WOR 2 The Future of Fish – The Fisheries of the Future | 2013

Deep-sea fishing


Exclusive economic zone The Exclusive Economic Zone (EEZ) is also referred to as the 200-nautical-mile zone. Here, coastal states have sovereign rights to the explora-tion and exploitation of living and non-living resources. This includes the exclusive use of fish stocks in one’s own EEZ. Furthermore, within its own EEZ a state may erect offshore drilling rigs or wind farms

Today there are around 300 known black smoker sites worldwide. Most of them are in the Pacific. There are, however, almost no commercially important fish species living in these extreme habitats. It has only been known for a few years that cold seeps in the deep sea are special and important habitats. Cold nutrient-rich water flows out of the sea floor here. During an expedition off the coast of Pakistan in 2007 scientists discovered densely populated cold seeps. There are mussel banks, crabs, snails and sea cucumbers. Although experts had long known about heavily populated cold seeps in the Gulf of Mexico, they were believed to be an exceptional case. Actually, however, cold seeps are found in numerous ocean regions. Off the coast of Pakistan, for example, the Arabian continental plate is being pushed beneath the Eurasian plate. In the process, water contained in the sediments is pressed out. It flows back into the ocean through fissures in the bottom. Substances contained in the water provide nutrition for bacteria and small animals, which in turn become food for higher organisms such as crustaceans.

The fish of the deep sea

In the nutrient-rich and highly productive coastal regions, massive reproduction is typical of many species, and this ensures their survival. Many deep-sea fish species, on the other hand, are characterized by slow growth, late sexual maturity, long life, and the production of fewer offspring. They are adapted to life at great depths, to a habitat in which unchanging environmental conditions prevail. The strong temperature fluctuations that can impact the reproduction of fish in shallow coastal regions are absent here. However, the deep sea is not as rich in nutrients as the coastal waters. The carrying capacity is almost exhausted and competition for food is great. Most species have therefore adapted by producing fewer, but highly competitive offspring. This reproduction strategy is called K-strategy (K refers to the carrying capacity of the environment). There is a high parental investment in the offspring. The eggs of many deep-sea fish are relatively large and rich in nutrients so that the larvae have a good chance of developing well.
3.16 > Many fish species of interest to fisheries occur in the deep water layers. Some do not reach sexual maturity until a relatively late age.
3.16 > Many fish species of interest to fisheries occur in the deep water layers. Some do not reach sexual maturity until a relatively late age. © maribus
One example of this is the deep-sea orange roughy (Hoplostethus atlanticus), which does not reach sexual maturity until the age of around 25 and can live to be 125 years old. The orange roughy lives at seamounts and builds up very large stocks over time. These fish grow slowly and can survive periods of scarce food supply. Furthermore, thanks to the long life expectancy of the individual fish, the stock can compensate for times of low offspring production. Fish species of the K-strategy type are especially threatened by deep-sea fisheries. When the older fish are continuously removed by fishing, at some point there will be too few sexually mature animals remaining to sustain the population. However, not all fish living in the deep sea are K-strategists. The blue whiting (Micromesistius poutassou), for example, occurs on the continental slopes at depths from 100 to 1000 metres. It is, however, a species that produces great numbers of offspring. The reason for this is that the immature fish spend most of their time in the shallow shelf areas in water depths around 100 metres, where there are numerous predators and food competitors. Massive reproduction is therefore the ideal strategy for the blue whiting.

High seas The “high seas” are the areas of the ocean to which all states have free access. No country may claim sovereignty over any part of the high seas. The high seas, where freedom of naviga-tion, research and fishery are interna- tionally recognized, begin at the boundary of the 200-nautical-mile zone. Much of the deep-sea region lies outside the EEZ, and is therefore part of the high seas. All nations have the right to exploit fish stocks there.

Fisheries in the deep sea

Commercial fishing has only been carried out in deep waters over the past few decades. Although longline fishing has been practised since the 18th century, industrial fishing far out in the ocean first became practicable in the 1950s with the availability of seaworthy refrigeration ships. Deep-sea fishing received a boost in the early 1970s with the introduction of the 200-nautical-mile zone, or Exclusive Economic Zone, which made it impossible for foreign ships to fish close to the coasts of another country. The high seas, including the deep sea, were an alternative fishing area. The Soviet Union and Japan in particular were soon specializing in the deep-sea regions. In the beginning the catch amounts were enormous – especially around structures such as seamounts and banks. To the extent that fish stocks were gradually shrinking in the coastal areas, deep-sea fishing became increasingly interesting for other countries as well. According to a survey by the FAO, there were 27 countries conducting deep-sea fishing in the year 2008, with Spain, South Korea, New Zealand and Russia at the forefront. Around 70 per cent of the ships employ trawl nets, and these are often demersal-trawl nets. Today these can be deployed to a depth of 2000 metres.
3.17 > The orange roughy lives at depths down to 1800 metres.
3.17 > The orange roughy lives at depths down to 1800 metres. © Courtesy of JNCC
It soon became obvious that deep-sea fishing is problematic in two respects. For one, valuable habitats such as cold-water corals or the ecosystems at seamounts are destroyed when nets come in contact with the bottom. Secondly, fish species are quickly decimated, particularly the K-strategists. For example, newly discovered stocks of orange roughy were reduced to 15 to 30 per cent of their original size within just 5 to 10 years. In many areas the species was commercially depleted. This “boom and bust” kind of fishery is typical in the pursuit of deep-sea fish species. The reason for this is that species like the orange roughy not only produce a small number of offspring, their reproductive performance is also very erratic and episodic. Several years can pass with low production of offspring before a strong season occurs again. It is still not known what controls or triggers these fluctuations. Investigations at the Great Meteor Seamount west of Madeira have indicated an influence of changes in the winds affecting eddy currents above the seamount. >