Tag Archive for: Active acoustics

Spatial distribution of tropical fish assemblages

Sea bottom

Comprehensive spatial distribution of tropical fish assemblages from multifrequency acoustics and video fulfils the island mass effect framework.

Describing fish distribution and associated environmental features is the first step toward understanding how fish communities are spatially structured and is a necessary step to conduct Marine Spatial Planning (MSP) and operate relevant protection policies.

Abstract

Tropical marine ecosystems are highly biodiverse and provide resources for small-scale fisheries and tourism. However, precise information on fish spatial distribution is lacking, which limits our ability to reconcile exploitation and conservation. We combined acoustics to video observations to provide a comprehensive description of fish distribution in a typical tropical environment, the Fernando de Noronha Archipelago (FNA) off Northeast Brazil. We identified and classified all acoustic echoes into ten fish assemblage and two triggerfish species. This opened up the possibility to relate the different spatial patterns to a series of environmental factors and the level of protection. We provide the first biomass estimation of the black triggerfish Melichthys niger, a key tropical player. By comparing the effects of euphotic and mesophotic reefs we show that more than the depth, the most important feature is the topography with the shelf-break as the most important hotspot. We also complete the portrait of the island mass effect revealing a clear spatial dissymmetry regarding fish distribution. Indeed, while primary productivity is higher downstream, fish concentrate upstream. The comprehensive fish distribution provided by our approach is directly usable to implement scientific-grounded Marine Spatial Planning..

Synthetic representation of the island mass effect as illustrated by the case of Fernando de Noronha.

Synthetic representation of the island mass effect as illustrated by the case of Fernando de Noronha.

Reference

Salvetat, J., Bez, N., Habasque, J., Lebourges-Dhaussy, A., Lopes, C., Roudaut, G., Simier, M., Travassos, P., Vargas, G., and Bertrand, A. 2022. Comprehensive spatial distribution of tropical fish assemblages from multifrequency acoustics and video fulfils the island mass effect framework. Scientific Reports 12(1): 8787. Nature Portfolio, Berlin. doi:10.1038/s41598-022-12409-9.

RESILIENCE oceanographic cruise – 19 April to 24 May 2022

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Marion Dufresne vessel

RESILIENCE campaign logo

The RESILIENCE oceanographic campaign will take place in the Indian Ocean from 19 April to 24 May 2022. About 50 international scientists, led by Jean-François Ternon, IRD researcher at UMR MARBEC, have embarked on board the ship Marion Dufresne, from Reunion Island, to study the interactions between physics and biology at “small scale” (~10km). The scientists will travel to eddy-front areas in the Mozambique Channel and the east coast of South Africa.

RESILIENCE cruise route

RESILIENCE cruise route with the three sampling sites: southern Mozambique Channel, north of the east coast of South Africa and south of Durban

Scientists from France (MARBEC, ENTROPIE, LEMAR, LOCEAN, LOG, LOPS, MIO), South Africa (3 Universities – Qqeberha, Cape Town, Stellenbosch), Mozambique, the UK and the USA are participating, including members of our acoustic platform.

The campaign hosts a Floating University with 20 students and 2 supervisors, from the Universities of Bretagne Occidentale (UBO), Littoral Côte d’Opale (ULCO) and Côte d’Azur (UCA).

Understanding the role of eddies in biological productivity and ecosystem structuring

The main objective of the RESILIENCE campaign is to study physical-biological interactions at small scales (~1-10 km), particularly on front zones at the edge of mesoscale eddies (~100km) that are numerous in the Mozambique Channel. The aim of the mission is to understand the role of physical processes (vertical exchanges in particular) on a small scale – well described by modelling but difficult to observe at sea – on the biological productivity and structuring of pelagic ecosystems. Coupled measurements of the various parameters will help to answer these questions. Frontal areas are often the place where fish, birds and marine mammals aggregate. In the context of climate change, it is predicted that the intensity of these fronts will vary in the future with possible consequences for these ecosystems. “The results of the campaign will therefore contribute to a study of the consequences of these changes on the exploited ecosystems of the area (food security issue for the riparian countries),” explains Jean-François Ternon. The geographical area sampled will be the centre of the Mozambique Channel and the east coast of South Africa. There are marked eddy structures in these areas, in contrasting hydrodynamic contexts (numerous fronts in the centre of the Mozambique Channel, eddy-coast interactions to the north of the east coast of South Africa, a semi-permanent eddy south of Durban, located between the coast and the Agulhas Current). As the eddies studied are by nature mobile structures, the sampling plan will be continuously adapted by real-time analysis of satellite data (altimetry, water colour) carried out on board.

Find here the press release on the campaign.

You can follow the RESILIENCE campaign, in English or French, https://www.isblue.fr/universite-flottante-campagne-resilience-2022/, with the hashtag resilience_science and by subscribing to the Twitter and Instagram pages below ↓

Twitter: https://twitter.com/UF_Resilience @UF_Resilience

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Acoustic ecology

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Passive and active acoustics each contribute to the development of an acoustic ecology through different but non intrusive and non destructive methodologies. At the scale of aquatic ecosystems, active acoustics (sounder, sonar) allows the description of the “biotic landscape”, at high spatial and temporal resolutions, providing the distribution and density of nekton, micronekton and zooplankton present between the surface and the sea bed; fronts such as the thermocline or oxycline, can also be detected. Trophic relationships or physical/biological interactions can thus be highlighted. However, clarifying these remains a complex subject. Furthermore, for the intermediate trophic levels, biomass estimates, which are essential for many research projects (trophic environment of predators, hot spots to be preserved, contribution of nycthemeral migrations to carbon flows, improvement of biogeochemical or ecosystem models), require the recognition of organisms (gelatinous, crustaceans, mesopelagic fish), which remains a real challenge. Passive acoustics listens to and studies sounds from anthropophony (boats, threshing, fishing, etc.), from geophony (rain, waves, etc.) and from biophony. In invertebrates, passive acoustics is used in a wide range of applications, including the detection and identification of cryptic or endangered species, the estimation of population density, the location of individuals, and the monitoring of activity rhythms and the reproduction period. In the near future, passive acoustics should be able to offer new tools for assessing the health of marine ecosystems by combining biology, ecology, signal processing and artificial intelligence.

Tag Archive for: Active acoustics

FINZWIO

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BIOPELAGOS

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Nectalis 5

Tag Archive for: Active acoustics

Anne MOUGET thèse

Tag Archive for: Active acoustics

Gulf of Guinea