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 3 University 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 ( ) -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

Gulf of Alaska Lynn Canal Icy Strait/ Cross Sound Stephens Passage Chatham Strait Frederick Sound

JANFEB MARAPR ~30% in Lynn Canal

MAYJUN JULAUG ~31% in Lynn Canal ~38% in Cross Sound ~60% in Frederick Sound ~30% in Cross Sound ~50% in Frederick Sound

NOVDEC OCT SEP

Classification of seasonal distribution patterns

Type 1 Up to 55% in winter Up to 56% in spring Up to 78% in summer Up to 44% in fall

Womble & Sigler (2006) 325: MEPS Benjamin Island ( ) Type 1

Womble & Sigler (2006) 325: MEPS

Gran Point Type 2

APR MAY Spawning eulachon Type 2 Womble et al. ( 2005 ) 294: MEPS Spawning herring Spawning capelin

Type 2

Type 3

Type 4

JUL AUG Type 3 and Type 4 Pollock primary prey species with FO of salmon up to 35% in late summer and fall in Frederick Sd with (Tollit, UBC) SEP Salmon migratory corridor

MAR APR MAY JUN JUL AUG SEP OCT NOV DEC JAN FEB Pollock (available year-round) Spring-spawning forage fish (herring, eulachon, Capelin)) Summer-spawning salmon Fall-spawning salmon Over-wintering herring

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