Otter Scats Research Articles

Predation by River Otters (Lutra canadensis) on Juvenile Coho Salmon (Oncorhynchus kisutch) and Dolly Varden (Salvelinus malma) in Southeast Alaska

The effect of predation by river otters (Lutra canadensis) on juvenile coho salmon (Oncorhynchus kisutch) and Dolly Varden (Salvelinus malma) in a Southeast Alaska watershed was inferred by examining the number and size distribution of sagittal otoliths that were found in otter scats. Individual scats contained up to 408 otoliths, indicating that at least 200 fish had been eaten between defecations. Otoliths from juvenile salmonids outnumbered those from coastrange sculpins (Cottus aleuticus) by about six to one. Based on examination of over 8000 otoliths found in otter scats, at least 3300 juvenile salmonids were eaten by two river otters and their two young in the Kadashan River system during a 6-wk period in late spring 1985.

Organochlorine pesticide and PCB contents in otter (Lutra lutra) scats from western Scotland

Organochlorine pesticide residues and PCBs were measured in 113 otter (Lutra lutra) scat samples from 94 sites in the River Clyde catchment, its estuary and neighboring coastal waters in western Scotland. Contents of pesticide residues were generally low. PCB amounts were high in some regions in the study area (geometric mean contents up to 19.5 mg kg−1 lipid). Potential sources of contamination included industrial areas, a sewage sludge dump and shipping facilities, both naval and commercial. PCBs in tissues were estimated from scats. Analysis of scats provides a useful technique of estimating potential contamination threats to otter populations and can be used to identify biologically significant hot-spots of contamination which may be missed by more familiar surveillance methods.

Summer Feeding Habits of River Otter (Lutra canadensis) on the Mendocino National Forest, California

The diet of otters was studied over one season on the Mendocino National Forest in northern California. Undigested prey remains were analyzed from 94 otter scats collected between 18 April and 29 August 1982. Fish were found to be the predominant food, occurring in 89.4% of the scats with a mean volume estimate of 63%. Fishes consumed were primarily catostomids and salmonids. Crayfish and snakes were common prey items as well. Insects were often found in otter scats, but repre- sented little volume. Bird, turtle, frog, and snail remains occasionally were found in the scats. Feeding habits of the North American river otter (Lutra canadensis) have received considerable attention in the literature of wildlife biology, with special emphasis often placed upon the relative proportions of game and non-game fish species taken. One approach has been to study the remains of prey in stomachs or intestines of otters taken by commercial trappers (Lagler and Ostenson 1942; Ryder 1955; Hamilton 1961; Toweill 1974, Lauhachinda 1977). While this method permits relatively accurate esti- mations of prey size and numbers (Lagler and Ostenson 1942), it requires grave com- mitment on the part of the otter. In areas where otter are fully protected, analysis of scats is a workable alternative to digestive tract analysis (Trautman 1936; Wilson 1954; Greer 1955; Sheldon and Toll 1964; Knudsen and Hale 1968; Modafferi and Yocom 1980; Melquist and Hornocker 1983). Scat analysis has certain inherent shortcomings. First, the digestive process renders even some hard parts less identifiable. Second, hard indigestible portions of prey are over- represented compared to soft parts. Mech ( 1970) hypothesized that because of this, smaller prey with greater surface area:volume ratios would be over-represented in scats of carnivores. Floyd et al. (1978) tested this idea with captive wolves and found that smaller animals were indeed over-represented in frequencies of remains in scats. Last, assessment of feeding habits by frequency of occurrence in scats has been shown to be inherently biased, over-estimating food items occurring in low proportions and under-estimating at high proportions (Lockie 1959). Because of this last problem, it has been recommended (Korschgen 1980) that some estimate of volume or weight be included with frequency of occurrence data in all feeding habits studies. Lagler and Ostenson (1942) estimated volumes of otter stomach contents, and Modafferi and Yocom (1980) measured volumes of food items found in otter scats. This communication presents feeding habits information obtained from river otter scats collected in 1982 on the Mendocino National Forest in northwestern California. Data are expressed as percent frequency of occurrence and mean percent estimated volume.

Radioactivity in otter scats in Britain following the chernobyl reactor accident

Radioactivity was determined in samples of otter (Lutra lutra) faeces (scats) collected from various regions of Great Britain in 1986 and 1987, following the Chernobyl nuclear reactor accident, and compared with a sample of scats collected in 1985 from central Wales. Samples of scats were also collected from the seashore adjacent to the Dounreay nuclear power station, northern Scotland, and compared with a control site, 40 to 60 km distant. Samples collected in 1986 from central Wales, Galloway and northern Scotland all contained significantly higher amounts of radioactivity than the 1985 sample from central Wales, with Galloway (mean 13 000 Bq kg−1 dry weight) having significantly more radioactivity than other regions. A sample collected in central Wales in January 1987 had returned to the 1985 level of radioactivity, but a sample from Galloway in January 1987 remained high; this difference in response may be related to the acidic nature of Galloway rivers. No significant differences were found between samples collected from near Dounreay and the control site, though fallout from Chernobyl may have masked the effects of local discharges of radioactivity. The significance of the results to otter populations is discussed.

Food habits of mink (Mustela vison) and otter (Lutra canadensis) in northeastern Alberta

Scats of mink (Mustela vison) and otter (Lutra canadensis) in northeastern Alberta contained different food items in different habitat types according to type of water body. Brook stickleback (Culaea inconstans) was the most frequently encountered food item in scats of both species from a drainage system dominated by lakes and for otter from a second drainage system dominated by streams. However, mink had varying hare (Lepus americanus) as their primary food item by frequency of occurrence in this latter situation and mammalian items were significantly (P < 0.01) more frequent. Otter scats contained more fish and invertebrates (P < 0.01) and fewer mammals (P < 0.01) and birds (P < 0.05) than mink scats. Both otters and mink appeared to exploit avian species to a greater degree (P < 0.01) in the lake-dominated drainage. The frequency of avain remains in otter scats was very high and probably reflected high utilization of breeding and moulting waterfowl.

Food Habits of the Otter Lutra lutra L. and the Mink Mustela vison Schreber in a Trout Water in Southern Sweden

The feeding habits of otter and mink were studied in a trout water in southern Sweden in 1966-68. 350 otter scats and 122 mink scats, collected from all the seasons, were analysed. The fish fauna was studied by means of electrofishing. The food of the two predators greatly overlapped (60-70% approximately) as they both exploited easily available prey. The otter fed for most of the year almost exclusively on fish (frequency analysis indicated 90.8 % of food). The mink fed not only upon fish but also upon water-fowl and mammals, mainly small rodents (24.4% and 9.5% respectively of food). The corresponding figures for the otter were 5.5 % and 0.2 %. The two predators tended to feed upon fish of different sizes. About 30% of the fish taken by otter exceeded the maximum size of fish