Seasonal distribution of late larval and juvenile rockfish (Sebastes spp.) and associated environmental conditions off Oregon and Washington: New insights based on genetics

Abstract

Surveys of juvenile and larval stages can be useful for management of commercially important marine fishes but require definitive species identification. From May through October 2005–2008, mid-water (30-m) trawls collected 78,407 late-larval and juvenile rockfish (Sebastes spp.) in shelf and slope waters off Oregon and Washington. Because of their small size and lack of pigmentation, we could identify only 4.1% (3266 individuals) of sampled rockfishes to species morphologi-cally, representing a total of 17 species. An additional subsample (2534 individuals), representing 24 species and a 4-species complex, was identified by sequencing the mitochondrial cytochrome b gene and matching sequences to a reference data set. Incomplete overlap between identified species meant that a total of 29 species were identified overall. Community analyses showed that rockfish collected during the early upwelling season (May–June) were distinct from samples collected in the late upwelling season (July–October). Most rockfish were collected from outer-shelf or upper-slope stations, but distributions varied by month and year. Combining genetic and morphological identifications vastly improved our ability to assess seasonal distributions and abundances of planktonic rockfishes and is a step toward performing species-level surveys for this speciose and commercially important genus. Definitive identification based on visual and molecular methods as used here provides key information to enhance understanding of early-stage rockfish ecology.