Feeding Interactions between Fishes in a Coastal Ecosystem in the Southern Gulf of St. Lawrence, Atlantic Canada

Abstract

Diet composition, diet similarity, and major predator–prey interactions between the 15 most abundant demersal and pelagic fishes (N = 12,163 stomachs) during the period 1999–2003 were described for Northumberland Strait, a semi‐enclosed, marine coastal ecosystem. Of the five pelagic species, Rainbow Smelt Osmerus mordax ate benthic prey (shrimps and polychaetes); Atlantic Herring Clupea harengus and American Shad Alosa sapidissima consumed small copepods and crab zoeae; and Atlantic Mackerel Scomber scombrus and Alewives Alosa pseudoharengus ate small copepods and moderate amounts of benthic prey and small fishes. Three demersal species were strongly piscivorous but with minimal diet overlap: Sea Ravens Hemitripterus americanus consumed small benthic fishes (especially flounders); Winter Skate Leucoraja ocellata consumed sand lances Ammodytes sp. and Rainbow Smelt; and White Hake Urophycis tenuis consumed Atlantic Herring and Atlantic Mackerel. Cluster analysis revealed seven feeding guilds, of which four contained a single species; consequently, the potential for compensation of predatory function was nonexistent for these guilds. The three multispecies guilds comprised consumers of (1) small copepods and crab zoeae; (2) small benthic invertebrates and polychaetes; and (3) shrimps and crabs. Based on diets, the principal route of energy transfer seemed to be the benthic–detrital pathway; however, confirmation requires representative abundance estimates for the various fishes. Moreover, abundances of many fish species have changed (i.e., most have decreased) since this study was completed, with unknown consequences for food web structure and functioning.

Global Systematic Review of Methodological Approaches to Analyze Coastal Shelf Food Webs

“…In the reviewed studies, prey items were analyzed either individually or were aggregated into groups according to taxonomic status, functional characteristics, body size (e.g., Oakley et al, 2014), life history stage (e.g., Whitehouse et al, 2017), or association with different habitat types and depth (e.g., Giraldo et al, 2017). Similarly, the biological traits of the sampled predators, such as body or gape size, and ontogenetic shifts in feeding (e.g., Abdurahiman et al, 2010;French et al, 2013;Dunic and Baum, 2017;Hanson, 2018) were taken into account in some studies, to allow a more detailed assessment of the feeding habits of a species. The consideration of such biotic traits were sometimes also used to aggregate species into trophic guilds (non-taxonomic groups of species which exploit the same resources; Abdurahiman et al, 2010;Whitehouse et al, 2017;Hanson, 2018), estimate trophic spectra (e.g., Torruco et al, 2007), and calculate indices which were used as basic inputs in respective food web models (e.g., the consumption per biomass ratio; Ullah et al, 2018).…”

“…Similarly, the biological traits of the sampled predators, such as body or gape size, and ontogenetic shifts in feeding (e.g., Abdurahiman et al, 2010;French et al, 2013;Dunic and Baum, 2017;Hanson, 2018) were taken into account in some studies, to allow a more detailed assessment of the feeding habits of a species. The consideration of such biotic traits were sometimes also used to aggregate species into trophic guilds (non-taxonomic groups of species which exploit the same resources; Abdurahiman et al, 2010;Whitehouse et al, 2017;Hanson, 2018), estimate trophic spectra (e.g., Torruco et al, 2007), and calculate indices which were used as basic inputs in respective food web models (e.g., the consumption per biomass ratio; Ullah et al, 2018). Gut content analysis was also used to verify or complement dietary information obtained through other types of trophic level determination techniques, such as stable isotope or fatty acids analysis (e.g., Rodríguez-Graña et al, 2008;Paiva et al, 2013), to estimate bioaccumulation levels of heavy metals (e.g., McMeans et al, 2015), and to build up complex ecosystem-based models (e.g., Lassalle et al, 2011).…”

Long‐term evolution of the structure of the St. Lawrence (Canada) marine ecosystem in the context of climate change and anthropogenic activities: An isotopic perceptive

“…In contrast, copepods showed a notable reduction in δ 13 C values during the most recent period, with American sand lance, mainly a consumer of copepods (Staudinger et al., 2020 ), and capelin (Chamberland et al., 2022 ; Dalpadado & Mowbray, 2013 ) both echoing this trend. However, other secondary consumers (e.g., Arctic cod, Atlantic herring, and fin whales) known to feed to some extent on copepods and euphausiids but also on other species (Cabrol et al., 2021 ; Darbyson et al., 2003 ; Hanson, 2018 ; Nelson et al., 2020 ), varied in the direction of their isotopic shifts during the most recent period, challenging the possibility of a shift in the ecosystem baseline. A study tracking parallel changes in DIC and DIN concentrations and in isotopic signature of community constituents up to secondary consumers over time indicated that isotopic variations attenuate rapidly with trophic level (Gavrilchuk et al., 2014 ).…”