Irish Marine Life
inshore offshore play science coral-reefs crabs ag snámh news think imeachtaíArchive for March, 2010
Will Clew Bay bloom this Spring?
The south shore of Clew Bay might have been tropical, driving west on the first weekend in March, if one didn’t look up to the left and the cold white capped reek. To the right, the underwater reefs and the sand filled spaces between them were shimmering beneath a translucent green sea, remarkably clear and suggesting a temperature far greater than its actual 9 or 10 degrees.
An extraordinary three month episode of east winds and hushed seas meant the water column, usually so clouded with sediment and nutrients stirred up from below by the hefty swells of winter, was settled and clear. Divers across the fjord at ScubaDiveWest in the Little Killary were describing unusually sharp visibility in the month where one’s hand often murkily disappears at arms length underwater.
In the strict calendar of marine ecosystems, where everything has a function, such nutrients are hungrily awaited. The Spring phytoplankton bloom is this months big event; an event where the tiniest of marine organisms hint at their importance in an explosion of life.
Phytoplankton (microscopic algae) need light to grow and when daylight levels reach a critical point at the end of March and beginning of April, the abundance of nutrients in the water causes the sudden and out of control growth in their population resulting in a discolouring bloom stretching over hundreds or thousands of square kilometres in places.
Though tiny, phytoplankton’s contribution to the planet is not insignificant; it is know believed they contribute as much, if not more, oxygen to the earth as the rainforests do and soak up carbon dioxide equally industriously.
The Spring Bloom is all over in a few weeks as growth is so wild and uninhibited that the nutrient supply is rapidly used up. But what happens when the daylight hours come and nutrients still sit unroused on the sea floor? Such a run of inactivity as we have had is almost unprecedented so it’s hard to say, but swell is promised for next week; the water column will likely become replenished in time.
Blooms which occur from time to time in nutrient loaded estuaries, and can be dangerous to shellfish, are sometimes obvious to coastal observers; the Spring bloom however usually comes and goes unnoticed. Occurring offshore and covering large expanses of surface ocean it is best appreciated from above. Satellite images of Ireland are a good place to view it, or maybe if one timed it right, the top of Croagh Patrick.
This article appeared in the March 30th edition of The Mayo News
Ranching The Salmon of Knowledge
The first salmon of the 2010 season was caught on The River Moy on the last weekend in February and in the Delphi valley in the other corner of the county the day before. Almost 30% of Ireland’s total salmon catch is taken in the Mayo / West Sligo region and aptly enough, the region creates most of the quality, up to date knowledge on salmon, not just for Ireland, but for the entire North Atlantic.
Midway between these two locations, The Burrishoole fishery at Lough Furnace outside Newport has been quietly establishing itself as an internationally recognised salmon research centre since the 1950s, also becoming the world’s longest running salmon trapping facility.
The scale of research they have undertaken in that time is impressive including salmon genetics, stock enhancement with salmonoids and climate change studies.
One of the activities which Burrishoole pioneered is a most terrestrial sounding pursuit; salmon ranching. Ranching is the rearing of smolts (salmon ready for salt water) which are derived from grilse (salmon which return after one year at sea). A fish farm must provide all the food necessary in a fish’s life cycle; however ranching entails the fish living where and how nature intended once released.
Ranching, as it protects the juvenile salmon until the smolt stage produces much more fish than the river otherwise would. When the mature fish return to the river of spawning, as many as possible are caught and the eggs and milt (male gamete) harvested to spawn the next generation in the ranch’s line. Experiments on the Delphi fishery have shown good returns, matching or outdoing the native stocks’ returns from the Atlantic.
Micro-tagging and tag retrieval initiatives directed by the Marine Institute mean that Burrishoole does not just have a healthy stocky, they have a useful informative ‘herd’ of ranched fish. Data from the fish are used by the International Council for the Exploration of the Seas to determine the state of Irish stocks and according to the Irish Marine Institute, the Burishoole fishery system is one of the key index systems for salmon in the North Atlantic. This and other recent research utilising Burishoole salmon as indicators of global climate change means Mayo’s salmon are doing quite well in living up to their Salmon of Knowledge legend.
This article appeared in The Mayo News edition 16/3/2010
Lutra lutra
The sea is cold and quiet these weeks; a freshening visit to the shore seems for many unnecessary with endless icy weather streams from the North. Marine life is consulted and found through other means in spells such as these. One such mammal which is represented in more than its fair share of poetry and literature is the otter whose scientific name is the musical Lutra lutra and occasionaly better known in the West as the not very wild sounding water-dog. West Mayo’s sometimes resident Michael Longley highlighted some of its ecology to conclude a poem about mortality when he wrote:
I watched a dying otter gaze right through me
At the islands in Clew Bay, as thought it were only
Between hovers and not too far from the holt.
The holt being its home constructed in the river bank and a hover a resting place for passing a part of the day. Lutra lutra is one of our most intriguing marine animals perhaps because it is not marine at all. It has a cousin which is restricted to the sea, the Californianotter, but Ireland’s otter is as terrestrial as we are. Its forays to the shore are a consequence of living beside the tide and if it is born to an inland holt it will only know the bog runs and freshwater streams of that area. Its diet is also as varied as ours and will switch from fish to shellfish and urchins if availability is low which increasingly happens due to coastal pollution. A study of otter spraints (droppings) in Clare Island in 2007 by a student of NUIG’s department of Zoology suggested seaweed may even be a part of diet at times.
Their mystery and strong lore may also stem from their impressive elusiveness. I can count with two sightings: one jumping in the kelp on a sheltered shore; another running bravely along an exposed beach and ultimately into the small waves where it faced us and mocked my curious dog.
If the halting northeasterlies turn back to the southwest quarter and the shore is welcoming again, look for the otter in areas where freshwater comes close to the sea. The otter needs to rinse the salt from its dense fur after a fishing session to maintain the fur’s insulation property, so the low duachs west of Louisburgh or townlands beginning with Barna- (Barna means passage to the sea as Gaeilge) are good places to catch one returning from the tide at sunset.
irishmarinelife
lenny antonelli
