Biological processes in seagrass beds of coastal lagoons to maintain estuary-dependent marine fisheries.

Following the planned FAO Ecosystem Restoration Programme for estuarine habitats to support estuarine fisheries and early life stages of estuary-dependent marine fish, direct relationships of total seagrass and eelgrass Zostera m. capricorni areas and biomass with fish harvest were derived for a range of slightly to highly urbanized coastal lagoons that are expected to support the larvae and juveniles of estuary-dependent marine fisheries. Fish harvest and seagrass area and biomass in the lagoons increased with moderate catchment total suspended sediment and total phosphorus loads due to lagoon flushing rates directing excess silt and nutrients out to sea via the lagoon entrances. Well managed, sewered catchment management works are shown that could assist estuary managers maintain seagrass for estuarine and offshore estuary-dependent fisheries by maintenance of seagrass and fishery ecological processes. Further research is suggested to investigate estuary-dependent post-juveniles leaving estuaries and lagoons migrating to nearshore, offshore and shelf marine fisheries.

An analytical solution to ecosystem-based FMSY using trophic transfer efficiency of prey consumption to predator biological production.

A theoretical basis for Ecosystem-based Fisheries Management (EBFM) was derived for pelagic fish by applying marine ecology theory of analytical relationships of predator-prey biological production transfers between trophic levels to FAO guidelines for an ecosystem approach to fisheries. The aim is to describe a simple method for data-limited fisheries to estimate ecosystem-based FMSY and how EBFM modellers could mimic the way natural fish communities function for maintaining ecological processes of biological production, biomass and ecosystem stability. Ecosystem stability (ES) FMSY were estimated by proportion of biological production allocated to predators, giving ESFMSY of 0.23 for small pelagic and 0.27 for pelagic finfish, prioritising ecosystem over economics. To maintain both stability and biomass (SB) a full pelagic EBFM SBFMSY of about 0.08 was obtained for both small pelagic and pelagic finfish, having mostly ecosystem considerations. As the FMSY are single-species averages of catchable species targeted in a specific trophic level, multispecies fishing mortalities were proportioned by the biological production of each species in the trophic level. This way catches for each species are consistent with the average ecosystem FMSY for a trophic level. The theoretical estimates gave similar results to other fisheries for sustainable fish catches that maintain the fishery ecosystem processes. They were also tested using six tropical Ecopath Models and showed the effects of imposing commercial fishing mortalities on predominantly EBFM conditions. The ecosystem stability ESFMSY is suggested to be investigated for sustainable fish catches and the full EBFM SBFMSY for protected areas or recovery of heavily depleted stocks.