Since the 1950s, the flipper tag has been a standard research tool of sea turtle biologists. Its key features include a ‘unique’ identification code on the front of each tag and a return address on the back, often offering a reward as an incentive for the return of the tag. (Most programmes that offer rewards do so only for international tag returns. And increasingly, the type of reward offered is a t-shirt or a cap.)
The original flipper tag was a ‘cow ear tag’ made of monel metal. But, over the years new versions have been developed with improved locking mechanisms and corrosion resistant alloys. Plastic tags are sometimes used but may be more liable to entanglement in gill nets.
Currently, the most commonly used flipper tags are the following:
- Stockbrands Titanium tags (40 x 11 x 10 mm) - produced by Stockbrands Company, Mt. Hawthorne, Western Australia, Australia; and
- Style 681 Inconel (25 x 8 x 9 mm) - produced by National Band & Tag Company, Newport, Kentucky, USA.
The flipper tag enables researchers to recognise individual tagged turtles when they are subsequently encountered, either by the taggers themselves or by other persons who find and return the tag or report the tag number. This tool has enabled scientists to obtain information about the following:
Site fidelity in nesting females;
Periodicity of nesting (i.e., numbers of days separating nestings within a season; and years separating nesting seasons);
Numbers of egg clutches laid per season per female;
Migrations of adult turtles between nesting & foraging habitats;
Growth rates & age to maturity;
Local movements & long distance migrations of juvenile turtles relative to their developmental foraging habitats;
Survival rates of turtles; and
Baseline assessment of mortality factors caused by artisanal & commercial fisheries; etc.
To minimise unnecessary disturbance of the turtles and to maximise information gain, however, tagging studies need to be well planned.
Early tagging studies demonstrated long distance migrations of turtles between adult nesting and foraging habitats separated by 100s or even 1,000s of km. More recent studies show that migrations of immature turtles can be even more extensive -- sometimes involving the circumnavigation of entire ocean basins.
For the turtle tag to remain an effective tool with which to identify individual turtles, each tag needs to be unique. It is critical to prevent duplication of the tag numbers used. Given the extensive migrations of individual turtles, and the profusion of new tagging programmes around the world, it follows that there is a need to coordinate and standardise the codes used in the various tagging programmes -- both at the domestic and international levels.
Nor can one assume that the use of different tag styles or the presence of an address on the back of the tag will eliminate confusion. In fact, it is rare for people to check the back of a tag unless they actually remove it from the turtle. And in most cases, for example in long term monitoring programmes, the tag is not removed at all -- only the number is recorded. Nor can one assume accurate recording of tag style.
Proposal for Standardisation of Flipper Tag Codes
There is a need for simplicity to ensure accuracy.
Efforts to prevent duplication of tag numbers must take into account the following:
Success of any tagging programme hinges on accurate recording of the identification code. If even a single letter or number is omitted, misread, or transposed the information gathered will be useless (at best), or misleading;
Tag numbers are often read under difficult field conditions -- at night, in the rain, at sea on a rocking boat, etc; and
Critical information is often provided by relatively uneducated individuals -- i.e., fishermen or field personnel in third world countries. Often the code is reported, but the tag is not returned.
For these reasons, tag ID codes needs to be as simple as possible. The following guidelines would promote simplicity:
Use alphabetic letters as prefixes in the code, followed by numbers. But, use letters only in the prefix; the remainder of the code would be numeric; and
Minimise the numbers of numerals used. Most mistakes in tag transcription involve the numbers. To minimise error, ideally no more than four (4) numbers should be used in a code.
Desirability of National Codes:
If each country used a unique prefix code, the following problems would be solved:
Tagging programmes in separate countries would never again duplicate each others tag series; and
The country of origin would be obvious, thus facilitating international coordination of information gathered outside the country of origin.
It is suggested that in future, each country use its own unique ISO country code as the prefix for its tagging series. The two letter ISO country codes (produced by the International Organisation for Standardisation) for each country in the world can be found at: http://www.iso.org/.
The next issue is to maximise the numbers of unique codes possible, while maintaining the simplicity of a four number suffix.
A two letter prefix (the ISO country code) followed by a four or five digit number would produce almost 10,000 unique numbers (in the case of 4 digits).
For example, Kenya is currently a series based on “KE” followed by four numbers (KE 0001 to KE 9999).
A country that anticipates eventually needing more than 10,000 tags, but wishes to maintain the simplicity of a code having no more than four numbers could modify the system by adding a third letter to their (2-letter) ISO code.
For example, after Kenya has used tag number KE 9999, she may wish to produce a new series of tags with the following codes:
KEA 0001 - 9999
KEB 0001 - 9999
KEC 0001 - 9999 and so on to KEZ 0001 - 9999.
Such a system would allow almost 270,000 different combinations. In this case, accuracy might be enhanced by spacing the code to improve clarity. For example: KE A 0001.
Overview of the Current Situation:
Adoption of one the above systems as a standard, would apply to future production of tags. Good turtle tags are expensive, and most programmes currently have stocks of tags that they are using. In most cases, this would not be a problem.
An immediate need would be:
- To identify all tag series currently in use in the IOSEA region;
- Where confusion seems likely, to discontinue the use of duplicate tag series; and
- Identify a stable repository for the tag series in use, such as the IOSEA MoU Secretariat.