Summary

Description

Abundance, stage structure and population dynamics of brine shrimp Artemia franciscana in pond M4 of the San Francisco Bay National Wildlife Refuge were documented from September 29, 1991 to September 27, 1992 using weekly quantitative samples. Brine shrimp densities varied seasonally between 1 and 55 adults liter1, and total daily standing stock varied between 57 and 50,000 kg dry weight. Brine shrimp harvest was well correlated with brine shrimp abundance, but had no measurable impact on population size or stage structure. Temperature limited population growth during the winter, resulting in low population densities. High salinity, caused by reduced inputs from the lower salinity pond A21, produced a second abundance minimum in the fall of 1992. Food abundance set maximum population densities, and at peak brine shrimp densities, adults were the most abundant stage class apparently due to higher grazing efficiencies. A stagestructured simulation model was developed to test the effects of different pond management strategies on yearly production. Given appropriate timing and duration, flows from upstream could double yearly brine shrimp production. January salinity level was found to be the most important salt pond management factor affecting yearly brine shrimp production. The model was also found to be sensitive to changes in nutrient availability, suggesting the need for future research of nutrient dynamics. Field and model results were used to estimate maximum sustainable yield MSY. Assuming constant nutrient availability and optimal temperature and salinity, a daily harvest rate of 16 18 day1, given nonselective harvesting, and 37 day1, given .sizeselective harvesting was sustainable. MSY was 0 for temperatures 12 C and salinities 260 o. Total yearly harvest could exceed 1000 mt yr1, or 5 mt ha1 yr1, given constant inputs from upstream and an optimal harvest strategy. However, physical refugia and processing limitations imposed constraints that limited the realized catch to about 110 of the potential. Processing limitation was found to be the more limiting of the two constraints. Results from this research suggests ways in which cooperative management between the wildlife managers US Fish and Wildlife Service, salt producers Cargill Salt Co., and brine shrimp harvesters Novalek Inc., could simultaneously insure brine shrimp availability as a food source for local and migrating avifauna, and increase efficiency of salt and brine shrimp production.