Lifetime residency of capelin (Mallotus villosus) in West Greenland revealed by temporal patterns in otolith microchemistry

Capelin (Mallotus villosus) is a marine fish species that spawns along the shorelines of Greenlandic fjords during late spring/early summer, but its migration patterns from hatching to spawning are largely unknown. This prohibits optimal fisheries advice and management of the stock. In this study, we examine spatial population structure through the lifetime of capelin in West Greenland using otolith microchemistry of 421 individual fish, caught while spawning at 16 different localities.

In order to investigate the life-time residency of each fish, otolith core-to-edge measurements of Ba, Li, and Pb concentrations are classified to either of two West Greenland regions (north/south of ~68° N). Classifications suggest that West Greenland capelin reside mostly within one region throughout their life.

Secondly, examination of Pb profiles indicate local residency on a smaller geographical scale. Otolith Pb levels, which most likely reflect bioavailable Pb derived from local geological and anthropogenic sources, vary between localities, but are found to be largely consistent throughout otolith chronologies of individual fish.

Fish from neighboring localities are in some cases found to have contrasting otolith Pb levels, which suggests the existence of locally segregated populations with little or no connectivity. Significant Pb increases are observed towards the otolith edge, which indicates relatively high Pb exposure during the spawning period, where the fish enter shallow waters.

These findings are in stark contrast to what is seen in other North Atlantic capelin stocks, such as those spawning in the Barents Sea, around Iceland and off East Canada, which exhibit long-distance migrations between spawning, feeding and overwintering areas. The information presented here has implications for West Greenland capelin stock management, which should be fitted within a high spatial resolution framework that takes locally segregated populations into account to avoid local collapses.