Hi Andy

 

            I thought you would be interested in this. And I have attached the photos

 

                        Regards, Doug

 

 

 

Hi Everyone

 

            When I quickly examined this fish in the Fish Market I noted a relatively large eye and in particular I thought the pectoral fin looked too long for a bluefin and came to the conclusion that it was probably a bigeye.  Unfortunately I did not do a gill raker count.  On examining the photos and doing morphometrics on these ( as best you can from photos) I found the pectoral was 20 – 21% in fork length.  This is right at the upper end for Bluefin, but below the 22 – 31% of bigeyes and apparently it can be longer in specimens of less than 110 cm as this one was (86.5 cm).  It is a shame I did not get a gill raker count as that would have been a clincher; Bluefin 34 – 43, while bigeye, yellowfin and albacore are all 23 -34, and the West Atlantic blackfin is 19 -25.

 

            I therefore sent the pictures to Bruce Collette, who does not like IDing tunas from photos.  I have attached his comments, but I did reply pointing out that we have two yellowfins and three bigeyes recorded for British waters.  A paper on this - Powell et al. is in press for J. Fish Biol.

 

“I hate identifying tunas from photos! However, the short pectoral, second dorsal and anal fins and the lack of a white margin to the caudal fin all indicate that it is an Atlantic Bluefin Tuna, Thunnus thynnus. Geographically, this makes sense because only Bluefin and Albacore are found that far north. Albacore (or long-fin tuna) have much longer pectoral fins, a white margin to the caudal fin, and have the body deepest further back than bluefin.”

 

            So the conclusion is that the fish was almost certainly an Atlantic Bluefin tuna Thunnus thynnus.

 

                        Sorry for misleading you.  Regards Doug

 

 

Hi Folks

 

                        We had a small 12.6 kg tuna on Plymouth Fish market this morning.  Caught in gill net off Mevagissey.  It was on its way to the wholesalers so I was only able to get some photos.  On the basis of pectoral fin length, unmarked belly, dark yellow 2^nd dorsal (but 1^st dorsal was black), yellow finlets with black edges, and relatively large eye; I came to the opinion that it is Thunnus obesus.  I would appreciate your opinions.  If it is I reckon it is fourth for UK.  Any Irish ones, Declan?

 

                        Regards, Doug

 

p.s. Adam, can we get a note on the end of our paper?

 

Douglas Herdson
Information Officer
National Marine Aquarium
Rope Walk
Coxside
Plymouth  PL4 0LF
UK

Telephone: (+44)01752 275216/01752 600301
Fax: (+44)01752 275217
Email: Douglas.Herdson@national-aquarium.co.uk
website www.national-aquarium.co.uk
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