Variation in wind and piscivorous predator fields affecting the survival of Atlantic salmon, Salmo salar, in the Gulf of Maine

Abstract

Observations relevant to the North American stock complex of Atlantic salmon, Salmo salar L., suggest that marine mortality is influenced by variation in predation pressure affecting post-smolts during the first months at sea. This hypothesis was tested for Gulf of Maine (GOM) stocks by examining wind pseudostress and the distribution of piscivorous predator fields potentially affecting post-smolts. Marine survival has declined over recent decades with a change in the direction of spring winds, which is likely extending the migration of postsmolts by favouring routes using the western GOM. In addition to changes in spring wind patterns, higher spring sea surface temperatures have been associated with shifting distributions of a range of fish species. The abundance of several pelagic piscivores, which based on their feeding habits may predate on salmon post-smolts, has increased in the areas that serve as migration corridors for post-smolts. In particular, populations of silver hake, Merluccius bilinearis (Mitchell), red hake, Urophycis chuss (Walbaum), and spiny dogfish, Squalus acanthias L., increased in size in the portion of the GOM used by post-smolts. Climate variation and shifting predator distributions in the GOM are consistent with the predator hypothesis of recruitment control suggested for the stock complex. K E Y W O R D S : climate, migration, post-smolt survival, predation, recruitment, temperature.

Retrospective analysis of Atlantic salmon (Salmo salar) marine growth and condition in the northwest Atlantic based on tag‐recovery data

“…Although growth of post‐smolts in North America has not been identified as a direct cause of poor marine survival, stock abundance in a Canadian river was negatively correlated with surface temperatures during marine entry. Warmer temperatures in the GOM during the post‐smolt stage have been shown to negatively affect stock size (Friedland et al ., ) and to alter predator–prey distributions and abundances in this area (Friedland et al ., ). A brief window‐of‐opportunity exists for optimal smolt run timing.…”

“…A brief window‐of‐opportunity exists for optimal smolt run timing. Speculation on climate effects causing a detrimental mismatch in river‐to‐ocean temperatures already exists in the discussion of post‐smolt survival (Friedland et al ., ; Russell et al ., ). This mismatch is believed to be responsible for lower river return rates of adult salmon (McCormick et al ., ) and may have some impact on growth.…”

“…If growth in the GOM is hindered by warmer SSTs, increasing ocean temperatures in the future are not likely to improve the situation faced by U.S. Atlantic salmon stocks. Sub‐optimal growth at the beginning of the marine migration puts salmon at greater risk to stronger predator fields that may be shifting into the GOM (Friedland et al ., ).…”

Modeling Predator–Prey Linkages of Diadromous Fishes in an Estuarine Food Web

“…Harbor seals have exhibited increasing biomass in the GOM within the last few decades, with the potential to occupy estuaries at a greater frequency (Baraff and Loughlin 2000;Friedland et al 2012). According to the results from the mixed trophic impact analysis, sturgeon species and Striped Bass could be negatively affected in the GOM if the biomass of harbor seals continues to increase (Yodzis 1998).…”

“…This factor was used to calculate the capacity by which biomass can be perturbed for each species group in the modeled food web. Groups of interest included Striped Bass and harbor seals, which have demonstrated increasing biomass due to their expanding distribution and abundance in similar ecosystems within the GOM (Friedland et al 2012).…”