Lecture 12 Flashcards
When is the earliest evidence of fishing?
With hooks 42,000 years ago
When did intensive exploitation of marine fishes begin?
1000 years ago
Where are fisheries concentrated?
On continental shelves or productive areas of the epipelagic
Four methods of fishing
Passive: gill nets and longline
Active: purse seine and trawl
Also harpoons, explosives, spears, fish traps
North Sea cod populations
-Fishery may be collapsing due to overfishing
-Modern North Sea cod individuals are approx 10cm smaller than the same populations 4500 years ago - fish more likely to survive if they are smaller so produces a selective pressure
-Population size reconstructed using otoliths (earbones)
Limburg et al. 2008
Ways to manage a fishery
- Limiting total catch and closing the fishery when the catch is reached
- Limiting length of fishing season
- Limiting areas open for fishing
- Limiting number of boats permitted to fish
- Limiting gear size or type
- Limiting size of fish caught
- Limiting catches per boat
- Limiting fishing methods
What is the Maximum Sustainable Yield?
The highest catch that can be maintained year after year without affecting the stock (population size maintained)
The problems with fishery management
- Determining the real abundance of fish - when fish populations dwindle, the fish can aggregate so seem to be present in higher numbers
- Ensuring consistent behaviours of fishers
- Ensuring fish are not unreported - gross misreporting of catches for FAO by China
- Ensuring that fish are not mis-sold at port - 80-90% smoked fish is mislabelled
What are the most important factors in successfully managing fish populations?
Leadership and quotas
Social cohesion
Protected areas
Impact of fishing on seabed structure
Impacts depend on substrate
For taxa in sandy shallow seabed’s which are adapted to stress (waves), impacts are minimal
For taxa on rocky or biogenic habitats there are long-term impacts
Impacts of fishing on seamounts
Deep water coral is rapidly destroyed and recovers very slowly
Impact of fishing - bycatch
Seabirds caught in longline and gillnet fisheries
Birds dive after baited hooks
Use bird scarred?
Dynamite fishing
Extensively used in parts of south-east Asia
Kills many juvenile and non-target species
Destroys reef habitat
Impacts of ghost fishing
- Nets, lines, hooks or pots are lost, but continue fishing for years afterwards
- Now that gears are made from synthetic material, last even longer
- Caught fish may act as bait for larger predators
Evolutionary effects of fishing
- Size selective, removes largest individuals from populations
- Can reduce genetic diversity of species
- Shorter life histories selected for
