November 16, 2010 Featured Article Read More →

An overview of the tags we use

ID tags:

We currently use Dart tags produced by Floy with a small dart head.

Floy recommend that these tags are used on fish 8” – 24” (~20 – 61 cm) but we have decided to use this size for all our fish (for sharks, the minimum tagging size is currently 90cm – well in excess of the minimum size suggested) as shark skin is much tougher than ordinary fish and holds the tag in place more securely.

A lot of data on small fish is currently being lost due to our self imposed tagging size restriction. Small fish are arguably the most important to track as often with shark species, life stage (mature, immature) dictates the migration behaviour of the fish. It is important to note that male Spurdog mature at ~2.5lb, and females at ~4.5lbs, so these fish are still at least 10yrs old.

We are continually looking to improve our tagging methods and are currently trialling the Floy T-bar tag.

This tag is physically shorter and slimmer than the Dart tag. It requires a special ‘gun’ applicator to insert this into the fish. The gun itself has a needle on it that is 2.5cm long before reaching the main body of the gun, preventing it from going any further into the fish. The needle diameter is approximately 1.5mm, much more suitable for the smaller fish.

These are similar sized tags that CEFAS use to tag Thornbacks recently hatched from eggcases.

The tag applicator itself is quicker, easier and less intrusive to the fish.

Acoustic tags:

The Acoustic tags we are using are Vemco V13. These were chosen over other tags due to the length of their battery life.

Many fish biologists adhere to the 2% guideline where the transmitter weight in air should be 2% or less of the fish weight in air. (shown in table 1.1). Again, we shall err on the side of caution and use 1% as the guideline to help minimise any stress to the fish.  

tags

Table 1.1

Fish tagged with these internal acoustic tags must be anaesthetised before the tag is inserted and then be placed in a recovery tank until fully conscious before begin carefully released. These methods are strictly controlled by the Home Office and only certified personnel can carry them out.

The SSACN / SSTP project officer has been fully trained and certified to carry out these procedures by the Home office.

Posted in: Infocentre, Shark Bites
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