fisheries powerpoint - Mater Academy Charter Middle/ High

Brian Diaz
Braulio Socarras
The Food We Rely On
 Many people rely on fisheries for food.
 Fish and shellfish supply about 7% of the global food supply and are the
primary source of animal protein to 1 billion people (about 15% of the human
population), mostly in developing countries.
 High demand= many fish species have become overharvested.
 As fisheries become depleted, those species that used to rely of the fish die off
as well.
Fishing Down the Food Chain
 Cod, tuna, and snapper are top carnivores in ocean food webs.
 As they are depleted, lower trophic level fish are caught for food. These smaller
fish are usually much more undesirable.
 The UN says that overall trophic levels in fisheries have decreased.
 As these lower trophic level fish die off, so does the fishing business (like the
North Atlantic cod fisheries).
Sustaining Fisheries
 Few countries manage their fisheries in a sustainable manner.
 Potential solutions include:
 Making “no-take” zones, where fishing is not permitted
Fish are plentiful here
When populations are high enough here, large fish go back to fishing zones.
No take zones are a recovery mechanism.
 Aquaculture means raising fish and shellfish as crops instead of hunting them.
It is the world’s fastest-growing food production.
 There are two kinds:
 Fish farming: cultivating fish in a controlled environment
 Fish ranching: Raising fish young, releasing them, and recapturing them when they
grow and return to spawn. (Salmon)
 Aquaculture is highly efficient and has little use of fuel, but it requires a lot of
land, feed, and water. It also produces concentrated waste. Tanks become too
contaminated to use after about 5 years.
Methods of Fishing (Trawler fishing)
 Trawler fishing is used to catch food species on the ocean bottom. A funnel
shaped net help open at the neck is dragged along the bottom.
 These nets capture everything on the ocean bottom, not just target species.
They cause enormous damage to the sea environment and are huge, meaning
they can take up large amounts of fish.
 A lot of bycatch
Purse seining and Longlining
 Purse saining catches surface fish like tuna and anchovies. After finding a large
school of fish, a purse like net closes up (drawstring purse), capturing the fish.
Dolphins are sometimes captured.
 Longlining involves putting out fishing lines that are 80 mile long, with
thousands of baited hooks. These hooks catch swordfish, tuna, and sharks.
They also may catch sea turtles, albatrosses (birds), and occasionally dolphins.
Dfrift-net Fishing
 Drift nets that are as long as 40 miles are set out. Anything that gets into
contact with the net quickly becomes entangled. These include huge amounts
of prey species and bycatch (including marine mammals and sea turtles).
 The UN banned drift nets longer than 1.6 miles long in 1992. Still, long nets are
used because compliance is only voluntary.
Overfishing and Bycatch/ What our
Oceans Should be like
5 Important points
 7% of the global food supply comes from fish and shellfish and over 1 billion
people rely on fisheries for food.
 As overfishing of top predator fish occurs, they are replaced by lower trophic
level species.
 Aquaculture may be an alternative hunting wild fish, but they produce
contaminants and infected water as well as require a lot of resources.
 The four main fishing methods are trawling, purse-seining, drift-nets, and
 These methods can catch a lot of desirable fish, but cause overfishing and large
amounts of bycatch.
 Living in the Environment (Tyler Miller)
 “Purple Environmental Book”

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