Historical spawning grounds for sea lampreys (Petromyzon marinus L.) in most Portuguese river basins are becoming inaccessible due to the construction of impassable dams and/or weirs. Studies like the one described in this paper are particularly important in areas like the Vouga river basin, where there is a considerable fishing effort from both professional fishermen and poachers. In fact, for management and conservation purposes, it is important to clarify several aspects of the sea lamprey spawning run in this particular watershed. Therefore, a total of 30 radio tagged, migrating sea lampreys were released in the River Vouga and some of its main tributaries during 2004 and 2005. Results from the tracking sessions were used to determine the effect of poaching on the spawners' population and the characteristics of the resting sites used during the upstream movement. The rivers' stretches were also characterized according to the type of substrate present in the riverbed and flow type, in order to determine its aptitude to constitute appropriate spawning habitats for sea lampreys. We have identified in the upstream stretches of River Vouga, and in the tributary River Caima, characteristics that are particularly suitable for the construction of nests by the spawners. Presence of larvae provided evidence that spawners migrated into the River Vouga's upper reaches. However, abundance and age class diversity appeared to be higher downstream of Sernada and Carvoeiro weirs, corroborating the telemetry data which suggested difficulty in passing these obstacles during low precipitation years. In the River Caima, migration was most predictable, which might be related to daily water releases from a small hydropower dam at dusk, that stimulated the lampreys to resume migration. Poaching has had a considerable negative effect on the success of the tagged lampreys' migration: 76% of the animals released during 2005 were captured.

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SummarY: Composition of fatty acid profile of muscle neutral lipids (nl) and phospholipids (Pl) of sea lamprey that enter the Portuguese rivers minho, tagus and Guadiana during their non-trophic spawning migration was analysed. the fatty acid profile exhibited differences in the percentage among nl and Pl and between river basins. Similarities were found in the fatty acid profile of nl. monounsaturated fatty acids (muFa) were the most representative, followed by saturated fatty acids (SFa) and finally by polyunsaturated fatty acids (PuFa). monoenic 16:1 and 18:1ω9 formed a considerable percentage of total fatty acids, followed by SFa 14:0 and 16:0. ePa and dHa were the dominant PuFa fatty acids. in terms of nl, the fatty acid that contributed for the discrimination between the three river basins was 18:1ω7. individuals from the minho river basin exhibited a different fatty acid profile of Pl characterised by a low PuFa percentage when compared with lampreys from the tagus and Guadiana river basins. muscle Pl fraction showed that the two monoenes, 16:1 and 18:1ω9, occurred at high percentage, followed by 16:0 and 14:0 (SFa). among PuFa, dHa was the most representative fatty acid. the fatty acids that contributed to the separation between the three river basins were 16:0, 18:4ω3 and 24:1ω9. although the results point in the direction of a possible difference between the fatty acid composition of the nl and Pl fractions in the muscle samples from the three river basins, further studies, especially in tissues where fatty acid composition will be less sensitive to diet and environmental factors, are necessary to confirm this hypothesis.Keywords: Petromyzon marinus, fatty acids, spawning migration, minho, tagus, Guadiana, Portugal.reSumen: Comparación del perfil de ácidos grasos en los lípidos neutrales y en los fosfolípidos de los músculos de la lamprea marina anádroma (Petromyzon marinus L.) (Agnatha) de la cuenca hidrográfica de tres ríos portugueses. -Se ha analizado la composición del perfil de ácidos grasos de los lípidos neutrales (nl) y fosfolípidos (Pl) en el músculo de la lamprea marina que entra en los ríos miño, tajo y Guadiana durante su migración reproductora, no-trófica. el perfil de ácidos grasos presentaba diferencias en los porcentajes entre nl y Pl y entre las distintas cuencas. Se encontraron semejanzas en el perfil de ácidos grasos de los nl. los ácidos grasos monoinsaturados (muFa) fueron los más representativos seguidos por los ácidos grasos saturados (SFa) y, finalmente, por los ácidos grasos poliinsaturados (PuFa). los monoenoicos 16:1 y 18:1ω9 representaban un porcentaje considerable del total de ácidos grasos, seguidos por los SFa 14:0 y 16:0. ePa y dHa fueron los ácidos grasos PuFa dominantes. a nivel de nl, el ácido graso que permitió la discriminación entre las cuencas de los tres ríos fue el 18:1ω7. los individuos de la cuenca del río miño, en comparación con las lampreas de las cuencas de los ríos tajo y Guadiana, presentaban un perfil de ácidos grasos distinto a nivel de los Pl, que se...