Effects of by-catch
Hall MA, Alverson DL, Metuzals KI. 2000. By-Catch: Problems
and Solutions. Marine Pollution Bulletin.
41:204-219
Read AJ, Drinker P, Northridge S. 2005. By-catch of Marine
Mammals in US and Global Fisheries. Conservation
Biology. 20(1):163-169
The unintentional catching of many marine mammals is having
profound effects on marine ecosystems around the world. A study done by Read
and colleagues estimated the by-catch for 125 different marine mammal
populations in three geographical US water regions (Atlantic-Gulf of Mexico,
Pacific, and Alaska). The data collected
in this study was taken from observers which were placed on different fishing
vessels from 1990-1999. They also used this data to estimate the total global marine
mammal by-catch.
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Photo 1 source: http://www.bycatch.moonfruit.com/
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They found that the average annual by-catch of marine
mammals in US waters was approximately 6,215 +/- 448. They used this
information to estimate that approximately 653,365 marine mammals are
accidentally captured a year globally. However, these numbers are only
approximations as the major downfall to their methods is that they are using
information from log books and observers. Many by-catch animals are assumed to
not be reported by fishermen, or are grossly understated.
Though the current estimates of by-catch in the US and
globally may seem unbelievable, this is actually a huge reduction in numbers.
According to a study done by Hall et al. (2000) it was believed that in the 1960’s
several hundreds of thousands of dolphins alone were caught while fishing for
tuna. The major decrease in mortality rates was due to introduction of fishing
acts and by-catch laws put in place (Hall et al. 2000).
Some gear improvements has helped to reduce by-catch. Some
fishermen use “pingers” which are electrical devices which deter many animals
which use echolocation as their mode of sensing there environment. However,
these methods are not as successful when it comes to other species of animals such
as sea birds, turtles, and pinnipeds (Read et al. 2005). Thicker mesh,
selective lines and baits are also some mechanisms put in place to avoid
by-catch. But by far the most effective method of reducing by-catch is through
public awareness and political policy placement (Hall et al. 2000).
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Though it is great to know that the annual by-catch numbers
have decreased substantially over time, I still think there is room for
improvement. It seems that a major problem with dealing with by-catch is the
lack of knowledge and the low accountability of the data. Though fishers are
required by law to record any by-catch, this is not always what happens. Having
more programs with observers on board fishing vessels and also more research
may help bring realistic numbers out into the open. With these numbers it will
help drive further research and investigation into improving policies, fishing
gear, and training of fishermen to help avoid by-catch.
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