Studies of the Genetic Stock Structure of Nearshore Rockfishes of Interest to the California Marine Life Protection Act.
Russ Vetter and the Genetics Program have been studying the genetics of nearshore rockfishes taken by recreational fishers and the commercial live-fish fishery. They have used a number of techniques to:
Define and characterize species and subgeneric relationships within the genus Sebastes.
Identify larvae taken in plankton surveys.
Define unit stocks for rockfish species found along the West Coast.
Reef associated rockfishes rarely move long distances as adults so that natural dispersal and replenishment of overfished local populations is via the oceanic dispersal phase that consists of larvae and pelagic juveniles. The pelagic phase lasts one to three months suggesting that dispersal could be great. However, larvae are extruded fully hatched and soon develop lateral swimming and vertical migration behaviors. Thus, the extent to which they truly disperse on currents or are locally retained is largely unknown.
Initial genetic studies were based on mitochondrial markers that were useful for differentiating species and defining stocks on a broad scale. For example, genetic markers were able to detect a barrier to dispersal and hence separate stocks of the rosethorn rockfish, Sebastes helvomaculatus, occurring north and south of Vancouver, the division between the Alaska Gyre and the California Current. More sensitive markers were needed to detect population divisions on a smaller scale, e.g. along the coast of California.
They then developed a series of nuclear microsatellite markers that appear to be informative on a smaller geographic scale in a number of nearshore rockfish species. To date substantial data sets (>6 loci, >100 individuals) have been analyzed for a number of nearshore rockfishes and more samples are continually being added. In the studies that are completed or near completion they have found that copper rockfish, Sebastes caurinus, grass rockfish, Sebastes rastreliger, kelp rockfish, Sebastes atrovirens, show significant population structure and hence barriers to free larval dispersal at different locations and scales along the California coast. Bocaccio rockfish, Sebastes paucispinus, and widow rockfish, Sebastes flavidus, do not. Gopher rockfish, Sebastes carnatus, and black-and-yellow rockfish, Sebastes chrysomelas, were shown to be separate species but so far have not shown population subdivisions along the California coast. These two species and the brown rockfish, Sebastes auriculatus, are presently being studied in more detail.
In general it appears that species such as bocaccio and widow that are more loosely associated with reefs and structure and that may school and move greater distances as adults do not show local population structure. Those that are solitary, near-shore, and highly associated with structure are not as widely dispersing and are hence of greater concern regarding local depletions and the need for smaller management units.