A temperature- and size-dependent model of sand shrimp (Crangon septemspinosa) predation on juvenile winter flounder (Pseudopleuronectes americanus)

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We investigated the temperature-mediated vulnerability of postsettled winter flounder (Pseudopleuronectes americanus) to sand shrimp (Crangon septemspinosa) predation. Small increases in flounder growth rates substantially decreased predator-induced mortality. Recent warming trends in Northwest Atlantic estuaries can increase flounder survival by accelerating growth and minimizing the duration during which juveniles are susceptible to size-dependent predation. Extreme temperature increases, however, depress growth because a disproportionate amount of energy is devoted to increased metabolism, leaving less for somatic development. Flounder survival is also reduced during warm years because of intensified shrimp predation. Moreover, interannual variations in temperature affect the relative timing of shrimp migration and flounder settlement, thus controlling the spatial and temporal overlap between predator and prey. Predicted flounder abundance and survival were statistically unrelated to observed flounder abundance sampled annually during late spring. However, model predictions and field data suggest that flounder abundance is maximal in years when seasonally averaged temperature is approximately 16°C. Above and below this temperature, flounder year-class size is considerably lower, possibly as a result of temperature effects on trophic dynamics. We conclude that shrimp predation is a significant source of mortality for postsettled flounder, but it is not the sole determinant of interannual variations in recruitment.

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Canadian Journal of Fisheries and Aquatic Sciences