FOOD FOR THOUGHT: HOW DOES WASHINGTON SEA OTTER DIET VARY ACROSS A GRADIENT OF OCCUPATION?
Lance et al. 2004
Jessica R. Hale, Kristin L. Laidre, Ronald J. Jameson, Steven J. Jeffries, M. Tim Tinker, Shawn E. Larson, James L. Bodkin Clara L. Minard Lance et al., 2004 1977199020002010-1989199920092014 Cumulative Density Where does WA fit?
Tinker (2015) Site Cumulative # years Density occupied Koitlah Point KOITLAH POINT 0.03 22
DUK POINT 47.86 27
CANNONBALL 58.03 33
SAND POINT 34.52 29
YELLOW BANKS 43.26 29
NORWEGIAN 33.59 24 MEMORIAL GIANTS 19.51 37 GRAVEYARD BEACH 4 0.32 9 C. Hempstead
C. Hempstead Sea otter foraging analysis - SOFA
• Monte Carlo re-sampling algorithm (Dean et al. 2002; Tinker 2004, 2008, 2012; Weitzman 2013) • Used previously assembled information on diameter-biomass relationships & calorific densities for each prey type (Oftedal et al. 2007) • Algorithm output included: 1. rate of energy gain (kcal/min) 2. rate of mass gain (g/min) 3. estimates of diet composition • Uncertainty estimates for each
Tinker (2015) 60 General foraging results 40 20 Percent of Diet of Percent • Approximately 77% of dives resulted 0
in successful prey capture 15 • Average dive time was 51.30 ± 31.11 s, average surface time was 39.13 ± 10
53.29 s (g/min) 5
• Average rate of energy gain was Rate Intake Mass 0
14.21 kcal/min 10 8 6 4 2 Energy Intake Intake Energy
Rate (kcal/min) Rate 0 crabs clams snails Butter clam (Saxidomus gigantea)
Koitlah Point Butter clam (Saxidomus gigantea) Unidentified clam
Koitlah Point Butter clam (Saxidomus gigantea) Unidentified clam Northern kelp crab Pugettia producta) Koitlah Point ( Butter clam (Saxidomus gigantea) Unidentified clam Northern kelp crab Pugettia producta) Koitlah Point (
Unidentified crab Butter clam (Saxidomus gigantea) Unidentified clam Northern kelp crab Pugettia producta) Koitlah Point (
Unidentified crab
Unidentified snail Butter clam (Saxidomus gigantea) Unidentified clam Northern kelp crab Pugettia producta) Koitlah Point (
Unidentified crab
Unidentified snail
Kelp crab (Pugettia spp.) Butter clam (Saxidomus gigantea) Unidentified clam Northern kelp crab Pugettia producta) Koitlah Point (
Unidentified crab
Unidentified snail
Kelp crab (Pugettia spp.)
Red rock crab (Cancer productus) Butter clam (Saxidomus gigantea) Unidentified clam Northern kelp crab Pugettia producta) Koitlah Point (
Unidentified crab
Unidentified snail
Kelp crab (Pugettia spp.)
Red rock crab (Cancer productus)
Pacific razor clam (Siliqua patula) 35 30 25 20 15
Kcal/minute 10 5 y = 0.0009x2 - 0.1445x + 18.675 R² = 0.0989 0 1.6 1.4 1.2 1 0.8
0.6 y = 0.0003x2 - 0.0076x + 0.878 Diet Diversity Diet 0.4 R² = 0.2848 0.2 0 0 10 20 30 40 50 60 70 Sea Otter Cumulative Density WA Pug Sz1 100
90
80
70
60 Mean = 36.5 s
50
40
30
20
10
0 0 50 100 150 200 250 300
CA kcr Sz1 300
250
200 Mean = 56.7 s
150 (Hakai: 57)
100
50
0 0 50 100 150 200 250 300 WA Pug Sz 2 40
35
30
25
20 Mean = 51.0 s 15
10
5
0 0 50 100 150 200 250 300 350
CA kcr Sz2 100
80
60 Mean = 101.2.5 s
40 (Hakai: 90)
20
0 0 50 100 150 200 250 300 350 30
25
20
15
Kcal/minute 10 y = 0.0103x2 - 0.7472x + 23.79 R² = 0.7815 5
0 1.6 1.4 1.2 1 0.8
0.6 y = 0.0003x2 - 0.0076x + 0.878 Diet Diversity Diet 0.4 R² = 0.2848 0.2 0 0 10 20 30 40 50 60 70 Sea Otter Cumulative Density Core Area - North Segment 500 Nt() 450 Nt(+= 1) Nt ( ) + 0.29 Nt ( ) 1 − 342.55 400 350 NORTH 300 250 200
Independent Count Independent 150 Observed 100 Predicted 50 0 1966 1976 1986 1996 2006 2016 Year Expanding front - South Segment 1600
1400 Nt() Nt(+= 1) Nt ( ) + 0.23 Nt ( ) 1 − 1200 1223.87
1000
800
SOUTH 600
Independent Count Independent Observed 400 Predicted 200
0 1966 1976 1986 1996 2006 2016 Year Site Cumulative Rate of Diet Density Energy Diversity (otters/km2) Gain (kcal/min) Koitlah Point 0.03 7.23 1.22
Sand Point 34.52 14.41 1.33
Yellow Banks – 43.26 11.46 0.83
S. segment Duk Point – 47.86 13.62 1.40 N. segment Washington Washington Cannonball 58.03 15.41 1.25
Washington Washington Beach 4 0.32 28.58 0.64
Giants Graveyard 19.51 21.24 0.47 Tinker (2015) Future work
• Investigate habitat correlations (kelp, substrate type) with diet composition using linear mixed effects models • Compare diet overtime (1990s vs 2010s) • Bayesian population model
Kate Thompson, NOAA Acknowledgments • Co authors Kristin Laidre (UW), Ron Jameson (USGS), Steve Jeffries (WDFW), Tim Tinker (UCSC), Shawn Larson (Seattle Aquarium) & Jim Bodkin (USGS) • Makah Tribe, Olympic National Park & OCNMS for permits & collaboration • Everyone involved with annual sea otter survey (Rite Bros. Aviation, WDFW, USFWS, Seattle Aquarium, Point Defiance Zoo and Aquarium & many more) • Advisor Kristin Laidre, lab mates Donna Hauser, Erica Escajeda, Jenny Stern • Technicians Allison Northey, Amanda Witt, Abby van Hemmen, Carter Johnson & Christine Phelan • Funding from NOAA Dr. Nancy Foster Scholarship Program, UW School of Aquatic and Fishery Sciences & Dr. Holly Reed Conservation Fund (PDZA) Questions?