Modern status of Sea otter population on the Commander Islands Alexander Burdin, Kamchatka branch of Pacific Institute of Geography, RAS, University of Alaska, Fairbanks, ASLC, Sergey Zagrebelny, Commander preserve
Commander Islands (population growing) Population declines
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. Increasing (13%/year) sea otter population on the Commander Islands.
Research Objectives Research Objectives Commander-Aleutian islands comparisons to better understand ultimate reasons for the decline to characterize physiology, behavior, and demography of sea otter population near K. to expand studies of sea otter-kelp forest interactions
2004-2005 winter field work 2004-2005 winter field work Sea otter mortality, disease, physical conditions monitoring: Carcasses collection / capture : Age/sex composition Necropsy: disease, causes of death, virology, female reproductive tracts, parasites, stomach contents Biosampling
2006 summer work on the Bering Island Totally 33 sea otters were caught using nets and release.
2006 summer work on the Bering Island 27 sea otters (22 females and 5 males) were instrumented with TDR and radio tag
Ongoing investigation and future research Goal 1. Ecosystem research: long-term changes in near shore communities under sea otter predation. availability and abundance of sea otter food recourses. analysis of TDR s data. direct observation on feeding sea otters. scat analysis. Retrospective analysis of sea otter feeding habits on the Commanders.
Ongoing investigation and future research Goal II. Monitoring of sea otter population: annual survey (skiff and shore based). tracking of radio tagged sea otters (movement and observation on focal feeding animals). mortality (sex/age composition. cause of mortality, disease monitoring). birthrate and survival of young sea otters.
Sea Otter Body Condition Comparison 35 30 25 Weight (kg) 20 15 10 5 Aleutian females, 2004 Commander Isl. females, 2006 Aleutian females, 1960s Aleutian females, 1993 0 5 10 15 20 25 Age
Results of sea otter survey on the Commander Islands in 2005 and 2007 2005 2007 Total number Total number (with pups) Pups (with pups) Pups Bering 3948 783 4218 996 Medny 2502 665 2813 779 Total on the Commanders 6450 1448 7031 1775
Sea otter numbers on the Commander Islands. Bering (1) and Medny (2) Islands 1 2
Sea otter mortality and birthrate (%%) on the Bering Island 1980-2005 30 mortality 25 birthrate 20 15 10 5 0 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004 %
8000 7000 6000 5000 4000 3000 2000 1000 0 Dynamics of sea otter population on the Commander Islan (Bering and Medny) in 1985-2007 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 year
Daily sea otter dynamics on the NW cape (Bering Isl.) in summer 2005. 7/27/05 6/15/05 253 61 6/17/05 200 313 6/19/05 6/21/05 6/23/05 6/25/05 6/29/05 7/1/05 7/4/05 7/6/05 7/8/05 7/11/05 7/14/05 7/16/05 7/18/05 7/20/05 7/25/05 169 2 218 255 244 232 174 301 379 393 353 433 334 326 404 487 484 420 497 543 430 441 400 551 579 452 517 430 594 663 698 7/30/05 8/1/05 74 189 219 423 800 700 600 500 400 300 200 100 0 date
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 years? Positive Negative Low mortality rate? Positive Negative Immigration??? Negative Killer whales pressure as a predator? Negative Positive
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 all 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). 2007 Complete Sea otter survey on the Commander Islands showed that the sea otter population was over 7,000 animals.
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 you! Photo by R. Davis