Cetacean sightings and strandings: evidence for spatial and temporal trends?

Abstract

Cetacean species and their habitats are under threat and effective marine management mitigation strategies require knowledge and understanding of cetacean ecology. This requires data that are challenging and expensive to obtain; incidental sightings/strandings data are potential underused resources. In this study, incidental cetacean sightings (N = 6631) and strandings (N = 1856) in coastal waters of Cornwall, south-west Britain (1991 to 2008) were analysed for evidence of spatial and temporal patterns or trends. Eighteen species were recorded sighted and/or stranded; key species were identified as bottlenose dolphin (Tursiops truncatus), harbour porpoise (Phocoena phocoena), common dolphin (Delphinus delphis), Risso's dolphin (Grampus griseus) and minke whale (Balaenoptera acutorostrata). There were significant decreases in bottlenose dolphin sightings and pod size but an increase in harbour porpoise and minke whale sightings. Cetacean strandings showed a recent decrease over time although there was a significant positive trend in harbour porpoise strandings that correlated with sightings. Incidence of sightings and strandings were both greater on the south coast than the north coast. When Marine Tour Operator data were analysed, distinct species-specific inshore and offshore habitat use was evident. With rigorous interrogation and editing, significant patterns and trends were gained from incidentally collected data, highlighting the importance of public engagement with such recording schemes and the potential of these underused resources.

Understanding the Distribution of Marine Megafauna in the English Channel Region: Identifying Key Habitats for Conservation within the Busiest Seaway on Earth

“…The significance of these waters is also evident for dolphins and porpoises [81]–[82]. Environmental characteristics that influence the distribution of small cetaceans appear to differ geographically, and by season as we found in this study; nevertheless factors such as depth, slope, proximity to the coast, tidal state, and SST repeatedly surface as being important habitat features [22], [89], [92]–[101].…”

Sixteen years later: Occurrence, group size, and habitat use of humpback dolphins (Sousa plumbea) in Algoa Bay, South Africa

“…(), which may have caused a change in grouping pattern (Arcangeli and Crosti , Pikesley et al . ) and displacement of individuals from the study area over time, as suggested earlier by Karczmarski et al . () and as seen in bottlenose dolphins off western Australia (Bejder et al .…”

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

“…The applied method provides a low-cost approach to obtain valuable long-term information for areas with limited or no specific monitoring effort over a wide geographic area (Delefosse et al, 2018). Although interpretation of nonsystematically collected data is difficult without measure of effort (Evans and Hammond, 2004), with stringent data filtering and quality control, valuable information can be obtained (Pikesley et al, 2012).…”