The North Sea needs to be managed as a complete ecosystem if fish stocks and fishing livelihoods are to be maintained for the future.
Urgent action is needed for fish stocks to recover, experts say
So say social scientists and marine experts who carried out a three-year study of fishing practices in the area.
After interviewing fishermen, nature conservationists and NGOs, they have drawn up a Fisheries Ecosystem Plan which they unveiled at the recent International Council for the Exploration of the Sea (Ices) conference in Aberdeen.
Once the European Commission-funded plan is refined, the authors hope to present it to politicians with the ultimate aim of seeing it incorporated into marine management policy.
"Traditionally, species have been managed in isolation on a stock-by-stock basis; so first you'd look at cod, then haddock, then whiting," explains Chris Frid, professor of marine biology at the University of Liverpool, UK.
"In the last 20 years, there's been a certain amount of recognition that what you do to cod affects what happens to whiting because they eat each other; but there's been no recognition that cod and haddock are eating other things in the sea or that the temperature of the sea and the year-to-year variation in climate can affect the survival rates of eggs and how fast fish grow.
"So, there's been no integration of these wider affects into fisheries management," he told the BBC News website.
Professor Frid, along with colleagues at the University of Newcastle (where Frid was professor of marine ecology at the time of the research), and associates at a number of international institutes, used the information gathered in interviews to work out which issues were most important and to understand what the fishing sector felt about current management methods and potential future alternatives.
"Essentially, human activity is the only thing we can actually manage, so we've tried to put together a suite of tools to manage human impacts that will deliver sustainability," explains Professor Frid.
"In other words, a healthy sea that supports a catch capable of sustaining a fishing community."
Cod are in trouble, but some fish are thriving
With overfishing putting increasing pressure on North Sea stocks, some scientists have suggested the only solution is to enforce vast no-take areas.
In his presentation at the Ices meeting, Ronald Fricke, of the Staatliches Museum für Naturkunde in Stuttgart, Germany, called for a third of the North Sea to be declared a Marine Protected Area, with the remaining two-thirds being exploited on alternate years.
However, Professor Frid feels that while this action may help nourish fish stocks back to health, it would be to the detriment of fishing communities.
While protected areas would potentially become relatively healthy, those where fishing was allowed would be rapidly degraded as concentrations of fishers tried to extract sufficient fish to keep their livelihoods going.
Instead, of large no-take zones, the Fisheries Ecosystem Plan proposes a network of small no-take zones designed to protect specific habitats, such as locations containing vulnerable sponges which are important at trapping organic matter and supplying nutrients to the ocean.
At the same time, the amount of fishing would be limited by means such as restricting the number of boats, or limiting the amount of fish that any one boat can catch.
Finally, there would be technical measures such as replacing particularly destructive fishing equipment, such as drag nets with line fishing.
Any plans designed to manage the North Sea ecosystem in the future will also have to consider the likely effects of global climate change on the marine environment.
Ken Drinkwater, senior research scientist at the Institute of Marine Research in Bergen, Norway, studied the likely impact of climatic changes over the next 100 years on cod stocks in the North Atlantic, and concluded that cod generally inhabit areas with bottom temperatures of 12C or less.
A rise of two degrees in seawater temperature would mean that cod populations might not exist at all in the southern North Sea.
"If the pressure from fishing stays high, fish populations are going to be more susceptible to collapse by climate change," he says. "There's an interplay between the environment and climate."
Professor Frid concurs: "As climate changes, we will have to take account of it in setting the levels of sustainable fish catch.
"If cod retreats northwards, the amount of cod you can take from the southern North Sea that's sustainable will go down.
"But you might be able to catch more sea bass and red mullet than in the past, as they appear to be increasing. The environment is forever fluctuating and we are, perhaps, accelerating that process.
"However, we're fortunate that we now have a better understanding of the system and therefore the potential to cope better with those changes than 100 years ago."