Ruth Joy University of British Columbia Marine Mammal … · 2011-04-06 · Ruth Joy University of British Columbia Marine Mammal Research Unit. K e l o w n a 2. K e l o w n a 1960

Decline of the Steller sea lion :

Challenges to addressing a dramatic signal

in the dynamics of a marine ecosystem.

Ruth JoyUniversity of British ColumbiaMarine Mammal Research Unit

Kelowna

2

Kelowna

1960 1970 1980 1990 2000Year

0

20

40

60

80

100

1950

Per

cen

t o

f M

axim

um

Fur Seals

Sea LionsHarbour Seals

DeMaster et al. 2006

Dramatic Signal

3

4

Section 7 of the ESA –states that federal agencies must

ensure that“any action authorized, funded, orcarried out does not jeopardize the

continued existence of anyendangered species”.

MISSING

5

1955 1960 1965 1970 1975 1980 1985 1990 1995 2000

0

25

50

75

100

125

150

Biom

ass

caug

ht (m

etri

c to

nnes

)

Year

Pollock Fisheries Data, Aleutian Islands

21

Start ofdecline

1976 2000

0

150

75

Ecosystem

Shift?

Harvest?

Emigration?

Entanglement?

Toxins?

Whaling?

6

A change in food availability?

Fisheries reduced stock size so that SSL did not have enough to eat.

Environment change increased stock size so that sea lions eat a less nutritious diet (Junk food Hypothesis)

7

Available Data and Approaches

Captive animal studies

Computer and animal models

Field studies

8

9

2004

1977

1955

WEST EAST 10

ALASKABering Sea

Aleutian IslandsGulf of Alaska

Counts

Year

ALASKABering Sea

Aleutian IslandsGulf of Alaska

2004

1977

1955

WEST EAST 11

Nutritional Stress: A problem of proof

• What evidence there is – reduced body size in 1980’s over 1970’s in the 1 area in which we have data (Calkins and Goodwin 1988).

• No change in blubber depth

• No change in skull size

12

Limitations of the field data

• No pre decline data

• No consistency of collection methods

• Opportunistically collected

• Biology is such that you never know what exactly you are collecting

13

We try to make a link between the captive animals in a controlled environment and the wild population

Captive animal experiments : Physiology

14

NUTRITIONAL STRESS

Two aspects to nutritional stress:

There is the restriction in QUANTITY of food, but there is also the restriction in QUALITY of that diet.

15

Metabolism

Thermoregulation

ForagingLocomotion

Growth/condition

Digestion

16

Captive Results

• We have shown that young animals cannot buffer the effects of low quality diet. For example, feeding young animals as much as they can eat, they still lose mass on a low energy diet due to restrictions of stomach capacity and digestion efficiency.

17

Week 4

Pro

po

rtio

n o

f b

od

y m

ass

lost

as

bo

dy

fat

or

as le

an m

ass

(%)

-120-100-80-60-40-20

020

Week 4

-120-100-80-60-40-20

020

Restriction Jeanniard du Dot et al. in review

Summer Winter

Herring Herring

Pollock Pollock

Week 4 Week 4

Lipid massProtein mass

Body composition response to nutritional stress

18Recall pollock = “junk food”

An adult male would require 30 kg of herring per day (C.I.: 22.3, 37.7),

but would require 41 kg of pollock per day (C.I.: 31.3, 50.7)

a 37% increase in prey biomass

19

“Real World” Implications

Limitations on Captive Experiments

Although we have a “huge” number of marine mammals by captive standards, it’s only 12 animals, and they differ by gender, age, and captive environment.

At the end of the day, the inference for the results is for a captive environment, and the link to the wild is not always obvious.

20

1955 1960 1965 1970 1975 1980 1985 1990 1995 20000

25

50

75

100

125

150

Biomass caught (m

etric tonnes)

Year

Standardized counts of SSL begin 1973

Pollock Fisheries Data, Aleutian Islands

Broad scale diet data begins 1990

21

Start of decline

Was it fisheries?

• Classical statistics GEE’s attempt to link biomass fished to rates of population change (Dillingham et al. 2006).

• Ecosystem modeling (Guenette et al. 2006)

• Population Dynamic Modeling (Matthiopoulos et al. 2008, Wolf et al. 2006?)

22

Modeling limitations

Dependent on assumptions about things we don’t know, and modeling this complex system is only as good as our understanding of the system.

23

Challenges

There’s no reliable PRE DECLINE data

Heterogeneity of the environment and the complexity of sea lion biology make it difficult to separate cause and effect.

No ecosystem level experiments to directly test the question

24

$ 190 million question

Do fisheries jeopardize the survival and recovery of the Steller sea lion?

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Closing comments

As a statistician, it is a challengeto work on such a high profile

problem and yet have suchlimited data.

Thank you

• www.marinemammal.org