Apparent persistence of a landlocked population of Gulf pipefish, Syngnathus scovelli.
Hubbs et al. (2008) included S. scovelli as one of three species of the pipefishes known from rivers in Texas. The database of fishes of Texas (D. A. Hendrickson and A. E. Cohen, 2010, Fishes of Texas Project and Online Database, http://www.fishesoftexas.org) contains 186 records of S. scovelli from Texas, with 33 from fresh water or from brackish water of very low salinity based on descriptions of locations. Viola (1992) collected specimens from Lake Texana, Texas, in 1991 but, despite the reported presence of reproductive males with eggs, could not demonstrate this to be a reproducing population because he could not discount a recent introduction. All of these sources offer strong circumstantial evidence that S. scovelli is capable of reproducing in fresh water; we add more evidence that supports this hypothesis.
On 23 June 2011, 20 years after collections by Viola (1992), we sampled fishes in Lake Texana (Jackson County, Texas). We sampled the Navidad River entering the lake (at the public boat ramp upstream from united States Highway 59, 29.02236[degrees]N, 96.56959[degrees]W) and 13 km from there in a slough at the second bridge within Lake Texana State Park (28.96123[degrees]N, 96.54320[degrees]W). We seined at each site using a 6-m x 1.8-m seine having 0.64-cm Ace mesh until at least three hauls of the seine produced no new species (<30 min of total sampling at each site). Extremely low levels of water at the reservoir might have facilitated sampling, but our efforts produced a single specimen of Gulf pipefish at each location. Samples of tissue from one individual were preserved in ethanol, and whole specimens were preserved in the field in 10% formalin. These were deposited in the Texas Natural History Collections as TNHC 47327 (and tissue TNHC-FT 370), a male (94 mm in standard length) with eyed embryos in the pouch, and TNHC 47303, a probable juvenile (69 mm in standard length). Bolland and Boettcher (2005) found in their study of Gulf pipefish in Alabama that sex of individuals <75 mm in standard length could not be determined.
Lake Texana, is a reservoir for drinking water with low levels of dissolved solids (HDR, Engineering Inc., Coastal Bend Regional Water Planning Group, 2010, http://sanpatwater.com/Library files/RWPG Sect. 1 to 9.pdf) and all canals or streams that connect Lake Texana to any estuarine source for entry by S. scovelli are blocked by Palmetto Bend Dam. Therefore, brackish water was not available to this population; thus, our collection of S. scovelli, combined with collections by Viola (1992) two decades earlier, provide strong circumstantial evidence that the population in Lake Texana is widespread, well-established, and strictly freshwater, with no need to enter estuarine or marine waters to complete its lifecycle.
It is likely that this population was present in the Navidad River and trapped in the reservoir at the time of construction of the dam and inundation (completed in 1981), but the possibility of secondary introduction, although unlikely, cannot be dismissed. Some estuarine fish, such as Gulf killifish (Fundulus grandis) have been introduced into fresh water through use as live bait (Hubbs et al., 2008); however, pipefish are almost never used as bait and are unlikely to be included as contaminants among live bait. We have found no record of this species being introduced at any other freshwater location intentionally or otherwise, and there is no evidence of successful introductions in Lake Texana of other species likely to co-occur with Gulf pipefish, such as Poecilia latipinna or F. grandis (D. A. Hendrickson and A. E. Cohen, 2010; Fishes of Texas Project and Online Database, http://www.fishesoftexas.org), through bait buckets. Our rate of capture would indicate that, while not abundant, Gulf pipefish have populations larger in size than would be expected if the population is being maintained by introductions through bait buckets. The possibility of natural invasion, or movement in and out of the reservoir, is unlikely as well because Palmetto Bend Dam, which retains Lake Texana, is >19 m high and pipefish in general are not fast or strong swimmers (Dumay et al., 2004) and almost certainly not strong enough to move up the spillway during high-water events. Thus, persistence of this population in Lake Texana is most likely due to being trapped upon completion of the reservoir and reproduction and recruitment in fresh water.
Most freshwater pipefishes are amphidromous: Microphis brachyurus (Gilmore, 1977; Frias-Torres, 2004; Miran-da-Marure et al., 2004; Maeda and Tachihara, 2010); Microphis leiaspis (Ishihara and Tachihara, 2008; Maeda and Tachihara, 2010); and seven other species in two genera (Donaldson and Myers, 2002). McDowall (1992, 2007) describes freshwater amphidromy as a life-history strategy with reproduction in fresh water followed by larval or earliest juvenile stages migrating from fresh water into estuaries or marine waters to undergo critical developmental stages before returning to fresh water as juveniles to complete their life cycle. That S. scovelli is predominantly amphidromous is supported by the fact that museum records of the species in Texas and elsewhere are limited to coastal creeks, and, while they include a mix of life stages, they are dominated by adults and larger juveniles (D. A. Hendrickson and A. E. Cohen, 2010, Fishes of Texas Project and Online Database, http://www.fishesoftexas.org). Our finding that the population in Lake Texana may not be amphidromous suggests the species could be found further inland than collections-to-date document. The population in Lake Texana may be unique in this respect; however, Burgess (1980) provides a map showing specimens at what appears to be >350 km upstream in the Mississippi River. This species is cryptic and easily overlooked by collectors and may be more wide-spread than available records demonstrate. To determine whether this apparent restriction is real or an artifact of methodology will require collecting efforts that target the species.
Submitted 4 December 2011. Accepted 13 October 2013. Associate Editor was Mark Pyron.
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F. DOUGLAS MARTIN, * ADAM E. COHEN, BEN J. LABAY, MELISSA J. CASAREZ, AND DEAN A. HENDRICKSON
University of Texas at Austin, Texas Natural Science Center, Texas Natural History Collection, J. J. Pickle Research Campus, 10100 Burnet Road, PRC176/R4000, Austin, TX 78758-4445
* Correspondent: email@example.com
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|Author:||Martin, F. Douglas; Cohen, Adam E.; Labay, Ben J.; Casarez, Melissa J.; Hendrickson, Dean A.|
|Date:||Sep 1, 2013|
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