REVISED ESTIMATES OF HISTORICAL SPAWNING BIOMASS OF THE PACIFIC MACKEREL, SCOMBER JAPONICUS

We present revised spawning biomass estimates for the Pacific mackerel stock off southern California for the years 1929-69. These new estimates include corrected assumptions about fecundity, individual growth, underreporting of catches. and the distribution of fishing effort throughout the season. The time series of new estimates shows a more pronounced spawning population decline preceding the population‘s collapse. Spawning appears to be more limited to the older fish than previously thought; cumulative egg production curves reveal an increased impact of exploitation on spawn production. Such a pattern might reduce the stock’s stability at high levels of exploitation. In examining the weight-at-age time series, we observed clear evidence of densitydependent growth; fish attained much higher weights at age when the population size was small.