Thornback tails.

In recent years I've noticed that some female thornbacks in Swilly area have particularly stumpy tails, almost as if someone had chopped half of it off! However yesterday I caught two and the tail looked as though it was badly deteriorating halfway down and would probably fall off at some stage.

Is there any marine biologist types or just clued in anglers who could explain this to me? Both fish were very fat with purses so I'm thinking maybe they throw the tail before they lay or is it something to do with thier mating process? Or is it maybe some sort of hereditary illness?

Any replies appreciated, sad I know, but stuff like this perplexes me

I have seen a number of tailless thornies down here. The skin had grown over the wound and was completely healed. I did notice that they rise to the surface easily when being played in.
I was told by someone that the commercial boys when they cannot sell them cut the tails off to get them out of the net. whether this is true or not I do not know but it is the only plausibly explanation I have heard.

it looks like its a common practice for the net men viewtopic.php?f=62&t=22191 found this in an old post.

Could it be autotomy, similar to when a lizards tail breaks, not familiar enough with rays to know how strong their tails are but i bet a juvenile ray would be on somethings menu

Similar scenario with alot of sting ray ive seen landed.Only a stump of a tail left,me thinks the likes of these fish would get caught up easily in certain types of netting [ie tangle netting] due to stings/thorns on their tails and the tails would be just caught off in order to get them out of the net and disposed of .
A bit barbaric but at least the fish are let go i suppose.

Looks anthropogenic rather than biological to me mate. There are no parasites that would invoke tail loss for thornbacks and fish can't drop their tails and regenerate - they would have to actually be bitten or cut of. There are also no reports of tails with regenerated ends that i can see in the literature and most of the caught fish show scar tissue rather than growth tissue. On the very outside, it could be mass deformity due to a genetic mutation, similar to scoliosis in other species, but that's just speculation and would need some serious research to prove. Its unlikely to be the case though.

Most likely to be tail removal by fishermen. Anyone else know of or actually seen this happening on the commercial boats??

Hope this helps

K

hi Bazzer
i've seen a fair few of these in the swilly this last two/three years. There was two trawlers in the swilly last week but i thought ray would sell ok so why would the cut off the tails and throw them back???
i'd have to agree (no proof though) that nets men releasing these by chopping the tail so maybe its a smaller netter targeting something else and has no use for the ray??
glad to see some rays still in the lough though. because i blanked twice after the trawler had been.

dave