BURKHEAD , N.M., J.D. WILLIAMS, AND R.W. YERGER . 1 992. OKALOOSA DARTER. ETHEOSTOMA OKALOOSAE , PAGES 23-30. IN: C. R. GILBERT ( ED. , RARE AND ENDANGERED BIOTA OF FLORIDA. VOLUME II. FISHES . UNIVERSITY PRESS OF F 1 LORIDA , GAINESVILLE . Endangered Okaloosa Darter Etheostoma okaloosae FAMILY PERCIDAE Order Perciformes ■• , , 4- ..IMMINW."••• 1% 16 V X 4. moMONI.N■7•. .' •4 `1./. .4' 4:41 , 4 , - ' ,9/‘ /•11■I' /%141‘'•.= P al, A 4, " A{ Itc‘‘'%41 11. Okaloosa darter, Esheostoma okaloosae (Fowler, 1941). UP 74516. Adult female, 45.0 mm SL Long Creek (tributary to Rocky Bayou), Eglin Air Force Base, Okaloosa County, Florida. 17 January 1973. OTHER NAMES: None. DESCRIPTION: Etheostoma okaloosae is a darter of relatively small to mod- erate size (maximum 49 mm standard length [SL]), which is character- ized by the following features: a well-developed humeral blotch; body color in life red-brown to yellow-brown dorsally, lighter ventrally, the pigment broken up into small dots arranged in 5 to 8 rows along sides of body; midside of body with 9 to 10 dark dashes or blotches, which vary in degree of prominence; suborbital bar present but thin and not particu- larly prominent; cheeks and prepectoral area with well-developed spot- ting, but latter without a prominent bar; both sexes without red spots on body, but dorsal fin with a thin orange-red submarginal stripe; lateral line yen, slightly arched anteriorly (nearly straight), separated from origin of dorsal fin by 3 to 4 scale rows; lateral line complete or nearly complete, the total number of scales ranging from 32 to 37 (usually 34 to 36), with no more than 4 unpored scales; cheeks, opercle, belly, and nape fully scaled, the breast fully or partly scaled; premaxillary frenum present and 23 24 OKALOOSA DARTER well developed; branchiostegal membranes narrowly connected, the apex forming a broad "V" and located at a point below posterior part of cheek; dorsal-fin rays 10-13 (usually IX, 11-12); pectoral-fin rays, 12-14 (usually 13); anal-fin rays II, 6-8 (usually II, 7). TAXONOMIC REMARKS: Collette and Yerger (1962) believed that E. oka- loosae was most closely related to Etheostoma tdivini, the brown darter (a species whose geographic range surrounds that of the Okaloosa darter), and that these two species were the sole representatives of the subgenus Villora. Page (1981) subsequently decided that the relationships of E. okaloosae are actually closer to Etheostoma mariae and Etheostoma fricksium, 77 Tr r, :72 t ti 2p-t, Distribution map of Etheostorna okaloosae. Etheostoma okakosae 25 two geographically disjunct species occurring on the lower Atlantic slope from Georgia to southeastern North Carolina and that these three spe- cies comprise the subgenus Belophkx. RANGE: The Okaloosa darter is endemic to the panhandle of northwest- ern Florida. It is confined to two bayou systems, Boggy and Rocky bayous, of the Choctawhatchee Bay drainage in Okaloosa and Walton counties. The principal tributary watersheds are Toms, Turkey, and Mill creeks of Boggy Bayou (90.9 total stream miles), and Swift, Turkey, and Rocky creeks of Rocky Bayou (151.9 stream miles). The vast majority of the darter's range is in streams draining approximately 115,000 acres of Eglin Air Force Base and about 12,000 acres outside the base (Mettec et al. 1976). This region is notable for its relatively high endemism of other plants and animals (Yerger 1978; Moler 1985). HABITAT: Etheostoma okaloosae inhabits small- to moderate-sized streams (4-40 ft wide) of generally low gradient but with persistent discharge. Because of consistent groundwater discharge, most streams are clear and cool and exhibit only minimal did temperature fluctuation throughout the season. During February, when the air temperature was 0° C, the lowest observed water temperature was 12.0° C, whereas in midsummer (when daytime air temperatures range from about 32° to 37° C), the highest water temperature was 24.5° C (mean = 22.0° C). Most streams inhabited by the species drain sandhill terrain with man- aged mixed deciduous or coniferous forests and typically have a sand bot- tom with clear to slightly tea-colored water. In the Turkey Creek water- shed of Boggy Bayou, many stream reaches are moderately incised (50-100 ft) in the surrounding terrain. The streams are fairly soft, with reported pH extremes ranging from 5.6 (Crews et al. 1977) to 8.4 (Bor- tone 1989). The latter extreme is considered exceptional and perhaps er- roneous; typical pH extremes are in the subneutral range. Detritus is usu- ally present along stream margins, in backwaters, macrophyte beds, and in the bottoms of slow-flowing pools. The Okaloosa darter is typically as- sociated with cover, principally submerged macrophytes in open sunlit stream sections and with detritus in well-canopied areas. Etheostoma oka- loosae may sometimes occur over open sand or nonsheltering detritus, but if so sheltered areas are usually nearby. Some stream reaches are heavily silted by sediment runoff from road crossings, sand and clay pits, old railroad beds, and other sources of dis- turbance. Etheostoma okaloosae seems to be intolerant of extensive siltation, as it is observably less abundant in extensively silted sections of stream. 26 OKALOOSA DARTER LIFE HISTORY AND ECOLOGY: Life history and ecological data have not previously been published but are available in state and federal reports by Mettee and Crittenden (1979) and Ogilvie (1980). Stomach analyses of 325 specimens revealed that chironomid midges (70.3% of total food items), ephemeroptcran larvae (17.4%), and tricop- reran larvae (7.6%) dominate the diet. Miscellaneous food items included oligochaetes, copepods, ostracods, gastropods, °donates, plecopterans, and dipterans (simulids, ceratopogonids, and maids) (Ogilvie 1980). The duration of the spawning period greatly exceeds reproductive quiescence. Spawning extends from March into October, with most ac- tivity in April but with a minor peak in October (Ogilvie 1980). Spawn- ing observations were reported on by Collette and Yergcr (1962) and Mettee and Crittenden (1979). Detailed observations of spawning were videorecorded by Burkhead and Williams (1989, 1990) in June and July between 0845-1215 hours, with none noted after midday. Water tem- perature during the spawning observations ranged from 20° to 21.5° C. Reproductive behavior is presently being studied in the laboratory. During spawning courtship, a male follows a single female as she slowly moves over and through fine-stemmed algae or macrophytes, in- cluding Nitella sp. (stonewort), Myriophyllum heterophyllum (variable-leaf milfoil), and Ekocharis sp. (spike rush). At fairly regular intervals, the male will mount the female dorsolaterally, sometimes curving his pedun- cle downward and at other times keeping it relatively straight. Very subtle to overt lateral vibrations by one or both sexes attend this activity, after which the female again moves a short distance away. The area covered by the darters during the series of spawning acts tends to be fairly linear. Mettee and Crittenden (1979) observed males spawning with several females. Fecundity is low, as is true of darters in general. Ogilvie (1980) re- ported the mean total number of ova to be 79 and the mean number of mature ova as 29. Etheostoma okaloame is probably a fractional spawner (i.e., eggs develop and mature over an extended period), and thus ovarian egg counts indicated above may be less than actual total seasonal fecun- dity. The mature ova are large for darters (2.0-mm diameter [Ogilvie 1980]), as are the water-hardened ova (2.9-mm diameter [Mettee and Crittenden 1979]). Larval development is poorly known, the only refer- ence being a brief description by Mettee and Crittenden (1979). A newly hatched prolarva measured 4.9 mm TL. Egg deposition is by attachment, although the female genital papilla is not pendulous. In the laboratory, only one egg shed per spawning act has been observed. Based on the number of spawning acts per day and Etheostoma okaloosae 27 the low fecundity of the species, it is probable that only one egg is shed at a time in the wild as well. Based on our interpretation of length-frequency data ( Mettee and Crit- tenden 1979; Ogilvie 1980), individuals typically live to be two years old, and occasionally may live three years. Average adult size is about 28-38 mm SL (Ogilvie 1980), with the smallest mature female observed at 27 mm SL; although there are no data regarding the smallest mature male, the length is likely comparable. Because of the small size at maturation, it is possible that young spawned during the early spring may themselves spawn by late fall. BASIS OF STATUS CLASSIFICATION: The Okaloosa darter was nationally listed as "endangered" by the U.S. Fish and Wildlife Service on 4 June 1973 (Federal Register, vol. 38, no. 106). The principal reason for listing this species was its extremely small geographic range. Within this limited range, E. okaloosae is persistently present in most reaches of stream, and in some cases it is fairly abundant. Density is very low in the wooded, well-canopied stream sections that represent the vast majority of occupied stream miles, but it can be relatively high in open sunlit reaches. Al- though rigorous population estimates have not been made, educated guesses range between 1,500 and 10,000 individuals (Yerger 1978). Based on our recent (1988—present) survey efforts, the total population proba- bly numbers in the thousands. Several abiotic and biotic factors appear to be negatively affecting Okaloosa darter populations. As noted, the majority of the home range of E. okaloosae occurs on Eglin Air Force Base (AFB), a situation that might normally be viewed positively. Unfortunately, Air Force steward- ship has not been entirely benign. Poor land-use practices on Eglin AFB have resulted in extensive siltation in localized stream reaches, including Florida Route 285 crossing on Little Rocky Creek (near the type locality).