Southern Newfoundland waters under changing ocean conditions: diets and spatial distributions of emerging and re-emerging gadoids within NAFO subdivision 3Ps

Rockwood, Hilary (2016) Southern Newfoundland waters under changing ocean conditions: diets and spatial distributions of emerging and re-emerging gadoids within NAFO subdivision 3Ps. Masters thesis, Memorial University of Newfoundland.

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Abstract

Quantifying species interactions and spatial dynamics increases understanding of ecosystem function in marine environments affected by climate change. The region containing Newfoundland’s warmest, most spatially variable sea temperatures historically supported large haddock (Melanogrammus aeglefinus) and Atlantic cod (Gadus morhua) fisheries. Recently, spring survey catches contained pollock (Pollachius virens) and silver hake (Merluccius bilinearis), gadoids typically more abundant farther south. Recent increases in spring bottom temperatures may lead to the establishment of these ‘southern’ species, with implications for resident species. Analyses of diet and spatial data of four gadoids relative to temperature increases over time were used to better understand a transitioning ecosystem. Atlantic cod had the most varied diet of the four species, while haddock consistently consumed mainly benthic prey. Pollock and silver hake were more piscivorous, with the level of piscivory increasing with body size. Pollock exhibited no significant spatial shifts, while silver hake shifted northward, increased in abundance and biomass, and expanded its range within the region. Atlantic cod and haddock were caught more frequently in cooler waters, and the mean depth at which cod was caught decreased over time. The gadoids had distinct depth distributions, potentially contributing to low degrees of diet overlap.

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