Paddlefish: Ecological, Aquacultural, and Regulatory Challenges of Managing a Global Resource

<i>Abstract</i>.—Inadequate recruitment is a concern in many stocks of Paddlefish <i>Polyodon spathula</i>. Despite the importance of maintaining adequate recruitment, little understanding exists of specific recruitment factors and mechanisms. In this chapter we review and synthesize the results of the relatively few studies and observations of Paddlefish reproduction and recruitment and the factors potentially responsible for observed variations. Comparisons are made with studies on sturgeons. Although Paddlefish and sturgeon show many anatomical, life history, and behavioral similarities, some key features of Paddlefish differing from other Acipenseriform species are lifelong zooplanktivory, filter feeding, midwater foraging behaviors, and lack of armoring. Data from both sturgeon and Paddlefish show higher reproductive success associated with higher river discharge; greater Paddlefish reproductive success in some adfluvial populations has also been linked to increasing and high reservoir levels. Whereas several sturgeon studies suggest that recruitment (and year-class strength) are determined within 2–3 months of hatching, results from Paddlefish suggest that year-class strength may be determined later in their first year or in their second year. Observations and field results lead to the hypothesis that young Paddlefish must grow fast in their first and early second years of life to reach a size where they can successfully overwinter, avoid predation from piscivorous fishes and birds, and recruit. Support for this grow-fast-or-be-eaten hypothesis comes from several sources, both indirect (e.g., the relation between fish length and rostrum length) and direct (higher survival of larger fish released and higher lipids in age-0 fish in years of good recruitment). However, more research is needed to adequately test this hypothesis. Paddlefish rearing habitat changes include river-backwater and side-channel sedimentation, reservoir sedimentation and aging, and threats from increased native and nonnative predator populations. Managers of Paddlefish will need a more detailed understanding of the habitat conditions needed for successful recruitment in the wild.

Paddlefish: Ecological, Aquacultural, and Regulatory Challenges of Managing a Global Resource

<i>Abstract</i>.—Paddlefish <i>Polyodon spathula</i> are behaviorally, morphologically, and physiologically adapted for prolonged free-swimming at moderately high speeds but not for maneuverability which makes them prone to impacts from submerged structures. These structures include low-head dams, weirs, dikes, levees, high-head dams, dredges, diversions, intakes, and vessels. Impacts include blocked migrations, reduced access and quality of habitat, entrainment, impingement, trauma, and stranding. Effects of these impacts on individuals are displacement, injuries, and death; effects on populations are fragmentation, lower gene flow, lower reproductive success, and elevated rate of mortality. Despite this, the status of the Paddlefish in most parts of its historic range is secure. Management techniques, like stocking and habitat restoration, are typically implemented at the local level but appear effective at conserving the species range wide. Refinement of management techniques, however, is still possible by modifying operations of structures and by rescuing stranded Paddlefish.

Paddlefish: Ecological, Aquacultural, and Regulatory Challenges of Managing a Global Resource

<i>Abstract</i>.—With the break-up of the Soviet Union in 1991, and the unhalting collapse of the Caspian Sea sturgeon fisheries from desperate management policies to maintain production, law enforcement investigators in the U.S. encountered increased poaching of Paddlefish <i>Polyodon spathula</i> caviar throughout the Mississippi River basin. The steady rise of caviar prices has encouraged the illegal, unreported, and unregulated (IUU) taking of Paddlefish and the same over-harvesting that devastated the Caspian and Atlantic Sturgeon caviar fisheries of the past. International, federal and state regulations have been enacted to conserve Paddlefish, but still allow responsible commercial development where supported by population status. However, critical to conservation plans, there is not general agreement as to how Paddlefish populations are structured. Genetic research efforts have provided conflicting results with different demographic histories suggested by nuclear microsatellite and mitochondrial DNA (mtDNA) markers. Nor is it possible to answer key law enforcement questions in the commercialization of Paddlefish—to differentiate wild from aquaculture derived Paddlefish products in trade, or to distinguish the geographic origins of wild Paddlefish and their products in order to identify areas of poaching activity. This review summarizes the findings of genetic studies that have addressed questions of genetic diversity and phylogeographic structure in Paddlefish, as well as the need for further study of mtDNA diversity and fine scale structure of nuclear variation. Lastly, the use of available resources for genetic tagging assessments, and expressed sequence tag (EST) marker discovery to resolve Paddlefish phylogeography are also discussed.

Paddlefish: Ecological, Aquacultural, and Regulatory Challenges of Managing a Global Resource

<i>Abstract</i>.—In this chapter we outline and update Missouri’s Paddlefish (<i>Polyodon spathula</i>) experience, including efforts to culture the species and the use of those fish in its fishery management program for reservoirs. The Osage River, historically one of the nation’s premier Paddlefish rivers, underwent major habitat alterations in the twentieth century, including the construction of two major mainstem reservoirs (Lake of the Ozarks and Harry S. Truman Lake), resulting in the loss of nearly all natural spawning habitat for the Paddlefish. In response, the Missouri Department of Conservation (MDC) began a program of artificial propagation for the species at Blind Pony Hatchery (BPH) in the 1960s. Early propagation developments in Missouri and elsewhere included research on early life history, feeding, and improving growth rates. In the early 1970s, the MDC determined that a Paddlefish population could be established in Table Rock Lake and supplementation could build and maintain harvestable populations in Lake of the Ozarks and Harry S. Truman Lake. As of 2019, these three reservoirs support quality Paddlefish fisheries and are known globally for their harvest potential. Even though Paddlefish propagation in Missouri has been fruitful, additional efforts through collaboration with other entities and states are underway to continually improve success. Through collaboration, unique intricacies in culture and stocking techniques have surfaced that should be implemented as propagation and restoration programs commence around the world. To this end, Paddlefish propagation has been successful and will continue to play a role in restoring, maintaining, or creating Paddlefish fisheries.

Paddlefish: Ecological, Aquacultural, and Regulatory Challenges of Managing a Global Resource

<i>Abstract</i>.—Detailed knowledge of the life history of Paddlefish <i>Polyodon spathula</i> is a relatively recent scientific chapter. The foundation was initially established in Missouri, where there was a significant sport fishery for Paddlefish; initial observations on natural spawning and subsequent techniques for artificial propagation were developed there. Building on this impetus, a different trajectory was initiated in the late 1970s by our research group, one focusing on aquaculture with a goal of developing a breeding program to produce all-female progeny; our collaboration continued over the next three and one-half decades. Managed reproduction through artificial propagation, nursing of juveniles and grow-out for commercial production were components of this program, but more detailed techniques such as ploidy manipulation, sperm physiology, and cryopreservation were also developed. Our present objective is to highlight the improvements in artificial propagation that have been incorporated into hatchery programs. Initially, ovulation was induced with pituitary glands, but today Luteinizing Hormone Releasing Hormone analog (LHRHa) is used; ovulated eggs were collected by laboriously stripping, then a caesarian-section technique used in sturgeon was adopted, and subsequently the Minimally Invasive Surgical Technique (MIST) was introduced. Today, a Modified MIST technique offers a more efficient means of collecting eggs. Nursing of juveniles continues to evolve; primary nursing is now commonly done in tanks where fish may be offered live food during training to a prepared diet instead of starting culture in enriched ponds managed for zooplankton. The development of Paddlefish artificial propagation has benefitted from techniques which were initially developed and used in sturgeon culture. These operational hatchery techniques are common to both culture for restoration stocking and food fish production.

Paddlefish: Ecological, Aquacultural, and Regulatory Challenges of Managing a Global Resource

<i>Abstract</i>.—Recent advances in fisheries techniques have provided insights into distribution, abundance, habitat use, and life history for several fish species, many of which are applicable to Paddlefish <i>Polyodon spathula</i>. We highlight three new, promising techniques for assessing Paddlefish populations, including: hard-part chemistry for identifying sources of recruits (both wild and stocked fish) and reconstructing environmental history of individual fish, advances in sonar technology for habitat mapping and abundance estimation, and development of eDNA as a detection tool where traditional fisheries gears are insufficient. We also identify potential impediments to applications of these techniques and suggest steps needed to further assess and enhance their applicability to Paddlefish management and conservation.

Paddlefish: Ecological, Aquacultural, and Regulatory Challenges of Managing a Global Resource

<i>Abstract</i>.—Many studies have demonstrated components of Paddlefish <i>Polyodon spathula</i> movements or migrations between spawning, feeding, and overwintering areas. However, the extent, timing, purpose, and potential consequences of these movements have not been summarized. With advances in tagging and telemetry technology, information regarding spatial ecology of Paddlefish populations is increasing and has demonstrated that individuals move greater distances and occupy greater home ranges than previously described. Increased implementation of these techniques has provided new information about migration routes, timing of migration, spawning and nursery locations, interactions with dams and other anthropogenic modifications, habitat use, and the influence of environmental factors on cues to movement and migration. The importance of upstream migrations to Paddlefish reproductive success has been documented by many researchers; however, observations of smaller-scale movements (e.g., vertical or diel) suggest that these might be equally important for completion of the species’ life history cycle. This review chapter focuses on synthesizing results of tagging studies to characterize seasonal movements and migrations of Paddlefish throughout their range, identification of knowledge gaps to be addressed in future efforts, and investigation of how this information affects current issues related to conservation and management strategies in a broad ecological sense. Given the propensity of Paddlefish to conduct both large- and small-scale movements throughout their life cycle, understanding spatial and temporal movement patterns will be critical in defining populations and determining the future scope of management to restore these populations and ensure sustainability throughout their range.

Paddlefish: Ecological, Aquacultural, and Regulatory Challenges of Managing a Global Resource

<i>Abstract</i>.—The North American Paddlefish <i>Polyodon spathula</i> was first introduced into China from the United States in 1988, with the importation of 3,000 larvae. From this and subsequent introductions, successful spawning of broodstock raised in China was first achieved in Hubei Province in 2001. As of 2018, this nonnative Paddlefish is cultured in more than 10 provinces, including Hubei, Sichuan, and the southern area of Shaanxi, all throughout the Yangtze River basin, and Guangdong, in the Zhujiang River basin. Four large Paddlefish hatcheries with other, smaller, newly-established facilities produce about 10 million fingerlings per year. With feeding habits of Paddlefish being similar to those of Bighead Carp <i>Hypophthalmichthys nobilis</i>, a traditional fish species produced by Chinese aquaculture, fish farmers rear Paddlefish as a substitute species for Bighead Carp in their production systems. Typically, Paddlefish fingerlings (10 cm TL) are cultured to market sizes (0.6–0.75 kg) in ponds or cages in reservoirs. Paddlefish in China are cultured primarily for meat rather than roe. Acceptable market size can be reached within six months on prepared diets, whereas it takes one year on natural diet. Paddlefish are usually marketed live, as no processing industry has developed. Because Paddlefish have a low tolerance to hypoxia, long distance transportation of live market size Paddlefish is relatively limited. A few Paddlefish are also marketed as aquarium fish. Because of the limited supply of fingerlings and the difficulty of efficiently catching Paddlefish from large bodies of water, reservoir ranching as a production system has not been well developed. Also, reservoir ranching for Paddlefish was slowed due to concerns about potential hybridization between the nonnative Paddlefish and the critically endangered Chinese Paddlefish <i>Psephurus gladius</i> of the Yangtze River. The short supply and high price of fingerlings remain major factors limiting the expansion of North American Paddlefish production in China.

Paddlefish: Ecological, Aquacultural, and Regulatory Challenges of Managing a Global Resource

<i>Abstract</i>.—In the past decade, advances in our understanding of Paddlefish <i>Polyodon spathula</i> life history have provided additional insight into the information needed for sustainable harvest management of this long-lived species. Recovery of known-age fish in some stocks has enabled stock assessment biologists and managers to not only validate ages of individual fish, but to begin to validate the life histories. A framework for potentially recruited Paddlefish life history can be broken into five stages: 1) immature, 2) maturing, 3) somatic growth and reproduction, 4) prime reproduction, and 5) senescence to death. These stages involve measurable changes in growth in length and weight, gonadosomatic index (GSI), gonadal fat storage (GFBs), reproductive periodicity, natural mortality rates, and, in some cases, fish migrations. Stages 2–5 are typically initiated at younger ages for males than for females. Metabolic demands on Paddlefish result in them progressing through these life history stages more rapidly in southern stocks, inhabiting warmer waters, than in northern ones, inhabiting colder waters. Lifespans in most northerly stocks tend to be 2–3 times longer than for southern stocks. Natural mortality is also typically lower in northern stocks. These differences necessitate fundamentally different harvest management strategies among stocks. Regardless of the stock, however, in the prime reproduction stage, somatic growth is slow or negative, as energy is routed more strongly into reproduction, GSI is at a maximum, the period of gonadal recrudescence (i.e., spawning interval) is minimized, and GFBs are largely or completely depleted in females. Consistent with recommendations for other long-lived freshwater and marine species, harvest management strategies should be specifically planned to retain some older, prime spawning females in the population. In addition, sporadic or episodic recruitment in many stocks makes steady-state harvest models unrealistic, necessitating that harvest be appropriately matched to recruitment rates or events.