Oyster culture potential in the west arm of San Quintín Bay: Current biomass and preliminary estimate of the carrying capacity

Abstract

Biomass production of cultured Pacific oysters, Crassostrea gigas, from the west arm of San Quintín Bay (SQB) was quantified from 1995 to 1998. Filtration and ingestion rates were also mesured in situ (1999–2000) to estimate the oyster carrying capacity of the west arm. At the end of nine months oyster production varied between 0.8 and 2.8 kg oyster per string. Lower values were recorded for strings with a low initial density and during a year of high oyster mortality (1998). A maximum of 483 kg oyster rack^–1 yr^–1 was estimated, but this value should decrease by 30% if only commercial-sized oysters (≥ 90 mm) are considered. Percent water exchange (6% to 76% of total volume, referred to MSL) and seston levels (2.5 to 14.3 mg L^–1) were highly dependent on tides. However, adult oysters regulated their net ingestion rates (2.6 to 3.2 mg organic matter oyster^–1 h^–1), regardless of seston concentrations. It is suggested that establishing a 25% depletion limit for the available food, the carrying capacity of the west arm of SQB ranges from 1913 to 5974 t, and that the observed reduction of growth rates in cultured oysters during 2000 may have resulted from changes in the quantity/quality of the food available in SQB and/or competition for food with other filter-feeders.