California Sea Grant College Program

Connectivity at relevant scales for management and conservation of many marine species occurs through dispersal of larvae. The goal of this study was to assess dispersal and connectivity among populations of depth-limited rockfish using a combination of indirect and direct methods. In one component of the dissertation, kelp rockfish populations were examined for evidence of genetic structure using 8 coastal and 5 island locations from central California to Baja using seven microsatellite loci. Although no significant population structure was detected with all populations treated separately, significant differences were found when populations were pooled based on hydrographic regions identified using average sea surface temperature as a proxy for hydrography at the time of spawning and pelagic dispersal (Fst = 0.002). This structure appeared to be driven by an isolation by distance pattern of gene flow among coastal and nearshore island comparisons (Mantel Test, p = 0.01). An estimate of average dispersal was calculated using the relationship between the the isolation by distance regression and linearized density (Rousset 1997) as 9-13 km for coastal and nearshore island populations in kelp rockfish.

In another component of the thesis, larval distributions were examined directly by collecting early-stage (3-16 mm) rockfish samples through the California Cooperative Oceanic Fisheries Investigation (CalCOFI) surveys, completing species­ specific identifications on larvae and ageing the larvae using otolith-based methods on the squarespot rockfish, the most abundant species in the survey. A significant pattern of higher abundance and younger larvae (mean = 9.2 days) within eddies in the SCB and lower abundance and older larvae (mean= 15.6 days) outside eddies (F1 = 26.13, p < 0.001) was found.

The results suggest an overall pattern of retention of these early-stage larvae within the SCB and limitation to dispersal beyond that expected for the time in the pelagic for both the nearshore kelp rockfish and the more offshore but also depth­ limited squarespot rockfish. These data, collected using integrated methods support previous work on many species suggesting that pelagic fish larvae have a lower realized dispersal than expected considering the length of their pelagic dispersal period.