Assessing the diet of North American Atlantic salmon (Salmo salarL.) off the West Greenland coast using gut content and stable isotope analyses

Abstract

Investigations on the marine feeding of Atlantic salmon (Salmo salar L.) in the Northwest Atlantic are limited compared with the Northeast Atlantic. Climate‐induced changes to food webs in Atlantic salmon feeding areas have been noted, alongside increased mortality despite a cessation of most marine fisheries. As forage efficiency may be hampering survival, it was important to address this knowledge gap. Atlantic salmon were sampled at three sites on the West Greenland coast (Sisimiut, Nuuk and Qaqortoq) between 2009 and 2011. Gut content and stable isotope analyses were combined to assess spatial and temporal differences in feeding. Capelin (Mallotus villosus) dominated the diet at Nuuk and Qaqortoq, whereas boreoatlantic armhook squid (Gonatus fabricii) was the dominant prey at Sisimiut. Hyperiid amphipods (Themisto spp.) and sand lance (Ammodytes spp.) were also important. Significant differences were found among sites for both gut contents and stable isotope analyses, with fewer differences evident temporally. Dietary differences were also evident across larger scales, with little overlap demonstrated with Northeast Atlantic diets and the emergence of boreoatlantic armhook squid as an important prey item over time. Atlantic salmon diets are frequently anchored on one or two prey items, on which they appear to specialize, but they will diversify to consume other available pelagic prey. Thus, Atlantic salmon are an opportunistic, generalist predator within the pelagic food web. The variability evident in diet suggests that the limited data available are insufficient to appropriately understand potential vulnerabilities that the species may have to ecosystem changes, and suggest further research is needed.

The role of sand lances (Ammodytes sp.) in the Northwest Atlantic Ecosystem: A synthesis of current knowledge with implications for conservation and management

“…Climate change impacts on Ammodytes have been reasonably well investigated in the Pacific Northwest (von Biela et al, 2019; Robards, Anthony, Rose, & Piatt, 1999; Robards et al, 2002) and the North Sea (Arnott & Ruxton, 2002; von Biela et al, 2019; Burthe et al, 2012; Burthe, Wanless, Newell, Butler, & Daunt, 2014; Wanless et al, 2004, 2018). In contrast, very few studies have directly evaluated climate impacts on Ammodytes in the NWA (Danielsen et al, 2016; Dixon, Dempson, Sheehan, Renkawitz, & Power, 2017). Preliminary evidence suggests A. dubius may be a critical indicator of climate change and system thresholds.…”

Size‐dependent prey availability affects diet and performance of predatory fish at sea: a case study of Atlantic salmon

“…, Dixon et al. ). This habitat shift in general increases individual fitness, as the reproductive success due to the increased body size associated with the shift to the productive growth habitat is greater than the costs of migration (Gross , Fleming ).…”

“…Anadromous Atlantic salmon develop as juveniles in their birth river and migrate to marine areas where they undergo most of their body growth (hereafter referred to as the growth habitat). After one to several years feeding on fish, squids, and crustaceans in the growth habitat, salmon return, mature, and reproduce in the birth river (Karlsson et al 1999, Klemetsen et al 2003, Dixon et al 2017). This habitat shift in general increases individual fitness, as the reproductive success due to the increased body size associated with the shift to the productive growth habitat is greater than the costs of migration (Gross 1987, Fleming 1996.…”

Spawning‐strategy‐dependent diets in two North American populations of Atlantic salmon Salmo salar

“…were the other main components of the diet in Lear (), while the stable‐isotope analysis of the scales in this study indicates that M. villosus rather than A. rissoi was the other main component of the S. salar diet. Some differences between our study and Lear () may be expected given that S. salar diets can vary over time and space (Dixon et al, ; Renkawitz et al, ) and because the diets inferred from the scales integrate feeding over a broader span of time and space compared with stomach contents. Nonetheless, M. villosus as an important dietary contribution corresponds well with the analyses of Renkawitz et al .…”

“…However, as Dixon et al . () have noted, differences in prey consumption can be driven by differences in prey availability. Therefore, the significant difference in δ 15 N values between 1SWC and 2SWC repeat spawners from the Miramichi River indicates a difference in diet between these two groups, but not a shift to prey sources at higher trophic levels by the larger S. salar .…”