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A Paddlefish Entrained by the 2011 Mississippi River Flood: Rescue, Recapture, and Inferred Swim Speed
Jan Jeffrey Hoover, Steven G. George, and K. Jack Killgore

Southeastern Naturalist, Volume 12, Issue 4 (2013): N26–N30

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2013 Southeastern Naturalist Notes Vol. 12, No. 4 N26 J.J. Hoover, S.G. George, and K.J. Killgore A Paddlefish Entrained by the 2011 Mississippi River Flood: Rescue, Recapture, and Inferred Swim Speed Jan Jeffrey Hoover1,*, Steven G. George1, and K. Jack Killgore1 Abstract – We observed a large adult Paddlefish entrained from the Mississippi River through the Bonnet Carré spillway, south Louisiana, which was injured and underweight. We captured, measured (23 metrics), and tagged the fish. After it had spent a week at large on the floodway, we recaptured and released it back into the Mississippi River. The specimen was re-captured eight months later in northern Mississippi, 627 km upriver from where it was released. Distance traveled and water velocities in the river indicate that the fish was traveling at least 90–197 cm/s for prolonged periods, equivalent to gross speeds of 77–170 km/d. This incident suggests that a large entrained fish, trapped for several days in a hyperthermic and hypoxic habitat, can be viable when returned to the river. It also demonstrated that rescue efforts could reduce impacts of spillway operations to fish populations, and that comprehensive field assessment of fish morphology can be benign t o fish. Introduction. The rescue and recapture of a Polyodon spathula Walbaum (Paddlefish) entrained through the Bonnet Carré spillway provided the opportunity to calculate volitional swim speed, evaluate the effectiveness of rescue efforts, and evaluate the effects of taking detailed morphometric data on fish survival. The Bonnet Carré Spillway, near Norco, LA, in St. Charles Parrish, is one of the largest freshwater diversion structures in the world, diverting floodwaters from the main channel of the Mississippi River onto a floodway and into Lake Pontchartrain, to prevent flooding in New Orleans (USACE 2012a). The structure is located 52.5 river kilometers (RKm) upriver from New Orleans, with an opening of 2.1 km and a design capacity of 7079 m3/s. It has been opened 10 times since its completion in 1931, most recently 9 May to 20 June 2011, during the Mississippi River “flood of the century”, when maximum flow through the structure was 8948 m3/s. Following closure of the structure in 2011, state and federal biologists conducted survey and rescue operations to capture and release protected species back into the river. Morphometric data were collected on Paddlefish (23 variables) and Scaphirhynchus albus Forbes & Richardson (Pallid Sturgeon) (26 variables) prior to release, which increased handling time of those species. Rescue and recapture. On 23 June 2011, we used electro-fishing to collect a Paddlefish in Barbar’s Canal 0.5 km downstream of the diversion structure at 30.00411ºN, 90.43355ºW. The fish measured 924 mm eye–fork length (EFL), 1441 mm total length (TL), and 8.95 kg weight. A Paddlefish this length from Louisiana waters is typically 5–7 y old, has a high probability of being sexually mature, and is, therefore, capable of long-distance movement (Reed et al. 1992). This fish, however, exhibited multiple indications of physical trauma and low robustness, including: 1) superficial cuts laterally, anterior to dorsal fin; 2) frayed, broken lower lobe of caudal fin; 3) eroded tip of rostrum; 4) small girth; and 5) protruding bases of dorsal and anal fins (Fig. 1). The fish was held on-site in an aerated live-well filled with river water. We processed it for morphological data (using calipers), marked it with a unique number and our contact information using a Floy tag (FLOY TAG, Inc., Seattle, WA), returned it to the live-well, and released it into the canal. At that time, the river water was running high and overtopping the channel, it had a temperature of 28 °C, and was normoxic at 6.05 ppm dissolved oxygen (DO). Air temperature was 25 °C and weather was overcast during handling. Time in captivity was approximately 40 min, and time out of water was 5–6 min. 1US Army Engineer Research and Development Center, EE-A, 3909 Halls Ferry Road, Vicksburg, MS 39180-6199. Corresponding author - Notes of the Southeastern Naturalist, Issue 12/4, 2013 N27 2013 Southeastern Naturalist Notes Vol. 12, No. 4 J.J. Hoover, S.G. George, and K.J. Killgore During subsequent sampling at the same location, we collected this Paddlefish again in a gill-net on 28 Jun 2011. At that time, conditions in the canal were becoming unfavorable for Paddlefish. Adult Paddlefish require large volumes of open water, water temperatures <28 °C, and DO levels >2 ppm and >30% saturation (Crance 1987, Mims et al. 1999, Zigler et al. 1999). The canal water level was low and receding rapidly within the channel; the water had warmed to 29–31 °C, and was hypoxic at 2.7–3.3 ppm DO (35–51% saturation). We recorded these values 1.5–2 h after sunrise; we expected lower water levels, higher temperatures, and lower DO during the following 18 hours. Because of the deteriorating conditions in the canal, we released the fish into the Mississippi River at RKm 204.8; 29.99791ºN, 90.43031ºW. Air temperature at this time was 29 °C , and weather was clear. Time in captivity was <1 hour, and time out of water was <5 min. A commercial fisherman recaptured the Paddlefish on 3 Mar 2012 in a gill-net at Kentucky Bend, RKm 832.0, 33.11662ºN, 91.11374ºW, south of Greenville, MS. It was not measured or photographed, but appeared healthy and was one of four Paddlefish caught there that day. The tag was removed to verify the catch, and fish was released on-site. The Paddlefish had moved upriver 627.1 km over a period of 249 days, averaging 2.5 km/day or 2.9 cm/s net upriver movement. Inferred swim-speeds. To achieve the movement documented here, fish swim speeds would have averaged 3 cm/s greater than water velocities in the river. Water velocities in the Mississippi River, during the period that the Bonnet Carré Paddlefish was at liberty were high, 90–190 cm/s, due to receding flood waters in summer and rising river stages in winter (Table 1). Swim speeds of this magnitude are characteristic of fast-swimming pelagic Figure 1. US Army Corps of Engineers Natural Resource Specialist, Bill Maus, holding Paddlefish entrained at Bonnet Carré Spillway in Louisiana, 23 Jun 2011. Inset shows ventral view of rostrum. Note slimness of fish, lacerations on body, frayed fins, and erosion at tip of rostrum. 2013 Southeastern Naturalist Notes Vol. 12, No. 4 N28 J.J. Hoover, S.G. George, and K.J. Killgore marine species such as Xiphias gladius L. (Swordfish), Makaira nigricans Lacepède (Blue Marlin), sharks, and tuna (Block et al. 1992). These speeds are also credible for a Paddlefish when compared with previous laboratory studies. Estimated relative swim speeds, in body lengths per second, bls-1 (i.e., absolute swim speed in cm/s divided by the EFL in cm), were 1.0-2.1 bls-1. These values are comparable to or lower than sustained swim speeds of juvenile Paddlefish <90 mm EFL, which range from 1.1 to >4 bls -1 (Burggren and Bemis 1992, Hoover et al. 2009a). Long-distance upstream movements of Paddlefish are common and can occur over short time periods (e.g., Jennings and Zigler 2009, Pracheil et al. 2012, Russell 1986, Stancill et al. 2002), but the movement rate estimated from the recapture of this Paddlefish is exceptional. Annual and seasonal movements of 20 to more than 333 km have been documented (Rosen et al. 1982, Russell 1986, Stancill et al. 2002) but these are lower than the 670 km demonstrated here. Daily movements of 2–11.5 km in impounded reaches of rivers have been estimated from telemetry (Kerns et al. 2009, Moen et al. 1992, Zigler et al. 1999) but these are substantially lower than our estimated gross speeds here of 77.5–170.3 km/d traveled for 249 days. Our calculations are conservative because they assume unvarying, linear, mid-channel movement. This Paddlefish almost certainly navigated around some dikes and other shoreline irregularities, and made forays into habitats frequented by conspecifics such as off-channel backwaters, abandoned channels (Fremling et al. 1989), oxbow lakes, sloughs, and borrow pits (Baker et al. 1991). If lateral movements could be incorporated into our estimates, inferred swimspeeds would be substantially higher. Reducing impacts of entrainment. Survival of Paddlefish released as by-catch may exceed 90% (e.g., Kerns et al. 2009) and Paddlefish often thrive following surgical procedures and passage through structures (e.g., Pierce et al. 2011, Stancill et al. 2002). Survival and migration of this particular fish, however, are noteworthy due to the confinement of the fish and its poor condition—it exhibited multiple external minor injuries and its weight was low. Based on range-wide data, regression predicted that standard weight (Ws) for a fish this size, of unknown gender, should be 13.9 kg; its relative weight (i.e., weight/Ws x 100) was 64, placing it only in the 5th percentile for the species (Brown and Murphy 1993). Normal swimming, then, could have been impaired by damaged fins and long-range movements reduced by low energy reserves. Also, the fish was tightly confined in warm water and processed out of water during warm weather. Respiratory stress could have occurred from limited ability Table 1. Hypothetical passage and inferred swim speeds of an entrained Paddlefish following its release into the Mississippi River 28 Jun 2011. Upstream limits of each reach are based on a gage providing hydraulic data. Distances between points are measured in river km (RKm). Passage periods, in calendar dates, assume uniform net upriver movement of 2.5 km/day (2.9 cm/s) and are proportionate to length of reach. River velocities (cm/s) are based on average or mean (SD) velocity for corresponding dates (USACE, 2012b). Gross swim speeds: bls-1 = body lengths per second, km/ day = kilometers per day. Release to Baton Rouge to Red River to Natchez to Vicksburg to Baton Rouge Red River Natchez Vicksburg recapture Distance 162.7 119.1 98.0 116.5 130.8 Passage 28 Jun–01 Sep 01 Sep–18 Oct 18 Oct–26 Nov 26 Nov–11 Jan 11 Jan–03 Mar River velocity 149.6 (3.7) 94.9 (2.2) 86.8 (3.5) 194.2 (13.8) 143.7 (25.4) Fish speed bls-1 1.65 1.06 0.97 2.13 1.59 km/day 131.8 84.5 77.5 170.3 126.7 N29 2013 Southeastern Naturalist Notes Vol. 12, No. 4 J.J. Hoover, S.G. George, and K.J. Killgore to ram-ventilate (Burggren and Bemis 1992) and from exposure to temperatures >28 °C, which are considered unsuitable for adult Paddlefish (Crance 1987). This Paddlefish was able to recover following capture, likely due in part to our judicious handling and its prompt release. Our results have implications for assessment and mitigation of water-diversion structures that entrain protected and imperiled species like Paddlefish and Pallid Sturgeon. Under the Endangered Species Act, the presence of Pallid Sturgeon below the Bonnet Carré constitutes a “take”, but sampling and rescue operations offer a means of assessing and reducing that take. Field studies on fish morphology. Paddlefish show substantial morphological variation within a population and across their geographic range, apparently as a result of phenotypic adaptations to hydrology, and the variation is indicative of intraspecific diversity (Hoover et al. 2000, 2009b; Stockard 1907). Field measurements of morphological characters prior to release of fish enable verifiable identification of forms, and appreciation of ecomorphological adaptations. For other species, such as river sturgeon, field observations enable confident and verifiable identification to species (Murphy et al. 2007). Concerns exist among some agency biologists that such procedures, which add only a few minutes of handling time, are injurious to the fish. By documenting the successful release, recovery, and migration of this Paddlefish under less than ideal conditions, we have demonstrated recovery of the fish under study, and the likely safety of such protocols. Acknowledgments. Funding for field studies at Bonnet Carré was provided by the US Army Engineer New Orleans District, New Orleans, LA. Funding for our Paddlefish morphology study is provided by the Basic Military Engineering Research Program. Field collections were conducted by the ERDC Fish Ecology Team and Louisiana Department of Wildlife and Fisheries, Lacombe Office. Assistance with logistics and data-recording were provided by Chris Brantley, Bill Maus, Alan Katzenmeyer, and Todd Slack. Re-capture was reported by William Lancaster. Permission to publish was granted by the Chief of Engineers, Army Corps of Engineers. Literature Cited Baker, J.A., K.J. Killgore, and R.L. Kasul. 1991. Aquatic habitats and fish communities in the lower Mississippi River. 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