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

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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

  • Occurs in many species

    • Annual

    • Seasonal

    • Daily


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

  • 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


Photo: Jeff Mondragon


Serengeti Migration


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

  • 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

  • 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


Lynn Canal

Stephens

Passage

Icy Strait/

Cross Sound

Frederick

Sound

Chatham

Strait

Gulf of Alaska


~30% in

Lynn Canal

JAN

FEB

MAR

APR


~31% in

Lynn

Canal

~38% in

Cross

Sound

~30% in

Cross

Sound

~60% in

Frederick

Sound

~50% in

Frederick

Sound

MAY

JUN

JUL

AUG


OCT

SEP

NOV

DEC


Classification of seasonal distribution patterns


Type 1

Up to 55% in winter

Up to 56% in

spring

Up to 44% in fall

Up to 78% in

summer


Benjamin Island (2001-2004)

Type1

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


Type 1

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


Type 2

Gran Point 2001-2004


Spawning eulachon

Spawning herring

Spawning capelin

Type 2

APR

MAY

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


Type 2


Type 3


Type 4


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)


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

  • 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

  • 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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