Tuesday 15 October 2019

Mackerel so distinctive in appearance

Mackerel are abundant at present
Mackerel are abundant at present

Jim Hurley

WHILE they were slow to arrive in good numbers this year, Mackerel are abundant at present.

The colours of the very common species of sea fish are always striking. The back of a freshly caught individual is a beautiful, brilliant blue-green colour broken by a row of black, irregularly curved lines. The green on the back gives way to iridescent blue on the sides fading to white on the belly, the white enhanced with subtle pink reflections. After death the colours fade rapidly and the fish goes off very quickly.

Like Cod, Herring and Haddock, the Mackerel is a pelagic species, that is, it is a fish of open water. It can be found from mid-water up to the surface in the sea. Pelagic fish are prey for larger fish, seabirds, sharks, dolphins and whales and are very exposed in the open water. Since it lives in open water and has nowhere to hide, one wonders why the Mackerel is so strikingly coloured.

Nature's answer to this dilemma is that the fishes gather in a shoal and seeing that he or she has nowhere else to hide, each individual hides in the crowd. There is safety in numbers. The swirling shoal confuses predators and sheer numbers reduce the chance of any individual being caught. Each Mackerel has the shoal to hide in and can consequently be brightly coloured.

The colours have a survival value too. The broken lines of black on the back makes it harder for a predator to see the fish when attacking from above. Similarly, the white belly breaks up the fish's outline against the light of the sky when a predator is approaching from below.

Mackerel are highly migratory and move about in large, often huge, shoals. While they may wander as far offshore as the edge of the continental shelf, at this time of year adults regularly move inshore hunting shoals of Sprat, Herring and sand eels. With the arrival of autumn they make themselves easy for anglers to catch as they are voracious feeders with an urgent need to build up oil-rich energy reserves before winter sets in, the water gets colder and food becomes scarcer.

Slender bodied Mackerel have big eyes for hunting by sight and are slow-growing fish; a good-sized adult may be up to twenty years of age.

Soon the shoals of Mackerel will retreat offshore again bringing their late summer seasonal abundance to an end for another year.

Enniscorthy Guardian