26 Porto, Rua dos Bragas 289, P 4050-123 Porto, Portugal, cantunes@ciimar.up.pt, 27 mmota@ciimar.up.pt 28 Abstract 35 Understanding dispersal capacities for migratory species is crucial for their management. By 36 coupling otolith microchemistry and microsatellite genetic analyses, we provided information 37 on snapshot and long-term dispersal capacity of Allis shad, an anadromous clupeid in decline 38 throughout its distribution range. The allocation of natal origin was obtained from water 39 chemistry, signatures in otoliths of juveniles and spawners within a Bayesian model. The 40 majority of adults were assigned to a source river with high degrees of confidence, only 4% 41 were undetermined. Otolith natal origins were used to define a population baseline by 42 grouping individuals from the same natal river and not from the same sampling location as 43 usually done. While Alosa alosa exhibited a high level of natal site fidelity, this species 44 showed weak genetic structure which supported the evidence of a significant flow of strayers 45 between river basins in vicinity or at longer distances. However, long distance straying was 46 probable but not frequent. In a context of global change, straying would be a key mechanism 47 to drive dispersal and allow resilience of Allis shad populations.48 49 50

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In this study, the identification of major ontogenetic events and the duration of the fresh water and estuarine phases before the seaward exit of young allis shad Alosa alosa were investigated retrospectively, using the otoliths of spawners. Daily growth increment periodicity in the otoliths was validated with an accuracy of 4 days (9Á4%) for fish >30 days. The specific limits of the Sr:Ca ratios in the otoliths, indicating fish movements between salinity 'compartments', were up to 1Á1 Â10 À3 for the freshwater phase, 1Á1 to 1Á9 Â 10 À3 for the estuarine phase and 1Á9 Â 10 À3 for the marine phase. In early life history, a major event occured at 22 days, which was marked on the otoliths by a change in the direction of the otolith growth axis. This event was related to a change in larval swimming behaviour. Juvenile freshwater residence time was between 58 and 123 days, with a median duration of 88 days. Contrary to what has been estimated in previous studies, the present study showed that the estuarine phase lasted from 4 to 36 days, with a median value of 11 days. Seaward exit occurred in fish aged from 63 to 150 days, with a median age of 99 days. These results have important implications for the sustainable management of this species.

Bardonnet A, Jatteau Ph. Salinity tolerance in young Allis shad larvae (Alosa alosa L.).Abstract -Estuarine migration in Allis shad (Alosa alosa) usually does not take place before mid-summer, but exposure to salinity in brackish water may occur earlier as many spawning areas are of necessity located in upper estuarine zones due to the placement of dams. Therefore, Allis shad conservation programmes need to consider the risk of mortality due to the ability of young Allis shad to tolerate salinity. To evaluate larval mortality due to the inability of larvae to withstand salinity during early ontogeny, we exposed larvae of different ages (from few days old to 27 days old) to salinities ranging from 0 to 30 gAEl )1 . Results indicate that direct seawater exposure induces high mortality in young larvae whatever the ontogenetic stage. However, young larvae can easily deal with upper estuary salinity conditions.

-The objective of this study was to assess the potential effects of climate change on the survival of allis shad early life history stages. Embryos and larvae were exposed to temperatures ranging from 5 to 35• C. No embryonic survival was recorded at extreme temperatures ( 10 and 30• C), and no larval survival was observed at 5 or 35• C. Based on these experimental results, a survival model was developed to predict survival rates at different temperatures for embryos and larvae up to 14 days post hatch. The model confirmed that embryonic daily survival is more impacted by temperature than larval survival. The highest survival rates (greater than 80%) were found for temperatures between 15.7 and 25.6• C for embryos and between 14.6 and 26.7• C for larvae. This survival model can be used to explore the impact of temperature on recruitment of allis shad in southern France. Preliminary analysis from two different rivers suggests that cold temperatures may have a strong impact on embryonic and larval survival.