Use of the daily egg production method to estimate the stock size of Western Australian sardines (Sardinops sagax)

Abstract

The daily egg production method was used to estimate the spawning biomass of the sardine Sardinops sagax in the Albany region of Western Australia. Plankton surveys covering 10000 - 14000 km² were completed in July of 1991 and 1992 in three to five days using up to three boats. Adult sardines were obtained from the local purse-seine fleet. The spawning area was similar in both years at approximately 3800 km² (1100 nmile²), but the number of eggs collected was larger in 1991 with egg production values of 6.5 per 0.05 m² day^-1 compared with 3.9 per 0.05 m² day^-1 in 1992. The average batch fecundity values were similar (approximately 11000 eggs female^-1) as were the proportions spawning (0.13 in 1991; 0.09 in 1992). The calculated biomass estimates were 23 121 t (CV = 0.51) and 16 121 t (CV = 0.44) in 1991 and 1992 respectively.