subject: The Human Impact on the Ocean [print this page] Author: Simon Harding Author: Simon Harding
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.comwww.chronosconsulting.comAbout the Author:
