Percorrer por autor "Priester, C. Robert"
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- The impact of trammel nets as an MPA soft bottom monitoring methodPublication . Priester, C. Robert; Martínez-Ramírez, Lucas; Erzini, Karim; Abecasis, DavidWith the global increase of marine protected area (MPA) implementation, the need for monitoring and the evaluation of their effectiveness becomes ever more important. Currently there is a severe lack of information about the protection effects of soft-substrate ecosystems. While many different methods have been established for the monitoring of hard-substrate ecosystems, most of these minimally invasive methods prove ineffective for soft- bottom habitats. Information and quantification of the impact of monitoring methods is needed to provide decision makers with the necessary knowledge to choose appropriate and feasible monitoring methods. In this study we quantify the impact of experimental trammel net fishing as a monitoring method of the soft-substrate demersal fish community using the Arrábida MPA (Portugal) as a case study. Over the 14 biannual sampling campaigns (between 2010 and 2019) 21,873 individuals and 5.61 tonnes of fish were caught. The gear is highly effective with an average catch per unit effort higher than reported for commercial fisheries in adjacent areas. When excluding the pelagic species, mortality rates are 41.2% and 30.4% in numbers and biomass, respectively. Most of the dead individuals belong to small, non-protected species with relatively little commercial value while MPA conservation target groups such as Soleidae and Rajidae have high survival rates. Due to its low size- and species-selectivity and the high survival rate of protected valuable species, the trammel net experimental fishing proved to be an effective monitoring method for soft-substrate demersal fish communities. Given their relatively low impact on the local ecosystem experimental trammel nets are a good alternative for areas where nonextractive methods are not effective. Nevertheless, quantification of the impact of other monitoring methods is necessary to enable the determination of the methods with the lowest mortality and impact for future softsubstrate MPA monitoring.
- Trophic ecology and coastal niche partitioning of two sympatric shark species in the Azores (mid-Atlantic)Publication . Priester, C. Robert; Dierking, Jan; Hansen, Thomas; Abecasis, David; Fontes, Jorge M.; Afonso, PedroThe exploitation of marine resources has caused drastic declines of many large predatory fishes. Amongst these, sharks are of major conservation concern due to their high vulnerability to overfishing and their ecological role as top predators. The 2 protected and endangered shark species tope Galeorhinus galeus and smooth hammerhead Sphyrna zygaena use overlapping coastal areas around the globe as essential fish habitats, but data to assess their trophic ecology and niche partitioning are scarce. We provide the first comparative assessment of the trophic ecology, ontogenetic shifts, and niche partitioning of the co-occurring tope and juvenile smooth hammer head around the Azores Islands, mid-north Atlantic, based on δ13C, δ15N, and δ34S (CNS) stable isotope analysis of muscle tissue of the sharks and their putative prey species. Overall, isotopic niches of both species indicated a reliance on similar resources throughout the sampled sizes (tope: 35– 190; smooth hammerhead 54–159 cm total length), with significant ontogenetic shifts. Topes displayed a gradual shift to higher trophic levels and a more generalist diet with increasing size (increasing δ15N values and isotopic niche volumes, respectively), whereas smooth hammerhead diet shifted towards prey with lower δ34S at a constant trophic level and a more specialized diet than tope of comparable body size (decreasing δ34S and constant δ15N and δ13C values, respectively). Our results indicate contrasting ontogenetic shifts in δ13C and δ34S along with pronounced differences between niche overlap of life stages pointing to intra- and interspecific niche partitioning of habitat and prey.