Outplanting Larval Pinto Abalone Haliotis kamtschatkana kamtschatkana (Jonas) as a Recovery Tool in the Salish Sea

Abstract

Pinto abalone populations in Washington state have declined precipitously in the last few decades, despite closure of the fishery. Local restoration efforts have focused on outplanting juvenile abalone, which is costly because of the husbandry required to raise abalone to outplanting size. This study tested if hatchery-produced larval pinto abalone could be successfully outplanted and if postoutplant growth of larval abalone differed from hatchery-raised animals. Wild broodstock were spawned, and some larvae remained at the hatchery for rearing, whereas most were transported to the Shannon Point Marine Center (SPMC) for outplanting. At two sites in the Salish Sea, larvae were outplanted at a density of 13,000 larvae m–2 into two types of larval abalone modules (LAM): tented LAM (125 µm Nitex tenting) and open LAM (no tenting). There were also control LAM with no tenting and no abalone. Larvae were also seeded in LAM in aquaria at SPMC to compare field and aquaria survival and to estimate emigration. Shell lengths of field, laboratory, and hatchery-reared abalone were measured to better understand if hatchery life compromises early growth. Four months after outplanting, abundance of settled abalone was significantly greater in tented LAM than open and control LAM. Control LAM contained no abalone, suggesting reproduction by wild abalone did not occur at the field sites. Open LAM had a mean outplant success of 0.1% (0–12 settled abalone) and tented LAM a mean success of 0.4% (16–35 settled abalone). Outplant success was higher in SPMC aquaria. Open and tented LAM had 1.5% and 3.0% success, respectively. Abalone found on aquaria walls outside the LAM accounted for 0.2% of the seeded abalone for both open and tented LAM. Four months after outplanting, shell lengths of field abalone were not significantly different from lengths of hatchery-reared abalone, suggesting hatchery conditions did not compromise growth rates of newly settled abalone. These findings suggest that releasing larval pinto abalone into tented field modules has potential to supplement wild stocks in the Salish Sea as a lower cost alternative to outplanting juveniles.