Scar Tissue Formation Around Tag Sites

Floy Dart tags as used by the SSTP are widely used around the world and as such the effects of dart tagging is well researched. While healing from a tag may take longer than a normal wound due to the presence of the tag, the shark’s body will eventually form an area of fibrous scar tissue around the tag site. It is important to note that in the scientific study by Heupel & Bennett (1997) – cited in the above article – tagging produced only minor, localized disruption in sharks and that no secondary infections were ever observed. Inflammation was only observed as part of the natural healing process and formation of scar tissue.

The Common Skate tagging programme (particularly around the west coast of Scotland) has an exceptionally high recapture rate. The programme currently has an overall recapture rate of 50.39% and a higher recapture rate in popular fishing areas; the vast majority of shark tagging projects worldwide have a recapture rate of less than 5%, often over several decades. With so many recaptures and so many fish recaptured numerous times it is important to bear in mind that tagged skate will inevitably be seen at all stages of the of the healing process: recaptures have been recorded just hours after tagging up to 20 years after tagging, and everywhere in between!

Some swelling around the tagging site is entirely natural and is an important part of the shark’s immune response to a foreign body; this should not be confused with infection.

Over the past three months we asked anglers (and all boats participating in our annual Skate Tagathon) to take photographs of the tag site on any recaptures and to make a note of the tag number, this allows us to go to our database and find out when the fish was tagged. Some photos of tag sites are shown below.

This image shows a perfectly healed tag site, the dark area around the tag is an area of fibrous scar tissue. (>1 year at liberty) This image shows a perfectly healed tag site, the dark area around the tag is an area of fibrous scar tissue. (>1 year at liberty)
Another well healed tag, the circular scars on this skate are the result of large leeches feeding on the fish. We have been told that extensive parasitic infection is more likely to lead to infections in skate than tagging. The tag site above shows inflammation, a normal part of the healing process. Inflammation like this arises when the fish is trying to shed the tag, eventually the swelling will decrease and fibrous scar tissue will form around the tag as shown in the other images. (<1 year at liberty)
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Another well healed tag with a ruler to give an idea of scale (in cm’s) Another well healed tag with a ruler to give an idea of scale (in cm’s)


One fish captured during the Tagathon (pictured below, left) showed extensive scarring from “handles” often cut by commercial fishermen and used to return skate when they are caught accidently. These handles would have been cut right through the skate leaving two large holes, as you can see from the photograph this skate has healed completely. The second picture shows a skate with handles which have healed leaving holes. This gives some indication of the robustness and regenerative capabilities of a large Common Skate.

slit in fishphoto

We urge anyone who has concerns about the tag site on a recaptured fish to email with details which must include where/when captured, name of captor, the tag number and if possible a photograph of the tag site. Without these we are unable to make any meaningful analysis.

The SSTP have long recognised that appropriate tag placement and good tagging practice are vital to the programme. As such, the SSTP offer tuition in handling and tagging sharks in the form of a short, free course that has now been running for almost 2 years. Please refer to the SSACN Plastic Dart Tagging Guidelinesfor more information on good tagging practice.

Finally, we ask that anglers do not attempt to remove tags from fish. Floy dart tags are designed to resist removal and it is possible that forced removal will cause damage to a tagged fish. Please also be aware that inflammation is much more likely to arise through natural healing processes and the formation of scar tissue than through secondary infection due to tagging.

If you are interested in tagging sharks, or if you are experienced tagger who would like a refresher course, please send an email to


In an earlier article we discussed how the healing process around a tag site works and how the natural auto-immune response of elasmobranchs to plastic dart tags may in some rare cases appear to cause a sore around the tag.

In an update to the article we published a letter from Dr Francis Neat at Marine Scotland who has a wealth of experience in tagging and tracking fish. In this letter Dr Neat stated that the most likely cause of inflammation around a tag wound was that insufficient time had passed between tagging and recaptures to allow proper healing.

Note :: Tagging of Common Skate along parts of the west coast of Scotland has now ceased, thanks in part to the hard work of all the volunteer anglers and members of SSACN,  following the creation of a statutory instrument to protect many species of shark in Scottish waters (including Common Skate). However the SSTP will continue to record all recaptures.

Category: Shark Bites

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