Demographics and Seasonal Diet Composition of Shovelnose Sturgeon (Scaphirhynchus platorynchus Rafinesque) in Wabash River

Shovelnose sturgeon Schaphirhynchus platorynchus Rafinesque, one of the only sturgeon species that support a sustainable commercial harvest, are fished in a substantial caviar fishery in the lower Wabash River. However, ecological information on the population is sparse. In this thesis, I present information on the status and seasonal diet characteristics of the population. A 14-year long shovelnose sturgeon monitoring survey conducted by Illinois Department of Natural Resources shows that the population is in relatively good condition, faces low mortality rates, and has a high potential for recruitment. Study of the seasonal composition of diet suggests that shovelnose sturgeon generally get enough food throughout the year, and are thus, in good condition. I found that shovelnose sturgeon are opportunistic benthic invertivores, with Hydropsychidae and Chironomidae as the staple prey taxa for the fish. However, the sex-ratio of the population is highly male-biased, and the proportion of memorable-size fish is decreasing, likely due to the ongoing commercial harvest of ripe-and-running females. This poses potential problems regarding the sustainability of this fishery, and thus, management policies should be conservative until more information on optimal harvest of this fish is available

Demographics and Seasonal Diet Composition of Shovelnose Sturgeon (Scaphirhynchus platorynchus Rafinesque) in Wabash River

Shovelnose sturgeon Schaphirhynchus platorynchus Rafinesque, one of the only sturgeon species that support a sustainable commercial harvest, are fished in a substantial caviar fishery in the lower Wabash River. However, ecological information on the population is sparse. In this thesis, I present information on the status and seasonal diet characteristics of the population. A 14-year long shovelnose sturgeon monitoring survey conducted by Illinois Department of Natural Resources shows that the population is in relatively good condition, faces low mortality rates, and has a high potential for recruitment. Study of the seasonal composition of diet suggests that shovelnose sturgeon generally get enough food throughout the year, and are thus, in good condition. I found that shovelnose sturgeon are opportunistic benthic invertivores, with Hydropsychidae and Chironomidae as the staple prey taxa for the fish. However, the sex-ratio of the population is highly male-biased, and the proportion of memorable-size fish is decreasing, likely due to the ongoing commercial harvest of ripe-and-running females. This poses potential problems regarding the sustainability of this fishery, and thus, management policies should be conservative until more information on optimal harvest of this fish is available

High salinity tolerance of invasive blue catfish suggests potential for further range expansion in the Chesapeake Bay region

In estuaries, salinity is believed to limit the colonization of brackish water habitats by freshwater species. Blue catfish Ictalurus furcatus, recognized as a freshwater species, is an invasive species in tidal rivers of the Chesapeake Bay. Salinity tolerance of this species, though likely to determine its potential range expansion and dispersal in estuarine habitats, is not well-known. To address this issue, we subjected blue catfish to a short-term salinity tolerance experiment and found that this species tolerates salinities higher than most freshwater fishes and that larger blue catfish tolerate elevated salinities for longer periods compared with smaller individuals. Our results are supported by spatially extensive, long-term fisheries surveys in the Chesapeake Bay region, which revealed a gradual (1975–2017) down-estuary range expansion of blue catfish from tidal freshwater areas to habitats exceeding 10 psu [practical salinity units] and that large blue catfish (\u3e 200 mm fork length) occur in salinities greater than 10 psu in Chesapeake Bay tributaries. Habitat suitability predictions based on our laboratory results indicate that blue catfish can use brackish habitats to colonize new river systems, particularly during wet months when salinity decreases throughout the tidal rivers of the Chesapeake Bay

A Mechanistic Understanding of Range Expansion of Invasive Blue Catfish in the Chesapeake Bay Region

Blue catfish Ictalurus furcatus is an invasive species of great concern in coastal habitats throughout the eastern United States, inclulding the Chesapeake Bay and its tributaries. In this dissertation, I use field surveys, laboratory experiments and quantitative modeling to provide insights into several aspects of blue catfish biology at the individual level. In chapter 1, I characterize and compare patterns in growth and body condition in blue catfish populations in the James and York river subestuaries during two stages of invasion. Both the mean growth rate and mean body condition of blue catfish declined in the recent period in response to increases in population abundance. In chapter 2, I uncover life-history plasticity in the reproductive biology of the species: blue catfish in the James River mature at a smaller mean size but provision a greater amount of energy into reproduction than York River fish, which exhibit lower densities than James River fish. In chapter 3, I assess the food demands of blue catfish in a laboratory experiment. I demonstrate that blue catfish have low metabolic demands, as expected for a relatively sedentary benthic fish. Importantly, blue catfish had high survival and significant growth at food levels as low as one third of the maximum, suggesting that the species has a high tolerance of starvation and that individuals may be able to invade and establish in low food habitats in coastal waters. In chapters 4 and 5, I report the results of two laboratory experiments studying the effects of increased salinity on survival, growth and body condition of blue catfish. Blue catfish, typically considered a freshwater species, was found to have a higher salinity tolerance (72-hour LC50 = 15.7 psu) than many freshwater fishes, suggesting the potential of the species to expand its range into most subestuaries of the Chesapeake Bay particularly during wet seasons. Habitats with salinities around 4 psu seemed particularly suitable for blue catfish as growth and body condition were maximized at this salinity despite the lower mean ingestion rates than fish maintained in freshwater. Finally, in chapter 6, I parameterize a full life-cycle bioenergetics model for female blue catfish using data from the literature and from the other chapters of this dissertation. The model supported the implications from other chapters that blue catfish have low maintenance costs, relatively high resistance to starvation and a plastic ability to fuel reproduction even in environments with low food availability. The model, together with results from other chapters, also opened up avenues for further research on characterization of the energetic basis for the observed phenotypic plasticity, identification of physiological modes of action by which salinity might limit survival, growth and reproduction of blue catfish, and ultimately the identification of coastal habitats that might support self-sustaining populations of this invasive fish. This research highlights the need for management efforts to control blue catfish populations in subestuaries where they are already established and to limit the range expansion into novel habitats. Towards this end, this dissertation provides important information on vital rates of blue catfish needed for population models that can be used for management strategy evaluations

Sublethal effects of salinity and temperature on non-native blue catfish: Implications for establishment in Atlantic slope drainages

The distribution and further range expansion of non-native blue catfish Ictalurus furcatus in coastal waters throughout the United States Atlantic slope depend, in part, on the salinity tolerance of the fish. However, temperature-mediated sublethal effects of increased salinities on blue catfish biology are not yet known. We assessed the effects of salinity and temperature on growth, body condition, body composition and food consumption of juvenile blue catfish in a controlled laboratory experiment. Temperature and salinity had an interactive effect on blue catfish biology, although most fish survived 112 days in salinities up to 10 psu. At salinities 9 psu) likely will not support the full lifecycle of blue catfish, but the fish may use salinities up to 10 psu for foraging, dispersal and even growth. Many oligohaline and mesohaline habitats in U.S. Atlantic slope drainages may thus be vulnerable to establishment of invasive blue catfish, particularly given the increasing temperatures as a result of climate warmin

Reproductive Characteristics Differ in Two Invasive Populations of Blue Catfish

The management of invasive Blue CatfishIctalurus furcatusin Chesapeake Bay tributaries is hindered by the lackof information on its reproductive biology, which is a key component of population models used to forecast abun-dance. We quantified and compared the reproductive traits of female Blue Catfish from two populations from the tidalreaches of the James and York River subestuaries during 2015–2017. In these systems, Blue Catfish matured betweenthe ages of 6 and 10 years and spawned between May and July, with largerfish spawning earlier in the season. Dur-ing spawning events, Blue Catfish produced 2,613–68,356 eggs, with larger and olderfish producing more eggs. Fishin the more densely populated James River matured at a marginally older age but a significantly smaller size thanfishin the York River, but James Riverfish allocated more energy to reproduction. Fish in the James River also hadgreater mean values of the gonadosomatic index, relative fecundity, egg organic content, and proportion of organiccontent in the eggs. Relative fecundity of Blue Catfish decreased withfish size, contrary to observations in most otherfishes. Based on the observed variability in reproductive traits and the size dependence of relative fecundity, we recom-mend incorporation of population-specific reproductive rates into stock assessment models for invasive Blue Catfish

Effects of food limitation on growth, body condition and metabolic rates of non-native blue catfish

Establishment and range expansion of non-native species in novel habitats depend on their energetic requirements and food availability. Knowledge of growth and metabolic rates of non-native fishes at various food levels is particularly critical to inform models that assess their invasion potential. We compared growth rates, body condition and metabolic rates of juvenile blue catfish (Ictalurus furcatus), an invasive species in many lakes, coastal rivers and estuaries throughout the Eastern USA, at three ration levels: ad libitum (3.5% of fish body mass/d), two-third ad libitum and one-third ad libitum. All fish survived the entire duration of the experiment (4 months) regardless of ration level. Blue catfish exhibited routine metabolic rates similar to those of other benthic fishes but below the more active species. Mean growth rates were lower at reduced ration levels, but we found no evidence of ration size effect on body condition or metabolic rates. Blue catfish therefore appear to have mechanisms that enable them to survive low rates of food intake for long periods, indicating the potential of this invasive species to become established in habitats with low prey availability

Invasive Blue Catfish in the Chesapeake Bay Region: A Case Study of Competing Management Objectives

Freshwater fishes have been introduced outside their native range to establish recreational fisheries, but management conflicts arise when such introductions also result in potentially harmful effects on native species. In this case study, we focus on Blue Catfish Ictalurus furcatus, which were introduced in the Chesapeake Bay region and are now considered invasive. In many tidal tributaries, Blue Catfish have increased dramatically in abundance, expanded into high-salinity habitats (up to 21.8 psu), and negatively affected native species, prompting calls for the development of an effective management plan. However, management of this conflict species is complicated by multiple competing objectives, including control of population size, maintenance of trophy fisheries, and expansion of commercial fisheries for Blue Catfish. Seven management recommendations were advanced by the Invasive Catfishes Work Group to control the spread and limit the ecological impacts of Blue Catfish on native species. We highlight opportunities for addressing these complex management issues and guide our suggestions using results from research on invasive Blue Catfish ecology and population dynamics, as well as management of invasive species in general. A formal approach, such as structured decision analysis, is required to resolve conflicts among user groups and to address the wicked problem of Blue Catfish in the Chesapeake Bay region

Comparative Performance of Three Length-Based Mortality Estimators

Length‐based methods provide alternatives for estimating the instantaneous total mortality rate (Z) in exploited marine populations when data are not available for age‐based methods. We compared the performance of three equilibrium length‐based methods: the length‐converted catch curve (LCCC), the Beverton–Holt equation (BHE), and the length‐based spawning potential ratio (LB‐SPR) method. The LCCC and BHE are two historically common procedures that use length as a proxy for age. From a truncated length‐frequency distribution of fully selected animals, the LCCC estimates Z with a regression of the logarithm of catch at length by the midpoint of the length‐bins, while the BHE estimates Z as a function of the mean length. The LB‐SPR method is a likelihood‐based population dynamics model, which—unlike the LCCC and BHE—does not require data truncation. Using Monte Carlo simulations across a range of scenarios with varying mortality and life history characteristics, our study showed that neither the LCCC nor the BHE was uniformly superior in terms of bias or root mean square error across simulations, but these estimators performed better than LB‐SPR, which had the largest bias in most cases. Generally, if the ratio of natural mortality (M) to the von Bertalanffy growth rate parameter (K) is low, then the BHE is most preferred, although there is likely to be high bias and low precision. If M/K is high, then the LCCC and BHE performed better and similarly to each other. Differences in performance among commonly used truncation methods for the LCCC and BHE were small. The LB‐SPR method did not perform as well as the classical methods but may still be of interest because it provides estimates of a logistic selectivity curve. The M/K ratio provided the most contrast in the performance of the three methods, suggesting that it should be considered for predicting the likely performance of length‐based mortality estimators