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Observations of Raccoon (Procyon lotor) Predation on the Invasive Maculata Apple Snail (Pomacea maculata) in Southern Louisiana
Jacoby Carter, Sergio Merino, Drew Prejean, and Gary LaFleur Jr.

Southeastern Naturalist, Volume 16, Issue 3 (2017): N14–N18

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2017 Southeastern Naturalist Notes Vol. 16, No. 3 N14 J. Carter, S. Merino, D. Prejean, and G. LaFleur Jr. Observations of Raccoon (Procyon lotor) Predation on the Invasive Maculata Apple Snail (Pomacea maculata) in Southern Louisiana Jacoby Carter1,*, Sergio Merino1, Drew Prejean2, and Gary LaFleur Jr.2 Abstract - We used camera traps to determine which predators were responsible for depredated Pomacea maculata (Maculata Apple Snail) shells at 2 different study sites. Evidence of predation at these sites included operculums near the shells with a small amount of flesh attached and shells accumulating a meter or more from the water’s edge with no evidence of recent flooding. In both locations, the most frequently observed potential predators were Procyon lotor (Raccoon), which was the only species directly observed capturing and eating Apple Snails. Introduction. Pomacea maculata Perry (Maculata Apple Snail, hereafter Apple Snail) are an invasive freshwater snail, native to South America but widely introduced globally. Its distribution range has been expanding in freshwater wetlands across the Gulf of Mexico coast for over 10 years (Benson 2017). In Laos, a sister species, Pomacea canaliculata (L.) (Channeled Apple Snail), shifted the primary production in aquatic ecosystems from submerged aquatic vegetation to algae (Carlsson and Lacoursiére 2005), and there is evidence that Apple Snails may have the same potential in the Everglades (Baker et al. 2010). Anecdotally, it has been reported that as Apple Snail populations become established in south Louisiana they have reduced submerged aquatic vegetation (Bonin 2016), an important component in local wetland ecosystems (Bardwell et al. 1962, Castellanos and Rozas 2001, Chamberlain 1959, Marklund et al 2002). Another potential negative impact on native ecosystems is snail depredation on amphibian eggs (Karraker and Dudgeon 2014). Predators that eat Apple Snails may control them in some systems (Barr 1997, Yamanishi et al. 2012). Apple Snails have many potential predators (Dorn and Hafsadi 2016, Hayes et al. 2015, Yusa et al. 2006), with the smallest snails being the most vulnerable. As snails grow, they become too large for predators such as Lepomis microlophus Günther Redear (Sunfish) and crayfish (Family: Astacidea). Currently we only have anecdotal information about the identity of those predators in south Louisiana and along the coast of the Gulf of Mexico. Delany and Abercrombie (1986) reported finding operculums in the stomachs of Alligator mississippiensis Daudin (American Alligator) in Florida, as have alligator hunters in south Louisiana (D. Ledet, Alligator Farm, Houma, LA, 22 December 2016 pers. comm.; Elsey et al., in press; H. Cox Jr, Herb’s Pest Control, Houma, LA, 12 October 2016 pers. comm.). An anonymous writer to an online blog based in south Louisiana posted a photograph of partially digested Apple Snail shells inside the stomach of a frog, most likely in the genus Lithobates, that he or she had captured (Apple Snails 2014). There are 2 bird species in Florida that eat Apple Snails as their primary prey, Aramus guarauna L. (Limpkin) and Rostrhamus sociabilis Vieillot (Snail Kite), and both species’ ranges in the United States are restricted to the range of the native Pomacea paludosa Say (Florida Apple Snail) (Bryan 2002, Reichert et al. 2015). 1US Geological Survey, Wetland and Aquatic Research Center, Lafayette, LA 70506. 2Department of Biological Sciences, Nicholls State University, Thibodaux, LA 70310. *Corresponding author - Manuscript Editor: Roger Applegate Notes of the Southeastern Naturalist, Issue 16/3, 2017 N15 2017 Southeastern Naturalist Notes Vol. 16, No.3 J. Carter, S. Merino, D. Prejean, and G. LaFleur Jr. We investigated 2 locations in Louisiana where there is apparent Apple Snail depredation. Evidence that these are sites where predators are processing Apple Snails, as opposed to sites where dead snails are simply being washed up, are as follows: (1) the empty snail shells are often “fresh”, in that they are wet and not weathered; (2) the shells are a meter or more from the water’s edge when there has been no recent flooding; (3) the shells are concentrated in a few areas that can be characterized as patches rather than evenly dispersed along the shore or distributed in a linear fashion as if they had been carried in on a tide; (4) there are operculums with some meat still attached (Fig. 1) next to the shells where the opening of the shell matches the size of the operculum; and (5) there are remains of ovaries without any other flesh present (Fig. 1) next to several shells, suggesting that the predator was avoiding the toxins snails produce to protect their eggs (Giglio et al. 2016). To determine which predators were responsible for the observed predation, we set up camera traps in 2 different locations at the edges of a lake and a permanently floode d cypress swamp. Field sites and methods. The study sites were in south Louisiana at Mandalay National Wildlife Refuge (29°32'23"N, 90°49'2"W), and at the Chacahoula off-ramp of Louisiana Highway 90 (29°42'29"N, 90°54'5"W). All camera traps were manufactured by Moultrie (models: P-150, 150i, M880, and 880i.) and were set to take 10–15-second videos stored on SD cards. The cameras were triggered to take videos by a built-in motion detector. We used several models at the same time at both locations. We viewed the videos recorded on the SD cards and if a potential predator appeared, noted the species, apparent activity (resting, foraging, eating, or passing through), time, date, and video ID . Figure 1. The remains of depredated an Apple Snail at Mandalay NWR, LA. The shell is in the upper middle half of the frame. Circled on the left is the operculum with flesh still attached, and on the right the discarded ovary (red). 2017 Southeastern Naturalist Notes Vol. 16, No. 3 N16 J. Carter, S. Merino, D. Prejean, and G. LaFleur Jr. The Chacahoula study site was a permanently flooded cypress swamp encircled by a road and highway on- and off-ramps. Submerged and floating-leaved aquatic vegetation was sparse. Taxodium distichum (L.) (Rich Bald Cypress) dominated the overstory. Apple Snail egg masses had been observed on trees and other objects emerging from the water and depredated shells had been found on shore (J. Carter, unpubl. data). As part of a separate predation experiment (J. Carter et al., unpubl. data), Apple Snails were attached to tethers, which were in turn attached to stakes. We staked the tethered snails in the water near shore and placed between 6 and 8 camera traps so that they faced either the area where the snails were staked or the adjacent shore. We checked the stakes periodically to see if snails had been removed and examined the video to identify any non-aquatic predators. Camera-trap data for this study site was collected September through March 2016. The Mandalay study site was at the edge of a lake on Mandalay NWR. The most prominent near-shore habitat feature was a thick mat of Eichhornia crassipes (Mart.) Solms (Water Hyacinth). In January 2017, four camera traps were placed in different locations inside a 4-m buffer around the north and northwest side of a peninsula, covering an ~80-m2 area. We placed cameras so that they faced the water and adjacent shore area. Camera-trap data for this study were collected January through March 2017. Results. The cameras were frequently triggered by weather events. Of the videos that captured wildlife, most were not definitive enough to say an animal was capturing or eating snails. For example, of 884 videos recorded at Mandalay in one 4-week period, we recorded reasonably certain and clear instances of an animal handling or eating a snail only 12 times (Carter et al. 2017). Snails at Chacahoula were taken regularly from their tethers. Potential avian predators were seen infrequently. They included Ardea herodias L. (Great Blue Heron), Egretta caerulea L. (Little Blue Heron), and Egretta thula Molina (Snowy Egret). No birds were seen eating or handling Apple Snails. One potential non-avian predator observed was Neovison vison Schreber (American Mink), but only a single individual was recorded passing through the site once. The most frequently observed potential non-avian predator was Procyon lotor L. (Raccoon). One video, recorded on 5 January 2017, shows a Raccoon manipulating a snail. Figure 2. Raccoon capturing a snail under a Water Hyacinth mat, Mandalay NWR, LA. N17 2017 Southeastern Naturalist Notes Vol. 16, No.3 J. Carter, S. Merino, D. Prejean, and G. LaFleur Jr. The same potential avian predators seen at Chacahoula were seen at Mandalay, but they were seen more frequently. While birds were frequently seen foraging on the Water Hyacinth mat, no birds were observed handling or eating Apple Snails. Potential non-avian predators observed were Lynx rufus Schreber (Bobcat) and American Alligators. These species were either moving through the site or resting and were not observed foraging for or eating snails. Raccoons were responsible for almost all of the non-avian vertebrate observations. Raccoons were frequently observed foraging on the floating hyacinth mat by reaching into the water with their front paws while keeping their head above water. On more than 5 occasions, we recorded Raccoons pulling snails out of the hyacinth mat and then carrying them to shore to eat them (Fig. 2). On other occasions, Raccoons were observed eating snails that were caught off camera. We measured the shells to determine the size range of snails being depredated. Shell heights ranged from 32.7 to 88.9 mm; thus Raccoons are taking both juveniles and adults (J. Carter, unpubl. data). Discussion. We have documented that Raccoons are a predator of Apple Snails in 2 different wetland habitats (a swamp and the edge of a lake) 19 km apart in south Louisiana. It is unknown what overall impact Raccoons are having on the snails, but the presence of hundreds of snail shells at the Mandalay site suggests that it might be locally significant. For Raccoons to forage for Apple Snails they need either shallow water like the flooded forest at Chacahoula, or access to floating mats of vegetation they can walk on and can reach into with their forepaws as observed at Mandalay. Further studies are planned to estimate the impact of Raccoon predation on Apple Snails. Acknowledgments. Funding for this project was provided by the USGS Invasive Species Program and the USGS Wetland and Aquatic Science Center. Additional support and facilities were provided by Nicholls State University, Thibodaux, LA. We would also like to thank Brian Pember, US Fish and Wildlife Service’s Mandalay National Wildlife Refuge, for his support. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the US Government. Literature Cited Apple Snails. 2014. Louisiana Sportsman blog. Available online at http://www.louisianasportsman. com/lpca/index.php?section=reports&event=view&action=full_report&id=184031. Accessed 6 March 2017. Baker, P., F. Zimmanck and S.M. Baker. 2010. Feeding rates of an introduced freshwater gastropod, Pomacea insularum, on native and nonindigenous aquatic plants in Florida. Journal of Molluscan Studies 76:138–143. Bardwell, J.L., L.L. Glasgow, and E.A. Epps Jr. 1962. 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