Fisheries and conservation - Part 3 Flashcards
Rank, by selectivity, the different fishing techniques.
Trawling Purse seines Longlines Gillnetting Harpooning/angling
Describe trawling
Drag big net behind the boat for a large distance catching most every thing.
Least selective.
What are the benefits of trawling?
Easy, catches a lot, good economically
What can be regulated for trawling?
Mesh size.
Larger size will allow smaller fish and babies through.
What are the issues with trawling?
Least selective.
Destructive to habitat, specifically deep-water trawling. (coral reefs and seagrass beds)
How are purse seines more selective than trawling?
Only set when the target fish is found.
Selectively target fish species they catch.
Modified to avoid dolphin catching.
Describe longlines.
Long lines of hooks, km or more long, can be baited.
Come back to collect after a period of fishing.
How are longlines selective?
Primarily target larger, predatory fish.
Will catch any species large and hungry enough to bite hook.
Not selective in terms of species but, size and predatory selective.
How has bycatch changed the way longlines operate?
Modified to go deeper and changed to hooks to prevent non-fish bycatch.
What is a major issue to longlines?
By the time you come back, fish are already dead.
Can get lost and continually fish for a long time.
Describe gill nets.
Nets that catch fish by the gills.
Allow fish heads to go through the net but not the body. Fish will then try to swim back but get net caught in operculum.
Left then, harvested later.
How is gillnetting selective?
Size selective.
Large headed fish and baby fish will not be caught.
Size selective but not species selective.
Describe the controversy with longlines and gill nets.
These can be lost during a storm or due to a satellite issue.
They can keep killing fish and other animals for years.
What are the regulations for gillnetting and longlines?
Pretty much unregulated and heavily used.
Only regulation is on mesh size.
How can harpooning and angling be used commercially?
They have very little bycatch (if at all) and are the most sustainable.
However, they both arent particularly efficient and are only worthwhile is the fish is large enough.
As we overfish, we have a tendency to fish _____ the _____ _____.
down the food chain
Describe a redsnapper and a whitefish.
Anything semi red is called a redsnapper
Anything semi white is called a whitefish
Aquaculture.
What do most big fish eat?
What happens after fish eat?
1 - Other fish
2 - Fish poop
In aquaculture, _______ systems may be okay but oceanic ___ ____ are particularly bad.
Inland
Net pens
Why doesn’t aquaculture solve the fishing problem in some instances.
Have to feed the fish in the farm with other fish.
Fish _____ is a large issue in regulation of fish farms.
waste
Why is an inland system better than an oceanic system in terms of wastes?
Can treat inland wastes.
If the farm is in oceanic waters, just hope it washes away.
What are the different aquaculture set-ups?
Net pens
Ponds
Raceway
Recirculation
What are the benefits of net pens?
No water chemistry issues.
Can have high fish densities
Can keep in bay for high accessibility
Relatively inexpensive
What are the problems with net pens?
Fish density is high so, if not placed correctly, can get waste buildup
Habitat can get degraded due to wastes
Fish escape can occur whereby the fish outcompete the native ones (ex: Atlantic and Pacific salmon)
Diseases
Describe the benefits of a pond.
Inland system
Water comes from ocean so water chemistry is generally not an issue
What are the problems with ponds?
Generally near shore so can have issues with wastes and can be devastating to coastal environments
- i.e. may need to build near the coast and destroy estuary or forest buffer strip
- can have buildup of wastes in coastal areas, degrading them
What are the benefits to recirculation systems?
Waste problem eliminated
Less environmental damage
Doesnt need to be near an ocean or coastal areas
What are the problems with recirculation systems?
Expensive for maintenance
Have to carefully monitor water chemistry
Fewer fish
Still might not take care of overfishing issue
What is the best way to get around the overfishing issue with aquaculture?
Raising vegetarian fish like Tilapia.
What is the best aquaculture system?
Grow Tilapia in a recirculation system.
What is the main species for aquaculture in BC? Why?
Atlantic salmon.
Grows fast, productive species.
What are the main concerns with aquaculture and Atlantic salmon?
If these fish escape, they can potentially outcompete native endangered, Pacific Salmon.
High density of net pens may cause outbreaks of sea lice to affect Pacific Salmon when coming close to net pens during spawning.
What are some answers to the Atlantic Salmon aquaculture problem?
Grow Pacific salmon instead, less likely to get sea lice and less of a problem if they do escape.
Don’t grow as fast however.
What is point source pollution?
Is this easy to regulate?
Pollution deriving from a single source.
ex: factories discharging directly to the system.
Easy to regulate.
What is non point source pollution?
Is it easy to regulate?
Pollution from multiple different sources, can’t pinpoint exact location since it comes from everywhere.
ex: chemical lawn treatment, farms flow off, car emmisions
Hard to regulate
Describe the Lake Erie dead zone.
Every couple of years during the summer, get a dead zone in Lake Erie.
Large problem due to phosphorus run-off.
Algae grows and then dies off in the summer due to heat and sink to the bottom.
During the summer, there is less mixing due to decreased wind and bacteria decompose the algae, consuming the oxygen at the same time.
Fish either die or run away from anoxic conditions.
Describe bioaccumulation.
Accumulation/amplification of contaminants such as
PCBs as one goes up the food chain.
How does El-Nino affect fish populations?
Surface temperatures are warmer than usual and upwelling events aren’t present at the same scale as they usually are leading to decline in fish populations.
How does Global warming affect the state of the Worlds fisheries?
Warmer waters get even warmer and fish are forced to migrate to cooler waters.
This causes large migration events and possible death if fish populations cannot migrate.
See a disruption in local ecosystems as ice melts, water gets warmer, etc.
Draw the MMSY graph, axes are percent of maximum (y) and exploitation rate (X)
show where MMSY, and show total catch, total biomass, mean Length max and collapsed species.
refer to notes
