind during and shortly after spawning (April-May) was associated with high recruitment at age 1. Finally, we found that recruitment also increased with apparent retention of age-0 juveniles in favorable habitat upstream near the main spawning area. We hypothesize that windrelated retention in superior upstream habitat favors recruitment. Our results argue for including wind-driven transport in future walleye pollock recruitment models. We encourage more work on the juvenile stage of marine fishes aimed at understanding how transport and species-specific habitat suitability interact to affect population response to large-scale forcing.

Pollock and “the Blob”: Impacts of a marine heatwave on walleye pollock early life stages

“…Modeled May–June transport speed though Shelikof based on the Hybrid Coordinate Ocean Model (HYCOM) indicated slow current speeds in 2015 relative to other years 1991–2017 (Kimmel & Duffy‐Anderson, 2020), again suggesting retention as opposed to advection. Retention of larvae is consistent with observed surface winds, which lacked a strong southward component, and the buildup of low salinity water in 2015 (Wilson & Laman, 2020). Timing and location of spawning may affect the ultimate drift trajectory of eggs and larvae (Hinckley et al., 2001), but neither was anomalous in 2015 (McCarthy et al., 2016; Rogers & Dougherty, 2019).…”

The contribution of diet to the dramatic reduction of the 2013 year class of Gulf of Alaska walleye pollock (Gadus chalcogrammus)

“…The percent variance in age‐2 recruitment explained by age‐0 abundance was highest in the Kodiak (96%) and Shelikof (88%) regions, our domains C and B, respectively. Lastly, Wilson and Laman (2020) found no significant relationships between age‐0 abundance and age‐2 recruitment for the southwest region, our Domain A.…”

“…In summary, we believe that poor recruitment of the 2013 age‐0 pollock year class in the WGOA was mostly likely due to the combined effects of sub‐optimal diet in a large portion of the population (this study), wind‐driven advection of a large proportion of the population to the southwest (Wilson & Laman, 2020), and perhaps cannibalism from the 2012 year class. A large portion of age‐0 pollock consumed less energy‐rich prey could decrease the chances of reaching an adequate weight necessary for overwinter survival.…”

“…Even though it is possible that this larval aggregation was advected along the Alaska Peninsula and into Domain A, we have no applicable data from 2013 to test this hypothesis. However, a recent study by Wilson and Laman (2020) found that hypothetical displacement (based on cumulatively summed wind vectors and measured in km) of age‐0 pollock was strongest in 2013 compared with all other years of their study. They also found that age‐0 pollock population density and recruitment to age‐2 was dependent upon region.…”

Coastal winds and larval fish abundance indicate a recruitment mechanism for southeast Australian estuarine fisheries

“…When testing this hypothesis, Dannevig (1907) found a positive correlation between estuarine commercial catch rates and onshore winds lagged by three or four years (Suthers et al, 2020). Since the inception of this hypothesis, many studies have shown relationships between wind and juvenile recruitment with the effects largely being system specific (Nelson et al, 1977;Caputi et al, 2001;Takeshige et al, 2013;Wilson and Laman, 2021), likely due to complex estuary specific recruitment processes (Boehlert and Mundy, 1988).…”