A vulnerable species group, such as, the elasmobranchs, in a data-deficient context presents a complicated management problem. Evidence suggests that the Azores islands, a remote archipelago on the Mid-Atlantic Ridge, serve essential functions in the life-history of species across taxa. The diversity of marine resources within its EEZ are exploited by local to international fleets, and the full extent of fishing pressure can often be underestimated. Although sharks and rays appear to be of minor importance in the fishery, the possibilities of illegal, unreported, and unregulated fishing raises concerns about these threatened species. However, this group has failed to attract management attention, visible in the lack of regional studies focused on biodiversity, ecology, or threats of elasmobranchs. Our work attempts to review and update the information on elasmobranchs of the Azores and identify potential threats, mainly by the local fisheries. We aim to highlight knowledge gaps that require further research and conservation actions. We (1) update the annotated checklist of elasmobranch species, (2) compare species distribution across a biogeographically similar section of the North Atlantic, and (3) analyze the interaction of elasmobranch species with local fisheries. We confirm 61 chondrichthyan species for the Azores (39 sharks, 17 rays, and 5 chimaeras), adding 19 species to the previous annotated checklist of 1997. The Azores elasmobranch species assemblage most resembles Madeira, the neighboring Macaronesian archipelago. Biogeographic affinities between the chosen regions of the North Atlantic are reflected in the taxonomic structure of families. Although underestimated in the local fisheries, elasmobranchs constitute a regular but highly variable portion of total landings. Misreporting and misidentification is perhaps the greatest concern in the local fisheries records, further aggravated by few existing catch regulations for elasmobranchs. Local knowledge indicates that the Azores serves as essential habitat for at least a few species in coastal areas and shallow seamounts, and potentially so for a number of deep-sea elasmobranchs. The intersection of fishery threats and local essential habitat functions around the archipelago warrants greater research effort and studies.
Formulae for sediment thresholds of motion are commonly based on flume experiments on rounded quartz particles and it is unclear how well they predict thresholds in natural settings. Here, sediment threshold shear stresses were calculated from one such formula using surface grain‐size data from 112 sites around Santa Maria Island, Azores. To compare with those stresses, a Simulating Waves Nearshore model was run for three typical winter months to predict shelf stress maxima due to waves. As wind‐driven and other circulations also increase stresses, the model predictions are under‐estimates. Comparison of the two stress estimates suggests that the whole shelf of the island was mobile during extreme conditions. However, three forms of evidence contradict this. First, 129 rollovers of sandy clinoforms lying in 30 to 200 m water depths around the island were identified from boomer seismic data. It has been suggested that such rollovers mark depths at which hydrodynamic stresses fall beneath the sediment threshold of motion. Second, differences in grain‐size diversity between carbonate‐free and whole sediment indicate where carbonate particle fragmentation occurs. Third, seabed images reveal variations in ripple character and presence. The combined data suggest that deposition has occurred in the middle and outer shelf, overlapping where the model predicts sediment mobilization. However, by decreasing the model bottom shear stress or increasing the shear stress at threshold of motion by a factor of two to three, deposition is predicted to have occurred immediately deeper than the shallow active rollovers. Therefore, in practice, the ratio of wave‐imposed shear stress to stress at threshold of motion is two to three times smaller than predicted. This is speculated to be due to the presence of widespread hard substrates and other features shielding particles between them from wave stresses. Alternatively, the threshold of motion is higher than expected from the formulae for these sediments dominated by bioclastic particles.
Deep-water sharks are highly diverse, vulnerable, and understudied as a group, despite the increasing pressures on their populations. Twenty-five species of deep-water sharks have been recorded in the Azores, an oceanic archipelago in the mid-North Atlantic, that are regularly caught as bycatch in hook-and-line fisheries. Avoiding the bycatch of deep-water sharks presents multiple challenges due to their high catchability, difficulties in correctly identifying species, and the general lack of data on these species. This review summarizes the findings of recent studies from the region, providing an up-to-date science-based framework for mitigating bycatch effects of Azorean hook-and-line fisheries. Several depth-based, area-based, and gear-based measures have been studied that demonstrate the potential to either avoid or increase the survival of deep-water shark bycatch. However, these measures may have limited efficacy for some species (e.g. highly mobile species) and thus, limited widespread applicability. Convincing fishers to avoid deep-water shark bycatch is also a challenge given the antagonistic interactions with sharks damaging the catch and fishing gear, while simultaneously a market incentive for shark liver oil remains. It highlights the need to proactively engage fishers and incentivize the mitigation of bycatch of deep-water sharks in Azorean waters.
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