Download Larson RetreatPoster

Examination of Sea Otter Foraging Behavior to Address Resource Conflicts Between Fishermen and Sea Otters
in Southern Southeast Alaska
Sean Larson1, Zac Hoyt, Ginny L. Eckert, Stena Troyer, Christina Buck, Alice Smoker
Juneau Center, School of Fisheries and Ocean Sciences, University of Alaska Fairbanks
Abstract
Methods
Humans can change marine ecosystems through harvest and
management, and these changes may have dramatic repercussions
many years later. Sea otters were extirpated from Southeast Alaska by
18th and 19th century fur traders. After that time, marine invertebrate
populations thrived, many of which supported lucrative commercial
fisheries. Sea otters were reintroduced into Southeast AK in the 1960’s,
and in the ensuing decades, sea otter reintroductions took hold. Sea
otter populations are now rapidly expanding, at the rate of 13% per year,
and invertebrate fisheries are dramatically declining. The objective of
this study is to evaluate sea otter foraging on commercially important
species in southern Southeast AK; estimates will be used to inform
fishery stakeholders and managers as to resource viability under sea
otter predation pressure. In our 2011 field study commercially important
species represented 11 to 26% of sea otter diet, with 17 to 31 species in
the diet, depending on the duration of sea otter persistence. This threeyear study addresses multi-species interactions to predict future social
and environmental conditions and promote long-term resource
sustainability.
Preliminary Results
•We used the R/V Sea Weasel, a 14’ skiff, to access remote sampling
sites at four different study areas.
•Study areas varied in habitat type and duration of sea otter occupation
(Fig. 2).
•We recorded prey type, quantity, and size, dive duration, surface
duration, and various sea otter descriptors.
•Sea otters from all sampling regions foraged on a total of 45 prey
species (1330 observations).
Figure 3. In areas where sea otters have
been present since 1969, they consumed
31 prey species, with 11% of diet being
commercially important (n=615).
Figure 4. In areas where sea otters have
been present since 2003, they consumed
30 prey species, with 14% of diet being
commercially important (n=314).
Figure 5. In areas where sea otters have
been present since 2010, they consumed
17 prey species, with 26% of diet being
commercially important ( n=401
observations).
Figure 6. Percent of diet consisting of
species of interest for three areas of sea
otter persistence. Clams are included as
a reference species; they make up a
substantial portion of a sea otters diet at
all persistence levels. Percent of diet
consisting of clams is on the secondary
vertical axis.
Background
•Sea otters can significantly reduce the abundance and size distribution of
their prey and, in turn, shape community structure in rocky habitats
(Kvitek et al. 1992).
Figure 1. Researcher Christina Buck conducting sea otter foraging observations
near Divers Bay, AK using high powered Questar telescopes.
•Sea otters in WA have reduced populations of commercially important
invertebrates and are in conflict with tribal, commercial, and recreational
fisheries (VanBlaricom and Chambers 2003).
•ADF&G suspects that sea otter predation has resulted in the closure of
over 18 dive fisheries and a loss of over $4,040,646 in ex-vessel revenue
between 1993 and 2006 (Scott Walker, Zac Hoyt, ADF&G, unpub data).
•Alaska fishermen claim to have seen the deterioration of macroinvertebrate resources from certain fishing grounds due to presumed sea
otter predation, however very little empirical data exists to verify these
claims.
Discussion
Species of Interest
•Sea otters have more diverse diets in areas where they have persisted for
the longest time. Clams and red sea urchins make up the majority of a diet
in newly established areas.
Panopea generosa
Parastichopus californicus Strongylocentrotus fransicanus
Cancer magister
Haliotis kamtschatkana
Figure 2. Southern Southeast AK historical sea otter distribution. Sea otters
were reintroduced to Southeast AK between 1965 and 1969. Sea otters greatly
expanded their range from 1988 surveys (outlined in green) to 2003 surveys
(outlined in blue) to 2010 surveys (outlined in red). Camping locations and data
gathering sites are shown in yellow and red, respectively. (Esslinger and Bodkin
2009, Verena Gill, USFWS personal communication).
•Feeding rates on commercially important prey varies with species; sea
cucumbers are consumed at a greater rate in areas with longest sea otter
persistence, geoducks in areas with intermediate sea otter persistence,
and red sea urchins in recently colonized areas.
•Based on this preliminary foraging data, sea otters have great potential to
impact red sea urchin fisheries; however, sea cucumber, crab and geoduck
fisheries may also be at risk. Future studies will analyze fisheries data to
evaluate changes as a function of sea otter presence.
Acknowledgements: This project was successful do to our great crew, including; Zac Hoyt, Stena Troyer,
ecobirder.blogspot.com
Christina Buck, Alice Smoker, and Ginny Eckert and family. I would like to thank Alaska Sea Grant, NSF, and UAF
for providing essential funding to make this project and my involvement possible.
References:
cornforthimagesblog.com
Sea otter eating crab near Glacier Bay, AK. Feeding rates on invertebrate
prey can exceed 25% of their body weight per day (Oftedal et al. 2007).
The field crew after
collecting data at the
Barrier Islands.
The R/V Sea Weasel with an
Alpaka raft; used to transport
crew to and from shore based
vantage points.
Alice Smoker collecting
data on a reef near
Level Island.
Esslinger GG and JL Bodkin (2009) Status and trends of sea otter populations in southeast Alaska, 1969-2003. USGS. Sci Invest Rep No 2009–5045.
18 p.
Kvitek RG and JS Oliver (1992) The influence of sea otters on prey communities in southeast Alaska. Mar Ecol Prog Ser 82:103–113.
Oftedal OT, K Ralls, MT Tinker, and A Green (2007) Nutritional constraints on the southern sea otter in the Monterey Bay National Marine Sanctuary.
Mont Bay Nat Mar Sanct and Mar Mamm Comm Tech Rep, Washington, D.C., USA. 37 p.
VanBlaricom GR and MD Chambers (2003) Testing a charismatic paradigm: Consequences of a growing sea otter population for nearshore benthic
communities along the south shore of the Strait of Juan de Fuca. Final Rep of Mar Eco Health Prog to Wash Coop Fish and Wildlife Res Unit. 24 p.
1 Sean
Larson, University of Alaska Fairbanks, SELMR Fellow, Email: [email protected], Phone: (907) 518-0732