knowledge-based solutions, for sustainable choices kaarina kauhala & the ecoseal group finnish...

Knowledge-based solutions, for sustainable choices

Kaarina Kauhala & the Ecoseal group Finnish Game and Fisheries Research Institute

Photo: Mervi Kunnasranta

ECOSEAL– Balansing between sustainableseal population management and fisheries


2012-2013

Cooperation between Finnish, Swedish and Estonian researchers, hunters and fishermen

Varsinais-Suomen elykeskus


Aim of the project

ECOSEAL-project aimed at diminishing the seal – fishery conflict.

We collected samples and information of both by-caught and hunted seals to reveal their numbers, demographic structure, diet and the seal-induced damage to coastal fisheries.


Demographic structure and body condition of Baltic grey seals: are the problem seals a random sample of the population?

Kaarina Kauhala & ECOSEAL groupFinnish Game and Fisheries

Research Institute

Photo: Markus Vetemaa


Who are the problem seals?

• Three seal groups:• Seals hunted during normal hunting

mainly from the outer archipelago• ’Problem seals’:

• seals shot near fishing gear• seals by-caught in fishing gear.


Are the problem seals a random sample of the population?

• Age?• Sex?• Body condition?• Long-term diet?


• The samples from hunters and fishermen included:

• the lower jaw: age determination from lower canine teeth

• Reproductive organs: sex and birth rate• Body length: body size• Blubber thickness (measured from posterior end

of sternum): an index of body condition• Pieces of blubber, liver and muscle: long-term

diet


Age and sex of seals

Age structure did not differ between seal groups(p = 0.208).


Age structure differed between seal groups (p = 0.006).


Comparison between the samples and the population


Sex ratios (males/females) of the samples

Hunted Shot By-caught Total

Spring 1.2 (91) 2.3 (10) 1.4 (50) 1.3 (151)

Autumn 1.2 (50) 1.7 (16) 3.5 (68) 2.0 (134)

Total 1.2 (141) 1.9 (26) 2.3 (118) 1.6 (285)

Difference between seasons: p = 0.060Difference beween hunted, shot and by-caught: p = 0.034


Blubber thickness: condition index among marine mammals


Blubber thickness of original data


• We tested the effects of seal group (hunted, shot, by-caught), age (pup, subadult, adult), sex and month, and their interactions on the blubber thickness.

• ____________________________________________________ • Effect df F p • ____________________________________________________ • Seal group 2, 225 5.5 0.005 • Age group 2, 225 2.1 0.119 • Month 1, 225 23.2 <0.001 • Sex 1, 225 0.04 0.840 • Age group*month 2, 225 7.8 0.001 • Sex*age group 2, 225 5.0 0.007 • ____________________________________________________


Model predicted values


Effect of month

adult males: hunted: Y = 55.4 - 6.0 X + 0.55 X2, by-caught: Y = 54.9 - 9.0 X + 0.75 X2.


Are the problem seals a random sample of the population?• No• In spring, most problem seals were by-caught

pups, and the sample of by-caught seals was biased to pups.

• In autumn, most problem seals were subadult and adult males, and the the sample of seals shot near fishing gear was biased to adult males.

• By-caught seals were in poor condition.


Do seals come to fishing gear because they are starving?

• Probably, because the long-term diet of by-caught adult males seems to differ to some extent from that of hunted seals.

• Hungry seals in poor condition may become bold and incautious and easily go into the traps.

• In spring, pups probably go into the traps because they are inexperienced.

Adult males: long-term diet based on fatty acids

Comp. 1 (48.0%)

Co

mp

. 2

(2

5.4

%)

-5.11 -2.42 0.28 2.97 5.67-4.68

-1.98

0.71

3.41

6.10

29MA3m1605O30MA3m1594D 30MA4m1497N

30MA5m5643O

30MA6m5902O

32MA4m1586N32MA5m1606D

29MA3m1561O29MA4m5922N

29MA5m1598D

29MA5m1613D

29MA5m1618N29MA5m1620N29MA6m1616N

29MA6m1619N

29MAUm1615N

30MA3m1519O

30MA3m1588D

30MA3m5467O30MA3m5644O

30MA4m5083D

30MA4m5514O

30MA5m1610D30MA6m1629D

30MA7m5955O

32MA2m1553N

32MA3m1524N

32MA3m1574D

32MA3m1593N

32MA4m1596D

14:0

16:1n-7

18:1n-9

18:2n-6

18:3n-3

18:4n-3

20:4n-6

22:6n-3

Sprat & Salmonids

Bay predator fish

Herring

Hunted

Shot Near Traps

By-caught


What can we do to prevent damage and by-catch?• Hunt more males in autumn?• Hunt more often near fishing gear?• More research is needed on the long-term diet

and movements of seals to see, whether only some adult males specialise in catching fish near fishing gear.

• Use seal-safe traps to prevent by-catch.


What is the impact of human-induced mortality to the seal population?

• By-catch mortality may not be totally additive to natural mortality, because by-caught pups were small and in poor condition. At least some of them would probably have died anyway.

• By-caught adult males were in poor condition. Were they subordinate males which would not have reproduced?


• By-catch may not be a so severe threat to the population as expected but it is a serious ethical problem.

• When estimating the impact of by-catch on the population, we must take into account not only the numbers but also the quality of by-catch,because different individuals have different reproductive values.


The effect of hunting

• Both pups and adults are hunted in spring.• In autumn, most hunted seals are adults,

many males (in good condition) but also mature females, i.e. reproducing individuals.

• The mortality rate of females < 10 years of age is important for the population growth, i.e. not too many young females should be hunted.

• Hunting should be targeted more on males, especially those in poor condition.


Thank you for your attention!

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