Abstract
Warming of the oceans and shifts in the timing of annual key events are likely to cause behavioral changes in species showing a high degree of site fidelity. While this is well studied in terrestrial systems, there are fewer examples from the marine environment. Sandeel (Ammodytes marinus) is a small eel‐shaped teleost fish with strong behavioral attachment to sandy habitats in which they are buried from late summer through winter. When spring arrives, the sandeel emerge to feed during the day for several of months before returning to the sand for overwintering refuge.Using fisheries data from the North Sea, we investigated whether catch rates reflect the timing of emergence and if seasonal patterns are related to temperature and primary production.Catch per unit effort (CPUE) was used to describe sandeel emergence. We developed indicators of the relative timing of the emergence from the winter sand refuge and the subsequent growth period. Different modeling approaches were used to investigate the relationship with bottom temperature and primary production.Variation in emergence behavior was correlated with variation in sea bottom temperature. Warmer years were characterized by earlier emergence. Significant warming over the last three decades was evident in all sandeel habitats in the North Sea throughout most of their adult life history, though no net shift in the phenology of emergence was detected. Minimum temperature during spring was a better predictor of emergence behavior than, for example, degree days.This study emphasizes how temperature‐induced changes in behavior may have implications for predators and fisheries of sandeel. The method can be applied to other species for which the timing of exploitation (i.e., fisheries) and species life history are well matched.
Highlights
Temperature is an essential driver of a variety of ecosystem dynamics (Parmesan, 2006; Parmesan & Yohe, 2003; Root et al, 2003) and the general expectation is that warming of temperate and arctic regions will dampen seasonality or shift the timing of transitions between seasons (Burrows et al, 2011; Edwards & Richardson, 2004; Menzel et al, 2006)
Using fisheries data from the North Sea, we investigated whether catch rates reflect the timing of emergence and if seasonal patterns are related to temperature and primary production
If emergence of sandeel in the North Sea, as well as Ammodytidae species in other ecosystems, is stimulated by environmental triggers, such as temperature and food production, ocean warming may lead to shifts in the timing of emergence, and such shifts in phenology are likely to impact the many predators for which these species constitute a substantial fraction of their diet
Summary
Temperature is an essential driver of a variety of ecosystem dynamics (Parmesan, 2006; Parmesan & Yohe, 2003; Root et al, 2003) and the general expectation is that warming of temperate and arctic regions will dampen seasonality or shift the timing of transitions between seasons (Burrows et al, 2011; Edwards & Richardson, 2004; Menzel et al, 2006). If emergence of sandeel in the North Sea, as well as Ammodytidae species in other ecosystems, is stimulated by environmental triggers, such as temperature and food production (van Deurs et al, 2010, 2011; Winslade, 1974a, 1974c), ocean warming may lead to shifts in the timing of emergence, and such shifts in phenology are likely to impact the many predators (e.g., fish, seabirds and mammals) for which these species constitute a substantial fraction of their diet (de Boer, 2010; Engelhard et al, 2014; Furness, 2002; Gilles et al, 2016; Greenstreet et al, 1998; Harris & Wanless, 1991; Sharples et al, 2009). Two hypotheses were tested: (1) the increase in food availability in spring “wakes up” the sandeel (food trigger hypothesis) and (2) temperature acts as trigger stimuli that “wakes up” the sandeel (temperature trigger hypothesis) This first screening identified temperature as the most promising predictor of the timing of emergence, which motivated further testing of alternative temperature predictors to advance our understanding of the underlying mechanisms.
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