Seals, dolphins & salmon in the Moray Firth

Paul Thompson

University of Aberdeen

0

10000

20000

30000

40000

50000

60000

1950 1960 1970 1980 1990 2000

Year

Tot

al c

atch

of s

alm

on

0

10000

20000

30000

40000

50000

60000

1950 1960 1970 1980 1990 2000

Year

Tot

al c

atch

of s

alm

on

Breeding Stock Size

EggsParr

Smolts

.

Net & Rod Catches

Seals Dolphins

Food

Food

Climate variation/change

Breeding Stock Size

Net & Rod Catches

EggsParr

Smolts

.

Seals Dolphins

Food

Food

Climate variation/change

Industrial Pollution

Mergansers

CormorantsPorpoises

Killer whales

Pike

Cod

Poaching

Acid rain

Red deer

Over-grazing

Alien introductions

Goosanders

Afforestation

Tourism

• Is predation by seals and dolphins significant?

• If so, can we do anything about it?

• If so, is it cost-effective?

Is predation by seals and dolphins significant?

• Carry out an experiment

• Use a natural experiment

0

2000

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6000

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10000

12000

14000

16000

600 700 800 900 1000 1100

Moray Firth harbour seal abundance

Sal

mon

cat

ches

1000 2000 3000 4000 5000 6000 7000 8000 9000Size of Beauly River Salmon Run

10

15

20

25

30

35

Dol

phin

abu

ndan

ce

F 1,9 = 6.35, p < 0.05, r2 = 0.41

Is predation by seals and dolphins significant?

• Carry out an experiment

• Use a natural experiment

Requires info on predators’

population size diet

food consumption

•Model consumption of salmon

A little of what we know, and a lot of what we don’t

Grey Seal Bottlenose Dolphin

Harbour Seal

1980 1985 1990 1995 2000 2005Year

15000

20000

25000

30000

3500040000

Pup

Pro

d uct

ion

2001 UK population ~ 130,000 (+/- 15%)

0

50

100

150

200

250

300

350

400

450

500

Max

Mo

nth

ly C

ou

nt

1988 1989

Seasonal changes in haul-out counts

Movements of satellite tagged grey seals caught in the Moray Firth

Moray Firth

Cardigan Bay

Western Isles

NORTH SEA

Firth of Forth

129 individuals

(95% Confidence Limits = 110 - 174)

1990-1995

1996-2000

UK population ~ 50,000

Moray Firth ~ 1,000

1988 1990 1992 1994 1996 1998 2000 2002 2004500

600

700

800

900

1000

1100

1200

ME

AN

CO

UN

T (

+/-

s.e

. )

Moray Firth Trends

August Moult counts

June/July Pupping Counts

Harbour Seals Grey Seals0%

20%

40%

60%

80%

100%

Clupeids

Gadids

Flatfish

Sandeels

Salmonids

Cephalopods

Others

Grey & harbour seal diet

87/88 88/89 89/90 90/91 91/92 92/93 93/94 94/95

Year

0

20

40

60

80

100

Die

t Com

posi

tion

(%)

Year-to-year variation of clupeids in harbour seal winter diet

Breeding Stock Size

Net & Rod Catches

EggsParr

Smolts

.

Seals Dolphins

Food

Food

Climate variation/change

Mergansers

Cormorants

Porpoises

Killer whales

Pike

Cod

Poaching

Goosanders

• Is predation by seals and dolphins significant?

• Is predation by seals and dolphins significant?

0 1 2 3 4 5 6 7

0.0

0.1

0.2

0.3

0.4

0.5Probability

•If so, can we do anything about it?

• If so, is it cost-effective?

http://www.abdn.ac.uk/zoology/lighthouse

http://smub.st-and.ac.uk/