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