Seeing in the dark: A review of the use of side-scan sonar to detect and study manatees, with an emphasis on Latin America

Marine mammals are very diverse because of the oceanographic conditions of Mexican waters (where 36% of the current species worldwide are found); however, scientific research on many of these taxa is still at the basic stages. The goal of this study was to assess the scientific information available for these species and to determine research priorities through a GAP (from the acronym "Good", "Average", and "Poor”) analysis. Information from the abstracts of the meetings held by the Mexican Society of Marine Mammalogy (SOMEMMA) and online databases (SCOPUS and Web of Science) between 1998 and 2021 was analyzed using temporal (years), geographic (oceans or states), taxonomic (species), and thematic (topics) classifications. On average, of the 44 species included in the Mexican legislation, only 16 - included in 14 families (with most of the records) - are studied every year, Delphinidae (n = 500; 25.9%), Balaenopteridae (n = 335; 17.4%), and Otariidae (n = 316; 16.4%). The Gulf of California was the most studied region (35.4%), followed by the Northeast Pacific (19.3%), the Gulf of Mexico (15.5%), and the Caribbean Sea (6.9%). The most frequent topics were population ecology (32.9%), conservation (16.7%), and animal health (10.4%). A significant decrease in the taxonomic and thematic diversity of such studies has been noted since SOMEMMA meetings began to be held on a biennial basis. It is noteworthy that marine mammals are protected by Mexican Federal laws. However, stock assessments are not mandatory, therefore biological aspects and trends of several (mostly oceanic) species remain unknown in many places, especially in regions where academic and scientific institutions are not involved in marine science.

Section: Discussionmentioning

confidence: 99%

Trends and gaps in marine mammal research from Mexico during 1998 – 2021

Escobar-Lazcano

Morteo

Delfín-Alfonso

et al. 2023

“…The technique consisted of the use of side-scan sonar (Humminbird ® 998c SI Combo), referred simply as 'sonar' elsewhere in the manuscript, to detect and count manatees. This type of sonar has been used to detect manatees in various environmental conditions and habitat types (Gonzalez-Socoloske et al, 2009, Guzman et al, 2017Factheu et al, 2023;Gonzalez-Socoloske & Olivera-Gómez, 2023).…”

Section: Side-scan Sonarmentioning

confidence: 99%

Density and abundance estimation of West Indian manatee, Trichechus manatus, between the states of Ceará and Piauí, Northeast Brazil, using active acoustics

Choi Lima,

De Sousa Abessa,

Wedekin

et al. 2024

The West Indian manatee is one of the most threatened species in Brazil. The species has currently a patchy distribution from the state of Alagoas to the state of Amapá. The difficulty of observing manatees, especially in estuarine waters, is a challenge for conservation. Therefore, it is necessary to use new methodologies and technologies to solve manatee detection problems in their natural habitats. The goal of this study was to use an active acoustic method of detection to estimate manatee density and abundance in the estuarine complex of the Timonha and Ubatuba rivers, between the states of Ceará and Piauí, northeast Brazil. Data collection was conducted from a wooden boat with an outboard motor using a side-scan sonar. Sonar images were collected along line transects in three regions within the study area. Manatee abundance was calculated using distance sampling (Distance 6.0 software). There were 1,396 transection lines that totaled 863.6 km traveled in the study area. The observed general encounter rate was 0.089 group detected per kilometer traveled. The best detection model was the hazard-rate with no adjustment terms, resulting in a detection probability of 33.7%, and an estimated density for the entire study area of 9.19 manatees per km2. Abundance of manatees in the estuary was estimated to be 37 animals (CV% = 30.2, 95% CI = 21 - 66). The methodology using side-scan sonar proposed here was successful in the detection of manatees in the study area and in defining parameters for its use to estimate the population size using the distance sampling method. This study provides an estimate of manatee density and abundance in a key estuarine system along the northeast coast of Brazil, which can serve as a baseline for future studies and aid in the development of conservation strategies for the species. This is the first time this methodological approach has been used for manatee detection and abundance estimation in Brazil. We recommend the use of side-scan sonar in future West Indian manatee research.

“…Although these techniques have been shown to be useful to detect the presence of manatees, an efficient method to estimate density and abundance has not yet been developed; the low number of detections over a wide and variable area remains a challenge for the development of abundance and density estimates. New technologies such as passive acoustic monitoring and the use of multi-beam sonar are also being tested for this purpose (Gonzalez-Socoloske et al, 2022;Gonzalez-Socoloske & Olivera-Gómez, 2023).…”

Section: Habitat Distribution and Populational Aspectsmentioning

confidence: 99%

Advances in the knowledge of the biology and conservation of the Amazonian manatee (Trichechus inunguis)

Amaral

Marmontel

Souza³

et al. 2023

The last relevant work that reviewed the biological and conservation aspects of the Amazonian manatee (Trichechus inunguis) was published almost 30 years ago. In these three decades, scientific knowledge about the species has advanced substantially. This review article updates knowledge about the various biological and conservation aspects of Amazonian manatee, summarizing the information present in the literature. Topics such as morphology, habitat, distribution, population aspects, food and feedings habits, reproduction, behavior, health, threats, status, and conservation efforts were addressed. The main actions already carried out, as well as the future strategies needed for the conservation of the Amazonian manatee, are also highlighted.