Spatial and temporal variation of maturation schedules of lake whitefish (Coregonus clupeaformis) in the Great Lakes

Abstract

Fish maturation schedules vary greatly among systems and over time, reflecting both plastic and adaptive responses to ecosystem structure, physical habitats, and mortality (natural and fishing). We examined maturation schedules of commercially exploited lake whitefish (Coregonus clupeaformis) in the Laurentian Great Lakes (Lakes Michigan, Huron, and Superior) by estimating ages and lengths at 50% maturity, age-specific maturity ogives (age-specific probability of being mature), and probabilistic maturation reaction norms (PMRNs; a metric that accounts for effects of growth and mortality). Collectively, these estimates indicated variation in maturation schedules between sexes (i.e., males tend to mature at younger ages and shorter lengths than females) and among systems (midpoint estimates of PMRNs were smallest for Lake Michigan fish, intermediate for fish in the main basin of Lake Huron, and largest for fish in Lake Huron's Georgian Bay and Lake Superior). Temporally, recent increases in age at 50% maturity in Lakes Huron and Michigan may primarily reflect plastic responses to decreased growth rates associated with ecosystem changes (e.g., declines of the native amphipod, Diporeia spp.). As plastic and adaptive changes in maturation schedules of fish stocks may occur simultaneously and require different management considerations, we recommend the concomitant analysis of multiple maturation indices.Résumé : Les calendriers de maturation des poissons varient considérablement dans le temps et d'un système à un autre, ce qui reflète à la fois leurs réactions plastiques et adaptatives à la structure de l'écosystème, aux habitats physiques et à la mortalité (naturelle et due à la pêche). Nous examinons les calendriers de maturation des grands corégones (Coregonus clupeaformis) exploités commercialement dans les Grands Lacs laurentiens (lacs Michigan, Huron et Supérieur) en estimant les âges et les longueurs à 50 % de maturité, les ogives de maturité spécifiques à l'âge (probabilité d'être mature en fonction de l'âge) et les normes de réaction probalistes de maturation (PMRNs, une métrique qui tient compte de la croissance et de la mortalité). Dans leur ensemble, ces estimations indiquent qu'il y a une variation des calendriers de maturation entre les sexes (c'est-à-dire que les mâles tendent à arriver à maturité à un âge et une longueur inférieurs à ceux des femelles) et selon les systèmes (les estimations médianes des PMRNs sont plus basses au lac Michigan, intermédiaires chez les poissons du bassin principal du lac Huron et maximales chez les poissons de la baie Georgienne du lac Huron et ceux du lac Supérieur). À l'échelle temporelle, les accroissements récents de l'âge auquel 50 % des poissons sont matures dans les lacs Huron et Michigan peuvent représenter principalement des réactions plastiques à la diminution des taux de croissance associée aux changements dans les écosystèmes (par ex., le déclin des amphipodes indigènes Diporeia spp.). Puisque les changements plastiques et adaptatifs dans les calendriers de ma...

Size‐selective fishing and the potential for fisheries‐induced evolution in lake whitefish

“…Wang et al. (2008) analyzed variation in maturation schedules among multiple sites throughout the Laurentian Great Lakes, but did not analyze trends in prematuration growth rates or show the relationship between growth and maturation (i.e., the plastic effects of growth rate on maturation timing). Gobin et al.…”

“…For females only, logistic regression was used to estimate the age and length at 50% maturity ( A 50 and L 50 ) using procedure PROBIT in SAS. Females were used to be consistent with our optimization model, and because they typically mature at an older age and larger size than males (Beauchamp et al., 2004; Wang et al., 2008). Cohort‐specific estimates of A 50 and L 50 were retained if the intercepts and slopes were significant (≠0) at α = 0.01.…”

“…Our approach to estimate pMRNs differed slightly from Wang et al. (2008) in that we estimated age‐specific growth rates from fitted von Bertalanffy models, and, as described above, applied constraints on samples sizes and values of m ( a , L F ) to give more reliable estimates.…”

“…Among populations, faster prereproductive growth correlates with earlier age at maturity, which is consistent with life history theory (Charnov, 1993). Within the Laurentian Great Lakes, large‐scale spatial variation in size thresholds for maturation among basins and lakes (e.g., smaller size thresholds in Lake Superior) has been hypothesized to result from local adaptation to large‐scale spatial variation in prevailing growth and mortality regimes (Wang, Höök, Ebener, Mohr, & Schneeberger, 2008). …”

Intermittent breeding in the absence of a large cost of reproduction: evidence for a non‐migratory, iteroparous salmonid

“…A possible explanation for the problems we encountered is skipped spawning, because Barot et al's (2004) method assumes annual breeding following the age at first maturity. Given the issues we encountered, we carried on with the simpler approach of describing the MRN based on agespecific maturity ogives (Wang et al 2008).…”