linking seasonal migratory patterns with prey availability in steller sea lions
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Linking seasonal migratory patterns with prey availability in Steller sea lions. Jamie N. Womble 1 , Michael F. Sigler 2 , Mary F. Willson 3 1 National Park Service-Glacier Bay Field Station 2 Alaska Fisheries Science Center-Auke Bay Laboratory

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linking seasonal migratory patterns with prey availability in steller sea lions

Linking seasonal migratory patterns with prey availability in Steller sea lions

Jamie N. Womble1, Michael F. Sigler2, Mary F. Willson3

1National Park Service-Glacier Bay Field Station

2Alaska Fisheries Science Center-Auke Bay Laboratory

3University of Alaska Fairbanks-School of Fisheries and Ocean Sciences

migration
Migration
  • Occurs in many species
    • Annual
    • Seasonal
    • Daily
seasonal migration
Seasonal Migration
  • Movements among two or more areas that

are occupied in different seasons during

the annual cycle (Dingle 1996).

possible explanations for the evolution of migratory behavior
Possible explanations for the evolution of migratory behavior
  • Reduces the risk of predation
  • Enhances access to resources such as breeding sites
  • Enhances access to patches of high-quality food and/or shifting patterns of food abundance
objectives
Objectives
  • Assess the seasonal distribution and migratory patterns of sea lions
  • Classify seasonal distribution patterns
  • Determine to what extent seasonal distribution patterns of sea lions can be explained by seasonal prey concentrations
prediction
Prediction
  • Sea lions should aggregate at terrestrial

sites near where seasonal prey densities are

high in order to achieve energy intake to

meet seasonally changing energy demands.

methods
Methods
  • Aerial Surveys (2001-2004)

-24 sites (23 haulouts, 1 rookery)

- monthly (n = 39 surveys)

  • Classification of distribution patterns

-Standardized data by computing the

proportion of maximum count for each site

-Hierarchical cluster analysis

  • Estimation of proportion of sea lions associated with each pattern
slide10

Lynn Canal

Stephens

Passage

Icy Strait/

Cross Sound

Frederick

Sound

Chatham

Strait

Gulf of Alaska

slide12

~30% in

Lynn Canal

JAN

FEB

MAR

APR

slide13

~31% in

Lynn

Canal

~38% in

Cross

Sound

~30% in

Cross

Sound

~60% in

Frederick

Sound

~50% in

Frederick

Sound

MAY

JUN

JUL

AUG

slide14

OCT

SEP

NOV

DEC

slide20

Type 1

Up to 55% in winter

Up to 56% in

spring

Up to 44% in fall

Up to 78% in

summer

slide21

Benjamin Island (2001-2004)

Type1

Womble & Sigler (2006) 325: 281-293 MEPS

slide22

Type 1

Womble & Sigler (2006) 325: 281-293 MEPS

slide23

Type 2

Gran Point 2001-2004

slide24

Spawning eulachon

Spawning herring

Spawning capelin

Type 2

APR

MAY

Womble et al. (2005) 294: 271-282 MEPS

slide29

Type 3 and Type 4

Salmon migratory corridor

JUL

AUG

SEP

Pollock primary prey specieswith

FO of salmon up to 35% in

late summer and fall in Frederick Sd with

(Tollit, UBC)

slide30

Spring-spawning

forage fish

(herring, eulachon,

Capelin))

Fall-spawning

salmon

Summer-spawning

salmon

Over-wintering

herring

Pollock

(available year-round)

MAR APR MAY JUN JUL AUG SEP OCT NOV DEC JAN FEB

conclusions
Conclusions
  • Seasonal prey species available from a few weeks to several months
  • Pollock is available throughout the year and is supplemented with seasonal prey species
  • Migratory behavior of sea lions enhances access to patches of high-quality prey and shifting patterns of food abundance
acknowledgements
ACKNOWLEDGEMENTS
  • AFSC-Auke Bay Laboratory
  • NOAA Fisheries-SSLRI
  • Rasmuson Fisheries Research Center
  • Jacques Norvell-Tal Air
  • Julie Scott-Ashe, Kathleen White, Mervi Kunnasranta, Ben Williams, Dave Csepp, JJ Vollenweider, Ben Williams, Karen Blejwas
  • MMPA/ESA Permit No. 782-1532-02
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