Spatial distribution and environmental preferences of the mesopelagic fish <i>Maurolicus muelleri</i> in the Eastern Mediterranean

Abstract Mesopelagic fish constitute the most abundant vertebrate group in the marine environment. Mueller’s pearlside (Maurolicus muelleri) is present in the twilight zone across the Atlantic Ocean, including the Mediterranean; however, little is known about its distribution patterns and environmental preferences. Based on acoustic and biological sampling, we demonstrate that M. muelleri predominantly forms monospecific aggregations with characteristic echotraces. An ensemble of Species Distribution Models (SDMs) was applied, paired with satellite-derived environmental observations and model outputs to explore the potential habitat of the species in the Eastern Mediterranean Sea. Bottom depth showed the highest variable importance in all models, followed by surface chlorophyll-a concentrations (an index of phytoplankton biomass) and current geostrophic velocity. Extended areas of high probability of presence were identified near the shelf breaks throughout all sub-basins, in the zone of 150-250 m. M. muelleri is more likely to occur in productive regions than in oligotrophic ones, suggesting that ongoing Mediterranean ocean warming—which reduces primary productivity—may indirectly affect the species’ abundance by limiting food availability. Inter-model variability indicated low uncertainty, which was attributed to the species’ strong dependence on a narrow range of only a few environmental variables. The findings contribute to our understanding of the spatial distribution of a key mesopelagic fish in the Eastern Mediterranean Sea and its association with topographic and environmental drivers.