Effect of Sea Surface Temperature Variation on Productivity and Fisheries off Karnataka, West Coast of India

Variations of chlorophyll-a (chl-a), sea surface temperature (SST) and net primary productivity (NPP) along with fish catch were studied along the coastal waters off Karnataka, west coast of India from January 2007 to December 2016. These variations are linked with the Indian Ocean Dipole and El Niño/Southern Oscillation—Niño3.4 SST index. NPP was estimated by using vertically generalized production model. Change in NPP values over the decade (2007–2016) was studied in context of global reports of decline in productivity over the period. It is very important to understand the pattern of NPP variability as well the interrelationship with SST over a long period to study its impact on distribution of the fishery resources. Trend showed that there is reduction in productivity after 2012 and this trend continued in subsequent years. During the study period, an increasing trend in SST is observed along the Karnataka coast. The present study shows that a strong El Niño event was seen in 2015, along with declined productivity in the coastal waters off Karnataka by ~ 24% and increase in SST by ~ 1% from the average of 10 years (2007–2016). Increased SST and low ocean productivity resulted in reduced fish catch with the decline of 6.7% in total fish catch along the Karnataka coast from 2014 to 2015. In 2016, 5.29 lakh tones of fish catch, was estimated resulting in 19.6%, increase compared to 2015. During southwest monsoon, sea surface height anomalies (SSHa) showed negative anomaly trend and increased Ekman pumping resulted in upwelling over the study area.