Necturus punctatus
Dwarf Waterdog

Dwarf waterdogs (Necturus punctatus) are located in the Piedmont region of the Appalachian Highlands, and more commonly in the southern Atlantic Coastal Plain in the eastern United States. They are found in rivers and streams throughout eastern Georgia and reach as far north as Virginia. The westernmost boundary of their geographic range extends into the broad lowlands of the Triassic Basin in North Carolina. Dwarf waterdogs are present in the Chesapeake Bay region, but only in southeastern Virginia. (Duellman and Sweet, 1999; Dunn, 1918; Hardy Jr., 1972; Martof, et al., 1980)

Optimal habitat for dwarf waterdogs consists of silt-bottomed stream pools with leafy cover. They are also found in open sandy areas and prefer slow-moving water over areas with high flow rates. (Jenson, et al., 2008)

Dwarf waterdogs are the smallest of all water dog species. Adults range in head to tail length from 11.5 to 15.9 mm. For comparison, adult black warrior waterdogs typically range in size from 175 and 200 mm. Females generally have longer tails than males of the same body length, however, males and females of a given body length are typically the same mass. Dwarf waterdogs are slate-gray or brown with small, scattered pale spots. The dorsum tends to be dark, while the venter is often pale in color. In general, waterdogs have red external gills that protrude from both sides of the organism’s head. (Bart, et al., 1997; Conant and Collins, 1998; Lannoo, 2005; Martof, et al., 1980; Meffe and Sheldon, 1987)

Dwarf waterdogs do not undergo metamorphosis and larvae are considered adults once their reproductive system has fully matured. The larval stage lasts for a minimum of 2 years. The smallest reported larva was only 28 mm long. As larvae, their bodies are uniformly brown in color. Juveniles are often found in more shallow water than adults and commonly occur in bundles of leaves. Like larvae, juveniles are brown, but develop a bluish white color along the venter. Dwarf waterdogs become sexually mature by 5 years of age, and when fully mature, they range in length from 26 to 116 mm. (Lannoo, 2005; Willson, et al., 1999)

There is no information available regarding the mating system of dwarf waterdogs.

Little is know of the reproductive behavior of dwarf waterdogs, however, other waterdog species reproduce aquatically. The larger a dwarf waterdog, the greater the number of oocytes in the ovaries, which contain yolked and unyolked oocytes during mid-autumn. Most pregnant females carry 15 to 55 eggs. Average egg diameter has been reported as 4 and 4.2 mm and may depend on the number of eggs being carried. Prior to mating, which occurs during winter, male testes become large, firm, and yellow with dark pigmentation. Despite gender, individuals reach reproductive maturity by age 5 or when they become 65 to 70 mm in head-body length. Although no nests have been discovered, it is thought that dwarf waters attach their eggs to the underside of logs and other objects in the water. (Folkerts, 1971; Lannoo, 2005; Meffe and Sheldon, 1987)

There is no information available regarding parental care in dwarf waterdogs.

Only limited information on the lifespan of dwarf waterdogs exists. A single specimen captured in the wild and taken to the Cincinnati Zoo lived for 5 years and 8 months. Because they reach sexual maturity at 5 years of age, dwarf waterdogs likely live for more than 10 years. However, no information exists to confirm this. (Folkerts, 1971; Lannoo, 2005)

Little information is available concerning the general behavior of dwarf waterdogs. Numerous dwarf waterdogs are commonly found inhabiting a single area, suggesting these animals are not territorial. They do not hibernate, remaining active even during the wintertime. In order to minimize the effects of cold during winter, dwarf waterdogs often heap together in leaf litter. (Lannoo, 2005)

The average home range size of dwarf waterdogs is currently unknown. Black warrior waterdogs in the Grand River of northeastern Ohio have an average home range of 136.1 square meters during the summer. However, this is the largest of waterdog species and thus, it likely has a larger home range than do dwarf waterdogs. (Lannoo, 2005)

There is no information available concerning communication and perception in dwarf waterdogs. (Folkerts, 1971; Lannoo, 2005)

Dwarf waterdogs are predatory and commonly consume gastropods, pelecypods, oligochaetes, arachnids, isopods, cladocerans, ostracods, copepods, amphipods, chilopods, and a variety of insects. In addition, adults often comsume annelids, crayfish , and even other salamanders, suggesting they may be cannibalistic. Young have been known to eat annelids, amphipod, millipedes, and insects and their larvae. Evidence suggests that males reduce, or even discontinue feeding activity during the breeding season, though larvae are thought to feed throughout the entire year. (Braswell and Ashton Jr., 1985; Folkerts, 1971; Meffe and Sheldon, 1987)

Although no evidence exists suggesting predators specific to this species, dwarf waterdogs likely fall prey to predaceous organisms inhabiting the same areas. Potential predators include aquatic insects and snakes, crayfish, and large salamanders. Although no evidence exists regarding anti-predatory behavior in dwarf waterdogs, they likely hide from potential threats in the soft substrate. Their coloration camouflages them from potential predators and likely helps reduce risk of predation. (Lannoo, 2005)

Dwarf waterdogs prey upon the aquatic larvae of numerous arthropods, which may help control insect pests throughout its geographic range. Although parasites specific to this species are not known, the gills and skin of congenerics have proven to be prime habitat for a number of different endo and ectoparasites, such as trematodes. Proteochephalids inhabit the intestines of certain waterdog species. (Lannoo, 2005; Tobey, 1985)

Recreational fishermen commonly use waterdogs as bait for largemouth bass and catfish. (Lannoo, 2005)

There are no known adverse effects of dwarf waterdogs on humans.

Although dwarf waterdogs are classified as a species of least concern on the IUCN's Red List of Threatened Species, current population trends are unknown and thus, potential threats to their persistence are difficult to predict. Dwarf waterdogs occur in several protected areas throughout their geographic range. (Lannoo, 2005; Tobey, 1985)