Prey Selection by Walrus (Odobenus rosmarus rosmarus) in the Dutch Wadden Sea, the Netherlands

Between February 2021 and April 2022, a female walrus (Odobenus rosmarus rosmarus) was observed multiple times along the North Sea and Norwegian coasts. Scat samples from the walrus were collected on two occasions when it visited the Dutch Wadden Sea between September and November 2021. It was assumed that the walrus fed locally, so to determine the animal’s diet, scat samples were analyzed using molecular methods. In both scats, only the Atlantic razor (jackknife) clam (Ensis leei, M. Huber, 1843), a mollusk species invasive to the region, was found; this species had invaded the area relatively recently and is very abundant. The walrus did not seem to suffer from the warm water temperature, which reached more than 20°C in summer. We hypothesize that the temperature is not the reason for the walrus’s distribution being restricted in the Arctic, but, instead, it was potentially overhunting and ongoing disturbance. The concurrence of the recovering walrus population in the Northeast Atlantic and global warming causing loss of sea-ice for haul out and augmenting human pressure in the Arctic might drive an increase in walrus visits at lower latitudes in the future. We therefore suggest adequate management plans be drawn up to anticipate this.