SAMS take part in Tagathon2009

On Saturday Nov 14th a group of SAMS marine science students accompanied by Dr Clive Fox and Colin Griffiths (SAMS), Jane Dodd (SNH) and David McNair (SSACN Angling coach) headed into Loch Etive on the SAMS research vessel ‘Calanus’. The aim was to catch and tag as many spurdog as possible as part of Shark Tagathon2009. This event organised by the Scottish Sea Angling Conservation Network aims to promote interest in sea angling and conservation but also has an important scientific angle. Spurdog were once very common in Loch Etive and around the west of Scotland but anecdotal evidence and catch records suggests their numbers have declined substantially. Spurdog (Squalus acanthias) are small sharks distinguished by a sharp spine or spur, at the front of the dorsal fin. Spurdog can grow up to 9 kg but are normally around 7 kg. The maximum recorded age is 75 years. They are typically found close to the seabed on soft bottoms down to 200 m depth but they may come nearer the surface at night. Like many sharks, spurdog give birth to live young. Spurdog have a long gestation period (18-22 months) and only become mature when males are 60-70 cm long and females 75-90 cm. The species is considered vulnerable to over-fishing because of these life history traits. In common with much of the Scottish west coast, spurdog were once very common in Loch Etive but commercial fishing in the 1980s substantially reduced their numbers. It is also thought that the Loch Etive population may be resident but little is know about their real rates of exchange with other populations.

David McNair shows how to set the tackle	The students start fishing
Landing a small spurdog	Weighing the fish

In Tagathon, spurdog are tagged with a small dart tag bearing an identification code number and telephone number and returned to the sea un-harmed. Before being released the tagged fish are measured, weighed and details recorded on their sex and where they were caught. There is no data to suggest that tagging the fish in this way causes them any harm. It is hoped that anglers or fishermen recapturing the tagged fish will report the capture along with new length and weight data and if possible re-release the fish once more. Tagging has been widely used for many species and can provide valuable information on fish growth rates and movements. In addition, data on how the numbers of fish caught per hour of fishing has changed over time gives an indication of whether the population is increasing or decreasing.

 

Despite the wet and windy conditions the team fished for around 5 hours. Six small spurdog were caught (and re-released) but only one was large enough to be tagged. Towards dusk larger numbers of whiting were caught. The SAMS team were not the only ones fishing Loch Etive and larger numbers of spurdog were caught by some of the other boats. It is hoped that the Tagathon will become an annual event gradually accumulating a time-series of data which will allow a much improved understanding of spurdog status around Scotland.

In addition to the simple tags bearing just an identification number, scientists now have at their disposal powerful data recording tags. Data recording tags store environmental information such as water temperature, depth and light levels at a high frequency – every 15 minutes is common. Because memory chips have now become so small, these tags can operate for up to several years. The tags come in two forms. The smaller design must be returned to the laboratory to enable the data to be downloaded but on large fish pop-up tags can be used. Pop-up tags automatically release after a set time, float to the surface and transmit their data. Once the data has been recovered from the data storage tag it can reveal the fish’s behaviour in much more than can be inferred from the simpler identification tags. The disadvantage of data storage tags is their cost which runs into several hundred pounds per tag. Undertaking a large-scale tagging program with data storage tags is usually prohibitively expensive unless supported by a government or European Union research program. Nevertheless a lot can be learnt using even a small number of data storage tags providing the fish/tag recapture rates are high. For example Victoria Veramouth and David Sims from the UK Marine Biology Association have recently shown that although common skate tagged off the west of Scotland show strong site fidelity they undertake extensive vertical migrations which may be related to foraging (Vearmouth, Victoria J. & Sims, David W., 2009, Movement and behaviour patterns of the critically endangered common skate Dipturus batis revealed by electronic tagging. Journal of Experimental Marine Biology and Ecology, 380, 77-87).

Other exciting related news is that a project officer will soon be appointed funded by SNH to co-ordinate the shark tagging program and to undertake outreach activities. For further information please check the websites (www.sacn.org and www.tagsharks.com) and Scottish Natural Heritage (www.snh.org.uk).

Historical catch records

SACN would be interested to hear from anyone who has historical catch data, particularly if records have been kept over several decades. Historical data can provide valuable indications of fish population changes over time, especially if they can be corrected for the hours fished.

What to do if you catch a tagged fish

Please leave the tag attached in the fish unless it is a data storage type (see photos in this article to identify tag types).

For dart tags note the telephone number or address on the tag and write down the number of the tag. If you have a suitable sling and scales then record the total length and weigh the fish. You can submit the data electronically at www.tagsharks.com or by post.

Please keep the fish in water as much as possible.

Tagging and Handling Sharks

•    If possible, release without taking out of the water.
•    Shark skin can cause painful burns to exposed areas so hold firmly.
•    Have all equipment to hand to minimise time out of water.
•    Bring fish in horizontally supporting the abdomen as sharks have no ribcage and internal organs can be damaged.
•    A towel soaked in sea water placed over its head usually pacifies a fish.
•    When releasing the shark hold its head into the tide to get oxygen back into its gills.
•    Once the shark starts to kick it is a good indication it has recovered enough to be released.

What to do if you find a data storage tag

Data storage tags found in Scottish waters may have come from several tagging programs including cod, turtles and even jellyfish, in addition to sharks.  If the tag is still attached to the animal there is usually also a dart or streamer tag with contact details but sometimes the dart or streamer tag may be missing or data storage tags may be found detached from the animal. In this case contact Clive Fox (clive.fox@sams.ac.uk), Lauren Smith (l.smith@sharkiologist.com), Jane Dodd at SNH, David Sims at the SMBA or Dr Julian Metcalfe at Cefas and we will try and find out which tagging program the tag belongs to. There is often a financial reward to encourage returning of data storage tags.