Every year, towards the end of January, Michael Callaghan travels with his crew aboard his 51-metre fishing boat Pacelli to waters off the coast of the Shetland Islands in Scotland. The Killybegs-based fisherman, who has spent the last thirty years in the trade, knows that this is the point where mackerel fish – his main source of income – are at their prime for catching. They’ve fattened themselves during the months previous, feeding in the North Sea between UK, Norway and Denmark, and are beginning to migrate, following the continental shelf up over the top of Scotland and towards Ireland,…