Summary: Methods Of Capturing River Otters

Methods of Capturing River Otters
A literature review

Hunter Hollingsworth
Wildlife Biology 240: Fish and Wildlife Management Techniques
Fall 2012

Contents

Introduction……………………………………………………………..Page 1
Contrast of methods……………………………………………………..Page 1
Technology aiding in safe trapping……………………………………...Page 3
Criticisms of traps………………………………………………………..Page 3
Overview…………………………………………………………………Page 4
Literature Cited…………………………………………………………..Page 5
Figures……………………………………………………………………Page 7
Tables……………………………………………………………………..Page 8

Methods of capturing river otters
INTRODUCTION
Most forms of wildlife are so elusive, so completely wild, and have so many places they
can hide, that the obtaining of anywhere near an accurate estimate of their numbers has proven extremely difficult. In fact, most known methods have been so unsatisfactory that the Biological Survey has now detailed a research worker to the huge problem of studying methods of taking censuses of wildlife. Difficulties of observation apply particularly to mammals, many species live in underground dens, making them extremely difficult to monitor. Otters are extremely wary and trap shy, they are also very quick and powerful. Traps for otters must be heavy, fast, and strong ( Journal of the American Statistical Association 1937).

CONTRAST OF METHODS Hancock live beaver traps modified to capture river otter (Lutra Canadensis) have been used successfully in a number of locations including: Idaho, Alaska, British Columbia, Alberta, and Newfoundland. A similar trap known as the Bailey trap, has been used in Ontario with some success. Both traps are set so that when closed, the trapped otters are partially out of the water to avoid drowning. The Hancock trap has one stationary side, whereas the Baily trap has two moving sides. Many researchers had good luck with the Hancock trap and the condition of the animals caught was good (Northcott and Slade, 1976). Soft Catch traps were modified with weaker springs, to reduce injury to otters.
All Soft catch traps had chains, with five swivels, to prevent chains from binding when the otter thrashes and rolls. Traps were anchored with wooden steaks, and the surrounding area was cleared of debris to avoid the chain getting tangled. During periods of cold weather, chains were replaced with 11 gauge wire that acted as a slide to allow otters to exit the water. Season is important depending on area you are trapping. Young otters should be able to survive on their own; also temperatures should be above -5 degrees Celsius to avoid risk of freezing (Serfass et al.
1996). Hancock traps were often set in small streams in what was considered to be good habitat for otters.
The trap triggers were placed just under the surface of the water; the stationary side was stacked up against the bank, and concealed with grass. Baily traps were set completely under the water. Many traps were set on trails with sign of frequent otter activity, these sites did relatively well. Spill ways from beaver dams proved among the most productive locations. Sets at the tops of slides were much more successful than those placed at the bottom. Leg-hold traps were used after the study was well underway, they were smaller and easier to transport, they also caused less serious injuries to otter’s teeth. Baits and lures: Otter musk, used sparingly, is a good lure for otters. Beaver caster or beaver flesh is sometimes used when setting otter traps. Whole fish are also used as bait (Randall, Pepper 1993). A variety of restraining traps for live-capture of river otters have been evaluated in both Canada and the U.S., capture success with Hancock traps varied depending on season and setting technique (Northcott and Slade 1976). A modified Victor, number 11, double long spring modified spring trap was both practical, and efficient for live trapping otter in the Louisiana marsh. But they failed to capture any otters using the number 208 Tomahawk cage traps (Serfass et al
1996).

TECHNOLOGY AIDING IN SAFE TRAPPING Traps are sometimes monitored by trap transmitters that signal when a trap is sprung. This allows for speedy recovery of trapped animals so they undergo minimum stress. The sooner an animal is recovered from a trap the less likely it is to injure itself or get away. (Duffy et al 1993). Many otter traps are altered beaver traps. Making sure to choose a method that is effective and safe is important. Otters caught in the Soft-Catch traps with padded jaws received fewer severe injuries; there was no difference however in the severity of dental injuries.

CRITICISM OF TRAPS The Hancock trap had a slightly lower efficiency rate compared to the Number 11 Sleepy Creek double-jaw foothold traps. The Hancock trap also had a higher escape rate. Otters caught in Hancock traps had more dental damage than those caught in leg traps. Otters caught in leg traps suffered injuries to appendages. Otters are sometimes accidentally caught in Conibear traps. The Conibear traps that otters are caught in are usually intended for beavers. Conibear traps are kill traps, chances of catching an otter can be reduced by moving the trigger to one side of the trap. Otters are narrower than beavers, otters can often pass through the trap without triggering it while still catching beavers. Sometimes trapping seasons are open for beaver and closed for otter so it is important to be able to target your species (DEC, 1994)

OVERVIEW It is important to find a trap that is effective. In order for a trap to be effective it must be practical, safe, and economical. A trap must be a reasonable size, often otters are in well isolated areas, and traps must be transportable. Traps must also not take an unreasonable amount of time to set up. The trap needs to be safe for the targeted animal. Using scent such as liver oil or dead fish can attract non target carnivores such as raccoons. Animals being captured for relocation or study need to be alive. It is also best if the animal is not injured, leg traps can damage appendages on the caught animal. If you use the Hancock traps it was known to damage the otter’s teeth. When setting a trap it should be done so in a manner to avoid non-target species as much as possible. If you catch a non-target species you are missing opportunity to catch you targeted species and risk harming a non-target species because that trap is not designed for them. The trap should also be safe for humans so they are not injured while setting traps. Too effectively trap otters you need to set several traps so these traps need to be reasonable priced. There is no clear choice as to which trap is the most effective. There are a lot of variables that take place on each trap’s effectiveness. The best trap depends not only on location and habitat, but also on the season. How a trap is set up also depends on its effectiveness. The proper set for a trap is crucial for it to function properly, and the proper set varies depending on where it is being set at. It would be beneficial to have a method that would more specifically target otters and catch them in a manner that lowers their risk of injury. There is not a method that is head and shoulders among the rest each technique has its ups and downs.

Literature Cited

Bowyer, Terry, Gail M. Blundell, Merav Ben-David, Stephen C. Jewett, Thomas A. Dean, Lawrence K. July 2003 Duffey Effects of the Exxon Valdez Oil Spill on River Otters: Injury andRecovery of a Sentinel Species.

Capturing and Handling Wild Animals. Page 260 in C.E. Braun, editor. Techniques for wildlife investigations and management. Sixth edition. The Wildlife Society

DG Newman, CR Griffin – 1994 The Journal of wildlife management,- JSTOR

GM Blundell, JW Kern, RT Bowyer, LK Duffy -1999 Wildlife Society Bulletin, – JSTOR

JE Tabor, HM Wight -1977 The Journal of Wildlife Management, – JSTOR

Lee E. Yeager. American Midland Naturalist , Vol. 18, No. 6 (Nov., 1937), pp. 1072-1078

Merav Ben-David, Gail M. Blundell, John W. Kern, Julie A. K. Maier, Evelyn D. Brown, Stephen C. Jewett, Ecology, (May 2005) Vol. 86, No. 5 pp1331-1345.

Penak, B.,Code,T..(1987) The River Otter Live Capture Program in Ontario, Canada. IUCN Otter Spec. Group Bull. 2:12-20.

TA Gorman, JD Erb, BR McMillan, DJ Martin.2006 - The American midland …, - BioOne

TL Serfass, RL Peper, MT Whary, RP Brooks 1993,- Journal of Zoo and Wildlife …, – JSTOR

Wayne E. Melquist, Maurice G. Hornocker, April 1983, Ecology of River Otters in West Central Idaho

WE Melquist, MG Hornocker -1983, Wildlife Monographs, – JSTOR

Figure 1. Otter in Live Trap, caught by Carp pond (Westwood 2012).

Table 1. (Wildlife Society No 83. P 10)

Trap type Trap Nights Captures Trap nights/capture
1.) Leg-Hold 3,770 9 419
2.) Barrel 732 2 366
3.) *Tomahawk 303 2 152
4.) Hancock 5,425 44 123
5.) Culvert 640 1 640
6.) Floating 13 0
Totals 10,883 58 188

*Two Otters were caught with small Tomahawk traps intended for mink.