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Optimism on overfishing
Volume 30/Number lO/October 1995
other sources. Russia itself is increasing exports to other parts of the world as 20 Russian companies vie for a share of the licenses. In 1990, only two state-owned companies exported in the area from three ports: Restock in Germany, Ventspil in Latvia, and Klaipeda in Lithuania. The WWF report warns that with the many new oil terminals already in operation and more being built, environmental regulations are being broken and ignored at considerable risk to the environment. Some of the ships used for carrying the oil are not built for that purpose, which again increases the risk to the marine environment. Tramp ships, combination carriers and river vessels used for carriage are ill equipped and often substandard. The area is very vulnerable as many of the voyages are short and in areas of high navigational risk. PHILIPPA AMBROSE
Tests on Cleaner Fuels Methanol and hydrogen could become acceptable alternative fuels for marine installations, according to a report at the CIMAC congress. Both the Japanese company Mitsubishi Heavy Industries and the German company Dieselmotorenwerk Restock (DMR) have been involved in testing these fuels in appropriate engines. The Mitsubishi tests involved methanol burning in 450 mm bore, 1400 mm stroke, low-speed engines. They had two pre-chambers, which contained glow-plugs and a main chamber where the main combustion occurred. With NO, levels at less than one quarter of marine diesel engine emissions and water content and ferritic density down to one third, the tests were promising. Mitsubishi plans to extend its test to include the ignition qualities, performance and reliability of methanol. DMR have been working with hydrogen using large diesel engines which they consider to be highly suitable for this fuel as they can burn this currently expensive fuel economically. A draft design has been put forward for a fuel supply system for a 42 MW plant which would be able to power a tanker carrying hydrogen. As insulated fuel tanks for liquid hydrogen would have to be five times as large as conventional fuel tanks, this research is only currently applicable to hydrogen-carrying tankers.
saltier, warmer water appears to have originated in the Aegean Sea. Normally deep water from the Adriatic Sea supplies the input into the eastern Mediterranean Sea, but it has been replaced with Aegean water and hence the current reversed. Increased salinity at the surface of the Aegean has caused this change and increased evaporation or a reduction in fresh water inputs may be the underlying cause.
Optimism on Overfishing According to a report in Science, a recent study has indicated that severely overfished stocks are likely to recover if given a chance and if fishing pressure is reduced. This may appear to be an oversimplified and obvious statement but many fisheries scientists have for years been concerned that once a particular fish’s numbers fall below a certain threshold it may not be able to reproduce efficiently or may succumb disproportionately to predators. This phenomenon, called depensation, has been reported in studies of population dynamics in other species including insects and whales. The recent study analysed statistics gathered over 15 years on a wide range of commercially fished stocks. In particular, the ratio of recruits to the total number of fish in a stock reflects a population’s success at reproduction and survival. A drop in the ratio at low population numbers indicates depensation is occurring. Although, in the study, depensation could not be ruled out in several fish populations, the majority of stocks studied did not exhibit depensation. This finding provides some optimistic news to fisheries managers, giving them a more powerful case to argue that fish stocks collapse because of plain, simple overfishing and there is little evidence that fish stocks will not recover once fishing has stopped. However, the same scientists are cautioning that this argument should not be taken as justifying the fishing of stocks until they are almost completely gone simply because they will recover in time anyway. Other scientists are not convinced and believe that in some stocks factors similar to depensation may be occurring, but which cannot be detected using the parameters measured in the present study. Despite the theoretical arguments the basic and obvious message coming through remains the same for severely depleted fish stocks-reduce fishing mortality drastically. HAMISH MAIR
Mediterranean Current Reversal Causing Concern The reversal or flip of a Mediterranean deep water current is causing considerable concern, according to a report in the New Scientist. Wolfgang Roelher and his colleagues from the University of Bremen discovered inversions of the salinity and temperature gradients in deep water. A rise of 0.3”C and an increase of 0.2% salinity can now be found between 1200 m and 3000 m in the eastern section of the Mediterranean Sea. This
New Proposals on Crayfish Farming Controversial proposals to relieve the pressure from imported crayfish on native crayfish in English rivers were recently put forward by the UK Joint Nature Conservation Committee (JNCC) and the University of Nottingham. In British waters the proposals may have 629
other sources. Russia itself is increasing exports to other parts of the world as 20 Russian companies vie for a share of the licenses. In 1990, only two state-owned companies exported in the area from three ports: Restock in Germany, Ventspil in Latvia, and Klaipeda in Lithuania. The WWF report warns that with the many new oil terminals already in operation and more being built, environmental regulations are being broken and ignored at considerable risk to the environment. Some of the ships used for carrying the oil are not built for that purpose, which again increases the risk to the marine environment. Tramp ships, combination carriers and river vessels used for carriage are ill equipped and often substandard. The area is very vulnerable as many of the voyages are short and in areas of high navigational risk. PHILIPPA AMBROSE
Tests on Cleaner Fuels Methanol and hydrogen could become acceptable alternative fuels for marine installations, according to a report at the CIMAC congress. Both the Japanese company Mitsubishi Heavy Industries and the German company Dieselmotorenwerk Restock (DMR) have been involved in testing these fuels in appropriate engines. The Mitsubishi tests involved methanol burning in 450 mm bore, 1400 mm stroke, low-speed engines. They had two pre-chambers, which contained glow-plugs and a main chamber where the main combustion occurred. With NO, levels at less than one quarter of marine diesel engine emissions and water content and ferritic density down to one third, the tests were promising. Mitsubishi plans to extend its test to include the ignition qualities, performance and reliability of methanol. DMR have been working with hydrogen using large diesel engines which they consider to be highly suitable for this fuel as they can burn this currently expensive fuel economically. A draft design has been put forward for a fuel supply system for a 42 MW plant which would be able to power a tanker carrying hydrogen. As insulated fuel tanks for liquid hydrogen would have to be five times as large as conventional fuel tanks, this research is only currently applicable to hydrogen-carrying tankers.
saltier, warmer water appears to have originated in the Aegean Sea. Normally deep water from the Adriatic Sea supplies the input into the eastern Mediterranean Sea, but it has been replaced with Aegean water and hence the current reversed. Increased salinity at the surface of the Aegean has caused this change and increased evaporation or a reduction in fresh water inputs may be the underlying cause.
Optimism on Overfishing According to a report in Science, a recent study has indicated that severely overfished stocks are likely to recover if given a chance and if fishing pressure is reduced. This may appear to be an oversimplified and obvious statement but many fisheries scientists have for years been concerned that once a particular fish’s numbers fall below a certain threshold it may not be able to reproduce efficiently or may succumb disproportionately to predators. This phenomenon, called depensation, has been reported in studies of population dynamics in other species including insects and whales. The recent study analysed statistics gathered over 15 years on a wide range of commercially fished stocks. In particular, the ratio of recruits to the total number of fish in a stock reflects a population’s success at reproduction and survival. A drop in the ratio at low population numbers indicates depensation is occurring. Although, in the study, depensation could not be ruled out in several fish populations, the majority of stocks studied did not exhibit depensation. This finding provides some optimistic news to fisheries managers, giving them a more powerful case to argue that fish stocks collapse because of plain, simple overfishing and there is little evidence that fish stocks will not recover once fishing has stopped. However, the same scientists are cautioning that this argument should not be taken as justifying the fishing of stocks until they are almost completely gone simply because they will recover in time anyway. Other scientists are not convinced and believe that in some stocks factors similar to depensation may be occurring, but which cannot be detected using the parameters measured in the present study. Despite the theoretical arguments the basic and obvious message coming through remains the same for severely depleted fish stocks-reduce fishing mortality drastically. HAMISH MAIR
Mediterranean Current Reversal Causing Concern The reversal or flip of a Mediterranean deep water current is causing considerable concern, according to a report in the New Scientist. Wolfgang Roelher and his colleagues from the University of Bremen discovered inversions of the salinity and temperature gradients in deep water. A rise of 0.3”C and an increase of 0.2% salinity can now be found between 1200 m and 3000 m in the eastern section of the Mediterranean Sea. This
New Proposals on Crayfish Farming Controversial proposals to relieve the pressure from imported crayfish on native crayfish in English rivers were recently put forward by the UK Joint Nature Conservation Committee (JNCC) and the University of Nottingham. In British waters the proposals may have 629