Resource assessment of the penaeid prawn Metapenaeus dobsoni (Miers) along the Mangalore coast

Abstract

The fishery and certain aspects of the population characteristics of M. dobxoni from 1962 through 1971 are reported. The fishery was generally bimodal with peaks during March-April and September-October and showed wide annual fluctuations. Th-; total catch showed a gradually diminishing increase when the fishing effort reached a level of about 14,000 boat days. The catch per boat day also showed a downward trend, in general. It would appear, therefore that any additional increase in 'effort would be of little consequence in raising the yield. The fishery was dominated by larger size groups (above 95 mm) during JiilyiNovember. Recruitment of smaller size groups (60 mm onwards) was observed duping DeC'imber-January. The maximum number of broods entering the fishery was five. Age and growth studies indicated that the males and females attain a length of 85 and 105 mm and 95 and 120 mm at the end of one and two years respectively. Th-ereafter very little growth seems to take place. The late 'O' and the one year class formed the mainstay of the fishery. The mean length showed considerable annual fluctuations but these changes appear to be only due to natural causes. Females preponderated in all the years except during 1965-66. They often tended to exceed the males by more than 1.5 times during .April-May and November- December which more or less coincided with periods of intense breeding activity. The average annual instantaneous rate of mortality between one and two year olds was found to be 4.18 and 4.61 for males and females respectively. The fluctuations in the annual rainfall seem to bear a direct relation to the magnitude of the fishery. No clear-cut relationship between the juvenile abundance in the estuary and the marine fishery was discernible.