Projected changes to coastal
fisheries
Based on......
Outline
• Main components of coastal fisheries
• Indirect effects of climate change
• Direct effects of climate change
• Projected changes to coastal fisheries production
• Priority management measures
Coastal fisheries catch – Cook Islands
220 t/yr 231 t/yr
Commercial
Subsistence
Source: Gillett (2006)
What are coastal fisheries?
• Demersal fish
• Nearshore pelagics
• Invertebrates
Species not considered
• Deepwater snapper
• Sharks
Demersal fish
Nearshore pelagic fish
Invertebrates
Coastal fisheries catches – Cook Islands
14 t/yr
146 t/yr
240 t/yr
Total catch = 400 tonnes per year
Pratchett et al. 2011
Demersal fish catch composition
Availability
Percentage
Catch
Pratchett et al. 2011
Area (km2)
% Coral cover
Indirect effects of climate change
Effects of habitat degradation
Macroalgae
Proportional change
0.5
0
Habitat
complexity
-0.5
Coral cover
-1
0
1
2
3
4
5
6
7
8
Time after extensive coral loss (years)
9
10
Effects of habitat degradation
Macroalgae
Percentage change
50
0
Habitat
complexity
-50
Coral reef fishes
Coral cover
-100
0
1
2
3
4
5
6
7
8
Time after extensive coral loss (years)
9
10
Others
Caesionidae
Balistidae
Chanidae
Labridae
Kyphosidae
Siganidae
Mullidae
Holocentridae
Scaridae
Mugilidae
Lutjanidae
Carangidae
Acanthuridae
Serranidae
Lethrinidae
Average annual catch (kg/ year)
60000
Catch composition
50000
40000
Generalists
Not vulnerable
30000
20000
10000
Reef associated
Vulnerable
0
Coral associated
Highly vulnerable
Importance of herbivorous fish
Herbivorous fish in Cook Islands
Availability
Percentage
Catch
4
3.5
3
2.5
2
1.5 Temperature
1
0.5
0
now
2035
8.15
8.1
8.05
8
7.95
pH
7.9
7.85
7.8
2050
2100
Ocean pH
Temperature change
Direct effects of climate change
Effects of temperature
100
90
Growth (mg/week)
80
70
60
Damsel fish
Maximum growth
28-30oC
50
(Acanthochromis
polyacanthus)
40
30
Projected
increase
3oC by 2100
20
10
0
22
24
26
28
30
32
34
36
38
Temperature (oC)
Zarco Perello and Pratchett 2012
Effects of temperature
100
Declines in:
• growth
• lifespan
• reproduction
90
Growth (mg/week)
80
70
60
Maximum growth
28-30oC
50
Fewer &
smaller
fishes
40
30
Projected
increase
3oC by 2100
20
10
0
22
24
26
28
30
32
34
36
38
Temperature (oC)
Zarco Perello and Pratchett 2012
Normal spawning temperature
Effects of temperature
100
90
% Dead fish eggs
80
70
60
50
40
30
20
10
0
27.9
29.5
32.0
32.8
33.9
Temperature (oC)
34.7
Effects of ocean acidification
Abalone
80
20 deg C
22 deg C
24 deg C
% Larval survival
70
60
50
40
30
20
10
0
pH 8.2
pH 7.8
pH 7.6
Byrne 2012
Effects of ocean acidification
Munday et al. 2012
Projected coastal fisheries production
Cook Islands
Fisheries
Demersal fish
%
catch
2035
36
-2 to
-5%
Nearshore
pelagic fish*
60
Invertebrates
4
2050
2100
Main effects
-20%
-20 to
-50%
Degradation
of coral reefs
+10%
Changes in
distribution of
tuna
-10 to
-20%
Ocean
acidification
+15 to
+20%
+20%
0 to
-5%
-5 to
-10%
*Based on initial preliminary modelling for skipjack tuna
Ciguatera fish poisoning
Factors affecting ciguatera
• Dead coral &
seaweed surfaces
• Nutrients
• Water
temperature
From land-based activities and sewage
Priority management measures
1. Protect structural complexity and biological
diversity of coral reefs to sustain fisheries
2. Maintain adequate spawning stocks to help
overcome shocks of greater climate extremes
3. Recognise ecological importance of
herbivorous fish and ensure stocks are
sufficient to maintain ecosystem functions
Conclusions
• Coastal fisheries are important for food security
and livelihoods
• Effects of climate change will add to existing
pressures (e.g. overfishing)
• Improved catch data are needed for monitoring
effects of climate change on coastal fisheries:
 separate data for each main category of
coastal fisheries
 subsistence fisheries catches