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• surviving individuals no longer represent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
hoping to curb demand for endangered
species
e.g. www.oceanwise.ca
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. 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
– mangrove ecosystems are destroyed in Ecuador
and Asia to make room for shrimp farms which
quickly become polluted from accumulated wastes
and abandoned
– large numbers of fish must be caught to supply
food for shrimp and salmon aquaculture, making
these fish unavailable to support many fish
species in the wild
– antibiotics and pesticides along with nutrients
used in aquaculture become harmful runoff into
coastal waters