Overfishing: worldwide depletion of fish stocks

Pessimistic models predict a catastrophic drop in stocks.

After a period of strong growth after the Second World War, fish production has stagnated around the 90 million tonne mark over the past fifteen or so years, and this despite technological progress and research into new stocks to fish. The biological production capacity of the oceans appears to have been reached.

The over-exploitation of fishery resources is well documented around the world. According to statistics compiled by the FAO (Food and Agricultural Organisation – the UN agency dealing with this issue), 50% of fish stocks have reached the upper limits of their biological production capacity, 25% are over-exploited, and 25% are under-exploited. Over the past few years there has not been any significant improvement worldwide that could give grounds to hope for a reversal in this trend. Nevertheless, there is no reason to conclude that large fish stocks will disappear by 2050, an assertion based on speculative premises.

In addition to reducing fish stocks, fishing has other impacts on the entire ecosystem. Historically, the species fished have tended to be the larger ones, with a relatively long lifespan, which reproduce at a comparatively advanced age. These ecological characteristics mean they are vulnerable to pressure from fishing. Such species tend to be predatory. Their prey, however, are smaller-sized species, with a shorter lifespan, and which reproduce earlier with high fertility levels. Thus not only do they better resist pressure from fishing, they also benefit from the drop in predator numbers, which have been overfished. There has also been a drop in the abundance and number of species of the most fragile benthic* invertebrates inadvertently caught by fishing operations, crushed, or broken by trawl nets for example. Some of them are a major part of the diet of many other species (fish, crabs, octopuses, and so on). On the other hand certain other sorts of organisms such as gastropods* feed on the corpses of the many fish discarded by fishermen for being of no economic value, and are becoming more abundant due to this manna from above. The entire food chain is therefore altered, partly explaining the increase in the number of specific species of jellyfish and of plankton known as gelatinous zooplankton.

Whilst overfishing the oceans is the cause of most documented instances of the extinction of marine species (55%), other causes are the loss of habitat (37%), the introduction of invasive species, climate change, pollution, and disease. On the basis of these observations certain scientists are talking of the beginning of a new era of viscous life forms.

Given the context of shared resources becoming rarer and modifications to the ecosystem, the general trend is to economic over-investment in the fishing industry. Markets for sea produce are becoming global. Thus the total economic value of landed catch is declining in many instances. The model is therefore unsustainable in both economic and ecological terms.

Shrimp in the Guiana Shield region

The specific environment of the Guianas

French Guiana benefits from an ecological context that supports a large number of species and high levels of biological production, amongst the highest in the world. The North Brazilian current flowing from the south-east to the north-west draws fresh water from Brazil laden with organic matter from the Amazon, the influence of which is felt as far as the Orinoco in Venezuela. The downside, from the swimmer’s point of view, is the brown colour of the water carrying the material in suspension. This matter sediments out to make mudflats which, once they have formed on the coast, are then colonised by mangroves. Erosion by water currents and the swell drives these mudflats north-westwards. Thus the Pointe des Amandiers in Cayenne, for example, has been through a series of phases over recent years in which the mudflats and mangroves are present and the sea is therefore not visible, followed by periods when there are no mudflats due to erosion and the disappearance of the mangrove forest, with the sea being visible once again. In this way the coastal zone is unstable and ever-changing.

The ecology of the shrimp

Due to the organic matter carried from the Amazon and the presence of the mangrove forest on the coast, the coastal strip is particularly productive and provides favourable conditions for the development of numerous species. Certain typically coastal species remain there throughout their life-cycle. They have adapted to the turbid waters where the salts levels vary significantly between the dry season, from August to November, and the wet season, from December to July. Some such species of fish are weakfish (Sciaenidae), catfish (Siluridae), seabass (Centropomidae), rays (Dasyatidae), and the Atlantic goliath grouper (Epinephelus itajara) which can grow up to 450kg. Other more typically marine species only stay there whilst juveniles before heading out to where the water is over thirty metres deep when adults. This is the case in particular for penaeid* shrimp. This zone also acts as a nursery ground for this sort of species. It is thus essential for the maintenance of marine biodiversity including for stocks fished both along the coast and out at sea.

Penaeid* shrimp reproduce miles offshore in the sea depths. The eggs rise to the surface then hatch into larvae which float with the currents caused by the winds. When conditions are favourable they then return to the coastal zones of the nursery grounds to develop on the bottom for several weeks. This is the juvenile phase. After this short period the juveniles become adults and head out to sea to finish their life-cycle and reproduce in turn. They have a lifespan of about eighteen months. In French Guiana this is when the shrimp will be fished by a fleet of trawlers. Trawling is banned in the coastal zone, where the sea is less than thirty metres deep.

Possible explanations for falling stocks

Worldwide stocks of penaeid* shrimp fluctuate significantly from one year to the next, as these species are very sensitive to naturally occurring variations in environmental factors. Thus statistically speaking a bad year’s fishing is compensated the next year by a good year’s fishing. In French Guiana adult stocks as assessed by scientists working at IFREMER (the French Research Institute for Sea Exploitation) show that the two main species (Farfantepeneus subtilis and Farfantepeneus brasiliensis) conform to this rule. 1999-2000 was a very bad year. Regional cyclical climate phenomena were seen as the reason for this. But since then there have not been any good years to make up for the bad ones. Stocks are falling. Equally, the number of juveniles has also dropped a lot over the same period. Is the breeding success of the shrimp endangered by environmental changes relating to climate change? Has shrimp fishing been too intensive? It is possible that a combination of several of these factors may be behind these “disturbances” to shrimp stocks. Several hypotheses have been put forward to explain this decline in numbers.

Changes in dominant winds

Data analysis of wind measurements made by satellite or out in the field indicates significant changes in the frequency and intensity by wind direction between the years 1990 and 2000. These winds help create surface currents which enable the shrimp larvae to reach the coastal nursery grounds were they find ideal conditions to develop. The capacity of the larvae to reach the nursery grounds may thus be reduced by the change in dominant winds. It is possible they are also being carried out to sea instead of concentrating along the coast, in which case they would be less able to survive.

Temperature change

Once again analysis of data from satellite and field readings relating to surface seawater temperatures shows warming of about 1°C on the continental plateau. The biological functions of shrimp such as their growth and reproduction are very sensitive to variations in temperature, as they are for many other marine organisms other than mammals. For example, for a species of fish such as Pollock, found in temperate ocean waters, experiments have shown that a variation in temperature of 1°C when they are maturing (just prior to the reproductive season) can increase or decrease the number of eggs laid by a factor of ten, and can also have an impact on the survival rate of their eggs.

Overfishing in neighbouring countries?

The range of shrimp populations obviously extends beyond national borders. They are also fished by the neighbouring countries of Guyana, Surinam, and Brazil, and stocks are common to and shared by all. In Surinam there is a comparable trend with fewer boats and less production. Catches are even lower than in French Guiana. In Brazil fishing sometimes occurs very close to the coast with a large proportion of juveniles being caught. Given the direction and speed of surface currents and the duration of the larvae phase it is probable that juveniles living on the coasts of French Guiana come partly from eggs laid by adults off the north coast of Brazil. Furthermore, the hypothesis of adult migration between Surinam and Brazil has long been debated although not conclusively proven. Thus the stock dynamics observed in French Guiana needs to be analysed at the regional level, especially considering the increase in coastal trawling (at depths of between five and fifteen metres) in neighbouring countries which could have an effect on stocks and fishing activities throughout the region.

History and prospects for the future

In the 1960s shrimp was fished in French Guiana by a fleet of American and Japanese trawlers. At the time there were 120 boats in the Guiana Shield region as a whole for in those days EEZs* had not yet been set up. The fleet in French Guiana started to become more French-owned as of 1979, a process that was complete by the early 1990s when there were about 80 trawlers in all. The number of trawlers has progressively declined and in 2010 there were 24 in operation out of a potential of about 35 boats. This drop results from increased production costs, due primarily to the increase in the cost of fuel, compounded by a drop in the value of shrimp on the world market. Nowadays the industry has to confront an unprecedented decline in shrimp stocks. Due to the shrinking of the fleet the zones furthest away from the port of Larivot which are out at sea or to the west of French Guiana are being progressively abandoned, whilst nearer zones are preferred. At the same time the proportion of juvenile shrimp, which is higher in shallower zones, is increasing in the catch.

The drop in value of shrimp caught at sea is the result of world markets being flooded by sea produce such as farmed shrimp from Southeast Asia and Brazil in particular, countries which have massively increased their production over the past ten years. The cost of producing farmed shrimp in these countries is less than the production cost of fished shrimp in French Guiana and elsewhere. Furthermore, the average consumer does not distinguish between wild shrimp and farmed shrimp. This means that the price at which wild shrimp is sold, which varies with the size, has also dropped over the same period of time. The large shrimp (the adults) are sold at a higher price than the young ones (juveniles) and in French Guiana there has been a drop in the value of the catch as it is made up of a larger proportion of small shrimp. Given these difficulties (the unfavourable climates, saturated market, and lack of industry regulation in neighbouring countries) profitability has dropped and a strategy is now required if it is to remain profitable. In the long run, if current conditions prevail, shrimp fishing will not last in French Guiana. Therefore solutions are required to conquer new niche markets (see below) or else to diversify production by promoting fish caught by trawlers.

The ecological impact

Shrimp trawling is a major source of unintended catch. Without a system to reduce bycatch, no less than two tonnes of submarine species are accidentally fished each day by shrimp trawlers in French Guiana. This includes sea turtles, although there is little hard data, as well as large sharks, rays, and large pelagic* fish.

Consequently the shrimp fishing industry in French Guiana has expressed the need to carry on with research undertaken by the WWF and IFREMER, and wishes to play a larger part in this approach. In order to do so, numerous test campaigns have been conducted with all the owners of shrimp boats in French Guiana by the Regional Committee for Sea Fishing and Farming in French Guiana (Comité Régional des Pêches Maritimes et Elevages Marins, or CRPMEM) in collaboration with the WWF, and with the technical support of the NOAA (National Oceanographic and Atmospheric Administration). Precise parameters such as the form and distance between the bars on the selectivity grid have been tested. This has played a decisive role in enabling owners and teams on board to appreciate the full interest of the TTED (Trash and Turtle Excluder Device), which presents both ecological advantages (totally eliminating the catching of sea turtles, as well as reducing by between 25% and 40% the bycatch of other species) and technical advantages with new practices for shrimp fishing. The TTED facilitates the work of the fishermen by reducing the amount of time spent sorting the shrimp, reducing risks (potentially dangerous rays and sharks are no longer caught accidentally), and delivering a better quality end product (the shrimps are less crushed on the bottom by the trawl net). Equally, this selectivity grid can result in lower fuel consumption.

Looking for conscientious consumers

This change has been accompanied by other initiatives taken by the CRPMEM in French Guiana and the fishing industry to reduce the ecological impact: the banning of trawling in less than thirty metres of water (corresponding to 12 miles off the coast) so as to avoid any negative impact on the nursery grounds of marine resources which tend to be in this zone; the introduction of regulations on the mesh size to avoid catching juvenile fish and shrimp; monitoring via a traceability system to collect used oil and general waste so as not to dump them out at sea; using a smaller and more aerodynamic trawl door (a device which holds the net spread out under water) resulting in less drag and therefore lower fuel consumption. Furthermore, the shrimp industry is on the lookout for other means to improve practice. In October 2010 shrimp boat owners in French Guiana decided to launch the first stage of a procedure to set up an eco-label for the industry, providing it meets the criteria laid down by the MSC (Marine Stewardship Council).

Thanks to all these approaches the shrimp industry in French Guiana is an example for other countries fishing tropical shrimp. For the fishing industry in French Guiana it is a real success, making it possible to protect economic activity and the environment at the same time. Now it is up to consumers to do their bit by making a wise choice about the sea produce they consume.

There are also other fishing sectors which would like to obtain eco-labels. The Atlantic seabob (Xiphopenaeus kroyeri) trawling industry, based in Guyana and Surinam, is making waves. However, it is accused of being responsible for the drop in recruitment for other fishing sectors in these countries. People working in the shrimp and coastal fishing industry in Surinam state that they have seen a drop in catches of penaeid* shrimp and coastal fish since 1996, the year when the government in Surinam removed regulation forbidding trawling in waters of less than 27 metres depth. The Atlantic seabob is fished on the coastal strip, even though in French Guiana IFREMER has shown that this zone is the nursery ground for many marine species and consequently needs to be protected from trawling so as to maintain fish stocks. IFREMER also argues that the biological cycle of the Atlantic seabob is more or less identical to that of the Southern brown shrimp (Penaeus subtilis), with differences in the maximum and average size of adults, which tend to be smaller, and in the location of adults which tend to be nearer the coast than Atlantic seabobs do. This means that fishing for Atlantic seabob, with a recorded catch of 9,000 tonnes in 2009, could be responsible for catching large numbers of juvenile Southern brown shrimp, the predominant species in French Guiana, which could partly explain why it is becoming rarer.

The Atlantic seabob, which is also found in French Guiana, is not fished but is sometimes found in bycatch from fishing for the Southern brown shrimp. In Guyana there have been over 100 trawlers fishing the Atlantic seabob for over twenty-five years now. In Surinam a fleet of 25 trawlers has been active since 1996, the year when Penaeus shrimp and coastal fish stocks started to drop, as people in the fishing industry have observed. French Guiana is suffering from the collateral effects of this coastal trawling, with fishermen from Guyana sailing for over four days to fish illegally in our waters, looking for species which have become rare in their regions such as the acoupa weakfish. That is why the CRPMEM in French Guiana and IFREMER regularly share information and data in regional meetings organised by the WWF so as to influence those involved in the fishing industry of these countries. Once again, it is up to the consumer to find out about the origin of sea produce so that the efforts carried out by the fisheries to reduce their environmental impact are not overshadowed by “more profitable” ways of fishing.