Biología de la forma anádroma de la trucha común salmo trutta linnaeus,1758, en Galicia

Supervised by:
  1. Fernando Cobo Gradín Director
  2. Rufino Vieira Lanero Co-director

Defence university: Universidade de Santiago de Compostela

Fecha de defensa: 23 March 2021

  1. Oscar Soriano Hernando Chair
  2. Jesús Domínguez Conde Secretary
  3. Paloma Morán Martínez Committee member
  1. Department of Zoology, Genetics and Physical Anthropology

Type: Thesis


ABSTRACT Brown trout, Salmo trutta Linnaeus, 1758, like some other species of the family Salmonidae, presents populations with anadromous and potamodromous or resident morphs, a phenomenon called “partial migration”. Sea trout studies are, in general, relatively scarce in Europe and much more so in the Iberian Peninsula. Thanks to the combined analysis from the official sea trout catches and traps information, together with the age and reproduction marks determination through scale reading, back-calculation and sea trout smolts and adults mark/recapture, this study has been carried in Galician waters with the chief purpose of improve the sea trout biology and population features knowledge. To validate the information obtained, back-calculation results were compared with those fo the traps, detecting that the back-calculation offers size values higher than those of the stations. Sea trout populations obtained from angling data were also compared with those obtained from traps, verifying that the size of the river conditions the representativeness of the data obtained from fishing. The fluvial growth and age has been determined by back-calculation and scale reading. The freshwater stage duration was mostly 2 or 3 years. Less degree of fluvial growth is detected in the northern Galician rivers (with the exception of the Masma River) than in those located further south. The presence of smolts with B-Type growth in spring has also been detected, in 38% of the cases with the highest incidence in the youngest and smaller smolts. The mean smolt age (MSA) in the sea trout Galician populations is 2.34 years (from 2.04 for the Tambre River to 2.70 for the Sor River). The smolt migration takes place in spring, with a maximum in April, but the information collected suggests that many of the trout that migrate to the sea do not smolt. The studies carried out in the Ulla and Lérez rivers allow to affirm that the homing degree is high at least in adults, and that marine migrations of these trout are done near the coast and normally without straying too far from the native river, although movements of more than 500 km from the tagging site were detected. Marine growth from Ulla Sea trout is notably higher than the Lérez ones, and marine growth from southern Galicia Sea trout populations is also higher than that from the Central and northern populations. In general, the return to the main rivers after the marine stage occurs in two periods, one in spring and summer and, after a pause in September, another in autumn more related to movements towards spawning areas. However, the Sea trout run into the tributaries is delayed until the time of reproduction. The information from the Galician Sea trout fishery indicates that there are different patterns of return runs to the different analyzed rivers. There has been founded 4 river age classes (from 1 to 4 years) and 7 marine age classes (from 0 to 6 years), detecting 19 river/sea classes in Galician rivers, the populations with the highest number of these classes are those in which the highest average annual catches are registered in the series analyzed (1995-2010). The analysis of the weight tag & Sea trout recaptured in the river after their return from the sea made it possible to verify that during the period of stay in freshwater their weight decreases. Sea trout sex ratio in the Lérez, Ulla and Tea rivers is between 2 and 2.5 females for each male. In these rivers, sexual size dimorphism is also detected, since males have higher marine age and thus are bigger than females. Sea trout reproduces first time after being between a few months and 2 years at sea, mean maiden age (MMA) differs between the southern and northern populations, so that in the former the return age is lower than in the latter. The same happens with the proportion of previous spawners, since the percentage of Sea trout that have spawned at least once varies between 15% in the Tambre River and 35% in the Sor. This study also describes the migration to the sea of kelts after spawning, which is also carried out in two phases, one during winter, just after reproduction, and another in spring. After the first description of Galician Sea trout life cycle and analyzing their populations key features, we concluded that different population strategies are observed, with poorer growth both in river and sea, greater MMA and spawning frequency in the northern populations (Rías Altas) compared to southern ones (Rías Baixas), with the populations of the Central Rías showing intermediate values. All this allows us to affirm that the traits founded in these populations are compatible with the existence of local adaptations. The environmental variables detected in this work, which influence this variability found in the Sea trout Galician populations are: the surface of the estuaries/bays (Rías), the chlorophyll content of the estuaries, the fluvial length together with the silica content, the temporal hardness (TAC), the conductivity and the temperature of the river water, as well as the latitude and the accessible river length proportion to fish.