Fish Biomass


No-fishing zones provide fish with habitats where they can safely reproduce and grow larger without being caught by fishers. Fish biomass, here measured by gram per square metre, indicates the size and overall health of a fish. Biomass also has important implications for fisheries, as larger fish mean more money for local fishers. Fish biomass, both within and outside of no-fishing zones, will indicate the benefit both to fish populations and to fishers (using the nearby fishing zones) of the protection provided by the non-fishing zone.



Fish biomass has been increasing inside and outside of NFZs.


This indicates that the NFZs are successfully allowing fish to grow in abundance and size, which benefits their populations but it also benefits fishers in adjacent fishing areas who are catching larger yields.



The weight per square metre is determined from diving surveys occurring at depths of between 12-18m following the MedPAN standardised methodology for rocky reef monitoring in the Mediterranean. Four stations have been selected at each site within and outside of NFZs, spaced at least 1 km apart. Three 25 m-long and 5 m-wide transects occur at each station. Along each transect, a diver swims in a straight line at a constant speed, identifying and recording the number and size of each fish species encountered. Fish sizes are estimated visually in 5 cm increments of total length (TL). Fish biomass (wet mass) will be estimated from size data by means of length-weight relationships from the available literature and existing database. Fish biomass for the transect is then divided by the total survey area of the transect to produce values in gr/m2.



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