Temporal Variation in Diet Composition and Use of Pulsed Resource Subsidies by Juvenile Sablefish

Abstract

AbstractPulsed resources create an influx of energy that can provide individual and population level benefits to their consumers. As consumers, Sablefish Anoplopoma fimbria experience strong seasonal pulses in prey resources during their critical period of juvenile growth in the nearshore marine environment. This study described temporal patterns in diet composition of Sablefish (N = 1,081) ranging in size from 226 to 455 mm FL during July and September in St. John Baptist Bay, Alaska. Juvenile Sablefish exploited a large variety of prey taxa characteristic of a generalist predator and experienced significant diet shifts among sampling periods revealing seasonal and interannual variation in resource use. Diets appeared more diverse in 2012 when more invertebrate taxa were consumed compared with 2013 when diets were dominated by herring and salmonid offal. In September of both years, spawning Pink Salmon Oncorhynchus gorbuscha were observed within the study area and juvenile Sablefish capitalized on this high energy subsidy, and salmon carcasses were among the top contributors to their diets by weight. However, Sablefish also exploited in situ prey of lower energy, such as benthic invertebrates, suggesting that Sablefish are not entirely reliant on seasonally pulsed, high‐energy prey. This study further emphasizes the significance of salmon as a vector of energy across ecosystems and is one of the first to document a marine teleost species scavenging on adult salmon carcasses in coastal marine waters.