New insights into biology and ecology of the Minho River Allis shad (Alosa alosa L.): contribution to the conservation of one of the last European shad populations

Abstract

In spite of shrinking populations, the Allis shad (Alosa alosa Linnaeus, 1758) is a species of commercial importance in Europe. On the Iberian Peninsula, especially in the international Minho River, it also represents an important cultural heritage. From the mid-twentieth century on, a marked decrease in the number of spawners occurred in that river, following the reduction of available habitat due to dam construction. We investigated the biology and ecology of the Minho River’s Allis shad population, considering: spawners age structure and migration behaviour, reproductive biology, hybridization with Twaite shad (Alosa fallax Lacepède, 1803), juvenile growth, habitats and diet, as well as parasites. Results suggest that males migrated 1 year earlier than females and earlier in the season. Females’ gonadosomatic index increased with time and was higher within the spawning area. According to gill raker numbers, the level of hybridization is higher in juveniles than in adult samples (17 and 3.6 % respectively). To the best of our knowledge, we present the first report of the parasite Anisakis pegreffii in Allis shad, as well as other mouth and visceral cavity parasites. We also reported the first molecular confirmation of the parasite Rhadinorhynchus pristis to this species. Our results will be useful for future management and conservation of the studied population, which is one of the last stable European shad populations.