By Cris Little
A hot, sweaty trudge up Dorset's Chesil Beach is never one of my favourite experiences. On this particular dive, however, I was one of a group of divers from Bristol University BSAC with a special mission.
We were off to dive the wreck of the Royal Adelaide in the hope of seeing, and perhaps photographing, an unusual visitor to British waters - the grey triggerfish. We knew we were hot on the trail. Other divers returning from the wreck as we set off related tales of a trio of triggers waiting for us.
And there they were! The very first fish as we hit the wreck were three triggerfish. The sight of triggers among the more familiar wrasse and blennies was a strange experience. Many of us had seen brightly coloured triggerfish species on diving trips abroad. These triggerfish (Balistes capriscus) had a subtle blue-grey colouring. Their pancake-shaped bodies gave the impression of their being 'all head' - rather like that other oddity, the John Dory.
Inspecting them closer we could see the sharply pointed spine on the first dorsal fin. This can be locked into an upright position, enabling the fish to wedge themselves inside cracks when danger threatens. The mechanism is released by depressing a second, smaller spine - the eponymous trigger - behind the large spine.
These triggerfish, obviously used to divers, were tame and co-operative. Gently, they took pieces of food from our fingers with their pointed teeth. The food in the water attracted other creatures as well. Cheeky crabs, hordes of greedy tompot blennies, and a couple of cuttlefish, gathered round to muscle in.
The tompots' characteristic thick lips seemed to smile at us in anticipation of a handout. They had considerably fewer table manners than the triggerfish! The cuttlefish also came close enough to us for us to marvel at their amazingly rapid colour and texture changes. They lurked on the edge of the action with the intention of grabbing an unwary crustacean.
Balistes capriscus (the grey triggerfish) is a warm-water species with a normal range in the tropical Atlantic and the Mediterranean. During recent years, with the warming of the sea around Britain, there has been a dramatic increase in its occurrence in home waters.
Reports of sizeable schools of triggerfish come filtering back from the south-west coasts of Ireland and England. They have also been found in the North Sea, and one individual even reached as far north as Shetland!
The grey triggerfish is not a strong swimmer. It seems likely that they are brought in to British waters by the Gulf Stream from mid-Atlantic islands, such as the Azores, rather than travelling up from the Mediterranean against the currents.
Triggerfish are not resident in our waters and don't breed here. Adult fish (which may be up to 50cm in length) enter the area in the summer months, from around July onwards, when the sea around Britain is at its warmest, and die off when the water temperature falls below about 12C.
With higher sea temperatures, the grey triggerfish looks set to become an increasingly common visitor to our coastal seas. So the chances of divers seeing this distinctive fish are better than ever. Keep your eyes peeled when diving in the late summer!
Appeared in DIVER - September 1996