Publisher :
Place of publication :
Publication year : 2003
Thematic : Fisheries
Language : English
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Marine reserves should display net export of biomass if they are to be of use in fisheries
management. We assessed experimentally the export of fish biomass (‘spillover’) from 2 marine
reserves on the Great Barrier Reef. Using the mark-recapture technique with traps, and hook-andline
fishing, movements of serranids, lutjanids and lethrinids were monitored at 2 experimental and
2 control sites. Experimental sites were bisected by reserve boundaries into ‘zones’ open and closed
to fishing. Control sites were protected from fishing, with an arbitrary boundary creating 2 equal
zones. Between 1997 and 1999, 1374 individuals were externally tagged, and during 1999 densities
were manipulated twice. Underwater visual census (UVC) surveys revealed pre-manipulation density
gradients between zones that were weak at real boundaries, and stronger at the arbitrary control
boundaries. Movements were highly localized, with over 60% of recaptures being made within the
50 × 30 m block of initial capture. The mean distances moved differed between the 3 species with the
highest recapture rates: Plectropomus leopardus (Serranidae) moved distances >100 m, Lutjanus carponotatus
(Lutjanidae) occasionally moved over 50 m, while Cephalopholis cyanostigma (Serranidae)
was predominantly caught within the block of initial capture. Movements across real or control
boundaries were rare. Twice in 1999, fish densities in zones open to fishing at the experimental sites
were reduced by spearfishing (by 61 to 64% and 57 to 83%, respectively). UVC revealed density gradients
at the experimental boundaries and no changes at non-manipulated control sites. There was
no evidence of experimentally induced directional movements, using traps or hook-and-line
sampling; however, 3 species (C. cyanostigma, L. carponotatus, L. quinquelineatus) did show a
propensity for increased movements. Detection of spillover requires powerful sampling designs
incorporating strong density gradients across large numbers of reserve boundaries.
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Keywords : Arielulus societatis
Encoded by : Pauline Carmel Joy Eje
