Don’t forget the porpoise: acoustic monitoring reveals fine scale temporal variation between bottlenose dolphin and harbour porpoise in Cardigan Bay SAC

Abstract

Populations of bottlenose dolphin and harbour porpoise inhabit Cardigan Bay, which was designated a Special Area of Conservation (SAC), with bottlenose dolphin listed as a primary feature for its conservation status. Understanding the abundance, distribution and habitat use of species is fundamental for conservation and the implementation of management. Bottlenose dolphin and harbour porpoise usage of feeding sites within Cardigan Bay SAC was examined using passive acoustic monitoring. Acoustic detections recorded with calibrated T-PODs (acoustic data loggers) indicated harbour porpoise to be present year round and in greater relative abundance than bottlenose dolphin. Fine-scale temporal partitioning between the species occurred at three levels: (1) seasonal differences, consistent between years, with porpoise detections peaking in winter months and dolphin detections in summer months; (2) diel variation, consistent across sites, seasons and years, with porpoise detections highest at night and dolphin detections highest shortly after sunrise; and (3) tidal variation was observed with peak dolphin detections occurring during ebb at the middle of the tidal cycle and before low tide, whereas harbour porpoise detections were highest at slack water, during and after high water with a secondary peak recorded during and after low water. General Additive Models (GAMs) were applied to better understand the effects of each covariate. The reported abundance and distribution of the two species, along with the temporal variation observed, have implications for the design and management of protected areas. Currently, in the UK, no SACs have been formally designated for harbour porpoise while three exist for bottlenose dolphins. Here, we demonstrate a need for increased protection and species-specific mitigation measures for harbour porpoise.Electronic supplementary materialThe online version of this article (doi:10.1007/s00227-017-3081-5) contains supplementary material, which is available to authorized users.

Fine scale spatial variability in the influence of environmental cycles on the occurrence of dolphins at coastal sites

“…All possible interactions were included in the models as tensor products (function ‘ ti’ ), as recommended when the main effects and any lower interactions are also present 82 . The importance of each term was determined by removing them sequentially from the model 16 and exploring the variation in the Akaike Information Criterion (AIC) 83 . Once the main interactions were determined for each of the sites, full tensor product smooths (function ‘ t2 ’ and ‘ te’ ) were used in the final models.…”

“…As an example of that flexibility, marine mammals exhibit a full spectrum of responses to environmental cycles. Studies of the effect of seasonal, tidal and diel cycles on their behaviour have produced highly variable results 16,17 . However, whilst interactions between different environmental cycles have been described for some of their prey, there is a lack of information about more complex responses in marine mammals.…”

Presentation of Binning-Based Inter-Click Interval Data from Passive Acoustic Monitoring of Free-Ranging Harbour Porpoises (Phocoena Phocoena)

“…Harbour porpoises (Phocoena phocoena) are small toothed cetaceans that emit Narrow Band High Frequency (NBHF) communication and echolocation clicks almost constantly, 7,8 and can be collected with a range of underwater Passive Acoustic Monitoring (PAM) systems. 9,10 One example of a static (non-towed) PAM device is the C-POD (Chelonia UK), which has become increasingly popular because it is accurate, 11 robust, can be left in situ for many months (March 2018 record: 338d:09h:24m, Todd, V.L.G., unpublished observations), thus covering diel, tidal, and seasonal cycles, 12,13 and contains automatic processing software (C-POD.exe) which reduces signal analyses time significantly. 14 C-PODs (and their analogue predecessor, T-PODs), have been used widely to study many odontocete species, including inter alia, harbour porpoises.…”

High‐quality whole‐genome sequence of an abundant Holarctic odontocete, the harbour porpoise (Phocoena phocoena)

“…| 1471 pelagic fish and demersal prey (Fontaine et al, 2017;Hammond et al, 2008 and references therein), activity patterns (Nuuttila, Courtene-Jones, Baulch, Simon, & Evans, 2017) and fine-scale morphological features (Fontaine et al, 2017). This led to the suggestion that different ecotypes of harbour porpoise in the North Atlantic and Baltic Sea exist (Fontaine et al, 2014(Fontaine et al, , 2017Galatius, Kinze, & Teilmann, 2012).…”

“…Across their range, there is evidence for genetic subdivision among populations (Fontaine et al., , ; Wiemann et al., ) and significant isolation by distance (Lah et al., ). In addition to occupying different habitats, these populations differ in a number of features, including regional differences in diet with varying percentages of cephalopods, pelagic fish and demersal prey (Fontaine et al., ; Hammond et al., and references therein), activity patterns (Nuuttila, Courtene‐Jones, Baulch, Simon, & Evans, ) and fine‐scale morphological features (Fontaine et al., ). This led to the suggestion that different ecotypes of harbour porpoise in the North Atlantic and Baltic Sea exist (Fontaine et al., , ; Galatius, Kinze, & Teilmann, ).…”