Dispersal Processes in Puget Sound Brown Rockfish from Parentage and Oceanography

The extent of larval dispersal in marine species has attracted considerable interest, not only because of its importance for the distribution and evolution of marine species, but also because it underpins many strategies in fish stock assessment and conservation. With the emphasis on marine protected areas (MPAs) as a tool for marine conservation, the question of realized dispersal has found renewed significance, as the efficacy of MPAs depends critically on the demographic exchange with surrounding areas. Oceanographic features such as currents or eddies play an important role in dispersal and retention of pelagic larvae, and may also strongly affect larval mortality. Such mechanisms may be responsible for recent genetic estimates of mean dispersal distances of only about 10-30 km in several species of rockfishes (Sebastes spp) with long larval periods. Although such estimates are difficult to apply to specific MPAs, they suggest that populations in most MPAs may be largely self-recruiting, with 40% of recruits settling within 5 km of their release. Here, we test this hypothesis by quantifying self recruitment and dispersal distances in brown rockfish (Sebastes auriculatus) on Point Heyer reef, Puget Sound, from a combination of genetic parental identification, artificial marking of larval otoliths and oceanographic modeling. Oceanographic models and empirical drifter trajectories suggested a clockwise flow around Vashon Island, with strong seasonal variation that may influence dispersal patterns. Several parent offspring pairs could be identified, suggesting some self-recruitment in the study population, but at much lower levels than predicted from isolation by distance patterns. Recruitment in Puget Sound appeared largely random, although a significant decline of full sib pairs with geographic distance was also found. The results demonstrated the value of interdisciplinary approaches to the estimation of marine larval dispersal as well as the importance of MPA networks for rockfish conservation in Puget Sound.