Status of the Pacific Mackerel Resource During 1997 and Management Recommendations for the Fishery

The California fishery for Pacific mackerel (Scomber japonicus) has declined precipitously since 1990. Statewide landings during 1995 continued the downward trend, and totaled only 9,185 short tons. During the last few years, the principal cause of reduced catches has been low biomass and poor availability on the traditional fishing grounds in southern California waters. Cannery closures since 1993 may have also affected demand. Several sources of information are available on the status of the Pacific mackerel stock, all of which suggest a decline in stock biomass compared to the late 1970's and 1980's. Landing statistics, available since 1978 for both the U.S. and Mexican fisheries, show reduced catches during recent years. Catch rates for the southern California Commercial Passenger Fishing Vessel (CPFV) fleet have also shown declining trends since the 1970's. Other fishery- independent data from spotter pilot aerial observations and California Cooperative Oceanic Fisheries Investigations (CalCOFI) ichthyoplankton surveys indicate lower abundance compared to the early 1980's. We used a tuned virtual population analysis (VPA) model called ADEPT to estimate Pacific mackerel biomass. The model finds the best statistical fit between fishery-based, age-structured biomass estimates and other data from aerial observations, plankton surveys, CPFV catch data, and a spawner-recruit relation. Based on the estimated number of fish in each year class during the last quarter of 1995 (including the 1995 year class), and using certain assumptions for expected fishing mortality during the first half of 1996, we project that the Pacific mackerel biomass will be 52,000 tons at the beginning of the 1996/97 fishing season, on July 1,1996. There is a large degree of uncertainty in our 1996 biomass estimate because the 1995 year class (fish of age one) comprises most of the biomass. The Fish and Game Code specifies that when the biomass is between 20,000 and 150,000 tons, the season's quota shall be 30 percent of the total biomass in excess of 20,000 tons. Using that formula and our projection for July 1,1996, we recommend a commercial fishery quota of 9,600 tons for the 1996/97 fishing season. (26pp.)