A tale of two sharks and their many parasites (Alebion carchariae)

During a 2021 research trip, with the help of Shaun Scipio, Alex Knipe and Adriene Levknecht, visiting researcher Dr. Danielle Orrell from the Hussey Lab at the University of Windsor collected the first record of the fish parasite, Alebion carchariae, in Ascension’s waters. Through a collaboration with Alaska Fairbanks University, these samples now provide the first DNA barcode of this parasite species and the first record of its attachment to Galapagos sharks.

While fishing, two juvenile sharks were accidentally captured from ashore at Comfortless Cove and English Bay. In total, six parasites were plucked from the snout and face of these two sharks during hook removal, and the sharks were quickly returned to the water. Collected parasites were identified as copepods, a type of tiny crustacean distantly related to land crabs and lobster. This type of parasite is known to feed on tissue, mucus, or blood of marine fishes, ranging from small bait fish to large sharks.

To date, this parasite species has been recorded on at least 15 shark species and one fish species. The closest records of this species to Ascension were documented off the eastern U.S., São Paulo and the coast of West Africa. Its life cycle and reproduction are unknown. However, its distant parasite relative, the sea louse, has been relatively well studied owing to its impact on aquaculture (seafood farming). Studies of sea louse suggest that these parasites will gather near the water’s surface to increase their chances of finding a host. The infective stage lasts 1-9 days, and only once attached to a host can it fully develop and reproduce, with a > 210-day life span recorded. It is not yet known how this parasite species made it to Ascension Island. However, its long lifespan may allow it to hitchhike onto migratory species which travel across oceans, or it may incidentally arrive via ocean currents.

Further sampling of the parasitic assemblage around Ascension through water sampling or opportunistic collection during future tagging work could provide insight into the life cycle and ecology of this poorly studied group of parasites. They could also help identify the movements and genetic connectivity of their host, the Galapagos shark. In light of this discovery, the Marine science team welcome any photos of sharks with unusual “clingers on”. These tiny animals could help unravel many mysteries surrounding Ascension’s Galapagos sharks and the microscopic communities that Ascension hosts.

For more information, please contact the Conservation office or read the full paper which is now available online https://doi.org/10.1017/S0025315422001060.

Dr. Danielle Orrell, University of Windsor

Conservation and Fisheries Directorate 2023