The Black Bream Project
The Black Bream Project
Revealing the secrets of black bream breeding behaviour off the Dorset coast
Images and video by Matt Doggett and Martin Openshaw
Each year at around Eastertime, the seabed at sites throughout Dorset is transformed in a spectacle of nature as tens of thousands of black bream, Spondyliosoma cantharus arrive to breed. Two clues announce their arrival; firstly the seabed is transformed into a moonscape of craters and secondly, dozens of chartered and private fishing boats head to sea to catch the fish which are prized for sport and/or as delicious seafood.
Depending on the type of seabed, a male bream might clear up to 70kg of sand and gravel to reach the bedrock beneath. The shifted material forms ramparts around the nest perimeter.
In the image above, dozens of kayak anglers take part in a mixed-species, catch-and-release competition in Swanage Bay demonstrating the species’ social and economic value in addition to its intriguing breeding habits.
Despite this dense, breeding aggregation, divers rarely encounter bream underwater – the fish are shy and often move away until the divers have gone. Here a diver studying bream nests photographs the eggs.
So what happens when the divers are not there? What is life like on and around Dorset’s black bream nesting areas?
For a better understanding of natural breeding behaviour we placed video cameras on the seabed in the nesting areas between Kimmeridge and Poole Bay. Here’s what we discovered…
When they first arrive, the bream swim back and forth across the site in large shoals for several days before nesting begins.
The male fish, identified by their vertical white bars, start to build their nests which are small at first. They keep other males away and try to attract passing females by flicking their tail and quickly turning from silver to black to display their white bars.
As the nests get bigger some males try to muscle in on others’ hard work.
Successful males attract females (with a horizontal white stripe) down to the nest where they appear to inspect it for suitability. Spawning is thought to occur at around dawn.
The eggs have been laid. At this stage they are tiny, transparent spheres just 1-2 mm wide.
The male bream stays with the nest until the eggs have hatched. He must keep it clear of sediment and any would-be predators.
Predation pressure seems to be very site-specific. We recorded high pressure in Poole Bay from goldsinny wrasse (top two images), black gobies (bottom right), tompot blennies, bib and even juvenile bream. Predators were far less abundant around Kimmeridge with only a few opportunistic ballan wrasse (bottom left) and netted dogwhelks observed.
The footage below shows predation occurring either soon after cameras were placed, or whilst divers were in the water and before the male returned to the nest. With the male in residence, predation levels were lower although they still had to work hard to keep predators away.
The first video shows a male bream in Swanage Bay using his tail to waft silt from the eggs, keeping them clean and well-oxygenated.
This second video first shows a male in Poole Bay keeping goldsinny wrasse away from the nests. The few flashes are from a camera during a rare face-to-face encounter between a diver and a nesting bream.
The second part shows how high the levels of predation in Poole Bay can be if a male leaves the nest. Marauding black gobies and bib pile on to the nest – even a juvenile bream joins in the feast.
The final video shows a ballan wrasse off Kimmeridge taking advantage of an empty nest soon after a camera was placed. The male soon returns and even removes a small whelk trying to feed on the eggs.
In May 2015, the south coast was battered by stormy weather, destroying and damaging many of the Kimmeridge nests before the eggs had hatched.
We returned to nests which a week before had newly laid eggs only to find the nests covered over and the eggs scoured from the underlying rock.
