Frontiers in Marine Science (Nov 2015)
Life+ Trout Project (LIFE12 NAT/IT/0000940) for the recovery and conservation of Mediterranean trout (Salmo trutta complex) in the central Apennines (Italy).
Abstract
The Mediterranean brown trout (Salmo trutta complex) is one of the freshwater fish species complex at greater risk of extinction in the Mediterranean area. The introduction of alien invasive species and their interaction with the native fauna represent some of the major threats to the survival of this species (Caputo et al., 2004). Currently, the genetic integrity of the Mediterranean trout is being compromised by the introgressive hybridization with the Atlantic trout. This hybridization, which was favored by stocking programs carried out in the last century (Splendiani et al., 2013), is resulting in the loss of native genetic variability. The Life+ TROTA Project, which started in November 2013, is aimed to preserve the last populations of Apennine trout (Salmo cettii Rafinesque, 1810) and recover autochthonous genetic diversity. These action are being carried out in seven river basins of central Italy, where native populations have been threatened by stocking with Atlantic trout. The data collected are the indispensable premise for the adoption of the necessary strategies for conservation of the Apennine trout. The trout is a wide-ranging species complex native to Eurasia and North Africa. The northern limits to its range are represented by Iceland, northern Scandinavia and Russia, while the southern limits are represented by the mountain streams of northern Morocco. This species has also been introduced in several other locations around the world (North and South - America, Australia, etc). The Apennine trout is considered as critically endangered in the IUCN Red List of Italian vertebrates (Rondinini et al., 2013) due to water abstraction, overfishing and stocking with non-native trout (resulting in hybridization and competition). In the last 10 - 12 years the population has declined by almost 30%, and this trend is expected also in the future as water abstraction will most likely increase. The project focuses on 14 sites included in the Natura 2000 EU wide network of nature protection areas, established under the 1992 Habitat Directive. The project involved also the territory of the National Park of Monti Sibillini. The study area comprises 7 watersheds: Metauro, Cesano, Esino, Potenza, Chienti, Tevere and Tenna; a total of 25 watercourses were investigated with 32 sampling stations. A census of the fish fauna by electrofishing was carried out at each sampling location. For each specimen captured, total length and weight was measured, and a fin clip was collected for genomic DNA extraction. Genetic analyses were performed by using mitochondrial (D-loop fragment of 310 bp) and nuclear markers (locus LDH-C1* and 12 microsatellites). Bayesian clustering implemented in Structure 2.3.2.1 was used for estimating the number of groups (k) represented by all sampled individuals (Pritchard et al., 2000; Falush et al., 2003). The genetic and demographic characterization of trout populations in 32 sites allowed us to select: i) six sites for the collections of adults, needed for the production of genetically pure juveniles trout, ii) four sites for supportive breeding actions and iii) six sites to carry out the eradication of alien trout and successive re-introduction of Mediterranean trout. Another significant activity of the project is the hydrological characterization of the water courses by the Minimum Flow Analysis (MFA), adopting the MesoHABSIM method (Parasiewicz, 2007). This action is crucial to monitor the effect of water abstraction in the sites involved in the concrete conservation actions (e.g., eradication and re-introduction), and more generally, in the study area. In this way, we hope to increase the chances of long term survival of Apennine trout populations. Main expected results are the following: Identification of natural populations of Apennine trout in the study area and their protection through specific changes in existing regulation. Establishment of genetically pure wild populations with fish produced in an hatchery specifically adapted to manage wild native broodstock. Widening Apennine trout habitat availability by removal of non native trout in areas to be restocked. Restocking of streams selected in previous actions with pure juvenile trout. Assessment of the summer river flows in order to increase the chances of survival of Apennine trout populations in compliance with the regulations on minimum flow and water quality. Involvement of local sport fishing community to increase their awareness of the problem and ease their acceptance of more restricting fishery and fish management rules. At present the genetic and demographic characterization of the trout populations is completed. Table 1 and Figures 1-2 show the results of abundance analysis of the fish assemblages divided by basin. The standing crop’s mean values can be considered in the standard range, according to the small size and the limited productivity that generally characterized the watercourses analyzed, as most of the Apennine rivers. The differences of the mean values among basins were highly statistically significant according to the ANOVA analysis (density: F= 5.24, p=0.001; standing crop: F=12.42, p=0.001). The results of genetic analysis separated clearly native and aliene genomes (K = 2, Fig. 3a) and showed the presence of three distinct genetic stocks of native Apennine trout (K = 4, Fig. 3b): i) Tevere (green bars), ii) Tenna (red) and iii) Chienti /Potenza/Metauro/Esino (yellow). Populations characterized by very low introgression values will be the source of wild individuals to produce pure juvenile trouts in captivity. Four moderately introgressed populations will be subject to supportive breeding activities. Finally, six stream, where trouts showed almost exclusively an alien genetic make-up will be selected for the eradication activities. The data collected are the indispensable premise for the adoption of the necessary strategies for conservation of the Apennine trout in Central Italy.
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