Overfishing
Marine Biology Honors Presentation
Maddie Rita
Definition
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In basic terms, overfishing
exactly what it sounds like: the
practice of removing too many
fish from an ecosystem.
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The remaining adults are too
few to breed and replenish the
species to its original
population.
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Over time, this type of depletion
results in extinction.
Sources of Impact
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Although pollution and a combination of related issues (addressed by
other Honors students) have also diminished fish populations, human
demand is the sole, direct source driving overfishing and the subsequent
issues it causes.
Why is this happening?
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●
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Since the industrial revolution, the human population
has exploded.
The need to feed so many more mouths, coupled with
the introduction of 20th century technology, has made
huge, commercialized harvests the new fishing
standard.
Worldwide, and especially in developing countries,
(where population growth is strongest), fish represents
an important source of dietary protein.
Therefore, many governments subsidize commercial
fleets.
Fish populations simply cannot support the
current demand. In fact, our excessive
harvests are only decreasing their ranks:
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52% of fish stocks are fully exploited
20% are moderately exploited
17% are overexploited
7% are depleted
1% is recovering from depletion
(Overfishing Basics)
Example:
(Threat)
Why is this happening? (contd.)
● Many large, predatory species are already gone.
○ These have longer life spans; thus, they take longer to reach sexual
maturity, and are more vulnerable to extinction by overfishing.
● When one species vanishes, fleets, "fish down the food
chain," catching smaller species and further upsetting
predator to prey ratios.
● Since waters close to shore are often more regulated
and/or more polluted, fleets continue to venture
further and deeper, increasing fuel and operation
costs. In order to offset this, fisheries try to catch
virtually anything of value.
Destructive Methods are Used
●
Bottom Trawling
○
○
Large, weighted nets are dragged along the seafloor.
Trawls act like bulldozers, destroying corals and other bottom
dwellers, and stirring plumes of sediment and debris.
(contd.)
● Cyanide Fishing
○
Cyanide is used to temporarily stun tropical fish, which are then easy
to gather.
○
○
Only about 50% survive for sale as pets.
Other species, especially filter feeders, are poisoned by residual
cyanide.
Biotic Effects of Overfishing
●
●
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One of the greatest, and most obvious,
impacts is the removal of whole fish
populations.
But in-demand fish are not the only
marine species impacted.
○ Every year, millions of tons of nontarget species are involuntarily
harvested and then discarded.
Known as bycatch, this waste
includes marine mammals, seabirds,
and non-desired fish.
○ This is especially an issue with
trawling, which collects up to 90%
bycatch per catch.
With lack of predators, the lowest levels
of some food chains (plankton etc.) are
overly prosperous.
Abiotic Effects of Overfishing
● Sediment raised by bottom trawling
reintroduces previously-settled pollutants into
the ecosystem.
● Cyanide and other chemicals wipe out fragile
environments, especially reefs.
● Dumped bycatch = large amounts of organic
waste, increasing ammonia levels.
Extended Example
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The North Atlantic cod industry
was healthy and prosperous for
hundreds of years.
But with the introduction of
industrialized fishing techniques
in the 1950's, the cod population
began to shrink rapidly.
In 1992, no new cod arrived at
the start of the season.
The industry collapsed in the
course of that one year.
○ 30,000 jobs lost.
○ Cod population still has not
recovered.
Laws
●
Many attempts to address this issue legislatively have
been unpopular with national governments because a
higher degree of regulation is costly and timeconsumptive.
●
Example:
○
At the 2010 Convention on International Trade in Endangered Species
of Wild Fauna and Flora, restrictions were proposed to protect
bluefin tuna, which is on the brink of extinction.
○
These efforts failed (perhaps because of the fact that bluefin tuna is
a 7.2 billion dollar industry)(Threat)
Responses
● Some ideas, however, have been minimally
implemented, and could aid the situation if
implemented further.
● At the 2002 World Summit on Sustainable
Development, the Johannesburg Plan
introduced the concept of Marine Protected
Areas (MPAs).
Marine Protected Areas
● Fishing is highly regulated, or completely forbidden, in
MPAs.
● Currently, only 1% of the world's oceans are in MPAs.
● MPAs could allow some fish populations to safely breed
and recover.
○ But there must be many more Marine Protected Areas in order for
this to effectively take place.
(contd.)
● Environmentalists also stress the
importance of pressuring governments
to:
○ Establish further MPAs.
○ Limit or eliminate subsidies.
● New fishing techniques that reduce the
amount of bycatch are also needed.
(contd.)
● Consumers can play a crucial role by
purchasing sustainable seafood and
avoiding endangered species.
● Reducing demand will reduce
overfishing.
In Conclusion...
● The impact on some marine species is
already irreparable.
● Many others can only be saved by
aggressive and comprehensive measures.
● If we continue overfishing at the current
pace, scientists estimate that all of the
world's fisheries will collapse by 2050.
Works Cited
Brimblecombe, Peter, and Mary Ann Cunningham. "Overfishing." Environmental Encyclopedia.3rd ed. Vol. 2. Detroit: Gale, 2003.
1040-042. Print.
Lerner, K. Lee. "Commercial Fisheries." Environmental Science: In Context. Vol. 1. Detroit: Gale, 2009.160-61. Print.
Lerner, K. Lee. "Overfishing." Environmental Science: In Conext. Vol. 2. Detroit: Gale, 2009. 652-54. Print.
"Overfishing: A Threat to Marine Biodiversity." UN News Center. UN, n.d. Web. 22 Nov. 2012.
<http://www.un.org/events/tenstories/06/story.asp?storyID=800>.
"Overfishing Basics." Overfishing: A Global Disaster. Overfishing.org, n.d. Web. 22 Nov. 2012.
<http://overfishing.org/pages/what_is_overfishing.php>.
"Overfishing." The Ocean. National Geographic, n.d. Web. 22 Nov. 2012.
<http://ocean.nationalgeographic.com/ocean/critical-issues-overfishing/>.
"Threat 1: Overfishing." Overfishing. Save Our Seas Foundation, 2012. Web. 22 Nov. 2012.
<http://saveourseas.com/threats/overfishing>.
"Too Many People Chase Too Few Fish." Ocean Planet: perils-overfishing. NASA, 1995. Web. 22 Nov.2012.
<http://seawifs.gsfc.nasa.gov/OCEAN_PLANET/HTML/peril_overfishing.html>.