Spatiotemporal distribution of European hake Merluccius merluccius related to environmental conditions on the continental shelf of the Sea of Marmara

Abstract

Currently, knowledge of the spatial distribution of European hake Merluccius merluccius in the Sea ofMarmara is scarce, particularly regarding the dependency of this fish on biotic or abiotic conditions. Ageneralized additive model (GAM) was used to model hake abundances in relation to depth, temperature,dissolved oxygen, pH, and spatial location variabilities in the eastern Sea of Marmara (ESM). Furthermore, thesize distribution of European hake was analyzed by depth and season. Data were collected during a 4-yearsampling period (2014-2017) in the ESM using scientific demersal trawl surveys. The GAM results indicated thatalthough all given variables influenced the spatial distribution patterns of hake, the variables with the greatestcontributions in the ESM were longitude and depth. Hake abundance showed a strongly nonlinear dependenceon the explanatory covariates. The results concluded that areas with the highest hake abundances were locatedat approximately 90 m. The results also indicated that a bottom temperature between 15 and 15.5°C,representing relatively warm bottom waters in the ESM, had the highest hake abundances. Low oxygen valuesdid not adversely affect the abundance of hake. Hake preferences for areas with specific bathymetric and oceanenvironmental conditions are considered to be linked to the oceanography of the ESM ecosystem. This studyalso demonstrated that the size distribution of European hake differs by depth and season, and individuals largerthan 30 cm can mostly be found in waters deeper than 80 m.