Hi Niall, See this publication - if you haven't already - it should provide you with a pretty good start on transmitter effects on swimming performance and a universal method to evaluate transmitter effects on juvenile salmon across populations, transmitter types, and other fishes.

https://www.researchgate.net/publication/257920003_Comparing_Effects_of_Transmitters_within_and_among_Populations_Application_to_Swimming_Performance_of_Juvenile_Chinook_Salmon?ev=prf_pub

Cheers,

JP

Article Comparing Effects of Transmitters within and among Populatio...

Niall,  my research lab has worked on endangered sturgeons for many years and the rule of thumb is still that the tag's weight in water, must not exceed 2% of the fish's body weight.  Having said that, I can certainly understand your confusion, because we have done several tank experiments with captive sturgeon and found that it isn't really the "weight" of the tag that matters.  What seems to be much more important, is the size (and possibly shape) of the tag relative to the volume of the fish's body cavity.  We looked at both long and short term pathology of tags inside sturgeon and found that there were many more instances of adhesions, lesions and other deleterious effects than had been previously thought.  Of course, this probably doesn't answer your question very well, because no one (to my knowledge) has published anything that evaluated tag size relative to the volume of fish body cavity.  I have a couple of pubs on this on my researchgate page if you are interested.  Good luck and let me know what you find out from others.... This question has been dogging sturgeon researchers for years - especially with all the latest interest in vemco telemetry systems.  My suggestion would be to run a tank experiment with different sized tags and see how your fish do over a couple of months.

Hi Niall, most people try and stick to the 2% rule whenever possible, but like you have already said yourself, the science behind this rule (which Douglas has already stated, is based on weight rather than size) possibly isn't as clear as it should be. I've certainly seen fish performing 'naturally' with bigger burdens - I'd be inclined to think that 10% might be stretching it a bit for many species though.  I would certainly agree that there is a need to go back and look at this a bit more closely - and with the range of tags that we have available at the moment.

Hi Niall, See this publication - if you haven't already - it should provide you with a pretty good start on transmitter effects on swimming performance and a universal method to evaluate transmitter effects on juvenile salmon across populations, transmitter types, and other fishes.

https://www.researchgate.net/publication/257920003_Comparing_Effects_of_Transmitters_within_and_among_Populations_Application_to_Swimming_Performance_of_Juvenile_Chinook_Salmon?ev=prf_pub

Cheers,

JP

Article Comparing Effects of Transmitters within and among Populatio...

Here is a paper that looked at volume in carp: Penne, C., N. Ahrens, R. Summerfelt, and C. Pierce. 2007. Effect of Relative Volume on Radio Transmitter Expulsion in Subadult Common Carp. North American Journal of Fisheries Management 27:986-991, doi:10.1577/M06-187.1.

Niall, you'll surely find a wide range of opinions on your question.  The bottom line is that less is better, but anyone doing field work very long realizes that isn't a very helpful answer.  For years people adamantly cited the "2% rule" originally suggested by Dr. Jim Winter (see some of the older Fisheries Techniques books from American Fisheries Society).  It turns out he suggested that as a very general recommendation and it got greatly proliferated.  Others have suggested even 12% or more was OK (Brown et al. 1999. North American Journal of Fisheries Management 19:867-871); surely they can't both be right.  Most papers land somewhere towards the lower side of these numbers.  The literature on juvenile salmon suggests that part of the answer to your question depends on the size of the fish in question: once they get smaller than about 90-95 mm in fork length they simply can't accommodate the tag-weight-to-body-weight burden that larger fish seem to handle.  The answer also depends on how you want to measure the effects: stress response, swimming ability, buoyancy, predator avoidance, something else?  In the end you need to settle on what you find defensible and go with it.  I suggest you base your decision on cite-able results and veer towards conservatism.  There is a nice discussion of these issues in Liedtke and Rub.  2012. Techniques for telemetry transmitter attachment and evaluation of transmitter effects on fish performance. Pages 45-87, in N.S. Adams, J.W. Beeman, J.H. Eiler, Editors, Telemetry Techniques: a user guide for fisheries research.  American Fisheries Society, Bethesda, Maryland.

I definitely agree that conservatism is the best approach, if you can't get the burdens below 2% at least get as close as you can. That being said I've seen both 6% and 8% burdens being the threshold for decreased survival and decreased swimming ability respectively, in Collins (2013). If look at lengths of the fish tagged they were excessively small, no sane person would tag to these burdens on small wild fish in a field study. In fact, as you said, most studies that note a decreased performance have tagged small fish (

J Coast Conserv (2014) 18:97–109. Exorbitant mortality of hatchery-reared Atlantic salmon smolts Salmo salar L., in the Meuse river system in the Netherlands

Niels Brevé: The delivered smolts had a minimum weight of 180 g. The minimum weight was chosen based on the weight of the internal tags (11.5 g).

Studies in rainbow trout showed that tags with a ratio of 6–12 % of the total

weight of the fish caused no significant changes in behaviour (Brown et al. 1999). Klimley et al. (2012) indicate that acoustic transmitters, when ≤5.6 % of body weight, can be effectively used in 1 year old Chinook salmon to study their migratory movements. 

Klimley AP, MacFarlane RB, Sandstrom PT, Lindley ST (2012) A

summary of the use of electronic tagging to provide insights into

salmon migration and survival. Environ Biol Fish. doi:10.1007/

s10641-012-0098-y

Brown RS, Cooke SJ, Anderson WG, Scott McKinley R (1999)

Evidence to Challenge the “2 % Rule” for Biotelemetry. N Am

J Fish Manag 19(3):867–871