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Results of 2005 sea otter
survey on the Commander
Islands: More Questions.
Alexander Burdin, UAF, ASLC
Sergey Zagrebelny, Commander Islands State Preserve
Russia
Commander Islands
Aleutian Islands
USA
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 2005--sea otter surveys of the
Commander Islands (Kamchatka, Russia)
Bering Island – 2-3 June and 28-29
June
Medny Island – 24-25 June (about
75% of shore line were surveyed); 15-16
July (complete survey)
Results
• Most sightings in about 10-15 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).
Skiff-based sea otter surveys on the Commander Islands (Bering and Medny) in
1985-2005
7000
6000
5000
4000
3000
2000
1000
0
1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005
years
Some factors effecting to the sea otter
population status on the Commanders vs.
Aleutian.
Commanders Aleutian
Human activity?
Low
Low
Over/Underestimation of sea otter population
abundance in previous years?
Negative
Negative
High survival and birthrate in the past year?
Positive
Negative
Low mortality rate?
Positive
Negative
Immigration from the Aleutian Islands?
Positive??
Negative
Low predator pressure?
Positive
Negative
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 cookiecutter shark distribution
Commander Islands
Aleutian Islands
Conclusion
• 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.
• 2005 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.
Thank
Fromyou!
Russia with love!