Risso's dolphins (Grampus griseus) in a proposed Marine Protected Area off east Lewis (Scotland, UK), 2010–2017

Abstract

The coastal waters of east Lewis from the Butt of Lewis to Loch Erisort are a proposed Marine Protected Area (MPA) for Risso's dolphins (Grampus griseus). A total of 100.4 h (2006.4 km) of active search effort (Beaufort sea states ≤3) was collected during 72 dedicated boat surveys between 2010 and 2017 (primarily in August and September) in the southern part of the MPA and south to the Shiant Isles. Forty Risso's dolphin sightings and 24.1 h of encounter effort were recorded, predominantly along the southern and eastern Eye Peninsula in 20–40 m water depths and at distances <1 km from shore. Group size ranged from one to 50 animals (mean = 11.8 dolphins) and calves occurred in 37.5% of sightings. A total of 2404 shore-based scans (Beaufort sea states ≤3) carried out from Tiumpan Head between September 2011 and December 2017 resulted in 271 (11.3%) ‘dolphin-present’ scans. Dolphins were present year-round, with a seasonal increase between May and October. ‘Calf-present’ scans only occurred between April and October. Photo-identification images from 28 boat surveys produced a minimum population size of 117 animals. There was evidence of high inter- and intra-annual site fidelity, with individual dolphins photographically captured in up to six of the eight survey years, and between two and seven capture dates being recorded for over 45% of individuals within most years. The combined datasets support the importance of east Lewis for Risso's dolphins, and recommendations are made for ongoing monitoring of dolphin occurrence throughout the wider MPA.

Patterns and Trends in Cetacean Occurrence Revealed by Shorewatch, a Land-Based Citizen Science Program in Scotland (United Kingdom)

“…Shorewatch contributed to the proposal and subsequent designation of a Marine Protected Area (MPA), namely the North-East Lewis Nature Conservation MPA, particularly by providing data on winter sightings. Shorewatch data can be used to demonstrate inter-annual and inter-site variation in bottlenose dolphin sightings in a SAC (Embling et al, 2015) as well as more widely for harbor porpoise, minke whale and Risso's dolphin (Weir et al, 2019). As demonstrated in this study, they can be used to detect patterns, trends and changes in sighting rates of regularly sighted species.…”

First reported observation of an apparent reproductive bottlenose × Risso’s dolphin hybrid

“…In contrast, more than 200 Risso’s dolphins have been identified locally in various UK coastal studies, with indications that these individuals are part of a more open population (with individuals showing varying degrees of intra‐ and interannual site fidelity, matches between areas, and discovery curves that have not plateaued) (e.g. Atkinson, Gill & Evans, 1999; Baines & Evans, 2012; de Boer et al, 2013; Stevens, 2014; Eisfeld‐Pierantonio & James, 2018; Weir et al, 2019, and references therein). Furthermore, the total Risso’s dolphin population in European continental shelf waters has been estimated at >15,000 individuals for the summer of 2016 (Rogan et al, 2018; Hammond et al, 2021).…”

Using citizen science to better understand Risso’s dolphin (Grampus griseus) presence in northeast Scotland and the Northern Isles

“…Although there is limited understanding of the population structure of Risso's dolphins in the northeast Atlantic, previous research indicates genetic differentiation between UK (N=18; of which 16 were Scottish samples) and Mediterranean populations (Gaspari et al, 2007). In addition, whilst Risso's dolphins are believed to be fragmented in their distribution within Scotland, there is some evidence for site fidelity by known individuals (Weir et al, 2019).…”

“…Natural markings include distinctive nicks and notches in the dorsal fin, body scarring from intra-specific interactions, and injuries from fishing gears and vessels which do not re-pigment as readily as in other delphinids (Hartmann, 2018). Photoidentification is therefore appropriate for use as a research tool for Risso's dolphins (Atkinson et al, 1997;Hartmann et al, 2008;de Boer et al, 2013;Maglietta et al, 2018;Weir et al, 2019) to better understand the ecology of the species and identify potential threats (Hartmann et al, 2008;Urian et al, 2015;Weir et al, 2019).…”

“…However, research has shown that Risso's dolphins can sometimes occur in shallower waters, namely those less than 200m in depth, around the northeast Atlantic shelf (Jefferson et al, 2013;Bloch et al, 2012) and mainly over slopes of 50 to 100 metres along the European continental shelf, although in several areas of the British Isles they regularly inhabit coastal waters of between 20 and 30 metres depth (Evans et al, 2003). Around the west coast of Scotland, the Northern Isles of Orkney and Shetland, and the northern Scottish mainland, Risso's dolphins have frequently been encountered in shallow waters less than 20 metres deep and in close proximity to the shore (Robinson et al, 2007;Evans et al, 2011;Weir et al, 2019;Orkney Marine Mammal Research Initiative (OMMRI), 2021; OMMRI, unpublished data 1 ; OWIARC, unpublished data 2 ; SWF, unpublished data 3 ; WDC Shorewatch, unpublished data 4 ).…”