Knowledge-based solutions, for sustainable choices Kaarina Kauhala & the Ecoseal group Finnish Game...
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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
Knowledge-based solutions, for sustainable choices
2012-2013
Cooperation between Finnish, Swedish and Estonian researchers, hunters and fishermen
Varsinais-Suomen elykeskus
Knowledge-based solutions, for sustainable choices
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.
Knowledge-based solutions, for sustainable choices
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
Knowledge-based solutions, for sustainable choices
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.
Knowledge-based solutions, for sustainable choices
Are the problem seals a random sample of the population?
• Age?• Sex?• Body condition?• Long-term diet?
Knowledge-based solutions, for sustainable choices
• 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
Knowledge-based solutions, for sustainable choices
Knowledge-based solutions, for sustainable choices
Age and sex of seals
Age structure did not differ between seal groups(p = 0.208).
Knowledge-based solutions, for sustainable choices
Age structure differed between seal groups (p = 0.006).
Knowledge-based solutions, for sustainable choices
Comparison between the samples and the population
Knowledge-based solutions, for sustainable choices
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
Knowledge-based solutions, for sustainable choices
Blubber thickness: condition index among marine mammals
Knowledge-based solutions, for sustainable choices
Blubber thickness of original data
Knowledge-based solutions, for sustainable choices
Knowledge-based solutions, for sustainable choices
• 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 • ____________________________________________________
Knowledge-based solutions, for sustainable choices
Model predicted values
Knowledge-based solutions, for sustainable choices
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.
Knowledge-based solutions, for sustainable choices
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.
Knowledge-based solutions, for sustainable choices
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
Knowledge-based solutions, for sustainable choices
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.
Knowledge-based solutions, for sustainable choices
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?
Knowledge-based solutions, for sustainable choices
• 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.
Knowledge-based solutions, for sustainable choices
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.
Knowledge-based solutions, for sustainable choices
Thank you for your attention!