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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. [...]

Cisco (Coregonus artedi) once dominated fish communities in the Laurentian Great Lakes. Restoring the abundance and distribution of this species has emerged as a management priority, yet our understanding of Cisco spawning habitat use is insufficient to characterise habitat needs for these populations and assess whether availability of suitable spawning habitat could be a constraint to recovery. We characterised the distribution of incubating Cisco eggs in situ across gradients of depth and substrate types to describe the spawning habitat used by three Great Lakes populations. In Chaumont Bay, Lake Ontario, eggs were concentrated on shallow bedrock shoals and not found on deeper silt or sand substrate. In contrast, eggs in Thunder Bay, Lake Superior, and Elk Rapids, Lake Michigan, were found on deeper fine grain sediments with low utilisation of shallow rocky and cobble habitats. These patterns of egg incubation habitat use suggest a broad spawning habitat niche at the species level but distinct spawning habitat preferences at the population level. While our results indicate some historical diversity in spawning habitat use has been maintained across the species' range in the Great Lakes, comparisons of contemporary spawning habitat utilisation against historical accounts raise questions as to whether some spawning habitat use behaviours may no longer be prevalent within specific lakes. Thus, characterising the portfolio of spawning strategies remaining within lakes may improve our understanding of habitat needs and identify opportunities to maintain population diversity while supporting Cisco rehabilitation. [ABSTRACT FROM AUTHOR]

Catch‐at‐age data are used to inform important management decisions for recovering populations of Lake Trout Salvelinus namaycush. Age data for Lake Trout are commonly derived from interpretation of annual growth marks (annuli) on the fish's otoliths. Due to the tendency for annuli to vary in appearance and the subjectivity that is inherent to any age interpretation method, it is important that the common sources of interpretation error be well understood for any aging method used to inform management plans. In this study, coded wire tags were used to establish true ages for 153 Lake Trout to measure the precision and accuracy of age interpretations made from transverse‐sectioned otoliths and to identify sources of potential age interpretation error that researchers and managers may encounter when using this method. Precision of age interpretations, as measured by average coefficient of variation, ranged from 7.9% to 9.2%. Accuracy of age interpretations varied among readers, with exact matches ranging from 41.8% to 53.6% and accuracy within ±1 year ranging from 81.0% to 83.0%. Age interpretation errors were more likely to be overestimates of true age for Lake Trout under age 7 and underestimates for Lake Trout over age 13. However, only reader 1 exhibited significant systematic bias in their age interpretations. Poor clarity of the first annuli, growth checks resembling annuli, and faintness of narrow annuli near otolith margins in older fish were identified as likely sources of interpretation error in this study. A digital reference collection of known‐age Lake Trout otoliths is provided as supplemental material in the online version of this article. This collection can be used for training new readers, measuring the accuracy of age interpretations, and monitoring for aging bias by anyone using otoliths to obtain age data for Lake Trout. [ABSTRACT FROM AUTHOR]

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]