Growth models and longevity of freshwater pearl mussels (Margaritifera margaritifera) in Spain

Abstract

Growth rates of populations of the freshwater pearl mussel, Margaritifera margaritifera (L., 1758), in northwestern Spain were analysed based on measurements of annual annuli and using two nonlinear functions for length-at-age data sets: von Bertalanffy's growth model and a hyperbolic function. These populations reach the smallest maximum shell length (90.5 mm) and have the shortest life-span (35 years) and the highest growth rate (k in von Bertalanffy's model >0.1·year–1, on average) known for this species. The two models were similar in performance and were well fitted (around 99%) to shell-length-at-age data, although the hyperbolic function appears to be applicable only from 6 years of age. The growth rate (either k or k' from the hyperbolic function) showed a large and significant variation across populations, both among and within drainages.

Strategies for the conservation of endangered freshwater pearl mussels (Margaritifera margaritifera L.): a synthesis of Conservation Genetics and Ecology

“…The maximum age reached is highly variable among populations and seems to primarily depend on growth rates. Populations tend to be faster growing and shorter lived in the southern part of their range with Spanish populations only attaining 35 years (Miguel et al, 2004), whereas pearl mussels in cooler Scandinavian climates can exceed ages of 200 years (Mutvei & Westermark, 2001).…”

Growth parameters of endangered freshwater pearl mussel (Margaritifera laevis, Unionoida)

“…Therefore, we considered L ∞ estimated with the Gompertz function to be optimal, even though this function underestimated L ∞ somewhat (Table 2). In M. margaritifera, the L ∞ value calculated with the Bertalanffy growth function was also underestimated except in a population with a short life span (i.e., maximum age of 35 years; San Miguel et al 2004). In contrast, the L ∞ value for the same population calculated with the hyperbolic growth function was overestimated (San Miguel et al 2004).…”

“…In M. margaritifera, the L ∞ value calculated with the Bertalanffy growth function was also underestimated except in a population with a short life span (i.e., maximum age of 35 years; San Miguel et al 2004). In contrast, the L ∞ value for the same population calculated with the hyperbolic growth function was overestimated (San Miguel et al 2004). Therefore, these errors should be taken into account when using L ∞ to assess fecundity in Margaritiferidae.…”

“…The unimodal distribution of growth rate against age implied that the best-fi tting model for the growth of M. laevis should have an infl ection point. Therefore, although the Bertalanffy growth function is often used for describing margaritiferid growth (Hastie et al 2000a, San Miguel et al 2004, Outeiro et al 2008, this model is unsuitable for M. laevis because it has no left-hand 'tail'. Moreover, the maximum age that mussels in the Shiribetsu and Chitose Rivers attained was 21 and 55 years, respectively.…”

“…The hyperbolic saturation function, or Michaelis-Menten equation, is commonly used by ecologists (Li 1983, Kluth & Bruelheide 2004). San Miguel et al (2004 modifi ed this function by adding two parameters to apply the function to a mussel population after a certain age.…”