A Conceptual Life History Model For Pallid And Shovelnose Sturgeon

Author : William Dean Hintz
Publisher :
ISBN 13 :
Total Pages : 304 pages
Book Rating : 4.:/5 (99 download)

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Download or read book Behavior, Ecology, and Conservation of Scaphirhynchus Sturgeon written by William Dean Hintz and published by . This book was released on 2014 with total page 304 pages. Available in PDF, EPUB and Kindle. Book excerpt: Large rivers are perhaps the most modified ecosystems worldwide. Natural flow regimes, ecosystem connectivity, and habitat have been modified for human interests, and poor water quality has resulted from urban settlement and agricultural practices. Subsequently, such changes have had deleterious effects on riverine biota and many endemic species are of critical conservation concern. Due to the inter-jurisdictional nature and economic importance of large rivers, conservation efforts must be realistic and recognize human interests. To reach that point, however, we must understand behavioral and ecological patterns and processes at multiple scales, to ensure conservation strategies are successful. Fishes have been particularly affected by modifications to large rivers. Further, freshwater roe fisheries around the world have overfished several species to the brink of extinction; among the most notable are sturgeon populations. Pallid sturgeon (Scaphirhynchus albus ) and shovelnose sturgeon (S. platorynchus ) are two species that occur in large rivers of the central United States. Pallid sturgeon are primarily limited to the riverscapes of the Missouri and lower Mississippi Rivers, whereas shovelnose sturgeon are more widely distributed. Pallid sturgeon are a federally endangered species in the United States and shovelnose sturgeon are federally threatened where they overlap in range with pallid sturgeon. Like other sturgeon species around the world, Scaphirhynchus sturgeon habitat has been modified and degraded by dams, extensive levee systems, and pollution. To date, our understanding of habitat needs for Scaphirhynchus sturgeon--at multiple spatial scales--remains unknown. Furthermore, basic behaviors, e.g. anti-predatory behavior or foraging behavior, have yet to be identified. The goal of my dissertation was to fill knowledge gaps in Scaphirhynchus sturgeon behavior, ecology, and conservation. First, I identified a species-loss domino-effect, which may manifest from use of Similarity of Appearance Provisions in the U.S. Endangered Species Act. The aim of the legislative action was to protect pallid sturgeon by closing the shovelnose sturgeon roe fishery where shovelnose overlap in range with pallid sturgeon (Chapter 1). It was assumed that closing the shovelnose sturgeon roe fishery to prevent bycatch of pallid sturgeon would increase the number of reproductively viable females in the wild, thereby facilitating pallid sturgeon recovery. However, I show that this response may have unintended consequences by diverting fishing effort to other economically viable species (e.g. paddlefish Polyodon spathula ) and increase poaching. Further, I suggest that protecting the shovelnose sturgeon may increase the rate of hybridization and competitive interactions between pallid and shovelnose sturgeon. I recommend such legislative action be followed by contingency plans for any unintended consequences and protections be ready for species which may experience diverted fishing effort.Regarding sturgeon behavior, I used shovelnose sturgeon as a model species to test whether sturgeon exhibit predator avoidance behavior (Chapter 2), as predators, or interactions with predators, have strong regulatory effects on populations. My experiment showed that shovelnose sturgeon do exhibit predator avoidance behavior when they encounter a catfish predator ( Ictalurus punctatus ). This was the first experiment to document such behavior in any sturgeon species and suggested that it was a learned, rather than an innate behavior. The remaining chapters of my dissertation focus on the goals of elucidating the current status of Scaphirhynchus sturgeon and habitat selection at multiple spatial scales. In Chapter 3, I estimated the population size of adult pallid sturgeon (N = 1,516) and shovelnose sturgeon (N = 82,336) in the free-flowing middle Mississippi River. My estimates highlight the critical status of pallid sturgeon, and show that shovelnose sturgeon are faring comparatively well. In the same study, I found both sturgeon species were most abundant at the downstream ends of alluvial islands. I suggest restoration of alluvial islands, which were historically present in the Mississippi River, is a realistic goal to facilitate recovery of Scaphirhynchus sturgeon. Given pallid and shovelnose sturgeon were found in highest abundance around alluvial islands (Chapter 3), I wanted to understand the uniqueness of habitat surrounding alluvial islands (Chapter 4). Hydroacoustic techniques were used to quantify the abiotic attributes, and variability in those attributes, around two alluvial island complexes. At the same time, age-0 Scaphirhynchus sturgeon were sampled to examine whether they used similar habitats as adults. All sturgeon sampled were shovelnose sturgeon, but similar to Chapter 3, I found that the greatest abundance of age-0 sturgeon occurred at the downstream ends of the alluvial islands, particularly on the main channel side. This area had intermediate variability in depth and velocity, and contained sand dunes. I also found that vegetation was an important attribute of the islands, mostly when inundated by high spring flows. I suggest that if island restoration is pursued, as in Chapter 3, abiotic attributes identified in Chapter 4 should be replicated. Alluvial islands represent a coarse, albeit important, scale at which habitat is relevant to Scaphirhynchus sturgeon. However, for several abiotic attributes and mesohabitats that affect habitat selection by sturgeon, it is difficult to elucidate their relevance at the individual scale due to high flows, turbidity, and depth of large riverscapes like those of the Mississippi River. Therefore, carefully designed laboratory experiments are an alternative means of identifying pattern and process relevant to individuals. Velocity is an important abiotic attribute that influences the distribution of individuals in lotic ecosystems (e.g., Chapter 4). The goal of Chapter 5 was to evaluate how swimming behavior of Scaphirhynchus sturgeon was affected by velocity. I designed an experiment to specifically test whether sturgeon swimming behavior evolved in a way that reduced the energetic cost of occupying river energy landscapes. Further, a dynamic state variable model was developed to assess the optimal behavioral decision based on the expectation of food and energetic costs. Both pallid and shovelnose sturgeon showed a tendency to occupy faster velocity, but their swimming behavior from the experiment was consistent with cost minimization. The dynamic program revealed that the expectation of food and costs associated with the experimental energy landscape influenced the probability of a sturgeon moving upstream, downstream, or station holding. It appears the suite of swimming behaviors exhibited by fluvial specialists like pallid and shovelnose sturgeon may have evolved to maximize net energy gain. Lastly, I examined mesohabitat selection by age-0 Scaphirhynchus sturgeon (Chapter 6). Like velocity, substrates and other benthic structures can influence the distribution of individuals. I tested selection of four common mesohabitat types nested within alluvial island complexes: 1) sand only substratum with no structure, 2) sand substratum with sand dune structure, 3) sand substratum with simulated vegetation, and 4) a gravel only substratum. Sturgeon almost completely avoided gravel substrate and selected for the sand substratum, structure-less mesohabitat, followed by the mesohabitat with a sand dune. Vegetated habitat retained less sturgeon than these two habitats but more than the gravel mesohabitat. Scaled to the population level, the patterns revealed in Chapter 6 could have implications for the macro-distribution of both species. In summary, I hope that the illustration of a species-loss domino-effect will be considered in the conservation of threatened and endangered species. The issue of diverted effort, in particular, must be recognized when species are protected in a limited fashion to prevent or anticipate harvest cascading to other valuable and/or vulnerable species. We must also consider acquiring basic knowledge of sturgeon behavior if we are to understand how best to conserve them. Herein, the identification of predator avoidance behavior in shovelnose sturgeon suggests that predators in the wild may have regulatory effects on the distribution of young sturgeon. I also identified how Scaphirhynchus sturgeon--behaviorally--navigate large river velocity landscapes. Such contributions regarding sturgeon behavior have largely gone undescribed--I hope the present work will provide a framework for future ethological study. Lastly, my work has implications for the rehabilitation of large, sand-dominated rivers. Specifically, my research suggests the restoration of alluvial islands in the free-flowing Mississippi River will contribute to the recovery of Scaphirhynchus sturgeon. Restoration efforts should be mindful, though, of 1) the attributes that retain sturgeon, 2) habitat selection at multiple scales, and 3) selection differences among species at various scales. These considerations will assist in facilitating the success of large-river conservation programs.