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Grass carp Ctenopharyngodon idella are sometimes used as a biological tool for managing aquatic vegetation in reservoirs. Sterile, triploid fish were stocked in Devils Lake, Oregon, during 1986, 1987, and 1993 to control aquatic vegetation. We present a case study for using multiple measures on the same fish to determine whether illegal stocking of fertile, diploid grass carp occurred. An investigation into the estimated age of a dead grass carp found in Devils Lake suggested that it was significantly younger than would otherwise be expected, given the only stocking events occurred during 1986, 1987, and 1993. To determine whether illegal stocking or reproduction by presumed sterile grass carp had occurred in Devils Lake, we conducted a study that balanced the needs of lethally sampling grass carp for biological measures with the socially and politically sensitive sentiment of the pro–grass carp citizenry of Devils Lake. These considerations, in combination with a low catch per-unit effort, resulted in a modest sample size for grass carp. We sampled grass carp and recorded multiple measures for each fish. Ploidy testing of blood samples indicated the grass carp were all triploid. Based on gonadal histopathology, six fish were male, two were female, and two were sex-indeterminate with severe gonadal dysgenesis. Age estimates from lapillus otoliths were consistent with fish originating from the legal stocking events in Devils Lake. The grass carp were 21–30 y old, and we were unable to find published reports of grass carp anywhere else in the world that are older. The grass carp were significantly smaller than much younger fish from other regions. The small size of these grass carp relative to their age in Devils Lake suggests food limitations that stunted growth. The dead grass carp that was the impetus for this study was aged by anatomical structures that we have since found to be unreliable. This suggests that the dead grass carp was probably in fact older and originated from the legal stockings. The use of multiple biological measurements on a modest sample size of grass carp, combined with the knowledge that no juvenile grass carp have been observed since legal stocking occurred, lead us to conclude that the grass carp in Devils Lake are sterile fish that originated from legal stocking events.

The triploid Grass Carp Ctenopharyngodon idella has been used to control hydrilla Hydrilla verticillata infestations in southern U.S. reservoirs for several decades. After eliminating hydrilla in the water column, Grass Carp must be maintained in sufficient densities to control hydrilla regrowth from the tuber banks in the hydrosoil. We monitored the long-term response of triploid Grass Carp populations that had eliminated hydrilla within the water column in two Piedmont (Lake Norman and Mountain Island Lake, North Carolina) and two Coastal Plain reservoirs (the Santee Cooper system comprising Lakes Marion and Moultrie, as well as the connecting canal in South Carolina). Triploid Grass Carp stocked in Lake Norman and Mountain Island Lake exhibited both slow growth and erratic, but potentially high, mortality. Due to erratic survival in the two Piedmont reservoirs, we could not estimate mortality using a catch curve. Fish stocked into the Santee Cooper system not only grew larger and faster, they a...

We developed a three-step management strategy for hydrilla Hydrilla verticillata in five Piedmont reservoirs operated by Duke Energy Corporation. This strategy involves (1) early detection of hydrilla, (2) use of registered herbicides for plant suppression along with stocking 20 triploid Grass Carp Ctenopharyngodon idella per surface acre of infestation, and (3) maintenance stocking of triploid Grass Carp to prevent hydrilla regrowth from tubers. Following this strategy, hydrilla in the water column was eliminated within one calendar year after Grass Carp introduction in four out of five reservoirs. This suggests that integrating herbicide applications with stocking Grass Carp largely eliminates the multiyear lag effect normally associated with using Grass Carp alone. A maintenance density of at least one triploid Grass Carp per eight surface acres of the reservoir prevented hydrilla regrowth except for a brief and minor reinfestation in one of five study reservoirs. This management approach prov...

The development of effective and minimally invasive techniques to determine gender and gonad developmental stage is particularly important in performing accurate fisheries assessments for use in conservation and restoration. The initial and latent survival of shovelnose sturgeon Scaphirhynchus platorynchus was assessed after exposure to a modified endoscopic technique designed to collect that biological information. Rather than inserting the endoscope through the urogenital canal or directly into the body cavity, we inserted a threaded trocar through a ventral incision and used a low-pressure air supply attached to the trocar to gently insufflate the body cavity. The initial survival of both experimental and control shovelnose sturgeon was 100%. Latent survival was 100% and 90% for the experimental and control fish, respectively. Our study suggests that incision endoscopy coupled with insufflation of the body cavity through the use of a trocar and an air supply is a safe and effective way to dete...

A study of the seasonal movements of Gulf sturgeon Acipenser oxyrinchus desotoi was conducted in the Pearl River system and the Mississippi Sound from 2000 through 2003. We captured or recaptured, marked, and released 503 Gulf sturgeon, 98 adults being tagged with internal or external telemetry tags. Movement chronologies were generally similar to those reported in other studies. Summer habitats were found in the Pearl and Bogue Chitto rivers (Louisiana–Mississippi), and these habitats were occupied from April through November. Adults and subadults were spatially separated, the adults being concentrated in the Bogue Chitto River and the subadults in the Pearl River. Tagged adults began to leave the summer habitat during September and to arrive at the mouth of the Pearl River and the Rigolets Pass. The last departure from this location was in late November. Wintering habitat between Cat, Ship, Horn, and Petit Bois islands in the Mississippi Sound was used between November and early March. Gulf stu...

The Gulf Sturgeon Recovery/Management Plan defines a strategy for removing the threatened Gulf sturgeon Acipenser oxyrinchus desotoi (subspecies of the Atlantic sturgeon) from federal listing and invites revisions based on new information. The plan's objectives are reasonable and well-stated, but the criteria incorporated within the objectives may be unsuitable for monitoring some Gulf sturgeon populations. We propose the following revisions based on a 5-year study of Gulf sturgeon in the Pearl River system of Mississippi and Louisiana: (1) set specific statistical criteria for detecting population changes with emphasis on defining sufficient sampling effort to minimize type II errors; (2) use simple population models incorporating estimates of population size, mortality, and recruitment to ascertain population trends and define recovery; and (3) define a minimum number of adults within a self-sustaining population (in this case 100). These revisions, while perhaps not universally applicable, are...

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...

Two hundred of 295 shovelnose sturgeon Scaphirhynchus platorynchus captured in the Mississippi River near Rosedale and Vicksburg, Mississippi, were aged by examining sectioned pectoral fin rays. Ages ranged from 2 to 16 years, and the annual mortality was 20% for ages 7 and greater. The weight (W, g), to fork length (FL, mm) relation was W = 0.000001257 FL3.174 (R 2 = 0.87). The von Bertalanffy growth equation for fork length was FL = 730(1 − e −0.213(t+0.972)); the equation for weight was W = 1,604(1 − e −0.148(t−1.841)). Mortality and mean length at age were less than has been reported for upper Mississippi River populations of shovelnose sturgeon. Knowledge of causes of mortality of shovelnose sturgeon may have applications in management of the sympatric pallid sturgeon Scaphirhynchus albus.

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$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...

This 3-year study addressed the effectiveness of triploid grass carp Ctenopharyngodon idella as a replacement for herbicides to control nuisance aquatic vegetation in South Carolina farm ponds. Vegetation control achieved at three stocking densities as well as losses of grass carp to predation in ponds with largemouth bass Micropterus salmoides were examined. Triploid grass carp stocked at rates not potentially interfering with balanced communities of largemouth bass and bluegills Lepomis macrochirus failed to achieve an arbitrary measure of vegetation control approximately 70% of the time, There was no difference in degree of vegetation control from stocking 12, 25, or 50 fish/hectare, nor was there a decrease in mean plant biomass over a 2-year period. Predation studies with three sizes of largemouth bass demonstrated substantial, although inconsistent, losses of triploid grass carp after 1 month. Mean survival of triploid grass carp ranged from 57% in ponds with 46–51-cm largemouth bass to 72%...

Bioenergetic modeling provided insight into the potential for fishes to impact zebra mussel Dreissena polymorpha populations by predation across river and lake systems in eastern North America (13 deg latitude x 12 deg longitude). Food consumption modeling suggested that fishes in southern latitudes consumed up to 100 percent more food than those in northern systems. Much variation in food consumption was the result of differing water temperature regimes, which presumably dictated the bioenergetic demands of fishes. The potential for fishes to impact zebra mussels was also influenced by the standing crop of different species and the fish community as a whole. Fish community structures followed predictable patterns along both longitudinal and latitudinal gradients. Multivariate analyses indicated a tendency for central and southern U.S. systems to contain greater standing crops or biomasses of fishes likely to consume zebra mussels. Though analyses indicated northern systems had greater biomasses of some potential zebra mussel predators, net biomass increases of these species was not great enough to offset the decreases in food consumption due to cooler annual water temperatures. This study generally supports the premise that fishes in more southern (including central) U.S. waters have inherently greater potential to impact zebra mussels because of community composition and bioenergetics. Our simulations provide a partial explanation of why zebra mussel invasions have not been as rapid and widespread in southern U.S. waters compared to the Great Lakes region.

The removal of gizzard shad (Dorosoma cepedianum) had a positive but short-term effect on the largemouth bass (Micropterus salmoides) and bluegill (Lepomis macrochirus) populations in Chambers County Public Fishing Lake, Alabama. There was a favorable shift in community structure of the sport fishes 1 and 2 years after elimination of gizzard shad. The number of young-of-year largemouth bass and bluegill increased following gizzard shad removal and the survival of young largemouth bass increased considerably. Young-of-year largemouth bass and bluegills subsequently declined 2 to 3 years after gizzard shad removal to levels encountered when gizzard shad were present, indicating that species of fish other than gizzard shad may be effective in competing with largemouth bass and bluegill.