Direct and Indirect Effects of Fisheries Flashcards
What are some types of commercial fisheries?
- Industrial
- Single species
- Mulitiple species
What are the two types of fishing gears?
- Active
- Passive
Active fishing gears
Actively move through water
Passive fishing gears
Stay in one place
What are some examples of passive fishing gears?
- Gill nets
- Long lines
- Lobster / crab pots
What are some examples of active fishing gears?
- Trawls
- Dredges
What is the difference between pelagic (mid-water) trawls and demersal trawls?
- Pelagic trawls: pulled through the middle of the water
- Demersal trawls: pulled along the bottom substrate
What are some effects of bottom trawling?
- Alteration of physical structure
- Suspension of sediments
- Changes to biochemistry
- Changes in benthic (bottom of the water) community structure
What impacts does bottom trawling have on marine ecosystems?
- Resource depletion
- Damage to seafloor integrity and habitats
- Changes in the balance species abundance
- Compounding eutrophication (build of of nutrients ex: algae)
- Reducing carbon sequestration rates (rate at which Carbon is removed from an ecosystem)
What are the most destructive fishing gears in terms of habitat damage?
Bottom trawls and dredges
What is one of the most economically important fishing gears?
Bottom trawls
Describe the sliding baseline theorem
Each generation of fisheries scientist accepts the species composition that occurred at the beginning of their careers as a baseline and uses this to evaluate changes.
Why is this a problem
How does “fishing down” impact marine ecosystems?
Fishing down: Fisheries remove the larger organisms in an ecosystem first. These larger organisms are typically long-lived but take longer to recover (life histories). The result is more lower trophic level organisms than higher trophic level organisms. Fisheries will now end up targeting very small species such as fish and plankton.
What effects does fishing have on the ecosystem?
- Fishing drives down the abundance of target species
- Species removal has cascading effects
How can fisheries indirectly impact seabirds (in terms of their prey)?
Prey depletion
Ex:
- 1970s - High fishing pressure on long-finned squid result in squid disappearing from seabird’s diet
- 1972 - Peruvian Anchoveta crash lad to widespread starvation and nesting failure
Thought Exercise!:
Would a pelican or an albatross be hit harder in terms of prey depletion?
A pelican
Pelican cannot forage as far as albatrosses can (they cannot escape bad conditions
Key: Localized impact will mainly affect local species
Offal
Parts of fish that are discarded
How can fishery discards and offal positively affect seabirds?
- Provide fish and invertebrates that would otherwise be unavailable to seabirds
- Increase seabird populations
How can fishery discards and offal negatively affect seabirds?
- Seabird become reliant on fishery discards
- Decline in fishery discards have resulted in a decline in seabird populations
Bycatch
Unintended capture or entanglement of species in fishing gear
What species are particularly vulnerable to bycatch?
Long-lived species
Ex:
- Sea turtles
- Marine mammals
- Seabirds
- Sharks
Recruitment
Process by which new individuals are added to a population
Maximum Sustainable Yield (MSY)
Intermediate level of abundance at which recruitment is maximized
How does fishing affect MSY
Yield can be maximized at some intermediate level of fishing effort
How do Fisheries and MSY affect seabird populations (think life histories)?
Seabirds are…
- Long-lived
- Slow reproducing
- Vulnerable to rapid and large-scale depletion
Therefore…
- MSY for seabirds (bycatch) = much lower than MSY of target species (fish)
Catching target species leads to depletion of bycatch species
What type of fishing gear is the most impactful for seabirds?
Longline Fisheries
Birds get caught on fishing hooks and drown
How are trawls and gillnets problematic for seabirds?
- Seabirds can get entangled in nets
- Seabirds can collide with cables
How can bycatch be mitigated?
- Streamers (tori lines)
- Line weighing
- Night setting
- Bait caster and shooter
Streamers
Lengths of rope with brightly colored streamers that are towed behind longline vessels to deter birds from attacking hooks
Line weighing
Weight placed at the end of the fishing line so that bait sinks faster (could potentially harm fishermen)
Night setting
Setting lines at night when seabirds are not likely to follow fishing vessels
Dyed bait
Make bait darker so that it is harder for seabirds to see
Bait caster and shooter
Allows long-line to be deployed faster than the boat is moving
it is not clear that this is an effective way to mitigate bycatch as lines do not sink faster
What is the role and purpose of fishery observers?
- Trained government observers who record bycatch and gear-specific measurements
- Provides key data on bycatch
These programs typically occur in wealthy countries
Why is it hard to enforce fishery regulations on the high seas?
- They are not “owned” by any nation / government etc.
- It is harder to impose and enforce laws on these waters
Most fishing vessels turn off their long distance radars in the high seas to avoid being detected
Radar Tags
- Utilized on the high seas
- Deployed on large seabird species to track their location and detect radar signals from fishing vessels
- Researchers can tell which fishing vessels they interact with
Short distance radars are not turned off on fishing vessels
Global Fishing Watch
Utilizes GPS locations from longline vessels to learn when and where vessels on the high seas are fishing
