Ecological response to changes in the structure of water masses in the pelagic of the Canary Current Marine Ecosystem

Abstract

Based on the results of sea expeditions, interannual changes in structure of the ichthyocenosis in the pelagic zone of the southern shelf of Morocco in the Atlantic Ocean were studied in connection with changes in the habitat. Mass pelagic fish were selected as reference biological species: European and West African horse mackerel, European sardine, Eastern mackerel, sea bream, sea snipe, myctophids, as well as non-commercial fish species. Field data were obtained during the implementation of complex oceanographic surveys in the fall seasons (October-November) 2015–2018. The results of control trawls were used, in which any species amounted to at least 70 % of the catch. The analysis of the species composition of the control trawls, data of hydroacoustic tracking of trawls, thermohaline water characteristics is carried out. Data pairing was carried out by phased extraction and transformation using standard computer programs for processing various types of data (acoustic, hydrological, ichthyological), as well as specially designed programs that allow you to create a single database. It has been established that recent changes in the number of commercial and by-catch species observed in the ARZ of Morocco in recent years are associated with the presence or absence of so-called “settlement windows”, which appear in the T, S‑diagram field by regions of different configurations, which indicates changes in the ratios of water masses. Based on the identified relationships between changes in the ratio of water masses and changes in the species composition of the control trawls of accounting replenishment surveys, estimates of the expected changes in the biomass of mass pelagic fish in the coming years are made.