K. Jack Killgore

Distribution and Abundance of Fishes Associated with Submersed Aquatic Plants in the Potomac River

Abstract The distribution and abundance of fishes in submersed aquatic plants of three relative densities (no plants, intermediate plant density, high plant density) were estimated in the tidal Potomac River near Alexandria, Virginia. Fish were sampled with a boat-mounted electroshocker at night in May (when plants were emerging), August (peak plant densities), and November (plant senescence) of 1986. Mean densities of all plants ranged from 9 to 33 g/m2 (dry-weight basis) in May, and 400 to greater than 1,000 g/m2 in August and November. Hydrilla verticillata was usually the dominant aquatic plant. In May, overall mean fish abundance was highest in areas of high plant density (36 fish/5 min shocking), whereas in August and November fish abundance was highest in areas of intermediate plant densities (100 and 62 fish/5 min electroshocking, respectively). Areas without plants contained a relatively high number of filter-feeding fishes, including Atlantic menhaden Brevoortia tyrannus and blueback herring Alo...

Observations of Swimming Ability in Shovelnose Sturgeon (Scaphirhynchus platorynchus)

ABSTRACT Swimming performance and behavior of five adult (57—69 cm fork length) shovelnose sturgeon, Scaphirhynchus platorynchus, were studied in a 945-L swim tunnel at 16° C. Fifteen-minute critical swimming speeds ranged from 65 to 116 cm s−1. Sturgeon swam volitionally at low speeds (5—30 cm s−1), but at higher speeds (40—120 cm s−1) sturgeon alternated between active swimming and appressing themselves to the bottom of the tunnel. This second behavior is enhanced by sturgeon morphology—streamlined body shape, flat rostrum, and large pectoral fins. It allows shovelnose sturgeon to exploit river bottoms as a refugia from current and maintain position in high velocities.

Effect of Pectoral Fin Ray Removal on Station-Holding Ability of Shovelnose Sturgeon

Abstract The effect of fin ray removal on swimming performance was evaluated for shovelnose sturgeon Scaphirhynchus platorynchus from the lower Mississippi River. Immediately upon collection, the marginal pectoral fin ray was removed from some fish, and others were left unclipped as a control group. Fish were promptly returned to the laboratory and held in 1,300-L recirculating tanks at 21-26°C. After a minimum recovery time of 48 h, individual fish were placed in a 1,000-L, Brett-type swim tunnel, and their ability to maintain station in flowing water by swimming, skimming, or substrate appression was tested by subjecting fish to increasing speeds beginning at 10 cm/s. After a 60-min swimming bout, speed was increased by 10 cm/s. This was repeated until the fish could no longer maintain station. Fin ray removal had no significant effect on critical station-holding speed (CSHS). The CSHS (mean ± SE) of fin-ray clipped fish was 60.1 ± 4.2 cm/s, and that of unclipped fish was 59.2 ± 3.0 cm/s. Correlation an...

Evaluation of Propeller-Induced Mortality on Early Life Stages of Selected Fish Species

Abstract The mortality of ichthyoplankton entrained through a scale model of a towboat propeller was evaluated in a large (>2 million L) circulating water channel. Five species of fish (larval shovelnose sturgeon Scaphirhynchus platorynchus, larval lake sturgeon Acipenser fulvescens, the larvae and eggs of paddlefish Polyodon spathula, larval blue sucker Cycleptus elongatus, and juvenile common carp Cyprinus carpio) were tested. Replicate groups of individuals were subjected to one or more shear stress levels (634, 1,613, 3,058, and 4,743 dynes/cm2 (1 dyne = the force that would give a free mass of 1 g an acceleration of 1 cm/s2). Mortality was a linear function of shear stress for all species and life stages. Paddlefish eggs and common carp juveniles were more resistant to shear stress than all larval fish. Smaller larvae (lake sturgeon and blue suckers) experienced higher mortalities (>75%) than larger larvae (shovelnose sturgeon and paddlefish). The conditional mortality (i.e., treatment less control m...

Stranding Potential of Young Fishes Subjected to Simulated Vessel-Induced Drawdown

Abstract During early life stages, fish in the Mississippi River system may become stranded by shoreline drawdowns induced by the passage of commercial vessels. We examined the stranding of larval shovelnose sturgeon Scaphirhynchus platorynchus, paddlefish Polyodon spathula, and bigmouth buffalo Ictiobus cyprinellus and of juvenile blue catfish Ictalurus furcatus, largemouth bass Micropterus salmoides, and bluegill Lepomis macrochirus in a laboratory flume. Stranding was measured at three vertical drawdown rates (0.76, 0.46, and 0.21 cm/s) and two bank slopes (1:5 and 1:10). Blue catfish, shovelnose sturgeon, and paddlefish were not tested at both bank slopes. Susceptibility to stranding varied among species and was independent of drawdown rate. At a slope of 1:5, shovelnose sturgeons had the highest stranding percentage (66.7%), followed by paddlefish (38.0%), bluegills (20.0%), bigmouth buffalo (2.2%), and largemouth bass (0.0%). At 1:10, blue catfish had the highest stranding percentage (26.7%), follow...

Swimming Performance of the Topeka Shiner (Notropis topeka) an Endangered Midwestern Minnow

Abstract The Topeka shiner (Notropis topeka) is imperiled by extensive changes in stream hydrology. Responses of shiners to changes or variation in stream hydraulics, however, have not been quantified, hampering conservation efforts. We quantified swimming endurance and behavior for Topeka shiners in a laboratory swim tunnel. Sustained swimming (>200 min) was observed at water velocities of 30–40 cm/s. Prolonged and burst swimming (approximately 10 min to less than 0.1 min) was observed at water velocities of 40–75 cm/s and endurance was negatively correlated with water velocity. Larger individuals (4.4–5.5 cm standard length) exhibited greater sustained swimming ability than smaller individuals (3.0–4.2 cm standard length). Oral grasping of wire mesh within the swim tunnel was frequently employed at moderate water velocities (35–50 cm/s); this behavior may limit downstream displacement of shiners during freshets. Topeka shiners are capable of swimming speeds faster than water velocities which they typically inhabit. Fishways and culverts, therefore, may be employed to facilitate dispersal and recolonization. Swimming endurance data are used to determine optimal size and water velocities for such structures.

Effects of Turbulence on Yolk-Sac Larvae of Paddlefish

Abstract A laboratory experiment was designed to test the effect of turbulence on mortality of yolk-sac larvae of paddlefish Polyodon spathula. High turbulence (6,320 dynes˙cm-2) resulted in larval mortality of 87 and 80% in frequent (one event per hour) and infrequent (one event every 3 h) treatments, respectively. Larvae exposed to low turbulence (1,838 dynes˙cm-2) suffered mortality of only 3 and 13% in the frequent and infrequent treatment groups, respectively. Frequency of events was not as important as intensity of turbulence in causing mortality.

Status and Recovery Potential of Gulf Sturgeon in the Pearl River System, Louisiana–Mississippi

Abstract From 1992 through 1996, 257 Gulf sturgeon Acipenser oxyrinchus desotoi were captured in the Pearl River system of Louisiana and Mississippi, but adults (>130 cm fork length) constituted less than 2% of the catch. The summer population size in 1996, estimated by mark–recapture methods, was 292 individuals that were age 2 or older. Instantaneous total mortality rate (Z), estimated with a catch curve, was 0.41, for an annual mortality rate of 34%. Modeling the population with Z = 0.41 resulted in declining populations under two different recruitment scenarios. Mortality rates will have to be reduced to Z = 0.16–0.24 for the population to be self-sustaining by 2023, the target year in the Gulf Sturgeon Recovery Plan. Mean fork length of Gulf sturgeon in the Pearl River system was significantly larger in 1970 than in 1985 and 1992–1996, indicating that the population may not have improved since 1985. An increase in population size should be detectable within 6 years of achieving acceptable levels of m...

Collection, Age, Growth, and Population Attributes of Triploid Grass Carp Stocked into the Santee-Cooper Reservoirs, South Carolina

Abstract Collection techniques were developed for monitoring populations of triploid grass carp Ctenopharyngodon idella stocked into the Santee-Cooper reservoirs, South Carolina, to control hydrilla Hydrilla verticillata. Skilled bowfishers, who were paid a bounty of US

Feeding Habitats of Young-of-year River Sturgeon Scaphirhynchus spp. in the Lower Mississippi River

50.00 per fish, collected 69, 125, and 160 triploid grass carp in 1992, 1993, and 1994, respectively. Fish were fully vulnerable to bowfishing by age 2. Examination of sectioned utricular otoliths (lapilli) revealed annual marks formed during May–June. Weight (W) increased linearly with age (t, years), for ages 1–6; W = –2,360 + 3,016t. Age-specific weights ranged from 0.39 kg to 15.68 kg for fish of ages 1–6. The weight to total length (TL, mm) relation varied little during the study and was W = 0.00000425(TL)3.185. A von Bertalanffy growth equation was fitted to describe the relation between length and age. TL t = 1,044(1 – e –0.615(t – 0.590)). The annual rate of mortality was 22% in 1994. We estimate that 350,000 triploid grass carp, w...