“…They are therefore crucial for ensuring the sustainability of a number of marine fisheries in both the northern and southern hemispheres (Pollard, 1981, Kennish, 1990, Whitfield, 1998and Sardiña and Cazorla, 2005. Furthermore, some estuaries contain substantial fisheries that are based on certain marine species and on species that complete their life cycle within estuaries (Lenanton and Potter, 1987, Costa et al, 2002, Jaureguizar et al, 2003, Jung and Houde, 2003and Chuwen et al, 2009). The productivity of estuaries is also exploited by a number of bird species as a means of replenishing their energy reserves as they migrate to and from their breeding grounds (Elliott and McLusky, 2002).…”