Analyses of Bering Sea bottom- trawl surveys in Norton Sound: Absence of regime shift effect on...

Analyses of Bering Sea bottom-Analyses of Bering Sea bottom-trawl surveys in Norton Sound: trawl surveys in Norton Sound: Absence of regime shift effect on Absence of regime shift effect on

epifauna and demersal fishepifauna and demersal fish

Toshihide “Hamachan” HamazakiToshihide “Hamachan” HamazakiAlaska Department of Fish & GameAlaska Department of Fish & Game

Division of Commercial FisheriesDivision of Commercial FisheriesAnchorage AlaskaAnchorage Alaska

ICES Journal of Marine Science 62: 1597-1602 (2005)

Effects of Regime Shifts are Effects of Regime Shifts are Real!Real!

Anderson 2000

Effects of Regime Shiftson the Bering Sea Ecosystem is well documentedSeveral mechanisms have been proposed-Ocean current pattern -Sea ice distribution-Location of upwelling-Bottom up vs. Top down

However, most studies are limited to However, most studies are limited to the Gulf of Alaska and Southeastern the Gulf of Alaska and Southeastern Bering Sea.Bering Sea.

GMT FEB 01 15:30:22 2000 FIGURE 1

180º

180º

160ºW

160ºW

140ºW

140ºW

120ºW

120ºW

30ºN 30ºN

40ºN 40ºN

50ºN 50ºN

60ºN 60ºN

Hare & Mantua 2000

Bering Sea Ecosystem Consists of Bering Sea Ecosystem Consists of Several Distinct Water Masses / Several Distinct Water Masses / EcosystemsEcosystems

Are the effects Are the effects of Regime Shift of Regime Shift the same the same among various among various ecosystems? ecosystems?

Norton Sound EcosystemNorton Sound Ecosystem

• Inshore water system Inshore water system isolated from major isolated from major ocean currentsocean currents

• Shallow water depth (< Shallow water depth (< 30 m)30 m)

• Ice Cover for 6 monthsIce Cover for 6 months

• Influx of freshwater and Influx of freshwater and nutrients from rivers nutrients from rivers

• Dominated by Dominated by InvertebratesInvertebrates

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#Nome

70 0 70 140 Kilometers

Alaska

63° 63°

64° 64°

65° 65°

168°

167°

167°

166°

166°

165°

165°

164°

164°

163°

163°

162°

162°

161°

161°

Norton Sound Trawl Norton Sound Trawl SurveySurvey

• One of a few long-term One of a few long-term survey data available in survey data available in the north Bering Seathe north Bering Sea

• Started 1976 for Started 1976 for development of red king development of red king crab fishery. (There has crab fishery. (There has been no major fisheries in been no major fisheries in Norton Sound)Norton Sound)

• Triennially by NMFS (76-Triennially by NMFS (76-91) and by ADF&G (96-02)91) and by ADF&G (96-02)

• Identify & weigh all Identify & weigh all vertebrates and vertebrates and invertebrates captured.invertebrates captured.

Total Biomass ChangeTotal Biomass Change

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

1976 1979 1982 1985 1988 1991 1996 1999 2002

Year

CP

UE

Ind

ex

Sea stars Crabs

Snails Corals

Other invertebrates Flatfishes

Cods Sculpins

Other fishes

Increasing TrendsIncreasing Trends

R2 = 0.8085

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

1976 1981 1986 1991 1996 2001 2006

TotalR2 = 0.8262

0

1000

2000

3000

4000

5000

6000

7000

8000

1976 1981 1986 1991 1996 2001 2006

Sea-star

R2 = 0.5906

0

50

100

150

200

250

1976 1981 1986 1991 1996 2001 2006

CrabsR2 = 0.6231

0

100

200

300

400

500

600

700

800

1976 1981 1986 1991 1996 2001 2006

Flat fish

Total CPUE

Flat-fishesCrabs

Sea-Stars

Trends among 48 taxonomic Trends among 48 taxonomic groupsgroups

0%

5%

10%

15%

20%

25%

-0.4 -0.2 0 0.2 0.4 0.6 0.8

Pearson Coefficient

Pe

rce

nta

ge

Taxonomic CompositionTaxonomic Composition

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

1976 1979 1982 1985 1988 1991 1996 1999 2002Year

CP

UE

Ind

ex

Sea stars CrabsSnails CoralsOther invertebrates FlatfishesCods SculpinsOther fishes

Bottom Water Temperature Bottom Water Temperature

0

1

2

3

4

5

6

7

8

9

10

1976 1979 1982 1985 1988 1991 1996 1999 2002

Year

Bo

tto

m W

ate

r te

mp

era

ture

(C

)

Other SpeciesOther SpeciesCoho Salmon

0

20,000

40,000

60,000

80,000

100,000

120,000

1961 1971 1981 1991 2001

Chum Salmon

0

50,000

100,000

150,000

200,000

250,000

300,000

350,000

1961 1971 1981 1991 2001

Chinook Salmon

0

5,000

10,000

15,000

20,000

25,000

1961 1971 1981 1991 2001

Sockeye Salmon

0

200

400

600

800

1,000

1,200

1,400

1961 1971 1981 1991 2001

Norm Annual Mean Temperature

-6

-5

-4

-3

-2

-1

0

1907 1917 1927 1937 1947 1957 1967 1977 1987 1997

Nome Air Temperature Coho Catch

Chinook CatchChum Catch

Sockeye Catch

ConclusionConclusion• Norton Sound benthic biomass Norton Sound benthic biomass

increased by 3 folds from 1976 to increased by 3 folds from 1976 to 2002 across major taxoninc groups. 2002 across major taxoninc groups.

• Benthic composition did not Benthic composition did not significantly change from 1976 to significantly change from 1976 to 2002.2002.

•No Apparent Regime Shifts No Apparent Regime Shifts Effects were detected. Effects were detected. – Increase of overall biomass can be Increase of overall biomass can be

attributed to temperature increase attributed to temperature increase since 1976 (Regime shifts effects?)since 1976 (Regime shifts effects?)

DiscussionDiscussion

• Norton Sound ecosystem Norton Sound ecosystem characteristics differ from SE Bering characteristics differ from SE Bering Sea, which resulted in the lack of Sea, which resulted in the lack of Regime Shift effectsRegime Shift effects

• Effects and influential mechanisms of Effects and influential mechanisms of Regime Shift would differ among Regime Shift would differ among regional ecosystemsregional ecosystems

•Need to study/monitor various Need to study/monitor various parts of Bering Seaparts of Bering Sea

FurtherFurther Study DirectionsStudy Directions•2006 Trawl Survey 2006 Trawl Survey (Pending: No bidders 2005 )(Pending: No bidders 2005 )

– This Survey may show a significant faunal change. This Survey may show a significant faunal change. – Virtual disappearance of sea star from winter king Virtual disappearance of sea star from winter king

crab survey since 2003crab survey since 2003

•Spatial-Temporal Analyses Spatial-Temporal Analyses (NPRB funding proposal)(NPRB funding proposal)– Identify areas of high biomass, species richness Identify areas of high biomass, species richness

and diversity and diversity – Examine changes in spatial distributionExamine changes in spatial distribution– Correlate spatial distribution of major species with Correlate spatial distribution of major species with

environmental variablesenvironmental variables– Construct potential habitat prediction model Construct potential habitat prediction model

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1976Red King CrabDistribution

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1988

Red King CrabDistribution

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What Caused Those Changes?

FurtherFurther Study DirectionsStudy Directions•2006 Trawl Survey 2006 Trawl Survey (Pending: No bidders 2005 )(Pending: No bidders 2005 )

– This Survey may show a significant faunal change. This Survey may show a significant faunal change. – Virtual disappearance of sea star from winter king Virtual disappearance of sea star from winter king

crab survey since 2003crab survey since 2003

•Spatial-Temporal Analyses Spatial-Temporal Analyses (NPRB funding proposal)(NPRB funding proposal)– Identify areas of high biomass, species richness Identify areas of high biomass, species richness

and diversity and diversity – Examine changes in spatial distributionExamine changes in spatial distribution– Correlate spatial distribution of major species with Correlate spatial distribution of major species with

environmental variablesenvironmental variables– Construct potential habitat prediction modelConstruct potential habitat prediction model

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