November 29, 2011 Featured Article Read More →

A History of Tagging

In this segment we will cover the history of fish tagging from its origins in the early 1600’s up to modern day shark tagging projects. For centuries humans have tried to develop non-destructive ways of monitoring the movements and dynamics of fish populations largely for the purpose of fisheries management, it was this need that drove the development of tagging early projects. Nowadays tagging projects operate worldwide in order to provide data for fisheries management and conservation.

In part 1 of this segment we will discuss the origins of fish tagging and the progressive sophistication of tagging technology in the years that followed.

The Origins of Tagging

Although it may seem like a relatively recent development, the fact is that people have been tagging fish since the early 1600’s. All early tagging projects involved salmonids, a particularly valuable source of food at the time. The earliest records of fish “"tagging” involved juvenile Atlantic salmon (Salmo salar) which were marked by tying coloured wool ribbons around the fishes tail to monitor movements from the river to sea. Although the methods may seem primitive when compared to modern day tagging projects that often employ a range of sophisticated electronic tags, the aims and principles of fish tagging projects have remained relatively unchanged for centuries.

OLYMPUS DIGITAL CAMERA         By the 1800’s tagging methods had changed dramatically, although still largely focused on salmon a wide range of tags and alternative methods of tracking individual fish were now available. This included fin clippings and wire tags that could be attached to the fins, jaw, gill cover or tail of the fish.

In 1893, the Fisheries Board of Scotland initiated a project that tagged 600 Atlantic herring (Clupea harengus) using small barbed hooks, each of which carried a unique number inscribed on a small metal plate. However, despite the accolade of being the first known record of an attempt to tag and track a pelagic species, no tags were ever returned from this project!

The Peterson Disc Tag

The introduction of the Peterson disc tag in 1894 represented the single most significant development in fish tagging at the time. This simple tag is made up of two plastic buttons which are bound together by a pin made of plastic or metal and is generally placed on the fin of a fish similar to an ear piercing. The simple concept and ease of use allowed the expansion of tagging programmes and applications worldwide. The tags were initially used to monitor the movement of plaice in the North Sea but soon expanded to include cod, haddock, pollock and halibut.

Despite their popularity the Peterson disc tag is not without its problems, correct placement of the tag is crucial to ensure a strong hold but to not interfere with growth. Although tagging instructions generally advised that the tagger leave a 5mm gap between the tag and the body of the fish, shedding rates – particularly on juvenile or fast growing fish – were estimated at well above 50% per year.

Even to this day this Peterson disc style of tag remains popular and is generally considered the most widely used tag in the history of fish biology.

Rototags

The Peterson disc tag would eventually pave the way for the development of Rototags, a type of tag similar to that used for cattle. Rototags are applied in the same was as a Peterson disc: by piercing a small hole through the fin of the fish through which the tag is placed using a special applicator.

Rototags had much better retention rates that Peterson discs with a shedding rate of around 6-8% per year when applied correctly. However the tag also shared many problems of the Peterson disc, once again the tag could interfere with growth if incorrectly fitted and was prone to tearing out when the incorrectly applied.

The Rototag was the first tag used to track the movements of sharks, a revolutionary project that yielded mixed results.

Rototags were found to have the highest retention rate when fitted to the dorsal fish of shark species. However if the tag was placed too close to the base of the fin on fast growing species it was often found to cause irritation and many sharks in early tagging projects were recaptured with abraded dorsal fins suggesting that the irritation had caused the shark to rub on the sea bed in an attempt to dislodge the tag. Conversely if the Rototag was placed too far from the base of the dorsal fin the tag was prone to tearing out and shedding rates increased dramatically.

Rototags are still used today and can prove extremely effective when properly applied. In 1998 a Rototag was returned from a fish 28 years after the tag was applied making it one of the longest “times at liberty” ever recorded for an external tag, a testament to this style of tags suitability for shark tagging projects.

A smoothhound caught off Holyhead, Wales. A Small, white Rototag can clearly be seen on the sharks dorsal fin.

Dart Tags

The demand for an external tag that was easily visible but had a high retention rate led to the development of the “internal anchor” tag by Rounsefell in 1936. The tags developed almost 80 years ago by Rounsefell where the forerunner of modern day dart tags that are used by tagging programmes worldwide, including the SSTP.

The first dart tags had a stainless steel, “M” shaped head that was used to anchor the tag under the fish’s skin and were applied using a mounted needle. Dart tags opened up a wide range of possibilities, sharks could now be tagged in the water using a needle mounted on a long pole. This meant that larger species such as great white and whale sharks could now be easily tagged and that smaller species could be tagged without the stress and danger of capture and handling.

By the 1950’s cheap vinyl tubing was readily available and would eventually replace the stainless steel dart tags used previously. Subcutaneous nylon dart tags (as used by the SSTP) were first used in the 1960’s. Although retention rates were slightly lower than Rototags the benefits of using nylon dart tags far outweighed any possible drawbacks.

Dart tags are easily applied, have high retention rates, don’t interfere with growth and cause little irritation to the fish due to their small size and streamlined profile which creates very little friction in flowing water.

The blunt end of the nylon dart tag is inserted into a sharp canula (hollow needle) or tagging gun. The tag is then inserted at a 45° angle into the dorsal musculature of the fish to anchor the barb ensuring the head of the tag is pointing towards the head of the fish as shown below, this ensures that the tag remains streamlined and does not irritate the fish by creating resistance or vibrations when the fish swims. Once the canula is removed, a light pull on the tag sets the nylon barb and makes sure the tag is fixed in place.

Dart tags are now one of the most popular styles of tags and are used in tagging projects worldwide.

A spurdog with an SSTP nylon dart tag. The inset picture above shows a close up of the SSTP dart tag inserted into the dorsal musculature of a spurdog, each tag carries a unique number to allow individual fish to be identified. Additional data on size, sex and fish condition is recorded by the angler.

We hope you found this introduction to the history of fish tagging interesting! In part 2 of this segment we will look at the development of internal and electronic tags which would go on to have a significant influence on tagging shark tagging projects around the world.

Posted in: Shark Bites, Shark Tales
Rss Feed Facebook button Webonews button Digg button Flickr button Newsvine button