Analysis of occurrence patterns and biological factors of cetaceans based on long‐term and fine‐scale data from platforms of opportunity: Madeira Island as a case study

Abstract

Management and conservation issues are addressed through the identification of areas of particular importance, which requires the acquisition of baseline information on species distribution and dynamics. These types of data are particularly difficult to obtain at high resolution for large marine vertebrates like cetaceans, given that dedicated surveys are complex and logistically expensive. This study uses daily presence–absence sighting data of cetaceans collected year‐round from whale‐watching boats to support the theory that fine‐scale data obtained from platforms of opportunity can provide valuable information on species occurrence and group dynamics. Data from 7,551 (daily) sightings comprising 22 species were collected from 3,527 surveyed days over 11 years (mean of 321 days per year, SD = 17) in the pelagic environment of Madeira Island. Cetaceans were observed on 92% of the surveyed days, and a mean of 15.4 (SD = 1.5), 8.2 (SD = 2.0) and 2.1 (SD = 1.2) species were recorded per year, month, and day, respectively. There were significant differences in the number of species per month (p < .001), with the highest diversity recorded in June. At least nine species, comprising 96% of all sightings, were found to use the Madeiran waters on a regular basis, such as the Atlantic spotted dolphin (Stenella frontalis), the short‐beaked common dolphin (Delphinus delphis), the bottlenose dolphin (Tursiops truncatus), and others featured in the Red List of the International Union for Conservation of Nature as Endangered, Vulnerable, and Data Deficient. In addition, 10 species were found to use the Madeiran waters for travelling, feeding, resting, socializing and calving, which suggests that the southern and southeastern waters of Madeira Island constitute an area of interest for cetaceans. This study characterizes the cetaceans’ community structure (occurrence, aggregation sizes, behaviours, proportion of calves, and inter‐specific relationships) of a poorly studied region, providing important information for managers. Finally, the advantages and limitations of using fine‐scale data from a type of platform of opportunity that is increasing along coastlines globally are discussed.

Complex biogeographical patterns support an ecological connectivity network of a large marine predator in the north‐east Atlantic

“…Possible biases include obtaining lower sighting rates from larger areas or from areas less used/preferred by the whales. It is known that short‐finned pilot whales prefer habitats located between the 1000 and 2500 m isobaths and in submarine canyons (Abecassis et al., ; Thorne et al., ), and in our study, those habitats comprised most of the surveyed areas (Alves et al., ; Servidio, ; Silva et al., ), thus minimizing bias. Nevertheless, researchers should standardize a sampling method in future surveys to allow comparing densities.…”

“…It has a wide distribution from tropical to warm‐temperate waters (Olson, ), and on a global scale, its conservation status is described as data deficient and its population trend is unknown (IUCN, ). In the north‐east Atlantic, the species is considered common in the biogeographical region of Macaronesia (which includes the archipelagos of the Azores, Madeira and Canaries), especially around the Canaries and Madeira where it is consistently among the most frequently sighted cetacean species reported throughout the year (Alves et al., ; Servidio, ; Silva et al., ), but only sporadically in the surrounding waters of the Iberian Peninsula (e.g., Nores & Pérez, ).…”

Using cost-effective surveys from platforms of opportunity to assess cetacean occurrence patterns for marine park management in the heart of the Coral Triangle

“…Since the amount of additional data was limited, no inferential statistical analysis could be performed, therefore it only was reported descriptively. Behavior of cetaceans was classified into four categories: (i) travellingnormally moving animals on a steady course, (ii) resting -stationary in one place, almost without movement, (iii) socializingclear and constant interaction between the animals in a normally stationary group, and (iv) foragingnon-synchronized movements and very active animals, normally involving the visualization of prey or aggregation of birds (Alves et al, 2018). We added (v) 'bow riding' as a special category, since the behavior is prevalent in small cetaceans, and it shows a cue of being attracted to vessels (Anderwald et al, 2013).…”

“…Due to the lack of GPS tracks, sighting frequency could not be reported as the number of sightings per km or per hours surveyed, as is commonly done (Alves et al, 2018). Instead effort was recorded as days surveyed.…”

Distribution and habitat modelling of common dolphins (Delphinus delphis) in the eastern North Atlantic

“…These factors include the conditions of the platform of observation, survey design, state of the weather during the survey, distance to the sighted animal(s), species detected, size of the group, and, ultimately, the ability of the observer to detect and identify the species. In the ENA, at least 36 cetacean species have been recorded, both resident and migrating, in coastal and oceanic areas (e.g., Hazevoet & Wenzel, 2000;Hazevoet et al, 2010;Weir et al, 2010;Carrillo et al, 2010;Alves et al, 2013;Hammond et al, 2013;Weir & Pierce, 2013;Goetz et al, 2014;Silva et al, 2014;Berrow et al, 2015;Correia et al, 2015;Dinis et al, 2016;Djiba et al, 2015;Tobeña et al, 2016;Jungbult et al, 2017;Dinis et al, 2017;Alves et al, 2018;Alves et al, in press). All In the ENA, common dolphins (Delphinus delphis Linnaeus, 1758), are among the most frequently sighted cetacean species (Correia et al, 2015;Goetz et al, 2014;Silva et al, 2014;Hammond et al, 2013;Tobeña et al, 2016;Jungblut et al, 2017;Alves et al, 2018).…”