Bivalves recently cracked by sea otters (Enhydra lutris) indicating re-occupation

We discovered numerous large marine bivalve shells (and two chiton shells) that had been cracked recently by sea otters. Ocean View Beach is around the southern extent of Vancouver Island and back again north in the Strait of Georgia. The present observation is evidence of sea otters traveling into the Strait of Georgia.

Tom Okey, Theo Okolowicz, and Phoebe Okey-Dobie reported:

Observation: Along the strand line on the sandy beach adjacent to the Tsawout First Nation reserve on the north end of Island View Beach in Saanich, British Columbia, we discovered numerous large marine bivalve shells (and two chiton shells) that had been cracked recently by sea otters (Enhydra lutris). These shells have a characteristic pattern of being 'otter-cracked' with one of the two valves broken (smashed) and with the ligament (at the valve hinge) torn non-symmetrically (see photos). These two characteristics indicate that these large clams were consumed by one or more sea otters.

Evidence and interpretation: Inspection of these sea otter-cracked shells also reveal that they are 'recent-otter-cracked' given the lack of growth of fouling organisms or discoloration on the inside of any of the shells, and due to the fresh flesh material on at least two of the shells (see photos). The bivalve shells in declining order of abundance of otter-cracked shells are Washington butter clams (Saxidomus gigantea), basket cockles (Clinocardium nuttallii), and bent-nosed clams (Macoma nasuta). These shells were relatively large, also indicating a recent re-occupation of this habitat. Two chitons of the genus Mopalia (Gould, 1846)(see Baldwin 2018) were also (very) recently consumed, likely also by sea otters. This is a clear indication that sea otters (Enhydra lutris) have re-occupied the Strait of Georgia after having been extirpated over a century ago.

Survey methods: We walked a 535 metre transect (measured later using Google Earth) on Ocean View Beach along the mid-intertidal strand line from the information signs on the south end of Tsawout First Nation territory (see photos) north to the rocky point (see photo of Theo on rocky outcrop) on April 7th, 2018 starting at 11:45 am. We soon discovered recent otter-cracked shells, and so we collected all otter-cracked shells visible on the surface of the sand along the strand line (~4 m transect width). We arranged all shells by species and photographed them all together, and took several close-up photos as well to show the evidence of them being recently sea otter-cracked.

Discussion: Sea otters have not been present in this particular area for over a century, but they were recently observed to have appeared at and near Victoria, British Columbia at the southern tip of Vancouver island after having recently expanded south down the west coast of Vancouver Island from their longer-term refuge along the northern section of the west coast of Vancouver Island (e.g. Checleset Bay and Kyuquot Sound) where they were reintroduced between 1969 and 1972. Ocean View Beach is around the southern extent of Vancouver Island and back again north in the Strait of Georgia. The present observation is evidence of sea otters traveling into the Strait of Georgia from the south (either from down the west coast of VI or from the Olympic Peninsula north across the Juan de Fuca Strait). In 2017, Sea Otters were observed by kayakers off Mittlenatch and Cortez Islands near Campbell River at the very northern extent of the Strait of Georgia, but those may have expanded from the North, around the northern tip of Vancouver Island. Sea otters have also been seen at Quadra Island. It appears that sea otters are suddenly reoccupying the Strait of Georgia from both the north and the south.

Literature Cited

Baldwin, Aaron. (2018). Illustrated Keys to the chitons (Polyplacophora).

.