Page 12 - Fishery_Regimes_2005

EMPAFISH Booklet nº 2 Fishery regimes in Atlanto-Mediterranean European MPAs

as “spillover”. Three mechanisms can be responsible of this biomass
exportation from a MPA: 1) random movements of fishes (home-range)
(Rakitin & Kramer 1996; Kramer & Chapman 1999); 2) migration of
individuals (trophic or reproductive) or home range relocation as a
consequence of density dependent factors and 3) egg and larval dispersal
(Gell & Roberts 2003). This process would result in a recovery of exploited
populations outside the limits of MPAs, therefore enhancing the yield of
neighbouring fisheries.

However, it must be taken into account that if home range of most individuals
of a given species normally exceeds the protected area, fishes that surpass
the MPA boundaries could be vulnerable to fishing mortality. Conversely,
fishes whose home ranges are centred outside the MPA but include its
boundaries could have reduced exposure to fishing. This is an important
question to be considered in the design of marine reserves as it is clear that if
the size of the protected area is not big enough in terms of home-range units,
the protection on these species populations would actually be incomplete
(DeMartini 1993). Thus, in this case consequences of spillover can benefit
yields of local fisheries but they could be merely a result of a partial
protection of several target fish populations.

Other expected effects of protection such as increasing reproductive potential
of target species (e.g. Goñi et al. 2003), or protecting genetic diversity (e.g.
González-Wangüemert et al. 2002, Pérez-Ruzafa et al. 2006), have received
little attention by researchers, but there are some recent evidences of their
functioning.

The best fishery evidence of fishing enhancement due to the effect of MPAs is
that fishing effort is often very high in the limits of protected areas suggesting
that catch rates are improved close to them (e.g. Shorthouse 1990;
McClanahan & Kaunda-Arara 1996). The change in the attitudes and
perceptions of fishers after the effects of protection in some cases, also
suggests that commercial catches in nearby areas have improved (Shorthouse
1990; Badalamendi et al. 2000).

However, numerous studies find difficulties in detecting or quantifying the
exportation of biomass from MPAs to surrounding areas (McClanahan & Mangi
2000; Sanchez-Lizaso et al. 2000; Gerber & Heppell 2004). And several
confounding factors, including habitat heterogeneity (García-Charton & Pérez-
Ruzafa 1998; 1999; 2001), inadequate sampling designs (García Charton et
al. 2000) and localised research, weaken the ability to determine the effects
of protection in many areas. In fact, after more than a decade of continuous
and intense research, current knowledge is extremely unbalanced (Palumbi
2001) and the long term effects of MPAs are still a matter of controversy
(Dawson et al. 2006; Steneck et al. 2006). Some of the main gaps in
scientific knowledge that must be filled if MPAs are to be effectively used as
fishery management tools relates with the dispersal capability of marine
larvae, the movement patterns of juveniles and adults, the complex effects of

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