Whistle repertoire analysis of the short-beaked common dolphin, Delphinus delphis, from the Celtic Deep and the Eastern Tropical Pacific Ocean By Emily T. Griffiths Master of Science, Marine Biology School of Ocean Sciences Bangor University 2009 In association with: Sea Watch Foundation Abstract: Understanding the vocal repertoire of a cetacean species enables us to understand how they interpret their environment and their social interactions. The short-beaked common dolphin Delphinus delphis is one of the most widely distributed dolphins in the world. They emit narrow-band tonal whistles generally between 5-20 kHz, but can range from 1-50 kHz. Whistle characteristics from two geographically separate populations of D. delphis were analyzed and compared: the Celtic Deep in the southern Irish Sea and Eastern Tropical Pacific Ocean communities. The whistle parameters of both populations were measured, external confounding factors were assessed to determine how they contributed to variation, and visual whistle contour classification was tested against a quantitative whistle contour classification. The range of frequencies emitted by dolphins in the ETP were generally broader than those emitted in the Celtic Deep (global R=0.043, p<0.001; χ2=44.654, df=1, p<0.001). The different populations also showed differences in their whistle contour composition (χ2=8.535, df=1, p=0.003). Spatial and temporal factors such as water column depth, time of day, year and encounter location were examined and their effects on the common dolphin repertoire were investigated. Encounter location, water column depth and time of day were all found to have a significant influence. The visual classification system used by Ansmann et al. (2007) and the quantitative contour similarity (CS) technique used by McCowan (1995) were both applied to classify whistle contours from the ETP. The CS technique provided a good description (proportions of ascending and descending) of whistle slope tendencies, but ultimately did not identify general or clear whistle contour categories. The different vocal repertoires of the two communities could be attributed to the nature of the different locations, environmental and anthropogenic situational factors. ii Table of Contents: Title page……..……………………………………………………………... i Abstract……………………………………………………………………… ii Table of Contents………………………………………………………….. iii List of Figures………………………………………………………………. v List of Tables………………………………………………………………... v Declaration………………………………………………………………….. vi Acknowledgments………………………………………………………….. vii 1. Introduction…………………………………………………………. 1 1.1 Auditory biology…………………………………………..... 1 1.2 Vocalisations and Communication………………………. 3 1.2.1 Narrow-banded tonal whistles…………….....… 3 1.2.2 Community communication……………………... 5 1.2.3 Signature whistles……………………………….... 7 1.3 The short-beaked common dolphin, Delphinus delphis 7 1.4 North Eastern Atlantic (The Celtic Deep)………….. 12 1.5 Eastern Tropical Pacific Ocean...................................... 14 1.6 Objectives and Hypotheses……………………..…........... 17 2. Materials and Methods……………………….…………………… 18 2.1 Passive Acoustic Monitoring (PAM)…………………….. 18 2.1.1 Celtic Deep data collection………………………. 18 2.1.2 Eastern Tropical Pacific data collection………. 22 2.2 Spectrographic analysis…………………………………… 24 2.3 Whistle characteristics……………………………………. 27 2.4 Whistle classification…………………………........……… 29 2.4.1 Visual whistle classification……………………… 29 2.4.2 Contour Similarity (CS) whistle classification 31 3. Results…………………………………………......……………....... 32 3.1 Whistle contour type classification – the Contour Similarity (CS) technique………………….……………... 32 3.2 Celtic Deep and Eastern Tropical Pacific while comparison………..………………………………………… 37 3.2.1 Whistle characteristics…….…..………………….. 37 3.2.2 Whistle contour type……….……….............…….. 40 3.2.3 Regional locals within the Eastern Tropical Pacific............................................................................... 46 3.3 External factor effects on whistle type and characteristics………………………………………………. 48 3.3.1 Celtic Deep whistles and common dolphin behaviour………………………………................... 50 3.3.2 ETP whistle strength……………………………… 53 iii 4. Discussion…………………………………………………………… 55 4.1 The Contour Similarity (CS) technique verse visual classification…………………………………...…………… 55 4.2 Whistle repertoire for the Celtic Deep and ETP………………………………………………………....... 59 4.2.1 Equipment limitations…….......………………….. 60 4.2.2 Mean power and harmonics……………………… 61 4.2.3 Whistle strength………………………………....... 64 4.3 Confounding variable effects on common dolphin repertoire……………………………………………...…….. 65 4.3.1 Year correlations…………………..………………. 65 4.3.2 Diel correlations……………………………………. 66 4.3.3 Encounter and water column depth correlations 67 5. Conclusions………………………………………………………….. 70 Recommendations for further research………………………… 72 6. Bibliography……………………………………………………….... 74 7. Appendices…………………………………………………………... 82 7.1 Full whistle characteristic descriptive statistics…….... 82 7.2 Mann-Whitney U tests for variety in tow lengths…….. 96 7.3 Vessel sightings data from Celtic Deep, 2009…………. 97 8. Electronic Appendices 8.1 Vessel/hydrophone data from the ETP 8.2 Vessel/hydrophone/sightings data from the Celtic Deep, 2004 8.3 Vessel/hydrophone/sightings data from the Celtic Deep, 2005 8.4 Whistle parameters 8.5 Whistle points 8.6 k-means cluster analysis summary 8.7 Celtic Deep 2009 audio breakdown iv List of Figures 1.1.1 General delphinid sound reception cross-section………….. 2 1.2.1 Example of whistle parameters……………………………….. 5 1.3.1 Global distribution of Delphinus delphis………………………. 9 1.3.2 Short-beaked common dolphin coloration……………………... 10 1.4.1 Distribution in the northeastern Atlantic Ocean…………….. 13 2.1.1 Hydrophone set-up……………………………….........………….. 19 2.1.2 Celtic Deep survey area………………….………………………. 21 2.1.3 Eastern Tropical Pacific survey area…………………………. 24 2.2.1 Example of Adobe Audition v. 30………………………………. 25 2.2.2 Example of weak, moderate and strong whistle strengths... 26 2.2.3 Example of Raven Pro v.1.3…………………………………....... 27 2.4.1 Visual whistle classification system…………………………… 30 3.1.1 Summed F values…………………........………………………….. 33 3.1.2 Examples of whistles from k-means cluster analysis…….... 34 3.1.3 k-means cluster discriminant function plot (k=3)……………. 35 3.1.4 k-means cluster discriminant function plots………………..... 36 3.2.1 Whistle parameters (a)..………………………………………...... 38 3.2.1 Whistle parameters (b)...………………………………………….. 39 3.2.2 Whistle classification composition………………………………. 41 3.2.3 Whistle subtype frequency………………………..……………… 42 3.3.1 Whistle strength contour proportion………………………… 53 4.1.1 Random selection of whistles when k=15……………………… 58 4.2.1 Examples of whistle densities in the Celtic Deep and ETP…. 63 4.3.1 Histogram of select whistle parameters……………………....... 66 List of Tables 1.4.1 Whistle parameter comparison…………………………………... 15 3.2.1 Descriptive statistics of whistle parameters……………….. 40 3.2.2 Whistle characteristics for total whistle contour type….. 43 3.2.3 Whistle characteristics for Celtic Deep contour type…………. 44 3.2.4 Whistle characteristics for ETP contour type…………………. 45 3.3.1 Celtic Deep Spearman rank correlation…………………….... 48 3.3.2 Eastern Tropical Pacific Spearman rank correlation………. 49 3.3.3 Behaviour comparison…………………………….....……………. 52 4.1.1 Tursiops truncatus and Delphinus delphis whistle parameters comparison……………………………………..…….. 56 v Declaration: This work has not previously been accepted in substance for any degree and is not being concurrently submitting for any degree. This dissertation is being submitting in partial fulfilment of the requirement of Master of Science (M.Sc.) in Marine Biology. This dissertation is the result of my own independent work / investigation, except where otherwise stated. Other sources are acknowledged by footnotes giving explicit references. A bibliography is appended. I hereby give consent for my dissertation, if accepted, to be made available for photocopying and inter-library loan, and the title and summary to be made available to outside organisations. Signed ………………………………………………… (Candidate) Date……………………………………………………. vi Acknowledgements Firstly, I would like to thank my supervisor, Dr. Peter G. H. Evans, for the advice and support he has provided to me throughout the ups and downs and turn arounds of this long, extended project. It has been a pleasure. I would also like to thank the staff of the Sea Watch Foundation, particularly Daphna Feingold, for allowing me the opportunity gain practical field experience, expand my knowledge of cetacean research, play with acoustic technology, and generally being all around helpful and supportive. I am grateful to Dr. Julie Oswald for trusting me, a complete stranger, with additional data that aided in making this an incredibly interesting project. To Dr. Jonathan Gordon, for taking me out on his boat, good conversation, and providing me with two opportunistic recordings. A huge thank you to Dr. Ian McCarthy, for being understanding when things looked grim (throughout the years) and never saying no despite his phobia of a cetacean’s smile. To Andrew Scullion, Ina Ansmann and Natalie Bush for paving the way to this study and offering advice along the way. Thank you to Steve Lewis, Hanna Nuuttila, Dr. Karen Stockin for their assistance and contributions. To Dr. Matthias Green and Holly Pelling at SOS who stifled their laughs at my feeble attempts to use Matlab. To my fellow pirates of Mount St, I couldn’t have asked for four kinder strangers.