08/06/2025
It was not whales and dolphins that drew me to the south west of Ireland over 50 years ago, but it's fantastic fish stocks.
I spent the best part of my life at sea as a fisherman before I took up whale watching. I did not go trawling like every other vessel at the pier but set about passive, sustainable fishing techniques like potting and netting and longlining, with no damage to the seabed and no bycatch of immature or unwanted fish.
The seas to the south and west of Ireland for all of recorded history were amongst the richest ever known fishing grounds in the north east Atlantic. The reason for this is the spectacular topography of the Porcupine Basin, where the deep abyssal plain of the Atlantic meets the European continental plate and it's shelf waters. The prevailing North Atlantic current flows unimpeded into the Porcupine basin, which is perfectly shaped to bring the cold, nutrient rich waters from the deepest part of the Atlantic up to the surface, about 100 kilometres to the south west of Ireland. The rich supply of nutrients in the warm, sunlit surface waters triggers an explosive growth of phytoplankton in vast quantities, usually referred to as a plankton bloom. These blooms are so intense they are visible from space and sometimes cover an area half the size of Ireland itself. All this phytoplankton is then a rich source of food for zooplankton which becomes super abundant with so much food in the water. All around the world's oceans, anywhere there is abundant sea life, it's the same scenario, and the start of the ocean food chain.
All this zooplankton doesn't go unnoticed and is taken up by forage fish species like herring, sandeels and sprats, that have evolved over millions of years to feed on this great abundance.
With forage fish in their billions, hoovering up all this food, you now have an ocean suitable to sustain predatory fish species in their millions as well as marine mammals and birds, all taking advantage of this supply of small edible fish species, an ocean teeming in marine life.
Sadly, the seas off Cork and Kerry are no longer teeming in life. The plankton blooms are still there, as rich as ever, but the forage fish are now seriously depleted by the fishing efforts of large pelagic trawlers. Pair trawling with huge nets, packed with fish detecting electronics, no shoal goes unnoticed, vessels of this type are a serious threat to fish stocks all around the world.
The most important forage fish by far in the coastal waters of Ireland is the humble sprat. There was no great demand for them in years gone by, so there was never a commercial fishery aimed at them. As a result they abounded in their billions all around the Irish coastline, making rich fishing grounds until about 30 years ago when they became of commercial interest, mainly as a cheap source of protein for animal feeds and notably fish farm pellets.
The stocks of these little silvery fish have been decimated by Irish pair trawlers over the last few decades. No longer in billions, along the south coast the shoals are dangerously depleted and close to extinction, on the west coast not far behind.. Inshore trawling grounds are now lifeless and barren as a result, mackerel that once teemed around the coast are gone, the staple diet of mackerel is larval sprats. Almost every species of fish exploited by the fishing industry feeds on sprats throughout their lives, larval or adult, they are an absolutely vital part of a healthy ocean. The message here for all fishermen is STOP FISHING SPRATS.
Salmon were known as the king of fishes, herrings as silver darlings, sprats should be addressed as silver miracles in the same vein. Millions of years of evolving in the upper layer of the oceans, evading their many predators, has made them into a sophisticated forage fish species. They are more silvery than salmon, herrings or any other fish in Irish waters, they are silvered like the mirrors we all use every day, to mirror the seawater around them and each other to confuse the many predators trying to catch them, even their flanks are flattened to maximize this effect. The scales on their dorsal surface reflect green light to perfectly match the green colour of seawater full of plankton. They are able to shed their scales at will to slip out of the grip of a predator. They believe in safety in numbers and crowd together in tight shoals when under attack, swimming in unison like murmarating starlings to confuse predators. Most plankton feeders have adaptations to filter their food from the sea, but not sprats. They take in their selected prey visually in tiny snatching movements, almost stationary when doing so. Their diminutive size makes them available to all predators like puffins, razorbills, guillemots, shearwaters, kittiwakes and smaller fish species that cannot manage to swallow a herring or mackerel.
To sustain their numbers under so much predation they are prolific egg producers and a full mature female will shed up to 20,000 eggs at spawning time in the Autumn or early winter. Of all the fish species I have ever caught and examined they are far and away the most fragile and delicate of all. Taken from the water they are dead in less than a minute if they are not returned to the water immediately, and very easily stunned or shocked. I think this a mechanism where some are sacrificed when under attack for the common good of the shoal, to engage a predator picking them off whilst the rest escape to live another day. The waters off West Cork have become a sad story without them. No fish about, no whales about and very few birds about from the thousands that were there up to a few years ago.
Today is World Oceans Day, so to commemorate that we share here a clip of humpbacks enjoying their day and interacting with the Holly Jo exactly 4 years ago. It was our only clip that ever went viral with over 8 million views !
