Assessing Connectivity In Coastal Systems As A Tool For Fish Management And Conservation

Connectivity is a critical component of marine fish populations as it drives population replenishment, determines colonization patterns and populations' resilience to harvest. Knowledge of individual movement patterns is pivotal to ascertain population dynamics and underpins sustainable management. Many marine fish species occupy spatially segregated habitats throughout their life history. Estuarine nursery function and the ecological link between estuaries and the coastal environment were reviewed with emphasis on quantifying estuarine contributions and assessing fish movement to coastal adult populations. The chemical composition of otoliths is one of the most promising natural tags to quantify fish movement, particularly for early life stages. Yet, many uncertainties remain regarding the factors affecting elemental incorporation in otoliths. Temperature, salinity and water composition variations were examined to evaluate their interactive effects on Dicentrarchus labrax otolith chemistry, which is a vital first step in reconstructing environmental histories and intra-estuarine movement patterns. The combined use of otolith chemistry and muscle stable isotopes provided corroborative and complementary information, at different spatio-temporal scales, of intraestuarine habitat use and outlined limited movement between segregated estuarine nursery areas. Otolith elemental signatures of juvenile Platichthys flesus and D. labrax collected in estuarine nurseries along the Portuguese coast were year specific; though variation among seasons did not hinder spatial discrimination. Juveniles were accurately assigned to their estuaries of origin. These elemental signatures constituted the baseline for assessments of connectivity between juvenile and adult populations. The quantification of the relative contributions of estuaries to coastal populations of P. flesus and D. labrax in two years enabled the identification of the estuarine systems which contributed most to the replenishment of coastal populations. Overall, results contributed to prioritization of the conservation of ecologically important habitats and to the development of integrated management strategies for these commercially important species.