Spatial, temporal, and ontogenetic patterns of predation on rockfishes by lingcod

Predators often play a key role in structuring their prey populations in aquatic systems. We described patterns of predation on rockfishes Sebastes spp. by lingcod Ophiodon elongatus, a top predator in nearshore rocky reef communities along the West Coast of North America, to improve our understanding of the variability, magnitude, and constraints of lingcod feeding on rockfishes. From spring 2004 through fall 2005 we collected diet data from 560 lingcod in the San Juan Archipelago, Washington. Rockfishes were a common component of adult lingcod diets, making up 6.8% of the total diet by number, 11.0% by mass, and 10.5% by frequency of occurrence. Rockfishes were consumed by lingcod in all of the time periods and locations sampled during this study, but rockfish mass and frequency of occurrence in lingcod stomachs varied temporally and spatially. The total mass of rockfish consumed by lingcod during fall 2005 was estimated to be approximately three times as high in marine reserves as in nearby nonreserve areas, providing preliminary evidence for differences in community structure between protected areas and those open to harvest of bottom fish. Prey size spectra demonstrated that lingcod are capable of ingesting rockfish larger than 25 cm in standard length (SL), but the diet data suggest that they more commonly consume rockfish measuring 4-24 cm SL, including the adult stages of the small-bodied Puget Sound rockfish S. emphaeus and possibly the juvenile stages of larger rockfish such as copper rockfish S. caurinus and quillback rockfish S. maliger. These findings will inform development of future modeling and empirical studies that will ultimately provide improved insight into the relative top-down effects of lingcod predation and fishing on rockfish populations.