Southeastern Naturalist E.G. Stell, J.J. Hoover, B.A. Cage, D. Hardesty, and G.R. Parsons 2018 Vol. 17, No. 2 230 2018 SOUTHEASTERN NATURALIST 17(2):230–238 Long-Distance Movements of Four Polyodon spathula (Paddlefish) from a Remote Oxbow Lake in the Lower Mississippi River Basin Ehlana G. Stell1,*, Jan Jeffrey Hoover2, Bryan A. Cage3, Darrin Hardesty4, and Glenn R. Parsons1 Abstract - Short-term movements of adult Polyodon spathula (Paddlefish) are welldocumented, but long-term movements are underreported. In this study, we describe extraordinary distances traveled by 4 Paddlefish that were captured, tagged, and released in Moon Lake, a remote oxbow lake in Coahoma County, MS. After 8–24 months at large, the 4 fish were recaptured in the Missouri, Mississippi, and Ohio rivers, having traversed 1408–2433 km from Moon Lake through multiple waterways downstream to the Mississippi River at Vicksburg, MS, and then upriver to 4 geographically disparate locations. The multiple waterways used by these fish and the extensive distances traveled demonstrate the potential importance of backwater habitats located away from th e mainstem river, and also underscore the need for interstate cooperation to protect Paddl efish populations. Introduction Historically, Polyodon spathula (Walbaum) (Paddlefish) ranged across the entire Mississippi River Basin and several Gulf Coast rivers, but it declined significantly throughout the 20th century (Wilson and McKinley 2004). The species occupies a unique position in freshwater ecosystems of North America as the only large-bodied (>2 m in length, >70 kg in weight), zooplanktivorous, filter-feeding, continuously swimming, obligate ram-ventilating fish (Kuhajda 2014). In the early 20th century, Paddlefish were abundant throughout the Yazoo River drainage (also known as the Mississippi Delta). Many individuals caught during the early 1900s were in better condition (i.e., were more robust for their length) than modern-day Paddlefish, and populations briefly supported intense commercial fisheries for meat and for caviar (e.g., Stockard 1907). These fisheries could not be sustained, and populations were rapidly depleted until lakes re-flooded and were re-colonized from the river (Alexander 1914, Stockard 1908). Interest in the movements of Paddlefish through US waterways has increased because of overexploitation and the hydrologic alteration of nearly every major water system in the US (Baker et al. 1991, Zigler et al. 2004). Hydrologic alterations to the mainstem Mississippi River and tributaries include flood-controlling 1Department of Biology, The University of Mississippi, 120 Shoemaker Hall, University, MS 38677. 2US Army Engineer Research and Development Center, Vicksburg, MS 39180- 6199. 3Department of Biology, James Madison University, 330 Burruss Hall, Harrisonburg, VA 22807. 4Mississippi Department of Wildlife, Fisheries, and Parks, 1505 Eastover Drive, Jackson, MS 39211. *Corresponding author - egstell@gmail.com. Manuscript Editor: Hayden Mattingly Southeastern Naturalist 231 E.G. Stell, J.J. Hoover, B.A. Cage, D. Hardesty, and G.R. Parsons 2018 Vol. 17, No. 2 levees, floodways, dredging, revetments, dikes, navigation structures (i.e., locks and dams), and water-retention structures (i.e., reservoir dams). Such alterations over the last 2 centuries have not only stabilized the meandering river, but effectively cut off many vital feeding areas in backwaters (e.g., oxbows and sloughs) for Paddlefish (Baker et al. 1991). Movement patterns of Paddlefish have been documented primarily over relatively short distances and in the upper Mississippi River basin (Zigler et al. 1999, 2003, 2004), whereas the long-distance movements of Paddlefish remain largely understudied with few exceptions (Moen et al. 1992, Rosen et al. 1982), especially in the lower Mississippi River basin. Without this information, stock assessments and informed management decisions will continue to be hindered. In this report, we document long-distance longitudinal movements of Paddlefish in the Mississippi River Basin from a single point of release. Field-site Description Moon Lake is an oxbow lake near Clarksdale, MS, in Coahoma County, ~2 km east of the Mississippi River (Fig. 1). Despite this short, 2-km overland distance, water and fish leaving Moon Lake must travel 516 km to reach the main channel of the Mississippi River by first exiting Moon Lake’s outlet into Yazoo Pass, which, in turn, flows through a series of waterways (Coldwater, Tallahatchie, and Yazoo rivers) downstream to the Mississippi River at Vicksburg, MS. Moon Lake’s surface area is 9.3 km2 (9300 ha) and it reaches water depths up to 9 m within a 0.45-km2 area (Cage 2015). In the early 20th century, large populations of Paddlefish inhabited Moon Lake, which supported a commercial fishery producing meat, caviar, and fish oil (Hussakof 1911). Commercial fishing in Moon Lake was limited to short, regulated seasons from 1950 to 1986; was prohibited from 1986 to 2010; and was briefly reinstated from December 2010 to February 2011,when 468 Paddlefish were harvested and another 954 were captured and released (MDWFP 2011). An additional commercial season for Paddlefish took place in February 2 014. Despite almost a century of having a long-distance connection to the Mississippi River, Moon Lake continues to support a large population of robust Paddlefish. In 2010, the estimated population size based on mark–recapture data for that year was 1625 adults (MDWFP 2011). This estimate is equivalent to a density of 1.7 fish/ha, which exceeds the values of 0.21 to 1.2 fish/ha for 9 of 12 Paddlefish populations reviewed by Quinn (2009). Paddlefish in Moon Lake are also unusually heavy for their size, with the majority of individuals sampled during 2013–2014 equivalent to or exceeding 75th-percentile weight for the species throughout its range (Fig. 2). Figure 1. The map above depicts the pathway of tagged Paddlefish from (0) Moon Lake, Coahoma County, MS, through the Yazoo Pass to the Tallahatchie River, to the Yazoo River, to the Mississippi River (at Vicksburg). Each symbol represents the location of a recauptured Paddlefish (1) near Gavin’s Point Dam along the Nebraska/South Dakota border, (2) Sibley, MO, in the Missouri River, (3) Grand Tower, IL, in the Mississippi River, (4) Paducah, KY, in the Ohio River. Southeastern Naturalist E.G. Stell, J.J. Hoover, B.A. Cage, D. Hardesty, and G.R. Parsons 2018 Vol. 17, No. 2 232 Figure 1. [Caption on previous page]. Southeastern Naturalist 233 E.G. Stell, J.J. Hoover, B.A. Cage, D. Hardesty, and G.R. Parsons 2018 Vol. 17, No. 2 Methods Paddlefish were marked during 2 recent studies: (1) a population-size assessment prior to commercial harvests regulated by the Mississippi Department of Wildlife, Fisheries, and Parks (MDWFP) (2010 and 2014, n = 57; MDWFP 2011); and (2) a Paddlefish ecology study by the University of Mississippi (2012–2014, n = 26; Cage 2015). In each study, researchers used gillnets to collect, mark with jaw tags, and promptly release Paddlefish back into the lake. Jaw tags were 9 mm x 45 mm stainless steel bird-bands (model #1242-16 Monel; National Band and Tag Company, Newport, KY), imprinted with the agency abbreviation, a unique 4-digit identification code, and a telephone number; tags were attached to the dentary bone of the lower jaw prior to release (Fig. 3). Most Paddlefish were not measured because the objectives of the population-assessment studies were short-term and did not include growth estimates. However, some Paddlefish were measured from the anterior orbit to the shortest caudal rays—eye-to-fork length (EFL). Paddlefish were subsequently recaptured by anglers or during commercial harvest. We employed Google Earth’s® measuring tool to estimate travel distances to point-ofrecapture for the 4 individuals recaptured outside of Moon Lake. For each fish, we delineated a route from the outflow of Moon Lake and through waterways along the shortest path to the recapture point. Results and Discussion Thirty-three of the 83 fish tagged were recaptured at least once in the lake (primarily by commercial harvesters), but 4 other fish were recaptured by recreational anglers in water bodies remote from Moon Lake (Table 1, Fig. 1). For these 4 Figure 2. Comparison of log length (mm)–weight (g) relationships of Moon Lake Paddlefish (n = 53) collected in 2013–2014 for metabolic and telemetry studies, shown as black squares and solid regression line (Cage 2015) with that of the upper 75th percentile of US Paddlefish, shown as dashed regression line (Brown and Murphy, 1993). Southeastern Naturalist E.G. Stell, J.J. Hoover, B.A. Cage, D. Hardesty, and G.R. Parsons 2018 Vol. 17, No. 2 234 individuals, distances between Moon Lake and the recapture sites ranged from 1408 km to 2433 km. Recaptures occurred after 8 months but within 2 y of tagging. Rates of movement for the 3 fish with known release and recapture dates ranged from 1.9 km/day to 4.6 km/day, whereas the fourth fish was estimated to have moved at a rate of ~8..9 km/day. Of the 4 recaptured fish, 2 were collected near dams, where Paddlefish are impeded from further upstream movement and sometimes congregate. Paddlefish #1 was collected at the base of Gavin’s Point Dam, a reservoir that does not provide fish passage upriver. Paddlefish #4 passed through 3 lock-and-dam structures Table 1. Release and recapture dates of 4 individual Polyodon spathula (Paddlefish) in Moon Lake, Coahoma County, MS, and the minimal distances traveled while at large. For Paddlefish #1, an estimate of 272 days is provided because exact dates of release and recapture were unavailable. AEstimate. Time at Distance Rate large traveled per day # Release date Recapture date (days) Recapture location (km) (km/day) 1 1 February 2010A 31 October 2010A 272A Gavins Point Dam, 2433 8.94A Yankton, SD 2 22 March 2013 21 March 2014 364 Missouri River, 1681 4.61 Sibley, MO 3 14 February 2014 22 February 2016 738 Mississippi River, 1440 1.95 Grand Tower, IL 4 6 July 2014 8 July 2016 733 Ohio River, 1408 1.92 Paducah, KY Figure 3. Jaw-tag placement on an individual Paddlefish captured in Moon Lake, MS (Photograph © MDWFP). Southeastern Naturalist 235 E.G. Stell, J.J. Hoover, B.A. Cage, D. Hardesty, and G.R. Parsons 2018 Vol. 17, No. 2 (Olmsted Lock and Dam, and Lock and Dams 52 and 53) to reach Paducah, KY, which is downriver from Smithland Lock and Dam and 17 other upriver structures. Distances traveled by the 4 Moon Lake Paddlefish exceeded those documented in most previous studies, in which movements of 400–1900 km were observed in the Mississippi River (moving downstream) and Cumberland River (Moen et al. 1992; Rosen et al. 1982; Stancill et al. 2002; Zigler et al. 1999, 2003, 2004). Zigler et al. (2004) recorded Paddlefish movement through a series of navigational obstacles and showed that Paddlefish are likely to move upstream during open river conditions when gates are raised out of the water instead of locking through with vessels. Stancill et al. (2002) also reported tagged fish passing through 5 lock-and-dam structures prior to recapture, similar to the results presented here for Paddlefish #4. Rates of movement by Moon Lake Paddlefish of ~2–9 km/day are similar to those reported in previous studies. Kerns et al. (2009), Moen et al. (1992), and Zigler et al. (1999) reported movement rates of 2–11.5 km/day. Rates of movement of Moon Lake Paddlefish presumably vary depending on whether they are moving downriver, through the smaller waterways (presumably at higher rates), or upriver, through the Mississippi River (presumably at lower rates). Our rates approximate those for a single Paddlefish that moved upriver from Norco, LA, to Greenville, MS, at an overall rate of 2.5 km/day (Hoover et al. 2013). Slower daily rates of movement, ≤5 km/d, suggest that Paddlefish in the lower Mississippi River expend a great deal of energy during their upriver movements and/or are making extensive lateral movements into littoral areas and backwater habitats to feed or rest. Paddlefish #3 and #4 were at large for 2 years; thus, it is possible that they made this migration twice and the rate of travel would be twice the estimated swim speed (~3.9 km/day), which is similar to Paddlefish #2. In the southern US, Paddlefish reach sexual maturity at 4–12 y and 7–19 kg mass (Jennings and Zigler 2009). We believe that backwaters and oxbow lakes, even those remote from the mainstem river, can be vitally important to Paddlefish and maybe analogous to the pre-migratory fattening habitat-use observed in other species of vertebrates (King and Farner 1963, Nicieza and Metcalfe 1997). These habitats provide velocity refugia (reducing energy needs) and abundant sources of zooplankton (increasing energy acquisition); thus, they have historically enabled Paddlefish to build energy reserves and mass (Cage 2015, Stockard 1907). Moon Lake Paddlefish are especially robust in comparison to Paddlefish elsewhere (Fig. 2). Mature males and females in Moon Lake have substantial girth and fat deposits that make it difficult to distinguish gender based on external appearance, which suggests that backwaters and oxbow lakes in the Lower Mississippi River basin can play a role in facilitating long-distance migrations by Paddlefish. Rosen et al. (1982) suggested that mature Paddlefish make extensive migrations for reproduction. Before their recapture, the Paddlefish described here all passed by at least 3 documented spawning grounds (J.K. Killgore, US Army Engineer Research and Development Center, Vicksburg, MS, unpubl. data) in the mainstem Mississippi River, based on USACE trawling and seining surveys in which early young-of-year Paddlefish (<40 mm EFL and <60 mm TL) were collected. Each of Southeastern Naturalist E.G. Stell, J.J. Hoover, B.A. Cage, D. Hardesty, and G.R. Parsons 2018 Vol. 17, No. 2 236 the 4 Moon Lake Paddlefish, however, traveled through these 3 known spawning reaches with movements extending >520 km past the lowermost reach and >160 km past the uppermost reach. More research is needed to determine whether these longer-distance movements were for spawning purposes. Paddlefish of the Mississippi River basin differ genetically and morphologically from those in the Tombigbee and Alabama River drainages but are relatively similar among locations within the basin (Epifanio et al. 1996, Heist and Mustapha 2008, Hoover et al. 2009). Lack of significant genetic heterogeneity within the Mississippi River drainage suggests a panmictic population with widespread movement of individuals throughout the system as opposed to local populations remaining in isolated sections of the Mississippi River and tributaries. The long-distance movements of the 4 Moon Lake Paddlefish we studied are consistent with the types of movements needed to yield low genetic heterogeneity in the popu lation. If hydrological alterations and barriers continue to be introduced into the Mississippi River drainage, then Paddlefish populations such as those in Moon Lake could be isolated, thereby eliminating their genetic contribution. Yazoo Pass, the outflow from Moon Lake and beginning of Paddlefish egress through the Mississippi Delta, is at times as shallow as a 0.5 m and frequently blocked by woody debris. The 516-km distance from Moon Lake to the Mississippi River is composed of smaller water systems; if any of these tributaries became blocked, then all Paddlefish utilizing this area would be isolated. Paddlefish do not confine themselves to any one jurisdictional region; thus, their movements demonstrate the need for interdepartmental and interstate cooperation to maintain clear fishways and preserve local populations. Pracheil et al. (2012) and Hupfeld et al. (2016) emphasized the need for consistent regulation in major rivers throughout the geographic range of Paddlefish. However, as evidenced by the movement of fish from Moon Lake, we also need to include backwater areas, even those indirectly connected to the main channel, in regulatory or conservation decisions. 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