Results of 2005 sea otter survey on the Commander Islands: More Questions. Alexander Burdin, UAF, ASLC Sergey Zagrebelny, Commander Islands State Preserve

Aleutian Islands Commander Islands RussiaUSA

Background Only 200 nm strait between Commander Island and western Aleutian islands. Dramatic decline of sea otter populations (up to 90% and more reduction), and some other marine mammal species (harbor seal, SSL) across the Aleutian Archipelago and Alaska Peninsula during past several decades. Stable To possibly increasing sea otter population on the Commander Islands.

Methods In sea otter surveys of the Commander Islands (Kamchatka, Russia) Bering Island – 2-3 June and June Medny Island – June (about 75% of shore line were surveyed); July (complete survey)

Results Most sightings in about m water depth, the seaward margin of kelp canopy. 83 sea otter groups (5 or more individuals—to 200 animals) were recorded. Largest concentrations of sea otters on northern ends of both Islands. Average group 8-12 sea otters; maximum – 200. On Medny Isl. about 25% of sea otter population concentrated on the relatively small area, about 10 sq. km

Results On Bering Isl. About 30% of sea otters were located also in Northern part of the Island (about 40 sq. km) Kelp beds around both islands (Bering and Medny) were very sparse; relatively dense kelp beds recorded on the Northern part of Bering and Medny Islands (this slide).

Some factors effecting to the sea otter population status on the Commanders vs. Aleutian. CommandersAleutian Human activity?Low Over/Underestimation of sea otter population abundance in previous years? Negative High survival and birthrate in the past year?PositiveNegative Low mortality rate?PositiveNegative Immigration from the Aleutian Islands? Positive ?? Negative Low predator pressure?PositiveNegative

Question to discuss: Why is the sea otter population on the Commander Islands not declining, and resisting influence of such negative factors, like KW predation?

Hypotheses “ Availability, not selectivity” –All observed transient killer whale attacks happened in specific place and for specific prey. “Shield” –Northern fur seal – is the most common prey of killer whales on the Commander Islands (>200,000 ). –All recorded KW attacks on the Commander Islands happened close to the northern fur seal rookeries and almost 100% attacks were on Northern Fur Seals.

Approximate northern boarder of cookie- cutter shark distribution

Commander Islands Aleutian Islands

The data we have presented shows that the population dynamics of the sea otter populations is different even in the nearby area (Aleutians/Commander Islands). Compared with the Aleutian Islands we have seen growth of the sea otter and some other marine mammals populations such as Steller sea lions and harbor seals in the Commander Islands Complete Sea otter survey on the Commander Islands showed that the sea otter population was over 6,000 animals, including about 1,300 pups. According to the results of sea otter counts on the Commander Islands in previous years, the number of sea otters in the Commander Archipelago reached maximum, at least for the last 150 years. Conclusion

We consider northern fur seal to be the most important prey for transient killer whale predation near the Commander Islands, and other areas where this species is present, protecting other marine mammals species from killer whale predation. In areas where fur seals are not abundant or absent, mammal eating Killer whales can be a significant factor of marine mammal declines.

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