Temporal patterns in habitat use by small cetaceans at an oceanographically dynamic marine renewables test site in the Celtic Sea

• Published in: Deep Sea Research Part II: Topical Studies in Oceanography
• Main Authors: Cox, SL, Witt, MJ, Embling, CB, Godley, BJ, Hosegood, PJ, Miller, PI, Votier, SC, Ingram, SN
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2017
• Subjects: Earth Observation - Remote Sensing; Marine Sciences; Oceanography; Harbour porpoise; Phocoena phocoena
• Online Access: http://plymsea.ac.uk/id/eprint/7479/; http://plymsea.ac.uk/id/eprint/7479/1/Cox_PaperRevisions_MarineMegafaunaSpecialIssue_Draft.pdf; https://doi.org/10.1016/j.dsr2.2016.07.001

Shelf-seas are highly dynamic and oceanographically complex environments, which likely influences the spatio-temporal distributions of marine megafauna such as marine mammals. As such, understanding natural patterns in habitat use by these animals is essential when attempting to ascertain and assess the impacts of anthropogenically induced disturbances, such as those associated with marine renewable energy installations (MREIs). This study uses a five year (2009–2013) passive acoustics (C-POD) dataset to examine the use of an oceanographically dynamic marine renewable energy test site by small cetaceans, dolphins (unspecified delphinids) and harbour porpoises Phocoena phocoena, in the southern Celtic Sea. To examine how temporal patterns in habitat use across the site related to oceanographic changes occurring over broad seasonal scales as well as those driven by fine scale (bi-weekly) localised processes (that may be masked by seasonal trends), separate analyses were conducted using (1) all daily animal detection rates spanning the entire five year dataset and (2) daily animal detection rates taken only during the summer months (defined as mid-June to mid-October) of 2010 (when continuous monitoring was carried out at multiple discrete locations across the site). In both instances, generalised additive mixed effects models (GAMMs) were used to link detection rates to a suite of environmental variables representative of the oceanography of the region. We show that increased harbour porpoise detection rates in the late winter/early spring (January–March) are associated with low sea surface temperatures (SST), whilst peaks in dolphin detection rates in the summer (July–September) coincide with increased SSTs and the presence of a tidal-mixing front. Moreover, across the summer months of 2010, dolphin detection rates were found to respond to small scale changes in SST and position in the spring-neap cycle, possibly reflective of a preference for the stratified waters immediately offshore of the front. Together, ...