INDIVIDUAL IDENTIFICATION OF GREEN TURTLE (CHELONIA MYDAS) HATCHLINGS Ellen Ariel, Loïse Corbrion, Laura Leleu and Jennifer Brand Report No. 15/55 Page i
INDIVIDUAL IDENTIFICATION OF GREEN TURTLE (CHELONIA MYDAS) HATCHLINGS Report No. 15/55 OCTOBER 2015 Prepared by Ellen Ariel, Loïse Corbrion, Laura Leleu and Jennifer Brand Centre for Tropical Water & Aquatic Ecosystem Research (TropWATER) James Cook University Townsville Phone : (07) 4781 4262 Email: TropWATER@jcu.edu.au Web: www.jcu.edu.au/tropwater/ Page ii
Information should be cited as: Ariel, EM, Corbrion, L, Leleu L & Brand, JR, 2015, Individual Identification Of Green Turtle (Chelonia Mydas) Hatchlings, Centre for Tropical Water & Aquatic Ecosystem Research (TropWATER) Publication, James Cook University, Townsville, 8 pp. For further information contact: Ellen Ariel Centre for Tropical Water & Aquatic Ecosystem Research (TropWATER) James Cook University ellen.ariel@jcu.edu.au Building 97, 1 Solander Drive, James Cook University, Douglas 4811, Queensland, Australia This publication has been compiled by the Centre for Tropical Water & Aquatic Ecosystem Research (TropWATER), James Cook University. James Cook University, 2015 Except as permitted by the Copyright Act 1968, no part of the work may in any form or by any electronic, mechanical, photocopying, recording, or any other means be reproduced, stored in a retrieval system or be broadcast or transmitted without the prior written permission of TropWATER. The information contained herein is subject to change without notice. The copyright owner shall not be liable for technical or other errors or omissions contained herein. The reader/user accepts all risks and responsibility for losses, damages, costs and other consequences resulting directly or indirectly from using this information. Enquiries about reproduction, including downloading or printing the web version, should be directed to ellen.ariel@jcu.edu.au Acknowledgments: Thanks to the many dedicated volunteers who were involved in collecting, hatching and raising these green turtle hatchlings. Page iii
EXECUTIVE SUMMARY This study assessed the viability of three methods for identification of specific green turtle hatchlings in environments with multiple individuals. Methods tested were: plastron markings with permanent and nonpermanent marker, plastron markings with nail polish, and physical characteristic recognition. Results show that non-permanent marker pen markings dissolved immediately, followed by non-permanent marker pen markings within one week, and these methods are the least successful for long term study. Nail polish markings remained on the marginal scutes for the study duration (three weeks), and identification was both rapid and accurate. Unique characteristics were observed in all 12 hatchlings, proving it is possible to differentiate between a limited number of individuals based on features such as number and positioning of scutes, colouration and symmetry. Ease of method and speed of identification were considered, as well as invasiveness of methods and subsequent distress. Both nail polish markings and characteristic recognition were successful in individual hatchling recognition. However due to relatively low invasiveness and capture and handling stress caused to the individual, as well as ease of marking application and identification, the nail polish method is concluded to be the most appropriate method for individual hatchling identification during the 3 week study. Future research should monitor the longevity of nail polish markings over an extended period, as well as comparing this marking with novel methods. Monitoring individual characteristics over the life cycle of individuals will also provide greater insight into how features may change and develop, which will benefit individual identification both in captivity and in wild populations. Page i
TABLE OF CONTENTS EXECUTIVE SUMMARY... Error! Bookmark not defined. 1 INTRODUCTION... 2 2 METHODOLOGY... 3 2.1 Markings with permanent and non permanent marker pens... 3 2.2 Markings with nail polish... 3 2.3 Individual characteristic recognition... Error! Bookmark not defined. 3 RESULTS... 5 3.1 Markings with permanent and non permanent marker pens... 5 3.2 Markings with nail polish... 5 3.3 Individual characteristic recognition... 5 4 DISCUSSION... 7 5 CONCLUSION... 8 Page 1
1. INTRODUCTION In captivity it is vital to be able to identify specific hatchlings within a group in order to monitor growth, development and behaviour. Gross morphology of green turtle hatchlings (Chelonia mydas) is consistent across individuals; however subtle physical characteristics may differ between individuals. These notable differences occur particularly on the plastron and carapace, such as scute numbers and relative position, pigment concentration, and asymmetry. Whilst these features can be useful to identify individuals, markings may allow for faster, more accurate identification of individuals. However, the invasiveness and longevity of such markings must be taken into consideration to maximise efficacy and ensure minimal stress to the animal. This study investigates three methods of individual identification, considering the aforementioned factors. Page 2
2. METHODOLOGY Twelve C. mydas hatchlings, raised from eggs at the James Cook University (JCU) turtle research health facility, were used in this study, ranging from 6-7 cm curved carapace length (CCL) in size, and weighing 36-45 g. For the first two weeks of the study, hatchlings were kept individually in 12 small tubs in shallow, 20 C water. In the third week, the 12 hatchlings were all transferred into a single tank with 28 C water, large and deep enough for swimming and diving. They were fed daily on a diet of turtle hatchling pellets, while separated into individual tubs to monitor food consumption. Hatchlings were cleaned under running tap water each day, by rubbing the carapace and plastron to remove dirt, and dried once a week with paper towels prior to weighing. The turtle hatchlings were kept under JCU Animal Ethics A2124 and a QPWS/EHP management action directed by Dr Andrew Dunstan. The methods to be tested were as follows; 2.1. Markings with permanent and non-permanent marker pens Each hatchling was marked across the pectoral scutes on the plastron (same position for each hatchling), three in permanent marker (red) and three non-permanent (blue), (Figure 1). Figure 1: Markings made with pens across plastron pectoral scutes. Blue markings made with a non-permanent marker, red markings with a permanent marker. 2.2. Markings with nail polish Nail polish markings were painted according to a numbering system of marginal scutes. Chelonia mydas have one central scute behind the head (nuchal scute) and 11 marginal scutes on each side. Scutes were counted in a clockwise fashion from the first marginal scute on the right hand side (Figure 2); the scute closest to the nuchal scute on the right is the 1st scute, and the scute closest to the nuchal scute on the left hand side would be the 22nd marginal scute. Hatchling 1 had the 1st marginal scute painted, hatchling 4 the 4th, and so on. The whole scute was covered with white nail polish to observe if chips formed over the duration of the study. Page 3
A B C Figure 2: Markings made with nail polish on marginal scutes. A) Blue circle indicates first marginal scute. Red circle exemplifies a marked scute, in this case the 4th marginal scute, identifying it as hatchling 4. B) 9th marginal scute marked, identifying it as hatchling 9. C) 12th marginal scute marked, identifying it as hatchling 12. Photographs taken 23/06/15. 2.3. Individual characteristic recognition Photographs of the plastron and carapace of every hatchling were taken to identify any distinguishable individual characteristics (Figure 3). To assess if these features were sufficient, blind tests were undertaken, in which volunteers matched live hatchlings with labelled photographs. Each photograph could be used more than once to prevent process of elimination bias in results. Noticeable features included plastron characteristics such as relative proportions of scutes, colour markings and chin spots on the head. Figure 3: Plastron photographs of 6 hatchlings, showing variation in physical characteristics. Identity of hatchlings was hidden during blind tests. Arrows point to chin spots on some individuals. Page 4
3 RESULTS 3.1 Markings with permanent and non-permanent marker pens Non-permanent marks (blue) disappeared immediately upon immersion. Permanent marks (red) lasted longer; some disappeared by day three (3), others after one week (Figure 4), but some lasted the duration of the three week study. After three weeks, three hatchlings lost all marking, but three remained with at least one distinct marking. In most cases, the markings on the periphery were lost before those in the centre. Figure 4: Photograph of each hatchling s plastron 1 week after marking. 3.2 Markings with nail polish Two weeks after marking, the nail polish on two of the 12 turtles were chipped, but most of the polish remained on the scute. The polish on the other 10 hatchlings was intact. This condition remained for the duration of the study. 3.3 Individual characteristic recognition Initial observations noted a difference in the number of central scutes on the carapace, as three hatchlings had six central scutes whereas the other nine had only five (Figure 5). Further observations noted differences between presence of extra scutes, plastron colouration and symmetry, chin spots, peripheral scutes, and scute collars (Figure 6). After final observations, defining characteristics were identified for each of the 12 hatchlings. Results of blind test show that only one individual was very difficult to recognise, as only 20% of blind test subjects could recognise it. Another two hatchlings had 60% of subjects recognise it, but all other individuals had 100% recognition across the blind tests. The hatchlings with 100% recognition had more obvious characteristics, making identification much easier. Page 5
A B Figure 5: A) Hatchling 9 with five central scutes. B) Hatchling 12 with six central scutes. Figure 6: Photographs of plastron highlighting examples of observable individual characteristics, text boxes give hatchling ID and date of photograph taken. H11) Hatchling 11 had two extra scutes on the tail. H1) Hatchling 1 had a more pronounced scute collar than most. H4) Hatchling 4 had an asymmetrical plastron. H7) One of the peripheral scutes on Hatchling 7 touches only two other scutes, whereas most touch three others. Page 6
4 DISCUSSION Markings made with marker pens (both non-permanent and permanent) faded very quickly, usually faster on the peripheral scutes. This could be as a result of regular contact and abrasion with the floor of the tanks, as well as flippers during swimming. Furthermore, daily cleaning of hatchlings to remove dirt may accelerate the fading of the markings. If this method was to be employed for individual identification, markings would have to be reapplied every few days, which would be inefficient and distressing to the animal. Therefore, this is considered the weakest method for identifying individual hatchlings out of the three methods tested in this study. Nail polish markings on the carapace remained completely intact on ten hatchlings for the study duration (three weeks), with two hatchlings showing only minor chips. This method is more suitable for individual identification than marker pens, as nail polish markings need to be reapplied less frequently. Nail polish markings are also advantageous over marker pens as they are on the carapace, rather than the plastron, making it possible to identify individuals from above. This is beneficial as in order to clearly see markings on the plastron, the individual must be caught and turned over, which can be distressing to the animal, and as they grow, more challenging for the handlers. As such, not having to do this by marking the carapace instead makes identification easier as well as reducing stress to the animal. Lastly, whilst there are only 22 marginal scutes on C. mydas, other scutes could be incorporated into the numbering system, as could different shapes and colours of markings, allowing for a much larger pool of mark identities. Identifying individuals according to physical characteristics proved successful when one specific feature, unique to each hatchling, was identified. It also became easier for individuals to be recognised as the handlers spent more time with them. However, in order to identify distinguishing characteristics, the hatchlings must be closely examined, and out of water to view the plastron (which often shows the greatest inter-individual variation). This may be distressing to the individual, particularly if the examination takes a while. Furthermore, some features such as colouration may change throughout the individual s life, particularly in hatchlings and juveniles; turtles over 15 years of age often have a completely white plastron. It is also possible that scutes may change in relation to each other. As a result of this, identifiable characteristics may change or be lost over time, so these changes would have to be monitored regularly. However, during the three weeks of this study, no significant changes to identifiable features were observed. This shows that over a short timescales, individual characteristics can provide reliable identification of individuals, although it is a slower and potentially more distressing method than using markings. Page 7
5 CONCLUSION In order to recognise individual hatchlings, different methods of marking and recognition were tested. Nail polish appears the most successful method tested in this study, as it is a long-lasting and easily-applied marking, and identification is fast and accurate. However, it is also possible to identify individuals based on characteristic recognition. Most of these characteristics occur on the plastron, but sometimes the carapace can also show unique features. Although initial examination and identification of these characteristics is slow and potentially distressing, the process of identification quickens as handlers recognise individuals more easily over time. This study concludes that nail polish carapace marking is the least invasive and stressful for the animal, the marking process is the most straightforward, and identification of individuals is the fastest of the three methods tested. Page 8