Lecture on Salmonid Management and conservation

Nuria Sanz

Nuria Sanz

In the extraordinary world of stream salmonids, the Mediterranean trout group comprises several species and many evolutionary lineages that are distributed in a highly complex pattern which makes management and conservation really difficult. There is a high diversity of phenotypes and life histories that do not always correspond to genetic differences. Moreover, the discordances between phylogenetic histories inferred from different molecular markers have led to a confusing taxonomy and a continuous reclassification and definition of species over the years. In addition, human-induced introgression of exogenous brown trout has eroded native gene pools and increased complexity in the identification of conservation units. Therefore, one of the first topics to deal with in the management and conservation of these salmonids is to clarify the taxonomic classification and to define appropriate units of management. Genetic analyses are required to understand the evolution of the high variability of morphology in populations, and to elucidate the controversies on the definitions of species.

Another important topic is to find factors that determine stability of populations and model patterns of population structure. This is especially important because most of the Mediterranean salmonids inhabit streams with unstable climatic conditions and high variation of water flow. Genetic studies allow to estimate effective population sizes and to infer family relationships and gene flow among populations.

As a global example for all these topics, microsatellite genotyping of Iberian populations has revealed complex population structure, even at a microgeographical scale. Studies combining molecular and ecological data showed that natural factors as kin-biased spatial distribution and boom-and-bust population dynamics (associated to water flow fluctuation) explained population size variations and modeled population structure. Also, anthropological factors, such as artificial barriers that prevent fish dispersion and stocking with hatchery fish, can explain some patterns of structure. The understanding of these factors is critical to design strategies to restore gene flow and to maintain genetic diversity of these population inhabiting unstable hydrologic environments.

Last but not least, a main topic in the management and conservation of Mediterranean trout is diminishing the consequences of repeated stoking with hatchery-reared non-native fish. Genetics also provides effective tools to assess the impact of stocking, introduction and translocation of populations and/or species, and to evaluate the native status of a population. In eastern Pyrenees, some management measures have been designated to protect native gene pools. The declaration of ‘genetic refuges’ ,in which fishing activities were maintained but hatchery releases were completely banned, has proved useful to protect native gene pools in streams with limited or no evidence of non-native genome. However, additional measures as educational efforts to promote catch and release fisheries are necessary.