Otter nuisance

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Frequently, death of otters at the hands of people is brought on to the animals by their own activities: in some places they affect fisheries, or they take domestic fowl. Although, especially in Europe and North America, otters may have achieved remarkable popularity, in the not too distant past, say more 50 years ago, they were considered as vermin, no better than foxes, raccoons or polecats. They still are considered to be vermin in many developing countries. In ecological terms, otter nuisance is a manifestation of direct, interspecific competition between predators: otters prey on the same species as humans do, and they interfere with fishing nets and fish farms.

Now, in a more tolerant age and with few otters left, conservationists tend to deny what are seen as the otters' bad deeds, but perhaps it should be acknowledged that the view of countryfolk of old was not totally off the mark, at least not everywhere. In our own recent research in Scotland we recorded Eurasian otters eating many salmon, often large ones, and in some rivers they consumed almost half of the productivity of fish populations, as documented in Chapter 8. More recently, researchers in western Scotland confirmed that otters took 28% of tagged adult salmon within a few weeks (Reynolds 2003). This leaves some people concerned that the salmon populations in Scottish rivers, which have seriously declined for unknown reasons, are being delivered a final blow by the otters.

In Austria the government pays compensation for damage by Eurasian otters to trout and carp populations in fish ponds and stocked streams. There has been a large increase in this since the recovery of the otter populations in the 1980s and 1990s, and in 1995 the level of compensation had reached the equivalent of almost US$200,000 per year (Bodner 1998). Similarly, in the USA, the sport-fishing public in Missouri is worried about the alleged dramatic increase in damage by river otters to the inhabitants of fish ponds and streams, following a successful otter reintroduction programme (Hamilton 2004). Within 1 year, the government received over 500 complaints.

Fisherfolk in Europe have suffered damage to nets, caused by otters, and I have seen this elsewhere. In Thailand, where my Thai colleagues and I used gill nets in rivers, Eurasian otters frequently tore up the nets (they were actually seen doing so) and took much of the catch, as did the spotted-necked otter with gill nets during my work on Lake Victoria. In Rwanda, this last species took an estimated 15% of the catch from the nets of local fisher-folk (Lejeune 1989, 1990), and there are similar reports from other species. Not infrequently the otters are caught in fish nets themselves, and drown. Little wonder that people whose livelihood depends on fish catches show less sympathy for the animals than do the urban viewers of spectacular television documentaries. Persecution of otters, therefore, is not based solely on prejudice (although this does not imply that I approve of it; nor do I think that it is effective in preventing damage).

Anywhere in the world, fish farms may occasionally be visited by otters, if there are chinks in the armour of the ponds or of the floating fish cages, such as holes in the protective netting, or absence of anti-predator wiring, and substantial numbers of fish may be taken. Some types of fish farm are easy to protect, and are ignored by the animals. In Shetland, for instance, where a large, well protected fish farm with floating fish cages was established right in the centre of our study area, we frequently saw

Eurasian otters swim closely past the cages full of salmon, never taking any overt interest in them. But in South Africa (Southern Cape province) I watched a Cape clawless otter for about half an hour attempting, unsuccessfully, to get into a floating fish cage similar to those in Shetland; it was walking on the boardways and biting at the netting.

Kranz (2000) confirmed the widespread occurrence of predation by Eurasian otters in central European fish farms; especially in Austria and the Czech Republic the species is generally perceived as a pest. Adamek etal. (2003) documented serious problems in Czech fish farms, with otters taking substantial numbers of large carp, up to 11 kg in weight, as well as perch and zander. Often the otters ate only the viscera, leaving 63-73% of the fish body mass on the bank. Farmed fish also died from stress caused by otters hunting them under the ice in winter.

Elsewhere in Europe depredations by otters in fish farms are a cause for concern, with significant quantities of salmonid fish being taken in Finland, especially in winter (Ludwig et al. 2002), often as surplus kills left uneaten. Annual losses were estimated at US$75,000 in the 1980s, but are likely to have increased substantially since then. Similar observations of otter damage in fish farms have been made in Poland (Kloskowski 2000), France (Leblanc 2003) and the north of England (Morgan 2003), and no doubt fish farms in other continents will have records to match. Both the smooth and the small-clawed otter have been mentioned as taking fish and shrimps from aquaculture projects in Malaysia (Foster-Turley 1992).

Otters occasionally lower their popularity ratings by taking poultry: ducks, hens and geese. My own three ducks, free-roaming in the garden in Scotland, were taken from the pond one snowy March, by a Eurasian otter. They disappeared one at a time at night, over a couple of weeks, carried off and eaten in the marsh about 1 km away, with good tracking snow to record it all. A large Eurasian male otter regularly raided the hen-house of one of my then PhD students on Skye, Paul Yoxon, who studied the animals along the coasts there, and on the Scottish mainland one of our radio-tagged otters, followed by Leon Durbin, often foraged from a collection of captive ducks (the owner blamed mink). Shetland farmers frequently lose hens and ducks to otters, and a Scottish newspaper (Press and Journal, 23 October 1996) recounted the loss of several scores of hens, ducks and geese around crofts on the Outer Hebrides island of North Uist (headline: 'Killer otters should be shot').

Fanshawe et al. (2003) conclusing that along Californian coasts, sea otters and fisheries for abalone are incompatible: sea otters take such a high proportion of harvestable sizes of these molluscs that not enough is left for people to fish. In Alaska, the increasing populations of sea otters in the 1970s caused serious disruption and the end of many clam fisheries (Johnson 1982a,b; Wendell etal. 1986).

The otter-loving public often doubts or denies such damage, a response that, I believe, is short sighted. Conservation management policies for otters will have to take account of problems with people's use of resources, and of the perception of problems. Maintaining that they do not exist inevitably leads to loss of credibility of observers and conservationists, and therefore loss of effectiveness.

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