On the pattern of decrease in the abundance of mackerel in the inshore waters off Karwar within a fishing season

Abstract

It is a well known fact that the mackerel fishery in India shows wide fluctuations from year to year. This intra-seasonal fluctuation is generally reflected by the mean seasonal index of abundance which is obtained by dividing the total catch (either in number or by weight) by the total effort in the season. Apart from this intra-seasonal fluctuation, there is the inter-seasonal variation in the abundance of mackerel. While there is no pattern in the intra-seasonal fluctuations in abundance, a definite pattern is noticed in the variation of abundance of mackerel within a season. In the inshore waters off Karwar, the mackerel fishery starts generally in the month of October ; then the fishery reaches its peak when the maximum abundance of mackerel is noticed in the inshore waters and thereafter the abundance of mackerel begins to the fall down till the mackerel population completely disappears from the inshore waters by about the month of April or May. This decrease in abundance of mackerel population in the inshore waters during a season is due to several factors viz., (a) decrease due to fishing, (b) decrease due to migration away from the fishing grounds, (c) decrease due to natural mortality etc. It is of interest to examine if the rate of inter-seasonal decrease in abundance of mackerel stock is in any way dependent on the seasonal abundance of mackerel or it is independent of the seasonal abundance of mackerel. This aspect of the mackerel fishery has been examined in this paper with reference to fishery data of Karwar from 1948-49 to 1958-59 and the implications of the findings have been discussed. It is felt that the same aspect of the fishery needs examination with respect to data of other regions.