population dynamics and foraging ecology of northern sea otters (enhydra lutris kenyoni) in...
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Population Dynamics and Foraging Ecology of Northern
Sea Otters (Enhydra lutris kenyoni) in Washington State
Jessica Hale1, Kristin Laidre2, Ron Jameson3, Steve Jeffries4
1University of Washington, SAFS2University of Washington, SAFS & Polar Science Center
2USGS3WDFW
Clara L. Minard
WDFW, 2004
Objectives
1. Understand population growth and range expansion of northern sea otters in Washington State since reintroduction;
2. Quantify changes in the diet of sea otters over the 46-year period of population growth since reintroduction.
Methods
• Develop a spatially explicit demographic population model for northern sea otters in Washington State
• Compare diet across a gradient of occupation time using space-for-time approach
• Evaluate diet changes overtime by comparing foraging data collected in 1993-1999 to current diet at same sites
Most recent index of population size: 1573 total
1975 1980 1985 1990 1995 2000 2005 2010 20150
200
400
600
800
1000
1200
1400
1600
Independents
Pups
Year
Inde
x of
Pop
ulati
on S
ize
0 5 10 15 20 25 30 35 400
200
400
600
800
1000
1200
1400
1600
ObservedPredicted
Year
Inde
pend
ent C
ount
1975 1980 1985 1990 1995 2000 2005 2010 2015
( )( 1) ( ) 0.19 ( ) 1
1149.59
N tN t N t N t
WDFW, 2004
NORTH
SOUTH
1975 1980 1985 1990 1995 2000 2005 2010 20150
10
20
30
40
50
60
70
80
90
100
% North
% South
Year
Perc
ent o
f Tot
al P
opul
ation
Inde
xPopulation Distribution between
North and South
NORTH
SOUTH
1975 1980 1985 1990 1995 2000 2005 2010 20150
50
100
150
200
250
300
350
400
450
500
North Segment
Observed
Predicted
Year
Inde
pend
ent C
ount
( )( 1) ( ) 0.30 ( ) 1
336.69
N tN t N t N t
NORTH
1975 1980 1985 1990 1995 2000 2005 2010 20150
200
400
600
800
1000
1200
South Segment
Observed
Predicted
Year
Inde
pend
ent C
ount
( )( 1) ( ) 0.23 ( ) 1
1150.64
N tN t N t N t
SOUTH
Prey frequency was different among years (χ2=10012, d.f. = 60, p <0.001).
1993-1999 Foraging Analyses by Year
© Caroline Hempstead
Prey frequency was different among seasons (χ2=7139, d.f. = 30, p <0.001).
1993-1999 Foraging Analyses by Season
Prey frequency was different between male and female sea otters (χ2=148, d.f. = 10, p <0.001).
1993-1999 Foraging Analyses by Sex
Fisheries Species
1993-1999 Foraging Analyses – Fisheries Species
1993 1994 1995 1996 1997 1998 19990
10
20
30
40
50
60
70
80
90
100
Fisheries SpeciesNon-fisheries Species
Year
Perc
ent o
f Die
t
Preliminary Foraging Observations
Planned Analyses
• Bayesian State-Space Model
• Re-calculate carrying capacity using recent survey indices
• Create a Spatially Explicit population model
• Space-for-time diet comparison
• Historical diet comparison at same sites
Tinker et al. 2008
Acknowledgments• Pilot Jeff Well from Rite Bros. Aviation• Mick Cope, Anita McMillan, and Shelley Ament from WDFW• Deanna Lynch and Sue Thomas from USFWS• Shawn Larson, Pat McMahon, and Caroline Hempstead from the
Seattle Aquarium• Lisa Triggs, Mandy Betz, and Terre Zorman from Point Defiance Zoo
and Aquarium• Richard McGovern, Donna Hauser, and Erica Escajeda• Funding from NOAA Dr. Nancy Foster Scholarship Program
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