Issue
Knowl. Manag. Aquat. Ecosyst.
Number 422, 2021
Topical Issue on Fish Ecology
Article Number 6
Number of page(s) 3
DOI https://doi.org/10.1051/kmae/2021006
Published online 18 February 2021

© G.P.J. Denys, Published by EDP Sciences 2021

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Tyrrhenian trouts are native of Corsica and Sardinia and belong to the Salmo trutta Linnaeus, 1758 species complex (Berrebi et al., 2019; Delling et al., 2020). Their taxonomy has been extensively debated: alongside a number of other Mediterranean populations, they were first assigned the name Salmo macrostigma (Duméril, 1858), a species originally described from Algeria, due to the presence of a diagnostic colour pattern comprising parr mark being retained in adult individuals (e.g., Boulenger, 1901; Roule, 1933). However, the first molecular studies suggested that Tyrrhenian trouts were more closely affiliated to an Adriatic lineage, which is clearly distinct from North African populations (e.g., Schöffmann et al., 2007). In the wake of these results, Kottelat and Freyhof (2007) included the Tyrrhenian trouts within Salmo cettii Rafinesque, 1810 (or potentially Salmo ghigii Pomini, 1941, but the latter name was invalidated by Bianco (2014) and is currently a synonym of Salmo farioides Karaman, 1938). Furthermore, mitochondrial data has demonstrated that S. macrostigma is invalid (Tougard et al., 2018), and it is currently considered a junior synonym of S. cettii (Splendiani et al., 2019). Berrebi et al. (2019) conducted molecular investigations, focussed on the Adriatic lineage, and highlighted that eight Corsican populations (U Furcone, A Tassineta, Aqua d'Acelli, E Maghjine, Speloncellu, Pozzi, Val d'Ese, and Lataga Rivers) and three Sardinian populations of the Cixerri basin were genetically-separated from the cluster corresponding to S. cettii. Most recently, Delling et al. (2020) analysed both morphological and molecular data and concluded that Tyrrhenian trouts are morphologically distinct from both Atlantic and North African trouts, but that the morphological data are incongruent with mitochondrial lineages. The authors further suggested that their results leave Tyrrhenian trouts without a taxonomic identity and that they should be referred to as Salmo sp. until this issue is resolved.

However, the unique native populations in Corsica and Sardinia are threatened by restocking operations leading to introgression with non-native Atlantic and Mediterranean trout lineages, habitat fragmentation by hydroelectric dams, poaching and competition with non-native rainbow trout Oncorhynchus mykiss (Walbaum, 1792) and brook trout Salvelinus fontinalis (Mitchill, 1814) (e.g., Massidda, 1995; Berrebi, 2015; Lobón-Cerviá et al., 2019). Ancestral (or native) Corsican populations are currently the most conserved and exhibit low intra-population genetic diversity as well as a high level of inter-population differentiation. Sardinian trout populations are more degraded by introgression with domesticated Atlantic trouts (Berrebi et al., 2019).

In France, all brown trout lineages and phenotypes (denominated Salmo trutta ssp.) are protected within the framework of a ministerial order 8/12/1988. The Corsican lineage is also included in Annex II of the European Habitats Directive with the denomination “S. trutta macrostigma”. Keith and Marion (2002) evaluated the status of the ancestral Corsican trouts “S. trutta macrostigma” as “Critically Endangered”. Some important conservation measures were then undertaken to protect the native populations in Corsica, such as the Life program “conservation de la truite macrostigma en Corse” 2003–2009 (see https://truitecorse.org/#). In Sardinia, some restocking programs focussed on native populations have resulted in the eradication of introgressed trouts (Sabatini et al., 2011, 2018).

Taxonomic changes may exert negative impacts on conservation and management of threatened species (Isaac et al., 2004). In the most recent French national IUCN Red Lists for freshwater fish species, Tyrrhenian trout populations have either been included within S. cettii and assessed as Endangered (UICN France et al., 2010), or within S. trutta as Near Threatened (UICN comité français et al., 2019). They have not been considered as a distinct taxonomic unit, and this could negatively impact their conservation in case of a legislative revision. Moreover, IUCN Red List assessments have a great influence on fund allocation for species conservation efforts as well as when changes to legislation and policy are considered. Trouts are among the most prominent freshwater fish species in French conservation and management policies (Bouleau, 2019; Betts et al., 2020). In particular, the ancestral Corsican trout lineage has an important patrimonial value on the island and a change in taxonomic status may be detrimental to its long-term preservation (Keith et al., 2020).

Delling et al. (2020) refers to the Tyrrhenian trout populations as “Salmo sp.”. This is detrimental to the conservation measures in favour of these populations, as a species needs to be named, formally identified and recorded in the legislation in order to benefit from conservation measures (Mace, 2004). An undefined species cannot be recorded in any legislative text and can not receive the benefits associated with specific conservation management. Renaming these threatened populations Salmo sp. may therefore adversely affect current and future conservation efforts. It can be argued that it might be better to give a broad name and then characterize lineages using concepts like Evolutionary Significant Units (ESU; see Mayden and Wood, 1995 when considering the spatial distribution of genetic diversity), or Operational Conservation Units (OCU; Dodson et al., 1998, to reflect ESUs and their interaction with socio-economic issues). Such an approach conveys the intrinsic ecological and genetic properties of these populations, and conservation management actions can be undertaken independently of the taxonomical discordance within the Salmo trutta complex (e.g., Tougard et al., 2018; Splendiani et al., 2019). These concepts are already applied to some Mediterranean trout lineages (e.g., Machordom et al., 2000; Almodóvar et al., 2006). Therefore morphological data do not corroborate with molecular data in Delling et al. (2020), this lineage cannot be then considered as a distinct species according to integrative taxonomy (e.g., Padial et al., 2010). In order to safeguard their long-term survival, and based on the available evidence (e.g., Tougard et al., 2018; Delling et al., 2020), Tyrrhenian trout populations should thus be considered as belonging to Salmo trutta pending further studies and a decisive taxonomic resolution, with an additional recognition as an ESU or OCU.

Acknowledgements

I warmly thank M. Hautecœur and A. Dettai for checking the English as well as the anonymous referees who improved the text.

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Cite this article as: Denys GPJ. 2021. A comment on “Morphologic and genetic characterization of Corsican and Sardinian trout with comments on Salmo taxonomy” by Delling et al. (2020): protected Tyrrhenian trouts must be named. Knowl. Manag. Aquat. Ecosyst., 422, 6.

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