Hubbs -SeaWorld Research Institute has been stocking white seabass in coastal waters of southern California since the 1980’s. Considerable expertise has been developed during this time on the culture and release of marine finfish for replenishment , and in recent years interest in expanding this approach to other species has increased. California halibut Paralichthys californicus have emerged as a primary candidate due to their importance, popularity, and depleted status in the region. Here we outline the progress to date in developing a replenishment program for California halibut, including the biological challenges associated with culturing this species, ongoing research to address these challenges, and next-steps for program expansion.
Efforts initially focused on establishing region-specific broodstock populations (in co-operation with local volunteer anglers) and reliable egg production in the hatchery. Once achieved, ensuring cultured juveniles intended for release are as morphologically, physiologically and behaviorally as wild-like as possible has become the primary research focus . Similar to other flatfish species, irregular pigmentation patterns (both albinism on the eye-side and excessive pigmentation on the blind-side) have become apparent in cultured California halibut. A series of experiments focusing on larval nutrition and husbandry practices have succeeded in increasing the rate of properly pigmented fish from <5% to 40% , and additional experimental work is being planned to eliminate this issue entirely. S ex determination is another important aspect in the culture process; j uvenile cohorts have been male-biased to va rying extents (66–96% male) and these preliminary results, supported by evidence from re lated paralichthids , suggest that masculinization may be occurring under certain stressful conditions during early development (e.g. suboptimal rearing temperatures). In-depth sex determination experiments are currently being designed, in addition to the use of q uantitative modeling to examine the potential effect s on fishery and population metrics of releasing juveniles with skewed sex ratios.
To date, small-scale releases of cultured California halibut have been undertaken in San Diego, serving as important opportunities to field test tagging methodologies, culture and release strategies, and post-release assessment. It is hoped that continued success in the prioritized areas of research (e.g. pigmentation, sex determination) will allow for larger-scale releases to occur, and incorporation of this fledgling program into the established framework for marine stock enhancement in southern California, the Ocean Resources Enhancement and Hatchery Program.