Commercial Fisheries
How to Define a fishery
Traditional definition: The union of aquatic organisms and humans for consumptive purposes
Narrow definition because it treats aquatic organisms as an extractive resource
Fish are used by humans in both extractive and non extractive ways
Needs to be clear when defining the way fish are used by humans
Commercial fishery
Extraction and sale of fish for consumptive purposes
Exists in an industrial level and a small-scale level
Have to view fisheries economically as total as well as relative
Marine and inland fishing declining, aquaculture increasing
As the pressure on wild fish stocks to satisfy consumer demand increases, so does fish mortality
Majority of species are moderately or fully to healy exploited already
Commercial Industrial Techniques
Bottom trawling
Large net is dragged across the ocean floor by a boat
Float line above and lead line below to keep it open vertically
Lead line encourages stuff on the bottom to come up and go in the net
Damages ocean floor=habitat destruction
Everything in front of the net gets scooped up
Smaller fish can sometimes escape the net unless too crammed in the net
Non-target species often end up in the nets
Target species include: pacific cod, rockfish, halibut, shrimp
Trawls can last many hours (3-5; 10-12) and travel to speeds of up to 7 knots
Often have motherships with freezers out on water as well
Cause habitat disturbance by disturbing ocean floor
Can dredge up settled sediments
Suspension of sediments
Increase water turbidity
Deplete sea floor vegetation that are important for the ecosystem
Reduce habitat heterogeneity
Resuspension of contaminants such as PCBs
Impact food web
Often results in bycatch
Probability of bycatch surviving being caught is extremely low
Bycatch: part of the capture that is discarded at sea, dead (or injured to an extent that death is the result)
capture=catch+bycatch+released alive
Can include the target species and non-target species
Various reasons for discarding: wrong species, size, sex, or the fish are damaged, the quota is reached, high grading, lack of space, chance of spoiling
Most bycatch are crustaceans and demersals
Most bycatch are from bottom trawls and shrimp trawls (on ocean floor)
Longline Fishing
Boat releases a main line containing snoods with baited hooks attached and buoy lines.
Can be at varying depths, typically middle, top
Different bycatch from bottom trawling
No crustaceans or demersals
Higher numbers of pelagic and migratory species caught
Very dangerous work
Target species include: swordfish, tuna, sablefish, pacific cod
Bycatch also often includes marine megafauna
Tens of thousands of albatrosses killed annually by Japan
Hundred of thousands of seabirds killed by southern ocean patagonian toothfish fishery
Estimated annual bycatch is at least 200,000 loggerheads and at least 50,000 leatherbacks caught by the longline hooks set for a different target species.
Drift nets
Free-floating gill net
Net stays suspended in the water column
25-50 km long
Target species: tuna, squid, pelagic species
Often results in ghost nets
Lost nets
Cause other species to get caught in them
Impacts on Fish Populations
Reduction in sundance of target and non-target species
Disturbance and loss of essential (critical) habitat
Spawning locations
Depending on time of year
Impacts on rare or threatened species
Disruption of food web
Remobilization of contaminants
Fishing induced selection
Fitness
How to Define a fishery
Traditional definition: The union of aquatic organisms and humans for consumptive purposes
Narrow definition because it treats aquatic organisms as an extractive resource
Fish are used by humans in both extractive and non extractive ways
Needs to be clear when defining the way fish are used by humans
Commercial fishery
Extraction and sale of fish for consumptive purposes
Exists in an industrial level and a small-scale level
Have to view fisheries economically as total as well as relative
Marine and inland fishing declining, aquaculture increasing
As the pressure on wild fish stocks to satisfy consumer demand increases, so does fish mortality
Majority of species are moderately or fully to healy exploited already
Commercial Industrial Techniques
Bottom trawling
Large net is dragged across the ocean floor by a boat
Float line above and lead line below to keep it open vertically
Lead line encourages stuff on the bottom to come up and go in the net
Damages ocean floor=habitat destruction
Everything in front of the net gets scooped up
Smaller fish can sometimes escape the net unless too crammed in the net
Non-target species often end up in the nets
Target species include: pacific cod, rockfish, halibut, shrimp
Trawls can last many hours (3-5; 10-12) and travel to speeds of up to 7 knots
Often have motherships with freezers out on water as well
Cause habitat disturbance by disturbing ocean floor
Can dredge up settled sediments
Suspension of sediments
Increase water turbidity
Deplete sea floor vegetation that are important for the ecosystem
Reduce habitat heterogeneity
Resuspension of contaminants such as PCBs
Impact food web
Often results in bycatch
Probability of bycatch surviving being caught is extremely low
Bycatch: part of the capture that is discarded at sea, dead (or injured to an extent that death is the result)
capture=catch+bycatch+released alive
Can include the target species and non-target species
Various reasons for discarding: wrong species, size, sex, or the fish are damaged, the quota is reached, high grading, lack of space, chance of spoiling
Most bycatch are crustaceans and demersals
Most bycatch are from bottom trawls and shrimp trawls (on ocean floor)
Longline Fishing
Boat releases a main line containing snoods with baited hooks attached and buoy lines.
Can be at varying depths, typically middle, top
Different bycatch from bottom trawling
No crustaceans or demersals
Higher numbers of pelagic and migratory species caught
Very dangerous work
Target species include: swordfish, tuna, sablefish, pacific cod
Bycatch also often includes marine megafauna
Tens of thousands of albatrosses killed annually by Japan
Hundred of thousands of seabirds killed by southern ocean patagonian toothfish fishery
Estimated annual bycatch is at least 200,000 loggerheads and at least 50,000 leatherbacks caught by the longline hooks set for a different target species.
Drift nets
Free-floating gill net
Net stays suspended in the water column
25-50 km long
Target species: tuna, squid, pelagic species
Often results in ghost nets
Lost nets
Cause other species to get caught in them
Impacts on Fish Populations
Reduction in sundance of target and non-target species
Disturbance and loss of essential (critical) habitat
Spawning locations
Depending on time of year
Impacts on rare or threatened species
Disruption of food web
Remobilization of contaminants
Fishing induced selection
Fitness