The Role of Size in Trophic Niche Separation between Two Groundfish Predators in Alaskan Waters

To minimize negative effects of competition, predators must divide resources along one or more niche dimensions. Trophic separation is a principal method resource partitioning in marine environments and often assessed by quantifying diets fishes with similar lengths. Taxonomic differences allometric growth, however, suggest that the degree gape limitation at given body size varies among species. We studied overlap between two potential competitors Southeast Alaska: Pacific Halibut Hippoglossus stenolepis Arrowtooth Flounder Atheresthes stomias. quantified length–gape relationships fork length (FL; cm), height (GH; mm), width (GW; mm) on interpretations trophic separation. Gape sizes for were nearly twice those FLs. Predators smaller gapes exhibited moderate to high dietary ( = 0.554; 0.731), whereas larger had lower distinct diet compositions 0.421; 0.265). These findings greatest food competition small-bodied relatively large-bodied Halibut, increasing as these progress throughout their ontogeny. When comparing use FLs, we found but significantly different 0.657). Thus, postulate GW appropriate than FL when sympatric fishes, especially disparate are detected. Studies would benefit from examining multiple metrics explicitly considering thereby addressing mechanisms hypothesized competitors.