Get your own Free Home PageThe evidence is in and the verdict is damning. Several fishing techniques are undoubtedly involved in the by-catch of porpoises, but by far the most destructive is the increasing use of bottom-set gill-nets, including trammel and tangle nets, particularly those made of man-made mono-filament (i.e. single strands of extremely strong plastic). It is a sad irony that whilst some gill-netting techniques can be reasonably efficient in selecting fish by both species and size, and, unlike techniques such as beam trawling, do little if any damage to the sea-bottom, they are undoubtedly among the most dangerous and detrimental for animals such as marine mammals.
Around the British coast, in areas such as the North Sea and Celtic Sea, at least ten thousand porpoises are dying every year as a direct result of being caught in these nets, a level of by-catch scientists believe may not be sustainable.
Of course, it is also unacceptable that any civilized society tolerates the drowning of animals. This by-catch is no exception and unquestionably causes terrible suffering. Indeed, as air breathing mammals, unused to the concept of restraint, the agony of porpoises trapped underwater in an unforgiving and effectively invisible net, can hardly be imagined. Entanglement turns an impressive breath-holding capability into a cruel elongation of death as an animal may struggle for well over five minutes before succumbing.
Caught by red tape! Extinction is forever and the demise of a porpoise population such as that recorded recently in the Mediterranean may well be permanent. Another porpoise species, the highly endangered Mexican 'vaquita', has already been brought to the brink of extinction by fishing activity. Both are portents of what may lie ahead if authorities fail to act on the growing body of evidence and take wide-ranging measures to protect the marine environment. Some governmental agencies now acknowledge the problem, prompting limited research into threats and possible solutions but also raising concerns that the issue may become bogged down in the back-rooms of government and academia. Action to save porpoises must not be delayed.
Throwing precaution to the wind The International Whaling Commission's Small Cetacean Subcommittee recently agreed a provisional precautionary value of 1% of estimated harbor porpoise abundance as the by-catch level above which mortality may not be sustainable. Furthermore, it concluded that, of the porpoise populations in the North Atlantic for which it has sufficient data, all are probably unable to sustain the calculated levels of by-catch.
However, some populations may be at more immediate risk than others. For instance, an independent observer scheme conducted from 1992 -1994, calculated that the number of harbor porpoises caught in the Celtic Sea by Irish and UK set gill-net fisheries was 2,237. This by-catch represents 6.2% of the estimated population of 36,280, SIX times the 1% figure. Incredibly, no further monitoring has followed and no attempt yet made to reduce this by-catch.
Such calculations are made possible by, among others, the 1994 Small Cetacean Abundance in the North Sea survey (covering the North Sea, Skagerrak, Kattegat, western Baltic Sea, English Channel and Celtic Sea - see map). SCANS estimated that only 352,000 harbor porpoises live in this entire area. With 10,000 of these killed annually in nets, this carnage is simply unacceptable. Yet, despite these shocking statistics, governmental action to implement by-catch reduction measures remains virtually non-existent.
Sea change? Many fishermen are genuinely concerned about catching marine mammals in their nets but their sympathy is naturally tempered by the need to make a living. Consequently, schemes encouraging voluntary reporting of by-catches have yielded little reliable data. However, some fishermen are now allowing independent observers on board to ascertain by-catch levels (e.g. the Celtic Sea survey was made possible by Cornish and Irish gill-netters). The application of such valuable information, perhaps in facilitating time and area closures for fishing grounds or the use of devices such as 'pingers' (acoustic alarms), could yield substantially reduced by-catches without large scale disruption to the fishing industry.
Another excellent example of the fishing community's co-operation is the saving of porpoises from herring 'weirs' in Canada. A substantial number are released alive and some are tagged, providing researchers with new details of the animals' range, seasonal movements and diving capability - essential insights if porpoises are to be conserved.
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