Impact of environmental changes on the fishery of motorized and non-motorized sub-sectors of the upwelling zone of Kerala, southeastern Arabian sea

Abstract

Abstract The marine waters of Kerala state along the southwest coast of India are among the most productive upwelling regions in the southeastern Arabian Sea. Analyses were made to assess the impact of environmental changes on the marine fish catch using motorized and non-motorized craft operating off the coast. The catch per unit effort (CPUE) of total landings, OBGN (outboard gillnet), OBTN (outboard trawlnet), NM (non-motorized) crafts, as well as the catch of 5 major fish resources Indian mackerel, lesser sardines, Stolephorus spp., scads, and penaeid prawns were obtained. Sea surface temperature (SST), chlorophyll, salinity, rainfall, sea level anomaly, multivariate ENSO index, dipole mode index, local temperature anomaly, degree heating month (DHM), degree cooling month (DCM) and surface currents were used as variables to investigate the relationship between environment and fishery. Principal component analysis was used to select the minimum data set and GAM (Generalized additive model) was used to detect the influence of the environment on the fisheries. The adjusted R2 value of the GAM was 0.68, taking the CPUE of the total landings as the response variable. For the case of the selected fish resources, the adjusted R2 value of the GAM was 0.73 for penaeid prawns, followed by Stolephorus spp. (0.44), scads (0.33), lesser sardines (0.31), and Indian mackerel (0.25). Considering the CPUE as the response variable for the GAM also returned high adjusted R2 values for fishing method (OBGN\xa0=\xa00.59, OBTN\xa0=\xa00.53 and NM\xa0=\xa00.31). SST, chlorophyll, rainfall, salinity, yearly DCM and surface currents all had significant influences on the marine fisheries along the Kerala coast. Lower SST, high salinity and rainfall promote the fisheries of both small pelagics and large pelagic groups like scads. Along with the negative relationship between SST and fishery, the present analyses also indicate a positive relationship with yearly DCM, which clearly indicates that the warming of coastal waters has a negative impact on fisheries along the Kerala coast. From these results, we find that ocean currents can play a crucial role in fish recruitment in the coastal waters of Kerala. Primary production, the key factor for marine fishery production, was found to be controlled by environmental factors like SST and currents. These results point to the vulnerability of the small-scale fisheries sector of the tropical upwelling zone to increasing SST and climate change.