The main fishing methods. Commercial fishing accounts for 90% of the
world catch. The main fishing methods have changed over time since commercial
fishing really began in the 15th century. The advent of freezer ships after the
Second World War has increased the ability of vessels to stay out fishing and
improved fishing gear, longer lines, larger nets and more effective ways of
locating fish have all contributed to overfishing. In modern commercial fishing
just six species make up over half the catch ( cod, herring, anchovies, sardine,
pollack and mackerel ). Modern commercial fishing relies on several main
methods. Purse seiners, trawlers, oceanic long liners, and drift nets.
Let us take each of
these methods in turn. Purse seine nets encircle a whole shoal of fish and the
net is then tightened like a purse string. This method is effective for
sardines, anchovies and tuna. Trawling is the method used for dimersal fish.
Here trawl nets are dragged along the bottom of the sea , usually on the
continental shelf and these nets taper to the cod end. The nets are then drawn
in. This method is effective for cod, hake, haddock, shrimp, prawn and lobster.
Next we have the longliners. This is basically a series of lines with hooks.
Some lines can be 30 kilometers in length. This method is effective for tuna,
Marlin and billfish. Drift nets are another method used to catch fish. These are
vast nets sometimes tens of kilometers long but they entangle many unwanted
species. Trammel nets have a similar effect.
This is known as the
by catch and fishing methods have been developed to prevent bycatch in some
cases. However, over 30 million tonnes of bycatch still result per year and many
turtles, sharks, birds and dolphins die in this way. Finally we have gill nets
which are designed to catch fish of a certain size by their gills but they also
ensnare many other animals such as turtles., These main fishing methods have led
to overexploitation of fish stocks, particularly on the continental shelves and
the targeting of pelagic species such as blue fin, yellow fin tuna (Thunnus
albacares) by encircling nets and rod and reels. Also the deep sea is being
exploited more and its species e.g. Orange Roughy, which is a problem as many of
these species take a long time to mature. The overexploitation of almost all the
world's fisheries is now an issue with some catastrophic examples such as
Peruvian anchoveta stocks. Finally another method of "fishing" could be
aquaculture but as this takes vast amounts of protein to grow the fish it is
hardly a viable long term alternative. Marine Protected Areas and no take zones
may help the situation.
Whaling: Whaling began with subsistence
whaling by aboriginal hunting methods but by the 18th century commercial whaling
had become dominant as demand for oil and other whale products grew. Initially
the Right whale, Bowhead and Grey whales were targeted but a depletion in their
numbers by the end of the 19th century led to new species being targeted. With
the advent of factory ships and explosive harpoons the exploitation of whales
continued , especially in the Southern Ocean with Blue, Fin, Sperm and Humpbacks
all targeted. The numbers of whales killed paints a grim picture. Around a
million Sperm whales have been killed, half a million Fin, a third of a million
Blue Whales and a quarter of a million Humpbacks. Some of the whale populations
will struggle to ever recover despite bans on whaling e.g. Northern Right whale.
Gray whales have become extinct in the Northern Atlantic. Perhaps only 5%
of the once great whale populations remain. This has many consequences on the
ecosystem as we have seen from previous units with whale carcasses proving such
an important source of food in the deep oceans. Overexploitation led to the
International Whaling Commission being established in 1949 and the Moratorium
set up in 1986 but countries such as Japan lobby to circumvent these bans so the
partial destruction of certain whale species continues. In 2006 the many members
voted for a return to whaling threatening to overturn the progress of the last
20 years.
The problem of global
warming: Global warming
refers to the recent increase in the average temperature of the Earth's
atmosphere and oceans. This has risen by approximately 0.6 degrees Celsius in
the 20th century. There is a broad consensus that this is due to human activity
with increased emissions of carbon dioxide, methane, burning of fossils fuels
and deforestation. The effects are almost certainly anthropogenic in origin as
evidence from studies such as the Mona Loa research in Hawaii show. It is
estimated that the temperature could rise as much as 5.8 degrees Celsius by
2100. The problem of global warming is an immense topic but we can break this
brief discussion down into the effects of global warming on 1 ) Weather, 2)
Oceans, 3) Living organisms. Naturally all three interact though. We can
conclude with a brief mention of some solutions.
1) The rise in temperatures
is already influencing weather patterns with extremes of weather such as
flooding, droughts, heatwaves, hurricanes and tornadoes. Storms are becoming
stronger e.g. Hurricane Katrina. Heatwaves lead to wildfires e.g. Southern
California and we see frequent flooding in the UK.
2) Related to this we have
effects on the world's oceans. The sea levels are rising, polar caps thinning,
and there could be disturbances in the ocean currents and slowdown of
thermohaline circulation in the Gulf Stream which would lead to localized
cooling effects with dire consequences in the long run.
3) The above changes
also influence animal and plant life in almost all ecosystems. The polar bear's
( Ursus maritimus) problems are famous as the ice thins but we can see
influences throughout the world from El Nino effects on animals , to coral
bleaching to storm damage to environments.
There are
five main sets of solutions to the problem of global warming. 1) Reduction of
energy use and conservation of fuel supplies e..g. more efficient engines,
planes, power stations . 2) Using sustainable energy e.g solar, wind, tidal,
waves, hydro, geothermal. 3) Sequestering carbon by removing from atmosphere
e.g. more natural carbon sinks in forests, and the controversial iron sulfate
sowing in the sea. 4) More carbon storage in geological faults for example but
perhaps this is also controversial. 5) Planetary engineering but this is in its
absolute infancy. A political solution is
needed and the Kyoto Protocol in 1997 was a start even if some of the worlds
worst polluters either refuse to ratify (USA) or are exempt e.g. China and
India.
The main threats to
the marine environment
The main threats to the environment can be
broadly grouped in the following way. 1) Problems of overfishing, 2) Threats of
global warming 3) Threats of pollution, oil and non oil related 4) Other human
induced threats.
1) We have mentioned the
problems of overfishing in section one above but we should add that overfishing
leads ultimately to destruction of species and ecosystems. Whaling, shark
finning, targeting of species such as Marlin and Yellow fin tuna all disturb the
complex food webs and effect marine life. In addition the physical damage to the
ocean bed and large by catches are also threats to the marine environment.
2) The threats caused by
global warming have been mentioned above from changes in sea level to coral
bleaching to disturbances in circulation systems with consequent bad effects on
the marine environment.
3) Pollution
threats. These can be broadly divided into
two sections. Oil and non oil. We rely and need oil but it has a unique place in
the history of pollution as a threat to the marine environment because it is so
visible e.g. Torrey Canyon 1967, Amoco Cadiz off Brittany in 1978, the Sea
Empress off Milford Haven and the Exxon Valdez off Alaska. The oil spills killed
many types of marine life in every case including seabirds. Even attempts to
clean up oil spills with dispersants are sometimes misguided and actually cause
problems with marine life. Let us now consider non oil pollution. This covers a
variety of pollution from plastic rubbish which turtles eat , pesticides,
chemicals, heavy metals such as cadmium, copper and mercury to radioactivity.
Agricultural run off can also be deadly and cause oversupply of nutrients to one
species to the detriment of others.
Pathogens may accumulate
in these ways and find their way into the food chain. Finally we can consider,
4) i.e. other human
caused or anthropogenic effects. These include commercial shipping with its
pollution, waste disposal, disturbance of marine life, military use of the sea
with polluting effects plus nuclear bomb testing to gas, oil and mineral
extractions which cause damage to the marine environment. Recreational use and
tourism also pose a threat to the marine environment with spear fishing of rare
species, litter, waste,damage to corals, disturbance of species and hotel
development effecting the littoral area. However, the oceans provide vital
resources so ways will need to be found of limiting the main threats to the
marine environment which we have outlined here.
Dr Simon Harding, www.coberongreen.com,
www.chronosconsulting.com.
Have a good weekend
all,