Effects of calendar time, temperature and growing degree-day on Pacific Herring (Clupea pallasii) length-at-age
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Forage fish species are essential to global marine ecosystems as conduits of energy transfer from low to high trophic levels. Pacific herring (Clupea pallasii) are an important forage fish species in northeast Pacific marine and estuarine ecosystems. Pacific herring length-at-age (LaA, mm) has declined markedly over the past several decades in California and British Columbia (BC) regions thereby influencing physiological processes and biological interactions. Assessing variability in herring LaA is relevant to population and ecosystem studies in addition to sustainable fisheries management and informing fisheries policy. In this study, herring LaA for north coast BC, south coast BC and California (San Francisco Bay) populations were used to estimate how much of the variation is explained by time (year, calendar time), sea surface temperature (°C), and growing degree-day (a metric combining sea surface temperature and calendar time, GDD, °C·day). Time (year) explains more of the interannual variability in herring LaA compared to sea surface temperature and the GDD metric. In addition, a complete removal of older age classes was evident for all areas, suggesting that factors other than those assessed in this study have influenced herring LaA. The results of this research suggest that future studies should focus on modeling multiple factors that may influence variability in herring LaA such as ocean regime shifts influencing prey quality and quantity, environmental pressures (e.g., seawater temperature), and impacts from size-selective fishing that may affect population recovery of this species.
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