Date Published: April 18, 2019
Publisher: Public Library of Science
Author(s): Kyle J. Krumsick, Jonathan A. D. Fisher, Geir Ottersen.
Exploitation and changing ocean conditions have resulted in altered species interactions and varied population dynamics within marine fish communities off northeast Newfoundland and southern Labrador, Canada. To understand contemporary species interactions, we quantified the isotopic niches, niche overlap, and ontogenetic niche change among seven dominant fish species using stable isotope analyses. Analyses used fishes from three regions differing in fish and prey diversities. Differences in fish and diet composition diversity among regions were found using Simpson’s inverse diversity index. The regions of lowest diversities had higher instances of niche overlap and higher percentage of niche overlap area. The region of highest diversity had the widest spread of niches with greater distances from the community centroid. Ontogenetic shifts were observed such that larger individuals shifted towards the community centroid with the exception of Atlantic cod. Atlantic cod in particular was found to consistently be the top predator of the analyzed species. Our results reveal: (a) overlap in isotopic niches and spread within niche space was correlated with fish and diet diversity; (b) ontogenetic shifts are important when considering a species’ niche and quantifying spatial variation in community niche profiles.
Knowledge of diet and consumption by dominant predatory species is a key input to ecosystem approaches to fisheries management as species interactions are one of the main factors regulating fish populations [1–5]. In fisheries ecosystems of Newfoundland and Labrador, since the collapse of groundfish stocks in the early 1990s , numerous changes have been observed including rising ocean temperatures [6–7], a southward shift in Atlantic cod (Gadus morhua) and capelin (Mallotus villosus) distributions [8–10], and observed declines in Atlantic cod stocks followed by increases in snow crab (Chionocetes opilio) and northern shrimp (Pandalus sp.) populations [11–15]. Therefore quantifying spatio-temporal variation in feeding interactions and trophic structure studies is required to understand ecosystem functioning and predict future changes within this region.
To understand interactions within recovering fish communities in Newfoundland and Labrador, we investigated how regional variation in fish and prey diversity, and fish size, influence four stable isotope metrics of community trophic structure. Trends in fish and prey diversity followed trends in the four metrics, indicating the potential importance of diversity in determining a species’ isotopic niche. Our study further quantified the importance of considering ontogenetic shifts in Bayesian ellipse analyses of community trophic structure.