Aquatic Food Resources Flashcards
(36 cards)
Why, despite its size, is the ocean less biologically productive than land?
Only a small proportion isn’t heavily restricted by limiting factors against the growth of algae
How does variation in light level affect marine productivity
Photosynthesis requires light and is therefore restricted to the photic zone (surface layer of water) with anything below this depth relying on food produced near the surfac
How does Nutrient Availability affect marine productivity?
Algae absorbs nutrients from the water, some of which are abundant (like carbon) while others are rarer like phosphates. The oceans are typically deficient of rarer nutrients except in areas where those nutrients are made, limiting availability to these locations and where organisms with those nutrients go
Why is Freshwater productivity different to saltwater productivity?
Freshwater receives more run-off as they are in land and receive more light due to their shallowness, increasing productivity compared to saltwater
What is fishing for species on or close to the seabed called?
Demersal Fishing
What is fishing for species in open water or closer to the surface called?
Pelagic Fishing
What is trawling? Is it Pelagic or Demersal?
Trawling is dragging a net behind a ship to catch anything in its path. It can be either Demersal or Pelagic
What is long line fishing? Demersal or Pelagic?
It involves letting out a long line with smaller lines attached, covered in bait to attract fish. It can be either Demersal or Pelagic
What is drift net fishing? Pelagic or Demersal?
Long curtain nets that are used to trap fish swimming into them. Pelagic
What is Purse Seining? Pelagic or Demersal?
Using a net that encircles the fish shoal and then the bottom is pulled tight to trap them in. Pelagic
What threat does overfishing pose?
If too many are caught, mortality rate my exceed birth/breeding rates leading to a huge population decline, especially if the fishing does not let up.
k-selected species are more vulnerable to this, while r-selected can recover quickly
What are the 3 kinds of Bycatch?
- Immature or otherwise worthless individuals
- Individuals that could be sold, but the catch quota has been met
- Species with no commercial value
How can fishing methods get bycatch?
- Many large net methods catch more than just the intended target
- Pelagic long lines can attract seabirds that can get tangled and die in the lines
- Trawling done for small organisms don’t let much escape through their nets due to the small holes
- Natural predators to the intended target my get got when trying to hunt
What is ghost fishing?
Fishing gear that has been discarded may continue to entrap and kill marine animals, which in turn act as bait for more animals to get caught
How can fishing methods cause habitat damage?
- Demersal methods can cause seabed damage by disturbing sediments
- Demersal or shallow water methods can destroy coral reefs or sea grass
- Dynamite fishing has huge impacts, stunning or killing fish, upturning sediment and destroying coral
- Obvious food web impacts
How can legislation help minimise environmental impacts of fishing?
- Catch quotas
- Restricted fishing efforts that limit size, engine power and work days per year for fishing boats
- Restrictions on fishing methods, for example banning dynamite fishing, or other disruptive methods all together or in certain sensitive areas
- No take zones, where fishing is entirely prohibited
- Maximum and Minimum catch sizes
- Protected individuals (e.g. V-notching lobsters)
How can fishing equipment design minimise environmental impacts of fishing?
- Mesh size, allows smaller species to escape
- Mesh design to prevent gaps closing up
- Escape panels such as Turtle Exclusion Devices
- Acoustic deterrents for dolphins and whales
- Hook shapes to avoid catching seabirds
- Decoys to attract seabirds
- Night fishing
- Biodegradable and radio tracked equipment to reduce ghost fishing
Why is some fishing overfishing, but some fishing not affect total population?
The natural breeding rate of animals exceeds the necessary amount to keep their population stable, though carrying capacity prevents the actual population from rising. Overfishing only happens when the breeding rate is exceeded, fishing that does not exceed the additional rate of breeding is fine
What is MSY? How is it estimated?
The Maximum Sustainable Yield, the greatest biomass that can be removed from a population without causing long term decline.
It can be estimated using the Russell formula:
starting biomass + (new biomass + growing biomass) - (caught biomass + natural mortality biomass loss)
Why is fish population data hard to measure?
- Fish populations are highly mobile
- Population distribution is often very uneven
- Collecting representative data may require an impractically large scale experiment
How can fish population data be estimated?
- Using catch size and catch per effort
- Using mean caught size and age
- Collecting planktonic egg data for info on breeding success and next generation size
What is extensive aquaculture?
Aquaculture in natural and less maintained environments
What is intensive aquaculture?
Aquaculture in artificial habitats with all abiotic and biotic factors controlled to maximise productivity
What factors are considered in species selection for aquacultures?
- Local conditions
- Species adaptation
- market demand
