Direct and Indirect Effects of Fisheries

Question 1

What are some types of commercial fisheries?

Answer 1

• Industrial
• Single species
• Mulitiple species

Question 2

What are the two types of fishing gears?

Answer 2

1. Active
2. Passive

Question 3

Active fishing gears

Answer 3

Actively move through water

Question 4

Passive fishing gears

Answer 4

Stay in one place

Question 5

What are some examples of passive fishing gears?

Answer 5

• Gill nets
• Long lines
• Lobster / crab pots

Question 6

What are some examples of active fishing gears?

Answer 6

• Trawls
• Dredges

Question 7

What is the difference between pelagic (mid-water) trawls and demersal trawls?

Answer 7

• Pelagic trawls: pulled through the middle of the water
• Demersal trawls: pulled along the bottom substrate

Question 8

What are some effects of bottom trawling?

Answer 8

• Alteration of physical structure
• Suspension of sediments
• Changes to biochemistry
• Changes in benthic (bottom of the water) community structure

Question 9

What impacts does bottom trawling have on marine ecosystems?

Answer 9

• 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)

Question 10

What are the most destructive fishing gears in terms of habitat damage?

Answer 10

Bottom trawls and dredges

Question 11

What is one of the most economically important fishing gears?

Answer 11

Bottom trawls

Question 12

Describe the sliding baseline theorem

Answer 12

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

Question 13

How does “fishing down” impact marine ecosystems?

Answer 13

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.

Question 14

What effects does fishing have on the ecosystem?

Answer 14

• Fishing drives down the abundance of target species
• Species removal has cascading effects

Question 15

How can fisheries indirectly impact seabirds (in terms of their prey)?

Answer 15

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

Question 16

Thought Exercise!:
Would a pelican or an albatross be hit harder in terms of prey depletion?

Answer 16

A pelican
Pelican cannot forage as far as albatrosses can (they cannot escape bad conditions
Key: Localized impact will mainly affect local species

Question 17

Offal

Answer 17

Parts of fish that are discarded

Question 18

How can fishery discards and offal positively affect seabirds?

Answer 18

• Provide fish and invertebrates that would otherwise be unavailable to seabirds
• Increase seabird populations

Question 19

How can fishery discards and offal negatively affect seabirds?

Answer 19

• Seabird become reliant on fishery discards
• Decline in fishery discards have resulted in a decline in seabird populations

Question 20

Bycatch

Answer 20

Unintended capture or entanglement of species in fishing gear

Question 21

What species are particularly vulnerable to bycatch?

Answer 21

Long-lived species
Ex:
- Sea turtles
- Marine mammals
- Seabirds
- Sharks

Question 22

Recruitment

Answer 22

Process by which new individuals are added to a population

Question 23

Maximum Sustainable Yield (MSY)

Answer 23

Intermediate level of abundance at which recruitment is maximized

Question 24

How does fishing affect MSY

Answer 24

Yield can be maximized at some intermediate level of fishing effort

Question 25

How do Fisheries and MSY affect seabird populations (think life histories)?

Answer 25

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*

Question 26

What type of fishing gear is the most impactful for seabirds?

Answer 26

Longline Fisheries *Birds get caught on fishing hooks and drown*

Question 27

How are trawls and gillnets problematic for seabirds?

Answer 27

- Seabirds can get entangled in nets - Seabirds can collide with cables

Question 28

How can bycatch be mitigated?

Answer 28

- Streamers (tori lines) - Line weighing - Night setting - Bait caster and shooter

Question 29

Streamers

Answer 29

Lengths of rope with brightly colored streamers that are towed behind longline vessels to deter birds from attacking hooks

Question 30

Line weighing

Answer 30

Weight placed at the end of the fishing line so that bait sinks faster (could potentially harm fishermen)

Question 31

Night setting

Answer 31

Setting lines at night when seabirds are not likely to follow fishing vessels

Question 32

Dyed bait

Answer 32

Make bait darker so that it is harder for seabirds to see

Question 33

Bait caster and shooter

Answer 33

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*

Question 34

What is the role and purpose of fishery observers?

Answer 34

- Trained government observers who record bycatch and gear-specific measurements - Provides key data on bycatch *These programs typically occur in wealthy countries*

Question 35

Why is it hard to enforce fishery regulations on the high seas?

Answer 35

- 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*

Question 36

Radar Tags

Answer 36

- 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*

Question 37

Global Fishing Watch

Answer 37

Utilizes GPS locations from longline vessels to learn when and where vessels on the high seas are fishing