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Invasive grass carp Ctenopharyngodon idella spawning was confirmed in Lake Erie with the collection of fertilized eggs in the Sandusky River, Ohio in 2015. Managers responded with initiation of adult grass carp removal in 2017. Hydrodynamic modeling revealed a potential spawning location in downtown Fremont, Ohio (41.3455; -83.1110), which was supported by the presence of sexually mature adults. Egg detection and adult removals appear to coincide with periods of elevated discharge and suitable water temperatures. Electrofishing is the primary method for removing adults during spawning, however, it is unknown if this has indirect effects such as disruption of grass carp spawning; thereby lowering egg presence in ichthyoplankton samples. We used a binomial generalized linear model to predict the probability of grass carp egg presence (≥ 1 egg) in a paired ichthyoplankton net based on the presence of electrofishing in the spawning grounds and net depth using 2017-2022 data. Further, we carried out a field experiment to isolate the effect of electrofishing by sampling eggs at two sites before and during electrofishing in the spawning grounds in 2022. Analysis of 2017-2022 egg and electrofishing data suggested that grass carp egg presence in a paired ichthyoplankton net was significantly higher without electrofishing and in nets towed at a depth of 1.5 m compared to surfacetowed nets. Data analysis from the field experiment revealed a significant negative relationship between electrofishing in the spawning grounds and grass carp egg collections downstream. Both analyses suggested lower egg capture rates associated with electrofishing in the spawning grounds, although other factors should be further quantified. Consequently, electrofishing may cause a short-term disruption in grass carp spawning in the Sandusky River and could reduce spawning during preferred conditions. [ABSTRACT FROM AUTHOR]

Identifying spawning and hatching locations is vital to controlling invasive fish and conserving imperiled fish, which can be difficult for pelagically spawning species with semi-buoyant eggs. In freshwater systems, this reproductive strategy is common among cyprinid species, such as Chinese carp species currently threatening the Great Lakes. Following the confirmation that one of these species, grass carp (Ctenopharyngodon idella), was spawning in a Great Lakes tributary, we developed a modeling framework to combine field data with hydraulic models to calculate the most probable spawning and hatching locations for collected eggs. Our results indicate that the estimated spawning location encompassed habitat consistent with spawning sites in grass carp's native range. Additionally, all eggs were identified to have hatched in the river, increasing the likelihood of successful recruitment. This modeling framework can be used to estimate spawning and hatching locations for Chinese carp species, as well as all pelagic, riverine spawners. Spawning and hatching locations provide key information to researchers about the reproductive requirements of species and to agencies about how best to manage populations for control or restoration. Si la reconnaissance des lieux de frai et d'eclosion est d'importance cle pour le controle des poissons envahissants et la conservation d'especes de poissons menacees, elle peut s'averer difficile pour les especes a frai pelagique dont les reufs sont semi-flottants. Dans les systemes d'eau douce, cette strategie de reproduction est repandue chez les especes de cyprinides comme les especes de carpes chinoises qui menacent actuellement les Grands Lacs. Dans la foulee de la confirmation du frai d'une de ces especes, l'amour blanc (Ctenopharyngodon idella), dans un affluent des Grands Lacs, nous avons elabore un cadre de modelisation permettant de combiner des donnees de terrain a des modeles hydrauliques pour calculer les emplacements de frai et d'eclosion les plus probables pour des reufs recueillis. Nos resultats indiquent que l'emplacement estime du frai comprend des habitats qui concordent avec les lieux de frai dans l'aire de repartition naturelle de l'amour blanc. En outre, il a ete determine que tous les reufs avaient eclos dans la riviere, ce qui accroit la probabilite de leur recrutement efficace. Le cadre de modelisation peut etre utilise pour estimer les emplacements de frai et d'eclosion pour des especes de carpes chinoises, ainsi que pour tous les poissons pelagiques frayant en riviere. Les emplacements de frai et d'eclosion fournissent des renseignements cles aux chercheurs sur les exigences de reproduction des especes et aux agences sur les meilleures approches pour gerer le controle ou le retablissement de populations., Introduction Identifying spawning and hatching locations is vital to both controlling invasive fish and conserving imperiled fish. If spawning locations are not known, this essential habitat cannot be protected for [...]

Evaluating population trends in dynamic estuarine environments can be challenging, especially when survey data include a high percentage of zero observations. In fishery‐independent surveys, zeros that come from reduced susceptibility to sample gears and reduced availability of the population to the survey impact survey catchability and negatively bias relative abundance indices. A zero‐inflated negative binomial model was used to standardize a juvenile Atlantic Sturgeon (Acipenser oxyrinchus oxyrinchus) relative abundance index (Hudson River, New York) that included a high proportion (42%) of zero observations and intra‐ and interannually variable covariates. Reduced susceptibility was related to low water temperature, with the percentage of zeroes increasing rapidly below 7°C. Availability was influenced by temperature and distance to salt front, as catch rates increased with temperature and peaked in mesohaline waters ~27 km downstream of the predicted salt front. An alternative index suggested significant population growth (r = 0.15; p‐value = 0.007) occurred from 2004 to 2015. The zero‐inflated model helped better understand Hudson River juvenile Atlantic Sturgeon ecology and relative trends in abundance, to better inform future management and monitoring decisions along the Atlantic Coast. [ABSTRACT FROM AUTHOR]