On their own: migrations of northern fur seal pups from increasing and decreasing

populations

Mary-Anne Lea, Tom Gelatt, Devin Johnson, Jeremy Sterling, Rolf Ream, Sharon Melin and Rod Towell

National Marine Mammal Laboratory, NOAA Fisheries, Seattle

Small increasing populations

Northern fur seal breeding sites

56% of population & decreasing

NFS pup production – Pribilof Islands

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St. Paul

St. George

Post-exploitation Commercial harvest Sustainable harvest

North Pacific Regime shifts

2006 St. Paul : 109,937, = 10.5% less than 2004

St. George: 17,070 = 1.2% greater than 2004

- Alternates between terrestrial and aquatic environment

- Congregate on islands during the breeding season ~ 4 mo. Then migratory – in the North Pacific Ocean ~ 8 mo.

-Pribilof population has continued to decline for unknown reasons and is now at the 1917 population level when it was increasing at approximately 8% annually following the termination of pelagic sealing.

-Bogoslof population has increased at 12%/yr since 1997

Northern fur seal life history

Why study pup dispersal?

• Northern fur seal breeding populations currently exhibit markedly different population trajectories

• consequently post-weaning dispersal and migratory behavior may vary between populations and age classes• mortality of juvenile animals is high and environmental conditions encountered during the first year likely influence survival

Study objectives

1. Record the winter movements of newly weaned NFS pups from increasing and decreasing populations in Alaska and California

2. Document the diving behavior of a subset of these pups to examine relationships between diving, age and oceanographic features

3. Assess the degree of overlap in foraging habitat use between breeding sites and age classes

4. Determine environmental factors influencing the spatial and temporal distributions of migration and foraging within and between years.

Tag deployment – Oct/November 2005

Kiwisat 101Location datan=59

Tag deployment – November 2005 n=99

SPLASHLocation &

dive datan=40

Timing of pup departures

St Paul Is. – 10 Nov (28 Oct – 18 Nov 2005, n=44)

St George Is. – 9 Nov (7-14 Nov 2005, n=20)

Bogoslof Is. – 9 Nov (29 Oct – 26 Nov 2005, n=20)

Alaska

San Miguel Is. – 26 Nov (13 Nov- 3 Dec 2005, n=15)

California

Aleutian Pass usage – St Paul Is pups

20% used Amukta Pass Median was 7.5d

Aleutian Pass usage – St George Is pups

St George Island (n=17)

24% usead Seguam Pass Median was 9.6d

Aleutian Pass usage – Bogoslof Is pups

33% used Samalga Pass Median was 2.9 days

(n=17)

Median transit time to Aleutian passes

St Paul Is. – 11.0d (n=31) – max d in Bering Sea: 79.1d

St George Is. – 10.3d (n=18) – max d in Bering Sea: 35.1d

Bogoslof Is. – 6.1d (n=17) – max d N of Aleutians: 220.1d

Male-female transit times

St Paul M: 21.0d F: 13.5dSt George M: 17.0d F: 9.2d P<0.05Bogoslof* M: 16.7d F: 9.0d

*220d max transit removed

Synchrony of mother-pup departuresconcurrent NPRB/NMML work provided opportunity to compare

• mean interval between the departures of 17 mother-pup pairs was 5.8 ± 2.4d

• 59% of pups departed earlier than mothers

• in three cases mother and pups departed on the same day

Mother-pup departures: same day 13 hrs apart

61098Bogoslof

mother

pup

Mother-pup departures: same day

Bogoslof Is.

Mother and pup Traversed same region 12 h apart

pup

female

Environmental conditions on the day of departure may influence travel direction

Distribution of 97 northern fur seal pups (Nov 2005 – Aug 2006)

St George Is.

Distribution of 97 northern fur seal pups (Nov 2005 – Aug 2006)

St Paul Is.

Distribution of 97 northern fur seal pups (Nov 2005 – Aug 2006)

Bogoslof Is.

San Miguel Is.

Distribution of 97 northern fur seal pups (Nov 2005 – Aug 2006)

Transition region

Distribution in relation to age class and sex

Russia

Alaska

Canada

USA

Modeled hourly instantaneous speed

ms-1

215 days

Summary

• little to no synchrony in departures between mother and pups independent dispersal patterns

• high degree of overlap in dispersal patterns of Alaskan pups from St Paul, St George and Bogoslof

• pups exhibit large scale migrations from Russia to California – pups ranging farther west than adult females • current results are preliminary and future analysis will incorporate 67 pups from 2006/7

•35/67 still transmitting as of 22 January: •St. George: 9/18 •St. Paul: 19/25 •Bogoslof: 7/15•San Miguel: 0/9

Inter-annual comparison NFS pup

distribution (Oct-Dec)

Acknowledgements•Alaska Fisheries Science Center

• Rolf Ream, Alain Springer, Sara Iverson and Alison Banks for the kind use of their NPRB-funded female tracking data.

• Jason Baker, Kate Call Tony Orr, and Jim Thomason, Mike Williams and Tonya Zeppelin for help in the field

• St George and St Paul Island communities for helpful support

• National Marine Mammal Lab

• National Academies of Science NRC Research Associateship Program

• Research was conducted under the marine mammal Permit No. 782-1708 issued to the NMML.

Time spent plot for 97 pups – Nov-Aug 2006

Longitude

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Time spent per 25 x 25km grid cell

San Miguel Is.

Distribution of 97 northern fur seal pups (Nov 2005 – Aug 2006)

Transition region

Warm core eddy feature and adult female tracks

ClockwisePositive SSH

! Female tracks

Pup tracks (n=17)

Tracks of 17 mother-pup pairs

• The migratory movements and winter destinations of northern fur seals (NFS) in their first year at sea;

• The foraging activity of this age class as inferred from diving data, when available, or with less certainty, from the amount of time spent in an area; and

• Determine environmental factors influencing the spatial and temporal distributions of migration and foraging within and between years.

Additional secondary aims include: 1. examining island effects on migration parameters; 2. determining the effects of sex on migration parameters; and 3. the ontogeny of dive behaviour throughout the winter for pups

instrumented with satellite relayed dive loggers (SDRs).

Study objectives

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Northern fur seal Bogoslof Island pup production

2005

12,631 (SE = 335)

+12% per year since 1997

Female movements 2005/6 & surface Chl-a conc.

0 mg/m3

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Aleutian Pass usage – St Paul Is pups

Amukta Pass (20%)

(n=31)

Amukta - 7.5d

Aleutian Pass usage – St George Is pups

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Seguam Pass (24%)

(n=18)

St George Island (n=17)

Seguam Pass

Aleutian Pass usage – Bogoslof Is pups

Bogoslof Island (n=18)

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SamalgaPass (33%)

Samalga Pass

(n=17)

Mother-pup departures

10-15d apart5-10d apart

1-5d apart