Amphibians of North Carolina

Scientific Name:	Common Name:		Family (Alpha):

NC Records
Proteidae Members:
Necturus lewisi - Neuse River Waterdog

Taxonomy

Class: Amphibia

Order: Caudata

Family: Proteidae


Taxonomic Comments: Necturus lewisi was originally described by Brimley (1924) as a subspecies of N. maculosus, but has been recognized since 1937 as a valid species. Electrophoretic and chromosomal comparisons of Necturus by Ashton et al. (1980) and Sessions and Wiley (1985) provide convincing evidence that N. maculosus, N. punctatus, and N. lewisi are all distinct species.
Species Comments:

Identification

Description: The Neuse River Waterdog is a medium-sized Necturus with a rusty brown to yellowish-brown dorsum that is marked with numerous large spots or blotches that are bluish black. The sides are usually noticeably darker than the dorsum on younger specimens, and a dark line is often evident that extends from the gill region through the eyes to the snout. The venter varies from dull brown to gray and is also spotted, but the spots are smaller than those on the dorsum. The spots in this species tend to be larger and less numerous than those on N. maculosus, and the ground color is lighter (Beane et al. 2010, Petranka 1998). The adults have 14 costal grooves and the snout is dorsally compressed and truncated. The tail is laterally compressed and keeled, and there are four toes on each hindlimb. This is a permanently aquatic species with bushy, reddish gills that are retained throughout life. Sexually active males have a swollen cloaca and two enlarged cloacal papillae that point to the rear. The sexes are similar in size, and the adults range from 16.5-28 cm TL.

The hatchlings vary from 15-16 mm SVL (22-24 mm TL) and are uniformly dark brown above with a white spot behind each eye (Ashton and Braswell 1979). The undersides are immaculate and contrast sharply with the pigmented lower sides of the body. Individuals 21-41 mm SVL have a broad, light tan dorsal stripe that extends from the head to the tail. The light dorsal stripe is usually flanked on either side by a dark lateral stripe that extends from the snout to the tail (Ashton and Braswell 1979, Petranka 1998). The lateral stripes gradually disappear as individuals mature and are sometimes poorly defined in small larvae. The venter is either white, or has a faint, reticulate pattern.

Online Photos: Google iNaturalist

AmphibiaWeb Account

Distribution in North Carolina

Distribution Comments: Necturus lewisi is endemic to the Neuse and Tar-Pamlico River basins in the eastern Piedmont and Coastal Plain of North Carolina.
County Map: Clicking on a county returns the records for the species in that county.


GBIF Global Distribution

Key Habitat Requirements

Habitat: Braswell and Ashton (1985) found that populations in the Piedmont Plateau and along the Fall Line were most likely to be encountered in clean, moderate to swift flowing streams with widths over 15.5 m. Smaller streams were less frequently inhabited and specimens were only occasionally encountered in streams less than 5.5 m wide. Specimens from the Coastal Plain were mostly found in or near the mainstream of the Neuse and Tar rivers or their largest tributaries, and were found downstream close to waters that are occasionally influenced by salt water.

Braswell and Ashton (1985) noted that individuals were most abundant in stream sections where the main channel flow is > 10 cm/second and the stream is > 15 m wide and 1 m deep. Capture success was highest in stream sections with clay or hard-soil substrates and lower in leaf beds, even though some consider leaf beds to be the preferred habitat (Brimley 1924, Martof et al. 1980). Smaller streams with sluggish or stagnant summer flow during droughts were not occupied. The prey that was consumed by the adults indicates that they feed in a broad range of habitats, including in flowing and slack waters, in leaf beds, under logs and rocks, and in sand and gravel beds. Immature individuals were mostly collected from leaf beds in relatively quiet water, but it is uncertain how essential this habitat is for completing the life cycle.

Biotic Relationships: Brandon and Huheey (1985) injected mice with skin extracts of N. lewisi and observed evidence of distress. This suggests that individuals may have chemical defenses against predatory fish.

Life History and Autecology

Breeding and Courtship: The adults mate during the winter months and most females appear to lay eggs in May or early June. Fedak (1971) found that the testes of males from North Carolina were swollen in early fall, and the vasa deferentia were packed with sperm from November through May. The cloacal glands were swollen during this period, but swelling progressively decreased from late March through May. Sperm was present in the spermathecae of females from December through May, and the largest yolked eggs were found in April and May.

The only description of courtship is that of Ashton (1985) who observed partial courtship between a pair of adults in an aquarium on 8 March (Petranka 1998). The pair was first observed crawling slowly with a male following 2-4 cm behind the female's tail. When the female stopped, the male moved forward and positioned his snout just behind the rear leg of the female. The male then moved across her body at the base of her tail. Once their bodies were parallel, the male began to stroke and rub the female with his chin. Stroking began on the top of the head, then posteriorly along the female's neck and mid-dorsum, then back again to the head. The female raised her head at a 30 degree angle with the substrate every time the male's chin contacted her neck or head. This sequence was repeated 12 times during a 5 minute interval. The entire chin rubbing phase lasted 18 minutes. During the second phase the male slowly circled the female in a clockwise direction while maintaining contact with her. Three complete circles were made in 6 minutes, at which point the male moved parallel to the female and placed his limbs over her dorsum. The pair remained in this position for 30 minutes, then moved to a retreat.

Reproductive Mode: The females move to nesting sites beneath large rocks or other cover that is in fast currents during the spring. They are presumably capable of long-term sperm storage in their spermathecae since mating often occurs several months before egg laying begins. Oviposition occurs in April and May based on the time when ovarian eggs reach their maximum seasonal size (Ashton 1985, Cooper and Ashton 1985, Fedak 1971, Petranka 1998). Ashton and Braswell (1979) found a nest on 2 July beneath a flat rock in 1.3 m of water that was attended by a male. The nest contained 35 egg capsules attached singly by a blunt stalk to a 60 cm2 area on the underside of a flat granite rock. The nest was in midstream, about 2 m from shore and 1.2 m below the water surface. All but three of the embryos had hatched, and the capsules that remained were 8-9 mm in diameter. Seven additional nests were subsequently observed by Alvin Braswell (AmphibiaWeb 2021) during May and June and all were under rocks in water 25–41 cm deep in areas that received only about 2 hours per day of direct sunlight. Six nests had a single attending female, with the females ranging from 93–120 mm SVL. The other attending adult escaped and could not be sexed. Clutch sizes for the seven nests were 19, 21, 22, 20, 22, 36, and 32 eggs. Populations in the Coastal Plain probably use substrates such as sunken logs and debris piles to nest since flat rocks are unavailable in many areas of the Neuse and Tar-Pamlico River basins.

Aquatic Life History: Very little is known about the ecology of the hatchlings and small juveniles. They appear to seek out quiet waters and are often found in leaf beds that provide both cover and foraging sites (Braswell and Ashton 1985). However, Ashton (1985) reported that the juveniles mostly remained beneath granite boulders, except in early spring when some moved into leaf beds. The most numerically important prey in 36 juveniles that were examined by Braswell and Ashton (1985) were ostracods, copepods, mayflies, true flies and beetles. Earthworms, cladocerans, isopods, amphipods, collembolans, odonates, and stoneflies were also consumed.

The adults generally remain beneath cover during the day and actively move about at night when fish and other potential predators are less active. Although precipitation seems to have no direct effect on activity, Braswell and Ashton (1985) found that individuals are more active during periods with rising water levels and higher turbidity. The functional cover of sorts that turbidity provides -- along with the increase in terrestrial food items produced by runoff and rising water -- may trigger greater activity under these conditions.

The home ranges of two adult females that were monitored by Ashton (1985) were 16-19 m2, while those of three males were 49-90 m2. The males tended to move greater distances than females between captures. The movements of both sexes increased following moderate rains. Movements also increased whenever barometric pressure fell or remained low, or when the moon phase changed from full to dark. The adults mostly resided in burrows in the banks or under granite rocks during the winter. As the spring warm-up progressed, they moved to large bedrock outcrops or beneath large boulders in relatively fast, well oxygenated current where nesting presumably occurred. During the summer, individuals used relatively cool and well-oxygenated microhabitats. The home ranges of individuals typically contained bank areas with animal burrows or rock overhangs, large flat rocks on sand-gravel substrates, and slack water areas where leaves and detritus formed mats during the fall and winter.

Adults that Ashton (1985) maintained in laboratory aquaria construct retreats by shoveling sand and gravel with their snouts to form a cavity beneath a cover object. In the field, adults constructed entrances to their retreats on the downstream side of rocks. Females actively defended their retreats from intruders by exhibiting threat displays in which they flared and pulsated the gills and curled the upper lip. Intruders that failed to retreat were often attacked and bitten at the base of the tail or, less frequently, on the snout. Males were generally less defensive than females.

Braswell and Ashton (1985) found a variety of prey in 118 adults that they examined. Snails, earthworms, isopods, amphipods, mayflies, stoneflies, caddisflies, true flies, and fishes were the most important prey items. Other prey that were taken included both terrestrial and aquatic taxa. These included slugs, leeches, spiders, crayfish, centipedes, millipedes, odonates, hellgrammites, beetles, caterpillars, unidentified salamanders, and even an adult Worm Snake. The authors noted that fast-moving or agile taxa that are more likely to evade capture were underrepresented in the diet. Examples include crayfishes, palaemonid shrimp, amphipods, plecoptera nymphs, odonate naiads and small fishes.

In addition to being nocturnally active, the Neuse River Waterdog and other Necturus species tend to be inactive during the warmer months of the year. This has been hypothesized to be a defense against predatory fishes (Neill 1963, Shoop and Gunning 1967). Braswell and Ashton (1985) noted that fish migrations and spawning activity markedly increase in April in North Carolina when minimum stream temperatures routinely exceed 18 degrees C. This is the critical threshhold temperature where N. lewisi became seasonally inactive in their studies. Reduced catch after the spring warm-up might also reflect the fact that females are nesting and guarding eggs at this time and food is more plentiful. Activity resumes with the arrival of cooler weather in the fall (Ashton 1985). Earlier researchers believed that the adults overwinter in leaf beds during the winter, but catch data from Braswell and Ashton (1985) suggests otherwise.

The growth rates of individuals is rather slow and several years are required to reach sexual maturity. Fedak (1971) found that males mature sexually after reaching 102 mm SVL, while females begin to yolk their first clutch and develop thickened and coiled oviducts at 100 mm SVL. The estimated ages at maturity are 5.5 years for males and 6.5 years for females.

General Ecology

Adverse Environmental Impacts

Status in North Carolina

NHP State Rank: S2

Global Rank: G2

Status in North Carolina: T

Global Status: T

Environmental Threats: The Neuse River Waterdog was historically adapted to clean, cool, fast-flowing streams and rivers with minimal inputs of sediment and pollutants. Its habitat has been degraded in most areas of the range due to urbanization, agricultural activities, industrial and commercial development, land clearing, and infrastructure development. These activities have altered thermal regimes, increased sediment loads, and affected flow and flooding regimes with subsequent bank erosion. They have also resulted in chemical spills and have added numerous non point-source chemical pollutants and nutrients that have impacted local populations.

Status Comments: Resurveys of N. lewisi since Braswell and Ashton's (1985) comprehensive study show that this species has experienced significant and widespread declines throughout its range. The most notably are in the Piedmont and the southern portion of its range, including a large portion of the Neuse River basin and the Trent River basin (McRae 2021). It currently occupies approximately 73% of its historical range, and many of the remaining populations are small, fragmented, and in some cases isolated from one another. The status of this species is expected to worsen in the future as population growth continues and climate change results in increased warming of rivers and streams. This species was listed as Threatened under the Endangered Species Act in July 2021.

Photo Gallery for Necturus lewisi - Neuse River Waterdog		7 photos are shown.
	Recorded by: L. Osteen Orange Co.	Recorded by: Jeff Beane Johnston Co.
	Recorded by: Jeff Beane Johnston Co.	Recorded by: Jeff Beane Halifax Co.
	Recorded by: Jeff Beane Halifax Co.	Recorded by: Jeff Beane Wilson Co.
	Recorded by: Jeff Beane Wilson Co.

Necturus lewisi - Neuse River Waterdog

Photo Gallery for Necturus lewisi - Neuse River Waterdog

7 photos are shown.