Stock assessment and management recommendations for Pacific sardine (Sardinops sagax) in 1997

The primary goal of sardine management as directed by the California Fish and Game Code is rehabilitation of the resource with an added objective of maximizing sustained harvest. Accordingly, the Code states that the annual sardine quota can be set at an amount greater than1,000 tons, providing that the level of take allows for continued increase in the spawning population.We estimated the sardine population size to have been 464,000 short tons on July 1, 1997. Our estimate was based on output from a modified version of the integrated stock assessment model called CANSAR (Deriso et al. 1996). CANSAR is a forward-casting, age-structured analysis using fishery-dependent and fishery-independent data to obtain annual estimates of sardine abundance, year-class strength and age-specific fishing mortality for 1983 through thefirst semester of 1997. Non-linear least-squares criteria are used to find the best fit between model estimates and input data.Questions about stock structure and range extent remain major sources of uncertainty in assessing current sardine population biomass. Recent survey results and anecdotal evidence suggest increased sardine abundance in the Pacific Northwest and areas offshore from central andsouthern California. It is difficult to determine if those fish were part of the stock available to the California fishery. In an attempt to address this problem, the original CANSAR model was reconfigured into a Two-Area Migration Model (CANSAR-TAM) which accounted for sardinelost to the areas of the fishery and abundance surveys due to population expansion and net emigration. While the model includes guesses and major assumptions about net emigration and recruitment, it provides an estimate which is likely closer to biological reality than pastassessments. The original CANSAR model was also used and estimates are provided for comparison.Based on the 1997 estimate of total biomass and the harvest formula used last year, we recommend a 1998 sardine harvest quota of 48,000 tons for the California fishery. The 1998 quota is a decrease of 11% from the final 1997 sardine harvest quota for California of 54,000tons. (55pp.)