Southern flounder (Paralichthys lethostigma) populations have declined over the last 25-30 years throughout its range. With this rapid decline, the sustainability of the southern flounder fishery and population viability of this commercially and recreationally important fish has come into question. Previous research conducted in the Northern Gulf of Mexico and North Carolina, has shown that southern flounder often reside in freshwater for significant periods of time during the juvenile life history stage. Juvenile southern flounder have been collected at salinities below 10 in Aransas Bay (TX), suggesting that Texas southern flounder might also have critical periods of freshwater residency. However, the presence of a low salinity residency period in southern flounder in Texas has not previously been tested. Patterns of low salinity residence were determined using otolith microchemistry, using Ba/Ca ratios to determine movements across salinity boundaries. Water samples were collected from the major tributaries to the area in order to establish the Ba/Ca freshwater signature. Otolith Ba/Ca values revealed a high degree of variability in habitat use patterns among individuals. The mean percent time that an individual spent in low salinity habitat was skewed toward the lower end (15%) but a significant proportion of the individuals sampled (59%) used low salinity habitat at some point during their life. The remaining individuals (49%) never entered low salinity habitat. This work indicates that there are two distinctly different groups of habitat use patterns in the population. This work demonstrates that southern flounder in Texas exhibit different habitat use patterns from their congeners in North Carolina and the Northern Gulf of Mexico and can help contribute to the spatial management of the southern flounder population on the Gulf Coast of Texas. / text

Modifications to Brandon Road Lock and Dam (BRLD), located on the Des Plaines River in northeastern Illinois, have been proposed to prevent the upstream transfer of aquatic invasive species, particularly Asian carps, into the Great Lakes Basin. These modifications, including the installation of an electric barrier, acoustic fish deterrent, and air bubble curtain, are designed to completely eliminate all upstream fish passage and may negatively impact native fish populations in the Des Plaines River by reducing upstream movement and potentially fragmenting populations. BRLD is situated just 21 km upstream of the Des Plaines River mouth, and fish are only able to pass upstream via the lock chamber. Fish species richness within the Des Plaines River watershed has increased over the last 35 years. It has been suggested that the majority of new species to the upper Des Plaines River have migrated upstream past Brandon Road Lock and Dam (BRLD), from the Illinois, Kankakee, and lower Des Plaines rivers. However, documentation of emigration needed to support that contention is lacking and there is limited knowledge of the current rate of BRLD passage by native species. To assess native fish passage through the lock, a microchemical study was conducted using fin rays from fish collected from the Des Plaines, Illinois, and Kankakee Rivers. The edge of each fin ray, which contained the most recently deposited material, was assumed to contain a microchemical signature reflective of residency in the river where the fish was sampled. Fin ray edge strontium:calcium ratio (Sr:Ca) was used to define taxonomic and river-specific signature ranges for four taxonomic groups: centrarchids, catostomids, ictalurids, and lepisosteids. Fin ray edge Sr:Ca data were input into a random forest classification model, and the classification accuracy of fish to their river of capture based on their fin ray edge Sr:Ca was > 97% in each taxonomic group. The classification model was then applied to the entire fin ray of each fish sampled upstream of Brandon Road to infer retrospective environmental history. Upstream BRLD lock passage was suggested by the presence of Sr:Ca signatures indicative of prior downstream residency in the Illinois or Kankakee rivers in a fish sampled upstream of BRLD. Results indicated some evidence of downstream residency that suggested upstream BRLD lock passage for centrarchids, catostomids, ictalurids, and lepisosteids, ranging from 15 – 37% of individuals sampled depending on taxa. An additional 19 – 80% of individuals within each taxonomic group were classified as fish with uncertain downstream residency, whereby the possibility of BLRD lock passage could not be rejected, but there was higher uncertainty in establishing downstream residency in the Illinois or Kankakee rivers. The impact of BRLD modifications and passage restriction on Des Plaines River fish populations is unknown and merits further investigation.

Aquatic invasive species are a widespread issue throughout the central United States. Black Carp (Mylopharyngodon piceus) are an aquatic invasive species and are an issue due to their unknown ecological and biological impacts that they may cause to the environment that they invade. Determining movements of an aquatic invasive species such as dam passage or inter-river movement may aid in agency efforts to reduce the spread of an invasive or implement strategies to mitigate its potential expanding range. In this study, I used otolith microchemistry paired with water samples to infer movement and dam passage of Black Carp between eight study regions within the Mississippi River basin. A total of 127 Black Carp otoliths were used and 112 (88%) were classified as immigrants, 14 were classified as potential residents, and one otolith was vateritic so no inferences about movement could be made for that fish. Of the 112 fish classified as potential immigrants, 102 (91%) showed signs of upstream dam passage, and the average instance a Black Carp was inferred to move between rivers was 7 times during their lifetime (SD ± 6.23). These results show that Black Carp may exhibit frequent occurrences of inter-river movement throughout their lives and have high instances of dam passage associated with their movement. This paper presents the first confirming evidence of lock and dam passage by Black Carp, although the apparently expanding range of the species in recent years based on reported captures suggested that lock and dam passage had likely occurred. Evidence of frequent upstream movement and lock and dam passage suggests that future studies should evaluate the efficacy of potential deterrents at locks and dams for preventing or reducing upstream passage by Black Carp.

Channel Catfish are broadly distributed in the U.S. and are important commercially and recreationally in many rivers, lakes, reservoirs, and streams. Since they are a popular sportfish, many state-owned lakes are stocked with a variety of sizes to enhance population sizes and provide angling opportunities. The goals of this study were to determine the contributions of stocked fish, determine the fish size at stocking, and to assess the contribution of yearling and catchable sizes to the stocked percentage. Fish samples were obtained from three hatcheries and six lakes within different ecoregions across Arkansas to assess whether chemical signatures were different among locations. Sectioned pectoral spines were analyzed for Sr:Ca and Ba:Ca using laser ablation-ICPMS to determine whether location-specific Sr:Ca and Ba:Ca signatures were reflected in pectoral spine samples, and to assess the accuracy with which fish could be assigned to their collection location using spine Sr:Ca and Ba:Ca. Fin spine core Sr:Ca and Ba:Ca data were also used to identify stocked fish and determine size at stocking for hatchery-origin fish sampled from each of the six lakes. Spine microchemistry represents a non-lethal approach to identify stocked catfish and infer size at stocking, which will better inform allocation of hatchery-produced fish. Differences in pectoral spine Sr:Ca edge signatures among locations were detected, which were primarily driven by differences in geology among ecoregions. Assignment accuracy of fish to collection location using Random Forest Modeling was 88% or greater for all but one of the study lakes. This allowed for application of the random forest model on pectoral spine core Sr:Ca and Ba:Ca to assign individuals sampled from the lakes as hatchery or wild origin. Among all the Channel Catfish sampled from the six lakes, 45% were identified as hatchery origin and 46% of those were stocked as catchable size fish. Contributions of stocked fish varied among study lakes from 0% to 100%. This was the first study to demonstrate that pectoral spine microchemistry can be used for assessing both stocking contribution and inferring fish size at stocking. Overall, this study will aid in the allocation of hatchery-reared catfish by management biologists, and could lead to more projects focused on exploring stocking contribution by microchemistry, such as assessment of how habitat enhancement may influence the contribution of natural reproduction to catfish populations.

It has always been the desire to get away from the use of hydrogen sulphide (H2S) in the laboratory. In the macro system Brockman (16) developed a method which dispensed with its use. In the June issue of Journal of Chemical Education for 1934 there appeared a system developed by Gerstenzang (17) which dispensed with the use of HaS in micro analysis. With the idea that the system might prove useful here in the University, I undertook a semi-quantitative investigation of it, under the direction of Professor W.0. Walker, to determine the sensitivity of the tests. Solutions of the cations were made up in 500 c.c. bottles so that each c.c. contained 20 mg. of the cation. Smaller dropping bottles were provided so that 1 mg. quantities were easily available. Test reagents were made up according to Treadwell-Hall (19) as specified in the instructions. In all procedures the instructions were followed closely in the first attempts. If difficulties were found in procedure, quantities were varied in an attempt to clear up or overcome the difficulty. / Thesis / Master of Arts (MA)

Range expansion events of the Humboldt squid reveal our inadequate understanding of populations of this species. Despite recent hatching, reproductive, tagging, genetic and dietary studies of Dosidicus gigas, much speculation remains concerning geographic migration, stock assessment and habitat preferences. This study provides evidence that statolith trace elemental variations can be useful in distinguishing among geographic populations. Specimens were collected from the Galapagos Islands, southern California, and Washington State. A dissection method was recorded and published. By using laser ablation methods, discrete measurements of 10 elements were collected at 6 to 7 ablation sites covering embryonic, paralarval, juvenile and adult stages. Analysis of Variance revealed important ontogenic elemental variations among ablation locations. Multivariate Analysis of Variance, ordination techniques and discriminant function analysis with permutation testing were all utilized to compare and characterize the variations found in elemental concentrations. Significant ontogenic variations were found for 8 out of the 10 focus elements; this is the first report for 5 of these elements for this species. The geographic populations were effectively classified as distinct group for the first time using these methods. Elemental fingerprint signatures were found to be significantly different at multiple ontogenic growth regions of the statolith. Seattle and California paralarvae exhibited similar elemental signatures despite significant differences in those found in the embryonic core and juvenile regions of the statolith. These methods are a useful tool in providing stock assessment and can be improved for use in future population dynamics models.

Capelin is an important forage fish species in the Northwest Atlantic and the primary prey species of many top predators. Capelin undergo extensive inshore migrations (> 350 km) to coastal spawning grounds in the spring where the timing of inshore arrival is highly variable. I investigated the influence of intrinsic factors and proxies for extrinsic factors on the timing of arrival of capelin at spawning sites on the northeast coast of Newfoundland (2012 and 2013). Despite high inter-annual variation in almost all factors examined, intrinsic factors, specifically length and age, consistently varied with timing of arrival at spawning sites for both males and females, unlike proxies for extrinsic factors. These results are important for the management of this critical fish species, as selective harvesting by the capelin fishery of early-arriving fish may impact the age/size structure of the population, recruitment, and result in increased variability in the timing of spawning.

Knowledge of habitats used by riverine fishes throughout their life history is important for management and conservation. Naturally occurring chemical markers in otoliths have recently been used to determine natal origins and environmental history of fishes in a variety of marine and freshwater environments. However, to our knowledge no studies have examined the applicability of this technique in large floodplain rivers in United States. We evaluated otolith microchemistry and stable isotopic composition as tools for determining origins of fishes in the upper and middle Mississippi and lower Illinois Rivers, their tributaries, and associated floodplain lakes. Fishes were collected from 21 sites during summer 2006 and 2 additional sites in spring 2007. Water samples were obtained from the same 23 sites plus three additional sites during summer and fall 2006 and spring 2007. Otoliths and water samples were analyzed for δ18O, and a suite of trace elements; otoliths were also analyzed for δ13C. Tributaries, floodplain lakes, and the Illinois and Mississippi Rivers had distinct isotopic and elemental signatures. Tributaries on the Missouri and Illinois sides of the middle Mississippi River could also be differentiated by their elemental and isotopic fingerprints. Otoliths reflected differences in water chemistry among habitats. Results indicate that otolith microchemistry and stable isotope analyses provide a potentially effective means of determining origins and environmental history of fishes in large river-floodplain systems.

Insight into environments and habitats that contribute recruits to adult fish stocks in riverine systems is vital for effective population management and conservation. Catfishes are important recreational species in the Mississippi River and are commercially harvested. However, contributions from main channel and tributary habitats to catfish recruitment in large rivers such as the middle Mississippi River (between St. Louis, MO and Cairo, IL) are unknown. Stable isotope and trace elemental signatures in otoliths have been useful for determining environmental history of fishes in a variety of aquatic systems, including the Mississippi River. The objectives of this study were to identify the principle natal environments of channel catfish Ictalurus punctatus and blue catfish I. furcatus in the middle Mississippi River (MMR) using otolith stable oxygen isotopic composition (δ18O) and strontium:calcium ratios (Sr:Ca). Catfish were sampled in the MMR during July-October 2013 and 2014 and lapilli otoliths were analyzed for δ18O and Sr:Ca. Water samples from the MMR and tributaries were collected seasonally from 2006-2014 to characterize site-specific signatures. Persistent differences in water δ18O and Sr:Ca among the MMR and tributaries (including the upper Mississippi, Illinois, and Missouri rivers as well as smaller tributaries) were evident, enabling identification of natal environment for individual fish. Results indicated that blue and channel catfish stocks in the MMR primarily recruited from the largest rivers (Missouri and Mississippi rivers) in our study area and received minimal influence from smaller tributaries. Recruitment and year class strength investigations and efforts aimed at enhancing blue and channel catfish spawning and nursery habitats should be focused in the large rivers with less emphasis in the smaller tributaries.

Understanding spatial patterns in population demographics and the principal natal environments supporting riverine fish populations are important for fisheries management. Although the black basses are among the most popular groups of game fishes in North America, relatively little information exists regarding demographics and environmental history of spotted bass Micropterus punctulatus in riverine environments. Fin ray microchemistry was used to identify natal environment and age estimates from sectioned fin rays used to estimate growth and mortality rates for spotted bass in Smithland pool of the Ohio River and three tributaries. Spotted bass were collected from 2014-2016 in headwater reaches of tributaries using electrofishing, angling, and a seine net, while electrofishing was used exclusively in the Ohio River and lower tributary reaches. Spotted bass in the Ohio River generally lived longer and grew larger than conspecifics in tributaries, although mortality rates were not definitively different. Differences in water Sr:Ca and Ba:Ca among the Ohio River and tributaries were reflected in fin rays from age-0 and age-1 fish. Eighteen percent of spotted bass ≥ age-2 captured in the Ohio River originated in tributaries, whereas 15% captured in tributaries originated in the Ohio River. Although most fish remained in their natal environment, small tributaries can be a supplemental recruitment source for spotted bass populations and fisheries in large rivers. This study highlights the utility of fin rays for microchemical analysis and age estimation of spotted bass.