Commercial Fisheries

What is a traditional definition of a fishery?

What is a traditional definition of a fishery?

The union of aquatic organisms and humans for consumptive purposes.

How is a commercial fishery defined?

Extraction and sale of fish for consumptive purposes.

As pressure on wild fish stocks to satisfy consumer demand increases, so does…

fish mortality

What is bottom trawling?

A commercial fishing technique where a large net is dragged across the ocean floor by a boat.

What are the primary target species in bottom trawling?

Includes pacific cod, rockfish, halibut, and shrimp.

Downsides to bottom trawling

• Non-target species often end up in the nets

• Trawls can last many hours

• Habitat disturbance

• Bycatch caught rarely survives: target or non target species

How can bottom trawling disturb the habitat?

• Can dredge up settled 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

Reasons for discarding a fish

Wrong species, size, sex, or the fish are damaged, the quota is reached, high grading, lack of space, chance of spoiling.

Toal capture =

catch + bycatch + released alive

What is bycatch?

The part of the capture that is discarded at sea, often dead or injured.

What is longline fishing?

A fishing method where a main line with baited hooks is released from a boat, varying depths.

What types of species are primarily caught as bycatch in longline fishing?

Pelagic and migratory species. Also marine megafauna (albatrosses and sea turtles)

What are the target species of longline fishing?

Swordfish, tuna, sablefish, pacific cod

What are drift nets?

Free-floating gill nets that stay suspended in the water column. Often results in ghost nets.

What is 'ghost net'?

Lost drift nets that continue to catch species unintentionally.

Impacts of commercial fisheries on fish populations?

• Reduction in abundance of target and non-target species

• Disturbance and loss of essential (critical) habitat

  • Spawning locations

• Impacts on rare or threatened species

• Disruption of food web

• Remobilization of contaminants

• Fishing induced selection

  • Reduces fitness