Trophic and size spectra modeling reveal key species interactions and quantify community recovery dynamics within Newfoundland and Labrador fisheries ecosystems.

• Main Author: Krumsick, Kyle
• Format: Text
• Language: English
• Published: Memorial University of Newofundland 2020
• Subjects: Newfoundland; Snow crab
• Online Access: https://dx.doi.org/10.48336/02y0-vd21; https://research.library.mun.ca/14539/

Recent efforts to shift towards ecosystem approaches to fisheries management require multi-species analyses across dynamic food webs and an understanding of trophic dynamics. My research analyzed the marine food web dynamics of Newfoundland and Labrador using stomach contents data and stable isotope ratios from fishes and invertebrates. A key facet of trophic ecology is the role a species fills in the food web. My first chapter quantified realized isotopic niches, a proxy for trophic niche, of representative dominant species using Bayesian ellipses and assess the potential competitive interactions that could prevent population recovery of groundfish species. Also essential in trophic ecology is the assessment of nutrient flow through an ecosystem. To understand the origin for the spatially varying isotopic niches, isotope mixing models were created in my second chapter to assess the strength of the interactions between all fish species and prey species and assess the key pathways of nutrient flow to the upper food web. Considering bioenergetic transfer through a system requires consideration of productivity resulting from growth and reproduction. This productivity analysis lends itself to the study of size spectra and the question of whether they may be used to assess community recovery. To do so, in my third chapter the empirical size structure I derived from the ecosystem surveys was compared to a theoretical pristine size structure derived through a combination of nitrogen stable isotopes and macroecological principles. Strong regionality was observed in isotopic signatures, with more trophic niche overlap, increased connectance and shorter food chain length in the less diverse, northern sites. Ontogenetic variation was observed in the isotopic niches and in the reconstructed diets. These trophic considerations may contribute to the observed differential recovery rates of fish stocks, illustrating the importance of considering competition and diet composition. The interactions of recovering groundfish species and economically important invertebrate species (i.e. shrimp and snow crab) were also highlighted. Although the Newfoundland and Labrador marine ecosystems were still far from fully recovered, recovery and continued sustainability of fish communities could be facilitated through balanced harvesting (though presently mostly theoretical) to limit the damaging impacts of fishery exploitation.