Relationships between indices of condition and measures of proximate body composition were examined among and within nine populations of mature walleyes Sander vitreus that varied widely in growth rate and lipid status. Body condition, measured as the residuals from mass versus length regressions, was negatively related to mean water content and positively related to mean lipid content among populations. When the roles of water and lipid content were examined simultaneously within populations, most of the variance in condition was accounted for by lipid content. The strength of the relationships between various condition indices and body proximate composition varied considerably among populations but less between sexes within populations. Furthermore, the strength and nature of these relationships was not strongly influenced by the choice of mass-at-length index (residuals, relative condition, relative weight, or Fulton's K). The visceral-somatic index and muscle lipid content both exhibited slightly stronger relationships with body proximate composition than did mass-at-length condition indices for both sexes. The hepatosomatic index was more consistently related to somatic lipid content for females than for males in most populations. Relatively simple condition indices can provide reliable surrogates of body proximate composition in many adult walleye populations, but caution should be exercised in extrapolating from condition-composition relationships among populations.

Analysis of the growth characteristics of 215 populations of walleye Sander vitreus across Ontario revealed that female walleyes reached larger asymptotic lengths in lakes in which ciscoes Coregonus artedi provided a relatively large prey species for them. The stomach contents of walleyes from a set of intensively studied lakes revealed that walleyes of all sizes depended on ciscoes but that ciscoes were most important to larger walleyes. In lakes without ciscoes, the walleye diet closely tracked the availability of young‐of‐year yellow perch Perca flavescens; when such prey were in short supply, walleyes consumed invertebrates. The prey size in walleye stomachs was significantly larger in lakes with ciscoes, but the probability of finding empty stomachs was also greater. This suggests that although walleyes in lakes with ciscoes foraged less often, more energy was available for growth. Exceptions to this general pattern occurred when ciscoes were too large to be consumed by walleyes or ciscoes were absent but small prey (i.e., yellow perch) were very abundant. We propose that lakes without ciscoes will provide higher catch rates for anglers, whereas those with ciscoes (particularly small ciscoes) are more likely to provide opportunities for trophy size fish.

Optimal foraging behaviour in walleye (Sander vitreus) was tested in eight lakes: four containing large prey (cisco, Coregonus artedi) and four without cisco. All eight lakes contained small prey (yellow perch, Perca flavescens). Activity costs and growth potential of walleye were estimated using white muscle enzymes. Anaerobic capacity, measured by lactate dehydrogenase (LDH), increased with walleye size and was lower in lakes with cisco. Aerobic capacity, measured by citrate synthase (CS), decreased with walleye size only in lakes without cisco. Growth potential of walleye, estimated by nucleoside diphosphokinase (NDPK), increased with size only in lakes with cisco. Overall, when cisco were available walleye were less active, able to maintain aerobic capacities, and increased their growth potential as they grew larger. Yellow perch LDH, CS, and NDPK were lower in lakes with cisco. This suggests that yellow perch were less active in lakes where walleye had an alternative large prey species, but yellow perch had higher growth potential when they were the only prey, reflecting the advantage of growth beyond edible sizes. This study reveals that there are physiological benefits for both predators and prey in communities with a wider range of prey sizes.Résumé : Nous avons évalué les comportements de quête optimale de nourriture chez le doré (Sander vitreus) dans huit lacs, quatre contenant des ciscos de lac (Coregonus artedi), des proies de grande taille, et quatre sans ciscos. Les huit lacs contenaient tous des perchaudes (Perca flavescens), des proies de petite taille. Nous avons estimé les coûts de l'activité et le potentiel de croissance du doré à l'aide des enzymes du muscle blanc. La capacité anaérobie, mesurée par la lactate déshydrogénase (LDH), augmente en fonction de la taille des dorés et elle est plus faible dans les lacs contenant des ciscos. La capacité aérobie, mesurée par la citrate synthase (CS), diminue en fonction de la taille des dorés, mais seulement dans les lacs sans ciscos. Le potentiel de croissance des dorés, mesuré par la nucléotide diphosphokinase (NDPK), augmente en fonction de la taille seulement dans les lacs contenant des ciscos. En général, lorsque des ciscos de lac sont disponibles, les dorés deviennent moins actifs à mesure qu'ils grandissent, mais ils sont capables de maintenir leur capacité aérobie et ils augmentent leur potentiel de croissance. Les activités de LDH, de CS et de NDPK chez les perchaudes sont moins fortes dans les lacs qui contiennent des ciscos. Cela indique que les perchaudes sont moins actives dans les lacs où les dorés ont des proies de rechange de grande taille; les perchaudes ont, cependant, un plus fort potentiel de croissance quand elles constituent les seules proies, ce qui reflète l'avantage de la croissance au delà des tailles comestibles. Notre étude révèle qu'il y a des avantages physiologiques, tant pour les prédateurs que pour les proies, dans les communautés qui présentent une gamme étendue de tailles de proies.[Traduit par la Rédaction] Kaufman e...

In lake trout (Salvelinus namaycush) lakes of northeastern Ontario, Canada, aerial surveys of fishing activity on individual lakes (N = 589) and quantitative gillnet surveys (N = 65) were used to assess the effects of road access on angling effort and the presence of introduced smallmouth bass (Micropterus dolomieu). Angling effort, particularly during the open-water season, was highest and often exceeded estimated sustainable levels on lakes with good road access. Approximately 25% of the remote lakes also received excessive pressure during the winter season. Angler numerical responses to lake trout abundance were detected in remote lakes, but not in road-accessible lakes. Smallmouth bass were more prevalent in lakes with road access and human settlement (either cottages or lodges), supporting the theory that they were introduced into these lakes. Lake trout populations were depleted throughout much of the study range. Even without road access or smallmouth bass, lake trout abundance was still 47% lower than in unexploited reference lakes. When bass and (or) road access were present, lake trout abundance decreased by 77%. Remote lake trout populations in this area are clearly vulnerable to the negative impacts of improved access, a vector for both overexploitation and species introductions.Résumé : Des inventaires aériens de l'activité de pêche sur des lacs individus (N = 589) et des inventaires quantitatifs au filet maillant (N = 65) nous ont servi à évaluer les effets de l'accès routier sur l'effort de pêche sportive et sur la présence d'achigans à petite bouche (Micropterus dolomieu) introduits dans des lacs à touladis (Salvelinus namaycush) du nord-est de l'Ontario, Canada. L'effort de pêche, particulièrement durant la période d'eau libre, est le plus élevé dans les lacs facilement accessibles par la route et il dépasse souvent le niveau admissible estimé. Environ 25 % des lacs éloignés subissent aussi une pression excessive durant la saison d'hiver. On remarque une relation entre le nombre de pêcheurs et l'abondance des touladis dans les lacs éloignés, mais pas dans les lacs accessibles par la route. Les achigans à petite bouche sont plus présents dans les lacs à accès routier et à présence humaine (chalets ou auberges), ce qui laisse croire qu'ils ont été introduits dans ces lacs. Les populations de touladis sont réduites dans presque toute la région d'étude. Même en l'absence d'accès routier et d'achigans à petite bouche, l'abondance des touladis est tout de même de 47 % inférieure à celle des lacs témoins non exploités. Quand il y un accès routier et (ou) présence d'achigans, l'abondance des touladis est réduite de 77 %. Les populations éloignées de touladis sont visiblement vulnérables aux impacts négatifs de l'amélioration de l'accès routier, un vecteur représentatif à la fois de la surexploitation et de l'introduction d'espèces.[Traduit par la Rédaction]