AN INVERSE EGG PRODUCTION METHOD FOR DETERMINING THE RELATIVE MAGNITUDE OF PACIFIC SARDINE SPAWNING BIOMASS OFF CALIFORNIA

Abstract

The California Department of Fish and Game is required by state law to determine annually whether the spawning biomass of the Pacific sardine (Sardinops sagax) is more or less than 20,000 short tons'. The sardine biomass appears to be increasing; however, the population level is too low to be reliably estimated by existing techniques. An inverse egg production method is proposed, to allow an objective determination of the relative magnitude of the spawning biomass of Pacific sardines. The normal egg production method estimates adult biomass by measuring daily egg production in the spawning area and specific fecundity of the population. The inverse method estimates the area over which a specified spawning biomass (20,000 tons) would be assumed to occur. Components of egg production and specific fecundity for sardines-including average female weight, batch fecundity, spawning fraction, and daily egg production rate-were estimated from previous studies. A survey was designed to cover the Southern California Bight and provide a 95% probability of encountering the calculated spawning area if the spawning biomass is at least 20,000 tons. Recommendations are made, based on possible survey results. RESUMEN