Academic journal article The American Midland Naturalist

Population Status and Nesting Biology of the Rare Barrens Darter, Etheostoma Forbesi

Academic journal article The American Midland Naturalist

Population Status and Nesting Biology of the Rare Barrens Darter, Etheostoma Forbesi

Article excerpt

ABSTRACT.-

The Barrens darter Etheostoma (Catonotus) forbesi (Teleostei: Percidae) is a rare stream fish endemic to the upper Caney Fork River system in the Barrens Plateau region of middle Tennessee. We studied the darter's population characteristics and selected aspects of its nesting biology at 10 sites surveyed during April 2004. In our survey, we caught a total of 75 Barrens darters at a rate of 21 individuals per hour of backpack-electrofishing effort. At least one male Barrens darter was present at six of the 10 sites. Females outnumbered males by a ratio of 1.4 to 1. Total lengths ranged 44-97 mm, averaging 62 mm for females and 78 mm for males. The number of Barrens darters seen in the present survey was similar to a 1994 survey. However, both surveys reveal a species in need of conservation, with low abundance at most known sites within its limited geographic range. We found 20 Barrens darter nests located on the flat undersides of cobbles with a mean length, width and thickness of 17 × 13 × 5 cm. Nests in one stream, Duke Creek, were located at a mean water depth of 22 cm, column current velocity of 15 cm/s and bottom velocity of 7 cm/s. Stream channel widths averaged 3.5 m at nest rock locations. Nests contained a mean number of 463 eggs (range 69-976) arranged in a monolayer. Male size and the number of eggs per nest were positively correlated with nest rock size for eight nests where we captured the attending guardian male; however, egg number was not correlated with rock size for all nests in the study.

INTRODUCTION

The Barrens darter Etheostoma forbesi is endemic to Caney Fork River system of the Barrens Plateau region in Tennessee, and is one of the rarest fishes in North America (Page et al., 1992). It is among 10 species of the E. squamiceps complex (subgenus Catonotus) and shares closest common ancestry with the blackfin darter E. nignpinne and fringed darter E. crossopterum. Barrens darters inhabit pools or gently flowing riffles with slabrock cobble substrate within small headwater streams (Etnier and Starnes, 1993).

A survey of the upper Caney Fork River system in 1994 found Barrens darters limited to 11 sites within nine streams (Madison, 1995). Current distribution and abundance are unknown. Potential threats to the species include hybridization with the fringed darter and stream habitat degradation resulting from land use practices. Due to its restricted distribution, small population sizes, and current threats, the Barrens darter warrants consideration for federal listing as an endangered species (Page et al., 1992; Etnier, 1997).

Relatively little is known of the biology of the Barrens darter. Spawning occurs during April and May (Madison, 1995), yet most details of reproduction remain undocumented. Madison (1995) noted that Barrens darters use slabrocks as nest sites, as is common for Catonotus species (Page, 1983,1985), and speculated that recruitment could be limited by slabrock availability.

Here we summarize our 2004 survey of most sites known to contain Barrens darters in 1994. We then describe selected characteristics of Barrens darter nesting biology, including the dimensions of a typical nest rock, number of eggs per rock and water depth and velocity at nest locations. We also test whether male size was related to nest rock size or egg cluster size.

METHODS

Barrens darter identification.-Female Barrens darters are not readily distinguishable from other females in the Etheostoma squamiceps complex (Page et al., 1992). However, breeding male Barrens darters are differentiated from other males in the complex (except the allopatric crown darter E. corona) by 14-15 dorsal rays and a yellow-gold margin on the second dorsal fin (Page et al, 1992). Consequently, our 2004 survey was conducted during the breeding season in April to allow reliable identification of males. Individuals were categorized as female, male or "not sexed" (small individuals for which gender was difficult to determine). …

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