SEASONAL VARIATIONS OF OCEANOGRAPHIC CONDITIONS AND THEIR INFLUENCE ON PELAGIC FISHERIES OFF MANGALORE COAST,KARNATAKA

摘要

Studies on the characteristics of the marine environment are essential in fisheries research, as the conditions in the sea play a key role in the accessibility of fishery resources. The present investigation was carried out in the fishing grounds offMangalore coast as this area covers the most important fishery zones of the state. The mechanized fishing vessel RTV Netra vati belonging to the College of Fisheries, Mangalore was used for the sample collection during the period from October 2014 to May2015. The monthly variations of air temperature, sea surface temperature, pH, salinity, dissolved oxygen and chlorophyll-a at 30 and 40 meter depth zone were collected and analyzed. The result showed that highest air temperatures were observed during May (29.3 "C) and lowest values during October (26.5°C); SST reached the maximum during the May (32.2 °Q and lowest values during October (28.5 °C); water pH ranged from 7.70 to 8.38 during May and November respectively. Throughout the study period thesurface water salinity ranged from 26.51 to 34.26 psu with minimum salinity was during the month of October and highest was in May. The total dissolved oxygen in the study area fluctuated from 4.92 to 7.05 mg/1 with maximum value documented during the month of October (7.05 rng/l) and minimum in May (4.92 mg/l). The results of the present study depicts that SST showed significant negative (p<0.01) correlation with pH, dissolved oxygen, chlorophyll-a, and Oil sardine whereas significant positive (p<0.05)correlation with Indian mackerel. Dissolved oxygen showed significant negative (p<0.01) correlation with air temperature, SST, salinity and Indian mackerel whereas significant positive (p<0.05) correlation with Chl-a, pH and Oil sardine. Chlorophyll-a showed significant negative (p<0.01) correlation with air temperature, SST, salinity and no correlation with Indian mackerel whereas significant positive (p<0.05) correlation was observed between pH and Oil sardine. In the present investigation fluctuations in Oil sardine and Indian mackerel catches were also correlated and it was found that there was negative correlation with oil sardine and mackerel (r= -O.825/K0.0/). During the study period an inverse relationship was observed between the catches of Oil sardine and Indian mackerel. The effects of large scale, environmentally driven change on the distribution and abundance of the fish population have been a major concern for fishery scientists and managers for decades, particularly those dealing withthe assessment and management of pelagic fisheries.