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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. [...]

Biological invasions are among the most serious threats to ecosystems. The golden apple snail Pomacea canaliculata (Lamarck, 1822) is considered one of the top 100 worst invasive alien species in the world. These snails consume benthic primary producers, including submerged macrophytes, which may lead to an increase in nutrient concentration in the water, enhance growth of phytoplankton, and decrease growth of macrophytes, thereby shifting the primary production from benthic to pelagic habitats in shallow systems. To test this hypothesis, we conducted a short-term experiment with and without the invasive P. canaliculata in mesocosms with high abundance of the native submerged macrophyte Vallisneria natans (Lour.) Hara. Compared with snail-free control, the snail increased the concentrations of total nitrogen (TN), nitrate nitrogen (NO3−–N), total and organic suspended solids (TSS and OSS), decreased the concentrations of soluble reactive phosphorous (SRP), but had no effect on total phosphorus (TP) and the TN:TP ratio. In addition, the snails decreased the biomass, leaf length and tiller number of V. natans, and decreased light intensity. Although snail presence did not change the biomasses of nanophytoplankton and picophytoplankton, it did increase the biomass of microphytoplankton leading to an increase in total phytoplankton biomass. Our study shows that P. canaliculata shifted primary production from benthic to pelagic habitats, altered the phytoplankton community size structure, and decreased water quality. The results add further evidence of negative ecosystem impacts of this invasive apple snail and call for its control in invaded shallow lake ecosystems.

Size spectra analysis (SSA) is used to detect changes in food webs by simplifying complex community structures through abundance-versus-biomass considerations. We applied SSA to 10 years (2006-2015) of data on Great Lakes organisms ranging in size from picoplankton to macrozooplankton. Summer pelagic size spectra slopes were near the theoretical value of -1.0, but spring slopes were steeper, reflecting seasonal differences in abundance of small and large individuals. Pelagic size spectra slopes were relatively stable over the time period we examined. Height (the predicted number of organisms at the spectra midpoint) varied among lakes and was slightly higher in summer than spring in more productive basins. Including benthic data led to shallower slopes when combined with pelagic data, suggesting benthic organisms may increase food web efficiency; height was less affected by benthic data. Benthic data are not routinely included in SSA, but our results suggest they affect slopes and therefore SSA-based predictions of fish abundance. The ability of SSA to track changes in trophic energy transfer makes it a valuable ecosystem monitoring tool. L'analyse des spectres de taille (AST) est utilisee pour detecter des changements dans les reseaux trophiques en simplifiant la structure de communautes complexes sur la base de considerations concernant l'abondance et la biomasse. Nous avons applique l'AST a 10 annees (2006-2015) de donnees sur des organismes des Grands Lacs de tailles allant du picoplancton au macrozooplancton. Les pentes des spectres de taille pelagiques estivaux s'approchent de la valeur theorique de -1,0, mais les pentes des spectres printaniers sont plus fortes, refletant des variations saisonnieres de l'abondance des petits et grands individus. Les pentes des spectres de taille pelagiques sont relativement stables durant la periode etudiee. La hauteur (le nombre predit d'organismes au point median du spectre) varie d'un lac a l'autre et est legerement plus grande en ete qu'au printemps dans les bassins plus productifs. L'inclusion de donnees benthiques produit des pentes plus faibles quand elles sont combinees aux donnees pelagiques, ce qui donne a penser que les organismes benthiques pourraient accroitre l'efficacite du reseau trophique; l'incidence des donnees benthiques sur la hauteur est moins importante. Des donnees benthiques ne sont pas systematiquement incluses dans les AST, mais nos resultats indiqueraient qu'elles ont une incidence sur les pentes et donc sur les predictions de l'abondance des poissons issues de l'AST. La capacite de l'AST de faire ressortir les variations des transferts energetiques trophiques en fait un bon outil de surveillance des ecosystemes. [Traduit par la Redaction], Introduction Understanding and predicting ecosystem productivity requires knowledge about the current state of the ecosystem and how it influences production of different organisms. However, ecosystem modeling is challenging because food [...]

Human-driven environmental change underlies recent changes in water clarity in many of the world's great lakes, yet our understanding of the consequences of these changes on the fish and fisheries they support remains incomplete. Herein, we offer a framework to organize current knowledge, guide future research, and help fisheries managers understand how water clarity can affect their valued populations. Emphasizing Laurentian Great Lakes findings where possible, we describe how changing water clarity can directly affect fish populations and communities by altering exposure to ultraviolet radiation, foraging success, predation risk, reproductive behavior, or territoriality. We also discuss how changing water clarity can affect fisheries harvest and assessment through effects on fisher behavior and sampling efficiency (i.e., catchability). Finally, we discuss whether changing water clarity can affect understudied aspects of fishery performance, including economic and community benefits. We conclude by identifying generalized predictions and discuss their implications for priority research questions for the Laurentian Great Lakes. Even though the motivation for this work was regional, the breadth of the review and generality of the framework are readily transferable to other freshwater and marine habitats. Si des modifications de l'environnement causees par les humains sous-tendent les changements recents de la clarte de l'eau dans bon nombre des grands lacs de la planete, notre comprehension des consequences de ces changements sur les poissons et les peches qu'ils soutiennent demeure incomplete. Nous presentons un cadre pour organiser les connaissances actuelles, orienter la recherche future et aider les gestionnaires des peches a comprendre l'incidence possible de la clarte de l'eau sur les populations qu'ils gerent. En mettant l'accent, dans la mesure du possible, sur des constatations relatives aux Grands Lacs laurentiens, nous decrivons l'incidence directe que peuvent avoir les variations de la clarte de l'eau sur les populations et communautes de poissons en modifiant l'exposition au rayonnement ultraviolet, le succes d'approvisionnement, le risque de predation, le comportement de reproduction ou la territorialite. Nous abordons egalement l'incidence que peuvent avoir les modifications de la clarte de l'eau sur les prises et revaluation des peches par le biais d'effets sur le comportement des pecheurs et l'efficacite d'echantillonnage (c.-a-d., la capturabilite). Enfin, nous tentons d'etablir si les modifications de la clarte de l'eau peuvent avoir une incidence sur des aspects sous-etudies de la performance des peches, y compris les avantages economiques et pour les collectivites. Nous concluons en formulant des predictions generales et discutons des questions de recherche prioritaires qu'elles font ressortir pour les Grands Lacs laurentiens. Meme si l'intention a l'origine du present article etait regionale, la portee de la synthese et le caractere general du cadre font qu'ils peuvent etre transposes aisement a d'autres habitats marins et d'eau douce. [Traduit par la Redaction], Introduction Although scientists have increasingly documented changing water clarity in freshwater ecosystems worldwide, we do not fully understand its effects on aquatic food webs and the fisheries that they support. [...]

Acoustic surveys are important for fish stock assessments, but fish responses to survey vessels can bias acoustic estimates. We leveraged quiet uncrewed surface vessels (USVs) to characterize potential bias in acoustic surveys. Five conventional motorized ships overtook USVs from astern over 2 km transects at night in Lake Superior in 2022. We examined the difference in acoustic backscatter, average target depth, and average target strength (TS) between USV and motorized vessels. Although sound level measurements from the motorized vessels sometimes exceeded recommendations for scientific vessels, we did not detect differences in acoustic measures among survey vessels. However, the USVs recorded 2 dB higher acoustic backscatter and TS than motorized vessels, leading to ∼15% higher fish densities with drones when using in situ TS and echo integration. Differences in fish density would increase to 30%–60% if a standard TS value was applied. Target depth did not differ between USVs and motorized ships. These results are consistent with a change in orientation but not depth of insonified fish and limited horizontal avoidance of motorized survey vessels. [ABSTRACT FROM AUTHOR]

We studied the consequences of a nonnative species introduction and changes in temperature on early mortality and recruitment of native rainbow smelt (Osmerus mordax) and nonnative alewife (Alosa pseudoharengus) in Lake Champlain using a simulation model. Distribution patterns of adults and young-of-the-year (YOY) fish were predicted using a model based on observed distribution of different age groups as a function of temperature and light profiles simulated on a daily basis. Mortality rates averaged over the growing season were calculated as a function of fish densities and overlap between adults and YOY. Survival of YOY rainbow smelt and alewife depended on which predator was most abundant. Rainbow smelt YOY mortality rates are highest when rainbow smelt adults are abundant, and alewife YOY mortality rates are highest when alewife adults are abundant, potentially allowing coexistence. August and September mortality rates were higher in the climate change scenario because of increased overlap of adults and YOY of both species. These results indicate that accounting for spatiotemporal fish distribution patterns can be important when forecasting the interacting effects of climate change and aquatic invasive species on fish recruitment. Nous avons etudie les consequences de l'introduction d'une espece non indigene et des changements de temperature sur la mortalite precoce et le recrutement d'eperlans arc-en-ciel (Osmerus mordax) indigenes et de gaspareaux (Alosapseudoharengus) non indigenes dans le lac Champlain en utilisant un modele de simulation. Les motifs de repartition de poissons adultes et jeunes de l'annee ont ete predits en utilisant un modele base sur la repartition observee de differents groupes d'age en fonction de la temperature et de profiles de lumiere simules sur une base quotidienne. Les taux de mortalite moyens pour la saison de croissance ont ete calcules en fonction des densites de poissons et du chevauchement des adultes et des jeunes de l'annee. La survie des eperlans arc-en-ciel et des gaspereaux jeunes de l'annee depend du predateur qui est le plus abondant. Les taux de mortalite des eperlans arc-en-ciel jeunes de l'annee sont les plus eleves quand les eperlans arc-en-ciel adultes sont abondants et les taux de mortalite des gaspareaux jeunes de l'annee sont les plus eleves quand les gaspareaux adultes sont abondants, permettant possiblement une coexistence. Les taux de mortalite en aout et septembre sont les plus eleves dans le scenario de changement climatique en raison du chevauchement accru d'adultes et de jeunes de l'annee des deux especes. Ces resultats indiquent que la prise en consideration des motifs de repartition spatiotemporelle des poissons peut etre importante pour la prediction des effets interactifs des changements climatiques et d'especes aquatiques envahissantes sur le recrutement de poissons. [Traduit par la Redaction], Introduction Environmental and biological mechanisms causing variable recruitment in fish populations have long been of interest to fisheries science (Cushing 1975; Wootton 1990; Diana 1995) and have received increased attention [...]

Cisco (Coregonus artedi) are an important component of native food webs in the Great Lakes, and their restoration is instrumental to the recovery of lake trout (Salvelinus namaycush) and Atlantic salmon (Salmo salar). Difficulties with visual identification of larvae can confound early life history surveys, as cisco are often difficult to distinguish from lake whitefish (Coregonus clupeaformis). We compared traditional visual species identification methods with genetic identifications based on barcoding of the mitochondrial cytochrome c oxidase I gene for 726 coregonine larvae caught in Chaumont Bay, Lake Ontario. We found little agreement between the visual characteristics of cisco identified by genetic barcoding and the most widely used dichotomous key, and the considerable overlap in ranges of traditionally utilized metrics suggests that visual identification of coregonine larvae from Chaumont Bay is impractical. Coregonines are highly variable and plastic species and often display wide variations in morphometric characteristics across their broad range. This study highlights the importance of developing accurate, geographically appropriate larval identification methods to best inform cisco restoration and management efforts. Les ciscos de lacs (Coregonus artedi) constituent un element important des reseaux trophiques indigenes dans les Grands Lacs, et leur regeneration est utile pour le retablissement des touladis (Salvelinus namaycush) et des saumons atlantiques (Salmo salar). Les difficultes que presente l'identification visuelle des larves peuvent fausser les evaluations des premiers stades de vie, les ciscos etant souvent difficiles a distinguer des grands coregones (Coregonus clupeaformis). Nous avons compare des methodes traditionnelles d'identification visuelle des especes a l'identification genetique reposant sur le codage a barres du gene de la cytochrome c oxydase I mitochondriale pour 726 larves de coregonine capturees dans la baie de Chaumont du lac Ontario. Nous avons note peu de concordance entre les caracteristiques visuelles de ciscos identifies par codage a barres genetique et a l'aide de la cle dichotomique la plus largement utilisee, et le chevauchement considerable des fourchettes de parametres utilises traditionnellement indiquerait que l'identification visuelle de larves de coregonine de la baie de Chaumont n'est pas une approche pratique. Les coregonines sont des especes tres variables et plastiques dont les caracteristiques morphometriques presentent souvent de grandes variations a l'echelle de leur grande aire de repartition. L'etude souligne l'importance du developpement de methodes d'identification des larves adaptees a l'emplacement afin de mieux eclairer les efforts de regeneration et de gestion des ciscos. [Traduit par la Redaction], Introduction Cisco (Coregonus artedi) were an important component of both native food webs and commercial fisheries in the Laurentian Great Lakes before their collapse in the middle of the 20th [...]