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Trophic interactions are drivers of ecosystem change and stability, yet are often excluded from fishery assessment models, despite their potential capacity to improve estimates of species dynamics and future fishery sustainability. In Lake Ontario, recreational salmonine fisheries, including Chinook salmon (Oncorhynchus tshawytscha) and lake trout (Salvelinus namaycush), depend on a single prey species, alewife (Alosa pseudoharengus). To accommodate strong trophic interactions among species, we developed a multispecies statistical catch-at-age assessment (MSCAA) model that links the dynamics of the salmonine fisheries and alewife via prey consumption and predator growth. We found that prey availability had declined since 2015 due to decreased alewife recruitment and increased Chinook salmon biomass, leading to higher alewife mortality rates and lower predator growth rates. Forward projections of predator-prey dynamics suggest that Chinook salmon stocking reductions may improve the probability for alewife population growth, but could be counteracted by increased natural Chinook salmon recruitment. Combined with predator- and prey-monitoring efforts, multispecies assessments show promise as models of intermediate complexity to support a transition to ecosystem-based approaches to fisheries management. Si les interactions trophiques sont des facteurs de changement et de stabilite des ecosystemes, elles sont souvent exclues des modeles d'evaluation des peches, bien que leur integration puisse ameliorer les estimations de la dynamique des especes et de la perennite des peches. Dans le lac Ontario, les peches sportives aux salmonines, dont le saumon chinook (Oncorhynchus tshawytscha) et le touladi (Salvelinus namaycush), dependent d'une seule espece de proie, le gaspareau (Alosa pseudoharengus). Pour permettre l'integration de fortes interactions trophiques d'especes, nous avons mis au point un modele statistique plurispecifique d'evaluation des prises selon l'age qui relie la dynamique des peches aux salmonines et celle du gaspareau par l'entremise de la consommation de proies et de la croissance des predateurs. Nous constatons que la disponibilite de proies a diminue depuis 2015 en raison de la baisse du recrutement de gaspareaux et de l'augmentation de la biomasse de saumons chinooks, se traduisant par des taux de mortalite accrus des gaspareaux et des taux de croissance plus faibles des predateurs. Des projections de la dynamique predateurs-proies indiqueraient que des reductions de l'empoissonnement de saumons chinooks pourraient accroitre la probabilite de croissance de la population de gaspareaux, mais qu'elles pourraient etre contrecarrees par la hausse du recrutement naturel de saumons chinooks. Combinees aux efforts de surveillance des predateurs et des proies, les evaluations plurispecifiques constituent des modeles de complexite intermediaire prometteurs pour appuyer la transition vers des approches ecosystemiques de gestion des peches. [Traduit par la Redaction], 1. Introduction Ecosystem-based approaches to fisheries management are becoming increasingly common as the complex effects ecosystem interactions can have on management and conservation outcomes become increasingly apparent (Pauly et al. [...]

Lake Ontario boasts a diverse fish community comprised of native and introduced species that support vibrant recreational, commercial and Indigenous fisheries. The effective delivery of a program to assess and control the sea lamprey (Petromyzon marinus) is crucial to achievement of Lake Ontario Fish Community Objectives of rehabilitating native fish stocks while protecting and maintaining the abundance of introduced salmonines. During 2000–2019, the Great Lakes Fishery Commission (GLFC) and its control agents, Fisheries and Oceans Canada (DFO) and the U. S. Fish and Wildlife Service (USFWS), delivered a consistent program of sea lamprey assessment and control. Beginning in 2004, rising sea lamprey abundance and marking rates on lake trout (Salvelinus namaycush) in Lake Ontario coincided with a decline of large lake trout in gillnet surveys. Efforts were undertaken to identify and control important sources of juvenile sea lampreys, including larvae that survived treatment, inhabited deepwater areas, or colonised previously uninhabited stream reaches and tributaries. A renewed reliance on proven conventional controls, including lampricide treatments and barriers, has resulted in consistent suppression of sea lamprey abundance and lake trout marking to prescribed targets in Lake Ontario during 2014–2019. This achievement is unprecedented in the 49-year history of Sea Lamprey Control Program delivery in Lake Ontario, and is attributable to the collaborative efforts of the GLFC, the control agents, and federal, provincial, state, and Indigenous partners. [ABSTRACT FROM AUTHOR]

Morphometric data from fish are typically generated using one of two methods: direct measurements made on a specimen or extraction of distances from a digital picture. We compared data on 12 morphometrics collected with these two methods on the same collection of Cisco Coregonus artedi from Lake Ontario, North America, to assess the degree of bias in measurements made directly on a specimen- vs. an image-based method. We also assessed the degree of reproducibility within the image-based method by evaluating the amount of variation between different analysts for each morphometric method. Our results indicate specific morphometrics may be more prone to bias across the two methods and between analysts. Four of 12 morphometrics evaluated showed significant deviation from a 1:1 relationship that would be expected if the imaged-based method produced accurate specimen-based measurements. Pelvic fin length and pelvic–anal fin distance had the highest between-analyst variation for image-based landmarks, indicating low reproducibility for these metrics, compared with pectoral fin or total length, which had lower between-analyst variation. Although some morphometric measurements can be accurately obtained with either method, and therefore potentially used interchangeably in studies on Cisco morphology, our findings highlight the importance of considering method bias in morphometric studies that use data collected by different methods. [ABSTRACT FROM AUTHOR]

Mobile hydroacoustic surveys are routinely used to estimate pelagic fish abundance. In the Great Lakes, alewife are commonly surveyed with mobile hydroacoustics, however, their behavior often has them associated with epilimnetic habitats which increases the potential for vessel avoidance to bias hydroacoustic observations. Abundance estimates from mobile hydroacoustic surveys are typically made using depth and size thresholds to classify targets to species. In hydroacoustic surveys, fish can appear to be smaller when oriented off horizontal axis, as is common with fish displaying vessel avoidance behaviour. This presents a problem where alewives that are diving may appear too small to be correctly classified. We compared alewife swimming behaviours and target strength distributions between stationary up-looking and mobile down-looking hydroacoustics to quantify how vessel avoidance may bias hydroacoustic observations. Alewives from the mobile survey were found to be diving away from the surface, moving faster and in more linear paths than the undisturbed fish from the stationary survey. In the mobile survey, alewives were observed at smaller target strength values than would be expected if boat avoidance was not occurring. Our results suggest that alewife behavioral changes associated with vessel avoidance affect the number and size of targets classified as alewife from mobile hydroacoustic surveys in Lake Ontario. [ABSTRACT FROM AUTHOR]

Competitive fishing has become an important element of recreational fisheries for black bass Micropterus spp. in North America. The vast majority of competitive events involve a "live‐release" format, where fish are held in a boat's live well after being angled and are then released following the weigh‐in. We examined the frequency and importance of physical impacts between Smallmouth Bass Micropterus dolomieu and the walls of the live well when tournaments are held on large water bodies. Using an experimental live well that included a video recorder, we determined the number of collisions between Smallmouth Bass and the walls of the live well when a 5.6‐m boat was driven on Lake Ontario. During these experiments, 10 of 28 Smallmouth Bass lost equilibrium and became inverted. Live‐well transport also resulted in elevations of intracellular enzymes in blood plasma that were used as indicators of cell damage. The results of these experiments indicate that physical impacts with the walls of the live well may be an important factor contributing to the physiological disturbance experienced by Smallmouth Bass in tournaments on large water bodies. Our results also show that this disturbance can be reduced by simply padding the live well. These findings have important implications for fisheries managers, as well as the competitive angling community. [ABSTRACT FROM AUTHOR]

Oligotrophication of Lake Ontario has led to increased water clarity and an increased proportion of zooplankton residing in the metalimnion during the day, which may affect the utilization of different depth regions for planktivorous fish. We investigated day and night distributions of fish using hydroacoustics and suspended vertical gillnets during the summer of 2013 when a deep chlorophyll layer (DCL) was established. We related fish distributions to concurrent measures of temperature and prey (zooplankton) density. Alewife dominated in vertical gill net catches, indicating that most acoustic targets were alewife. Alewife schooled during the day in the bottom of the mixed layer, and at dusk alewife schools broke up and fish moved towards the surface. We hypothesize this movement followed migrating zooplankton to allow feeding at night; alewife sampled from vertical gillnets fed on cyclopoid copepods and cladocerans, prey groups that migrate into the epilimnion at night. Some alewife remained at the bottom of the mixed layer at night and these fish ate deep-water calanoid copepods such as Limnocalanus . Vertical distributions were best predicted by temperature and the interaction between temperature and zooplankton density. We include uplooking acoustics data to complement our downlooking datasets, which provided evidence for potential bias in downlooking acoustic assessments of alewife due to high proportions of alewife found in the surface exclusion zone. Our approach combining several datasets provides a new perspective to understand summer diel distribution of alewife and the factors driving their distribution. [ABSTRACT FROM AUTHOR]