Antecedentes históricos de la República Dominicana

The use of MPAs as a fishery management tool was originally based on the idea that not only will stocks increase within MPAs, but that yield will also increase outside MPAs (Polunin, 2002). For this to occur there must either be ’spill over’ of mobile adult stocks (Rowley, 1994), or increased recruitment to recruit limited populations outside the MPA due to larval export from within the MPA (Crowder et al., 2000). Increasingly MPAs are being used in a greater variety of management roles. Temporary or rotational opening of areas to fishing allows the stock to build up within the reserve and does not rely on beneficial effects spreading outside reserve boundaries (e.g. Murawski et al., 2000). The proposal to manage migratory stocks with large scale MPAs (Polunin, 2002) no longer uses MPAs as a tool to totally protect a subsection of the stock throughout its life cycle, but instead uses MPAs as a more traditional tool to reduce the fishery pressure applied to the population as a whole.

The spatial extent of larval dispersal is not only relevant to how far the benefits of the reserve will spread, but also determines whether the protected population itself receives sufficient recruitment (Crowder et al., 2000; Sala et al., 2002). This larval supply can be self-recruiting from within the reserve, from the remaining fished stocks outside the reserve, from other reserves set up as part of a network, or from a combination of these sources. Understanding larval dispersal is critical to making decisions on the siting, spacing and size of a protected area or network of areas

(Crowder et al., 2000; Palumbi, 2003; Roberts, 1997; Warner et al., 2000).

The ability for widespread teleplanic dispersal by benthic invertebrate larvae has been demonstrated (Scheltema, 1986) and modelling has shown that recruits may come from source areas 10s or 100s of km ’upstream’ of a local population (Roberts, 1997), leading to the concept of open populations where recruitment is decoupled from local reproductive output (Gaines and Lafferty, 1995). However, contrary to this, there is increasing evidence that in many cases local populations are dominated by local recruitment (Heipel et al., 1998; Knowlton and Keller, 1986; Sponaugle et al., 2002; Todd, 1998; Warner et al., 2000) operating over scales of a few kms (McQuaid and Phillips, 2000) to a few 10s of kms (Palumbi, 2003). The increase in acceptance that recruitment may be predominantly local coincides with increases in understand- ing that there are a range of structures and processes occurring in the water column over the relevant scales to physically constrain and reduce larval dispersal (Archam- bault and Bourget, 1999; Denny et al., 1992; McCulloch and Shanks, 2003; Shanks, 1983; Shanks and McCulloch, 2003; Shanks et al., 2003; Talbot and Bate, 1987b; Wolanski et al., 1989; Wolanski and Hamner, 1988). Hydrodynamic modelling also indicates that in areas of topographic complexity particles can become trapped and remain near the source point for several weeks (Black et al., 1990).

If populations are dominated by recruitment over small spatial scales this could undermine the utility of MPAs to increase fishery yield outside protected areas as the benefits of increased spawning stock would not translate to increased recruitment outside of reserves. There is scant information to date as to whether MPAs do actually increase recruitment in the surrounding unprotected areas (see Halpern, 2003; Polunin, 2002, for reviews) and few studies have examined the effect of reserves on recruitment of sessile and sedentary species outside of reserves. Hockey and

Branch (1994) examined recruitment of Patella aspera adjacent to refuges in the

Canary Islands and found that recruitment was an order of magnitude higher close to the refuges than distant, however there was little observable difference in recruitment beyond 5 km from the refuge.

Further evidence of the scale of larval dispersal has come from a number of sources.

Following the collapse of the bay scallop Argopecten irradians population in Bogue

Sound was recruit limited as the population did not naturally regenerate. Petersen et al. (1996) tested this hypothesis by transplanting spawners into the Sound: over the following three years recruitment increased by 568% and adult biomass increased by 258% whilst adjacent control areas showed no significant change. This indicated that the population was recruit limited, and that larval dispersal was limiting over Sound-basin scale. Similar low levels of larval dispersal have been inferred from a

genetic study of blacklip abalone, Haliotis rubra, around south Australia. Although

there was large scale genetic homogeneity following a general trend of isolation by

distance there was also evidence of differentiation between populations<3km apart

(Brown, 1991).

Small scale larval dispersal has also been demonstrated from observations of the

range expansion of invasive species. The barnacle Elminus modestus spread by

about 20-30km a year following its introduction to north west Europe (Crisp, 1958).

The mussel Mytilus galloprovinicalis had a single point introduction to the south

eastern South African coast and the subsequent spread was followed by McQuaid and Phillips (2000). Four years after introduction the full range was asymmetrically distributed around the introduction site, the furthest spread recruits were 166km downcurrent to the north east and 29 km upcurrent to the south west, however 90% of recruits were within 5km of the initial site of introduction. These observa- tions coincide with Palumbi’s (2003) conclusions based on genetic data sets from five different species indicating that pelagic larvae of shallow water benthic inver- tebrates frequently disperse by 20-50 km, although the demographically significant recruitment may occur within a few kms.

The above examples demonstrate the importance of understanding the scale a which at population operates when evaluating the implications of theoretical population models on the effects of different types of fishery management strategy.

Before discussing the more specific aims and objectives of the thesis I will provide a brief review of patellid limpet biology, ecology and fisheries. I will particulary focus

1.7

Patellid Limpet Biology, Ecology, and Fish-