Will a highly visible tag bias data in a mark resight?

[lyanneb]

Hi,

This is more a conceptual question than a MARK questions.

I am designing a mark resight study and originally intended to use florescent tags as they would be easily identifiable; however a colleague has pointed out that because florescent is so visible it may also bias the results.

Obviously tagged individuals need to be distinguishable from non-tagged individuals, but is there a problem with tagged individuals being too visible?

Any one have an opinion or thoughts on this that might clarify this for me.

[bmcclintock]

Hi Lyanne,

Your colleague raises a very important point. The sighting probabilities of the marked individuals must be representative of the unmarked individuals. If the tags on the marked individuals are so eye-catching that they make the marked population much more sightable than the unmarked individuals, then the sighting probabilities will be overestimated (and population size therefore underestimated). For example, suppose fish were marked with bright fluorescent tags on the dorsal side and sighted from a bridge above. If the bright tags made the marked individuals sightable from depths where unmarked individuals were not, then there would be a problem.

Cheers,
Brett

[shannonbarbermeyer]

FYI - Tag visibility issues are also very important if your study species is subject to any hunting pressures.

Shannon Barber-Meyer