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Knowledge of the distribution of ages of fish within a stock, and subsequently individual growth rates, allows managers the ability to calculate key metrics (i.e., recruitment, mortality, and stock growth rate) that greatly improve stock assessment models. Two remnant stocks of Lake Sturgeon Acipenser fulvescens exist near and within the Niagara River, one primarily occupying the headwaters and the other primarily occupying the mouth. Though initial efforts in the late 1990s collected data on the lower Niagara River stock, a long-term comprehensive examination of age and growth is lacking and the age structure of the stock found at the headwaters has yet to be formally described to our knowledge. To ascertain the current age structure of these two stocks we sampled Lake Sturgeon in the lower Niagara River and at the headwaters of the Niagara River between 2012 and 2017 and took a portion of the leading pectoral fin spine of captured Lake Sturgeon for age estimation. Ages ranged between 4 and 42 y, with females generally being older and larger than males. The median age appeared to increase from 14 to 18 y throughout our study in both stocks. Lengths at age of both stocks were larger than those reported in other systems and growth rates appear to have increased over the past decade in the lower Niagara River. Despite efforts to improve age estimation accuracy, age estimates from fish whose ages were partly known (derived from multiple age estimates from fish that were captured multiple times) demonstrated that assigned ages may have greater error than expected. Additionally, a lack of young individuals confounded growth analyses. Although there was uncertainty in the assigned ages, this study still provides evidence of consistent recruitment in both stocks and, to our knowledge, the first characterization of the age structure of the Lake Sturgeon stock occupying the headwaters of the Niagara River.

Lake Erie supported the greatest yield of lake sturgeon within the Laurentian Great Lakes near the end of the 19th century with >2000 metric tons caught at the peak of the fishery. The fishery collapsed by the 1920s when

Information about spawning fish is important to stock-assessment data needs (i.e., recruitment and fecundity) and management (i.e., habitat connectivity and protection). In Lake Erie, information about Lake Sturgeon Acipenser fulvescens early-life history is available for the Detroit River and Lake St. Clair system in the western basin, but fisheries biologists know comparatively little about Lake Sturgeon in the eastern basin. Although researchers have summarized historical spawning areas, no known natural Lake Sturgeon spawning site is described in Lake Erie proper. Researchers documented a remnant population of reproductively mature Lake Sturgeon near the headwaters of the Niagara River in eastern Lake Erie in 2011. Researchers hypothesized that a spawning site was likely in the immediate vicinity of the Niagara River headwaters near Buffalo Harbor, New York; however, its exact location was unknown. We attempted to locate spawning sites near the confluence of the Niagara River using egg traps at three potential spawning sites. We identified Lake Sturgeon eggs at one of these sites using morphological and genetic techniques. Lake Sturgeon eggs collected on one sampling trip began to emerge when placed in preservative, confirming that eggs deposited at this site are fertilized and viable, and that the area supports viable embryos. This discovery fills data gaps in the early-life history for this population, which has domestic and international management implications with respect to proposed recovery targets, stock assessment models, habitat remediation efforts, and status determinations of a protected species in a geographic region designated as an Area of Concern by the International Joint Commission.

Stream-dwelling salmonids that spawn in the fall generally experience their lowest survival during the fall and winter due to behavioral changes associated with spawning and energetic deficiencies during this time of year. We used data from Brook Trout Salvelinus fontinalis and Brown Trout Salmo trutta implanted with radio transmitters in tributaries of the Hunts Run watershed of north-central Pennsylvania to estimate survival from the fall into the winter seasons (September 2012–February 2013). We examined the effects that individual-level covariates (trout species, size, and movement rates) and stream-level covariates (individual stream and cumulative drainage area of a stream) have on survival. Brook Trout experienced significantly lower survival than Brown Trout, especially in the early fall during their peak spawning period. Besides a significant species effect, none of the other covariates examined influenced survival for either species. A difference in life history between these species, wi...

workshop, collectively referred to as “Propagated Fishes in Resource Management (PFIRM).” Each of the previous cycles yielded a proceedings book (Fish Culture in Fisheries Management [Stroud 1986], Uses and Effects of Cultured Fishes in Aquatic Ecosystems [Schramm and Piper 1995], and Propagated Fishes in Resource Management [Nickum et al. 2004]), and most recently a guidance document, “Considerations for the Use of Propagated Fishes in Resource Management.” The so-called “PFIRM Considerations” guide, published by AFS in 2005 (Mudrak and Carmichael 2005), provided resource managers with general recommendations for decision making and bilitation, and restoration programs.

Efforts to restore Lake Trout Salvelinus namaycush in the Laurentian Great Lakes have been hampered for decades by several factors, including overfishing and invasive species (e.g., parasitism by Sea Lampreys Petromyzon marinus and reproductive deficiencies associated with consumption of Alewives Alosa pseudoharengus). Restoration efforts are complicated by the presence of multiple body forms (i.e., morphotypes) of Lake Trout that differ in habitat utilization, prey consumption, lipid storage, and spawning preferences. Bioenergetics models constitute one tool that is used to help inform management and restoration decisions; however, bioenergetic differences among morphotypes have not been evaluated. The goal of this research was to investigate bioenergetic differences between two actively stocked morphotypes: lean and humper Lake Trout. We measured consumption and respiration rates across a wide range of temperatures (4–22°C) and size-classes (5–100 g) to develop bioenergetics models for juvenile Lake Trout. Bayesian estimation was used so that uncertainty could be propagated through final growth predictions. Differences between morphotypes were minimal, but when present, the differences were temperature and weight dependent. Basal respiration did not differ between morphotypes at any temperature or size-class. When growth and consumption differed between morphotypes, the differences were not consistent across the size ranges tested. Management scenarios utilizing the temperatures presently found in the Great Lakes (e.g., predicted growth at an average temperature of 11.7°C and 14.4°C during a 30-d period) demonstrated no difference in growth between the two morphotypes. Due to a lack of consistent differences between lean and humper Lake Trout, we developed a model that combined data from both morphotypes. The combined model yielded results similar to those of the morphotype-specific models, suggesting that accounting for morphotype differences may not be necessary in bioenergetics modeling of lean and humper Lake Trout.Received January 6, 2014; accepted August 5, 2014

Dams and their associated effects on the migration and mortality of the American Eel Anguilla rostrata have been implicated as a significant factor in the current depleted status of the species along the Atlantic coast of North America. Female American Eels that mature in areas below dams may be smaller and have lower fecundity than individuals that mature in more upstream reaches of a river system. However, increased mortality associated with downstream migration through hydroelectric turbines may negate any reproductive advantage afforded to American Eels occupying areas upstream of hydroelectric facilities. We developed an American Eel egg-per-recruit (EPR) model to investigate how various levels of upstream and downstream passage may affect the reproductive output from rivers with hydroelectric facilities. We applied our model to the Susquehanna River and found that if American Eels are passed upstream of multiple dams on the river, cumulative downstream passage survival must be ≥33% for the u...

Uncertainty and risk abound in making natural resource management decisions. Population viability analysis (PVA) includes a variety of qualitative or quantitative analyses to predict the future status of a population or collection of populations and to predict the risk of extinction (or quasi-extinction) over time given some assumptions of the factors driving population dynamics. In this paper, we review the various PVA models applied to Atlantic and Pacific salmon for determination of listing under the Endangered Species Act and in planning recovery actions. We also review the numerous cautions involved in developing PVA models and in interpreting their results. There have been a larger number of PVA models applied to Pacific salmon compared to Atlantic salmon due to the greater geographic range and number of species of Pacific salmon. Models for both Atlantic and Pacific salmon have ranged from simple models that view populations as simply a number of organisms to complex age- or stage-structured models depending on the purpose of the model and available data for model parameterization. The real value of PVA models to salmon conservation is not in making absolute predictions of the risk of extinction, but rather in evaluating relative effects of management alternatives on extinction risk and informing decision making within an adaptive management framework. As computing power, quantitative techniques, and knowledge of mechanistic linkages between terrestrial, freshwater, and marine environments advance, PVA models will become an even more powerful tool in conservation planning for salmon species.

In 2007, a team of U.S. scientists performed a status review of Atlantic sturgeon Acipenser oxyrinchus oxyrinchus and concluded that the species would likely become endangered (U.S. Endangered Species Act 1973, as amended) in the foreseeable future over much of its range, including populations of the New York Bight, which is comprised of the Hudson and Delaware rivers. Therefore, we evaluated an experimental release of hatchery-produced Atlantic sturgeon that took place in 1994 to determine the value of using stocked fish as a population recovery tool. We obtained recapture data on hatchery fish (identified by presence of pelvic fin removal) from the Atlantic Coast Sturgeon Tagging Database. Our evaluation of retention for a pelvic fin removal mark on hatchery fish showed that 36% of clipped individuals retained a clean fin clip after 49 d. The minimum survival rate for hatchery fish to age 5 was estimated to be in the range of 0.49–0.66% using documented recaptures (N = 24), known number of fish stocked, and results of the pelvic fin removal evaluation. Length and weight-at-age for recaptured hatchery fish at known ages 5–17 were within the range of values reported for wild fish whose ages were estimated by pectoral spine analysis. We also report that one ripe male hatchery fish at age 15 was captured along with other spermiating males at its parental spawning area in the Hudson River in 2009.

Atlantic salmon Salmo salar in the USA have declined dramatically and their persistence is heavily dependent on stocking juvenile fish, predominantly fry. The success of stocking hatchery fry is evaluated annually throughout New England by electrofishing surveys targeting age-1 parr. The objective of this study was to examine temporal trends in Atlantic salmon parr densities throughout New England and determine how trends vary among river basins. We fit generalized additive mixed models to investigate potential linear and nonlinear temporal trends in parr density. Akaike's information criterion was used to evaluate competing hypotheses about how temporal trends vary regionally. The top-ranked model suggested two types of trends. The first type (the Penobscot River) showed a nonlinear trend in which parr densities increased until the 1990s and then rapidly decreased through 2008. The second type (all other rivers) showed a linear decrease throughout the time series. Parr density trends reflected t...

Adaptive management requires that predictive models be explicit and transparent to improve decisions by comparing management actions, directing further research and monitoring, and facilitating learning. The rufa subspecies of red knots (Calidris canutus rufa), which has recently exhibited steep population declines, relies on horseshoe crab (Limulus polyphemus) eggs as their primary food source during stopover in Delaware Bay during spring migration. We present a model with two different parameterizations for use in the adaptive management of horseshoe crab harvests in the Delaware Bay that links red knot mass gain, annual survival, and fecundity to horseshoe crab dynamics. The models reflect prevailing hypotheses regarding ecological links between these two species. When reported crab harvest from 1998 to 2008 was applied, projections corresponded to the observed red knot population abundances depending on strengths of the demographic relationship between these species. We compared different simulated horseshoe crab harvest strategies to evaluate whether, given this model, horseshoe crab harvest management can affect red knot conservation and found that restricting harvest can benefit red knot populations. Our model is the first to explicitly and quantitatively link these two species and will be used within an adaptive management framework to manage the Delaware Bay system and learn more about the specific nature of the linkage between the two species.

In this study, we resurveyed stream habitat and sampled brook trout Salvelinus fontinalis populations 6 y after large woody debris additions to determine long-term changes in habitat and brook trout populations. In a previous study, we added large woody debris to eight streams in the central Appalachians of West Virginia to determine whether stream habitat could be enhanced and brook trout populations increased following habitat manipulation. The large woody debris additions had no overall effect on stream habitat and brook trout populations by 6 y after the additions. The assumption that a lack of large woody debris is limiting stream habitat and brook trout populations was not supported by our results. In high-gradient streams, habitat complexity may be governed more by the abundance of boulders and large woody debris may have a lesser influence on trout populations.

Atlantic salmon Salmon salar are at critically low levels in Maine rivers and maintaining current populations depends heavily on the stocking of hatchery-produced fry. Fry survival varies greatly not only among rivers but also within rivers. Better understanding of this spatial variability is needed to improve population recovery efforts. Quantile regression was used to examine how parr density varies along stream gradients as a function of the upstream cumulative drainage. Regression quantiles (τ = 0.15–0.90) had significant negative slopes indicating that, in general, as cumulative drainage area increased, parr density decreased. The τ = 0.90 quantile model, which may be viewed as an upper limit to parr density for a given cumulative drainage area, was density = [10⁁(1.0679 − 0.0013 · km2)] − 1. Quantile regression models were then combined with river-specific habitat data in a Geographic Information System to predict total Atlantic salmon parr production in several rivers. This analysis will help managers determine the potential of a stream reach or entire river to support Atlantic salmon parr and to prioritize and increase the effectiveness of management activities such as fry stocking and habitat restoration.

Terrestrial invertebrates are an important component of stream fish diets, especially during the summer months, when aquatic invertebrates are limited. The seasonal diet composition of the brook trout Salvelinus fontinalis inhabiting two West Virginia streams was used in a bioenergetics model to simulate yearly prey consumption for two cohorts of age-1 brook trout in each stream. Baseline simulations were run by fitting the model to observed growth from June 2000 to June 2001 for the first cohort and from June 2001 to June 2002 for the second cohort. Terrestrial invertebrate inputs can be negatively impacted by anthropogenic effects (e.g., timber harvest and pesticide application). To determine the degree to which growth would be suppressed by a reduction in terrestrial invertebrate consumption, we ran simulations in which the amount of terrestrial invertebrate consumption was reduced by 25, 50, 75, and 100%. Simulations were then run to determine the consumption of aquatic invertebrates that wou...

Populations of Atlantic sturgeon Acipenser oxyrinchus are at historically low levels along the Atlantic coast of North America. Atlantic sturgeon is a long-lived species with a complex life history, making population assessment difficult. The purpose of this study was to determine seasonal habitat use by juvenile Atlantic sturgeon in the Hudson River estuary and provide recommendations for future population monitoring. Our study focused on Newburgh and Haverstraw bays in the Hudson River, as these are areas of known juvenile sturgeon concentrations. The habitat within each bay was coarsely stratified according to substrate (hard versus soft) and depth (deep versus shallow). Sampling occurred during fall 2003, spring and fall 2004, and spring and fall 2005. Fall sampling occurred from October through November and spring sampling occurred from March through April. We used anchored gill nets of 76-, 102-, and 127-mm stretch mesh fished together at a sampling site. A total of 562 individual juvenile ...

25403 ABSTRACT: The objective of this simulation study was to create an age-structured population model for horseshoe crabs (Limulus polyphemus) in the Delaware Bay region using best available estimates of age-specific mortality and recent harvest levels. Density dependence was incorporated using a spatial model relating egg mortality with abundance of spawning females. Combinations of annual female harvest (0, 50, 100, and 200 thousand), timing of female harvest (before or after spawning), and three levels of density-dependent egg mortality were simulated. The probability of the population increasing was high (. 80%) with low and medium egg mortality and harvest less than 200 thousand females per year. Under the high egg mortality case, the probability of the population increasing was , 50% regardless of harvest. Harvest occurring after spawning increased the probability of population growth. The number of eggs available to shorebirds was highest when egg mortality was lowest and female abundance was at its highest levels. Although harvest and egg mortality influenced population growth and food availability to shorebirds, sensitivity and elasticity analyses showed that early-life stage mortality, age 0 mortality in particular, was the most important parameter for population growth. Our modeling results indicate areas where further research is needed and suggest effective management will involve a combination of harvest management and actions to increase early juvenile survival.

The horseshoe crab fishery on the US Atlantic coast represents a compelling fishery management story for many reasons, including ecological complexity, health and human safety ramifications, and socio-economic conflicts. Knowledge of stock status and assessment and monitoring capabilities for the species have increased greatly in the last 15 years and permitted managers to make more informed harvest recommendations. Incorporating the bioenergetics needs of migratory shorebirds, which feed on horseshoe crab eggs, into the management framework for horseshoe crabs was identified as a goal, particularly in the Delaware Bay region where the birds and horseshoe crabs exhibit an important ecological interaction. In response, significant effort was invested in studying the population dynamics, migration ecology, and the ecologic relationship of a key migratory shorebird, the Red Knot, to horseshoe crabs. A suite of models was developed that linked Red Knot populations to horseshoe crab populations through a mass gain function where female spawning crab abundance determined what proportion of the migrating Red Knot population reached a critical body mass threshold. These models were incorporated in an adaptive management framework wherein optimal harvest decisions for horseshoe crab are recommended based on several resource-based and value-based variables and thresholds. The current adaptive framework represents a true multispecies management effort where additional data over time are employed to improve the predictive models and reduce parametric uncertainty. The possibility of increasing phenologic asynchrony between the two taxa in response to climate change presents a potential challenge to their ecologic interaction in Delaware Bay.

Removal estimators for stream fish abundance are widely used but can result in biased population estimates at the site level. We conducted computer simulations to examine how the Carle and Strub (1978) estimator, coupled with variation in catchability, influences the accuracy of population estimates at the site level. Site-level population estimates were then used to examine what effect potential bias in the population estimate at a site had on basinwide abundance estimates. Historic electrofishing data collected from Atlantic salmon Salmo salar in the Narraguagus River, Maine, were used as the baseline for construction of these simulations. At the site level, mean percent bias of population estimates was −23% when catchability was low (0.30–0.40) and when the true population was low (1–20 fish). Bias was reduced as the true population size increased and catchability increased. The negative bias at the site level affected total population estimates for the entire river basin. Under current sampli...

We estimated the gastric evacuation rate (GER) of brook trout Salvelinus fontinalis at five different temperatures (4.3, 9.1, 12.1, 15.6, and 17.0°C). Fish were fed a mixed meal of fly larvae and beetle larvae, and stomach contents were sampled by gastric lavage at various times over a 48–72-h period to determine the proportional dry weight of an initial meal remaining in the stomach after feeding. The relationship between the proportional amount of a meal remaining in the stomach and the time postfeeding was best described by a linear function over all temperatures. As temperature increased, the instantaneous rate of gastric evacuation increased, but the rate of increase slowed at temperatures greater than 12.1°C. Brook trout GERs were much lower than those reported in the literature for other species at similar temperatures. These data will be useful for future field studies attempting to estimate daily ration.

We determined how turbidity affected the reactive distance and foraging success of smallmouth bass, Micropterus dolomieu. Smallmouth bass reactive distance decreased exponentially with increasing turbidity, from 65 cm in clear water to 10 cm at the highest turbidity. Turbidity significantly decreased the probability of a fish reacting to a prey item, but did not influence foraging success following reaction to the prey. Elevated turbidity may reduce stream fish foraging efficiency and decrease prey consumption.

Past research has focused on the effects of sediment action on stream morphology and the habitat of brook trout Salvelinus fontinalis. Throughout the Appalachian Mountains, the watersheds in which brook trout reside are being influenced by timber harvesting and related road construction. Although these streams may have gradients steep enough to prevent deleterious sediment deposition, elevated stream turbidity is nevertheless common. An understanding of the sublethal effects of increased sedimentation and turbidity is essential to further our knowledge of the effects of increased sediment loading on stream fish production and how these effects differ among species living in sympatry. The specific objectives of this study were to determine (1) the effects of turbidity on the reactive distance of brook trout, (2) how turbidity affects encounter rates between brook trout and their prey, and (3) how turbidity affects brook trout's foraging success. We used videographic techniques to study brook trout...