Friday, June 19, 2009
Atractosteus spatula ( alligator gar )
None given (Lacepède 1803:333).
Etymology/Derivation of Scientific Name
Atractosteus: spindle bone; spatula: spatula, in reference to the broad, elongate snout (Ross 2001).
- Lepisosteus spatula Lacepède 1803:333; Cook 1959:60.
- Lepidosteus spatula Wailes 1854:333.
- Atractosteus tristoechus Hay 1881:333.
- Lepisosteus tristoechus Evermann 1899:304; Hildebrand and Tower 1928:113 (Ross 2001).
Maximum size: Up to 300 cm TL (Lee and Wiley 1980). In 1951, a 127 kg fish from the Rio Grande in Texas captured the U.S. hook-and-line record (IGFA 1999).
Coloration: Generally dark olivaceous brown above and white to yellowish beneath (individuals in aquaria may be nearly black dorsally). Numerous dark spots may be present on sides, but only below lateral line anteriorly. Rays of all fins dark brown, with darker spots on the dorsal, anal and caudal. Young fish have a light median dorsal stripe which is bordered by dark brown area, extending from tip of snout to origin of dorsal, and from posterior insertion of dorsal to upper base of caudal fin; dark irregular lateral band present (Suttkus 1963).
Counts: 58-62 lateral line scales; 59-66 gill rakers; 7-10 dorsal rays; 7-10 anal rays (Suttkus 1963).
Body shape: Elongated, suited for surface feeding.
Mouth position: Short but broad. Terminal (Goldstein and Simon 1999).
External morphology: Diamond-shaped and stout ganoid scales; origin of dorsal fin posterior to origin of anal fin; abbreviated heterocercal caudal fin.
Internal morphology: Large teeth in upper jaw in two rows on each side (Hubbs et al. 1991; 2008).
Distribution (Native and Introduced)
U.S. distribution: Gulf of Mexico drainages from Florida to Mexico including Ohio and Missouri rivers of the Mississippi River drainage (Suttkus 1963; Wiley 1976); a disjunct population reported from the Rio Sapoa and Lake Nicaragua (Wiley 1976).
Texas distribution: Coastal streams from the Red River to the Rio Grande (Hubbs et al. 2008). Warren et al. (2000) listed the following drainage units for distribution of Atractosteus spatula in the state: Red River (from the mouth upstream to and including the Kiamichi River), Sabine Lake (including minor coastal drainages west to Galveston Bay), Galveston Bay (including minor coastal drainages west to mouth of Brazos River), Brazos River, Colorado River, San Antonio Bay (including minor coastal drainages west of mouth of Colorado River to mouth of Nueces River), Nueces River.
Abundance/Conservation status (Federal, State, NGO)
Listed as Vulnerable by the American Fisheries Society; categories of threats: present or threatened destruction, modification, or reduction of habitat or range; and over-exploitation for commercial, recreational, scientific, or educational purposes including intentional eradication or indirect impacts of fishing (Jelks et al. 2008). Vulnerable in southern US (Warren et al. 2000). Some states are listing alligator gar as a game fish to regulate harvest. Species appears to be declining in the upstream segment of the lower Rio Grande (Edwards and Contreras-Balderas 1991).
Macrohabitat: Large rivers, bays, and coastal marine waters (Suttkus 1963; Lee and Wiley 1980).
Mesohabitat: Generally associated with near surface habitats in slack water and backwater habitats of rivers. Preferred pool, pool-bank snag, pool-channel snag, pool-snag complex, pool-edge, and pool-vegetation habitat groups, in the Sulphur River, Texas (Gelwick and Morgan 2000). Zueg et al. (2005) reported collection of four specimens in the Middle Brazos River, Texas and one in a deep, frequently connected oxbow. Robertson et al. (2008) collected specimens from the Middle Brazos River, Texas and associated oxbow lakes; abundance significantly greater in oxbow habitats during a wet year. All specimens collected from oxbows were juveniles (409-810 mm), while only adults (1474-1850 mm) were captured in the river channel; this perhaps due to large individuals escaping capture in oxbow sampling, as evidenced by large holes in gillnet and the visual record of a large individual in an oxbow during flooding. Adults may move into oxbows during flooding to exploit abundant prey, returning to the river channel later. Factors including enhanced foraging, growth and survival may influence juveniles to remain in oxbows for extended periods (Robertson et al. 2008). Knapp (1953) noted that adults are abundant in brackish waters and in coastal harbors where they feed on refuse from fish cleaning houses; young fish taken in freshwater. Prior to 1955, large adults frequently taken from middle and upper parts of the Red River arm of Lake Texoma (Oklahoma-Texas); only a few captured annually since that time; no young known to have been taken in the lake (Riggs and Bonn 1959). May and Echelle (1968) reported collection of three young-of-the-year fish from shallow, turbid water in Wilson Creek cove (Red River arm of Lake Texoma), in July 1965. McCarley and Hill (1979) reported collection of two young-of-the-year specimens from a stockpond that connects to the main body of Lake Texoma when the lake level is high, and capture of a single young-of-the-year specimen from a cove in Lake Texoma (Red River arm), in July 1978. In May 1950, six larval fish were collected from a backwater slough off Red River (Oklahoma; Moore et al. 1970).
Spawning season: In Louisiana, April to June (Suttkus 1963; Lee and Wiley 1980); from early to mid-May, in Oklahoma (May and Echelle 1968); and late May, in Mississippi (Cook 1959).
Spawning Habitat: Phytophils; plant material nesters that have adhesive eggs and free embryos that attach to plants by cement glands (Simon and Wallus 1989; Simon 1999).
Spawning behavior: Nonguarders; open substratum spawners (Simon and Wallus 1989; Simon 1999). Cook (1959) observed spawning, noting that fish struck the water and created an uproar nearby.
Fecundity: Mean fecundity 157,291 eggs; mean egg diameter 2,060 microns (Ferrara 2001). Lifetime reproductive output = 90.4 female offspring per female, in Alabama (Ferrara 2001).
Age at maturation: Ferrara (2001) reported age of maturation to be 14 years.
Growth and Population Structure: Unknown; first year growth is rapid (Douglas 1974).
Longevity: Long-lived. 50 years, in Alabama (Ferrara 2001).
Food habits: First and second trophic classifications are carnivore and whole body, respectively; trophic mode – ambush; very opportunistic predator (Goldstein and Simon 1999), consuming a variety of food items; primarily fishes (Bonham 1941) and crabs (Darnell 1958, 1961; Lambou 1961; Suttkus 1963); also birds (Raney 1942) and refuse (Goodyear 1967). Based on a limited sample size, shad and Suckers (Catastomidae) were the most important prey for this species in the Middle Brazos River, Texas (Robertson et al. 2008).
Phylogeny and morphologically similar fishes
Previously placed in Lepisosteus by Suttkus (1963); placed by Wiley (1976) in the genus Atractosteus (Lee and Wiley 1980). Species is separable from Lepisosteus osseus (longnose gar) and L. oculatus (spotted gar) by its large size and broad, short snout (Suttkus 1963); young A. spatula distinguishable from young of L. oculatus, L. osseus, and L. platostomus (shortnose gar) by the light dorsal stripe versus a dark middorsal streak (Suttkus 1963; Simon and Wallus 1989).
Hybridization between A. spatula and L. osseus has been reported (Gilbert 1992). Herrington et al. (2008) provided conclusive evidence of intergeneric hybridization in A. spatula and L. osseus and described hybrid specimens spawned in an aquarium: body coloration and transverse scale rows were similar to those of longnose gar; snout length and shape intermediate between those of longnose and alligator gars; two rows of teeth on the upper jaw as seen in alligator gar.
Descriptions of postlarval A. spatula provided by Moore et al. (1973), and juveniles described by Suttkus (1963) and May and Echelle (1968). Early development of specimens from Lake Texoma (Oklahoma-Texas) described by Simon and Wallus (1989).
Cestoda: Proteocephalus ambloplitis. Trematoda: Clinostomum, Rhipidocotyle lepisostei. Nemata: Contracaecum spiculigerum, Dechelyne lepisosteus (Wardle 1990; Mayberry et al. 2000), and Crustacea: Ergalis versicolor (Hoffman 1967).
Commercial or Environmental Importance
Popular recreational target for bowfishing; some populations sustain a commercial harvest. With their large size, large teeth, and opportunistic feeding behavior, alligator gars are intimidating and often a concern to human swimmers. Attacks on humans have not been confirmed. However, one credible account was described by an old fisherman from the Rio Grande Valley. As a young boy, he and his brother were swimming in a deep, slack water area of the Rio Grande near a makeshift dock. While swimming, he felt something grasp and scrap his leg. Feeling pain, he turned and swum toward the dock. Halfway to the dock, he felt something attempt to grasp and then scrap his bare chest. He immediately grabbed for the attacker, feeling the mouth and head of a gar. After reaching the dock, he called for his brother to get out of the water. By this time his leg and chest were superficially scraped and bleeding although the gar’s teeth did not penetrate the dermis layer of his skin. He and his brother waited for a few minutes on the dock and visually confirmed the presence of an alligator gar in the immediate vicinity of the attack.
[Additional literature noting collection of this species from Texas locations includes, but is not limited to the following: Linam and Kleinsasser (1987); Gelwick et al. (2001); Morgan (2002).]
Bonham, K. 1941. Food of gars in Texas. Trans. Amer. Fish. Soc. 70(1):356-362.
Cook, F.A. 1959. Freshwater fishes in Mississippi. Mississippi Game and Fish Commission, Jackson. 239 pp.
Darnell, R.M. 1958. Food habits of fishes and larger invertebrates of Lake Ponchartrain, Louisiana, an estuarine community. Univ. Texas, Publ. Inst. Mar. Sci. 5:353-406.
Darnell, R.M. 1961. Trophic spectrum of an estuarine community, based on studies of Lake Ponchartrain. Ecology 42(3):553-568.
Douglas, N.H. 1974. The Fishes of Louisiana. Claitor’s Publishing Division, Baton Rouge, LA. 443 pp.
Edwards, R.J., and S. Contreras-Balderas. 1991. Historical changes in the ichthyofauna of the lower Rio Grande (Rio Bravo del Norte), Texas and Mexico. The Southwestern Naturalist 36(2):201-212.
Evermann, B.W. 1899. Report on investigations by the U.S. Fish Commission in Mississippi, Louisiana, and Texas, in 1897. Rept. U.S. Fish Comm. 24:287-310.
Ferrara, A.M. 2001. Life-history strategy of Lepisosteidae: Implications for the conservation and management of alligator gar. Ph.D. dissertation, Auburn University, Auburn. 126 pp.
Gelwick, F.P., and M.N. Morgan. 2000. Microhabitat use and community structure of fishes downstream of the proposed George Parkhouse I and Marvin Nichols I reservoir sites on the Sulphur River, Texas. Report to the Texas Water Development Board. 124 pp.
Gelwick, F.P., S. Akin, A. Arrington, and K.O. Winemiller. 2001. Fish assemblage structure in relation to environmental variation in a Texas gulf coastal wetland. Estuaries 24(2):285-296.
Gilbert, C.R. 1992. Rare and Endangered Biota of Florida, Volume II. Fishes. University Press of Florida, Gainesville.
Goldstein, R.M., and T.P. Simon. 1999. Toward a united definition of guild structure for feeding ecology of North American freshwater fishes. pp. 123-202 in T.P. Simon, editor. Assessing the sustainability and biological integrity of water resources using fish communities. CRC Press, Boca Raton, Florida. 671 pp.
Goodyear, C.P. 1967. Feeding habits of three species of gars, Lepisosteus, along the Mississippi Gulf Coast. Trans. Amer. Fish. Soc. 96(3):297-300.
Hay, O.P. 1883. On a collection of fishes from lower Mississippi valley. Proc. Bull. U.S. Fish Comm. 2:57-75.
Herrington, S.J., K.N. Hettiger, E.J. Heist, and D.B. Keeney. 2008. Hybridization between longnose and alligator gars in captivity, with comments on possible gar hybridization in nature. Trans. Amer. Fish. Soc. 137:158-164.
Hildebrand S.F. and I.L. Towers. 1928. Annotated list of fishes collected in the vicinity of Greenwood, Mississippi, with descriptions of three new species. Bull. of the Bureau of Fisheries 43(2):105-136.
Hoffman, G.L. 1967. Parasites of North American Freshwater Fishes. University of California Press, Berkeley. 486 pp.
Hubbs, C., R.J. Edwards, and G.P. Garrett. 1991. An annotated checklist of the freshwater fishes of Texas, with keys to identification of species. The Texas Journal of Science, Supplement 43(4):1-56.
Hubbs, C., R.J. Edwards, and G.P. Garrett. 2008. An annotated checklist of the freshwater fishes of Texas, with keys to identification of species. Texas Journal of Science, Supplement, 2nd edition 43(4):1-87.
IGFA (International Game Fish Association). 1999. World Record Game Fishes. Pampano Beach, Florida. 352 pp.
Jelks, H.L., S.J. Walsh, N.M. Burkhead, S. Contreras-Balderas, E. Diaz-Pardo, D.A. Hendrickson, J. Lyons, N.E. Mandrak, F. McCormick, J.S. Nelson, S.P. Platania, B.A. Porter, C.B. Renaud, J.J. Schmitter-Soto, E.B. Taylor, and M.L. Warren, Jr. 2008. Conservation status of imperiled North American freshwater and diadromous fishes. Fisheries 33(8):372-407.
Knapp, F.T. 1953. Fishes Found in the Freshwater of Texas. Ragland Studio and Litho Printing Co., Brunswick, Georgia. 166 pp.
Lacepede, B.G.E. 1803. Histoire Naturelle des Poissons. Hist. Nat. Poiss. V.5: i-lxvii + 1-803 + index, Pls. 1-21.
Lambou, V.W. 1961. Utilization of macrocrustaceans for food by freshwater fishes in Louisiana and its effect on the determination of predator-prey relations. Progressive Fish-Culturist 23(1):18-25.
Lee, D.S. and E.O. Wiley. 1980. Atractosteus spatuala (Lacepède), Alligator gar. pp. 47 in D. S. Lee, et al. Atlas of North American Freshwater Fishes. N. C. State Mus. Nat. Hist., Raleigh, i-r+854 pp.
Linam, G.W., and L.J. Kleinsasser. 1987. Fisheries use attainability study for Cow Bayou (Segment 0511). River Studies Report No. 5. Texas Parks and Wildlife Department, Austin. 12 pp.
May, E.B., and A.A. Echelle. 1968. Young-of-the-year alligator gar in Lake Texoma, Oklahoma. Copeia 1968(3):629-630.
Mayberry, L.F., A.G. Canaris, and J.R. Bristol. 2000. Bibliography of parasites and vertebrate host in Arizona, New Mexico, and Texas (1893-1984). University of Nebraska Harold W. Manter Laboratory of Parasitology Web Server pp. 1-100.
McCarley, H., and L.G. Hill. 1979. Reproduction of Lepisosteus spatula (Lepisostedae) in Lake Texoma. The Southwestern Naturalist 24(4):694-695.
Moore, G.A., M.B. Trautman, and M.R. Curd. 1973. A description of postlarval gar (Lepisosteus spatula Lacepede, Lepisosteidae) with a list of associated species from the Red River, Choctaw County, Oklahoma. The Southwestern Naturalist 18(3):343-344.
Morgan, M.N. 2002. Habitat associations of associations of fish assemblages in the Sulphur River, Texas. Thesis, Texas A&M University, College Station. 58 pp.
Raney, E.C. 1942. Alligator gar feeds upon birds in Texas. Copeia 1942(1):50.
Riggs, C.D., and E.W. Bonn. 1959. An annotated list of the fishes of Lake Texoma, Oklahoma and Texas. The Southwestern Naturalist 4(4):157-168.
Robertson, C.R., S.C. Zeug, and K.O. Winemiller. 2008. Associations between hydrological connectivity and resource portioning among sympatric gar species (Lepisosteidae) in a Texas river and associated oxbows. Ecology of Freshwater Fish 17:119-129.
Ross, S. 2001. The Inland Fishes of Mississippi. University Press of Mississippi, Jackson. 624 pp.
Simon, T.P. 1999. Assessment of Balon’s reproductive guilds with application to Midwestern North American Freshwater Fishes, pp. 97-121. In: Simon, T.L. (ed.). Assessing the sustainability and biological integrity of water resources using fish communities. CRC Press. Boca Raton, Florida. 671 pp.
Simon, T.P., and R. Wallus. 1989. Contributions to the early life history of gar (Actinopterygii: Lepistosteidae) in the Ohio and Tennessee River basins with emphasis on larval development. Transactions of the Kentucky Academy of Science 50:59-74.
Suttkus, R.D. 1963. Order Lepisostei, pp. 61-88. in: Bigelow et al. 1963. Fishes of the Western North Atlantic. Soft-rayed Bony Fishes, Vol. 1, pt. 3. Memoir, Sears Foundation of Marine Research, Yale University, New Haven, Connecticut.
Wailes, B.L.C. 1854. Report on the agriculture and geology of Mississippi. E. Barksdale, State Printer, Jackson.
Wardle, W.J. 1990. Experimental verification of the matecercarial stage of Rhipdocotyle lepisostei (Trematoda: Bucephalidae) with notes on the natural occurrence of its adult stage in gars in Texas and Virginia. Journal of Parasitology 76(2):293-295.
Warren, M.L. Jr., B.M. Burr, S.J. Walsh, H.L. Bart Jr., R.C. Cashner, D.A. Etnier, B.J. Freeman, B.R. Kuhajda, R.L. Mayden, H.W. Robison, S.T. Ross, and W.C. Starnes. 2000. Diversity, distribution and conservation status of the native freshwater fishes of the southern United States. Fisheries 25(10):7-29.
Wiley, E.O. 1976. The phylogeny and biogeography of recent gars (Actinopterygii: Lepisosteidae). Misc. Publ. Univ. Kans. Mus. Nat. Hist. 64:1-111.
Zeug, S.C., K.O. Winemiller, and S. Tarim. 2005. Response of Brazos River oxbow fish assemblages to patterns of hydrologic connectivity and environmental variability. Trans. Amer. Fish. Soc. 134:1389-1399.
credit from http://www.bio.txstate.edu/~tbonner/txfishes/atractosteus%20spatula.htm