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Marine Ecology Progress Series

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MEPS 640:189-200 (2020)  -  DOI: https://doi.org/10.3354/meps13275

Trophic position scales positively with body size within but not among four species of rocky reef predators

Angeleen M. Olson1,2,*, Alejandro Frid3,4, Jessica Borba Quintela dos Santos1, Francis Juanes1

1Department of Biology, University of Victoria, Victoria, British Columbia, V8P 5C2, Canada
2Nearshore Ecology, Hakai Institute, Heriot Bay, British Columbia, V0P 1H0, Canada
3Central Coast Indigenous Resource Alliance, Campbell River, British Columbia, V9W 4X1, Canada
4School of Environmental Studies, University of Victoria, Victoria, British Columbia, V8P 5C2, Canada
*Corresponding author:

ABSTRACT: Intra- and interspecifically, larger-bodied predators generally occupy higher trophic positions (TPs). With widespread declines in large predators, there is a need to understand their size-based trophic roles to predict ecosystem-level responses. In British Columbia, Canada, we examined size-based trophic interactions between predatory fishes—3 rockfish species (genus Sebastes) and lingcod Ophiodon elongatus—and their prey, converting predator δ15N signatures to TP and analyzing stomach contents. Intraspecifically, TP scaled positively with predator length and gape width, but the rates of change varied by species. Interspecifically, TP did not scale positively with the observed mean sizes or known maximum sizes of species. Lingcod TP was lower than that of yelloweye and quillback rockfishes, which were 51 and 37%, respectively, smaller than lingcod. Yellowtail rockfish had the smallest average size, yet their mean TP did not differ significantly from that of lingcod. Neither species differences in some morphometric traits known to influence body size-TP relationships nor phylogenetic history explained these results. Most prey consumed were <20% of the predator’s size, which might partially explain the lack of a size-based trophic hierarchy among species. Currently, large size classes of rockfishes are being lost due to fisheries and perhaps climate-driven changes. Our findings on intraspecific size-TP relationships indicate that fishery removals of large individuals may diminish trophic structures. Interspecific comparisons of TP suggest that, along with size, species remain an important factor in understanding trophic dynamics. In addition, smaller-bodied predator species may have significant ecological roles to be considered in ecosystem-based fisheries management.


KEY WORDS: Food webs · Stable isotopes · Size-based predator-prey interactions · Diet · Rockfish · Lingcod · Allometric scaling


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Cite this article as: Olson AM, Frid A, Santos JBQ, Juanes F (2020) Trophic position scales positively with body size within but not among four species of rocky reef predators. Mar Ecol Prog Ser 640:189-200. https://doi.org/10.3354/meps13275

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