2012 NORTHEASTERN NATURALIST 19(2):157–164 Winter Diet of River Otters in Kentucky Erin E. Barding1 and Michael J. Lacki1,* Abstract - Lontra canadensis (River Otter) have been reintroduced throughout much of their former range in North America, but our understanding of the function they serve in ecosystems to which they have been reintroduced remains incomplete. We examined the winter diet of reintroduced River Otters in Kentucky based on contents of 126 stomachs collected over three trapping seasons, 2006–2009. Fish and crayfish were the main prey, occurring in 86% and 27% of stomachs containing prey items, respectively. We identified 8 families and 11 genera of fish and 4 genera and 6 species of crayfish in the diet of River Otters. The most frequently consumed family of fish by occurrence was Centrarchidae (36%), followed by Catostomidae (11%), Cyprinidae (11%), and Clupeidae (7%). Centrarchidae were also found at the greatest volume (53%) of any family of fish, followed by Catostomidae (14%), Clupeidae (12%), and Cyprinidae (12%). Of the centrarchids, Group A fish (Lepomis, Ambloplites, and Pomoxis spp.; 28%) occurred at a higher percent in the diet of River Otters than Group B fish (Micropterus spp.; 5%). River Otter diets did not vary between males (n = 68) and females (n = 58), adults (n = 46) and juveniles (n = 80), or those from the western (n = 64) and eastern (n = 62) regions of the state. Introduction The diet of Lontra canadensis Schreber (River Otter) varies seasonally with prey availability (Melquist and Hornocker 1983, Modafferi and Yocom 1980, Stenson et al. 1984). Fish are important prey throughout the year, occurring in the diet of every population of River Otters examined (e.g., Cote et al. 2008, Manning 1990, Melquist and Hornocker 1983, Ryder 1955). River Otters have been reintroduced into much of their historic range across North America (Raesly 2001). In Kentucky, the Department of Fish and Wildlife Resources (KDFWR) reintroduced River Otters (n = 355) across 14 sites in the central and eastern part of the state from 1991 to 1994 (Cramer 1995). An increased frequency of sightings, roadkills, and nuisance complaints, combined with successful harvests (Barding et al. 2010), suggests that the River Otter population in Kentucky is now established. Since the reintroduction, there has not been a comprehensive examination of the Kentucky River Otter population (Barding et al. 2010), so the function this species serves in ecosystems to which it has been reintroduced needs to be evaluated. Here we present a statewide analysis of the winter diet of River Otters in Kentucky. Kentucky is comprised of seven physiographic provinces (McGrain 1983, Palmer-Ball 1996), each of which is dissected by one or more primary watersheds. We identified 12 major watershed basins in the state and subdivided them into eastern and western regions for comparisons. The eastern region 1Department of Forestry, University of Kentucky, Lexington, KY 40546. *Corresponding author - mlacki@uky.edu. 158 Northeastern Naturalist Vol. 19, No. 2 included the Big Sandy, Kentucky River, Licking River, Ohio River, Tygarts Creek/Little Sandy River, and Upper Cumberland River watersheds, while the western region included the Green River, Lower Cumberland River, Mississippi River, Salt River/Rolling Fork, Tennessee River, and Tradewater River watersheds. Due to settlement, vegetation and habitats across Kentucky have been highly altered from their original condition, and existing conditions likely affect reintroduced River Otters differently than those that were present pre-settlement. Surface mining in portions of both the western and eastern regions of the state has produced open habitats and alterations in land form that have negatively affected shape and form of drainage basins and water quality in some areas. Methods We used stomach contents to identify diets of River Otters, because carcasses could be readily acquired from trappers across all watersheds in the state, and because food items with a large proportion of hard material are typically overestimated when using scats to identify the diet of River Otters (Erlinge 1968). Regardless, our results were interpreted to reflect importance of prey items in the diet of River Otters without drawing inferences on either preference or availability of prey. We obtained frozen River Otter carcasses from Kentucky trappers during three statewide harvest seasons (November– February), 2006–2009. We attempted to obtain samples of otters from each of the 12 watershed basins. A lower canine was pulled from each individual, and age was determined by cementum annuli examination (Matson’s Laboratory, Milltown, MT). We considered a River Otter ≥2 years of age to be an adult. We removed stomachs from carcasses, placed them into plastic containers, and stored them at approximately -20 °C for future identification of contents. Stomachs were thawed, washed, strained, and the contents identified to lowest possible taxonomic group. We estimated percent volume (percentage of contents per stomach sample represented by a prey group) and percent occurrence (percentage of stomachs in which a prey group occurred), and calculated the average percent volume as the sum of individual volumes/number of stomachs x 100 for each prey group. We examined fish scales under a 25x dissecting scope and identified samples using a field guide (Daniels 1996) and a scale reference library. We categorized scales of Centrarchidae into three groupings: those which could not be identified beyond the family level (unknown); those which contained sunfishes, crappies, and rock bass (Group A); and, those which contained black bass such as Micropterus salmoides (Lacepède) (Largemouth Bass), Micropterus dolomieu Lacepède (Smallmouth Bass), and Micropterus punctulatus (Rafinesque) (Spotted Bass) (Group B). Scales belonging to families identified as other than Centrarchidae were verified with state geographic range information (KDFWR 2009). Crayfish remains were identified following Taylor and Schuster (2004). 2012 E.E. Barding and M.J. Lacki 159 We analyzed data with contingency tables and compared differences in food habits of males and females, juveniles and adults, and River Otters collected from eastern and western Kentucky. We used chi-square analysis to determine differences in percent occurrence. Differences were considered significant when P < 0.05. All methods used in this study were approved by the University of Kentucky Institutional Animal Care and Use Committee (IACUC No. 00992A2006). Results and Discussion We examined 170 River Otter stomachs: 93 collected during the 2006–2007 trapping season, 49 from 2007–2008, and 28 from 2008–2009. Ninety carcasses were collected from the western region of the state, and 80 from the east. Of the stomachs examined, 74% (n = 126) contained food item remains. An explanation for the high number of carcasses without food items present is not clear, although similar patterns were reported for populations of otters sampled in the Great Lakes region (Knudsen and Hale 1968). Vegetative material was observed in River Otter stomachs (17% by occurrence and 11% by volume). Other studies have reported vegetation in the diet of River Otters (stomachs and intestines: Knudsen and Hale 1968; scats: Skyer 2006), but concluded that vegetation was not likely eaten as food but instead ingested indirectly while consuming other items. Thus, we presumed vegetative material was taken in the process of eating other items and, therefore, was not considered in calculations of percent occurrence or percent volume. Fish and crayfish were the most important winter prey of River Otters in Kentucky, occurring in 86% and 27% of all stomachs examined which contained food items, respectively. Rana spp. (frogs), snakes, turtles, and Anas platyrhynchos L. (Mallard) were also identified in the diet. There was no difference in the relative percentage of prey items taken between males and females (χ5 2 = 5.04, P = 0.41), juveniles and adults (χ5 2 = 2.42, P = 0.79), or River Otters collected from eastern and western regions (χ5 2 = 10.62, P = 0.06). The outcome for the regional test approached significance, suggesting that some difference might exist between dietary patterns of River Otters in eastern and western Kentucky, with more predation on fish species and less predation on crayfish species in the eastern region (Table 1). Whether this pattern is due to varying availabilities between regions of these two food item groupings is not immediately clear. We identified 8 families and 11 genera of fish in River Otter stomach samples (Table 2). Centrarchidae were eaten most frequently, with Catostomidae (suckers), Cyprinidae (minnows), and Clupeidae (shads) also common in the winter diet of otters. Group A fish (sunfish and crappie species) comprised the majority of the Centrarchidae eaten, with Group B fish (black bass species) only occurring in 5% of stomachs that contained food items. There was no difference in the relative proportion of fish families taken between male and female River Otters (χ7 2 = 13.05, 160 Northeastern Naturalist Vol. 19, No. 2 P = 0.07). We identified four genera and six species of crayfish in stomach samples (Table 3). Crayfish in the genus Orconectes were eaten most frequently, with O. rusticus (Girard) (Rusty Crayfish) the most commonly recorded species of crayfish. Table 2. Percent occurrence and volume of fish families identified in stomachs of River Otters (n = 126) during three trapping seasons in Kentucky, 2006–2009. The number of stomachs containing prey items is indicated. Family n % occurrence % volume Amiidae Amia calva L. 1 1 1 Catostomidae 14 11 14 Erimyzon spp. 2 2 3 Catostomus spp. 4 3 1 Moxostoma or Hypentelium nigricans Lesueur 3 2 4 Unknown 5 4 6 Centrarchidae 45 36 53 Group A (Lepomis, Ambloplites, and Pomoxis spp.) 35 28 40 Group B (Micropterus spp.) 6 5 5 Unknown 8 6 8 Clupeidae Dorosoma spp. 9 7 12 Cyprinidae 14 11 12 Native minnow spp. 12 10 9 Eurasian carp spp. 2 2 3 Esocidae Esox spp. 3 2 2 Percichthyidae Morone spp. 4 3 5 Percidae Darters 1 1 0 Table 1. Percent occurrence and volume of prey groups identified in stomachs of River Otters: male (M) and female (F), juvenile (J) and adult (A), and those from western (W) vs. eastern (E) Kentucky during three trapping seasons, 2006–2009. The number of stomachs is indicated. Sex Age-class Region % occurrence % volume % occurrence % volume % occurrence % volume (n = 68) (n = 58) (n = 80) (n = 46) (n = 64) (n = 62) Prey group M F M F J A J A W E W E Fish 84 88 78 77 81 94 73 85 77 95 69 86 Crayfish 25 31 14 14 25 30 17 12 31 24 15 13 Frog 2 10 1 4 4 7 1 3 9 2 4 0 Reptile 2 2 2 2 3 0 3 0 3 0 3 0 Bird 2 0 2 0 1 0 1 0 2 0 2 0 Unknown 6 9 5 4 8 7 6 1 11 3 8 1 2012 E.E. Barding and M.J. Lacki 161 Catostomids, cyprinids, and clupeids were commonly consumed by River Otters in Kentucky and, thus, represent important items in the diet of these carnivores. These results are consistent with research on otter diets in similar habitats where these fish assemblages occur (Anderson and Woolf 1987, Knudsen and Hale 1968, Manning 1990, Toweill 1974). Centrarchids were consumed most frequently of any family of fish in our study (36% occurrence). This outcome corroborates patterns in winter and early spring diets of otters in New York (Skyer 2006), and across all seasons in Massachusetts (Sheldon and Toll 1964) and Illinois (Anderson and Woolf 1987), where centrarchids occurred in >50% of otter scats. The majority of centrarchid scales in River Otter stomach samples belonged to Group A, or the sunfishes, crappies, and rock bass. Our data indicate that black bass species are not being taken by River Otters to the same extent as the sunfish/ crappie group during winter months, and do not appear to represent a significant component of the diet of River Otters in Kentucky. However, observations from other seasons were not included in our analysis, and shifts in the diet of River Otters across seasons and among locations in the state are likely (Anderson and Woolf 1987, Sheldon and Toll 1964, Skyer 2006); more data are needed to document potential seasonal changes in diet. In areas where they are locally and seasonally abundant, crayfish are also important prey of River Otters (Knudsen and Hale 1968, Manning 1990, Sheldon and Toll 1964, Toweill 1974), and can replace fish as the most important food source during summer months (Noordhuis 2002, Roberts et al. 2008, Route and Peterson 1988). Crayfish were an important component, by both percent occurrence and percent volume, of the winter diet of River Otters in Kentucky, although many crayfish remains were reduced to minute fragments of exoskeleton and difficult to identify. We identified three genera (Fallicambarus, Orconectes, and Procambarus) and six species of crayfish previously Table 3. Percent occurrence and volume of crayfish identified in River Otter stomachs (n = 126) during three trapping seasons in Kentucky, 2006–2009. The number of stomachs possessing crayfi sh species/genera is indicated. Crayfish n % occurrence % volume Cambarus spp. 1 1 3 Fallicambarus fodiens Cottle 1 1 0 Orconectes spp. 2 2 6 O. cristavarius Taylor 1 1 2 O. juvenilis Hagen 2 2 6 O. rusticus Girard 6 5 16 Procambarus acutus Girard 1 1 0 P. viaeviridis Faxon 1 1 0 Unknown 21 17 66 162 Northeastern Naturalist Vol. 19, No. 2 unrecorded in the diet of River Otters (Table 3), along with Cambarus, a genus of crayfish common in the diet of River Otters elsewhere (Grenfell 1974, Lagler and Ostenson 1942). Half of the classifiable crayfish were identified as Orconectes spp., the majority of which are common and widespread throughout Kentucky (Fetzner 2008). Members of Orconectes rarely burrow (Taylor and Schuster 2004) and may be more vulnerable to River Otters compared with other crayfish genera (Taylor and Schuster 2004). We did record evidence of O. cristavarius Taylor (Spiny Stream Crayfish), a species of concern (Fetzner 2008), in one stomach sample, and Procambarus viaeviridis (Faxon) (Vernal Crayfish), a threatened species (KSNPC 2004), in another sample. Given that crayfish contents in many stomach samples could not be identified beyond the genus, it is likely that evidence of predation is underestimated in our analysis. This is especially the case with crayfish in the genus Cambarus, where we were unable to identify individual species and where numerous species are of special concern in Kentucky (Fetzner 2008, KSNPC 2004). We encourage continued monitoring of sportfish and crayfish populations in Kentucky, especially in watersheds with high River Otter densities, because studies in Michigan, New York, and Missouri have all demonstrated River Otters to switch their predation patterns between fish and crayfish among seasons (Knudsen and Hale 1968, Roberts et al. 2008, Skyer 2006). Acknowledgments Funding for this project was provided by Kentucky Department of Fish and Wildlife Resources and the College of Agriculture, University of Kentucky. We thank G. Schuster (Department of Biological Sciences, Eastern Kentucky University) and J. Krupa (Department of Biology, University of Kentucky) for assistance with identification of prey; E. Carlisle provided laboratory assistance. This paper (KAES No. 10-09-070) is a product of the Kentucky Agricultural Experiment Station and is published with the approval of the Director. Literature Cited Anderson, E.A., and A. Woolf. 1987. River Otter food habits in northwestern Illinois. Transactions of the Illinois Academy of Science 80:115−118. Barding, E.E., M.J. Lacki, and L.L. Patton. 2010. Recovery of the River Otter to Kentucky. Proceedings Annual Conference Southeastern Association Fish and Wildlife Agencies 64:112–117. Cote, D., H.M.J. Stewart, R.S. Gregory, J. Gosse, J.J. Reynolds, G.B. Stenson, and E.H. Miller. 2008. 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