Browsing by Author "Priester, Carl Robert"
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- Reserve effect of a small North-East Atlantic marine protected area (Arrabida, Portugal) on soft-sediment fish speciesPublication . Martínez Ramírez, Lucas; Priester, Carl Robert; Sousa, Inês; Erzini, Karim; Abecasis, DavidThe implementation of marine protected areas (MPAs) has been widely used as a tool to manage and conserve marine resources and services. Yet, to date, the reserve effect is still weakly evaluated, particularly for soft-sediment habitats. The Arrabida MPA, considered as a biodiversity hotspot, was fully established in 2009 on the west coast of Portugal and is characterized by large expanses of soft-sediment habitats. This MPA was established to protect biodiversity and to ensure the livelihood of the local small-scale fisheries community. Beyond before-after-control-impact (BACI) analyses were carried out on catch data (abundance and biomass) of 351 trammel net sets from experimental fishing campaigns (2007-2019) to study the reserve effect on demersal fish populations. The results show a declining trend in abundance inside and outside the protected area, with significant positive effects only found for undersize commercial species and Solea senegalensis, and a general increase in fish species total length. Despite the lack of any obvious reserve effect, the increase in fish length can be considered as a first sign. Anthropogenic pressures are generalized around the area, and transgressions of the restrictions are frequently observed inside the no-take zone. These can, among other aspects, delay or prevent the expected reserve effects. Therefore, enforcement and/or modification of the spatial plan must be incentivized to achieve the goals of the MPA.
- Trophic ecology and coastal habitat use of two sympatric shark species in the Azores using CNS stable isotope analysisPublication . Priester, Carl Robert; Afonso, Pedro; Abecasis, DavidThe anthropogenic exploitation of marine resources has severely altered ecosystems and caused drastic declines of large predatory fishes. Amongst these, sharks are the species of major conservation concern due to their critical role as top predators and high vulnerability to overfishing. The Azores are an oceanic archipelago in the mid-North Atlantic thought to serve as essential fish habitat (EFH) for some oceanic or semi-oceanic sharks such as coastal pupping and nursery grounds for tope (Galeorhinus galeus, Linneaus 1758) and smooth hammerhead (Sphyrna zygaena, Linneaus 1758) sharks. Yet, to date, the dependency of those juvenile sharks on coastal resources has not been investigated and crucial information on their trophic ecology is missing. This knowledge gap is relevant as it would allow to ascertain the importance of these areas for conservation and help developing management plans. Here, simultaneous δ13C, δ15N and δ34S (CNS) stable isotope analysis is used to investigate the trophic ecology, ontogenetic shifts and habitat use of the coastal life stages of G. galeus and S. zygeana around the Azores. A Bayesian ellipse approach (nicheROVER) and generalized additive mixed models (GAMM) are applied and interpreted in reference to isotope values of coastal and pelagic food web samples. The results show high diet overlap between tope and juvenile smooth hammerhead sharks with coastal-associated values. Tope shark showed a significant ontogenetic shift to higher trophic level coastal-benthic prey with growing size. Smooth hammerhead sharks exhibited significant decreases in δ34S, also suggesting a shift towards more coastal-benthic prey with increasing size. The diet of both species support their co-occurrence in shared nurseries with no evidence of sexual segregation or interspecific niche partitioning, but instead highly trophic competition, emphasizing the importance of healthy coastal habitats for conservation of these highly mobile sharks in the wider Atlantic.