IUCN/SSC Otter Specialist Group Bulletin
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©IUCN/SCC Otter Specialist Group Citation: Bisther, M. (2011) Otters Caught in Traps: A Minor Problem or the Tip of an Iceberg?. Proceedings of XIth International Otter Colloquium, IUCN Otter Spec. Group Bull. 28B: 23 - 25 Otters Caught in Traps: A Minor Problem or the Tip of an Iceberg? Mia Bisther1
1Brandt & Gröndahl AB, Allmänna vägen 13 D, 414 60 Gothenburg, Sweden. EmailL: mia.bisther@bog.se |
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| (Received 8th November 2011, accepted 16th January 2012) |
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Abstract:In Sweden, only four otters have been reported killed in mink traps during the last three decades. But one third of 1 024 traps found during otter surveys 1989-2010 were illegally constructed. The most frequent incorrectness was a too large entrance hole of the trap. This considerable increases the risk for otters to get caught in traps. There is a need for changed regulations as well as better information about trap selectivity. |
| Keywords: otter (Lutra lutra), mink (Neovison vison), illegal traps, non-selective traps |
| Française | Español |
INTRODUCTION
In Sweden it is legal to trap mink (Neovison vison). Most trapping is due to the fact that minks are considerate a threat to commercial values and native species. The economic values for pelts are too small to be cost-effective. The traps are positioned close to water in areas also frequently used by otters. Fully-grown otters cannot be caught in traps properly made for mink. But during 20 years of otter surveys, a large amount of illegal traps have been registered.
In order to prevent catching otters in mink traps, regulations were set by the Swedish government in 1980s. The entrance hole for both live box traps and beating traps had to decrease. Despite that, several “home-made traps” are found, as well as non-selective traps with unknown target. Some of the traps are normally used for catching other species than mink, e.g. pine marten (Martes martes).
Sometimes even legally sold mink traps do not follow governmental recommendations. For example a mink trap (live box) called “Östgötafällan” with an entrance hole larger than recommended. The trap has been frequently used since late 1990s. The manufactories reduced the size to the recommended 10 x12 cm in 2005. The Canadian so called Conibear beaver and otter trap is used in Sweden under supervision and a proper education provided by the County Administration Board. To our knowledge, only one otter has been killed in a Conibear trap in Sweden until now. This study summarizes the investigations of traps found during otter surveys between 1989 and 2010.
METHODS
Since 1989, traps found nearby water during Swedish otter surveys have been documented. The entrance hole was measured and the trap was checked if it was marked with the owners’ name and telephone number. After 2001 we also started to document the position of the trap because of the large amount of none-selective traps found.
RESULTS
A total of 1 024 traps were found, documented and measured during otter surveys in all over Sweden, between the years 1989 and 2010. 609 traps were found during the period 1989-1999 and 415 during 2000-2010 (Table 1). About every fourth trap was found to be illegal in some aspect. The most common incorrectness was the size of the entrance hole. They were too large. An example of our findings: in a northern county a total of 71 traps were found during a survey conducted in 2007. Out of these 71 traps, 24 % had an entrance hole that was larger than recommended by the government. Only four traps were marked with the owners’ name and telephone number, which is obligatory. If the results are compared between northern and southern parts of Sweden, there are only minor increases in non- selective traps found in the north.
| Table 1: The occurrence of incorrect and/ or illegal traps | ||||
| Time period | Illegal traps | None-selective traps |
Not marked | Homemade traps |
| 1989-1999 | 27 % | 4 % | 98 % | 17 % |
| 2000-2010 | 24 % | 7 % | 97 % | 6 % |
DISCUSSION
Despite government regulations, illegal traps do exist in Sweden. Between 24 and 27 % of investigated traps found nearby water, were illegal traps. These traps have the potential to catch otters. It is remarkable that there is no governmental control of how the regulations are followed, and if the traps are properly monitored during use. The control is solely the responsibility of the user. Swedish County Administration Board are not authorized to confiscate or remove illegal traps, they can only rapport the use of illegal trap to the police.
The Swedish Museum of Natural History regularly investigates otters found dead. Only four otters have been registered as killed in traps. Three of them were juvenile otters killed in mink traps. Considering the large amount of illegal traps found in the study, this is probably not a representative number. This is probably also the case for several other animals. For example the trap used for lynx (Lynx lynx) is also used for trapping fox. How selective can this type of live-catch trap be?
The decrease in number of traps found during the last decade in the study, are probably due to a rapid decrease in the mink population. The population decline started already during late 1990s and has become extremely obvious since early 2000. Since mink has no real conservation-value in Sweden there is no effort to find out the reason for the rapid population decline, we can only speculate. One reason for the decline could be the increase in the fox population (Vulpes vulpes). Foxes in Sweden have suffered from severe Sarcoptes scabeie infections during the last decade, but the populations are now starting to fully recover. Another reason could be trapping success in combination with an increasing otter population.
Still, the high number of illegal traps found during Swedish otter surveys suggests that there is a need for both a change in regulations and better information about trap selectivity.
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