Showing papers in "Transactions of The American Fisheries Society in 2016"

Forecasting the Impacts of Silver and Bighead Carp on the Lake Erie Food Web

Abstract: Nonindigenous bigheaded carps (Bighead Carp Hypophthalmichthys nobilis and Silver Carp H. molitrix; hereafter, “Asian carps” [AC]) threaten to invade and disrupt food webs and fisheries in the Laurentian Great Lakes through their high consumption of plankton. To quantify the potential effects of AC on the food web in Lake Erie, we developed an Ecopath with Ecosim (EwE) food web model and simulated four AC diet composition scenarios (high, low, and no detritus and low detritus with Walleye Sander vitreus and Yellow Perch Perca flavescens larvae) and two nutrient load scenarios (the 1999 baseline load and 2£ the baseline [HP]). We quantified the uncertainty of the potential AC effects by coupling the EwE model with estimates of parameter uncertainty in AC production, consumption, and predator diets obtained using structured expert judgment. Our model projected mean § SD AC equilibrium biomass ranging from 52 § 34 to 104 § 75 kg/ha under the different scenarios. Relative to baseline simulations without AC, AC invasion under all detrital diet scenarios decreased the biomass of most fish and zooplankton groups. The effects of AC in the HP scenario were similar to those in the detrital diet scenarios except that the biomasses of most Walleye and Yellow Perch groups were greater under HP because these fishes were buffered from competition with AC by increased productivity at lower trophic levels. Asian carp predation on Walleye and Yellow Perch larvae caused biomass declines among all Walleye and Yellow Perch groups. Large food web impacts of AC occurred in only 2% of the simulations, where AC biomass exceeded 200 kg/ha, resulting in biomass declines of zooplankton and planktivorous fish near the levels observed in the Illinois River. Our findings suggest that AC would affect Lake Erie’s food web by competing with other planktivorous fishes and by providing additional prey for piscivores. Our methods provide a novel approach for including uncertainty into forecasts of invasive species’ impacts on aquatic food webs.

Carbon Dioxide as a Tool to Deter the Movement of Invasive Bigheaded Carps

Abstract: Nonnative bigheaded carps are established in the Mississippi River and there is substantial concern about their potential entry into the interconnected Laurentian Great Lakes. While electrical barriers currently exist as a preventative measure, there is need for additional control mechanisms to promote barrier security through redundancy. We tested the effectiveness of infused carbon dioxide gas (CO2) as a tool to influence the movement and behavior invasive bigheaded carps, namely Bighead Carp Hypophthalmichthys nobilis and Silver Carp H. molitrix, as well as native Bigmouth Buffalo Ictiobus cyprinellus, Channel Catfish Ictalurus punctatus, Paddlefish Polyodon spathula, and Yellow Perch Perca flavescens in an experimental pond. Individuals were monitored with acoustic telemetry before, during, and after CO2 addition to the pond. We noted distinct changes in fish behavior following CO2 addition. Each species except Paddlefish maintained farther distances from the CO2 infusion manifold relative to ...

Can Weighted Useable Area Predict Flow Requirements of Drift-Feeding Salmonids? Comparison with a Net Rate of Energy Intake Model Incorporating Drift–Flow Processes

Abstract: We compared a process-based invertebrate drift and drift-feeding net rate of energy intake (NREI) model and a traditional hydraulic-habitat model (using the RHYHABSIM [River Hydraulics and Habitat Simulation] software program) for predicting the flow requirements of 52-cm Brown Trout Salmo trutta in a New Zealand river. Brown Trout abundance predicted by the NREI model for the constant drift concentration–flow scenarios were asymptotic or linear, depending on drift concentration, increasing through the mean annual low flow (MALF; 17 m3/s). However, drift concentration increased with flow, consistent with passive entrainment. The predicted fish abundance–flow relationship based on flow-varying drift concentration increased logistically, and more steeply, with flow through the MALF and beyond. Predictions for the relationship between weighted useable area (WUA) and flow were made for three sets of drift-feeding habitat suitability criteria (HSC) developed on three midsized and one large New Zealand ...

Novel Species Interactions in a Highly Modified Estuary: Association of Largemouth Bass with Brazilian Waterweed Egeria densa

Abstract: Frequent invasions in coastal ecosystems result in novel species interactions that have unknown ecological consequences. Largemouth Bass Micropterus salmoides and Brazilian waterweed Egeria densa are introduced species in the Sacramento–San Joaquin River Delta (the Delta) of California, a highly modified estuary. In this system, Brazilian waterweed and Largemouth Bass have seen marked increases in distribution and abundance in recent decades, but their association has not been specifically studied until now. We conducted a 2-year, bimonthly electrofishing survey with simultaneous sampling of water quality and submerged aquatic vegetation (SAV) biomass at 33 locations throughout the Delta. We used generalized linear mixed models to assess the relative influences of water temperature, conductivity, Secchi depth, and SAV biomass density on the abundance of both juvenile-sized and larger Largemouth Bass. Water temperature had a positive relationship with the abundance of both size-classes, but only ju...

Life History Diversity in Klamath River Steelhead

Abstract: Oncorhynchus mykiss exhibits a vast array of life histories, which increases its likelihood of persistence by spreading risk of extirpation among different pathways. The Klamath River basin (California–Oregon) provides a particularly interesting backdrop for the study of life history diversity in O. mykiss, in part because the river is slated for a historic and potentially influential dam removal and habitat recolonization project. We used scale and otolith strontium isotope (87Sr/86Sr) analyses to characterize life history diversity in wild O. mykiss from the lower Klamath River basin. We also determined maternal origin (anadromous or nonanadromous) and migratory history (anadromous or nonanadromous) of O. mykiss and compared length and fecundity at age between anadromous (steelhead) and nonanadromous (Rainbow Trout) phenotypes of O. mykiss. We identified a total of 38 life history categories at maturity, which differed in duration of freshwater and ocean rearing, age at maturation, and incidence...

Dynamics of Near-Coastal Fish Assemblages following the Deepwater Horizon Oil Spill in the Northern Gulf of Mexico

Abstract: Coastal ecosystems along the northern Gulf of Mexico are highly productive and are affected by fishing and petroleum industries in different, sometimes contrasting, ways. As a result of the Deepwater Horizon (DWH) oil spill in April 2010, oil and oil dispersants were introduced into the northern Gulf of Mexico. At the same time, large portions of the Gulf of Mexico were closed to commercial and recreational fishing for most of the 2010 summer. This presented a unique opportunity to study the dynamics of a fish assemblage exposed to changes in two disparate types of anthropogenic disturbances. We compared assemblage data for near-coastal fish (456 samples representing over 45,000 individuals and 109 species) from pre-DWH (before 2010) and post-DWH (2011–2014) to assess potential changes in abundance, diversity (alpha, beta, and gamma), and assemblage structure. In contrast to predicted oil-induced mortality, post-DWH assemblages were characterized by high abundance in 2011 (CPUE across all species ...

Avian Predation on Juvenile Salmonids: Spatial and Temporal Analysis Based on Acoustic and Passive Integrated Transponder Tags

Abstract: We evaluated the impact of predation on juvenile steelhead Oncorhynchus mykiss and yearling and subyearling Chinook Salmon O. tshawytscha by piscivorous waterbirds from 11 different breeding colonies in the Columbia River basin during 2012 and 2014. Fish were tagged with both acoustic tags and PIT tags and were tracked via a network of hydrophone arrays to estimate total smolt mortality (1 – survival) at various spatial and temporal scales during out-migration. Recoveries of PIT tags on bird colonies, coupled with the last known detections of live fish passing hydrophone arrays, were used to estimate the impact of avian predation relative to total smolt mortality. Results indicated that avian predation was a substantial source of steelhead mortality, with predation probability (proportion of available fish consumed by birds) ranging from 0.06 to 0.28 for fish traveling through the lower Snake River and the lower and middle Columbia River. Predation probability estimates ranged from 0.03 to 0.09 fo...

Reduction in Spring Flow Threatens Rio Grande Silvery Minnow: Trends in Abundance during River Intermittency

Abstract: Habitat fragmentation and changes in flow regime can structure fish assemblages, resulting in extirpations or invasions. A guild of freshwater stream fishes that spawn semi-buoyant, nonadhesive eggs directly in the water column are particularly susceptible to extirpation in fragmented streams. The pelagic broadcast-spawning Rio Grande Silvery Minnow Hybognathus amarus was listed as endangered in 1994 and has been intensely managed since. I used mean May flows and the number of times the channel dried within a year to predict numbers of Rio Grande Silvery Minnow captured in isolated pools in the Middle Rio Grande, New Mexico. Adult Rio Grande Silvery Minnow numbers increased as previous year’s mean May discharge increased, and generally decreased with each subsequent drying event. Similarly, numbers of young-of-year Rio Grande Silvery Minnow increased with increasing mean May discharge in the current year. However, young-of-year minnow were either very abundant or nearly absent in isolated pools, d...

Downstream passage and impact of turbine shutdowns on survival of silver American Eels at five hydroelectric dams on the Shenandoah River.

Abstract: Hydroelectric dams impact the downstream migrations of silver American Eels Anguilla rostrata via migratory delays and turbine mortality. A radiotelemetry study of American Eels was conducted to determine the impacts of five run-of-the-river hydroelectric dams located over a 195-km stretch of the Shenandoah River, Virginia–West Virginia, during fall 2007–summer 2010. Overall, 96 radio-tagged individuals (mean TL = 85.4 cm) migrated downstream past at least one dam during the study. Most American Eels passed dams relatively quickly; over half (57.9%) of the dam passage events occurred within 1 h of reaching a dam, and most (81.3%) occurred within 24 h of reaching the dam. Two-thirds of the dam passage events occurred via spill, and the remaining passage events were through turbines. Migratory delays at dams were shorter and American Eels were more likely to pass via spill over the dam during periods of high river discharge than during low river discharge. The extent of delay in migration did not di...

Population Dynamics of an Estuarine Forage Fish: Disaggregating Forces Driving Long-Term Decline of Longfin Smelt in California's San Francisco Estuary

Abstract: Forage fish production has become a central concern of fisheries and ecosystem managers because populations of small fish are a critical energetic pathway between primary producers and predator populations. Management of forage fish often focuses on controlling exploitation rates, but it is also possible to manage productivity of these species in coastal ecosystems, particularly estuaries. Like several forage fish species that are native to the San Francisco Estuary (SFE) in California, the Longfin Smelt Spirinchus thaleichthys has experienced dramatic population declines over the past few decades. This population is not fished commercially or recreationally; trends in its relative abundance have been described statistically, but the mechanisms that drive population dynamics are still poorly understood. Our objective was to evaluate alternative conceptual models of Longfin Smelt population dynamics to better understand the forces that may constrain the species' productivity during different phases...

Components of Mortality within a Black Bass High-Release Recreational Fishery

Abstract: Mortality after release can have a substantial impact on high-release recreational sport fishes, such as Largemouth Bass Micropterus salmoides. However, little work has explored the cumulative impact of catch-and-release mortality at the population level. We used a combined telemetry–tag return approach to estimate all components of total mortality, including instantaneous natural mortality (M) and instantaneous fishing mortality (F), for Florida Largemouth Bass M. salmoides floridanus (hereafter, Florida Bass) within a popular fishing lake in northern Florida. Fishing mortality was subdivided into harvest (FH), recreational catch-and-release (FR), and tournament catch-and-release (FT) components. Over 2 years, we monitored the fates of 181 Florida Bass that were tagged with high-reward external dart tags and internal radio transmitters. An additional 345 fish were tagged with variable-reward external tags. Annual FH values were seasonal, with an increase in FH occurring in the spring of both year...

Fish and Blue Crab Density along a Riprap-Sill-Hardened Shoreline: Comparisons with Spartina Marsh and Riprap

Abstract: Wetland managers have historically considered riprap-sill structures (a type of “living shoreline” consisting of a rock sill that is placed low in the intertidal zone, with native vegetation planted between the sill and the shore) to be more ecologically sound than the riprap that is traditionally applied for shoreline stabilization in estuaries. However, little research has been conducted to compare the macrofauna associated with riprap-sill and riprap-hardened shorelines. Density and diversity of fish and blue crabs Callinectes sapidus were compared via weekly sampling along a riprap-sill shoreline, a riprap shoreline, and a shoreline fringed with smooth cordgrass Spartina alterniflora marsh in the Delaware Coastal Bays during summer 2010. Seining was conducted to quantitatively sample the shore zone and shallow subtidal regions, and minnow traps were used to determine the presence or absence of fishes in the mid- to upper-intertidal zone of each shoreline type. Temporally persistent differences...

Early Feeding by Lake Trout Fry

Abstract: The restoration of Lake Trout Salvelinus namaycush in the Great Lakes and Lake Champlain has been challenging due to the bottlenecks in recruitment that occur mostly during early life stages. Among possible sources of fry mortality (e.g., predation, starvation, and disease), the least is known about the diet and starvation risk of pre-emergent fry. The first feedings by fry are generally assumed to be delayed until close to the absorption of the yolk sac and the emergence of the fry. The stomach contents of 374 wild-caught Lake Trout fry from Lake Champlain were examined from hatching to the exogenous feeding stage to identify the earliest occurrence of feeding relative to yolk sac absorption and to describe the diet. Within 2 weeks of hatching, 19% of fry had food in their stomachs. At 4–6 weeks and after yolk sac absorption, 98% of fry began feeding. Diet was primarily comprised of Bosmina as well as calanoid and cyclopoid copepods, and fry contained up to 215 items per stomach. Our finding that...

Evaluation of a Long-Term Predator Removal Program: Abundance and Population Dynamics of Invasive Northern Pike in the Yampa River, Colorado

Abstract: The Northern Pike Esox lucius is invasive in the upper Green and Yampa River basins of Colorado and Utah and impedes endangered fish recovery in the upper Colorado River basin. Mechanical removal was implemented in 2004, but Northern Pike population dynamics and removal efficacy were not well understood. We analyzed mark–recapture records from 8,929 individual Northern Pike captured during 2004–2010 from three reaches of the Yampa River: Hayden to Craig (upstream reach), South Beach–Little Yampa Canyon–Juniper (middle reach), and Maybell–Sunbeam (downstream reach), encompassing 175 river kilometers. Annual survival rates for Northern Pike of the mean TL (465 mm) were highest downstream (mean = 0.54; range = 0.36–0.71) and lowest upstream (mean = 0.25; range = 0.12–0.38). Annual abundance exhibited the opposite pattern, as it was highest upstream (annual range = 1,144–4,078 fish) and lowest downstream (range = 232–746 fish). After removal occurred each year, Northern Pike abundance increased annual...

Effects of Passive Integrated Transponder Tags on the Physiology and Swimming Performance of a Small‐Bodied Stream Fish

Abstract: Within the past few decades, telemetry has proven to be a valuable tool for tracking and monitoring fish. Although the advent of smaller transmitters has made these methods increasingly applicable to small-bodied fishes, limited information currently exists regarding the efficacy of these transmitters or their putative effects on small-bodied fishes. I evaluated the physiological and performance consequences of PIT tag implantation in a small-bodied, sexually dimorphic stream fish, the Blackspotted Topminnow Fundulus olivaceus. First, I used a common-garden experiment in an outdoor mesocosm setting to assess the long-term effects (184 d) of PIT tag implantation on a suite of physiological and phenotypic metrics. I randomly assigned 216 individuals (50–73 mm SL; equal sex ratio) to one of three tagging treatments: control (no PIT tag), small (8 mm) PIT tag, or large (12 mm) PIT tag. Survivorship did not vary among treatment groups, and the presence of the tags had no apparent effects on the conditi...

Thermal Regimes, Nonnative Trout, and Their Influences on Native Bull Trout in the Upper Klamath River Basin, Oregon

Abstract: The occurrence of fish species may be strongly influenced by a stream’s thermal regime (magnitude, frequency, variation, and timing). For instance, magnitude and frequency provide information about sublethal temperatures, variability in temperature can affect behavioral thermoregulation and bioenergetics, and timing of thermal events may cue life history events, such as spawning and migration. We explored the relationship between thermal regimes and the occurrences of native Bull Trout Salvelinus confluentus and nonnative Brook Trout Salvelinus fontinalis and Brown Trout Salmo trutta across 87 sites in the upper Klamath River basin, Oregon. Our objectives were to associate descriptors of the thermal regime with trout occurrence, predict the probability of Bull Trout occurrence, and estimate upper thermal tolerances of the trout species. We found that each species was associated with a different suite of thermal regime descriptors. Bull Trout were present at sites that were cooler, had fewer high-t...

Low Annual Fidelity and Early Upstream Migration of Anadromous Arctic Char in a Variable Environment

Abstract: The life histories of anadromous Arctic Char Salvelinus alpinus are complex and vary greatly between populations and environments. Here, we detail key aspects of the physical environment and life history of a population of Arctic Char from Nulahugyuk Creek, Nunavut, Canada, to characterize migration traits in a highly variable environment. Over the course of this migration, creek discharge declined precipitously, forcing Arctic Char to migrate through shallow water with large diel temperature fluctuations (>10°C) and high temperature extremes (>21°C). The downstream migration of adults (>55 cm) began in mid-June and continued into early July, while the downstream migration of smolts (<30 cm) began in late June and continued until late July. The upstream adult migration began in late June and ended in late July, far earlier than most upstream migrations in the region. There was no appreciable upstream migration of juveniles, and Arctic Char 30 to 55 cm in length were absent from the up- and downstr...

Juvenile Lake Sturgeon Go To School: Life-Skills Training for Hatchery Fish

Abstract: Hatchery supplementation of declining fish populations is commonly employed to try to increase year-class strength. However, the success of such programs is often hampered from low postrelease survival as a result of the failure of hatchery fish to appropriately recognize predation threats. Not surprisingly, there has been considerable effort to train prey to recognize predators prior to release. The objective of our current work was to characterize the antipredator response of hatchery-reared, predator-naive young-of-the-year Lake Sturgeon Acipenser fulvescens (an endangered species) to alarm cues from injured conspecifics and test whether these alarm cues could be used to train sturgeon to recognize unknown predators. We found that skin-derived alarm cues elicited an antipredator response without learning and that learning required cues coming from whole-body grinds, presumably because they represent a much more reliable indicator of risk. When the experiment was repeated with older sturgeon fro...

Examination of Predation on Early Life Stage Delta Smelt in the San Francisco Estuary Using DNA Diet Analysis

Abstract: We examined predation by nonnative Mississippi Silversides Menidia audens, other small fishes, and invertebrates on the early life stages of the endangered Delta Smelt Hypomesus transpacificus, which is endemic to the Sacramento–San Joaquin Delta in California. Mississippi Silversides and other putative predators were collected primarily via boat electrofishing in the northern reaches of the upper San Francisco Estuary, an area targeted for substantial tidal wetland restoration to enhance habitat for Delta Smelt and other endangered fishes. Predators’ digestive tracts were removed and analyzed for the presence of Delta Smelt DNA by using quantitative PCR TaqMan assays. Across all sites, 69 of 550 Mississippi Silversides tested positive for Delta Smelt DNA. The number of sampled Mississippi Silversides that were positive for Delta Smelt DNA was significantly greater in offshore habitats than in nearshore habitats. Delta Smelt DNA detection data indicated that a wide variety of other species were al...

Loss of Naivety to Angling at Different Rates in Fished and Unfished Populations of Largemouth Bass

Abstract: Recreational fishing represents a coupled human and natural system subject to complex feedback processes. Learned lure avoidance represents one feedback process that may influence a fish population’s vulnerability to angling. In the present study, naive Largemouth Bass Micropterus salmoides originating from fished and unfished populations were raised in a pond and subjected to standardized angling. Our objectives were to evaluate the initial angling vulnerability and the rate at which naivety to angling was lost for fished and unfished populations. While no difference in initial angling vulnerability existed among fish from fished and unfished populations of origin, individuals from fished populations learned lure avoidance faster than individuals from unfished populations. Cumulative catch events, a metric that incorporates the number of opportunities individuals had to directly and indirectly experience angling, best predicted declining daily catch rates for both fished and unfished populations,...

An Analysis of Lake Morphometric and Land-Use Characteristics that Promote Persistence of Cisco in Indiana

Abstract: Remnant populations of Cisco Coregonus artedi persist at the southern extent of their range among northern Indiana's glacial lakes, where most of their populations have become extirpated during the past century. Land-use practices have likely accelerated lake eutrophication, while climate change threatens to further degrade the habitat necessary to sustain Ciscoes in Indiana. However, because the effects of these stressors have not been ubiquitous, an understanding of the factors that have contributed to either extirpation or persistence of Cisco populations will better inform future conservation practices. We analyzed lake morphometric and land-use data to identify lakes that (1) are most likely to sustain Ciscoes, (2) are most likely to lose Ciscoes, and (3) have lost Ciscoes but are similar to current Cisco lakes and hence may be targets for restoration. We found that large, deep lakes located further north were more suitable for Ciscoes in the past, but that smaller lakes with a high ratio of ...

Age, Growth, and Reproduction in Two Coastal Populations of Longnose Gars

Abstract: Measurements of age, growth, and reproduction are excellent tools for determining the ecological role and impact of a species within an ecosystem. Longnose Gar Lepisosteus osseus is a large, ubiquitous top predator in fresh and saline waters of the eastern United States. Even though the species is common, their basic biology has been largely uncharacterized in brackish and marine waters. Specimens were collected from two estuaries: Winyah Bay and Charleston Harbor, South Carolina, from May 2012 through July 2013 to examine age, growth, and reproduction in tidally influenced systems. This species is fairly long-lived, with maximum ages of 17 and 25 years for males and females, respectively. The von Bertalanffy growth model yielded significantly higher growth rates for males than for females. Reproductive histology and the gonadosomatic index indicated that Longnose Gars exhibit determinate fecundity and spawn in late spring following a long development period during fall and winter. These life hist...

Brook Trout, Brown Trout, and Ectoparasitic Copepods Salmincola edwardsii: Species Interactions as a Proximate Cause of Brook Trout Loss Under Changing Environmental Conditions

Abstract: Changes in environmental conditions are expected to affect stream temperature and ultimately the presence of native Brook Trout Salvelinus fontinalis in Wisconsin streams. While change in climate may be an ultimate cause of Brook Trout loss, proximate causes may involve factors other than intolerance to high temperatures. Here I present data to support the hypothesis that species interactions among Brook Trout, naturalized Brown Trout Salmo trutta, and ectoparasitic copepods Salmincola edwardsii in the context of changing environmental conditions can lead to declines in Brook Trout recruitment and abundance. While S. edwardsii are endemic to Wisconsin streams and infect Brook Trout, they do not infect Brown Trout. Salmincola edwardsii were first documented in Ash Creek, Wisconsin, in 2010 and became epizootic in 2012. Conditions in 2012 conducive to an epizootic included anomalously warm stream temperatures, relative drought conditions, and an increasing sympatric population of Brown Trout. Infect...

Feeding Ecology of Native and Nonnative Salmonids during the Expansion of a Nonnative Apex Predator in Yellowstone Lake, Yellowstone National Park

Abstract: The illegal introduction of Lake Trout Salvelinus namaycush into Yellowstone Lake, Yellowstone National Park, preceded the collapse of the native population of Yellowstone Cutthroat Trout Oncorhynchus clarkii bouvieri, producing a four-level trophic cascade. The Yellowstone Cutthroat Trout population’s collapse and the coinciding increase in Lake Trout abundance provided a rare opportunity to evaluate the feeding ecology of a native prey species and a nonnative piscivore species after the restructuring of a large lentic ecosystem. We assessed diets, stable isotope signatures, and depth-related CPUE patterns for Yellowstone Cutthroat Trout and Lake Trout during 2011–2013 to evaluate trophic overlap. To evaluate diet shifts related to density, we also compared 2011–2013 diets to those from studies conducted during previous periods with contrasting Yellowstone Cutthroat Trout and Lake Trout CPUEs. We illustrate the complex interactions between predator and prey in a simple assemblage and demonstrate ...

Life Histories, Demography, and Distribution of a Fluvial Bull Trout Population

Abstract: To describe the life histories and demography of a fluvial population of Bull Trout Salvelinus confluentus, we PIT-tagged and radio-tagged Bull Trout captured in Mill Creek, a tributary of the Walla Walla River (Washington–Oregon), during 1998–2009. Adult abundance declined 63% during 2006–2010, driven primarily by a 10-fold reduction in subadult-to-adult returns. Larger subadults and fall–winter emigrants survived at higher rates, but they were a small proportion of the subadult migrants. The survival rates of larger, generally older adults were also more than 40% greater than those of smaller adults. Changes in abundance influenced other characteristics of the population. For example, adult upstream movement into spawning areas during 1999–2005 peaked in late July, whereas the smaller runs observed during 2006–2010 peaked in early September, and the relationship between fish size and migration timing shifted. Unlike many adfluvial populations, more than 90% of the adults in Mill Creek spawned an...

Estimation of the Length‐at‐Age Relationship of Mississippi's Spotted Seatrout

Abstract: Spotted Seatrout Cynoscion nebulosus are a highly valued recreational inshore species in Mississippi coastal waters. The accurate description of the length-at-age relationship is critical for assessment efforts of the stock. Because Spotted Seatrout exhibit small-scale movements, the stocks in the Gulf of Mexico are managed as state-specific units. Therefore, local demographic estimates of length at age are needed for assessment. We estimated the length-at-age relationship of Spotted Seatrout in Mississippi by using tag recapture records and otolith-derived age estimates. Three nonlinear length-at-age models were fit to sex-aggregated, tag recapture data and four nonlinear length-at-age models were fit to sex-specific, otolith-derived age data. For each suite of models, model support was determined using Akaike information criteria. The Francis (1988a) GROTAG method had the greatest support of the three models fit to the tag recapture data, and the resulting parameter estimates from the model were...

Trends in Relative Abundance and Early Life Survival of Atlantic Menhaden during 1977–2013 from Long-Term Ichthyoplankton Programs

Abstract: The Atlantic Menhaden Brevoortia tyrannus, a commercially important clupeid, supports one of the oldest and largest commercial fisheries on the U.S. East Coast. Despite recent increases in adult biomass, juvenile indices have declined coastwide and have remained particularly low in Chesapeake Bay. In order to understand the underlying causes of this decline, knowledge of larval recruitment is essential. We developed an index of larval abundance by using larval data collected from two large-scale ichthyoplankton sampling programs that occurred from Nova Scotia, Canada, to Cape Hatteras, North Carolina, during 1977–1987 and 1999–2013. Larval abundance data were standardized to a day-0 age by applying an age–length key from a study of larval ingress into Chesapeake Bay; a delta-lognormal model was used to account for spatial and temporal changes in sampling. We found that Atlantic Menhaden larval abundance increased from 1977 to 2013 and was highest in the winter; most individuals were detected at ne...

Using Radiotelemetry to Compare the Initial Behavior and Mortality of Hatchery-Reared and Wild Juvenile Florida Bass

Abstract: Stocking evaluations for pellet-reared, advanced-fingerling Largemouth Bass Micropterus salmoides often result in low contribution and survival, but little information exists on their survival and behavior soon after release. This study investigated the behavior and mortality of pellet-reared, advanced-fingerling (90–120 mm TL) Florida Bass M. floridanus immediately after they were stocked in Lake Carlton, Florida. A radiotelemetry experiment was conducted to compare initial movement, habitat use, growth, and mortality between stocked hatchery and wild fish. In year 1, we inserted radio transmitters into 50 hatchery fish; in year 2, we tagged 30 hatchery fish and 20 wild fish. All mortality we observed for hatchery fish (from both years) resulted from predation by fish and birds, and most occurred in the first 7 d after tagging. When compared directly with tagged wild fish (n = 20), tagged hatchery fish (n = 30) exhibited greater movement (75 and 124 m/d, respectively), greater proportion of locat...

Residency and Movement of Juvenile Chinook Salmon at Multiple Spatial Scales in a Tidal Marsh of the Columbia River Estuary

Abstract: Use of the Columbia River estuary by juvenile Pacific salmon Oncorhynchus spp. is garnering more attention as managers look to improve salmon survival through estuary restoration. Studies have shown that juvenile salmon are abundant in shallow-water habitats within the Columbia River estuary, but information on how juveniles exploit specific estuarine habitats is lacking. We used a combination of physical marks and PIT tag technology to record residence time, movement, and growth of juvenile Chinook Salmon O. tshawytscha, particularly subyearlings, within an emergent marsh of the Columbia River estuary during 2005, 2006, and 2008. We documented marsh-scale residency and movement within the marsh complex and channel-scale residency and movement within two small secondary channels. Many juvenile Chinook Salmon remained in the marsh for 2–4 weeks and increased in FL by 10–20 mm, with an average growth rate of 0.53 mm/d. Chinook Salmon entered secondary channels most frequently in late afternoon and o...

Pronounced Genetic Structure and Site Fidelity among Native Muskellunge Populations in Lake Huron and Georgian Bay

Abstract: Conservation and management issues related to genetic diversity and stock structure of native populations of Muskellunge Esox masquinongy have largely been unexplored. In Lake Huron’s North Channel and Georgian Bay, Muskellunge populations have been impacted by historical commercial fisheries, recreational fisheries, loss of spawning habitat, historical water quality issues, and ecosystem changes. To determine the spatial genetic structure of native Muskellunge in Lake Huron and Georgian Bay, spawning adults were sampled from 10 sites in the North Channel and eastern Georgian Bay. Genotyping with 20 microsatellite DNA loci showed substantial spatial genetic structure, with significant pairwise divergences among spawning sites. Individual- and population-based analyses revealed hierarchical population structuring, with strong patterns of spawning site fidelity and isolation by distance; very low levels of dispersal and gene flow over historical and contemporary timescales were indicated. Estimation...