Lisa Sheffield, Ian C. Rose, Adrian Gall, Daniel D. Roby, David B. Irons, & Kathy Turco

transcript

Lisa Sheffield, Ian C. Rose,

Adrian Gall, Daniel D. Roby,

David B. Irons,

& Kathy Turco

2006 Alaska Marine Science Symposium, Anchorage, AK

Seabird Diet and Reproductive Success as Indicators of Ocean Conditions in the Northern Bering Sea

The Bering Sea and the “Green Belt”

shelf edge

Source: NOAA

The Anadyr CurrentThe Anadyr Current and the “Green Belt”

shelf edge

Source: NOAA

The Northern Bering Sea

• Sea surface temperatures rising

• Sea ice decreasing

• Possible shifts in Anadyr current flow

• Effects on marine life?

A Changing Ecosystem

Sea ice in the Bering Sea

Colonial Seabirds as Indicators

• Marine-dependent /

land-based

• Spatially concentrated & predictable

• Inexpensive (vs. ship time)

Ideal taxon to study ecosystem effects of climate change:

Research Question

• How does seabird diet and reproductive data reflect ocean conditions in the NBS?

Research Question

• How does seabird diet and reproductive data reflect ocean conditions in the NBS?

– What impact might these same conditions have on other upper-trophic level species?

St. Lawrence Island

• 3.6 million breeding seabirds

• 2 Yup’ik villages (Savoonga and Gambell)– Field bases

– Traditional knowledge

• Central location in NBS region

Source: NOAA

Seabird Foraging Guilds

Shallow-divingplanktivore

Deeper-divingplanktivore

Least Auklet:

Crested Auklet:

Murres (2 species):

Pursuit-divingpiscivores

Kittiwake:

Surface-feeding piscivores

Planktivores – The Auklets

• Dominant Bering Sea avian planktivores

• Colonies of >1 million

• ~ 3.2 million nest on SLI

Shallow-divingplanktivore

Deeper-divingplanktivore

Least Auklet:

Crested Auklet:

Auklet Distribution

• Native to deep water (most in Aleutians)

• Only large colonies on the shelf – SLI and Diomede

• Due to Anadyr Current

The Auklets - Diet

Copepods

Euphausiids

Amphipods

Calanus marshallae

Neocalanus cristatus

Neocalanus flemingeri

Thysanoessa raschii Themisto libellula

The Auklets - Diet

Copepods

Euphausiids

Amphipods

Least Auklet diet: Crested Auklet diet :

( Black = Other )

67% Copepods 66%

Euphausiids

2 Genera of Copepods

CopepodsCalanus marshallae

Advected by Anadyr Current

Resident on Bering Sea ShelfSmaller, lower mass

Larger, higher mass

2 Genera of Copepods

CopepodsCalanus marshallae

Advected by Anadyr Current

Resident on Bering Sea ShelfSmaller, lower mass

Larger, higher mass

Associated with higher reproductivesuccess in both auklets (Gall and Sheffield)

Neocalanus copepods

Copepods

Neocalanus spp.

Hypothesis: Auklets will eat more Neocalanus copepods in years of higher Anadyr Current flow.

Neocalanus copepods

Copepods

Neocalanus spp.

• Bering Strait current data used as an index (Woodgate et al.)

- >90% correlation

Neocalanus copepods

15 20 25 30 35

Copepods

Neocalanus spp.

Result: Neocalanus cristatus increase exponentially in auklet chick diets as July current flow increases.

July Mean Bering Strait Northward Flow (cm/s)

p = 0.003

R2 = 0.822

Anadyr Current flow and Auklets

July Anadyr Flow

More Neocalanus cristatus– Collected in August

Source: NOAA

May Anadyr Flow

Earlier LEAU nestingSource: NOAA

p = 0.009

R2 = 0.919

May Anadyr Flow

What is the mechanism?

p = 0.009

R2 = 0.919

If Anadyr Current (July) = more N. cristatus in chick diets (August),

Does Anadyr Current (May) = more N. cristatus during laying (June)?

Source: NOAA

May Anadyr Flow

What is the mechanism?

May Anadyr Flow

Early-season prey Early-season prey availability ??? availability ??? ( ( Neocalanus Neocalanus ))

Earlier LEAU nesting

Source: NOAA

Themisto amphipods

Cold-water Arctic species

Amphipods

Themisto libellula

Themisto amphipods

Amphipods

Themisto libellula

Hypothesis: Themisto will be less available as sea surface temperatures increase.

Themisto amphipods

AmphipodsResult: Higher early-summer SST = less Themisto in auklet diets.

0 0.2 0.4 0.6 0.8 1May Mean Sea Surface Temperature

Themisto libellula

p = 0.023

R2 = 0.863

Themisto amphipods

AmphipodsResult: Higher early-summer SST = less Themisto in auklet diets.

0 0.2 0.4 0.6 0.8 1May Mean Sea Surface Temperature

Themisto libellula

p = 0.023

R2 = 0.863

Will T. libellula decline throughout a warming Bering Sea?

Conclusions• Auklet monitoring:

– NBS ocean conditions affect zooplankton community structure:

• Higher Anadyr current = more Neocalanus cristatus (Monthly scale)• Higher Current = More Neocalanus = Higher auklet success• Higher SST = fewer Themisto amphipods

– Anadyr Current strength affects Least Auklet chronology

• Possibly by advection of early-season Neocalanus

Conclusions• Auklet monitoring:

– NBS ocean conditions affect zooplankton community structure:

• Higher Anadyr current = more Neocalanus cristatus (Monthly scale)• Higher Current = More Neocalanus = Higher auklet success• Higher SST = fewer Themisto amphipods

– Anadyr Current strength affects Least Auklet chronology

• Possibly by advection of early-season Neocalanus

Implications for other marine life?

Implications for other wildlifeP

Neocalanus

• Auklet prey species are also key prey items for Bowhead Whales (Neocalanus) and Arctic Cod (Themisto).

• Seabirds are the most inexpensive way to study these and other aspects of the NBS ecosystem.

Source: ChartingNature.com

Themisto

Acknowledgements

• Coauthors:– Dan Roby, Lisa Sheffield, Adrian

Gall, David Irons and Kathy Turco

Calvin Akeya, Tim and Roland Alowa, Blake Roberts, Mike Denega, Rebecca Woodgate, Karen Fischer, and everyone in Savoonga, AK!

• Funding:– USFWS, USGS-Oregon Cooperative Fish

and Wildlife Research Unit, Spencer Sealy (UM)

The Savoonga Native Corporation

Lisa Sheffield, Ian C. Rose, Adrian Gall, Daniel D. Roby, David B. Irons, & Kathy Turco

Documents