Acoustic methods are routinely used to provide broad scale information on the geographical distribution of benthic marine habitats and sedimentary environments. Although single-frequency multibeam echosounder surveys have dominated seabed characterisation for decades, multifrequency approaches are now gaining favour in order to capture different frequency responses from the same seabed type. The aim of this study is to develop a robust modelling framework for testing the potential application and value of multifrequency (30, 95, and 300 kHz) multibeam backscatter responses to characterize sediments’ grain size in an area with strong geomorphological gradients and benthic ecological variability. We fit a generalized linear model on a multibeam backscatter and its derivatives to examine the explanatory power of single-frequency and multifrequency models with respect to the mean sediment grain size obtained from the grab samples. A strong and statistically significant (p<0.05) correlation between the mean backscatter and the absolute values of the mean sediment grain size for the data was noted. The root mean squared error (RMSE) values identified the 30 kHz model as the best performing model responsible for explaining the most variation (84.3%) of the mean grain size at a statistically significant output (p<0.05) with an adjusted r2 = 0.82. Overall, the single low-frequency sources showed a marginal gain on the multifrequency model, with the 30 kHz model driving the significance of this multifrequency model, and the inclusion of the higher frequencies diminished the level of agreement. We recommend further detailed and sufficient ground-truth data to better predict sediment properties and to discriminate benthic habitats to enhance the reliability of multifrequency backscatter data for the monitoring and management of marine protected areas.
Community Based Ecotourism (CBET) has the potential to both improve the conservation status of mangrove ecosystems and stimulate local economies. However, these ecotourism initiatives often fail due to a lack of active local participation, poor management and a lack of an appropriate benefit sharing scheme. This paper explores perceptions, opportunities and challenges of community mangrove-based ecotourism in Gazi Bay, Kenya. Data collected from household surveys, key informant interviews and focus group discussions were used to examine local perceptions, challenges and opportunities with respect to their participation in ecotourism as a tool for mangrove conservation. The results obtained indicated that 81.4 % of the Gazi village community was aware of the ecotourism activities being undertaken in the area with 62.8 % acknowledging the socio-economic as well as the environmental impacts of the ecotourism activities. Also, 66.0 % of the local community identified cultural traditions and local skills possessed by the community as having the potential to promote sustainable ecotourism activities in the area. For the design and implementation of any ecotourism venture and the management of mangroves to be sustainable, including that undertaken by the Gazi community, this study recommends prioritising effective local participation and capacity building. In addition, private sector involvement is essential for the mobilisation of resources to further enhance the management and conservation of mangroves in the long-term. The results provide key insights needed not only to improve the design and management of community-led marine conservation initiatives but also for ensuring that optimal conservation benefits are achieved.
<p>Acoustic methods are frequently used to provide broad-scale information on the spatial extent, range and distribution of marine habitats and sedimentary environments. Although single frequency multibeam echosounders have dominated seabed mapping for decades, multi-frequency approaches are starting to present in the scientific literature. Multibeam survey strategies are generally optimized for the acquisition of bathymetry data, often overlooking the ecological and geological value of backscatter data. This study examines the benefits of combining multi-frequency backscatter responses to discriminate seabed properties in areas with strong geomorphological gradients and associated ecological variability. The frequency-dependence element of backscatter strength is linked to: (i) the dominant scattering regime, (ii) seabed roughness, and (iii) the input of volume scattering related to signal penetration. In 2019, we collected and analyzed multifrequency (200, 95 and 30-kHz) backscatter data from Hempton&#8217;s Turbot Bank, a marine protected area off the north coast of Ireland. We compare these data with legacy 300 kHz backscatter data from 2013 to explore the backscatter variability in the context of geomorphological change. We assess the explanatory power of multi-frequency vis-&#224;-vis single-frequency backscatter data in terms of bathymetry, sediment granulometry and infaunal community structure. Results improve our understanding of the link between backscatter properties and geomorphology, with specific recommendations towards minimizing information loss and establishing minimum data requirements for frequency-based benthic habitat discrimination. Improved discrimination of geomorphology and benthic habitat characteristics enhances the reliability of backscatter data as a monitoring technique for area-based protection of marine resources.</p>
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