A seminar to be held in Dublin later this month is a bold bid to co-ordinate a response to the decline in salmon numbers at sea, writes Dick Ahlstrom.
Where do salmon go when they swim out of our rivers and into the open ocean? More importantly, why are more and more of them dying there, and as a result causing a decline in overall stocks?
An international body headed by an Irish scientist hopes to answer this and other questions about the ongoing fall in salmon stocks. Dr Ken Whelan of the Marine Institute has invited some of the world's leading experts in salmon studies to a scientific meeting in Dublin next week at which a research response to the problem will be hammered out.
"It really is a kind of crunch meeting," says Whelan, director of the Institute's Aquaculture and Catchment Management Services Team. He is also president of NASCO, the North Atlantic Salmon Conservation Organisation which has a sister organisation, the International Atlantic Salmon Research Board.
"The meeting in October is to bring together the main salmon scientists from all participating countries in NASCO," says Whelan. Members include Canada, Denmark, Iceland, Norway, the Russian Federation, the US and the EU, and delegates hope to produce a plan of action under a project known as SALSEA.
It is an attempt to pool intellectual and scientific resources in a determined effort to locate the major causes of marine mortality of the Atlantic salmon, he explains. It will seek to answer questions about how salmon use the ocean, where they go, and how they make use of currents and food resources.
"The object, and it is a highly ambitious one, is to do this research collectively rather than individually," he says. Finding agreement will be no simple matter given the competing politics and economics between NASCO members.
The reasons for cooperation are clear, however. The latest research shows that survival rates of young salmon at sea have dropped by about a third, greatly reducing the numbers that return to spawn in their "home" rivers. This decline has huge implications both for commercial fisheries and angling-related tourism interests, says Whelan.
"The problem has to do with marine survival," he explains. "We are going to try and gather data about the actual extent of the problem. Next we have to look at where the mortality might be taking place," whether along coastal margins or in deeper water.
There are two types of Atlantic salmon, referred to as "large" - a fish that remains at sea two years - and "small", one that stays at sea maturing for one year. Stocks are also divided between northern and southern, with the latter occurring in Irish and UK waters and points south. It is the southern stocks that have experienced the heaviest decline in numbers.
The large southern salmon has been in decline for at least 20 years and the numbers of small southern salmon have also been falling since at least the early 1990s, says Whelan. Recent US research suggests that climate change is hurting the larger fish, with water temperature changes reducing the availability of "fodder fish" for the salmon.
Researchers are in a quandary over what is happening to the southern small salmon, he adds. "With the smaller fish, we don't really know at this stage."
Tagging technology should help to begin answering some of the questions, Whelan believes. "Data storage tags" have been developed that can capture hourly measurements of water temperature and depth where the fish are swimming over an entire year. The tags can then be collected when the fish come back to shore and enter their home rivers.
Researchers are also working on next-generation tags that can measure light intensity and the direction the light is reaching the tag, information that can give location to a distance within 60 to 70 kilometres. The latest device is known as a "pit tag" and features a passive transponder that will transmit recorded information as a fish swims past a receiver, says Whelan.
As scientists await the refinement of these devices, the Norwegians have done much to identify where Irish salmon go when they leave home. The fish travel half way up the Norwegian coast, riding strong sea currents on Norway's western seaboard.
"We think they hitch a ride on these massive currents and then swim back to stay for several months around the Faroes," Whelan says.