Search
deutsch
2 The Future of Fish – The Fisheries of the Future

Fish habitats

Page:

The environment also influences stocks

Fluctuations in the size of fish stocks are not only caused by fisheries. Changes in environmental conditions also affect the stocks. For example, in cold, salty water the Baltic Sea cod produce more offspring than in warmer water with a lower salinity. On the other hand, the animals reach sexual maturity later in colder water. But water temperatures and other environmental parameters fluctuate over time in many marine regions. These are often triggered by natural climate cycles that produce regular changes in winds or ocean currents. One example is the North Atlantic Oscillation (NAO), which influences the climate over parts of Europe and North America. The NAO is a fluctuation of the atmospheric pressure difference over the North Atlantic between the Azores high and the Icelandic low. Among its influences, the NAO affects the winter weather in Europe, and fluctuates with a 10-year rhythm. The wind and near-surface ocean currents in the North Atlantic also fluctuate with the atmospheric pressure.

Extra Info North Sea water for cod offspring

In contrast, the El Niño climate phenomenon operates in the Pacific. It alters the current direction in upwelling regions, in this case between the west coast of South America and Indonesia. The large upwelling region off the coast of Chile and Peru is part of a powerful ocean current called the Humboldt Current. This brings cold water from the Antarctic northward along the west coast of South America. Here, like off southwest Africa, nutrient-rich, cold water rises to the surface. The engine for this upwelling is provided by the prevailing trade winds that push the warm surface water from South America westward towards Australia and Indonesia. South American waters are among the world’s richest in fish. Around 15 to 19 per cent of the world’s catch comes from here, especially small species like sardines and anchovies. The larger horse mackerel, as well as wide-ranging species such as sharks and tuna, are also found here. But in the years of the El Niño, the westward-blowing trade winds decline and may even reverse direction. This also changes the current direction of the water. Warm, nutrient-poor surface water now flows from the western Pacific towards Peru. These conditions inhibit the production of plankton off the coast of Peru. Food for the planktivorous fish thus becomes scarce, and the stocks collapse. The larger predatory fish and birds, including penguins, are affected, but also mammals such as seals, which rely on the fish as their main food source. In El Niño years they often produce fewer offspring.
Vital conditions for fish thus change more or less regularly. This can affect both the size of the stocks as well as their geographic extent. The cod population in the eastern Baltic Sea is highly dependent on incursions of salt water from the North Sea. These massive inflows of water occur only every few years under certain weather conditions. They have to be strong enough to override the Darss Sill, a kind of shallows off the coast of Mecklenburg-Western Pomerania. Under normal conditions the heavy salty North Sea water cannot pass over this sill. But during the massive salt-water incursions, enormous amounts of North Sea water flow over the sill and along the bottom of the Baltic Sea as far as Gdansk Bay, and even farther into the Gotland Basin between Latvia and Sweden. This salt-water influx is important because along with the cold saline water it also brings oxygen into the depths where cod spawn. If the salt-water influx does not occur for a long time the spawning conditions deteriorate. Furthermore, it is now known that long-term climate fluctuations impact cod stocks in the eastern Atlantic, the North Sea, and the Baltic Sea. In the 1980s the stocks of gadoids, the cod-like fish, increased greatly in these regions. The environmental conditions that led to this “gadoid outburst” are still not known. There are a number of hypotheses. It may be that the cold winters of the 1960s and 1970s afforded ideal spawning conditions. In subsequent years the stocks decreased again, presumably not only due to fishing. It is generally true that when a population collapses it is usually associated with a combination of high fishery pressure and changes in environmental conditions.

Extra Info One species – multiple stocks

More data for stock assessment

In order to determine the impact that fisheries have on different ocean regions or to assess the status of a fish species – for example, whether it is overfished or not – many more details are necessary beyond the usual information about the annual catch statistics for a species. One factor of interest is how the stocks of other fish species in the same region develop, rather than focusing only on the species being fished. Special consideration should be given to the bycatch. This refers to the fish and other marine animals that are unintentionally caught along with the species of commercial interest such as cod or coalfish that are being fished for. As a rule, the bycatch is thrown back. Because bycatch amounts have not been systematically recorded in the past, an important parameter is missing that would help to assess the population development of several species, as well as the status of the marine region. Fortunately, there are a number of regions today where discarding the bycatch is not allowed. The Euro-pean Union also wants to make throwback illegal. This would make it possible in the future for fisheries to provide valuable data to scientists that would otherwise only be obtainable through expensive research cruises. There is continuing controversy among various specialists, not only about the status of individual species, but also about how the stocks of certain fish species can be best estimated. In any case, obtaining additional data would help a great deal. In this regard, it would also be important to gather data on the primary producers, the algae and other single-celled organisms, whose quantities and composition substantially contribute to the biomass in the marine region. Such a multiple indicator approach, which considers all of these parameters, could be very important in establishing future catch limits. This kind of comprehensive data set is presently only available for a few fish species, because obtaining the data for all of these parameters is extremely expensive. Furthermore, it requires an intensive exchange of information among scientists of various disciplines, including fishery biologists, oceanographers, and plankton specialists, which has so far only been accomplished for a few stocks such as the Baltic Sea cod and the West Atlantic cod.
1.7 > Clupeids frequently form dense shoals, such as here off the Moluccas. They are an important food source for many marine organisms and very important for the ecosystem.
1.7 > Clupeids frequently form dense shoals, such as here off the Moluccas. They are an important food source for many marine organisms and very important for the ecosystem. © Jason Isley – Scubazoo/Science Faction/Getty Images

Extra Info What does overfishing mean?

Large Marine Ecosystems

Most marine regions and habitats are so large that they extend across the coastal waters of multiple countries. Comprehensive conservation in these areas is only possible if the countries cooperate, for example, with regard to pollution of the ocean. Even larger fish stocks can only be sustained when the countries agree to joint policies of protective fishery management. For a long time, these kinds of international agreements regarding coastal regions had been lacking. For this reason the National Oceanic and Atmospheric Administration of the USA (NOAA) devel-oped the concept of Large Marine Ecosystems (LMEs) in the 1990s. This divided the coastal marine regions of the Earth into 64 LMEs. Each LME is characterized by a typical flora and fauna. The LMEs extend along the coasts out to the continental slope, where the continental shelf ends and starts its downward incline towards the deep sea. The characterization of certain marine regions by large currents is also considered. For example, the upwelling regions off South America and Southwest Africa are each defined as an LME. The LMEs comprise all of the coastal regions of the Earth. They are especially productive because they are well provided with nutrients from rivers or upwelling currents. The LMEs produce 95 per cent of the global fish biomass. These areas are also immensely important for humans. Hundreds of millions of people worldwide live near the coasts. Their existence depends more or less directly on fishing. Thus, in addition to the biological factors, the Large Marine Ecosystem concept also deals with socioeconomic aspects.
1.9 > The objective of the Large Marine Ecosystem concept is sustainable management of the oceans. Under this approach the status of marine regions is characterized in five different modules.
Fig. 1.9 > The objective of the Large Marine Ecosystem concept is sustainable management of the oceans. Under this approach the status of marine regions is characterized in five different modules. © after www.lme.noaa.gov
With the support of the World Bank and the United Nations Environment Programme (UNEP), an effort is being made to improve international cooperation towards protecting the joint ocean regions, particularly in the developing and newly industrialized countries. Researchers and politicians of the neighbouring countries meet at workshops and conferences. The major challenge is to achieve better protection of the marine environment in spite of differences in interests. Economic aspects such as offshore oil production often have priority over protection of the environment. The concept of the LMEs should provide a counterbalance and create an awareness of the importance of the marine habitat. Political crises and civil wars, however, like that in the Ivory Coast have continued to undermine cooperation in recent years. One focus of the work is to educate qualified people locally. Together with international experts, native scientists are trained to record and competently analyse the stocks of fish, primary producers, and other marine organisms according to current standards. However, in the past many countries have lacked both the funds and sufficient specialists to carry out sustainable fishery management within their territorial waters. Technical knowledge is thus a critical prerequisite for future fishery conservation efforts

Extra Info Near-coastal ocean regions

Promising examples are illustrated by the two West African LMEs, the Benguela Current LME and the Guinea Current LME. Numerous courses, workshops and conferences have been held in the countries concerned. One of the present goals is to find indicators for the various LMEs whereby the status of the marine regions can be assessed and described. A sustainable management of the seas should ultimately be achieved. Five working areas, referred to as modules, have been established for this purpose.
PRODUCTIVITY OF THE HABITAT: Record biodiversity of the phytoplankton and zooplankton and their biomasses, measure the photosynthetic activity, etc.
POLLUTION AND ECOSYSTEM HEALTH: Investigate the influences of biotoxins, eutrophication of the water, and the development of pathological changes in the marine organisms, etc.
FISH AND FISHERIES: Investigate the biodiversity and biology of finfish and shellfish, identify fish stocks and changes in their composition.
SOCIOECONOMY: Investigate the practical application of scientific findings for management of the ecosystems, assess diverse management methods based on economic and other criteria regarding the principle of sustainability.
GOVERNANCE: Consider ways in which various interest groups in the areas of fisheries, tourism, energy and environment can participate in the development of inter-regional management planning, etc.
he Large Marine Ecosystems programme has produced a series of studies in which scientists have investigated the development of the LMEs over recent decades. These have clearly illustrated the severe impact that fisheries can have on habitats, but in many cases it is still not clear to what extent natural processes have influenced the devel-opment of fish stocks. In some years, large oxygen-deficient zones form in the Benguela Current. In these years the stocks of pelagic fish collapse, causing a shortage of food for many species of seabirds and seals. This results in a decline in the survival rates of their young. Of course the upwelling areas generally exhibit low concentrations of oxygen at greater depths. But it is not yet known why the oxygen-poor areas sometimes extend nearly up to the surface. There is some evidence that the oxygen deficiency occurs after periods of especially intense upwelling currents. This suggests an initial development of large amounts of phytoplankton that later die in large volumes and are subsequently broken down by bacteria. In some cases it appears that a change in current conditions causes expansion of the oxygen-poor areas. This example illustrates again the importance of understanding the entire ecosystem in assessing the development of populations of marine organisms and ultimately also the fish stocks.
The concept of the Large Marine Ecosystems is important and necessary. But so far there is little indication that information gained from the international LME projects and activities have led to concrete political directives or national laws. Experts stress the need for action in the future. They agree, however, that LME activities are likely to lead to a greater awareness of marine protection and conservation of fish stocks for the future than has been the case up to now, even in developing and newly industrialized countries. Textende
Page: