Gulf Coast waterdog
© 2016 Dr. Joachim Nerz (1 of 10)
Necturus beyeri Viosca, 1937
1. Historical versus Current Distribution. Gulf Coast waterdogs (Necturus beyeri) are thought to occur in two distinct regions: western populations are found in eastern Texas and west-central Louisiana, eastern populations are found in northern and western Mississippi (Gunter and Brode, 1964; Guttman et al., 1990; Conant and Collins, 1998; Petranka, 1998). Supporting this interpretation, waterdogs from the major rivers draining into Mobile, Alabama (except for the Upper Black Warrior Drainage, which contains Black Warrior River waterdogs, Necturus alabamensis), are genetically indistinguishable from the eastern form of N. beyeri (C.G. unpublished data).
2. Historical versus Current Abundance. Petranka (1998) speculates that, similar to other river-dwelling fishes and amphibians, numbers of Gulf Coast waterdogs likely have been reduced due to siltation and pollution.
3. Life History Features.
A. Breeding. Reproduction is aquatic.
i. Breeding migrations. Unknown and unlikely; there is strong evidence for restricted home ranges that persist throughout the year (Shoop and Gunning, 1967; see "Home Range Size" below). Mating takes place in late autumn to early winter (Shoop, 1965b; see also Petranka, 1998). All females from a population in southern Louisiana collected from December–May had sperm stored in their cloacas, and females can apparently store sperm for ≤ 6 mo (Shoop, 1965b; see also Petranka, 1998).
Based on gravid females found throughout the winter and early spring, Bishop (1943) suggests an early spring breeding/nesting season. Shoop (1965b) found five nests without females in early May. Sever and Bart (1996) found four nests with brooding females in late May
ii. Breeding habitat. Underwater.
i. Egg deposition sites. Females attach their eggs singly to the undersides of underwater substrates, such as pine logs, large boards, and railroad ties, at depths of 16–65 cm (Shoop, 1965b; see also Petranka, 1998). Neural fold-stage embryos measure 5.6–5.8 mm in diameter. Embryos maintained in the laboratory hatch after a 2-mo incubation time at a size from 13–16 mm SVL.
ii. Clutch size. Egg numbers in untended nests ranged from 4–40; in tended nests, eggs numbered from 26–37 (Shoop, 1965b; Sever and Bart, 1996; see also Petranka, 1998). Mature females have an average of 47.5 ova (range = 28–76; Sever and Bart, 1996).
i. Length of larval stage. Older larvae generally resemble adults in shape and color pattern (Bishop, 1943). An abrupt metamorphosis does not occur.
ii. Larval requirements.
a. Food. Unstudied, but larvae undoubtedly are carnivorous and feed on an array of aquatic invertebrates.
b. Cover. Unknown, but likely use debris and detritus as cover objects.
iii. Larval polymorphisms. Unknown and unlikely.
iv. Features of metamorphosis. Unknown.
v. Post-metamorphic migrations. Unknown.
vi. Neoteny. Gulf Coast waterdogs, as is true with all species of Necturus, are neotenic, retaining gills and an aquatic lifestyle through adulthood.
D. Juvenile Habitat. Young juveniles inhabit bottom debris, especially leaf litter, where currents are slow and prey aggregate (Bart and Holzenthal, 1985; see also Petranka, 1998).
E. Adult Habitat. Permanently aquatic. Gulf Coast waterdogs are found in sandy, spring-fed streams; they are not found in the turbid, sluggish waters characteristic of bayous, rivers, and lakes of the Lower Mississippi River System.
Most adults are found in slow-moving sections of streams under large objects such as logs, flood debris, and other obstructions. Some Gulf Coast waterdogs live in stream bank burrows (Shoop and Gunning, 1967; see also Petranka, 1998).
F. Home Range Size. Apparently relatively small. Adults are known to remain in the same stretch of stream for over 2.5 yr (724 d). In a mark-recapture study, mean movement between capture for males was 16 m; for females, 10 m; and for juveniles, 25 m (Shoop and Gunning, 1967; see also Petranka, 1998). All recaptures were within 64 m of the original capture and release site.
G. Territories. Unknown.
H. Aestivation/Avoiding Dessication. Bart and Holzenthal (1985) suspect that Gulf Coast waterdogs aestivate in burrows during the summer and autumn, when invertebrate prey are scarce (see also Petranka, 1998).
I. Seasonal Migrations. Unlikely (Shoop and Gunning, 1967).
J. Torpor (Hibernation). Animals appear most active in the winter and spring, when breeding, nesting, and the bulk of feeding occur.
K. Interspecific Associations/Exclusions. The competitive relationships between Gulf Coast waterdogs and fishes have not been detailed; fish will prey on these mudpuppies (see Petranka, 1998).
L. Age/Size at Reproductive Maturity. From 112–123 mm SVL (males) and 115–135 mm SVL (females). According to Viosca (1937) and Bishop (1943), sizes average 203 mm TL (range = 160–223). Tails comprise 30.8% of TL (Bishop, 1943).
Time to reach sexual maturity is probably 4–6 yr, based on studies of other Necturus species (Cooper and Ashton, 1975; see also Petranka, 1998).
M. Longevity. Bart and Holzenthal (1967) suggest adults live at least 6–7 yr in nature (see also Petranka, 1998).
N. Feeding Behavior. Gulf Coast waterdogs feed on a variety of prey including crayfish, isopods, amphipods, freshwater clams, and insects including mayflies, caddisflies, dragonfly naiads, dytiscid beetles, and midges. Across species of Necturus inhabiting the Coastal Plain, diversity of prey ingested increases with prey availability during colder months (Bart and Holzenthal, 1985; Braswell and Ashton, 1985).
Adults appear to forage along logs, away from leaf-litter beds (Neill, 1963; Shoop and Gunning, 1967; Bart and Holzenthal, 1985; Petranka, 1998).
O. Predators. Predatory fishes (see Petranka, 1998).
P. Anti-Predator Mechanisms. Shoop and Gunning (1967) suggest that reduced feeding during summer and autumn is a predator avoidance mechanism, minimizing overlap between Gulf Coast waterdogs and predatory fishes.
Q. Diseases. Unknown.
R. Parasites. Unknown.
4. Conservation. Gulf Coast waterdogs occur in western populations, found in eastern Texas and west central Louisiana, and eastern populations, found in northern and western Mississippi (Gunter and Brode, 1964; Guttman et al., 1990; Conant and Collins, 1998; Petranka, 1998). Petranka (1998) speculates that numbers of Gulf Coast waterdogs likely have been reduced due to siltation and pollution.
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 25 May 2017.
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