Download Controlling Overfishing

Overfishing
i.e. catch exceeds replacement
– changes in genetic diversity
• harvesting larger specimens
selective pressure for smaller animals
• harvesting early in reproductive cycle
selective pressure for fast maturation
• surviving individuals no longer represent
full genetic variability (genetic drift)
increased risk of extinction
Northern Elephant Seal
Overfishing (continued)
– changes/loss in species diversity
• Extirpated (locally extinct) species cannot fulfill
their ecological functions
potential impact on ecosystem diversity
Controlling Overfishing
– Exclusive economic zones (EEZs)
coastal nations control fishing within 200 miles
counter-acting “Tragedy of the Commons”
Controlling Overfishing (cont.)
- New fisheries
e.g., Alaskan Pollock (surimi) or krill as a
consequence of decreasing traditional
fisheries (e.g., tuna; great whales)
Antarctic krill
Surimi
Controlling Overfishing (cont.)
– Consumer education
• curbing demand for endangered marine species
www.oceanwise.ca
• eating lower on the food chain
http://www.guardian.co.uk/environment/2010/jun/
02/un-report-meat-free-diet
Other factors affecting marine fisheries
– destruction/development of coastal
habitats
loss of feeding, breeding and nursery grounds for
commercial fishes
– wasteful and destructive fishing practices
• inefficient use of the catch (e.g. filleting, shark finning!!)
• incidental catch (a.k.a. bycatch or “trash fish”)
• habitat destruction (sea floor)
Trawling produces large by-catch and destroys benthic habitat
Drift nets produce large by-catch and lost nets ghost fish
Other factors affecting marine fisheries
– aquaculture: the use of agricultural techniques
to breed and raise marine organisms
Aquaculture (cont.)
• monoculture: only 1 species is raised
• polyculture: several species are raised together
• fish aquaculture: net cages vs. land-based pens
• raft culture: juveniles of commercially valuable
molluscs (clams, mussels, oysters) are collected
and attached to ropes suspended from rafts
• shrimp farming
• eco-friendly aquaculture
Aquaculture (cont.)
Problems
– Destruction of mangrove ecosystems for shrimp farms
– Over-exploitation of feed fish for shrimp and salmon
aquaculture
– Antibiotics, pesticides, excess nutrients
pollution of coastal waters
– Transfer of disease (viral/bacterial)and parasites to wild stocks
http://www.georgiastrait.org
Case study: BC Salmon
Salmon Facts
• 5 species in Eastern Pacific:
Chinook, Coho, Chum, Pink, Sockeye
• Spawn in fresh water
• Require streams that are
– clear, cool, shaded, fast-running, unpolluted
• One-time spawners
• Spend 1-5 years in ocean
• Terminal fisheries (intercepted as fish
return to rivers)
Salmon life cycle
(anadramous)
Fertilized by
milt in redd
Nourished
by yolk sac
Entering SW
Feeding in FW
Types of fishing vessels
Purse seiner
gillnetter
troller
BC Salmon- Issues
• Overfishing
• Climate change
• Spawning habitat loss
Bugaboo Creek clear-cut, Pt. Renfrew
– Logging
– Dams
– Development
– Pollution
• Aquaculture
– Introduced species
– Disease transfer
Sea lice
Salmon hatcheries increase numbers of fish, but with decreased genetic diversity
Non-Fish Marine Resources
• ~ 30% world’s salt (NaCl) from ocean:
evaporation ponds
• Water by desalination (expensive) where
necessary
• Sand, gravel, chalk – dredging damages
sea floor
• (Minerals and methane hydrate)
technological/financial/(ecological?!)
restraints
Not (yet) heavily exploited
Methane hydrate
“burning ice”