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Releasing Mackerel

Sep 20,2006 SACN

We often get enquiries 'Is it true that mackerel die if handled?'

So we asked the experts at CEFAS and this is what they said:

Hi Mike,
I wonder if you can answer this, or pass it onto someone who can?
Frequently the question of returning mackerel alive appears on the various angling internet forums.
There is a belief by many that once a mackerel has been touched by an anglers hands, even though the fish may swim away energetically, it is doomed.
Something to do with the heat/oil of the anglers hands (where it has been touched can often be seen as a handmark on the fish's skin).
Even though only microscopically damaged, the mackerel's skin continues to break down with death inevitable within 30 hours.
Shaking the fish off the hook or handling with wetted neoprene gloves is said to prevent the problem.
The problem is that when the mackerel shoals are on the beach, anglers will soon catch their self-imposed limit, but can't seem to stop fishing, often changing from feathers to a light spinning outfit and returning every fish they catch.
(If the above is correct, then they are better advised to cease fishing for mackerel and trying for the bass beyond/underneath the shoals perhaps, with less guarantee of catching).
Although this information is widely quoted, I can't find any authoritive reference to such information, although I vaguely mention talking to someone from CEFAS at the Recreational Angling Conference in Cardiff some years back, who confirmed that was the case.
It would be useful to quote an authoritive source to refer people (one way or the other) to when the subject comes up in the future.
Tight Lines - Leon Roskilly
Sea Anglers' Conservation Network (SACN)

SACN Latest: http://www.anglers-net.co.uk/sacn/latest

You are quite correct, and you've come to the right people! 
In the late 1970s we carried out several experiments to try to find out why dead mackerel were being found in vast numbers in the SW, co-incident with the purse seine and trawl winter fishery. 
The short answer is that the fish died due to skin damage interfering with their ability to maintain osmotic balance, and the skin damage was due to abrasion between crowded fish in the nets. 
We found that mackerel caught on barbless hooks and never handled, just dropped into keep tanks or nets, survived quite well if allowed to swim freely, but holding a mackerel caused enough damage to eventually kill it, sometimes two days later. 
I have a number of publications showing the results of all this work.

These are:

Lockwood, S. J., Pawson, M.G. and Mumford, B.C., 1977.   "Effects of holding mackerel at different densities in nets of various sizes."  M.A.F.F., Fish. Res. Tech. rep. No. 33, 10 pp

Pawson, M. G. and Lockwood, S. J., 1980.  "Mortality of mackerel following physical stress, and its probable cause."  I.C.E.S. rapp. proc. verb., 177: 439-443.

Holeton, G. F., M.G. Pawson & Shelton, G., 1982.  "Gill ventilation, gas exchange and survival in the Atlantic mackerel (Scomber scombrus L.)." Can. J. Zool, 60:  1141-1147.

Lockwood, S. J., M. G. Pawson and D. Eaton., 1983.  "The effects of crowding on mackerel (Scomber scombrus L) - physical condition and mortality".  Fisheries Research, 2: 129-147.

So, when anglers have caught enough mackerel for a fry or for bait, they should stop fishing for them unless they are using barbless hooks and can return the fish to the water without touching them.

Mike P.


So it seems that mackerel, unlike any other species, are likely to die if their incredibly thin and specialised skin is touched by human hands (you can often see the marks of your hand on the skin of a mackerel when it is returned to water).

Catching only what you need is the best advice, but if you do hook a mackerel that you don't need then it's best to shake it off the hook without touching it (use of barbless hooks will help).


Note: The Minimum Landing Size for mackerel is 30cm in the North Sea (that includes quite a bit of the area that anglers may regard as The English Channel) and 20cm elsewhere.


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comment Comments (1 posted) 
  • returning over caught fish. My grandfather was a Drifter skipper fishin out of Lowestoft. When I went 'down home' in the Twenties I was struck by the smell of rotting fish which covered the whole of the town. I was told that this was due to unsold of herring being used as fish manure.
(Posted on July 6, 2007, 5:23 pm alan rose)

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