Improving the quality of Australian crocodile skins A report for the Rural Industries Research and Development Corporation by S. Charlie Manolis, Grahame Webb and Ken Richardson February 2000 RIRDC Publication No 00/21 RIRDC Project No WMI-1A © 2000 Rural Industries Research and Development Corporation. All rights reserved. ISBN 0 642 58051 0 ISSN 1440-6845 Improving the quality of Australian crocodile skins Publication No. 00/21 Project No. WM1-1A The views expressed and the conclusions reached in this publication are those of the author and not necessarily those of persons consulted. RIRDC shall not be responsible in any way whatsoever to any person who relies in whole or in part on the contents of this report. This publication is copyright. However, RIRDC encourages wide dissemination of its research, providing the Corporation is clearly acknowledged. For any other enquiries concerning reproduction, contact the Publications Manager on phone 02 6272 3186. Researcher Contact Details S. Charlie Manolis PO Box 530, Sanderson, N.T. 0813 Phone: (08) 89224500 Fax: (08) 89470678 Email: [email protected] RIRDC Contact Details Rural Industries Research and Development Corporation Level 1, AMA House 42 Macquarie Street BARTON ACT 2600 PO Box 4776 KINGSTON ACT 2604 Phone: 02 6272 4539 Fax: 02 6272 5877 Email: [email protected]. Website: http://www.rirdc.gov.au Published in February 2000 Printed on environmentally friendly paper by Canprint ii Foreword There is no doubt that the demand for crocodilian skins that existed in the mid- to late 1980s is a thing of the past. Grading standards have become and will remain much stricter than they ever were before. Attempts to improve the quality of skins have largely been restricted to varying diet and husbandry techniques to minimise obvious external problems (e.g. scars, scratches, stretching). There has been no attempt to assess the structural correlates, and feedback in this area is a matter of simply waiting to see what happens when tanners and manufacturers deal with the results. Preliminary discussions with some of the world's best tanners of crocodilian skins (in France, Japan, Singapore) indicate that they are largely ignorant of the morphological characteristics that dictate skin quality. But they do know that wild skins are invariably of higher quality than farm-raised skins. This project, like the Australian research carried out on crocodilian egg incubation, takes a largely unknown field of critical commercial significance, and attempts to develop a sound understanding of the processes involved in skin development, that can be applied to existing problems. In many conventional animal industries (e.g. beef, pork, chicken), the emphasis is on increased size (for meat). This project directs research at the key marketable product of crocodile farming (the skin), rather than at what is essentially a byproduct (meat/size) of the industry. This report, a new addition to RIRDC’s diverse range of over 450 research publications, forms part of our New Animals Products R&D program, which aims to accelerate the development of viable new animal industries Most of our publications are available for viewing, downloading or purchasing online through our website: • downloads at www.rirdc.gov.au/reports/Index.htm • purchases at www.rirdc.gov.au/pub/cat/contents.html Peter Core Managing Director Rural Industries Research and Development Corporation iii Contents Foreword .................................................................................................................. iii List of Tables and Figures ....................................................................................... v Executive Summary................................................................................................ vii Introduction............................................................................................................... 1 Objectives ................................................................................................................. 2 Methodology ............................................................................................................. 2 Embryological development of skin.......................................................................................2 Skin samples.........................................................................................................................2 Variation in skin pattern ........................................................................................................3 Level of heritability and effect of incubation temperature on skin pattern .............................3 Industry perceptions..............................................................................................................4 Results....................................................................................................................... 5 Embryological development of skin.......................................................................................5 Variation in skin pattern ........................................................................................................8 Level of heritability and effect of incubation temperature on skin pattern .............................9 Farmed crocodiles ..............................................................................................................15 Wild versus farmed crocodiles ............................................................................................20 Industry perception .............................................................................................................22 Discussion .............................................................................................................. 24 Implications............................................................................................................. 27 Recommendations ................................................................................................. 27 References .............................................................................................................. 28 iv List of Tables and Figures Table 1. Distribution (%) of scale row counts for Crocodylus porosus hatchlings from 64 clutches, in areas from which 5 or more clutches were represented. Numbers in brackets indicate the numbers of clutches. Mean scale row counts (means of means) are also shown. Table 2. Difference between the highest and lowest scale row counts within 85 clutches of wild Crocodylus porosus eggs. Table 3. Mean scale row counts for 9 clutches of Crocodylus porosus eggs incubated at constant 31, 32 and 33C. Numbers in brackets are range, sample size and standard error respectively. Table 4. Mean scale row count of the progeny of adult Crocodylus porosus males for which two or more clutches were produced over three nesting seasons (1996/97 to 1998/99). N= sample size; SE= standard error. Table 5. Mean thickness of skin components and their percentage contribution to the total skin, from 19 sites (N) which have been divided into two groups (A and B; see text), for Crocodylus porosus at hatching (28 cm total length) and 0.7 m total length (1 year old). ‘Total Epidermis’ includes the keratin layer. Table 6. Mean thickness of skin components and their percentage contribution to the total skin, from 19 sites (N) which have been divided into two groups (A and B; see text), for Crocodylus porosus near (1.1 m; 2 years old) and at normal culling size (1.6 m; 3 years old). ‘Total Epidermis’ includes the keratin layer. Figure 1. Mean thickness of the periderm, stratum corneum keratin and total epidermis in the skin of Crocodylus porosus embryos, from 14 days to 1 day post-hatching. Lines indicate regressions. Age is time of incubation at 30C. Figure 2. Mean thickness of loose, dense and total dermis in the skin of Crocodylus porosusembryos, from 14 days to 1 day post-hatching. Up to 30 days, the total dermis is composed of loose dermis. Lines indicate linear regressions. Age is time of incubation at 30C. Figure 3. Figure 3. Mean thickness of the total skin of Crocodylus porosus embryos. Age is time of incubation at 30C. Figure 4. Relationship between mean scale row count and constant incubation temperature for hatchlings from 8 clutches of Crocodylus porosus hatchlings. See Table 3 for data. Figure 5. Mean scale row counts for clutches incubated at 32C for 13 days, ‘pulsed’ at different temperatures for the equivalent of 20 days of 30C development, and then returned to 32C to complete incubation. Means are means of clutch means (N= 3); error bars indicate 2 standard errors. v Figure 6. Difference between mean scale counts for Crocodylus porosus eggs at different pulse temperatures and that at 32C (standard). Eggs were pulsed for the equivalent of 20 days of 30C development. Means are clutch means; error bars indicate 2 standard errors. The regression relationship was highly significant (see text). Figure 7. Mean scale row count for Crocodylus porosus eggs shifted from 30C to 33C at different ages (2 day intervals). Data are means of clutch means (N= 3); errors bars are 2 standard errors. Figure 8. Mean scale row count for eggs shifted from 33C to 30C at different ages (5 day intervals). Data are means of clutch means (N= 3); errors bars are 2 standard errors. Figure 9. Mean scale row count for eggs shifted from 33C to 30C at different ages (2 day intervals). Data are means of clutch means (N= 2); errors bars are 2 standard errors. Figure 10. Mean