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PhD Studentship

Refining the tagging of wild fish and sharks

Dr Matthew Witt with two boats on grass in the background

At a glance

In progress
Award date
October 2021 - September 2024
Grant amount
Principal investigator
Dr Matthew Witt
University of Exeter


  • Refinement
Read the abstract
View the grant profile on GtR


Why did we fund this project?

This award aims to improve the welfare of wild sharks and large fish in research by quantifying the response of the animals to electronic tagging providing an evidence base for refining procedures.

Wild sharks and large fish can be tracked using electronic tags, a technique often used to study the behaviour and ecology of these animals for conservation research and population management in fisheries. This often involves boarding the animal, and implanting the tag using darting technology before the fish is released. The tag allows researchers to monitor swimming speed and location. These invasive procedures are stressful for the animal as evidenced by their behaviour immediately after release, where fish are likely to swim at a faster pace than would be typical for the species. Dr Matthew Witt has identified three areas where advances might be made to improve the tagging procedure; anaesthetic regimes, techniques to support optimal water flow over the gills, and tag attachment. To date, there is little objective quantitative data available about the best practises for tagging large fish.

The student will conduct a literature review and interview researchers to determine the procedures currently used by the field. They will then quantify the response of fish and sharks to tagging procedures to determine where refinements could be applied and how procedures could be standardised between researchers. The student will develop skills in large fish research as well as field techniques and infographic design.

Application abstract

Electronic data recording tags are increasingly used in scientific research for wildlife conservation, population management and pure research in large (>1 m body length) wild fish and sharks. Much attention has been paid to tag sensor development, data compression and power budgeting through decades of technological refinement. However, less attention has been paid to how large wild fish and sharks are instrumented; often requiring invasive procedures. Tag cost, logistical complexity, licencing restrictions, and a focus on resulting data and analytical techniques has overshadowed refinements in tag attachment and improvements in animal welfare. This situation is compounded by the risk to grant success of failed experimentation with attachment techniques, and the potential loss of tags and subsequent data. Management of the life support systems of these animals during invasive tag attachment procedures is also under-researched and scope for refinement exists.

Unlike laboratory settings, wild marine fish and sharks are subject to invasive procedures in largely uncontrolled conditions, and are set free to the wild immediately, as the size of these animals prevents the use of post-procedure recovery tanks at sea. As such, there is no scope to ascertain post-release health at biologically relevant time points to ensure that the assumed severity of tagging procedures, adverse and acumulative effects are not exceeded, and to ensure the assumed biases that tags introduce to resulting data are as predicted. The status quo is that procedures on large wild fish and sharks are carried out following largely anecdotally influenced protocols that are shared between research groups due to familiarity of procedures even if sub-optimal. Existing protocols suffer from a lack of quantitative understanding of the acute or chronic impact of procedures on these animals following setting free. In addition, the driving forces of tag loss (e.g. mortality, natural predation, tag-induced predation, poor life support during procedures, or hardware failure) cannot easily be disentangled from one another once the animal is set free, and this complicates the identification of potential avenues for refinement.

Structured investigation to seek refinements will:

  1. Promote improved welfare of animals during and following invasive procedures
  2. Increase survival of animals once released, and 3) increase relevance and utility of resulting data.

Specifically, the studentship will:

  • REVIEW existing literature (often old; from limited and poorly representative species i.e. zebrafish and salmon/trout) on the evidence base of large wild fish handling and tagging. We will identify the 25 most published research groups on the topic and conduct structured interviews to understand common practices, and barriers to uptake of new information.
  • GATHER EVIDENCE using laboratory and field studies to quantify physiological, histopathological and behavioural responses of fish and sharks in response to commonly used anaesthetic regimes, life support techniques and tag attachment (dart type, target host tissue). These studies will yield novel information on the optimum approaches to balance animal welfare with data quality.
  • PROMOTE findings via (a) Top down – we will send summarised infographics of the project findings to every academic institutional AWERB in the UK, and the ASRU, to enable them to direct all new applicants to the project findings: and (b) Bottom up – we will send the same infographics to all the user cases identified in (i) to encourage them to refine / incorporate findings into their own practices.

    The overall refinements will enhance fish welfare, progress the quality of the data collected, reduce tag effect bias, and increase the duration over which meaningful data can be collected.