Paddlefish Management, Propagation, and Conservation in the 21st Century

<em>Abstract</em>.—We assessed potential impacts of harvest and proposed channel modifications on the paddlefish <em>Polyodon spathula </em>fishery of Ozark Lake, Arkansas River, Arkansas. Ultrasonic telemetry was used to determine commercial and recreational exploitation rates, survival, spawning locations, and habitat use of gravid female paddlefish. Monthly searches were conducted for 40 tagged fish and we recorded 862 locations in Ozark Lake from January 2004 through December 2005. Adjacent reservoirs (i.e., Pool 13 and Lake Dardanelle) were tracked periodically, but interpool movement was not detected. Commercial fishing exploitation was determined at a mandatory check station and was estimated to be 30% during a 5-d special season. Annual recreational snag-fishing exploitation estimates were 8% (2004) and 3% (2005). Survival was different between years and was much lower the year (2004) with a commercial fishing season. Kaplan-Meier staggered-design survival estimates (±95% confidence interval [CI]) for 2004, 2005, and 2004 through 2005 were 0.60 ± 0.19, 0.92 ± 0.11, and 0.55 ± 0.18, respectively. With commercial and recreational harvests omitted from the analysis, the estimated 2-year survival rate was 0.91 ± 0.13 (±95% CI), which corresponds to 5% annual natural mortality. Gravid females migrated a median distance of 33 and 32 km in the spring of 2004 and 2005 and likely spawned in the tailwater of James W. Trimble Lock and Dam from late March to early April. Successful paddlefish reproduction was verified by capture of 23 prolarvae. Paddlefish selected tributary mouth habitat in all seasons (59% of locations). Tailwater and inundated creek channel habitats were selected in spring and summer, respectively. A navigation project to deepen the channel from 2.7 to 3.7 m will impact approximately 50% of the tailwater spawning habitat. Channel modifications (i.e., dredging and dike construction) near the mouth of the Mulberry River may disturb an important tributary mouth habitat for paddlefish where 55% of all locations were recorded. Our study identified biologically important habitats that need conservation and indicates that commercial harvest was the primary source of mortality for gravid female paddlefish in Ozark Lake.

Paddlefish Management, Propagation, and Conservation in the 21st Century

<em>Abstract</em>.—Paddlefish <em>Polyodon spathula </em>have been intensively harvested in both sport and commercial fisheries. Recent harvests (2000–2006) were surveyed from state agencies and compared to historical harvests (1965– 1975). Seven major sport fisheries had recent annual harvests greater than 1,000 fish, and most large sport fisheries appeared to have sustainable harvests due to intensive management. Recent commercial harvest was greater than sport harvest across the species’ range. Most of the commercial harvest was from Arkansas, Kentucky, and Tennessee. Annual commercial harvest from the Ohio River increased from 6,000 to 196,000 kg from 1965–1975 to 2000–2006. Annual harvest remained substantial from the Arkansas River (37,000 kg), the lower Tennessee River (121,000 kg), and the Mississippi River (103,000 kg). Harvests of paddlefish (sport and commercial) compiled from the literature were highly variable and ranged between 0.01 and 5.06 fish/ ha and 0.04–43.43 kg/ha (median = 0.12 fish/ha, 1.73 kg/ha). Stock depression has been associated with a first-year harvest as low as 1.46 kg/ha, and harvests greater than 5 kg/ha were usually associated with overfishing or opening a previously closed fishery. Case histories from the Tennessee and Ohio River systems documented that paddlefish were susceptible to overharvest in lentic waters and river reservoirs, but the threat posed by commercial harvest from large rivers will remain unresolved until more fisheries-independent data becomes available. Anthropogenic alterations to habitat, overreliance on harvest data, and lack of fisheries-independent data limit our historical understanding of the degree of threat that harvest is to paddlefish populations.

Paddlefish Management, Propagation, and Conservation in the 21st Century

<em>Abstract</em>.—We present information on delayed mortality of commercially exploited paddlefish <em>Polyodon spathula </em>released as bycatch in Kentucky Lake, Tennessee–Kentucky, an impoundment on the lower Tennessee River. Minimum size limits enacted in 2002 (864 mm eye-to-fork length [EFL]) and 2005 (914 mm EFL) sought to protect paddlefish from overfishing. In 2005, bycatch of sublegal paddlefish represented 75% of the total catch, and releasing undersized fish will not reduce fishing mortality unless those fish survive. Paddlefish caught and released by commercial fishers in 2005 and 2006 were externally tagged with radio transmitters and tracked a minimum of 2 weeks to estimate delayed mortality. Four of the 104 tagged paddlefish died following release, 94 survived, and 6 were censored because their fate could not be determined. Paddlefish that survived moved rapidly from release locations. Net movements of the 94 fish that survived averaged 12.0 km (SE = 5.3) upriver and ranged from 91.5 km downriver to 390.0 km upriver. Fish that died could not be distinguished from fish that lived on the basis of mean water temperature, fish length, net-soak time, or handling time. Given the low delayed mortality of discarded paddlefish, imposing minimum size limits is a reasonable approach to reduce fishing mortality of juveniles and reduce the likelihood of overfishing. Efforts to reduce fishing mortality should focus on avoiding fishing gear and seasons (e.g., early fall and late spring) that cause high initial bycatch mortality.

Paddlefish Management, Propagation, and Conservation in the 21st Century

<em>Abstract</em>.—Paddlefish <em>Polyodon spathula </em>populations in North America have long been exploited commercially for meat and roe; however, the history of paddlefish propagation and culture is more recent. Early efforts to artificially propagate and culture paddlefish were motivated by conservation following the construction of dams and destruction of spawning habitat on major rivers of the central United States. From these beginnings, paddlefish propagation and the species itself have spread from native U.S. waters to other countries, including Russia and China. In the United States, conservation is still an important aspect of paddlefish culture, although sport fishing and aquaculture production have been added to the mix. However, in those countries where paddlefish have been introduced, the motivation has been the perceived potential for producing food for domestic consumption and valuable products for export, including one of the most exotic and expensive food products in today’s world—caviar. The collective efforts of state and federal hatchery personnel in the United States, along with university researchers from the United States and worldwide have resulted in a more complete body of information on paddlefish propagation and culture. Included in this collection are methods for handling broodstock, induced spawning, and nursery stages of production, along with cryopreservation of milt and manipulation of sex ratios in the hatchery to produce a preponderance of female fish. We have assembled this collection here to provide a single source reference and have added information concerning hatchery design, regulations, and the grow-out stages of aquaculture food fish production.

Paddlefish Management, Propagation, and Conservation in the 21st Century

<em>Abstract</em>.—Paddlefish <em>Polyodon spathula </em>vanished from areas of the upper Tombigbee River basin in Mississippi and Alabama during the 1950s, long before channelization and damming associated with construction of the Tennessee-Tombigbee Waterway (TTW) were completed in 1984. This study was undertaken to assess distribution and population dynamics of any remaining stock. Paddlefish were not captured in upstream impoundments, but an unexploited remnant population was located in the downstream impoundment: Demopolis Lake, Alabama. Paddlefish in Demopolis Lake were characterized by a population density of 2.6 fish/ha, high growth rate relative to more northern populations, and natural annual mortality rate (<em>A </em>= 0.406) similar to other southern populations. Two wintering habitats (cutoff bendways) were heavily utilized by paddlefish. Large males primarily inhabited the more lotic bendway while females and small males were more common in the more lentic bendway, indicating differential importance of habitats among demographic groups. The restricted distribution of TTW paddlefish and demographic differences between habitats suggest that areas heavily utilized by paddlefish should be protected from further degradation. Sedimentation has resulted in reductions of bendway depth and reduced connectivity of backwaters, reducing availability of suitable paddlefish habitat. Restoring connectivity of bendways through dredging could reverse this trend and provide other benefits to fisheries.

Paddlefish Management, Propagation, and Conservation in the 21st Century

<em>Abstract</em>.—Invasive species are one of the dominant problems fisheries managers face when dealing with management, conservation, or preservation of native fishes. The primary concern is the potential for negative interactions between invasive and native species where the outcome is reduced abundance, fitness, growth, or extirpated native fish species. These negative interactions can come from direct competition for resources, vectors for the spread of disease or parasites, and subtle effects such as altering the flow of energy within and among other trophic levels. Paddlefish <em>Polyodon spathula </em>are not exempt from these threats and may even be at a higher risk because they are endemic to historically lotic systems in the central United States where many invasive species are now becoming established. The most prominent invasive threat to paddlefish may be from fellow filter-feeders bighead carp <em>Hypophthalmichthys nobilis </em>and silver carp <em>H. molitrix </em>because they consume similar food resources, possibly displace other pelagic species, and can also change the plankton community to one that cannot be as efficiently used by paddlefish. These two carp species have had a negative influence on native fish communities in other parts of the world, and have been shown to negatively interact with juvenile paddlefish in North America. Response plans that implement a movement barrier or removal of invasive species may also have ramifications for paddlefish in that they restrict movement patterns or reduce abundances as bycatch through harvest schemes. Gaining insights into potential invasive species threats to paddlefish is critical so that informed decisions can be made to prevent ecological damage from the invasive species while optimizing sustainability of native species.

Paddlefish Management, Propagation, and Conservation in the 21st Century

<em>Abstract</em>.—How paddlefish <em>Polyodon spathula </em>early-life history dynamics affect recruitment is relatively unknown. We quantified factors affecting age-0 paddlefish abundance, hatch time, growth, and survival in an unimpounded reach of the Mississippi River during 2000–2008. We trawled several habitats, collecting 2,074 age-0 paddlefish from 10 to 170 mm total length. Paddlefish hatch timing varied across years (30–60 d), generally commencing in the middle of April and ending in June when a threshold water temperature was reached and river stage variability increased. Correspondingly, an analysis of covariance revealed a strong interaction between year and habitat for catch per unit effort in the small (10–50 mm) (<em>P </em>= 0.025) and medium (51–100 mm) (<em>P </em>= 0.040) size-classes, indicating that habitat preferences were likely influenced by year. However, no relations between these variables in the large size-class (>100 mm) existed (<em>P </em>= 0.88). Age-0 paddlefish growth rates differed among years (i.e., 1.87–3.31 mm/d) and were positively related to water temperature (<em>r </em>= 0.64; <em>P </em>= 0.083). Mortality rates varied by year (range = –0.26 to –0.57) and were positively correlated with the number of days water temperature was below 28°C during April 15 through July 15 (<em>r </em>= 0.67, <em>P </em>= 0.070). Water temperature and river stage variability may regulate early-life dynamics of paddlefish. Early-life history dynamics are likely interrelated with habitat conditions present in the river. The highest catch rates of young paddlefish were on the main channel side and side channel of islands, suggesting that these habitats are important to paddlefish. Within these habitats, paddlefish frequently occupied moderate velocities (i.e., 0.4–0.6 m/s), moderate depths (i.e., 3–5 m), and sand substrate.

Paddlefish Management, Propagation, and Conservation in the 21st Century

<em>Abstract</em>.—As commercial paddlefish <em>Polyodon spathula </em>fisheries shifted from primarily flesh to almost exclusively roe harvest, agencies had to change their management strategies. Arkansas, Illinois, Indiana, Kentucky, Mississippi, Missouri, and Tennessee were the only states within the Mississippi River basin that were open to commercial paddlefish harvest in 2006. These seven states were surveyed in 2006 to summarize commercial paddlefish fisheries management in North America. Although commercial fishing license sales declined in most states since the mid-1980s, the number of commercial fishers targeting paddlefish steadily increased since the late 1990s. Total license fees for a resident commercial fisher to set 10 gill nets for paddlefish ranged from US$70.35 to $1,200, and those fees ranged from $242.35 to $2,500 for nonresidents (in the five states that allowed nonresidents). Management strategies employed in these seven states varied greatly in 2006. Arkansas, Mississippi, and Tennessee managed their fisheries with statewide seasons, and Kentucky had seasons for two of three major fisheries. Arkansas, Missouri, Kentucky, and Tennessee had minimum eye-to-fork length limits on all or some of their fisheries. There were numerous gear restrictions in the seven states, including minimum mesh size restrictions, net length limits, and net attendance requirements. Most states had a mandatory harvest report, but the information collected on these reports differed among states. The vastly different management strategies that were employed in the commercial fisheries throughout the Mississippi River basin have resulted in new problems as roe values increase. Future management will likely focus on development of management plans for biologically relevant areas. These management plans should include measures to prevent recruitment overfishing and minimize bycatch mortality. Interjurisdictional management and continued information sharing are necessary to effectively manage paddlefish fisheries in the future.

Paddlefish Management, Propagation, and Conservation in the 21st Century

<em>Abstract</em>.—Paddlefish <em>Polyodon spathula </em>are large, riverine fishes that occupy extensive home ranges and often migrate long distances in spring to spawn. As a result of these life history characteristics, paddlefish require many habitats to sustain their population over time. Largely as a result of anthropogenic activities, many of the habitats historically used by paddlefish have been altered or destroyed and remaining paddlefish habitats are being threatened by dam construction, channelization and dredging, and altered land use within watersheds. Understanding how habitat alteration may affect paddlefish populations, and identifying threats to current paddlefish habitat, is needed for the management of this species. We review the threats to paddlefish habitats and assess how anthropogenic habitat alterations, such as changes to natural hydrology through the construction of dams and channelization of large rivers or altered land-use patterns leading to increased sedimentation, have affected paddlefish populations. Recent river restoration and conservation measures that help protect and restore paddlefish habitats include fish passage structures and controlled water releases from dams to simulate a more natural hydrograph. New threats such as global climate change may alter paddlefish habitats in the future. Continued efforts to minimize the impact of anthropogenic changes to paddlefish habitats, and measures to restore natural riverine conditions, may help conserve vital habitats for paddlefish populations.