Steller sea lion decline perspectives

Transcription

1 Steller sea lion decline perspectives Andrew W Trites North Pacific Universities Marine Mammal Research Consortium Alaska Aleutian Islands Fishing Predation 4, Abund dance 3, 2, 1, Competitive Interactions Ocean Climate Change Guenette, Heymans, Christensen & Trites 26. CJFAS 1

2 Introduction Acoustic Monitoring Predation Rates Night-time Activity Conclusions 12: 14: 16: 18: 2: 22: : 2: 4: 6: 8: 1: 12: 5 1 T65B adult female Depth (m) 1512: 14: 16: 18: 2: 22: : 2: 4: 6: 8: 1: 12: : 14: 16: 18: 2: 22: : 2: 4: 6: 8: 1: 12: T2C2 1 yr. old juvenile T73A1 1 yr. old juvenile Predation is not limited to day-light hours. 12: 14: 16: 18: 2: 22: : 2: 4: 6: 8: 1: 12: T18 adult female Deecke et al. (in prep) Introduction Acoustic Monitoring Predation Rates Night-time Activity Conclusions Daytime Predation Rates: Biases in the Prey Spectrum Diet of West Coast Transients Observer Dedicated Reports Acoustic Follows (N=16) (N=31) Steller sea lion 36% 3% Unidentified 55% Harbour seal 36% killer whales consume the equivalent of one harbour seal per day. Harbour porpoise: 16% Harbour Dall s porpoise: % % Sea otter: % Sea otter: 7% Dall s porpoise 21% Harbour seal 26% 2

3 Predation? Likely insignificant at high populations But very significant when populations are low Rates of predation likely vary by region of Alaska 3

4 Steller sea lion haulouts are breeding locations for non-pregnant females Alaska Canada Rookeries Haulouts Trites & Coombs (in prep) Weaning: in summer, not 1, 2, or 3 y 4

5 Sample size and proportion suckling -1 y (Pups) 1-2 y (Yearlings) 2-3 y (2 year olds) % Males (dots) 1. Proportion Suckling MALES FEMALES Age (months) % branded animals observed suckling Pe ercent Suckling Females * Males = 1 = Age (years) 5

6 Skulls Measured Total males females skulls accessed skulls with info (sex, location, date) skulls of known age Isono et al. (in prep) 6

7 4 Age by tooth section n=136 Age by Suture Index n= Length of Skull (cm) n=133 n= Years Suture Index 4 35 After Asia Alaska BC - California After Before 3 25 Before Before After Skull Length (cm) After n=27 n=71 After n=34 n=63 After n=28 n= Before Before Before 15 n=26 n=9 n=56 n=37 n=44 n= AGE (Suture Index) 7

8 Discriminant Function Analysis 4 2 Asia 39 Skull Measurements Loading Alaska Asia BC California Region of collection correctly predicted 74-92% of the time -2-4 BC California Alaska Loading 1 Why did the sea lions get bigger? Staying 1-3 y longer with their mothers Young don t have stomach capacity for low energy prey 8

9 Steller sea lions evolved in a North Pacific Ocean that may shift periodically from one dominated by fatty fish (clupeids) to one dominated by lean fish (gadids) High Abundance Low Abundance Pacific Decadal Oscillation May explain the plasticity in the age at weaning Sea lions in the Laboratory Established female Steller sea Vancouver Aquarium 5 female Steller sea Open Water Research Lab 6 female Northern fur Vancouver Aquarium 9

10 Sea lions in the Laboratory To understand the reasons for the decline of marine mammal populations in the North Pacific and formulate science-based recovery plans. Variable Environment Controlled Environment Controlled change Presumed negative effect Interpretation to wild Observed effect Animals in the wild Animals in laboratory Captive Steller sea lions Food intake Allen (29). 1

11 Captive Steller sea lions Food intake Allen (29). Captive Steller sea lions food intake Females body mass food intake Males body mass Allen (29). 11

12 Diet Studies Correction factors required for scat analysis due to bias from prey type, size, animal activity, etc. Evaluation of new techniques (QFASA, stable isotope analysis, prey DNA) show varying levels of accuracy and precision There are true differences in the nutritional value of different prey items to sea lions Foraging Studies Various measures can be used to identify or quantify costs of changes in behavior - heart rate, accelerometry, ODBA but specific calibration coefficients are required 12

13 Foraging Studies Transit diving and foraging diving have different costs and should not be used interchangeably (model implications) Decreasing prey field density elicits switching to deeper prey, but with distinct energetic costs Bioindicators of Nutritional Status Some traditional indicators have limited value in stressed Steller sea lions (blubber depth, blood biochemistry) Others appear more promising (fecal and circulating hormones) 13

14 Effect of season on nutritional stress Effect of food restriction depends on seasonal conditions (even in captivity) More attuned to (natural) periodic food shortages in winter than in summer: Recover faster in winter than in summer Restriction Students, i in winter produces greater increase Volunteers in cortisol, Friends (may be and healthy Family reaction to restriction) Review effect of diet changes Rosen 29. Mammal Review 39: Different prey have different nutritional value 2. Quality matters if intake is insufficient (physiological or ecological limits) 3. Finite ability to adjust food intake (stomach) 4. Finite capacity for physiological compen- sation (metabolism) 5. Effect of nutritional stress depends on age, season, sex, extent of episode vs. recovery 14

15 Critical Habitat Qualitative Model Critical Habitat quantitative model Adult females, winter Distance to central place Depth Gregr & Trites 28. Marine Ecology Progress Series 365:

16 Alternative Critical Habitat definition Adult females, winter Transparency allows review and debate Ecological assumptions can be investigated Costs of various closures can be explored Critical Habitat Assessment Prey distributions are a good tool to assess critical habitat boundaries The amount of prey biomass enclosed within the critical habitat boundaries varied between region Critical habitat should be refined using prey distributions and seasonal and annual oceanographic information Flinn et al. (in prep) 16

17 Variability in Sea Lion Counts Sunset Island summer 23 ber of animals on lan nd num 2 1 8: 2: 1 days 19 before after 17