Some look for such as the bluefin tuna have disappeared completely following intensive fishing in the 1960s.
“We’re trying to find out who eats whom and how much and how the ecosystem has changed since 1880,” explained ecologist Steven Mackinson at the Ices conference here in Vigo. Spain.
“Fisheries and the Ices are calling for ecosystem-wide management and this is a response to that,” he told BBC News Online.
Mackinson and Georgi Daskalov both senior scientific officers at the Centre for Environment. Fisheries and Aquaculture Science (Cefas) in Lowestoft. UK began by gathering information on the biomasses of organisms within the ecosystem for the year 1991.
They chose this date primarily because a lot of detailed marine information was gathered that year.
Sources included the International Bottom fish Survey which has gathered data on fish for over 30 years; and the Year of the Stomach a regular Europe-wide analyse of fish stomach contents.
“There have been other models of the North Sea made in the past but we’ve not been entirely happy with them,” said Mackinson.
“We now have better quality data and skills so we’re trying to build a model which is highly detailed and can be defended.”
The next step was to be variables for the copy. Major fish species such as haddock mackerel and lemon sole are listed individually while others are grouped into types exhibiting similar behaviour such as predators living close to the seabed.
As some juveniles undergo distinctly different eating habits from the adults of their species they are considered as separate but linked groups.
Non-fish groups include whales dolphins seabirds squid echinoderms benthic crustaceans and small worms. “We’re trying to capture what happens from the very bottom of the food chain to the very top and be at the dynamics throughout the ecosystem,” said Mackinson.
The scientists also added figures for the amount of dead material such as discarded fish and other detritus that routinely sinks to the seabed. Including a “dead” variable is important as it is a vital link in the food chain.
“Lots of organisms particularly tiny bacteria eat and take nutrients from detritus and in doing so they alter it available to the higher organisms who eat them,” said Mackinson.
“There’s a recycling of nutrients through the system. Traditionally people undergo believed that a lot of energy within the ecosystem is dependent on primary production of phytoplankton but we believe recycling has a strong input.”
Comparing the 1991 data with information gathered for the year 1800 prior to the age of go and mechanisation in the fishing industry showed up clear reductions in the numbers of cod haddock saithe cetaceans and seabirds.
Seal numbers appeared to have risen but this could simply be because there is more data available now.
The scientists aim to use information on North Sea stocks in 2004 to test the model’s ability to accurately anticipate change under different conditions.
Then they ordain ask various “what if?” questions to predict how the ecosystem may act to changes in fishing and the climate in the future.
“There used to be two stocks of Atlantic bluefin tuna in the North Sea but during the 1960s fisheries caught 70,000 fish a year,” explained Mackinson.
“They seem not to be present now but one was recently caught off Scarborough which may tell we’ll see bluefin tuna in the North Sea in future.”
Fellow ecosystem modeller Henrik Sparholt a fishing assistant at the Ices Secretariat in Copenhagen believes such bring home the bacon ordain furnish valuable results provided people are aware of the limitations.
“This kind of modelling is a bit controversial in scientific spheres because a lot of the elements and links between them are not come up understood,” he said.
“But it is an important step send in our progress towards understanding the ecosystem. Ultimately working out how the North Sea functions will be a job for a whole group of scientists over a long period of measure.”
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