Long-term trends of bloater (Coregonus hoyi) recruitment in Lake Michigan: evidence for the effect of sex ratio

Abstract

Long-term population trends are generally explained by factors extrinsic (e.g., climate, predation) rather than intrinsic (e.g., genetics, maternal effects) to the population. We sought to understand the long-term population dynamics of an important native Lake Michigan prey fish, the bloater Coregonus hoyi. Over a 38-year time series, three 10-to 15-year phases occurred (poor, excellent, and then poor recruitment) without high interannual variability within a particular phase. We used dynamic linear models to determine whether extrinsic (winter and spring temperature, alewife predator densities) or intrinsic factors (population egg production, adult condition, adult sex ratio) explained variation in recruitment. Models that included population egg production, sex ratio, winter and spring temperature, and adult bloater condition explained the most variation. Of these variables, sex ratio, which ranged from 47% to 97% female across the time series, consistently had the greatest effect: recruitment declined with female predominance. Including biomass of adult alewife predators in the models did not explain additional variation. Overall our results indicated that bloater recruitment is linked to its sex ratio, but understanding the underlying mechanisms will require additional efforts.Résumé : Les tendances démographiques à long terme s'expliquent généralement par des facteurs extrinsèques à la population, tels que le climat ou la prédation, plutôt que par des facteurs intrinsèques, comme la génétique ou les effets maternels. Nous avons tenté de comprendre la dynamique de population à long terme d'un poisson proie indigène d'importance au lac Michigan, le cisco de fumage, Coregonus hoyi. Dans une série chronologique de 38 ans, il s'est produit trois phases de 10-15 ans, de recrutement faible, excellent et de nouveau faible, sans grande variation entre les années durant une phase donnée. Des modèles dynamiques linéaires nous ont servi à déterminer si la variation du recrutement s'explique par des facteurs extrinsèques (températures de l'hiver et du printemps, densité des prédateurs) ou intrinsèques (production d'oeufs de la population, condition des adultes, sex-ratio des adultes). Les modèles qui incluent la production d'oeufs de la population, le sex-ratio, les températures d'hiver et de printemps et la condition des ciscos adultes expliquent le maximum de variation. De ces variables, le sex-ratio, qui va de 47 à 97 % dans la série chronologique, a régulièrement l'effet le plus prononcé : le recrutement diminue lorsque les femelles prédominent. L'addition de la biomasse des prédateurs, les gaspareaux adultes, dans le modèle n'explique pas de variation supplé-mentaire. Dans leur ensemble, nos résultats indiquent que le recrutement du cisco de fumage est relié au sex-ratio, mais il faudra faire des travaux additionnels pour comprendre les mécanismes sous-jacents.[Traduit par la Rédaction] Bunnell et al. 844

Population synchrony of a native fish across three Laurentian Great Lakes: evaluating the effects of dispersal and climate

“…In a relative sense, however, the CPUE of recruits was reXective of relative year-class strength. In Lake Michigan, for example, bloaters fully recruit to the bottom trawl at age 3 (Bunnell et al 2006), but there is a strong positive correlation (r = 0.68; P < 0.0001) between age-0 CPUE and age-3 CPUE for the year-classes from 1962 up to and including 2000 (D .B. Bunnell, unpublished data).…”

“…php (accessed 24 November 2008). We chose winter because winter has been hypothesized as a critical period for survival of bloater eggs and embryos (e.g., Rice et al 1987;Bunnell et al 2006). We chose summer because bloater larvae occupy the epilimnion during these months (Rice et al 1987), and thus may be inXuenced by air temperature to a greater extent than the adult life stage that occupies the hypolimnion.…”

“…Bloater never occurred in Lake Erie, likely owing to its relatively shallow depth. Bloater have been best studied in Lake Michigan, where current knowledge suggests that the population is regulated by intrinsic factors, such as skewed sex ratios, rather than extrinsic factors, such as predation, winter and spring weather, or the relatively small commercial Wshery (Bunnell et al 2006(Bunnell et al , 2009. Bloaters undergo ontogenetic habitat shifts from the profundal (i.e., benthic, oVshore waters) zone as embryos, to the oVshore epilimnetic zone as larvae and early juveniles, and then return to the profundal zone as adults (Rice et al 1987).…”

Status of pelagic prey fishes in Lake Michigan, 2013

“…Recent stock-recruit modeling for bloater in Lakes Michigan and Huron indicated that sex ratio had an important impact on recruitment (Collingsworth et al 2014). Based on ages of bloater captured in the bottom trawl survey, relatively high levels of age-0 bloater in 2007-2009 acoustic surveys ( Figure 5) are reflected in age composition of YAO bloaters in recent years, as most of the larger bloater aged in 2009-2011 were hatched in 2007-2009, adding support to the belief that bloater become fully recruited to the bottom trawl by age-3 (Bunnell et al 2006). Data from both acoustic and bottom trawl surveys suggest that recruitment has not been sufficient to offset mortality.…”

Ecology of the River Darter in Canadian Waters: Distribution, Relative Abundance, Life-History Traits, Diet, and Habitat Characteristics

“…River Darters also generally appear to have a skewed sex ratio, with a predominance of females in most of the assessed populations. This phenomenon is found in many fishes, and there are a number of explanations for differential survival of the sexes including increased mortality due to predation, differences in growth rate and an associated survival trade-off, or differences in reproductive activity or maturation schedule [20]. The high female dominance may indicate poor recent recruitment events for these River Darter populations if males have lower survival and females become dominant at older ages.…”