Conservation status of the freshwater pearl mussel Margaritifera margaritifera in Portugal

Abstract

a b s t r a c tBased on new information, the current conservation status of the freshwater pearl mussel Margaritifera margaritifera (Linnaeus, 1758) in Portugal is revised. Between 2010 and 2013 surveys were conducted in eight different rivers to assess distribution, abundance, size-frequency and preferential habitat of this species. Rivers Neiva, Cávado and Terva presented very low abundances (in the Cávado no specimens were found) and showed acute signs of ageing, calling into question the future survival of these populations. Although abundances were low in Rivers Beç a, Paiva and Mente, juveniles were present and populations may improve their conservation status in the future, if appropriate management measures are applied. Rivers Rabaç al and Tuela presented the highest abundances of adults and juveniles and these two rivers have the highest potential for the conservation of freshwater pearl mussels in Portugal. However, these two populations have suffered severe declines in several stretches due to the construction of dams in recent years. Given that the Portuguese pearl mussel populations are at the southern range of the species distribution, their conservation should be a priority. This current description of the conservation status of M. margaritifera in Portugal can be used as a reference, and guide future research and management initiatives to better conserve this species.

Conservation status of freshwater mussels in Europe: state of the art and future challenges

“…Hastie et al ., ; Mouthon & Daufresne, ; Sousa et al ., ; Bódis, Tóth & Sousa, ). Even small temperature changes can strongly affect metamorphosis success and larval development in freshwater mussels (Taeubert, Gum & Geist, ; Taeubert et al ., ), with knock‐on consequences to recruitment success (Sousa et al ., , ). Particularly affected may be freshwater mussel populations at the edges of their distribution, such as those in the south of Europe, where intolerance to increased temperatures combined with low dispersal capacity may impair their survival in these regions (Santos et al ., ).…”

Influence of stock origin and environmental conditions on the survival and growth of juvenile freshwater pearl mussels (Margaritifera margaritifera) in a cross-exposure experiment

“…Jones (2013) further proposed that species can only show local adaptation to intact, but not to degraded habitats. Nearly all Central European freshwater pearl mussel streams are presently considered more or less degraded as evident from a lack of natural recruitment in most of them (Geist, 2010;Sousa et al, 2014). Additionally, differences during the parasitic stage may also contribute to variation, not only on mussel stock but even on an individual level, as unionid juveniles receive nutrients from their host fish (Fritts et al, 2013).…”

Effect of glochidia infection on growth of fish: freshwater pearl mussel Margaritifera margaritifera and brown trout Salmo trutta

“…Margaritifera margaritifera is an endangered species (e.g., Geist, 2010;Lopes-Lima et al, 2017;Oulasvirta et al, 2017) whose glochidia are produced in captive breeding programmes using brown trout as fish host (e.g., Buddensiek, 1995;Thomas et al, 2010;Gum et al, 2011;Eybe et al, 2015;Moorkens, 2018). One-way to strengthen declining M. margaritifera populations-or to restore the extinct populationswould be to stock juvenile brown trout infected with M. margaritifera glochidia to the target rivers (Wellmann, 1943;Buddensiek, 1995;Geist et al 2006;Thomas et al, 2010;Sousa et al, 2013Sousa et al, , 2015Sousa et al, , 2018. This is a realistic, though little utilized option in M. margaritifera areas where juvenile salmonids are stocked, either for recreational fishing purposes or to strengthen the salmonid populations, and where conditions for completion of the life cycle of M. margaritifera are otherwise favorable, like in northern Fennoscandia.…”