Largest croc loses ground

24 August 2005

Abstract Crocodile skins can be fairly accurately graded at all stages of processing so that faults such as brown spot and scarring, which impact on the final value of the leather, result in a large reduction in the raw skin value. Faults range from poor husbandry, through butchery to inadequate preservation. The opportunity for improvement in skin quality ceases at the point of slaughter so that husbandry should aim at having quality peaking at that point. Animals with skins that are less than first grade should be assessed for their potential and retained, if suitable, until a first grade is achieved. Competent butchering and effective preservation will then ensure maximum return. Faults due to poor preservation are very common in the industry, resulting in scale slip, grain damage and loss of strength. Salt alone is not sufficient to protect skins from bacteria for an extended period of time and this includes red heat and fungi. As an aid to determining the significance of faults seen on the live animal, marks and damage that are observable on the raw skin have been photographed and tracked through to finished leather. It has been found that some apparently minor brown spot infections can cause major pitting of the leather grain, while severe scale erosion may not affect the finished leather. Partially regrown scales often appear as crescents ('double scaling') on the leather and faint scars may also show up very clearly. Introduction The Australian Saltwater Crocodile (Crocodylus porosus) is the largest crocodilian species and reputedly produces the best quality crocodile leather in the world. High demand for skins and excessive poaching greatly reduced their numbers and resulted in the establishment of crocodile farming in Australia from 1972, which is credited with reducing the threat of extinction of C. porosus in the wild. The main farm income is derived from crocodile skins for the fashion leather industry, although crocodile farming also produces meat and generates significant tourism revenue. However, the market share and price for C. porosus skins is declining due, in part, to increased production overseas of other species with lower production costs and to declining quality as measured by the skin grades being achieved. The small scale of production and the limited capabilities for further processing in Australia may also be factors contributing to the decline. C. porosus is a slow-growing, aggressive animal involving relatively high costs. Although the skin attracts prices of the order of US$9 per cm of width for the first grade, or US$360 for a 40cm skin, profit margins are not large and are subject to drastic variability. In addition to changes in the US$ price offered by buyers, the amount received in A$ is subject to exchange rate fluctuations. Due to the ease with which faults can be seen in the raw skin, lower grade skins are heavily discounted. Traditionally, each downgrade has cost 25% of the potential value of a skin with 1st grade earning 100%, 2nd grade 75% etc. However the grade premium is at times even higher with some buyers refusing to take second or lower grades at all. Quantifying the loss in value from downgrading is problematic due to fluctuating exchange rates and prices and industry confidentiality. However, as an indication, in the last ten years, the proportion of 1st grade C. porosus skins being produced has reportedly fallen from about 50% to 20%. For an industry production currently of approximately 10,000 skins with a value as first grades of around A$600 each, the decline in first grades alone is a loss of around $0.4m pa and potentially well over $1 million for all grades. This fall in grade quality has both reduced returns and moved C. porosus skins more into competition with lower quality and cost species. Differentiation, cost reduction and increased quality are thus areas where the Australian industry can make significant improvements. Of the various causes of poor skin quality or productivity, the animal-husbandry problems such as poor fertility, growth and nutrition; skin damage from sharp edges and fighting; skin infections etc, have been or are being solved. For example, individual 'grow-out' pens are currently being trialled in the industry, to reduce skin cuts, scratches and scars before slaughter. Costs of skin processing and damage to skins after slaughter, for example from fleshing and poor preservation, were identified as areas still to be addressed. Effective preservation is critical because if poorly preserved, crocodile skins can quickly deteriorate in the warm humid environment in which they are produced. Putrefaction and the action of autolytic enzymes naturally present in the skin can cause scales to fall off ('scale slip') and the resulting leather to be scuffed, weak or even perforated. The development of rapid and effective short and long term preservation procedures that are appropriate to the Australian crocodile farm environment is a requisite to improving quality. An important component of preservation is storage under appropriate conditions. C. porosus skins are unusual compared with sheepskins and cattle hides (which comprise the vast majority of the tanning industry raw material) in that the grain surface of the raw skin in the prime cutting area from which the highest value items are made, can be clearly seen and graded according to the quality of leather it will make. This leads both to the high grade premium and losses due to faults, and also to an opportunity to influence the quality prior to slaughter. However, it was apparent that there was some uncertainty about the cause and identity of various blemishes seen in the skin of the live animal and their significance in the final leather. Therefore, experiments were conducted to analyse blemishes in the raw skin and track their appearance through to finished leather and develop a pictorial guide. Preservation The principle reason for crocodile farming to exist in Australia is to produce crocodile skins to satisfy market demand for C. porosus leather. It is, therefore, absolutely essential that, in the first instance, the quality of skin on the live animal prior to slaughter is as high as it can be and, second, that the quality be maintained right through to the finished leather. It must be borne in mind that the quality of the skin can still be improved up to the point of slaughter but only maintained or degraded from slaughter onwards. Also that, by virtue of their large surface area and pre-existing heavy microbial contamination, skins are at least as susceptible to putrefaction as the meat. As soon as the animal is slaughtered, there is both loss of immune response and development of autolytic protein breakdown which render the skin very susceptible to microbial damage. Microbial attack commences immediately, continues at low temperatures and is cumulative and accelerating. If not preserved adequately, severe damage will occur to skins held at 30°C for several hours (either continuously or in total with intervening cool storage) or up to several days at 5°C. Damage may be indicated by scale slip (Figure 1), discolouration such as 'red heat' (Figure 2), or the smell but there may be no signs at all until the end of tannage and finishing when the grain surface is found to be dull, discoloured or scuffed (Figure 3), resulting in a heavy loss in value for the tanner. Usually bacterial attack occurs first, resulting in scale slip and odour. Fungal attack is slower and results in staining and surface erosion but is much more difficult to prevent. To avoid or minimise damage, skins should be preserved against microbial attack as soon as possible, preferably commencing before skinning, with a preservative that is suited to the task and applied correctly. Untanned skins are also susceptible to heat, with damage occurring immediately on contact with any surface over 60°C, or on prolonged contact at 50°C. These temperatures can easily be reached by objects left in the sun, by operating machinery and even by the friction of hard rubbing. Contact with hot water and steam are also common sources of heat damage. Care must be taken to ensure that fresh skins do not dry out before preservation, especially on hot, windy days. Uncontrolled drying will cause brittleness and preservation problems as well as difficulties in tanning uniformly. Short term preservation processes are applied, usually starting before the carcass is skinned and proceeding through to several days after, to protect skins and allow them to be handled for grading, trimming, measurement or brief transport. If skins are to be held for more than about four days before processing to leather, it is necessary to apply a long-term preservation treatment. This should aim to preserve the skins for the anticipated time and conditions in storage including an appropriate safety margin in case of delay or high temperatures. The short-term preservation should contribute to the long-term preservation process, rather than having to be reversed or discarded. Long-term preservation has traditionally entailed the use of extremely large amounts of salt without other preservatives. However, halophilic bacteria and fungi are able to grow in these conditions and damage skins, and the salt adds weight, making grading and measurement more difficult. The halophilic bacteria commonly appear as red or purple stains ('red heat'). Although these bacteria are not themselves severely damaging, they are a clear sign of preservation failure and that other more damaging but less obvious organisms are likely to be present. Salted skins are routinely stored in a cool room because the salt alone is an inadequate preservative. During storage, preserved skins are still susceptible to damage from insect and rodent attack, overheating, or contamination from detergents, chemicals and solvents. Water can dissolve and remove or redistribute the preservative. Dirt or contamination can cause preservatives to break down prematurely or to be rendered ineffective. Iron or rust particles coming into contact with the skin cause a brown iron stain that is extremely difficult to remove or hide and which can react with tanning agents to form dark blue or black patches. In summary, skins should be undamaged, cool, clean, protected and preserved. It is important that preservation be appropriate, adequate and efficient and that the storage conditions do not cause deterioration or damage. The preservative must be safe to handle by the producer and by the processor and not interfere with the tanning process. Various countries impose import bans on leather containing particular chemicals and so it is important to ensure that only currently acceptable preservatives are used. Fault Identification The blemishes on crocodile skins, particularly in the valuable main panel area of the belly, are readily visible both in the live animal and post mortem. The various marks are used to estimate the value of the skin as finished leather and a grade given accordingly. For the live assessment, the option exists to slaughter the animal or retain it in order to allow blemishes (cuts, infections, scars, partial scales etc) to heal and fade, perhaps with intervention, depending upon the expected costs, risks and returns. Whether or not the animal is alive, the assessment allows the producer to identify causes of damage and, hence, loss and to make changes to the husbandry and early stage processing practices. In order to make changes that are cost-effective and successful, the producer must be in a position to accurately identify blemishes and predict their impact on the finished leather value. However, because of the subjective nature of the assessments, the lack of a permanent record and the very limited body of information relating raw skin appearance to finished leather quality, both identification and estimation of the significance of blemishes was highly variable. Therefore, the objective was made to capture a pictorial record of a batch of skins in the raw state, in the partially tanned state (wet-blue) and as finished leather and prepare a reference catalogue for producers. Methodology The approach taken was to photograph the blemishes on a batch of 100 raw preserved skins prior to dispatch to a processor in Japan; to intercept them at the partially tanned state during the Japanese visit; and again as the finished leather is in transit through Australia to their final destination. The views of the processor on these and other skins were also obtained. Approximately 1,000 digital images were collected of 20 raw skins from the batch of 100 bearing various faults. The corresponding partially tanned (wet-blue) and fully finished leather was also photographed as far as possible and assessed for their value in informing the producer about the appearance and consequence of various blemishes. Five examples of faults of interest that could be tracked and where images were sufficiently clear are presented below, as pairs of pictures of an area of raw skin and the corresponding finished leather. The images of wet-blue were of limited value because of practical difficulties and are not included. This may in fact be a preferable point at which to compare the raw skins as the chrome tanned leather (either in the wet-blue or dried state) is of uniform colour and surface gloss, and defects have not yet been hidden. Figure 4 illustrates the effect of brown spot (a common bacterial infection) on the raw skin (left) and the finished leather. Even relatively minor lesions can cause severe pitting in the grain surface that is a major contributor to loss in value. Also evident is a tooth cut that when processed to finished leather created a hole. This would also result in complete loss of this area of the leather at significant cost. Figure 5 illustrates the effect of recently healed teeth marks (left) in the final leather (right, arrowed), where they are clearly visible after finishing. Falling as they do in the central area of the main panel, the scars would have maximum negative effect on the value of the skin. Figure 6 shows one area of severe scale erosion analogous to brown spot (Figure 4), which results in a badly pitted grain surface (right, arrowed). However, other areas of scale erosion, particularly where it is associated with sloughing or abrasion, may look poor but nevertheless hardly affect the finished leather. It is important to be able to distinguish the cause and depth of damage to determine whether it is a high priority for remediation. Figure 7 shows the phenomenon of 'double scaling' which appears to be due to retention of partially sloughed scales as the new scales are growing. It results in a distinctive crescent or circular impression in the finished leather (right, upper edges of scales) and may cover much of the skin area. Also present are numerous eroded and scarred areas. Figure 8 demonstrates how even fully healed and very faint scars can still appear in the finished leather and oblige the tanner to apply a heavier or more opaque finish than would otherwise be needed. It is essential that as far as possible, cuts and lesions be prevented as even faint blemishes will show clearly in the most valuable pastel-coloured or lightly finished leathers. The development of a catalogue of faults to provide some guidance to producers was heavily constrained by a number of factors. As this objective was added to an existing project at short notice and with very limited resources, it should be viewed as a pilot exercise to explore the value, feasibility and logistics of a larger effort. A handheld digital camera and flash or ambient lighting was used. Many images were of limited value because of flaring and shading effects. Photography of this type of substrate is very problematic and requires specialised equipment and controlled conditions. Unfortunately, it was not possible to influence the finish applied to the various skins as the coating, colour and pigment were selected by the processor to hide the observable defects as far as possible in order to improve the leather value. Thus, the surface gloss, opacity, depth and colour vary drastically from one sample to another and make photography very difficult. This shows how faults in the skin result in the processor having to apply more time and resources to produce a lower value, more heavily finished leather. The skins were sampled at only one time in the year, when the production schedule was least appropriate, and at only one producer. A selection of times more appropriate to realistic production timetables and a broader representation of producers would ensure that the skins would be more representative of the range and appearance of the various faults. A future exercise should seek to conduct the photography in a studio environment. Conclusions and recommendations Despite the limitations of the present study, the results were well received by the industry and support exists for a more comprehensive effort. A preferable approach might be for a project to acquire all of the skins necessary and record good quality images of the raw skin faults. The skins could then be processed under contract to a uniform colour and finish, selected for the clarity with which faults are visible, and returned for final imaging. As the process is non-destructive, skins could be sold, faults, finish and colour notwithstanding, to recoup some of the cost.

Privacy Policy
We have updated our privacy policy. In the latest update it explains what cookies are and how we use them on our site. To learn more about cookies and their benefits, please view our privacy policy. Please be aware that parts of this site will not function correctly if you disable cookies. By continuing to use this site, you consent to our use of cookies in accordance with our privacy policy unless you have disabled them.