IUCN/SCC Otter Specialist Group Bulletin
© IUCN/SCC Otter Specialist Group

Volume 14 Issue 2 (October 1997)

Abstracts

How Standard is the Standard Technique of the Otter Survey?
Pages 57 - 61 (Article)
Jerzy Romanowski and Marcin Brzeziński
Many studies of otter distribution describe the method used as "standard" or "British" field survey. Surprisingly few studies in fact follow all the recommendations set by the early British field surveys. Many researchers propose some modifications to improve the efficiency of otter detection (additional spot checks and extended searches of river banks) or to reduce the amount of field work to reasonable time span by selecting fewer sites per 10 km square or fewer squares within a study area. All the modifications of field techniques and especially in the study design result in uncontrolled variation of results, that may range from 3.5-12% improvement in the otter detection when spot checks and extended searches are implemented, to several fold difference in results when single positive sites are referred to squares of increasing size. Since it seems impossible to set stricter criteria for the "standard" survey of otters, it is recommended that researchers show understanding of the consequences of any modifications in the study and that they describe in details the method used rather than call it "standard".
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Reintroduction of Otters a Successful Conservation Strategy?
Pages 62 - 74 (Article)
Rosemary Green
British otter populations had declined so much by the mid 1970s that fears of imminent extinction were rife. A working group was set up to assess the situation and studz measures to safe the otter. The 1st National Otter Survey results showed that only 5.8% of 2.940 survey sites in England were occupied by otters. Reintroduction of otters to areas from which they had already been lost was investigated. Captive bred otters were released in 1983, followed in 1985 by animals rehabilitated from the strong populations in Scotland. By the time the techniques of releases, monitoring and the neccessary safeguards were developed the results of the 2nd National Otter Survey were available, showing some natural improvement in the situation, so the emphasis changed from repopulating large empty areas to one of restocking. The programme aimed to strengthen fragmented populations, to demonstrate that causes of decline had been correctly assesseed and that rivers were again safe for otters, to aid recolonisation and hasten the end point of recovery. Releases took place in 3 ways; scattered groups on adjoining catchments, concentrated releases on large catchments and placing small groups ahead of active recolonisation by wild otters. Success is measured by the survival and expansion of breeding populations. Insufficient time has elapsed to judge any but the earliest releases, however those show promising results. The 2 areas involved have had enough breeding success and expansion of range to show up clearly on the 3rd National Otter Survey as isolated populations, distinct from natural recolonisation. Radio tracking showed the otters´ behaviour was comparable with wild otters. Monitoring has shown that breeding takes place within the first year and the population expands steadily. Mortality has been low and from usual causes. We are cautiously optimistic that value of the techniques have been demonstrated and could be applied elsewhere in Europe.
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The Prey of Otters: Calorific Content of Eels (Anguilla anguilla) and other Fish, Frogs (Rana temporaria) and Toads (Bufo bufo)
Pages 75 - 80 (Article)
Kenneth Nelson and Hans Kruuk
To evaluate energetic contents of otter diet, energy values are presented for some of the main prey species of otters in Europe, eels, frogs and toads, and compared with measurements on other prey from literature. Energetic values per gram increase with larger sizes of eels, and they are relatively high. Values for amphibians were lower, and no significant variation with size was found.
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The Giant Otter, Pteronura brasiliensis, in Caño la Brea, Sucre State, Venezuela
Pages 81 - 88 (Report)
Alex Lewis, Richard Cuthbert, Matthew Denny, Katharine Gotto and Geoff Hilton
An active, breeding population of Giant Otters was found on the Caño la Brea river, a tributary of the Rio San Juan in Sucre state, Venezuela, 200 km further north than previously known for this species. This otter population seems to be isolated from other Giant Otter populations, so inbreeding may be a threat, as may be pathogens from domestic dogs, and hunting. The government has also given permission for oil exploration in this area, and mangrove logging is taking place.
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