Donated dive gear helps keep track of grouper spawning

Dive equipment that allows divers to go deeper and stay underwater longer has been instrumental in enabling environmentalists to keep track of grouper spawning in the Cayman Islands. 

When the annual Nassau grouper spawning takes place in the islands later this month, at least one diver wearing a “rebreather” will be keeping an eye on the spectacular natural phenomenon. A rebreather donated to the Cayman Islands Department of Environment in 2009 by Silent Diving of Brockville, Ontaria – with all training and gases provided by Divetech – has meant that department officer James Gibb has not only been able to monitor the spawnings since 2010, but also act as a safety diver for other divers in the water cataloguing the event and other projects. 

“The rebreather has definitely helped our monitoring of the group spawning, especially in the case of Grand Cayman. We would have no idea what was happening down there if it wasn’t for the rebreather,” Mr. Gibb said. 

Mr. Gibb said that as a department team was trying to locate the grouper spawning site at the Coxswain’s Bank off the eastern side of Grand Cayman in early 2009, a diver at the end of the last dive of the day saw at 130 feet a rush of groupers release their eggs into the water. “It was by absolute chance she was in the water at the right place at the right time. Sometimes we get lucky,” Mr. Gibb said. 

With the exact GPS coordinate of the site now known, the Grouper Moon Project research team, made up of staff from the Cayman Islands Department of Environment and the Reef Environmental and Education Foundation, wanted to return and find out more the following year. 

“We knew it was deep water there, so in order for us to effectively monitor the numbers there and see what’s going on, we needed to spend more than 30 seconds at depth and be able to do it safety. When working at anything past 130 feet, which is the maximum safe recreational diving … you start running into problems like nitrogen narcosis, and from there you run into more issues like oxygen toxicity – oxygen becomes toxic at depth,” Mr. Gibb said. 

While groupers aggregate at certain sites, not all aggregation of groupers lead to spawning. “There’s a critical limit where they might aggregate but there might not be enough grouper for them to spawn,” he said. 

The team needed to be able to spend more time under water to determine the trigger for the spawning. That’s when Nancy Easterbrook from Divetech came in. The team approached her for advice and were told what they needed was a rebreather. 

“The advantages to the Department of Environment and any other research person are multiple,” Ms Easterbrook said. “Firstly, there are no bubbles. It is very quiet and silent and you can get up close and personal with the marine life, which is one of the goals when you’re monitoring a situation. Second, the gas you’re breathing is very warm. Even though the waters here is warm, when you’re down there a few hours, it gets chilly. The gas is also very moist, so you don’t get dehydrated as you’re not sucking dry scuba air. 

“Third, it optimises the amount of time you can stay at depth for a couple of reasons – you have a tremendous amount of gas available to you. You’re not breathing in and then exhaling into the water, you’re recycling what you breathe,” Ms Easterbrook said. Mr. Gibb completed his training on the rebreather unit at the end of 2009, in time to help monitor the 2010 grouper spawning event. 

The department’s rebreather has not just been used to keep tabs on the groupers but for a variety of other monitoring purposes. For example, Mr. Gibb said, “It’s been worth its weight in gold” in checking out deep water coral bleaching that is seen from time to time in local waters.  

The initial cost of a rebreather is about $10,000, but for repeated deep-water technical dives, it works out far cheaper in the long run. “If you dive to 200 feet with 20 minutes’ bottom time, the total dive time is two and a half hours with the final safety stop at 20 feet for 20 minutes, roughly speaking. With open circuit, it can cost $400 to $500 for the trimix gasses – oxygen, helium and nitrogen mixtures … With a rebreather, it’s about $50 to $70,” Mr. Gibb said. 

When the grouper spawning season came round again in 2010, Wayne Sullivan’s Glen Ellen boat was the base of operations for the East End site and West Indian Marine provided a 2,000-pound anchor, at which the boat moored.  

“We found 400 to 500 Nassau grouper and were able to confirm spawning events and so found that the east end of Grand Cayman has not reached critical mass yet,” Mr. Gibb said. 

In 2003, an eight-year fishing ban was introduced at Nassau grouper spawning sites in the Cayman Islands to protect the species, which is being pushed to extinction throughout the Caribbean due to over fishing. In 2011, based on the findings from the research group, the Marine Conservation Board extended the ban for a further eight years. 

“It was really, really important to be able to establish the fact that we still had a working aggregation in Cayman,” Mr. Gibb said.  

The Grouper Moon Project, which initially monitored Little Cayman and then Cayman Brac and extended to Grand Cayman in 2009, began in 2002, following two consecutive years of heavy fishing and imminent collapse of what was thought to be the Cayman Islands’ remaining viable spawning aggregation of Nassau grouper, located at the west end of Little Cayman.  

To alleviate the constraints of diving deep depths on regular scuba, Divetech and PM Gas of Grand Cayman, Silent Diving and Shearwater Research of Vancouver, British Columbia, donated equipment, training and gases to divers. Nassau grouper, which are usually solitary and territorial, travel during the winter full moons, sometimes over great distances, and group together to spawn.  

Around 50 spawning aggregation sites have been recorded throughout the Caribbean. Because the groupers tend to return to the same sites at the same time each year, it makes them easy targets for fishermen. This over fishing has led to between one-third to one-half of the known Caribbean aggregation sites to become inactive, according to REEF.