The influence of eutrophication and population biomass on common whitefish (Coregonus lavaretus) growth — the Lake Constance example revisited

Abstract

Accelerated growth of freshwater fish during anthropogenic eutrophication has been attributed almost exclusively to the increased nutrient content, while density-dependent effects have been largely neglected. We evaluated the relative importance of these factors by studying the growth of 43 consecutive year classes of common whitefish (Coregonus lavaretus) from Upper Lake Constance. This prealpine lake underwent eutrophication from the 1950s to 1970s, followed by reoligotrophication. Because whitefish are harvested with gill nets in a strongly size-selective way, we used back-calculated lengths of average fast-growing fish to compare growth among cohorts. Standing stock biomass was estimated based upon virtual year-class strengths. Multiple linear regression analysis revealed that growth of whitefish during their second year was most strongly related to standing stock biomass followed by PO 4 -P content during spring turnover and by calendar year, which was incorporated as a third independent variable (adjusted R 2 = 0.84). The negative correlation between whitefish growth rate and calendar year is interpreted as evidence of an evolutionary response to the highly size-selective fishery during at least four decades. We conclude that density-dependent effects on whitefish growth are more important than had been realized previously and that the impact of eutrophication on growth of whitefish needs to be reconsidered.Résumé : La croissance accélérée des poissons d'eau douce dans les conditions d'eutrophisation anthropique a été attribuée presque exclusivement à l'augmentation du contenu en nutriments; en revanche, les effets reliés à la densité ont été en grande partie négligés. Nous évaluons l'importance relative de ces facteurs dans une étude de la croissance de 43 classes d'âge consécutives de corégones lavarets (Coregonus lavaretus) du lac supérieur de Constance. Ce lac préalpin a subi une eutrophisation des années 1950 aux années 1970, suivie d'une ré-oligotrophisation. Parce que les corégones sont récoltés dans des filets maillants qui font une forte sélection en fonction de la taille, nous avons utilisé les longueurs obtenues par rétro-calcul de poissons moyens à croissance rapide pour comparer la croissance entre les cohortes. Nous avons estimé la biomasse du stock d'après les forces des classes d'âge virtuelles. Une analyse de ré-gression multiple linéaire montre que la croissance des corégones durant leur seconde année est surtout reliée à la biomasse du stock, puis au contenu de P-PO 4 durant le brassage du printemps et à l'année du calendrier qui a été incorporée à l'analyse comme troisième variable indépendante (R 2 ajusté = 0,84). Nous interprétons la corrélation négative qui existe entre la croissance des corégones et l'année du calendrier comme une indication de la réponse évolutive à la pêche très sélective au cours d'au moins de quatre décennies. Nous concluons que les effets reliés à la densité sur la croissance des corégones sont plus importants qu'on ne le croyait antérieurement et qu'...

Comparison of body composition and sensory quality of wild and farmed whitefish (Coregonus macrophthalmus [Nüsslin, 1882])

“…capture fisheries benefitted from widespread eutrophication, supportive breeding and the stocking of natural lakes. During this time, the supply was amply able to meet increasing demands (Eckmann, Gerdeaux, Müller, & Rösch, ; Thomas & Eckmann, ). However, the success of subsequent successful policy‐led efforts to restore freshwater ecosystems to their original oligotrophic conditions by reducing nutrient loads (Geist, , ) has been a major factor in decreasing yields from inland capture fisheries (Müller, Breitenstein, Bia, Rellstab, & Kirchhofer, ; Stich & Brinker, ).…”

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“…In many countries, natural whitefish populations dwindle and the continuation of the species is threatened in many areas (Thomas and Eckmann, 2007). Whitefish populations have to be supported with active protection measures including the creation of brood stocks and stocking programs which use material reared under controlled conditions (Wedekind et al, 2007;Szczepkowski et al, 2010).…”

Change in individual growth rate and its link to gill-net fishing in two sympatric whitefish species

“…Fishing is typically size-selective (Myers and Hoenig 1997;Fukuwaka and Morita 2008), and since significant heritabilities have been reported for traits that could be size-related in many fish [up to h 2 = 0.5, see (Theriault et al 2007;Carlson and Seamons 2008)], size-selective fishing is expected to induce rapid evolutionary changes (Palumbi 2001;Smith and Bernatchez 2008;Darimont et al 2009). Traits such as age or size at maturation (Heino et al 2002;Grift et al 2003;Sharpe and Hendry 2009), average reproductive effort (Yoneda and Wright 2004;Thomas et al 2009), or individual growth rates (Handford et al 1977;Ricker 1981;Swain et al 2007; Thomas and Eckmann 2007;Nusslé et al 2009) are likely to evolve in response to size-selective fishing. Such fishing has therefore been termed a 'large-scale experiment in life-history evolution' (Rijnsdorp 1993;Law 2000;Stokes and Law 2000), and studies on fishery-induced evolution have increased in numbers during the last decade (see Jørgensen et al (2007) for a review of phenotypic change attributed to fishery-induced selection).…”

“…For example, many freshwater systems have seen a change in phosphorus concentration and hence of biomass production over the last few decades (Müller et al 2007a, b). Such changes in phosphorus concentration could contribute to changes in growth rates of many fish (Gerdeaux et al 2006;Müller et al 2007b; Thomas and Eckmann 2007). Separating the effects of fishery-versus environmentally-induced changes on individual growth rates is usually difficult ) because phenotypic plasticity is important in fish (Thorpe 1998;Crozier et al 2008).…”

“…Alpine whitefish (Coregonus sp., Salmonidae) may be valuable models for studying human impacts on evolution of fish (Müller et al 2007b;Thomas and Eckmann 2007;Nusslé et al 2009;Thomas et al 2009). Populations of Alpine whitefish are comparatively well-defined because they are usually confined to individual lakes, and genetic analyses suggest that there is often little gene flow between populations (Douglas 1998;Vonlanthen 2009;Bittner et al 2010).…”