Active acoustics – Laboratoire LEMAR UMR 6539

ECHOS thematic network

Active hydroacoustic study of aquatic ecosystems (ECHOS, 2025-2029)

Active acoustics is an observation method used to understand, assess and monitor the functioning of aquatic ecosystems. The ability of acoustics to observe ecosystem processes at multiple spatial and temporal scales promotes a better understanding of the ecosystem. The scope of application of active hydroacoustics encompasses all offshore, coastal, lagoon, estuarine and continental ecosystems from polar to temperate regions.

Illustration of sampling methods for pelagic and mesopelagic fauna, showing the position of a trawl net and an acoustic recording cone in relation to the layers of organisms (source: A. Receveur)

This discipline is part of the range of tools available to INEE to provide essential information on scientific issues and current societal challenges, such as climate change and overexploitation of resources. In France, many researchers and engineers are already working on these issues, but there is now a need to pool efforts by sharing scientific knowledge and defining new, interdisciplinary areas of research. The RT’s mission is to raise the profile of the French scientific community in this field, which has a wealth of expertise that is recognised internationally and needs to be developed and consolidated. The RT aims to bring together scientists (permanent staff, post-doctoral researchers and doctoral students) from around ten laboratories belonging to several French research organisations (CNRS, Ifremer, INRAE, MNHN, IRD).
The objectives of the RT ECHOS are to: (1) structure a heterogeneous and dispersed scientific community, (2) define common scientific and methodological barriers, (3) standardise observation protocols, (4) promote the exchange of expertise, and (5) ensure the dissemination of knowledge through workshops, conferences and training courses.
The programme is organised around four main areas in line with the guidelines defined by the international working group in this field, the ICES Working Group on Fisheries Acoustics, Science and Technology (WGFAST):

Technologies and platforms: development and integration of new technologies (broadband echo sounders, acoustic cameras, eDNA, etc.) on various media (sailboats, drones, moorings, equipped animals) in order to collect data in environments that are difficult to access or sensitive.
Organism detection and classification: improvement of acoustic diffusion models, particularly for understudied species (crustaceans, gelatinous organisms), and expansion of the frequency signature database.
Data processing: use of artificial intelligence for the automatic analysis of large volumes of acoustic data, development of free and standard tools, and interoperability between databases.
Ecological and societal applications: biodiversity monitoring, biomass estimation, study of trophic interactions, spatial management support (protected areas, wind turbine installation), and contribution to international conservation objectives.

Network actions

Organisation of an annual meeting with the aim of promoting discussions and the presentation of work.
Targeted assistance for the mobility of RT members: doctoral students, project development, participation in conferences.
Organisation of technical workshops on specific topics and methodologies.
Encouraging the sharing of expensive tools and workspaces, enabling the supervision of the use, loan and calibration of these tools

Network partners

Network coordination

Mathieu Doray (DECOD), Jean Guillard (CARRTEL), Jérémie Habasque (LEMAR), François Martignac (DECOD), Aurore Receveur (MARBEC), based on a network that has been active since 2003.

Contact : If you are interested in the network, please contact Jérémie Habasque.

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28/05/2025/by sherve@univ-brest.fr

Fish acoustics for monitoring the effects of overfishing and climate change on food security in West Africa

An acoustic study, whose first author is a Senegalese former thesis student of Lemar, has revealed a notable northward shift in the spatial distribution of small pelagic fish species exploited in the waters of the Sub-Regional Fisheries Commission (northwest Africa). The results, covering a period of two decades of acoustic halieutic surveys conducted by sub-regional acoustics experts aboard the F. Nansen vessel (IMR, Norway), highlight the impact of rising sea surface temperature and changes in upwelling intensity on marine ecosystems in the sub-region. Mauritania and Senegal are observing a strong increase in sea surface temperature and a decrease in its primary productivity, while the region further north is experiencing a continuous increase in upwelling. Significant spatial anomalies in sea surface temperature have contributed to the northward shift of several small pelagic fish species, including Sardinella aurita (round sardinella), species highly prized in Senegal.

The study emphasizes that the Senegalo-Mauritanian zone has experienced the most pronounced warming of surface waters among all intertropical regions in the world in recent decades. The study identified significant anomalies in sea surface temperature around Cape Blanc and to the south, ranging from 0.1 to 0.3 °C per decade, influencing fish distribution. During the study period, Sardinella aurita displayed a northward shift of approximately 180 km, coinciding with an increase in sea surface temperatures and reduced primary productivity in the south. The northward shift of small pelagic fish poses potential economic and social challenges, particularly for countries such as Senegal, where fisheries are a source of numerous jobs and contribute to food security, and Mauritania, where fisheries contribute significantly to gross domestic product.

Fishmeal factories and fishing fleets are already contributing to severe overexploitation of small pelagics, particularly Sardinella aurita. The effects of climate change (cumulative with those of overexploitation) exacerbate the pressure on these valuable fishery resources. Changes in fish distribution can disrupt the entire marine food chain, affecting biomass production and species composition.

The study underscores the need for regular monitoring and increased research efforts to better understand the dynamics of this marine ecosystem and ensure the sustainability of fishery resources, vital for the countries concerned. This is particularly important for protecting food security and the economic well-being of coastal communities in West Africa.

The results call for strengthening national fisheries research structures, expertise in acoustic halieutics, and the need for sub-regional collaboration on transboundary fish stocks to prevent potential fishing-related conflicts and manage resources sustainably. Moreover, it is urgent to address overfishing and the impacts of fishmeal production, which adds an additional threat to the effects of climate change on exploited small pelagics.

The CRODT[1], IMROP[2], INRH[3], FD[4] and IRD, are committed to advancing marine research. They emphasize the importance of adaptive management strategies, concerted at the sub-regional level (countries of the Sub-Regional Fisheries Commission (CSRP)), to address current and future challenges posed by climate change and overfishing.

Scientific Contact

Patrice.Brehmer@ird.fr *

*Corresponding author of the scientific publication

Article Link (Springer nature, Scientific report)

Abdoulaye Sarre, Hervé Demarcq, Noel Keenlyside, Jens-Otto Krakstad, Salaheddine El Ayoubi, Ahmed Mohamed Jeyid, Saliou Faye, Adama Mbaye, Momodou Sidibeh, & Patrice Brehmer*. Climate change impacts on small pelagic fish distribution in Northwest Africa: trends, shifts, and risk for food security Scientific Report, 12434 (2024). https://doi.org/10.1038/s41598-024-61734-8

Photographs, including aerial and underwater:

https://multimedia.ird.fr/IRD/search.do?q=Brehmer+Patrice&lang=fr

[1] Centre de recherche océanographique de Dakar Thiaroye, Senegal

[2] Institut Mauritanien de Recherches Océanographiques et de Pêches

[3] Institut National de Recherche Halieutique, Morocco

[4] Fisheries Department, The Gambia

03/07/2024/by Sebastien Herve

The Warmalis 3 oceanographic campaign!

News, news homepage

Oceanographic Campaign Warmalis 3: Understanding the Functioning of the Pelagic Oceanic Ecosystem and Ultimately Determining its Influence on Tuna Resources in the Western and Central Pacific Region

The WARMALIS 3 campaign, taking place from September 25 to November 8 aboard the R/V ANTEA, aims to better understand the functioning of the pelagic oceanic ecosystem and determine its influence on tuna resources in the western and central Pacific region, which account for more than 50% of global catches. In particular, the campaign studies intermediate trophic levels (zooplankton and micronecton), which constitute the primary food for all large pelagic species in the Pacific. To achieve this, biological data (micronecton trawls, zooplankton nets, EK80 sonars, and acoustic profilers), as well as physical and chemical data, are collected.

Example of micronecton capture, with gelatinous organisms, small fish, and shrimp commonly consumed by tuna and other top predators (Photo: V. Allain, SPC-IRD).

WARMALIS 3 is the last in a series of three campaigns (2021, 2022, 2023) part of the MICROPAC project (Micronecton in the Pacific, 2021-2023) led by Christophe Menkès (IRD/UMR ENTROPIE) and Valérie Allain (CPS) with partner units: MIO, IMAGO, LEMAR, LOPS, LEGOS, and CLS. After exploring the western and central Pacific from south to north in previous years, the crew is undertaking a 45-day east-to-west traverse along the equator this year.
Four colleagues from LEMAR are on board: Laure Barbin, Jérémie Habasque, Anne Lebourges, and Anaïs Médieu.

Campaign plan for Warmalis 3.

You can follow the ship’s log on the mission blog.

03/12/2023/by sherve@univ-brest.fr

RESILIENCE oceanographic cruise – 19 April to 24 May 2022

News

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 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

Instagram:https://www.instagram.com/uf_resilience @uf_resilience

06/05/2022/by titodemora

Acoustic ecology

Discovery-thematic, research thematic

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.

05/10/2018/by sherve@univ-brest.fr

New methodologies for observing coastal marine environments are being developed.