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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. [...]

The forage fish communities of the Laurentian Great Lakes continue to experience changes that have altered ecosystem structure, yet little is known about how they partition resources. Seasonal, spatial, and body size variation in [delta][sup.13]C and [delta][sup.15]N was used to assess isotopic niche overlap and resource and habitat partitioning among the five common offshore Lake Ontario forage fish species (n = 2037; alewife (Alosa pseudoharengus), rainbow smelt (Osmerus mordax), round goby (Neogobius melanostomus), and deepwater (Myoxocephalus thompsonii) and slimy (Cottus cognatus) sculpins). Round goby had the largest isotopic niche (6.1[[per thousand].sup.2], standard ellipse area), followed by alewife (3.4[[per thousand].sup.2]), while rainbow smelt, slimy sculpin, and deepwater sculpin had the smallest and similar niche size (1.7[[per thousand].sup.2]-1.8[[per thousand].sup.2]), with only the sculpin species showing significant isotopic niche overlap (>63%). Stable isotopes in alewife, round goby, and rainbow smelt varied with location, season, and size, but did not vary in the sculpin species. Lake Ontario forage fish species have partitioned food and habitat resources, and non-native alewife and round goby have the largest isotopic niche, suggestive of a boarder ecological niche, and may contribute to their current high abundance. Si les communautes de poissons-fourrage des Grands Lacs laurentiens continuent de subir des changements qui ont modifie la structure des ecosystemes, les connaissances sur le partage des ressources dans ces communautes sont limitees. Les variations saisonnieres, spatiales et associees a la taille du corps du [delta][sup.13]C et du [delta][sup.15]N ont ete utilisees pour evaluer le chevauchement des niches isotopiques et le partage des ressources et des habitats entre cinq especes de poissons-fourrage pelagiques repandues du lac Ontario (n = 2037; le gaspareau (Alosa pseudoharengus), l'eperlan arc-en-ciel (Osmerus mordax), le gobie a taches noires (Neogobius melanostomus), le chabot de profondeur (Myoxocephalus thompsonii) et le chabot visqueux (Cottus cognatus)). Le gobie a taches noires presente la plus grande niche isotopique (6,1[[per thousand].sup.2], aire de l'ellipse standard), suivi du gaspareau (3,4[[per thousand].sup.2]), alors que l'eperlan arc-en-ciel, le chabot visqueux et le chabot de profondeur ont les plus petites niches, de tailles semblables (1,7-1,8[[per thousand].sup.2]), seuls les chabots presentant un chevauchement significatif de leurs niches isotopiques (>63 %). Les isotopes stables des gaspareaux, gobies a taches noires et eperlans arc-en-ciel varient selon le lieu, la saison et la taille, contrairement a ceux des chabots. Les especes de poissons-fourrage du lac Ontario presentent un partage des ressources alimentaires et des habitats, le gaspareau et le gobie a taches noires, des especes non indigenes, etant caracterises par les plus grandes niches isotopiques, ce qui indiquerait une niche ecologique plus large et pourrait contribuer a expliquer leur forte abondance actuelle. [Traduit par la Redaction], Introduction In the Laurentian Great Lakes (hereinafter Great Lakes), consumption by the offshore prey fish community transfers production from the lower trophic level to higher trophic levels and can influence [...]

Abstract: Mysis relicta and planktivorous fish feed on zooplankton in Lake Ontario and form a trophic triangle that includes intraguild predation by fish on mysids. Thus, fish affect zooplankton both [...]

Ref.: Can. J. Fish. Aquat. Sci. 75(5): 759-771 (2018). dx.doi.org/10.1139/cjfas-2016-0150. The original version of Fig. 4 contained an error. The correct version is presented here. The authors apologize for this [...]

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]

1. Biological invaders can provide a highly abundant novel prey, yet the effect this has on the body condition of native predators is unknown. 2. Since invading the Laurentian Great Lakes over two decades ago, the round goby (Neogobius melanostomus) has become an important food source for many native species. 3. We used long-term data from Lakes Erie and Ontario (1993-2012) to create quantile regression models of mass-length relationships for populations of four native predators: smallmouth bass (Micropterus dolomieu), yellow perch (Perca flavescens), walleye (Sander vitreus) and burbot (Lota lota). Model-based estimates of changes in mass-at-length following the invasion were used to compare the effects of round goby on relative trends in body condition. Water temperature data were also included in the models, to investigate its effects on body condition. 4. The condition of smallmouth bass increased after the invasion, varying in magnitude between lakes and among size classes. Condition of yellow perch changed variably in direction and magnitude, depending on the quantile of the mass-length relationship examined and fish length, whereas that of walleye increased only for larger fish in Lake Ontario. Minor increases in mass-at-length were observed for the smallest length class of burbot, while the body condition of burbot in the largest length class decreased during the study period. 5. Mean summer water temperature did not differ between pre- and post-invasion time periods in Lakes Erie and Ontario, although water temperature was a significant predictor of body condition. 6. Changes in body condition may have implications for additional population and life history characteristics. Future research should investigate the effects of the round goby on growth, age at maturity, fecundity and survival of native predators. [ABSTRACT FROM AUTHOR]