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In the last few decades industrial fisheries has grown so much that exce= ssive depletion of fish stocks is taking place world wide. Improved fisheri= es management has therefore become a necessity. As opposed to previous sing= le-species focused conventional fisheries management, there is now an inter= national consensus that an ecosystem-based approach should be followed. In = this context satellite remote sensing proves to be of help in identifying p= otential fishing zones and to assess fish stocks. Global, daily, systematic= , high-resolution images obtained from satellites are essential for the eco= system approach to fisheries management (EAFM), because they assist in unra= velling the complexity of changing abundancy and spatial distribution of ex= ploited fish stocks.
The EAFM approach requires knowledge on aspects of the entire ecosystem = including its geographic boundaries, the top-down pressure from predators o= r the bottom--up control from primary production, the natural variability o= f external forcing (including fluctuations in food supply and climate chang= e), and biotic and abiotic ecosystem indicators. Conventional means of samp= ling and monitoring the ocean using oceanographic research vessels are very= costly and limited in both time and space. Using these methods it is very = difficult to study the entire ecosystem. Satellite remote sensing however m= akes it possible to sample the global ocean on synoptic scales at a relativ= ely high temporal resolution. Both short- and long-term environmental varia= tions can be detected with satellite-derived patterns of ocean temperature = and primary productivity.
Changes in environmental parameters may affect the recruitment, survival= , condition, distribution patterns, and migration of fish stocks, either di= rectly or indirectly. Key environmental parameters for assessing fish stock= s that can be detected with satellite remote sensing include sea surface te= mperatures (SSTs), sea surface height anomalies and sea surface colour reve= aling the abundance of chlorophyll a. As phytoplankton concentration respon= ds to short-term changes in the marine environment, detection of chlorophyl= l distribution by visible spectral radiometry, (also referred to as ocean c= olour monitoring) shows a map of connectivity of the marine ecosystem to th= e source of its sustenance. Because primary production is a first-order ind= ex of local carrying capacity; phytoplankton production is directly related= to total fish landings. Harmful algal blooms, causing massive fish kills c= an also be detected with SRS. Composite images of phytoplankton biomass can= be constructed using data from a number of global ocean-colour sensors suc= h as SeaWiFS and MODIS.
Understanding the factors that influence survival of larvae of commercia= lly important fish and shellfish stocks is particularly important. Adverse = effects from fishing are hard to distinguish from environmentally driven de= clines in larvae concentrations. Information on how the environment i= nfluences underlying stock recruitment relationships is essential for defin= ing reference points and baselines in order to achieve sustainable fisherie= s. Satellite derived SST and chlorophyll data are also used to predict pote= ntial spawning habitat.
Identifying spawning and/or feeding grounds with satellite remote sensin= g (SRS) contributes to spatially oriented management measures; satellite-de= rived chlorophyll and SST data can be used to map fish habitats. Satellite-= derived habitat mapping can contribute to the sustainable management of for= example the Atlantic bluefin tuna, the European hake and fin whale in the = Mediterranean Sea and the yellowfin and skipjack tuna species in the tropic= al Atlantic and Indian Ocean. The mapping of feeding habitat of these speci= es is part of a EC project called FishReg, for which they make use of the J= RC habitat model which requires satellite data of Sea Surface Temperature (= SST) and surface chlorophyll content (CHL) from Modis-Terra (SST), SeaWiFS = (CHL) and from MODIS-Aqua sensor (NASA). For tuna also the spawning habitat= is computed.
It is evident that earth observation with satellite remote sensing facil= itates and improves the implementation of an ecosystem-based approach to fi= sheries management. The application of satellite technology for fisheries m= anagement questions is being promoted internationally by the Group on Earth= Observations (GEO). That group is leading the development of a Global Eart= h Observation System of Systems (GEOSS) to address a broad range of societa= l benefits, such as the improvement of fisheries management. In addition th= ere are a number of organizations and projects involved such as NOAA, JRC, = SAFARI (Societal Applications in Fisheries and Aquaculture using Remotely-s= ensed Imagery) programme, FISHREG and FISHSAT (Integrated Satellite Service= s for Fishing Support and Safety).
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