The negative impact human beings have had on marine life in the ocean is widespread and far reaching
The negative impact human beings have had on marine life in the ocean is widespread and far reaching into history and, without considered intervention in the form of increased protection or a review of fishing practices, will continue to blight marine ecosystems into the future. Other causes of marine habitat destruction such as climate change and pollution require a different approach and more broadly, we need to view the oceans as a global resource for which we are all responsible.
The marine life that we see in seas and oceans today is totally different to that we have seen throughout history. Traditionally, ocean habitats have remained relatively underexplored compared to those on the land and this was even more so the case in past times. With few marine surveys and even fewer written records on the ecological content of the seas before the first analysis in 1876 by HMS Challenger (Roemmich, Gould and Gilson, 2012) one can look towards secondary data such as fishing records to estimate the size, type and nature of marine life.
Flemish artists such as Frans Snyders, painting in the early 1600s, depicted market stalls overflowing with fish and crustaceans and varieties on display that would seem alien on a fish stall today. Not only were different species present in the market stalls of Europe, such as sturgeon and porpoises but the size of the more recognisable animals themselves, such as salmon and halibut were very much bigger than those we would expect to see at a fish stall today. It would not have been unusual to see a cod in excess of one metre in length while today few fish reach the upper limit of their growth, tending to be caught as they reach around forty centimetres instead. This gives the impression of a time, around four hundred years ago, when we had a highly bountiful sea, teaming with marine life that seems somewhat out of place today. Everyday species in the sixteen hundreds such as Common Skate were abundant in UK waters where now they are almost extinct. In fact ancient tales of ‘sea monsters’ in the Mediterranean are believed to be partly true, with species such as the Dusky Grouper possibly reaching the size where it would have been able to break a fishing line, capsize a boat or even eat a human being according to researchers at Stanford University studying first and fifth century mosaics which depict such scenes (Guidetti and Micheli, 2011). Today these groupers are listed as endangered on the International Union for Conservation of Nature (IUCN) Red List – the inventory that highlights the needs of certain species for conservation efforts.
Moving forward in history and the same scenes of plentiful abundance at fish markets are witnessed in more modern times. Every day during the late nineteenth century, right up until around 1950 large fish markets such as that at Grimsby docks saw their heyday. An area known as ‘The Pontoons’, a huge open air warehouse structure on Grimsby’s dockside, was deep with crates of freshly caught fish, such as cod and ling, and from there fish was exported and sold all over the UK. At the turn of the twentieth century, over one hundred fishing vessels were operating out of Grimsby port and a tenth of all the fish consumed in the UK had come through their docks.
Over time the number of fish being landed in UK docks went down as well as their average size. Fishermen were travelling further and deeper into the ocean in order to gain the same returns and in 1958 through to 1976, the so called ‘Cod Wars’ took place between the UK and Iceland. UK fishing vessels started to stray inside the boundaries of Icelandic territorial waters in search of cod, boundaries that the UK disputed. In the ensuing disputes, fishing nets were cut and warships deployed to guard the trawlers.
The view that we may actually run out of fish is a controversial one. In some areas species are experiencing ‘stock depletion’ where levels of breeding fish have fallen so low that their future survival as a species was extremely uncertain. In fact some bodies estimate that twenty four percent of global fish stocks are either over exploited or depleted (UNFAO, 2011a).
One should remember however that this may not represent a single direction of travel and a continual rate of decline. Some fish stocks are in a state of recovery such as Atlantic Herring in the North West Atlantic and the Cape Rock Lobster off the coast of Namibia, though these only represent one percent of all fish stock (UNFAO, 2011a)
Infographic: How has the marine ecosystem changed over time?
There is little doubt that the changes that have happened to marine wildlife since the 1800s can be put down to anthropogenic behaviour and an increased interaction between human beings and the oceans. A large part of this degradation is due to the increased demand for fish and crustaceans and the ways the fishing industry has changed to reflect this demand.
For thousands of years fishing has been undertaken by simple technological means – for the most part through hook and line methods as well as through traps and nets for crustaceans. The invention of steam power, and its subsequent incorporation into boat design in the 1800s, reduced the need for fishermen to stay relatively close to shore and with the force of the tides and the wind no longer prohibiting their movement, fishermen went far beyond their normal fishing territories. As well as being able to travel further, technological advances meant fishermen could also fish to greater depths, for longer hours (as well as at night) and could tow larger nets and fishing gear. Therefore, within a very short space of time, the impacts of fishing were felt over an increasingly wider area and to much more damaging effect.
Further technical advances saw diesel engines replace steam power and nets also changed in design, becoming more resistant to the sea and catches by being made of a single plastic filament rather than cotton or hemp. This meant that nets had greater tensile strengths and so larger catches were sought and landed. The abundance of fish in the sea quickly went down, as it continues to do so today. Unfortunately for marine ecosystems, this realisation has come a little too late and many concerned marine biologists would say that we have become preoccupied with our increased ability to catch fish regardless of the knowledge that it is ultimately unsustainable at its current rate.
Trawling and dredging are often targeted as the most destructive forms of modern fishing. In these practices, very large nets (that are often multiple times longer than the length of the fishing vessel itself), are towed behind the boat, capturing any sea life swimming at that particular depth. The nets are then hauled back on board the boat via hydraulic winches where the fish are separated into the target catch (those the fishermen intend to sell) and the by catch (those fish which are too small or which have low demand). Dredging methods follow a similar approach but are arguably much more devastating to marine ecosystems. A dredge is a steel framed scoop which is dragged behind the towing boat, scraping the bottom of the sea bed for all marine life, despite the target species most often being bottom dwelling scallops and prawns. Some scoops are fitted with metal teeth that protrude into the bed itself, dislodging clams and other buried fauna. Despite often having a wide mesh net attached which would allow juvenile shellfish to be freed, once the scoop starts to fill up this mesh becomes less effective. Dredging can denude a sea bed of all life and crushes many animals not caught in the scoop itself. It can also increases turbidity to high levels, reducing light penetration to the depths of the oceans.
Both of these methods have been heavily criticised for their lack of selection: despite a boat going out with a particular target fish or crustacean in mind, the nets are indiscriminate and many more species are hauled out of the sea as by catch. Unfortunately by the time the target fish have been separated from the by catch, the by catch species are already dead and in most cases thrown back into the sea. Given the high number of juvenile fish who will invariably belong to this group, one can see how quickly the breeding stock of fish can be decimated by such practices.
Since the 1500s, cod had been fished off the east coast of Canada in the North West Atlantic and was an important resource to both Inuit communities and later settlers. It reached a peak in the mid-1960s with over 800,000 tons of cod being landed a year on the Newfoundland coast (Myers and Cadigan, 1995). However in 1992, the Canadian cod stocks collapsed to below one percent of their previous recorded levels and the Canadian federal government was forced to issue a ban on the cod fishery industry in an attempt to allow stock levels to recover. However the continuance of prawn trawling during this ban has made the government’s efforts deeply ineffective, with juvenile cod being swept into the nets, offering little chance of the recovery of the species in the long term.
One should not however assume that more traditional fishing methods such as using hook and line fare any better with regards to levels of by catch and their effect on marine ecosystems. In the tropical waters off Costa Rica long line fishing is deployed in order to catch mahi-mahi, a fairly common surface dwelling fish. Since 1994, by agreement with neighbouring state governments and a collective of NGOs, circle hooks have been used in order to make the practice more turtle friendly. However olive ridley turtles in the by catch still outnumber the target mahi-mahi by over two to one from these lines.
One should remember that over fishing and damaging fishing practices are not the only causes of marine wildlife destruction. Pollution and climate change can also have a role in this and tend to offer more widespread damage while at the same time being more difficult to manage as the impacts are not felt solely or directly by those who behave irresponsibly.
Infographic: What has caused the degradation of marine ecosystems?
Many marine biologists will recognise that we are currently living beyond our ecological footprint and nowhere is this more obvious than in our marine ecosystems. The speed of change in fishing practices as well as the increased demand for marine life on our plates has meant that the future of our oceans looks bleak and the ability of the seas to be resilient in the face of these changes is uncertain. Accepting that nature is a huge and coherent system that requires our respect is a difficult concept when faced with people and their families who have fished the oceans and kept small communities (and indeed national economies) more financial secure by their actions. It can be argued that the first step towards working through this conflict is recognising that fishermen, instead of being portrayed as ecological criminals are in fact in the perfect position to become custodians of the sea. More sustainable practices such as using smaller nets, which are landed more frequently could see by catch returned to the sea more quickly, reducing the chance of wholesale juvenile mortality. Campaigns that work with fishermen and their buyers to create a market for sea life that becomes by catch can go a long way towards reducing the wasteful nature of trawler and dredge fishing as fishermen will be able to profit from fishing far less.
The movement to set up more protected marine parks has long been a subject of contention, mainly because of the scale of the desirable area. A third or more of the ocean surface needs to fall under a protection order to have any positive effect on marine life, with an outright ban on any fishing in areas that are most sensitive or damaged. The frequency and intensity of trawling and dredging needs to be reduced worldwide and a return to more traditional fishing methods employed in areas in which it can be sustained.
With further investment into the research and nature of aquaculture and the ‘blue revolution’, this form of farming may be made more sustainable and meet the demand for fish and crustaceans without damaging the oceans that lie in such a delicate balance.
Those who consume fish and shellfish may need to be persuaded that a higher price needs to be paid for these products, reducing the need for fishermen to act like fish wholesalers in an economy of scale. Just as some tastes for some marine life has diminished (for example, turtle soup) so too can consumers be persuaded to buy less well known fish that might otherwise be return to the sea dead as part of by catch.
Infographic: What can be done to conserve and restore marine ecosystems?
Guidetti, P. and Micheli, F. (2011) Ancient art serving marine conservation, Frontiers in Ecology and the Environment 9, p374.
Myers, R.A. and Cadigan, N.G. (1995) Was an increase in natural mortality responsible for the collapse of northern cod? 6:52, p1274-1285
Roemmich, D. Gould, W.J. and Gilson, J. (2012) 135 years of global ocean warming between the Challenger expedition and the Argo Programme, Nature Climate Change 2, p425-428
Thurston, R.H. Brockington, S. and Roberts, C.M. (2010) The effects of 118 years of industrial fishing on UK bottom trawl fisheries, Nature Communications, 1:15, p1-6
UNFAO (2011a) General situation of world fish stocks, United Nations Food and Agriculture Organization
UNFAO (2011b) Review of the state of world marine fishery resources, United Nations Food and Agriculture Organization
UNFAO (2012) FAO Yearbook Fishery and Aquaculture Statistics
Unless otherwise stated, all data in the above piece relates to figures taken from Professor Callum Robert’s lecture: Future Oceans – a sea of hope or despair? (Feb 2014)
The slow increase in pH of the oceans associated with the absorption of carbon dioxide.
The farming of fish and crustaceans in controlled conditions such as freshwater or seawater ponds.
The rise of fish farming and aquaculture to the point at which it exceeds the output from commercial fishing.
The fish unintentionally caught as part of trawling and dredging practices.
The, at times armed, conflicts between the UK and Iceland over the right to commercially fish in certain waters in the North Atlantic.
A set of marine invertebrates (corals) held together by their own calcium carbonate secretions to make up a marine ecosystem.
The scraping of the ocean floor by commercial fishermen to collect up sea bed dwelling sealife.
The ability of an ecosystem to recover back to its original state once it has been damaged by outside forces.
A set of living organisms that interact with non-living components to create a system of inputs, processes and outputs.
An environmental setting that is occupied specifically by a particular species or set of related species.
The fish species that is the intended catch by fishermen and that which they will sell once landed at port.
The dragging of a large net behind a boat (trawler) in order to catch fish, most often in the mid-depths of the ocean.
With the help of some additional research, students can design and create a graphical timeline that shows the changes that have taken place in commercial fishing in the past that has led to the depletion of marine ecosystems. The timeline can then be extended into future years to show what and when other changes may have to happen in order for the ecosystems to recover.
With further information on the lifecycle and formation of coral (and coral reefs) students can draw a system web to show how the reef occupies a unique part of the marine ecosystem. Students can then annotate this system diagram to show how each of the following factors disrupt the system: overfishing; acidification; pollution and dumping; tourism; dredging; climate change and invasive species.
Students can make a list of different players who have a role to play in the restoration and conservation of marine ecosystems. They should then individually rank them by level of importance and compare their ideas with their peers. This can lead into a discussion about who should and does hold most responsibility for the protection of the oceans.
Cabo Pulmo National Park
Fish Fight: A global campaign led by TV chef Hugh Fearnley-Whittingstall to make the whole fish industry more sustainable
Overfishing: Liam Carr
Ocean Acidification: Professor Nicholas Owens
By placing a booking, you are permitting us to store and use your (and any other attendees) details in order to fulfil the booking.
We will not use your details for marketing purposes without your explicit consent.
You must be a member holding a valid Society membership to view the content you are trying to access. Please login to continue.
Join us today, Society membership is open to anyone with a passion for geography
Cookies on the RGS website