Assessing the value of opportunistic and dedicated data to analyse cetacean occurrence and distribution

• Autor(a) principal: Branco, Alexandre Miguel Quelhas de Sousa Marques
• Data de Publicação: 2022
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10773/36573
• topic: Platforms of opportunity; Cetacean monitoring; Distribution; Delphinus delphis; Physeter macrocephalus; Ziphius cavirostris; Balaenoptera acutorostrata

The CETUS Project is a cetacean monitoring program that, in partnership with the TRANSINSULAR company and the Hydrographic Institute, uses the ships as platforms of opportunity to carry out cetacean monitoring along transects between mainland Portugal, the Macaronesian archipelagos, and Northwest Africa. In this project, data have been collected by dedicated cetacean observers, in monitoring effort (on-effort), as well as by other members of the crew or when observers were not in monitoring effort, and so, in an opportunistic way (off-effort). So far, on-effort sightings have been more widely used, as they allow a better standardization of data using survey effort measures. The main goal of this work is to determine the value of the data collected in a dedicated and opportunistic way to analyse cetacean occurrence and distribution. We used data from the most sighted species (with a greater number of records), more or less easy to detect / identify; a) Common dolphin - most sighted species, easily detected and identified; b) Cuvier’s beaked whales - species difficult to detect and to identify; c) Minke whale - species easily detected but difficult to identify; d) Sperm whale - species that are difficult to detect but easily identified. Data were processed in Excel, where some of the descriptive analyses were also carried out, the statistical tests were developed essentially in R environment, and the ArcGIS was used for the spatial analysis. We selected five environmental variables (depth, Slope, distance to coast, sea surface temperature, and chlorophyll), as proven by other works to have a bigger impact on these cetaceans’ occurrence. Cuvier's beaked whale showed significant differences in all variables except for distance to shore and the minke whale showed significant differences in distance from shore and chlorophyll, proving that these two species have a different distribution depending on whether they were recorded opportunistically, or dedicated. Therefore, for species with few records, opportunistic data plays an important role as complementary information. On the other hand, both sperm whales and common dolphins showed no significant differences between the two types of sightings We should continue to use opportunistic sightings to complement cetacean data with particular importance for offshore and difficult-to-identify species.