MEPS 700:125-143 (2022)  -  DOI: https://doi.org/10.3354/meps14134

ABSTRACT: Dungeness crabs Cancer magister support the largest fishery in Oregon (USA), which inputs millions of pounds of bait into the coastal ocean every year. We assessed evidence for seasonal consumption of commercial Dungeness crab fishery bait off the Oregon coast by that target species through δ¹³C and δ¹⁵N stable isotope and gut content analysis. Using Dungeness crab samples collected on the Oregon inner to mid-continental shelf, variation in δ¹³C and δ¹⁵N values were assessed according to sex, size class, region, and season using nested ANOVA, Euclidean vector statistics, and Bayesian standard ellipse areas corrected for sample size (SEAc) in R. The isotopic signatures of sampled crabs showed statistically significant variation by sex, region, and season; the differences in the isotopic niches of large male versus female crabs (carapace width ≥159 mm) were especially pronounced. δ¹⁵N in female crabs peaked in spring and declined toward fall with similar mean δ¹³C, which could be indicative of higher trophic level bait consumption in the winter when the fishery is the most active, while δ¹³C varied seasonally in males with similar mean δ¹⁵N. The approximated trophic niches (based on SEAc) of both male and female crabs were greatest in fall, suggesting broader foraging in the absence of bait inputs. This work provides a step towards understanding the ecological role of fishery activities on one of the most economically valuable species on the US west coast.

KEY WORDS: Commercial fishing · Benthic invertebrates · Dungeness crab · Oregon coast · Stable isotope analysis · Trophic ecology · Cancer magister