October 25, 2011 Featured Article Read More →

“Sores” on Tagged Sharks

OLYMPUS DIGITAL CAMERA         Recently, some anglers have reported ‘sores’ at tag sites on recaptured Common Skate. Below we explain the impact that tagging has to the body of an elasmobranch in order to explain that these ‘sores’ are formed from scar tissue as an auto immune response from the fish.

As tagging is a popular method for studying shark and skate species, there has been a lot of research into the effects of tags on elasmobranchs. Below is a synopsis from a piece of research work into this area.

In a study by Heupel & Bennett (1997), tissues from around tag sites were removed at time intervals ranging from 100 min to 284 days post-tagging. These samples showed acute and chronic responses to tagging.

Note: the use of the words ‘acute’ and ‘chronic’ do not refer to the severity of the reaction to the tag, but are makers of the time scale of the reaction with acute being short term effects (the insertion of the tag causing bleeding and tissue trauma) chronic refers to a reaction lasting longer than three months, in this case the permanent scar tissue.

Acute responses consisted of localized tissue breakdown and haemorrhaging, and occurred within the first few hours after tag insertion. At 10 h post-tagging, an intermediate response was apparent. This phase was characterized by further haemorrhaging and red and white blood cell movement into the wound area.

The chronic response observed in the 10–284-day post-tagging samples was characterized by fibrous tissue (scar tissue) formation to sequester the tag. Scar tissue presumably protects the adjacent musculature from further trauma produced by movement of the tag and provides a continuous barrier between the internal and external milieu.

Tissue repair appeared to progress consistently in all specimens and no secondary infections at the tag site were seen. Tagging produced only localized tissue disruption and did not appear to be detrimental to the long term health of individual sharks.

While healing from a tag wound may take longer than a normal wound due to irritation from the tag while scar tissue is formed, this doesn’t appear to be long term issue. There have been problems with previous tagging studies using inappropriate tags, such as the older fashioned ‘cattle ear’ tags, which restrict growth. Modern dart tags minimise irritation and in no way interfere with growth and are ideal for this type of work being used by many research programmes throughout the world.

Posted in: Shark Bites, Shark Tales
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