More than 100 sharks were counted by scuba divers in Cayman’s waters in January as part of a “citizen science” project to help keep track of numbers of the predators around the islands.
The shark logger program released its first year of data last month.
The statistics show that Caribbean reef sharks and nurse sharks are by far the most commonly sighted species in the islands’ waters. Tiger sharks, hammerheads and blacktip sharks have also been sighted around the island in the past year, but are comparatively very rare.
Johanna Kohler of the Department of Environment said the shark logger project deployed recreational divers and scuba instructors to collect data from their dives.
Each time they dive, participants record whether they see a shark. If they do see a shark, they record time, location, size and species and submit the data to the Department of Environment.
December 2016 and January 2017 were the biggest months for numbers, with more than 120 sharks spotted by divers in each of those two months. November, 2016 was the lowest, with just 14 sharks spotted.
Ms. Kohler cautions against reading too much into the monthly figures, however, since numbers vary depending on the weather and the number of divers involved. The number of divers has varied but is expected to increase as the program develops.
For a more useful guide to shark prevalence around the island, the department has organized the data by dividing the number of sharks spotted each month by the total number of dives carried out by the researchers.
On that scale, April 2016 was the busiest month, with divers encountering sharks on 62 percent of dives.
Ms. Kohler acknowledged there is no systematic way to ensure the same sharks are not counted twice, but she said the data is useful in creating a picture of how often sharks are seen in different locations around the island.
She said it dovetails with other research through the Cayman Shark Project, a partnership with Marine Conservation International, which uses multiple methods including tags to track shark movements to create an overview of the health of local shark populations.
The data is already helping to confirm theories about the seasonality of certain types of sharks in Cayman.
“The tiger sharks were seen only in December and January, whereas hammerheads were seen at different times throughout the year. It will be interesting to see if that trend is maintained as the project develops,” said Ms. Kohler.
Sharks are under threat globally and were recently declared a protected species in Cayman under the National Conservation Law.
Ms. Kohler said the project will help raise awareness and educate people about the importance of sharks to Cayman’s coral reef ecosystems.
Mauvis Gore of the Cayman Islands Shark Project said data from the studies will help with its research. Researchers on that project use a variety of methods, including monitoring reefs with baited cameras, to estimate shark populations at more than 30 test sites around all three Cayman islands.
She said, “The shark logger program ties in with other methods that we use to estimate the number and type of sharks around Cayman and any seasonality and location that is important, tying this in with the Marine Protected Areas.”
The Department of Environment is looking for more divers to get involved in the program. For information, contact [email protected]