Exploring the dynamics of small pelagic fish catches in the Marmara Sea in relation to changing environmental and bio-optical parameters

Authors: EKİN AKOĞLU

Abstract: The Marmara Sea has a large drainage basin that includes cities with heavy industrialisation and agricultural land use. Therefore, it is under the influence of significant anthropogenic activities that adversely affect the well-being of its ecosystem. The Marmara Sea is also an important fishing ground with many commercially important fish species. These fish species are also under the influence of the adverse impacts of anthropogenic activities. Fisheries catches in the Marmara Sea had experienced severe fluctuations since the onset of the 2000s. In this study, possible underlying reasons for these fluctuations were investigated between 2000 and 2019 using remotelysensed environmental and environmentally-influenced bio-optical parameters and fishery statistics. First, long-term inter-annual changes in the time series of sea surface temperature (SST), chlorophyll-a (Chl-a) concentration, net primary productivity (NPP), fishing effort, and catches of commercially important fish species, i.e. anchovy, sprat, Mediterranean and Atlantic horse mackerels and sardine, were scrutinised using trend analysis. Then, relationships between species? catches and the changes in the SST, Chl-a concentration, NPP, and fishing effort were investigated using correlation analysis. The results of the trend analysis showed that there were statistically significant declines in the catches of Mediterranean horse mackerel, sprat, and the total catch of the investigated species, although the decrease in the fishing effort was statistically not significant. The analysis of relationships between the environmental and bio-optical parameters and fishery statistics indicated that SST had statistically significant negative and NPP had statistically significant positive correlations with the catches of anchovy, sprat, and Mediterranean horse mackerel. Overall, the results indicated that the decreases in the fisheries catches were strongly correlated with the environmental and environmentally-influenced bio-optical parameters and fisheries management practices should consider environmental aspects of the ecosystem in addition to conventional fisheries regulations.

Keywords: The Marmara Sea, fisheries, fish stocks, remote sensing, chlorophyll-a, primary production

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