Testing an otolith geochemistry approach to determine population structure and movements of European hake in the northeast Atlantic Ocean and Mediterranean Sea

Abstract

Population structure of European hake (Merluccius merluccius) remains poorly understood despite the need for such information for effective fisheries management of the species. Otolith geochemistry was used to examine movements of individuals among local populations and test the accuracy of current stock boundaries for the species. Age-1 European hake were collected at 7 locations in the Atlantic Ocean and the Mediterranean Sea. Otolith geochemistry (Mg:Ca, Mn:Ca, Sr:Ca, Ba:Ca, δ13C, and δ18O) was assayed in cores and edge zones. Both otolith core and edge values varied significantly among the collection locations in the Atlantic Ocean and the Mediterranean Sea. The significant differences in the geochemical signatures between the two otolith zones (Sr:Ca, Ba:Ca, δ13C, δ18O) were possibly associated with ontogenetic changes in physiology and feeding habits of hake. Otolith edge signatures proved to be a valuable tool for classifiying individuals to the collection locations. Individuals were assigned to three different groups in the Atlantic Ocean and in the Mediterranean Sea based on otolith core values using nonmetric multidimensional scaling. Our results suggested movement of individuals among local populations within the Atlantic Ocean and also within the Mediterranean Sea. However, there appeared to be little or no movement of hake through the Strait of Gibraltar. The movement patterns observed do not support the stock boundary established in the northeast Atlantic Ocean but rather advocate for a re-evaluation of the most adequate and effective management units for this valuable demersal species.