seaturtle.org : MTN : ARCHIVES : Sign In

Marine Turtle Newsletter 2:4-8, © 1977

More on the Tag Loss Problem

A number of letters on tag loss have been received. The relevant excerpts of those letters are printed below with only minor editorial changes,

Rantau Abang in the State of Trengganu, Malaysia is one of the two known major nesting beaches for the Leathery Turtle (Dermochelys coriacea). The 12 miles nesting beach is facing the South China Sea. Turtles start to come in early April, and by the end of September, they disappear completely.

Trial tagging was conducted by the late Dr. E. Balasingam of the University of Malaysia, in 1966, The work was reported in the Malayan Nature Journal vol. 25 (1972) by Balasingam and Tho Yow Pong as follows.

"During the trial tagging two types of tags were used to mark and identify the female turtles, namely Monel metal tags and plastic tags. The former was obtained from the National Band and Tag Company, U.S.A. The plastic tags which are ordinary cow tags were obtained from Dalton supplies, United Kingdom. Both types of tags were fitted on to the animal with the aid of tag applicators. The tags are applied approximately half way down the fore flipper about 1.5 - 2 inches from the trailing edge of the flipper. The plastic tags were applied on the right flipper and the Monel metal tags on the left flipper.

Some initial difficulties were experienced in the application of the tags. This was particularly true of the Monel tags, some of which did not fit firmly into the flippers. This was possibly due to the fact that the flippers were too thick to accommodate the tag's clinching mechanism. Another common snag was that the turtle's flipper being rather fleshy, the Monel tags, especially when loosely applied, tended to enlarge the perforation and tear the flesh at the region of the application. A number of Monel tags were lost in this manner after tagging. The plastic tags on the other hand were far more satisfactory because they were easy to apply and fitted well into the flippers. Among turtles which returned to nest after tagging, no losses of the plastic tags were recorded.

The most satisfactory time for the application of tags was when the turtle had just finished egg-laying. The turtle then did not react adversely to the application of the tags."

Following the successful application of the plastic cow tag, full scale tagging was launched in 1967. Personnel engaged by the Fisheries Department patrolled the entire nesting beach throughout the night starting in April and ending in September, recording and tagging all turtles coming ashore. Up to the end of this year's season a total of 9,533 tags were applied. The return of tagged turtles is satisfactory, and a number of reports on sighting of the tagged turtle were received from Japan, Philippines, and Indonesia. In 1973 orange colored tags with the appeal "Please release this turtle and inform Fisheries Department Kuala Trengganu, Malaysia" were introduced to replace the original white tags with numbers only.

So far only a few turtles were found with enlarged holes on the right flipper indicating the loss of the plastic cow tag. However, these tags might have been removed by human beings as one report in 1972 informed us that the tag was removed and kept as a souvenir before the turtle was released.

On the whole, we found that the plastic cow tag or the "Jumbo Rototag" as the supplier calls it, is satisfactory for this tagging work, and it has the following advantages over the metal Monel tag:

1. It is easy to apply.
2. It secures firmly on the flipper.
3. It does not corrode.
4. It can have the color wanted and with wording printed.

Siow Kuan Tow,
State Director of Fisheries,
Kuala Trengganu, Malaysia.

Between 1970 and 1975, Peter Pritchard, Miguel Cifuentes (now Intendente del Parqu Nacional de Galapagos), and various assistants of Pritchard tagged about 800 green turtles. The tagging took place only during the nesting season and on selected nesting beaches, thus all animals, apart from a couple of males, were females. From Sept. '75, two beaches were studied for 5 1/2 months. At least 95% of the turtles nesting on Quinta Playa that season were tagged (315 tagged). Since the study started in September, we have used a double tagging system - the standard monel cattle ear tag on the right foreflipper and a colored plastic tag (Jumbo Rototag, Dalton, Henley, England) on the trailing edge of the right hindflipper. In the latter case a hole is made first with a leather punch in order to prevent buckling during insertion. Results so far have showed advantages and disadvantages of both. For nesting females on Quinta Playa, 3 out of 315 lost their metal tags but none lost their plastic ones. On Baltra, it was the reverse - out of 165 tagged, 3 lost the plastic ones and yet no metal ones were lost. On two occasions a plastic tag has been found near a net, where an entangled tagged turtle managed to free itself from the net but having its tag wrenched off during the process. With some turtles tagged either at the nesting beaches or at the feeding grounds, the plastic tags became covered with a filamentous green alga within a month which in a couple of cases made the number (but not the color) unreadable. This is perhaps indicative of a sedentary type of existence. The numbers on plastic tags could be read either on the beaches or whilst in the water without disturbing the turtles at all, whereas with the metal tags turtles either, have to be caught in the water or disturbed while nesting in order to read the numbers. On the other hand, a turtle tagged in 1970 by Peter Pritchard was seen nesting again this year (1976) - its tag in perfect condition and easily readable. One important advantage that the plastic tag has over the metal one is that it is fixed outside the flipper and can be seen to be good or not, whereas the metal one joins inside the flesh and can only be tested by trying to pry it apart.

We will continue to use the double tagging system as it serves our purposes - VIZ plotting inter-island migration (a different color for each nesting beach and feeding lagoon readily identifies the place tagged) and our efforts to determine the most suitable type of tag to use.

Derek Green,
Principal Field Investigator,
Galápagos Green Sea Turtle Ecology Study,
Estacion Biologica Charles Darwin,
Isla Santa Cruz, Galápagos

At Isla Aves, where I have been tagging since 1971, tag loss through failure of monel cattle ear tags is a major problem. For example, last year, we had two remigration returns with tags and twenty without. The latter were unquestionable tag losses which carried a callas with a central perforation in the area we normally position the tag. Additional possible tag losses with flippers torn or suspiciously scarred in that area were tallied separately.

This rate of loss does not reflect poor application techniques. Because of the small number of turtles handled each season (150-200), each tag is examined for proper clenching before an animal is released. As an aside, the number of tags damaged in application has been reduced by pre-punching a hole through the flipper with a modified vise grip welding clamp. This is a quick procedure and almost assures proper clenching.

Based on the use of a fairly permanent secondary mark, the rate of tag loss during our brief tagging season at the nesting site (3-6 weeks) is almost nil, contrary to Schulz's experience. Since the tag loss problem became apparent two years ago, we have been cutting coded notches in the marginal bones using a simple system derived from my computer work, which permits individual recognition of animals independent of the monel tags. We had a number of remigration returns from two years ago. On all animals retaining tags from two years ago, the notches had healed partly but the numerical code remained readily and unambiguously readable. No animal which bore a tagging scar in the flipper, but no tag, was notched.

The sample of recovered tags I have examined is small, but at least one shows significant corrosion and in another the clenched tip appeared to have been gradually straightened out. A significant proportion of smaller tags (chicken-wing) of the same style which were applied to animals held in captivity for a year showed corrosion and some were ready to break in the portion of the tag embedded in the flipper tissue.

My overall impression is that in a corrosive environment like sea water the monel tags in common use today are designed to self destruct at the small retaining bar which holds the clenched tip of a closed tag. Corrosion is excited at sharp, deformed corners, such as are adjacent to the bar and will produce cracks, eventually causing it to break away. The implication in the IUCN Marine Turtle Newsletter (No 1, 1976) that some sort of relative motion is necessary for crack formation is erroneous, but it would accelerate the process.

Cursory comparison of the tags I used this year with a few recovered examples suggests that the width of the retaining bar on the tags varies from year to year (presumably different dies) and I would be inclined to predict that survival of the tags used this year will be relatively poor because of more severe distortion at the end of the bar.

The form and mode of application of the present tag are convenient, but it needs to be redesigned so that there are no sharp corners in the closure. A minimum modification approach would be to lengthen the tag which is clenched and put round holes in the lower bar (see sketch).

A change of materials for the tag would be beneficial, but would not eliminate the need for tag redesign. Contrary to the statement of the Newsletter (no. 1, 1976) the present alloy, Monel, Inconel, and a third Chromel A (which was suggested to me as the most resistant) all contain substantial amounts of nickel:

Inconel work hardens rapidly so probably some modifications of the current tag-making process would be required. I do not favor a shift to a plastic tag, because, despite the superior resistance of some plastics to sea water, they are vulnerable to abrasion long-term.

William E Rainey,
Island Resources Foundation,
P.O Box 4127, St Thomas,
U.S. Virgin Islands 00801.

I now have 3,000 specially produced INCONEL tags. The National Band and Tag Company gave me the product that I asked for. Now only time will tell if they are as corrosion resistant as the alloy specialist at Huntington Alloys, International Nickel, predicted they would be. Contrary to Mr. Rainey's interpretation about relative motion being necessary for crack formation, the statement in the IUCN Marine Turtle Newsletter (no. 1, 1976) is in reference to "working" of the metal in the manufacturing process, that is, in the process of forming the metal into strips, and shaping and stamping in the tag production process. This "works" the metal and can cause microscopic cracks.

Again, corrosion doesn't always take place at the locking mechanism in MONEL tags. It most often takes place where the tag is in contact with the internal tissue. Granted, this is usually the locking mechanism end, but frequently the tag will move around to another site, sometimes intermediate between the locking end and the curved end. In such cases, the number or return address will become obliterated.

As you may recall, my main purpose in working so hard and long on this INCONEL project was to have an intermediate size (#681) tag of superior corrosion resistance for use in my studies of growth, survival and travels of less-than-adult size turtles.

I have thought about your suggestion in the newsletter concerning application of both INCONEL and a second type of tag on each turtle in order to assess performance. As far as MONEL goes as the second tag, I have decided against it. It would seem to me that by placing INCONEL and MONEL on the same turtle I might be creating a situation analogous to a storage battery. That is, dissimilar metals immersed in the body fluids. Perhaps I would be creating the conditions that would cause the alloys to deteriorate (though electrolysis). Perhaps I will try a plastic (chemically inert) tag as a second comparison.

George Balazs,
Hawaii Institute of Marine Biology
P.O. Box 1346,
Kaneohe, Hawaii 96744, U.S.A.