Assessing the passage of obstacles by fish and macro-crustaceans in the French tropical islands of the Atlantic and Indian Oceans. Concepts and design

Over 100 000 structures (dams, weirs, bridges, box culverts and culverts, etc.) have been inventoried in French rivers. Fragmentation of natural habitats has been acknowledged as one of the main causes of biodiversity loss. At different points in their life cycle, many species need to move freely, occasionally over large distances, in order to access specific habitats conducive to their growth, reproduction, feeding, rest and/or protection. The EU Water framework directive (WFD, 2000), thanks to efforts by the international community, highlighted the value of gaining knowledge of, preserving and restoring ecological continuity in hydrosystems and riparian corridors. In the French tropical islands of the Atlantic and Indian Oceans, a survey still under way has revealed the existence of over one thousand obstacles in rivers. But virtually all indigenous fish and macro-crustacean species in these territories move between the marine, estuarine and river environments in fulfilling their life cycle. Consequently, they are highly sensitive to physical barriers in rivers. How can the passability of these obstacles be assessed? For which species and types of structure? Is the scientific knowledge currently available concerning the French overseas territories sufficient to develop a standardised assessment and diagnostic procedure? It was with these questions in mind that the French Biodiversity Agency, in conjunction with the respective Environmental Directorates and Water Offices in the overseas territories, and in a partnership with the Ocea Consult' and Écogea consulting firms, decided to adapt the ICE (Information on the Continuity of Ecosystems) method, originally designed for continental France, to the conditions prevalent in the French tropical islands. This book in the Knowledge for action series pulls together and clearly presents the main scientific and technical knowledge available on ecological continuity for fish and macro-crustaceans in the overseas territories, the physical capabilities of the species in question, the various types of obstacles encountered and their potential impacts. Providing in-depth information and richly illustrated, it offers readers a precise description of the ICE method, its basic principles and applications, and instructs on how to implement the method in one's own local environment.