2010 SOUTHEASTERN NATURALIST 9(4):699–710 Observations of Physical and Environmental Characteristics of Suwannee Bass Spawning in a Spring-fed Florida River Will A. Strong1,*, Eric J. Nagid1, and Travis Tuten1 Abstract - We describe physical and environmental characteristics associated with Micropterus notius (Suwannee Bass) spawning in the Ichetucknee River, fl. We located 24 Suwannee Bass nests from March to June (75% found May and June). Nests were found in relatively shallow waters (mean = 95 cm) with substrates dominated by organic material (63%). Suwannee Bass nests were located near cover, in lowflow areas (mean velocity = 0.01 m/s), and at a mean temperature of 21.7 °C. We did not detect any relationships from regressions between the frequency of nesting and temperature, photoperiod, river stage, discharge or lunar cycle. Ninety-two percent of nests contained submerged aquatic vegetation (SAV), which are likely important to nesting areas as stream-velocity refuges that reduce sediment wash-in and egg disturbance during spawning. Descriptions of spawning habitat of this range-restricted species have implications for conservation and management decisions. Introduction Micropterus notius Bailey and Hubbs (Suwannee Bass) is a species of black bass that was described by Bailey and Hubbs (1949) from the Ichetucknee River, fl. This species, which inhabits the Suwannee River and Ochlockonee River drainages of Florida and Georgia (Bass 1974, Bass and Hitt 1973, Hellier 1967, Keefer and Ober 1977, MacCrimmon and Robbins 1975), has the smallest natural range of all Micropterus species (Koppleman and Garret 2002). Recently, Suwannee Bass have been found in the Wacissa (Cailteux et al. 2002a), St. Marks, and Wakulla rivers in northwestern Florida, although these populations may have been introduced (Cailteux et al. 2002b). Because of their relatively small range, Suwannee Bass are considered a species of special concern in Florida (Chapter 68A-27.005, Florida Administrative Code [FAC]) and rare in Georgia (Chapter 391–4–10–0.9, Georgia Administrative Code). Suwannee Bass are sympatric with the endemic and widespread M. salmoides Lacepède (Largemouth Bass). Largemouth Bass have been studied extensively and are generally considered habitat and feeding generalists. In contrast, relatively few studies have been conducted on Suwannee Bass (Bass 1974; Bass and Hitt 1973; Bonvechio et al. 2005; Cailteux et al. 2002a, 2002b; Hurst et al. 1975; Keefer and Ober 1977; Schramm and 1Florida Fish and Wildlife Conservation Commission, Fish and Wildlife Research Institute, 7922 NW 71st Street, Gainesville, fl32653. *Corresponding author - Will. strong@myfwc.com. 700 Southeastern Naturalist Vol. 9, No. 4 Maceina 1986; Smitherman and Ramsey 1972; Warren and Nagid 2008). While there is an abundance of published literature regarding Largemouth Bass spawning, there is very little information regarding the spawning of Suwannee Bass in lotic environments. Physical characteristics of nests for members in the Centrarchidae family have been commonly studied (Allan and Romero 1975, Bain and Helrich 1983, Bozek et al. 2002, Bruno et al. 1990, Lukas and Orth 1995, Phelps et al. 2009). In general, nests are circular depressions in the substrate, and located in relatively shallow waters along the littoral portion of a stream or lake. Environmental characteristics most associated with timing of spawning for centrarchid species have been temperature (Hurst et al. 1975, Kaya and Hasler 1972, Phelps et al. 2009, Smitherman and Ramsey 1972), photoperiod (Carlson 1973, Kaya and Hasler 1972, Mischke and Morris 1997), and water level and discharge (Graham and Orth 1986, Lukas and Orth 1995). Warren (2009) provides a concise summary of research regarding Suwannee Bass reproduction, which describes aspects such as the timing of spawning, fecundity, and egg size. Aside from Hurst et al. (1975) providing a general description of nests as shallow, circular depressions near stream edges, the spawning habits (e.g., habitat and flow use) and nest characteristics of Suwannee Bass in stream habitats have not been described. As management agencies develop conservation efforts for Suwannee Bass (FFWCC 2005), as well as water-conservation rules that consider fish and wildlife habitats (Subsection 373.042 (2), Florida Statutes; Chapter 62–40.473, FAC), scientific studies examining habitat use by fish and wildlife have become increasingly important. Deviation from the natural flow regime has been shown to affect fish community composition (Bain et al. 1988, Marchetti and Moyle 2001) and generally benefits species with wider environmental tolerances (Copp 1990). Given the limited range of the Suwannee Bass within and among a small number of fluvial systems, there is potential, with flow reductions, for an ecological shift towards Largemouth Bass if physical habitats of Suwannee Bass are not identified and managed for conservation (Warren and Nagid 2008). Research characterizing nestsite selection under natural flows can provide important information for future management decisions. Therefore, the objectives of this study were to describe the physical and environmental characteristics of Suwannee Bass nests and the timing of spawning. Field-Site Description The Ichetucknee River is an 8.85–km–long spring-fed river in Columbia and Suwannee counties, fl. The river is characterized by hard water, alkaline pH, minimal color and turbidity (Nordlie 1990), and a mean discharge of 10.22 m3/s (Rosenau et al. 1977). Approximately 5.6 km of the upper portion 2010 W.A. Strong, E.J. Nagid, and T. Tuten 701 of the river is located within the Ichetucknee Springs State Park, of which 4.8 km was included in our study area. The study area contains three distinct reaches: the Headspring Reach, Rice Marsh Reach, and Floodplain Reach (Fig. 1; Dutoit 1979, Kurz et al. 2003). The Headspring Reach includes the origin of the river, Ichetucknee Head Spring, and is characterized by relatively shallow depths (1–2 m) and a narrow channel width (10–15 m), with a prominent tree canopy (Acer spp. [maples]) and expansive coverage of submerged aquatic vegetation (SAV; e.g., Sagittaria kurziana Glück [Strapleaf Sagittaria] and Vallisneria americana Michx [Eelgrass]) and emergent vegetation (e.g., Zizania aquatica L. [Wild-rice]). The Rice Marsh Reach, or middle reach, is the widest portion of the river, averaging 60 m across. The main river channel in this reach composes roughly 10–20 m of the width and is characterized by swift flow, depths of 2–3 m, and vast coverage of Eelgrass and Strap-leaf Sagittaria. The remaining 40–50 m of width is primarily open tree canopy with expansive benthic coverage of Wild-rice, Chara spp. (muskgrass), and Ceratophyllum demersum L. (Coontail), and water depths Figure 1. Location of sampling reaches on the Ichetucknee River, fl. 702 Southeastern Naturalist Vol. 9, No. 4 generally less than 1 m. The Floodplain Reach, the most downstream portion of our study area, is similar to the Headspring Reach relative to tree canopy and SAV coverage. However, the Floodplain Reach canopy is dominated by Taxodium distichum (L.) Rich. (Bald Cypress), and the channel is wider (15–20 m) and deeper (2–3 m). Methods We used mask and snorkel to locate Suwannee Bass nests from 17 February through 23 June 2006 (17 trips in 19 weeks). Nests were only included in the study if Suwannee Bass were observed guarding the nest. Although a common definition of spawning is the act of depositing eggs (Holmes 1979), we define it in this paper as all activity related to nesting and reproduction (i.e., eggs or fry), including nests where we found parental Suwannee Bass but no other evidence of reproduction. Water depth was measured from the water surface to the center of the nest, and nest depth was measured from the center of the nest to the top of the nest. Nest diameter was calculated as the mean of the nest length, parallel to the channel, and width, perpendicular to the channel. Percent area covered (PAC; ≤100%) was estimated using a 1–m square to describe the immediate area within and around the nest and was defined as the percentage of the stream floor covered by structure (e.g., macrophytes, snags) within the square. Substrate was described qualitatively (e.g., organic debris, sand). Stream velocity (m/s) was measured at the upstream side and adjacent to the rim of the nest with a Marsh-McBirney™ Flo-mate 2000 portable velocity meter. An Onset Hobo temperature logger was placed in each of the three river reaches near the shoreline at 0.5–1 m depths and was set to record water temperatures every 6 h during our sampling period. Mean temperatures for the three reaches were compared using a Kruskal-Wallis test, where P < 0.05 was considered significant. Pair-wise comparisons were made using a Wilcoxon two-sample test with a Bonferroni adjustment. All statistical analyses were conducted with SAS (SAS Institute 2002). Photoperiod (duration of daylight in hours) and lunar cycle data for our study period were obtained from the United States Naval Observatory’s Astronomical Applications Department website (USNO-AAD 2007). Data were retrieved for the town of Fort White, which is approximately 6 km from the Ichetucknee River. River stage (m) and discharge (m3/s) data were obtained from the United States Geological Survey (USGS 2007) using the Dampier’s Landing gauge (USGS 02322698) for the Floodplain Reach and the Headspring gauge (USGS 02322685) for the Headspring Reach. We used linear regression to identify relationships between nest frequency and temperature, photoperiod, lunar cycle, river stage, and river discharge. Data included in the regressions were from the first date a nest was observed until the last date a nest was observed. 2010 W.A. Strong, E.J. Nagid, and T. Tuten 703 Results We located 24 Suwannee Bass nests: 14 were located in the Floodplain Reach, nine in the Headspring Reach, and one at the base of the Rice Marsh Reach. Over half of the nests (54%) were found in two sections of our study area. Of the nine total nests found in the Headspring Reach, six were at the launch site for recreational users. This is an area that is heavily used by canoeists, kayakers, and people on rafts; is 1–1.5 m deep; and is primarily composed of sand, organic material, and rock bottom, encircled with SAV. In the Floodplain Reach, we found 50% of the nests in a small depositional area along the margin of the river with a substrate largely dominated with a thick layer of mud and organic materials (detritus, leaves, and woody debris). Suwannee Bass began nesting in early March (first nest located 10 March) and ceased in early June (last nest located 5 June). Nests were found in water 33–137 cm deep (mean = 95 cm) (Table 1). Nests were relatively circular in shape, with a mean diameter of 36 cm and mean nest depth of 7 cm. Mean PAC was 48% (range = 5–90%) and was primarily composed of submerged aquatic vegetation (68%; e.g., Strap-leaf Sagittaria, Ludwigia repens J.R. Forst. [Red Ludwigia], filamentous algae) and woody material (27%; e.g., snags, fine woody debris). In general, new nests were fanned down into organic substrate or sandy bottom, depending on nest location. Nest substrate was dominated by organic material (63%); however, sand, leaf litter, fine woody debris, pebbles, limestone, and shell were also used. Suwannee Bass used low-flow areas for nest sites: stream velocity at 75% of the nests was ≤0.01 m/s (mean = 0.01 m/s). Mean temperatures of the Headspring (HR), Rice Marsh (RMR), and Floodplain (FR) reaches were 21.64 °C, 21.58 °C, and 21.63 °C, respectively, and were statistically different (Kruskal-Wallis: χ2 = 17.773; P < 0.001; Fig. 2). However, these differences were so small as to be biologically insignificant and were likely due to the large sample size (n = 1016) and relative lack in variance (SEHR = 0.0062, SERMR = 0.0082, SEFR = 0.0414). Therefore, although statistically significant, we chose to average the temperatures of the three Table 1. Mean, standard error, and range of physical and environmental metrics associated with Suwannee Bass nests in the Ichetucknee River, fl, from March to June 2006. n is the number of nests used for each given metric and PAC is percent area covered. Variable n Mean SE Range Water depth (cm) 24 94.7 6.2 33.0–137.0 Nest diameter (cm) 22 36.2 2.4 14.5–57.0 Nest depth (cm) 22 7.2 0.7 2.7–15.0 PAC (%) 24 48 5 5–90 Stream velocity (m/s) 24 0.01 0.002 0.00–0.04 Temperature (°C) 24 21.69 0.03 21.30–21.70 Daylight (h) 24 13.4 0.2 11.8–14.0 704 Southeastern Naturalist Vol. 9, No. 4 loggers. During our study, the mean water temperature of the Ichetucknee River ranged from 20.8 to 21.9 °C, and the mean water temperature at the time nests were located was 21.7 °C (Table 1). We found no relationship Figure 2. Daily temperatures (4/logger/day) from 17 February to 23 June 2006 in the three reaches of the Ichetucknee River, fl. 2010 W.A. Strong, E.J. Nagid, and T. Tuten 705 between nesting frequency and water temperature (R2 = 0.096). We plotted nest frequency, temperature (°C), and photoperiod (h), against date in order look at how nest frequency occurred with these environmental parameters (Fig. 3). Temperature in Figure 3 is represented as the trend line of mean daily temperature. Photoperiod during nesting ranged from 11.8 to 14 h of daylight, and of the 24 nests, 75% were found during the months of May and June (range = 13.4–14 h). Although nest frequency was highest in May as photoperiod was increasing, nest frequency was not related to day length (R2 = 0.198). Similarly, no relationships were detected between the timing or frequency of nesting with river stage, river discharge, or lunar cycle; river stage and discharge were fairly homogenous throughout our study. We found eggs or fry on 13 of 24 nests. The first reproductive nests were found on 12 May, approximately two months after the first nests were recorded (Fig. 3). The last reproductive nests were found on 5 June. Early in nest development, guarding males fanned out nests so that little to no organic material or algae remained, or down to relatively compact organic substrate. Through time, however, nests with guarding males and eggs or fry were found to be covered with organic debris, where the nest proper was often difficult to distinguish from the surrounding river bed. Discussion Spawning of Suwannee Bass in the Ichetucknee River was characteristic of other Micropterus relative to nest construction, nest depth, and guarding males, as well as relationships to stream flow in lotic habitats (Bruno et. al 1990, Chew 1974, Horel 1951, Hurst et. al 1975, Iguchi et al. 2004, Lukas and Orth 1995, Smitherman and Ramsey 1972, Warren 2009). Nests in the Ichetucknee River were principally located in two main areas in the Headspring and Floodplain reaches. Although we observed nesting activity of other centrarchids in the Rice Marsh Reach, Suwannee Bass nests in this reach were few by comparison. Nests were found in relatively shallow depths and were protected from high water velocities. Consequently, the nest substrate was mostly composed of flocculent organic sediments, and firm sandy substrate does not appear to be a habitat feature necessary for Suwannee Bass spawning. Suwannee Bass spawned in areas with a broad range in PAC; however, nearly 50% of the area adjacent to the nests contained some form of cover. Twenty-two of 24 nests contained SAV adjacent to nests, as opposed to eight nests with woody debris or leaf litter. Of the 22 nests constructed near SAV, 17 contained Strap-leaf Sagittaria and Eelgrass, two submerged aquatic macrophytes of conservation concern in spring-fed systems (Kurz et al. 2003). Proximity of nests to SAV in the Ichetucknee River suggested that aquatic plants may provide important velocity refuges that reduce sediment influx and egg disturbance during spawning. 706 Southeastern Naturalist Vol. 9, No. 4 Figure 3. Frequency of non-reproductive and reproductive Suwannee Bass nests found in the Ichetucknee River, flfrom 17 February to 23 June 2006, with the mean daily temperature trend (°C) and photoperiod (h). 0’s above the x-axis indicate sampling trips with no nests found. Bass and Hitt (1973) found that Suwannee Bass began spawning when temperatures reached 18–19 ºC and spawning occurred from February to June, with a peak in April and May. Suwannee Bass collected from the 2010 W.A. Strong, E.J. Nagid, and T. Tuten 707 Suwannee River system and stocked into ponds in Alabama spawned at 20 ºC (Smitherman and Ramsey 1972). Our findings were similar in that spawning occurred from March to June and peaked in May at a mean water temperature of 21 ºC. The mean temperature of the Ichetucknee River increased by only 1.1 ºC from February to June; however, the nests in the Headspring and Floodplain reaches underwent differences in diurnal and overall temperature patterns. While the spawning area near the headspring experienced nearly homogenous temperature throughout the study period, the spawning area in the floodplain experienced a relatively wide range in temperature. Bass and Hitt (1973) surmised that a variable other than temperature, whether environmental or chemical, must be driving reproduction in the Ichetucknee River. Caldwell et al. (1957) reported that the environment in Silver Springs, fl, was constant in temperature and nearly constant in water chemistry, but had seasonal changes in light intensity and general productivity. They surmised that even in constant temperature, there were factors in the life history of Largemouth Bass that caused periods of increased reproduction to coincide with periods of greater food production. Suwannee Bass spawned in areas with homogenous temperature and in areas with variable temperature, suggesting that water temperature may be a cue that is poorly understood or less important than other environmental factors in the Ichetucknee River. New information regarding rare species such as the Suwannee Bass is necessary to guide conservation and management strategies. As water demands increase, managers of these resources rely on the best available information to balance the needs of people and fish and wildlife. Although we described some aspects of Suwannee Bass spawning, there is a need for more detailed life-history studies in association with the habitat use of this species in order to provide fish and water managers with the best available information to aide in their management decisions. Determining Suwannee Bass spawning-site selection, such as available habitat versus utilized habitat, may provide valuable information as it relates to future water management actions and this species of concern. Acknowledgments We thank the Florida Department of Environmental Protection for their cooperation within the Ichetucknee Springs State Park. This study was funded by a Florida State Wildlife Grant (Project No. 98502532195). Literature Cited Allan R.C., and J. Romero. 1975. Underwater observations of Largemouth Bass spawning and survival in Lake Mead. Pp. 104–112, In H. Clepper (Ed.). Black Bass Biology and Management. Sport Fishing Institute, Washington DC. 534 pp. Bailey R.M., and C.L. 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