Reproductive output of two benthic resources (Fissurella latimarginata and Loxechinus albus) under different management regimes along the coast of central Chile

Abstract

ABSTRACT. The biological and ecological benefits of fully and partially marine protected areas are well documented. However, the benefits reaching areas beyond the limits of the reserves are still emerging in spite the fact that they are essential for fishing grounds recovery and to gain support for the protection of the ocean among stakeholders. We analyzed the influence of protection on gonadosomatic index, and also body dry weight, of two economically and ecologically important species: the keyhole limpet, Fissurella latimarginata and the red sea urchin, Loxechinus albus, in order to determine the value of protected areas in directly enhancing reproduction, and therefore potential seeding on exploited areas. We compared two levels of protection in central Chile, determined by fisheries management regimes (in turn associated to fishing pressure): a) areas with fishing restrictions (low or none fishing effort; territorial use rights for fisheries and no-take areas) and b) open access areas (high exploitation rates). We also evaluated the independent influence of upwelling on both variables. Our results show for both species that a) body dry weight is not affected by management regime, b) management regime did not show a consistent impact on gonadosomatic index and c) upwelling did not affect the response variables. Our findings help disentangling the main factors determining reproductive patterns under contrasting human impact scenarios, suggesting that the selection of sites for establishing marine protected areas seems to be less relevant than efficient control of fishing effort and minimum legal size to assure natural seeding.

Exploitation rates of two benthic resources across management regimes in central Chile: Evidence of illegal fishing in artisanal fisheries operating in open access areas

“…We are confident with these assumptions because previous studies in the same ecoregion [39], in exposed rocky shores, and using similar set of benthic species have shown no effect of site on relevant biological variables such as body condition and gonadosomatic index [38]. Moreover, no effect of upwelling was detected on relevant biological variables along the same study region (body condition and gonadosomatic index; [38]). Finally, the NT of Las Cruces is the best enforced marine protected area of Chile (although a minor level of poaching cannot be completely ruled out; [53]).…”

“…We do not expect that violations to the constant recruitment or constant natural mortality assumptions of the model could affect differentially the two gastropod species as to generate total instantaneous mortality of locos between 2.3 and 2.8 higher than for keyhole limpets between NT and exploited areas. Both species exhibit a larval phase transported by coastal currents to similar recruitment habitats [ 38 ]. We hypothesize that fishers’ preference for the most traditional and valuable resource may determine the difference in total mortality between species in exploited areas.…”

“…In addition to the assumptions of the catch curve model [51], we also assumed that (a) the growth parameter ( K ) is constant in both space and time ( K = 0.433 for loco [46] and K = 0.160 for keyhole limpets [42,52]), (b) natural mortality is constant over the entire sampling region, and (c) a reliable estimate of natural mortality can be obtained by measuring total mortality in the no-take area of Las Cruces [25]. We are confident with these assumptions because previous studies in the same ecoregion [39], in exposed rocky shores, and using similar set of benthic species have shown no effect of site on relevant biological variables such as body condition and gonadosomatic index [38]. Moreover, no effect of upwelling was detected on relevant biological variables along the same study region (body condition and gonadosomatic index; [38]).…”

“…Therefore, there is no clear evidence of special conditions within TURFs. Indirect evidence for similarity of environmental conditions in all fishing grounds comes from comparative studies examining body condition and investment in reproduction of keyhole limpets and sea urchins, which showed no differences between OAAs and protected areas (MAs and no-take areas; [ 38 ]). The total distance between the furthest north (Quintay) and furthest south location (Las Cruces) was 37 km, and the whole study area is located within the same oceanographic and ecological region [ 39 ].…”

“…Although previous studies did not show any effect of main environmental drivers (i.e. upwelling) on meaningful biological variables [ 38 ] along the study area, nested design was used to account for other local conditions that could affect each particular site. We pooled length data from all MAs (and OAA) within each site, obtaining a single set of observations for each level of management regime within sites.…”