Nate Bickford

Stock Identification of Walleye via Otolith Chemistry in the Eleven Point River, Arkansas

Abstract Otolith chemistry was used to identify two hatchery stocks (Missouri State Hatchery and Arkansas Federal Hatchery) and a possible wild stock of walleye Sander vitreus in the Eleven Point River in northeastern Arkansas. Previous population estimates by the Arkansas Game and Fish Commission using traditional tag-and-release techniques failed to identify the relative survival of these stocks or their spatial and temporal persistence. Using chemical analysis of otoliths combined with a priori knowledge of the hatchery source, we identified otolith chemical signatures unique to each stock. We collected 51 walleyes that bore the physical tag of a known hatchery, along with 46 nontagged walleyes. The efficacy of otolith chemistry in classifying walleyes to known stocks was assessed by analyzing unknowns via discriminant function analysis. Fish were classified to their respective stocks based on otolith chemistry, and 92% were assigned to known stocks. Fishery managers can assess the persistence of indiv...

Otolith trace element chemistry as an indicator of anadromy in yukon river drainage coregonine fishes

Abstract Eight coregonine species have been documented in the Yukon River drainage. They include inconnu Stenodus leucichthys, broad whitefish Coregonus nasus, humpback whitefish C. pidschian, Alaska whitefish C. nelsonii, least cisco C. sardinella, Bering cisco C. laurettae, round whitefish Prosopium cylindracium, and pygmy whitefish P. coulterii. Personal use, sport, and commercial fisheries within the drainage target several of these species. Some species are capable of anadromous life histories, as evidenced by their presence in estuaries, yet few studies have investigated the upstream migrations of anadromous components of these populations. Only inconnu migrations have been previously examined in the Yukon River drainage. We investigated the distribution of anadromous coregonine fish in the Yukon River drainage in Alaska using sampling and otolith chemistry procedures. Six species were identified in sample collections from eight regions of the drainage between 1,200 and 2,000 km upstream from the Be...

Population Structure of a Neotropical Migratory Fish: Contrasting Perspectives from Genetics and Otolith Microchemistry

Abstract Developing conservation strategies for migratory fishes requires an understanding of connectivity among populations. Neotropical rivers contain diverse and economically important assemblages of migratory fishes, but little is known about the population biology of most species. We examined the population structure of Prochilodus mariae, an abundant migratory fish species found in Venezuelan rivers that plays essential roles in both regional fisheries and ecosystem dynamics. By coupling otolith microchemistry and microsatellite genetic analyses, we were able to evaluate both natal origins of individual fish and genetic structure on a regional level. The chemistry of otolith cores inferred separate breeding grounds for four of six populations, with 75–85% of individuals from each river sharing a natal signature that is distinct from the other populations. In contrast, we detected no genetic structure, indicating that gene flow among these rivers prevents population differentiation. These disparate i...

Susceptibility of Pacific Herring to Viral Hemorrhagic Septicemia Is Influenced by Diet

Groups of specific-pathogen-free Pacific herring Clupea pallasii were highly susceptible to infection by viral hemorrhagic septicemia virus (VHSV); however, the level of mortality was influenced by diet during the 40-71 d before, during, and after the first exposure to the virus. Cumulative mortality was highest among the herring maintained on an experimental soy-based pellet, intermediate among those maintained on a commercially available fish-meal-based pellet, and lowest among those maintained on a second commercially available fish-meal-based pellet containing beta-glucans. Additionally, the herring maintained on the experimental soy-based feed demonstrated less growth than those on the commercially available feeds. The results indicate the importance of standardizing diet during empirical determinations of disease susceptibility and provide insights into the risk factors affecting VHS susceptibility in wild populations.

Variations in otolith elemental compositions of two clupeid species, Stolothrissa tanganicae and Limnothrissa miodon in Lake Tanganyika

Lake Tanganyika in East Africa has two primary basins (Northern and Southern) and borders four sovereign countries. Effective management of the fisheries of this lake requires sound biological understanding of the various fish stocks. The feasibility of fish stock identification within different basins and sub-basins of this lake was attempted through otolith elemental composition analysis. Element ratio signatures of whole sagittal otoliths (Mg/Ca, Sr/Ca and Ba/Ca) of two commercially important clupeid species (Stolothrissa tanganicae, n=18; Limnothrissa miodon, n=32) were used to classify individual fish to their resident basins. No element ratios in L. miodon otoliths were significantly different between Southern sub-basins, yet Ba/Ca and Sr/Ca ratios were significantly different for individuals from the Northern and Southern basins. Sr/Ca and Ba/Ca ratios were also significantly different between otoliths of sympatric L. miodon and S. tanganicae in the Northern Bujumbura Sub-basin. Species differences may be due to ontogenetic and environmental variables. Sr/Ca and Ba/Ca element concentration ratios contributed greatly to basin classification of individual fish. Canonical discriminant analysis correctly classified 91% of L. miodon and 83.3% of S. tanganicae to the Bujumbura sub-basin, compared to 59.9% of L. miodon collected from the Southern Basin that were correctly classified to this basin. These classification rates are similar to those found for estuarine species. Our results of a limited study suggest that otolith element compositions can be used as a natural tag to identify fish stocks in Lake Tanganyika and assist in the implementation of a multi-national fisheries best management plan.