Neuse River waterdog
Necturus lewisi Brimley, 1924
Alvin L. Braswell1
1. Historical versus Current Distribution. Neuse River waterdogs (Necturus lewisi) are known only from the Neuse and Tar river systems in the Piedmont and Coastal Plain regions of North Carolina (Bishop, 1943; Ashton, 1990; Petranka, 1998). A survey conducted between 1978 and 1980 demonstrated that apparently healthy Neuse River waterdog populations remained and that the historical range had not been reduced, but severely polluted streams are known to have lost their populations (Braswell and Ashton, 1985; see also Petranka, 1998).
2. Historical versus Current Abundance. Unknown, but if high levels of pollution eliminate populations (Braswell and Ashton, 1985; see also Petranka, 1998), low levels of pollution may reduce abundances within remaining populations.
3. Life History Features.
A. Breeding. Reproduction is aquatic. Details of a courtship are described by Ashton (1985). Sperm transfer has not been described. Testes morphology and spermatogenesis are reported on by Pudney et al. (1985).
i. Breeding migrations. Unknown. Bishop (1943) suggests a spring breeding season based on both male and female morphology (in March, one male had swollen cloacal glands; in April, one gravid female was found). Males have sperm in their vas deferens from November–May, and females, which store sperm following mating, have sperm in their spermathecae from December–May (Cooper and Ashton, 1985).
ii. Breeding habitat. Unknown, but probably not different from normal habitats occupied.
i. Egg deposition sites. One nest has been reported (Ashton and Braswell, 1979). In the spring, females lay eggs under large rocks in moderate currents (see Ashton, 1985; Cooper and Ashton, 1985). Seven additional nests (unpublished data) observed during May and June between 1980 and 1984 were all under rocks in water 25–41 cm deep. The rocks ranged in size from 27 cm length x 27 cm width x 5 cm height to ca. 80 cm x 50 cm x 25 cm. Nests were found at low-water conditions. At this time the minimum flow rate was ca. 2 cm/s. Nest sites were in areas that received only about 2 hr/d of direct sunlight.
ii. Clutch size. One nest observed on 2 July contained 35 egg capsules and had a male present (Ashton and Braswell, 1979). Male guarding of nests is unknown in Necturus, so there is some question as to whether or not this male was attending the eggs (Ashton and Braswell, 1979; see also Petranka, 1998). An attending adult was captured at six additional nests observed between 1980 and 1984 (unpublished data), and all were females that ranged in size from 93–120 mm SVL. The attending adult escaped from one other nest. Clutch sizes for these seven nests were 19, 21, 22, 20, 22, 36, and 32 (i.e., 31 eggs and 1 empty egg capsule).
i. Length of larval stage. Unknown.
ii. Larval requirements.
a. Food. Smaller larvae feed on invertebrates associated with leaf beds (Braswell and Ashton, 1985; see also Petranka, 1998).
b. Cover. Smaller larvae are found in quiet waters and in leaf beds, where they find cover and food (Braswell and Ashton, 1985; see also Petranka, 1998).
iii. Larval polymorphisms. Unknown and unlikely. Color patterns of larvae are described in Ashton and Braswell (1979).
iv. Features of metamorphosis. Unknown.
v. Post-metamorphic migrations. Unknown; long distance migrations unlikely.
vi. Neoteny. All mudpuppies (Necturus sp.), indeed all proteids, are neotenic, retaining larval features such as gills and tail fins through adulthood.
D. Juvenile Habitat. Ashton (1985) reported juveniles finding shelter under granite boulders on a sand/gravel substrate, and early spring use of leaf beds at an eastern Piedmont site (see Petranka, 1998).
E. Adult Habitat. Permanently aquatic. While Bishop (1943) notes animals generally are found in backwaters off the main current, where substrates are sandy or muddy, Braswell and Ashton (1985) found animals to be most abundant in streams greater than 15 m wide and 1 m deep, with flow rates of greater than 10 cm/s. Further, Braswell and Ashton (1985) found more animals associated with clay or hard soil substrates, while Brimley (1924) and Martof et al. (1980) found animals associated with leaf beds (see also Petranka, 1998). Neuse River waterdogs are distributed from larger headwater streams in the Piedmont to coastal streams up to the point of saltwater intrusion (Braswell and Ashton, 1985).
In the laboratory and in the field, juveniles and adults larger than 47 mm TL construct retreats under cover objects. In nature, adults construct retreat entrances on the downstream side of rocks (Ashton, 1985).
At night, adults become active and will leave their cover (Ashton, 1985; Braswell and Ashton, 1985). Daytime activity by adults is limited, as evidenced by no daytime trapping success (Braswell and Ashton, 1985). Neuse River waterdogs tend to become inactive away from cover when water temperatures are greater than 18 ˚C and cannot be trapped, but remain active at temperatures as low as 0 ˚C (Braswell and Ashton, 1985; Petranka, 1998).
F. Home Range Size. 16–19 m2 for two females, 49–90 m2 for three males (Ashton, 1985). Further, males tended to move greater distances between captures.
G. Territories. Retreats may constitute territories. Females actively defend their retreats; males also will defend retreats, but to a lesser extent (Ashton, 1985; Petranka, 1998).
H. Aestivation/Avoiding Dessication. Unknown and unlikely.
I. Seasonal Migrations. Movements are highest in the spring and fall; increase following moderate rains but decrease following heavy rains; increase when barometric pressure is low or falls; and increase during new moons (Ashton, 1985; see also Petranka, 1998). In the spring, adults move from winter shelters (see "Torpor" below) to outcrops or boulders associated with fast currents and well-oxygenated water. Here they nest and remain for the summer.
J. Torpor (Hibernation). Unlikely. During the winter adults find shelter in leaf beds, under rocks, or in burrows in river banks. Active feeding occurs through the winter and at near-freezing water temperatures; winter and early spring are the most productive trapping seasons (Braswell and Ashton, 1985).
K. Interspecific Associations/Exclusions. Resident Neuse River waterdogs inhabiting retreats exhibit threat displays that include flaring and pulsating their gills and curling their upper lip. When this fails they will attack intruders, including dwarf waterdogs (N. punctatus), by viciously biting them; intraspecific attacks are less vicious, whereas interspecific attacks occasionally resulted in death. Larvae and small juvenile Neuse River waterdogs may enter adult retreats without being attacked (Ashton, 1985).
Neuse River waterdogs are thought to compete with fishes for food (Petranka, 1998). The diets of Neuse River waterdogs and dwarf waterdogs also overlap, and these two mudpuppies likely compete for food where they are syntopic (Braswell and Ashton, 1985).
L. Age/Size at Reproductive Maturity. Males become sexually mature at 102 mm SVL, females at 100 mm SVL (Cooper and Ashton, 1985; see also Petranka, 1998). Bishop (1943) notes that the tail in males is about 28% of TL. Estimated age at maturity is 5.5 yr for males, 6.5 yr for females (Cooper and Ashton, 1985; see Petranka, 1998).
M. Longevity. Unknown.
N. Feeding Behavior. Adults will eat lampreys (Petromyzontidae; Nickerson et al., 1983), and can be caught using a baited hook and line and by dipnetting (C.S. Brimley and W.B. Mabee, in Bishop, 1943). Dietary analysis shows Neuse River waterdogs prey heavily on invertebrates such as ostracods, zooplankton such as copepods and cladocerans, snails, annelids, fishes, other species of salamanders, adult eastern worm snakes (Carphophis amoenus amoenus), isopods, slugs, spiders, crayfish, centipedes, millipedes, and insects such as mayflies, true flies, beetles, dragonfly and damselfly naiads, hellgrammites, caterpillars, and caddisflies (Braswell and Ashton, 1985; Petranka, 1998).
O. Predators. It is not known whether or not fish prey on Neuse River waterdogs, but workers have speculated that their inactivity during warmer months is in part due to the avoidance of fishes (Neill, 1963; Shoop and Gunning, 1967; Braswell and Ashton, 1985; see also Petranka, 1998).
P. Anti-Predator Mechanisms. Behavioral observations suggest that skin extracts from Neuse River waterdogs have a relatively low level of toxicity that causes moderate distress in mice (Brandon and Huheey, 1985).
Q. Diseases. Unknown.
R. Parasites. Unknown.
4. Conservation. Pesticide and PCB residues were reported in Neuse River Waterdogs from Piedmont and Coastal Plain localities (Hall et. al., 1985). Specifically, DDE, DDD, dieldrin, cis-chlordane, trans-nonachlor, and PCP 1254 were detected. Several other potential contaminants were not detected at the 0.01 ppm level of sensitivity. Neuse River waterdogs are considered a Species of Special Concern in North Carolina.
1Alvin L. Braswell
Literature references for Amphibian Declines: The Conservation Status of United States Species, edited by Michael Lannoo, are here.
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Citation: AmphibiaWeb. 2017. <http://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 21 Jul 2017.
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