Preprint volume - SIBM

Pre-print Volume – Oral presentations
Topic 3: INTEGRATED COASTAL ZONE MANAGEMENT
G. LA MESA, S. BAVA 1 , R. CATTANEO-VIETTI 2 , A. MOLINARI, L. TUNESI
Istituto Superiore per la Protezione e la Ricerca Ambientale (ISPRA), Via di Casalotti, 300 - 00166 Roma, Italia.
gabriele.lamesa@isprambiente.it
1 Area Marina Protetta Portofino, Viale Rainusso, 1 - 16038 S. Margherita Ligure (GE), Italia.
2 Dip.Te.Ris., Università di Genova, Corso Europa, 26 – 16132 Genova, Italia.
GRADIENTS OF ABUNDANCE OF DIPLODUS SARGUS
AND D. VULGARIS ACROSS THE RESERVE BOUNDARIES
OF THE PORTOFINO MPA (LIGURIAN SEA)
GRADIENTI DI ABBONDANZA DI DIPLODUS SARGUS E D. VULGARIS
ATTRAVERSO I CONFINI DELL’AMP DI PORTOFINO (MAR LIGURE)
Abstract – Gradients of abundance of the sea breams Diplodus sargus and D. vulgaris (Sparidae) across
the reserve boundaries of the MPA of Portofino were assessed in order to determine reserve effect and to
provide evidence of spillover. Fish was visually censused in shallow rocky habitat (4-7 m depth), within the
MPA zones and in adjacent fished areas. Density and biomass of both species were usually higher within
the reserve than outside, likely due to the enforcement of protection regime. The drastic drop of fish
abundance just 100 m outside the MPA and its partial recovery at greater distance from the protected zone
would suggest a moderate spillover across the eastern reserve edge.
Key-words: spillover, sea breams, Portofino MPA.
Introduction - One of the potential benefit of marine protected areas (MPAs) is to
maintain or enhance adjacent fisheries through the net emigration of adult and juvenile
fish to nearby fished areas (spillover effect) (Russ and Alcala, 1996; McClanahan and
Mangi, 2000). Assessment of spillover has been usually carried out by monitoring
catch rates and fish densities within and outside reserves (McClanahan and Mangi,
2000). Negative gradients of fish density and biomass across reserve borders have been
considered evidence of fish spillover (McClanahan and Mangi, 2000; Kaunda-Arara
and Rose, 2004). Studies on fish movement by tagging methods indicated spillover to
be usually limited to hundreds of meters to a few kilometers from the reserve boundary
(McClanahan and Mangi, 2000). Moreover, the effect of export of adult fish biomass
may require a lot of time (many years) to develop (Russ and Alcala, 1996). The
presence of gradients is likely to concern species and size classes which are more
vulnerable to local fishing activities. In Mediterranean rocky shore, the sea breams of
the genus Diplodus are heavily targeted by fishers, due to their high commercial value.
Nowadays very few investigations have attempted to collect experimental evidence of
fish spillover through reserve boundaries of Mediterranean MPAs (Harmelin-Vivien et
al., 2008). In the present study, the abundance and biomass of the sparids Diplodus
sargus and D. vulgaris were quantified at many sites within and outside the Portofino
MPA, in order to assess the presence of gradient across the reserve boundaries and to
provide evidence of fish spillover.
Materials and methods - The marine reserve of Portofino was formally established in
1999, though a real enforcement occurred some years later. This MPA is characterized
by one small (10 ha) “no entry-no take” area (A zone), two “entry regulated-take
regulated” zones (B) and two buffer zones (C). Only local professional fishermen
operating with traditional fishing gears are allowed to fish in the B and C zones. Sea
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