NATURE Climate change threatens our trout and salmon

Rain, rain and confused fish


Marine Life
John Paul Tiernan

Last winter is recalled in superlative terms – coldest, iciest, most snow, longest freeze and so on. But it opened on a completely different, and wilder, note. Before the halting chill, four impressive low pressure systems charged across the Atlantic in November and lurched over our island unloading unbelievable and unwanted quantities of rain.
And thanks to the work done by marine scientists at the Burrishoole branch of the Irish Marine Institute, we now know that on a local west-of-Ireland scale, there will be more of these ‘50 year’ flooding events; every seven to nine years, or so they estimate in a report published a few weeks ago.
This isn’t a huge surprise in an age where primary kids can explain climate change, but science likes hard facts and because the team at the Burrishoole fishery at Lough Furnace outside Newport have been collecting data, such as rainfall and water temperature, uninterrupted for over 50 years, they can make such scientifically sound assertions.
So what about the fish? Salmon and Brown trout start spawning in gravely areas of freshwater systems in November while Sea trout (which is actually just a same-species variation of the Brown trout that prefers to go to sea) precede them by a few weeks. Higher water temperatures in the latter part of winter, which is also predicted in the latest Burrishoole report, can adversely affect the survival of their eggs and the young fish. And if these cataclysmic flooding events were to come in April instead of November, say, they can wash the young fry away, of which only a small percentage ever survive anyway until the following winter.
If that’s not enough to stress a species, higher temperatures can also ‘confuse’ the salmon, causing some in parts of Ireland to head out to sea in March, thinking that it’s April already. When the salmon leave all together at the same time, as they have evolved to do, it gives most of them a better chance as they run the gauntlet of coastal predators such as seals and gulls. If they leave a few at a time, however, their predators can pick off the confused fish at their leisure.

John Paul Tiernan a marine scientist, runs Irishmarinelife.com, a website dedicated to awareness of our marine life. Hi is also currently teaching in West Mayo.