Friday, February 17, 2012
What is a conch wave?
We just heard about the conch wave that was observed near Staniel Cay and thought we’d throw in our scientist’s two-cents. Allan Stoner’s conch research group was the first to describe this mass migration phenomenon near Lee Stocking Island in 1988. He acknowledges that this unusual sight is something the fishermen have probably known about for a very long time. Dr. Stoner and his team observed 25 conch waves over a 6 year period in late 80’s – early 90’s. Short of asking the conch participating in the march, they tried just about everything to figure out what was going on!
So, we thought we’d share what they did learn…
* High density migrations of juvenile conch (lots and lots of young conch all stacked up on top of each other) are sometimes called conch waves or conch walls and can occur throughout the year, but occur predominately October – April. These aggregations can last for months.
* The conch waves are made up of juvenile conch aged 1 year and older (the teenagers), but did include a few younger adults here and there. The biggest aggregations had over 100,000 individuals.
* Conch waves occured on what are considered to be nursery grounds or shallow water areas less than 5 meters (15 feet).
The direction of the migration seemed to be strongly determined by the direction of ebb or flood tide.
* After a conch wave passes through an area, there is significantly less algae on the seabed. The conch were clearly eating the algae, but they were not eating seagrass.
* Most importantly, and the likely reason for these mass migrations, is that individual juveniles within the conch wave had a much lower probability of being eaten by a predator. So, like fish that school together to avoid predation, the young conch may be looking for safety in numbers.
As an update, Dr. Stoner said that even though the team was in the field regularly after studying the conch waves, sadly they see much after their last observations in 1992. Our recent work in the Exuma Cays found that conch nurseries in the same area have declined by at least one half.
The conch wave is still one of nature’s mysteries. We’re glad to hear they are still being observed in places, but are definitely concerned that this phenomenon is becoming more and more rare. If you see a conch wave, please think about the future of conch in The Bahamas and let them grow up to reproduce.
Courtesy of CommunityConch.Org
Original post on FaceBook and photo by Linda Besk