In comparison to fish tagging as a whole, shark tagging is a relatively recent activity. Shark tagging really began with the development of plastic Peterson disc and dart tags; before 1940 only 1,005 elasmobranchs had been tagged and released in UK waters, by 1950 shark tagging projects were well established in both the Atlantic and Pacific Oceans and tens of thousands of sharks had been tagged.
Early elasmobranch tagging projects were generally focused on spurdog (Squalus acanthias) and tope (Galeorhinus galeus) with a view to improving fisheries management measures. The development of distinct shark tagging programmes occurred across the globe almost simultaneously though were conceived with very different aims as discussed below.
The first shark tagging project in the Atlantic Ocean was carried out by Greenland Fisheries Investigations in 1936. The project used Peterson discs to tag Greenland sharks (Somniosus microcephalus) in the hope of gaining information on the shark’s growth rate. A total of 411 individual sharks where tagged over a period of several years, 28 of the sharks were recaptured (6.8%) after up to 16 years at liberty having travelled up to 1,296km. This project was extremely small and localised compared to future tagging projects that would take place in the Atlantic Ocean.
The first large scale shark tagging project in the Atlantic Ocean targeted spurdog. At the time spurdog were rarely targeted commercially in the North Atlantic Ocean, instead they were considered a pest and a massive hindrance to the extremely lucrative cod fishery that existed in the area. A tagging programme was initiated by the Newfoundland government the aim of which was to determine whether spurdog populations where local to the area or international with a view to managing the spurdog populations for the benefit of the cod fishery.
The study began in 1942 and continued until 1965, during this time a total of 2,855 spurdog were tagged of which 8.2% were recaptured, this included one fish that had travelled across the Atlantic Ocean and was recaptured off Shetland in the North Sea 11.2 years later.
Around this time several large scale tagging projects were initiated in the North Atlantic, between 1957 and 1963 over 20,000 spurdog were tagged in British waters in an attempt to understand the migratory patterns of the fish in UK waters.
In the 1940’s demand for vitamin A from the liver of the spurdog exploded driving a very intensive spurdog fishery along the Pacific coast of North America. The economic importance of the fishery and the realisation that catches were declining prompted the US Fish and Wildlife Service to start a tagging programme that aimed to gain information on the life history of the spurdog.
The tagging programme would look the extent and patterns of spurdog migrations, rate of growth and the level of fishing mortality. By 1946 a total of 9,705 spurdog had been tagged along the west coast of North America using Peterson discs. By 1953, 6.7% of the tagged spurdog had been recaptured with a maximum time at liberty of 10 years and distance travelled of 8,704km.
At the same time, a similar project was undertaken in the south Pacific by the Commonwealth Scientific and Industrial Research Organisation (CSIRO) in south-east Australia. This project was aimed to increase knowledge about the general biology of the tope (or school shark) which – like the spurdog in North America – was the target of an intensive fishery reporting declining catches.
The CSIRO project tagged 6,502 sharks between 1947 and 1956 with a variety of internal and external tags. One internal tag was recovered from a male tope a staggering 41.8 years after the tag had been implanted! This remains the longest recorded time at liberty of any tagged species of fish.
The CSIRO project would be restarted several times over the following five decades and eventually became part of a larger project known as the Southern Shark Tagging Project which, by 1996, had tagged over 20,000 sharks of 22 species in both the Pacific and Indian Oceans.
The first large scale shark tagging project in the Indian Ocean began in 1964, the project was run by the Oceanographic Research Institute and unlike other at the time projects was not related to the management of fisheries. Instead the project tagged over 1,000 sharks around Durban with Rototags in order gather data allowing the South African government to devise measures to protect swimmers from shark attacks based on predicting the seasonal movement of sharks.
This particular project encountered a range of problems and yielded mixed results. Initially the project operators offered a reward of 10 Rand for the return of a tag and associated information on where the fish was caught, within one year of the project 39% of the tagged fish had been recaptured (largely by commercial fishermen) with almost all recaptures from the area the sharks were originally tagged in. One particular Zambezi shark was recaptured the day after it was tagged.
Those running the project realised that the value of the returned data was relatively low in terms of monitoring the movements of sharks and so changed the incentive scheme to reward fishermen with just 4 Rand for every shark recaptured in the Durban area (where they were originally tagged) but 10 Rand for fish returned from outside of the Durban area. Unsurprisingly this led to an enormous amount of sharks being caught “"outside of the Durban area” by fishermen!
Within one day of introducing the incentive scheme, five tagged sharks were returned from outside the Durban area; within five days of introducing the incentive scheme ten more sharks had been returned from outside the tagging area. Bizarrely, before the introduction of the incentives no sharks had been recovered from the areas where they were now apparently appearing!
Finally it was accepted that the differential incentive scheme was introducing a bias to results and may have been encouraging fishermen to alter records of where tagged sharks were caught in order to receive a greater reward, as a result early data from this project was scrapped.
Lessons learned from these early projects would yield a huge range of information which would prove invaluable in both our understanding of sharks and the advancement of modern day tagging projects. At that point in time, elasmobranch tagging projects were generally carried out by a single organisation with a single goal or question to answer, in the final segment of the History of Tagging we’ll look at the progression of cooperative shark tagging projects which represents arguably the biggest step in tagging projects to date.