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Overfishing

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by

Monica Lester

on 23 January 2014

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Transcript of Overfishing

Bottom Trawling
Two methods: pelagic and dimersal
Pelagic
This method is designed to catch large schools of fish by dragging a net higher in the water column.
Dimersal
This method involves a boat dragging a funnel-shaped net along the seafloor to sweep up everything in its way.
Overfishing
Fishing Practices
Factory Fishing Vessels
A factory ship is used to freeze and process the fish caught in the ocean.
They also function to carry smaller fishing ships. These are known as mother ships, like from a movie about aliens. The smaller boats return to the larger vessel with their haul to be processed.
By-Catch
Sources
http://www.seaweb.org/resources/briefings/fishdownweb.php
https://awionline.org/content/driftnet-fishing
https://awionline.org/content/longline-fishing
https://awionline.org/content/trawl-fishing
Fishing Down the Food Chain
Fishermen exhaust the population of larger, longer-lived species of fish, so fleets are increasingly focusing on catching smaller, shorter-lived, plankton-eating species that are nearer to the bottom of the food chain.
When the species at the bottom of the food chain is targeted, itpushes the entire ecosystem to the brink of collapse.
Negative Effects of Biodiversity Loss
Decreases food security
Increases vulnerability to natural disasters
Destabilizes ecosystems and makes them more vulnerable to disturbances
Heavy fishing pressure can change the genetic characteristics of a population by selecting for or against certain genetically heritable traits.
For example, removing the larger fish over time results in favoring the survival of smaller fish
By Samantha Clark,
Monica Lester, and
Jennifer Miller
Longlining
Longlining involves placing thousands of baited hooks on a fishing line that stretches for miles.
This fishing practice became popular in the 1980's with the growing demand for highly valued fish like tuna and swordfish.
Whalers were used for the sole purpose of processing parts of whales, but the excessive use of these ships led to problems with the whale population, so the usage of them was reduced.
A factory trawler catches fish and then processes the haul. It can remain in the water for six or seven weeks.
When a trawling net is dragged between two trawlers, it is known as paired trawling.
The End
Driftnetting
This inludes gillnets that drift near the surface of the water. The tops have floats on the top and weights at the bottom to create a wall.
The net slides behind the fish gill covers to trap them.
Present day driftnets are made of nylon and can be up to 50 km in length.
They can become "ghost nets" when forgotten about; they can linger for a while since they are made highly resistant nylon.
By-catch is the unwanted fish and other aquatic species caught while commercial fishing.
It is often cause by less selective fishing gear like longlines and bottom trawls.
Longlines are left to soak, so they attract anything that swims by.
Bottom trawls catch anything in their paths.
Driftnets are sometimes left for a few days before they are retrieved, so air-breathing mammals will usually die if caught.
Fishermen don't like by-catch mostly because it wastes time and wears out the gear.
Fishing down the food chain causes two problems:
Lower-level competitors no longer have competition or predatory pressure for food.
With the targeting of lower-level organisms, predators are deprived of the food source necessary for population re-esablishment.
Causes of fishing down the food chain:
For decades, fishing fleets from all over the world have been taking unsustainable amounts of fish and marine life.
Consumer demand for more and different fish
Increased efficiency from technology in terms of locating and catching
Globalization of much of the fishing industry and markets
Lack of warnings about recommended catch levels
Government subsidies that encourage more larger fishing vessels with even more destructive gear
Illegal, unreported, and unregulated (IUU) fishing
Comics
Full transcript