Risultati finali
Evidence of biomass export from MPAs may be obtained by two means:
- Detecting a progressive increase over time of the mean density and biomass of target species in the MPA and in areas surrounding MPAs (which takes >10 years), or
- Detecting a gradient of abundance and mean size of target species across the reserve boundaries.
We follow the latter method, based solely on spatial sampling designs and develop :
- Protocol established for estimating the gradient of abundance and biomass of target species across the boundaries of MPAs using fish visual censuses.
- Protocol established for estimating the gradient of abundance and biomass of target species across the boundaries of MPAs using video surveys.
- Protocol established for estimating the production of eggs and larvae using a plankton survey within, and for describing the oceanography of the local region surrounding selected MPAs.
- Protocol established for estimating the gradient of abundance and biomass of target species across the boundaries of MPAs using experimental fishing.
- Protocol established for estimating fishing yields and economic value of commercial fishing within and around MPAs.
After analysis of results, we have defined some ecological bounds and appropriate geographical framework for management, determined the scientific tools and explained methods for the monitoring of fish populations.
With those protocols and guideline for management, We have made some Recommendations for the use of MPA s as fisheries management tools targeted to decision-makers.
This proposal aimed to investigate the efficiency of MPA as sources of biomass. The main objective was to assess the export of fisheries-related biomass from MPAs to surrounding areas. Measures of efficiency of MPAs for biomass export was based on a multidisciplinary approach that included biological and fisheries variables. Therefore, we defined three directions: Evaluate potential biomass export of adult fishes from MPAs; Evaluate potential pelagic export resulting from the dispersal of eggs and larvae from MPAs; Evaluate the potential contribution of adult fish export to fisheries.
Underwater visual and video census of adult fishes demonstrated a general evidence of significant increases in mean species richness, abundance and biomass of fishes inside marine protected areas, as has already been emphasized in the literature. Hence, depending on the geomorphological structure of the MPAs and adjacent areas, the habitats surveyed, and the species or group of species studied, the patterns were more or less clear. Differences in fish community parameters between inside and outside MPAs generally increased from species richness to abundance, and then to biomass. Biomass of fish represented thus the best parameter for studying reserve effects, and was more powerful to assess gradients across MPA boundaries. Overall, both methods showed high variability in the results precluding the identification of common trends across MPAs. At the end, the pattern we were showing implied interactions of fishing effort, large distance movement, spillover of post-settlers; competitive density-dependence; response to the spatial distribution of preferential habitats; and behavioural bias of fish towards divers or video equipment. In conclusion we can certainly advocate the existence of regular negative biomass gradients across MPA boundaries in the 6 MPAs studied, mainly detected from underwater visual censuses, that are consistent with the theoretical expectation of adult fish exportat from MPAs. Finally, it is important to emphasize the limited geographic extent of the gradients observed.
Surveys of the distribution of eggs and larvae exhibited an increase in the number of eggs and larvae in the MPA with a tendency of a decrease when moving away from the MPA area. The work on eggs and larvae emphasised the high variability in the distribution due to current patterns that might vary over time but also in a three dimensional space, behaviour of larvae that varied from species to species but also at the different growth stages, and production that varied in space because of habitat and distribution of adults. Nevertheless, it was a high success that even with such a highly variable component, we were able to observe gradients of biomass from inside to outside MPAs, consistent with production inside reserves and exportation to outside fished areas. As mentioned in the WP4 report, not all patterns were significant, but most important was certainly the main trends support the hypothesis set up initially. Increase in production was mainly visible in commercially targeted species that typically respond best to protection, and showing strong increase in abundance and mean size of individuals in MPAs.
The study of the contribution of adult fish export to fisheries was done by experimental fishing at increasing distance from the MPA boundaries and by surveying the commercial fisheries operating inside and around the MPAs. In both approaches we targeted fisheries and gears focussed on commercial fish species potentially affected by protection in the studied MPAs, such as Scianidae, Sparidae, Serranidae, Labridae, Scorpaenidae and Mullidae. Results from experimental fishing showed significant reduction of biomass with distance from the MPAs where habitat was continuous. Overall, this study recorded higher yields near the boundaries (up to 1000 m) that declined rapidly with distance to the MPA. The survey of the commercial fisheries indicated that globally effort concentrated in the vicinity of the MPAs. The catch per unit effort (CPUE), the catch per unit area (CPUA), and the mean body size showed significant negative trends with distance in about 20 to 30% of the cases studied.
In combining the results of biomass gradients from visual censuses of adult fish, experimental fishing with commercial fishing effort in the 6 different MPAs we obtained similar trends that were in agreement with the hypothesis of exportation from MPA with a decline in adult fish biomass from the reserve areas to the buffer, close and far areas; a decline in catch from experimental fishing from the reserve areas to the buffer, close and far areas; a decline in global commercial fishing effort from the reserve areas to the buffer, close and far areas.The results of these 3 surveys suggested adult fish spillover of some species from MPAs to fished areas.
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