IUCN Otter Specialist Group (2024)

Volume 19 Issue 2Pages 62 - 110 (October 2002)

Citation: Noordhuis, R.. (2002) The River Otter (Lontracanadensis) in Clarcke County (Georgia, USA) - Survey, Food Habits andEnvironmental Factors. IUCN Otter Spec. Group Bull. 19(2): 75- 86

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The River Otter (Lontra canadensis) in ClarckeCounty (Georgia, USA) - Survey, Food Habits and Environmental Factors

Rienk Noordhuis

Borgmanweg 22, 7558 PN Hengelo, The Netherlands, e-mail: rinoordhuis@hotmail.com

(received 19^th March 2002, accepted 16^thJune 2002)

INTRODUCTION

In the early 1950s, river otters (Lontra canadensis) were consideredrare in the Georgia Piedmont area (JENKINS, 1953).No records are known from Clarcke and surrounding counties from those years,though the original distribution included the whole of Georgia. The mostprobable cause of their decline and subsequent eradication was over-trapping (JENKINS,1983). However, by 1970 river otters had recolonized the Georgia Piedmontarea (JENKINS, pers. comm.). This recovery took place while pollution wasdramatically affecting ecosystems all over the world.

In 1993, the status of otters in Clarcke county was assessed through a surveyof local rivers for presence (tracks and spraints, and a survey of pollutionstatus through analysis of spraints and locally caught fish for heavy metals (Hgand Pb). Data on organochlorine and polychlorinated biphenyl (PCBs) loading wasassessed from previous studies. The results were compared to reports inliterature to see if food habits and pollution status have changed over time. Inaddition, a comparison was made with food habits of river otters in the nearbySmokey Mountains, where the rivers are clear, to see how water with a lowtransparency affects their food habits and the possible role of underwater scentin searching for food in turbid water is discussed

MATERIALS AND METHODS

The study site comprises most of Clarcke County and parts of the surroundingcounties in the Piedmont area of Georgia. Most otter spraints were collected inand around the town of Athens. Athens is a medium sized town with approximately80,000 inhabitants. The North and Middle Oconee River both run through Athensand join south of the town. The rivers and creeks are provided everywhere with adense riparian vegetation, also within the town limits. According to ODUM (pers.comm.) a lot of this riparian vegetation has been restored in the last fortyyears to prevent erosion. Large trees, such as sycamore (Platanusoccidentalis) and river birch {Betula nigra), are abundant along therivers and creeks. Rapids, rocks and logjams are common. All these structuresare known to be important to river otters (MELQUIST andHORNOCKER, 1983; MACDONALD and MASON, 1983).Beavers are abundant everywhere in the study area. It is well known that riverotters benefit from the activities and dens of beavers (TUMLISON et al., 1982)

The soil type is sandy loam and the pH of the North Oconee River is 7.35,total Organic Carbon content in summer is about 2.6ppm, and the total calciumconcentration is about 5.2ppm. All year round, but especially in winter, therivers and creeks are loaded with silt. Underwater visibility usually does notexceed 20cm.

In order to get an impression of the status of the river otter in the studyarea, the rivers and creeks were searched for signs of this animal. About 16stretches of approximately 100m of river or creek bank were surveyed. Sandstrips, rocks, rapids, logs and banks were checked for tracks and spraints.Looking for 'positive sites' of otters is one mean of surveying an otterpopulation (MASON and MACDONALD, 1987). Whenfootprints were found, the prints of the hind foot were measured. By doing thisit became possible to estimate if there was more than one individual present ata certain site. Adult male footprints are usually much larger (wider than 7cm)than female or subadult male footprints (MASON andMACDONALD, 1986).

Spraints, not older than about two weeks and non-weathered, were collectedfrom January through the end of March and from July until the end of September1993. After collection, they were dried and stored. Two hundred and fourteenspraints from nine different sites in the study area (of which four weresituated within the city limits) were collected on visits every fortnight. Thesewere used to determine food habits. The spraints were shaken in water containingcommercial washing powder and then rinsed on sieves with mesh sizes of 2 and0.5mm resp. and all the food remains of each sample were than collected from thesieves and dried.

Fish bones and scales and remains of other vertebrates were identified withthe help of the bone collection of the Museum of Natural History in Athens andwith LEE et al. (1980). Skeletal remains or gastrolithsindicated the presence of crayfish. Crayfish were keyed out according to HOBBS(1981).

The importance of the different types of food item is expressed as frequencyof occurrence and relative frequency. The frequency of occurrence was calculatedby dividing the number of occurrences of a particular food item by the totalamount of spraints. The relative frequency was calculated by dividing the numberof occurrences by the sum of the occurrences of all food items.

During January, February, and March, a total of 40 spraints, containingmainly crayfish remains, and a total of 11 spraints, containing mainly fishremains, were collected from 8 different sites in the study area. These spraintswere selected from spraint sites for heavy metal analysis. Four of these weresituated within the city limits; one site was upstream, and three sitesdownstream of Athens. Three to eight spraints per site were dried and ground ina glass mortar and analyzed for Pb and Hg. For the analysis of Pb, 1g driedspraint was muffled and dissolved in 10ml 30% HCL and 10% HNO₃. ThePb concentration was determined with a Thermo Jarrell-Ash 965 InductivityCoupled Argon Plasma (ICAP) with a detection limit of 1ppb for Pb. For theanalysis of Hg, 1.5g was muffled and dissolved in 20ml 15% HCl and 5% HNO₃and analyzed with an AVA800 Thermo Jarrell-Ash mercury analyzer with a detectionlimit of 1ppb.

Fifteen crayfish and three small catfish were caught in 'minnow traps',baited with catfood, in the North Oconee river. Five Procambarus spiculiferwere caught just north of Athens. Five Procambarus spiculifer, five Cambarusbartonii and three small snail bullheads Ameiurus brunneus werecaught close to the center of Athens. From the crayfish and the catfish, themuscle, intestine and fat bodies were freeze-dried. Five samples (5 P.spiculifer from north of Athens; 5 P. spiculifer from Athens; 5 C.bartonii; 1 larger catfish and 2 small catfish) were analyzed for mercury inthe same way as described for spraints.

RESULTS

Signs
The distribution of signs of river otters is given in Fig. 1.Most of the signs were found in winter. Footprints were always found on sandstrips that were often freshly deposited after heavy rains. It appeared thatanimals preferred to go on land on these coarse sand strips or on rocks, asprints on muddy sediment were never found. The map shows that river otters arealso present within the city limits. Prints of adult males (width hind footlarger than 7cm) were hardly ever found within the city limits, but were verycommon outside the city. Activity of otters within the city limits was foundboth in summer and winter.

Twelve of the sixteen surveyed river or creek stretches (75%) showed signs ofotters. In the study area, nine spraint sites were found. Spraints werecollected repeatedly from these sites. The average amount of spraints collectedon the visits to the sites was 5.3.

At eight spraint sites otter prints could be found as well. Four spraintsites were on sand strips; four were on banks on the forest floor and one was onrock.

The sprainting activity was higher in winter than in summer; four spraintsites regularly used in winter were abandoned in the summer. One spraint sitesparsely used in winter was more frequently used in summer and another one wasmoved 50m in summer. At four spraint sites, signs of heavy rolling in coarsesand were observed. At three of these places sliding trails were also found onthe sandy banks.

One winter site was on a creek in a park close to the center of Athens.Spraints were found at the entrance of a simple beaver den. The measurements ofprints from the hind foot were the smallest measured during the study (5.3cm).

Two large beaver dens in banks outside the city limits appeared to have beenused by otters. One den was heavily sprainted upon but the spraints were oldwhen found. The second one had a spraint site very nearby and trails led fromand to the den. The site was frequently used in winter and irregularly insummer.

Food habits
In winter, 149 spraints were collected for food analysis, whilst in summer only65 could be collected, a total of 214. The results of food analysis are given inTable 1.

Table 1. Food remains analysis from spraints collected in Clarcke County in 1993

One third of the winter food and two thirds of the summer food consisted ofcrayfish. Ninety percent of the crayfish remains could be identified as Procambarusspiculifer. This species can be seen and caught easily in the rivers andcreeks around Athens where it is abundant. It is restricted to lotic habitatsand can be found under stones, in litter and among roots. Procambarusspiculifer does not usually make burrows (HOBBS, 1981).About ten percent of the crayfish remains were identified as Cambarus sp..Five species are known from the area (HOBBS, 1981), but Cambaruslatimanus and C. bartonii are the species most likely to be caught.These two species only burrow under certain circ*mstances, while the remainingthree spend all their lives in a burrow (HOBBS, 1981).

Fish are the most important source of food in the winter months. Fifty-ninepercent (relative frequency) of the food remains were fish, against less thanhalf of this in summer. Sunfishes (Centrarchidae) form the most important groupeaten. It is hard to identify sunfishes to the species level; however, it waspossible to identify bones and otoliths of the largemouth bass (Micropterussalmoides) and the otoliths of bluegill sunfish (Lepomis macrochirus)in this study. Micropterus salmoides was found rarely. About one third ofthe sunfish ototliths were bluegill and most of the remaining part was thoughtto be redbreast sunfish (L. auritus), considering its abundance in thearea. Some spraints from winter consisted of only very small sunfish olotiths.They were of redbreasts or bluegills of the 0-generation. The largest redbreastfound was estimated at about 20cm. Most sunfishes caught were relatively small.

Minnows were second in importance in the winter and the remains identifiedbelonged either to creek chub {Semotilus atriomaculans) or bluehead chub(Nocomis leptocephalus). Because the otter eats pectoral spines ofcatfish, these bones can help to identify the species of catfish eaten and toestimate the fish length (PALOUMPIS, 1978). Mostcatfish caught were small, one brown bullhead (Ameiurus nebulosus)however was estimated at 28cm. Almost all suckers caught were large individuals,estimated to have been three to five years of age; judging from the annual ringsof the scales found. The larger individuals were estimated at about 40cm. In 6%of the winter spraints small molluscs were found. These remains were usuallyassociated with catfish remains and were therefore not counted as otter food.

Lead and mercury levels
The spraints with crayfish remains from eight different sites had a mean Pbconcentration of 18.2 ±2.2 ppm. Spraints with fish remains, collected from twosites downstream of Athens, had a lower Pb content, at 11.9 and 12.9 ppm. TheHg-concentration of all the spraint samples was below detection and thereforelower than 0.07 ppm. The level of Hg in all freeze-dried crayfish and fishsamples was below 0.07 ppm.

DISCUSSION

Food habits
Studies that analyze spraints of otters to assess their food habits may containa certain amount of error, however, comparative research in captive Eurasianotters (Lutra lutra) reveals that spraint analyses tend to show areasonable match with the actual diet (CARSS and PARKINSON,1996; JACOBSEN and HANSEN, 1996). The results ofwinter food habits are comparable to the data of LAUHACHINDAand HILL (1977). They investigated the winter food habits of the otter inAlabama and Georgia by analyzing 315 digestive tracts and 12 spraints, collectedfrom 1973 to 1977 (siltation was already a widespread problem at this time).Unfortunately, the data from Alabama and Georgia were mixed, but most otterscame from Alabama. Georgia otters were mostly collected from four counties justwest of Clarcke County. The relative frequencies of fish from 5 families -Centrarchidae, Catostomidae, Ictaluridae, Cyprinidae, and Esocidae, and crayfishwere 50.2; 27.7; 6.2; 5.4; 3.3; 2.6 and 37.7% respectively. Indeed,Centrarchidae, Cyprinidae, Catostomidae and Ictaluridae are the most commonlymentioned fish families in reports about the food habits of river otters. Theseresults are not very different from the results presented in Table1, although LAUHACHINDA and HILL (1977) foundslightly more amphibians and insects. Although Cyprinidae were found less thanin the present study, the authors found shiners in the tracts, four times morethan they found creek chubs. Even though extra attention was paid to very smallfish bones, shiners and darters may have been overlooked in the present study.

It could be concluded that there was little change in the food habits of theinland river otter in the southeast since the nineteen seventies.

Crayfish, as part of the river otter's diet, is reported in many foodstudies. In the Smokey Mountains National Park, 95% of the summer spraintscontained crayfish (GRIESS, 1987). McDANIEL(1963) examined 63 stomachs from Florida otters caught in the trappingseason and noted that crayfish had a relative frequency of 17.7%.

KNUDSEN and HALE (1968) found a higher percentageoffish in winter than in other seasons, whilst crayfish was eaten lessfrequently in this season. PARK (1971) suggests that otterseat what is available and accessible in the aquatic habitat; but could crayfishbe a preferred food item?

Because of the abundance and diversity of crayfish in the southeast (PENNAK,1978), one could expect that crayfish would be eaten more frequently in thisarea than elsewhere. The occurrence of crayfish in otter food of, for example,New York State and the Great Lakes Area (HAMILTON, 1961;KNUDSEN and HALE, 1968) is indeed lower than in theresearch of LAUHACHINDA and HILL (1977), GRIESS(1987) and the present research. However, in the three former mentionedpapers, crayfish is said to be an important food source.

Pond turtles are very abundant in the study area, but only once was a pondturtle found as food (Table 1). A similar observation wasmade by GREER (1955). It may be that turtles are eaten morefrequently but that the shell, skin and bones are left behind. This may also betrue with freshwater mussels. If the shells were not eaten, it would be hard todetect consumption without direct observation. Walruses feed largely onmolluscs, but remains were never found in their stomachs (LOCKLEY,1967).

Siltation and food habits
The major environmental problem of the rivers and creeks in the study area issiltation, causing widespread disruption to the ecology of these waters (BURKHEADet al., 1992). The problem is as old as the erosion problem, but is nowadaysmainly caused by road construction or maintenance. Especially in winter, thewater is highly turbid due to silt. Underwater visibility may be limited to 20cmfor most of the year (own observation, 1993). Despite this, the amount of ottersigns indicates a well-developed otter population, compared to data from MASONand MACDONALD (1987, 1993).In Wales, these authors found an average of 3.1 spraints per spraint site (MASONand MACDONALD, 1993), compared to 5.3 in the present research. Both speciesare closely related and show very similar ecology and behaviour and, therefore,this comparison can be justified.

In areas with healthy otter populations in Spain and Greece, MASONand MACDONALD (1987) found, on average, about 75% of the searched stretchespositive for otters. The river otters in our study area do not, therefore,appear to be limited by the heavy siltation.

Does turbid water change the river otter's food habits? The large amount ofcrayfish taken could be partly induced by the heavy siltation, since crayfishare easy to catch, even in turbid water. The research of GRIESS(1987) on Abrams Creek in the Smokey Mountains National Park showed that,from April to September, crayfish was the most frequently taken food item with afrequency of occurrence of 95%, compared to 98% around Athens. Fish wasencountered in 90% and 35% of the spraints resp. The water of Abrams Creek isvery clear (GRIESS, pers. comm.). It cannot be concluded that the high relativefrequency of occurrence of crayfish during summer around Athens is induced byheavy siltation, although relatively more crayfish (66% compared to 40%) andless fish (24% compared to 38%) were taken in summer around Athens than onAbrams Creek. Data on the relative abundance of crayfish in both places arelacking, but it is clear that crayfish is an important food source at bothlocations. In the present research, the majority of fish taken wereCentrarchids. Apart from Centrarchidae, the Cyprinidae, Catostomidae andIctaluridae were also important, the majority of them bottom feeders. In theresearch of GRIESS (1987), otters showed a preference forCyprinidae and Catostomidae amongst fish, the species taken of these groupsbeing mostly bottom feeders. Centrarchidae and Ictaluridae were not common inAbrams Creek; however, more bottom feeding fish were taken in the clear water ofAbrams Creek than in the turbid water of Clarcke County. The preference forbottom feeding fish does not, therefore, appear to be related to turbidity.

Underwater scent as an adaptation to turbidity
Although sight is considered very important for some aquatic mammals (ERLINGE,1968), they are capable of catching fish and other food without the use ofthe eyes. LOCKLEY (1967) describes a completely blindgrey seal (Halicho*rus grypus), living on a rocky coast, that didn'tstarve and even raised young. Also, he explains that the Weddell seal (Leptonychotusweddelli) often feeds in almost complete darkness under the ice. Vibrissae,according to LOCKLEY (1967), play an important role innavigation and feeding in murky or deeper water for aquatic mammals. GREEN(1977) showed that this was also true for otter, by cutting off thevibrissae of a European otter (L. lutra). He observed no difference inhunting success in clear water, but a significant loss of success in turbidwater.

PARK (1971) points out that much of the river otters'food is caught by 'rooting around' in the mud or debris at the bottom of pondsand creeks. This behavior was also often observed in captive otters from localorigin in a small zoo in Athens (own observation, 1993). PARK(1971) states that 'undoubtedly the vibrissae are important to locate foodin the mud'.

In the present research, 34% of the diet from January through March consistedof crayfish, however, crayfish are not active during January and February (HOBBS,1981) and may be very well hidden. MASON and MACDONALD(1986) state that otters in Great Britain forage for hibernating frogs inautumn and winter. KNUDSEN and HALE (1968) explainedfrogs and insects in the winter food by assuming that the otters didconsiderable digging in the bottom sediment.

Hidden immobile animals, such as crayfish in a layer of leaves or ahibernating frog, cannot be detected easily with the vibrissae. Scent may,therefore, play a major role to detect prey under these circ*mstances. DeJONGH (1986) showed that otters could pick up chemical stimuli with theirrhinarium ('wet nose') and he speculated that scent might play an important rolein locating fish at close range. Threatened sunfish, chub, catfish, crayfish,etc. may also hide under stones where vibrissae cannot always reach. Such ahidden animal in turbid water may be rediscovered by scent rather than by touch.Scent seems to be generally underestimated or forgotten by several authors as atool in hunting. The use of underwater scent may be of extra use in turbidwater. The most conspicuous difference between the river otter and the Europeanotter is that the river otter has a much larger rhinarium (MASONand MACDONALD, 1986). Because of this difference, it is possible that theriver otter is better adapted to living in turbid water.

PCBs, organochlorines and heavy metals
Of the pollutants present in the environment, PCBs are the most threatening tootter populations, followed by organochlorines (MASON,1988; BROEKHUIZEN and RUITER-DIJKMAN, 1988). HILLand LOVETT (1975), CUMBIE (1975) and HALBROOKet al. (1981) investigated pollutants in river otters in Alabama andGeorgia. In Georgia (Piedmont and two areas of the Coastal Plain), levels ofPCBs and organochlorines were moderately low. Only about 50% of the 94 ottersfrom the Coastal Plains had detectable levels of PCBs and only about 24% of the34 Piedmont otters. Average concentrations are low compared to data fromEuropean otters (MASON and MACDONALD, 1986), and arewell below the level of concern of 30ppm, and even below the level of no effect(13.3ppm), as defined by de VRIES (1989). However, someindividuals had levels higher than the critical level of 50ppm. Of theorganochlorines, only DDE was high and was detected in more than 50% of theotters. Mercury levels were a little elevated in the Coastal Plain area (CUMBIE,1975), but still below the levels that caused reproductive failure in mink,as found by WOBESER et al. (1976). The nineteen ottersfrom small rivers in Alabama examined by HILL and LOVETT (1975)had even lower levels of organochlorines and PCBs than those found by HALBROOKet al. (1981).

The levels of lead in the spraints analyzed in the present research werecomparable to, or lower than, that from the 450 spraints collected in fourdifferent areas in Great Britain (MASON and MACDONALD,1986). The mercury levels in the spraints of the present research were muchlower. In the crayfish and fish analyzed no elevated Hg-levels could bedetected.

OSOWSKI et al. (1995) examined trapped mink from 1989-1991 in North and South Carolina and Georgia. They suggest that mink from theCoastal Plain had suffered population declines because of elevated mercurylevels. Also, PCB levels were elevated compared to the controls. Mink from thePiedmont area were used as controls. Average PCB levels in 14 mink from threedifferent counties just west of Clarcke County were 0.005 ppm (wet weight liver)while mercury levels were 0.57 ppm (wet weight in kidney). The level oforganochlorines and PCB's was recently measured in a dam lake fed by the OconeeRiver south of Athens (Department of Natural Resources, EPA, Atlanta; personalcommunication). The levels of these pollutants were very low. The Oconeerivershed is known to be more pristine than many other riversheds in Georgia(Freeman, pers. comm.).

From the above it could be concluded with some optimism, that river otters inthe study area were, and are presently, not exposed to critical levels oforganochlorines, PCB's, lead and mercury. Micropollutants were probably not areal obstacle for the recovery of the river otter in the area. The restorationof riparian forests, reduced trapping and the return of beavers, however, mayhave facilitated the return of the otter.

CONCLUSIONS

At present, the river otter population in Clarcke County in the Piedmont areais well developed. The food of the river otter in the study area consists mostlyof crayfish and sunfish. Especially in the summer, crayfish is very important.When comparing food habits in winter in the 1970s (LAUACHlNDAand HILL, 1977) in Alabama and Georgia (when siltation was alreadywidespread) with data of the 1990s, little difference was found. Food habits ofthe river otter are similar in both clear and turbid water. The problem ofsiltation does not, therefore, appear to affect the river otter population orchange its food habits. Micropollutant levels in river otters in the area havebeen relatively low in the past, and remain so presently, as the exposure tomicropollutants still seems to be below critical levels.

ACKNOWLEDGEMENTS - This study would not havebeen possible without the cooperation of the Museum of Natural History inAthens. Special thanks goes to Dr. E.J Reitz, Amy Lynn Edwards and Tracey Jones.Thanks go to Becky Auxier of the Chemical Analysis Laboratory for giving me theopportunity to analyze samples, Terry Moore for helping me with the direction ofthe research and the fieldwork, Prof. Jenkins who gave me information aboutotters in the past, Jane M. Griess for being so helpful and sending me herthesis and other literature, and to Bud J. Freeman for helping me with fishdistribution.

Burkhead, N.M., Williams, J.D., Freeman, B.J. 1992.A river under siege. Is the beautiful Etowah of the cherokees succumbing toAtlanta's urban sprawl? Georgia Wildlife Summer 1992.
Broekhuizen, S., Ruiter-Dijkman, E.M. de 1988.Otters (Lutra lutra) met PCB's: De zeehondjes van net zoete water? Lutra31, 68-78.
Carss, D.N., Parkinson, S.G. 1996. Errors associatedwith otter (Lutra lutra) faecal analyis. I. Assessing general diet fromspraints. J. Zool. 238, 301-317.
Cumbie, P.M. 1975. Mercury levels in Georgia otter,mink and freshwater fish. Bull. Environ. Contam. Toxicol. 14,193-197.
Erlinge, S. 1968. Food studies on captive otters (Lutralutra L.). Oikos 19, 259-270.
Green, J. 1977. Sensory perception in hunting otters,Lutra lutra. J. Otter Trust. 1977, 13-16.
Greer, K.R. 1955. Yearly food habits of the riverotter in the Thompson Lakes Region, north-western Montana, as indicated by scatanalyses. American Midland Naturalist 54, 299-313.
Griess, J.M. 1987. River otter reintroduction inGreat Smokey Mountains National Park. Masters Thesis University of Tennessee,Knoxville, 109pp.
Halbrook, R.S. 1978. Environmentalpollutants in the river otter of Georgia. MScThesis University of Athens,Georgia.
Halbrook, R.S., Jenkins, J.H., Bush, P.B.,Seabolt, N.D. 1981. Selected environmental contaminants in river otters (Lutracanadensis) of Georgia and their relationship to the possible decline ofotters in North America. In: Chapman, J.A., Pursley, D. (eds.). World FurbearerConference Proceedings. World Furbearer Conference, Inc., Frostberg, Maryland.3, 1752-1762.
Hamilton, W.J. 1961. Late fall, winter and earlyspring foods of 141 otters from New York. New York Fish Game J. 8,106-109.
Hill, E.P., J.W. Lovett, J.W. 1975. Pesticide residuesin beaver and river otter from Alabama. Proceedings of the twenty-nineth AnnualConference South-eastern Association Game and Fish Commissioners 1975,365-369.
Hobbs, H.H. Jr. 1981. The crayfishes of Georgia.Smithsonian contribution to Zoology, Smithsonian Institution Press. City ofWashington nr. 318, 549pp.
Jacobsen, L., Hansen, H.M. 1996. Analysis of otterLutra lutra spraints: Part 1: Comparison of methods to estimate preyproportions; Part 2: Estimation of the size of prey fish. J. Zool. 238,167-180.
Jenkins, J.H. 1953. Game resources of Georgia.Georgia Game and Fish Commission. Atlanta Georgia. Fullton Lovell 1953 Edition.
Jenkins, J.H. 1983. The status and managementof the river otter (Lutra canadensis) in North America. Acta Zool.Fenn. 174, 233-235.
Jongh, A.W.J.J. de 1986. Possible evidence forunderwater chemoreception in European otter (Lutra lutra L, 1758). Lutra29, 141-144.
Knudsen, GJ., Hale, J.B. 1968. Food habits ofotters in the Great Lakes region. J. Wildl. Manag. 32, 89 - 93.
Lauhachinda, V., Hill, E.P. 1977. Winter foodhabits of river otters from Alabama and Georgia. Proceedings of the thirty-firstAnnual Conference South-eastern Association of Fish and Wildlife Agencies. 31,246-253.
Lee, D.S., Gilbert, C.R., Hocutt, C.H., Jenkins, R.E.,Allister, D.E., Stauffer, J.R. Jr. 1980. Atlas of North American freshwaterfishes. Publication nr 1980-12 of the North Carolina Biological Survey, 854pp.
Lockley, R.M. 1967. Animal navigation. Lowe &Brydone (Printers) Ltd., London.
Macdonald, S.M., Mason, C.F. 1983. Some factorsinfluencing the distribution of otters (Lutra lutra). Mamm. Rev. 13,1-11.
Mason, C.F., Macdonald, S.M. 1986. Otters:Ecology and conservation. Cambridge University Press. Cambridge, 229pp.
Mason, C.F., Macdonald, S.M. 1987. The use ofspraints for surveying otter Lutra lutra populations: an evaluation. Biol.Cons. 41, 167-177.
Mason, C.F. 1988. Concentrations oforganochlorine residues and metals in tissues of otters Lutra lutra fromthe British Isles. Lutra 31, 62-67.
Mason, C.F., Macdonald, S.M. 1993. PCBs andorganochlorine pesticide residues in otter (Lutra lutra) spraints fromWelsh catchments and their significance to otter conservation strategies. AquaticConservation: Marine and Freshwater Ecosystems 3, 43-51.
McDaniel, J.C. 1963. Otter population study.Proceedings 17th Annual Conference South-eastern Association Game and FishCommissioners 17,163-168.
Melquist, W.E., Hornocker, M.G. 1983. Ecology ofriver otters in west central Idaho. Wildlife Monographs 83,60pp.
Osowski, S.L., Brewer, L.W., Baker, O.E., Cobb, G.P.1995. The decline of mink in Georgia, North Carolina, and South Carolina:The role of contaminants. Arch. Environ. Contam. Toxicol. 29,418-423.
Paloumpis, A.A. 1978. A laboratory manual on fishosteology. Illinois State University. Normal Illinois.
Park, E. 1971. The world of the otter. J.B. LippincottCompany, Philadelphia and New York, 159pp.
Pennak, R.W. 1978. Freshwater invertebrates of theUnited States. Second edition. John Wiley & Sons, New York, 803pp.
Tumlison, R., Karnes, M., King, A.W. 1982. Theriver otter in Arkansas. Indications of a beaver-facilitated commensalrelationship. Proceedings Arkansas Acadamy Science 36, 73-75.
Wobeser, G., Nielsen, N.O., Schiefer B. 1976.Mercury and mink. II. Experimental methyl mercury intoxication. Can. J. Comp.Med. 40, 34-45.
Vries, T.H. de 1989. Effecten van PCB's op devoortplanting van marterachtigen. Institute for Environmental Studies, FreeUniversity Amsterdam.

Résumé : La Loutre de Rivière Nord-Américaine (Lontracanadensis) dans le Comté de Clarcke (Georgia, USA): Étude du RégimeAlimentaire et des Facteurs Environnementaux
Le statut de la loutre de rivière nord-américaine (Lontra canadensis)a été étudié dans et aux environs du Comté de Clarcke (Georgia, USA). Bienqu'ayant presque disparu dans les années 50, la population de loutres apparaîtflorissante actuellement. Le régime alimentaire a été étudié par l'analysed'épreintes en hiver et en été. Perches (Centrarchidae) et écrevisses sontles proies majoritaires. Nous avons cherché à tester si les loutres de cesecteur sont affectées par les pollutions environmentales. Des données de lalittérature et la recherche de quelques métaux lourds suggérent quel'exposition aux pollutions chimiques est relativement faible. La sédimentationdes rivières et ruisseaux n'apparaît pas porter atteinte à la loutre nimodifier ses habitudes alimentaires.Revenez au dessus

Resumen: La Nutria de Río (Lontra canadensis)en el Condado Clarcke (Georgia, USA): un Relevamiento, Hábitos Alimenticios yFactores Ambientales.
Serelevó el estado de la nutria de río (Lontra canadensis) en y alrededordel condado Clarcke (Georgia, USA). A pesar de haber estado casi extinguida enlos años cincuenta, la población de nutrias parece actualmente en buenascondiciones. Se estudiaron los hábitos alimenticios a través de unrelevamiento de fecas en verauo e invierno. Se encontró que los itemsalimenticios más importantes son cangrejos y langostas de rio. Se intentóevaluar si las nutrias en el área de estudio son afectadas por poluciónambiental. Datos de la literatura y algunos análisis de metales pesadosmostraron que la exposición a polución química ha sido relativamente baja. Lasilvatación de ríos y cañadas no parece dañar a las nutrias o modificar sushábitos alimenticios.Vuelva a la tapa

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