A keystone species is a species that a large number of other species in an ecosystem depends on. If a keystone species is removed from a system, the species that it supported will also be impacted, as well as any other dependent species. Nassau grouper are a keystone species and influence both the structure of reef communities and promotes coral health. Unfortunately, it is estimated that 60 to 80% of Nassau grouper aggregations have been wiped out due to overfishing at the spawning aggregation site. Because Grouper don’t reach maturity until four to eight years of age, and juveniles are frequently predated upon, Nassau groupers’ population is slow to rebuild. This is why the protection of the remaining aggregation sites, like the largest known site in Little Cayman so important to the protection and recovery of the species. 

The Cayman Islands government has taken a series of management actions aimed at recovering collapsed stocks of Nassau grouper as a result of overfishing. The government partnered with academic and nonprofit organizations to establish a research and monitoring program (Grouper Moon) aimed at documenting the impacts of conservation action. Over the last 15 years, the Nassau grouper population on Little Cayman has more than tripled in response to conservation efforts. The findings demonstrate that spatial and seasonal fishing closures aimed at rebuilding aggregation-based fisheries can foster conservation success. From 1 December to 30 April there is a closed season for Nassau grouper in the Cayman Islands. In May, the limit is 5 per person or 5 per boat per day, whichever is less. Additionally, once the fishing season begins in May, only Nassau grouper between 16″ and 24″ can be taken, and only with a hook and line.

Sunday evening marked the first evening that we observed the Nassau grouper spawning at the aggregation site! It was an incredible site to witness. The groupers would shoot upward into the water column as they were spawning, like fireworks.  As the female went up into the water column swimming to release her eggs, several male groupers would follow, swimming in spirals around her. We also had several Caribbean reef sharks swim through the Nassau grouper aggregation site, which was an exciting way to watch the food web in action with the incredible apex predators amongst the groupers.

The day of spawning, we noticed several things on the morning dive that were clues the spawning might  start later that evening. We noticed that the female groupers bellies were swollen with eggs, and many more of the fish were in the bi-color or dark phase. There were very few fish in the normal or barred color phase. We also noticed changes in the current and the presence of other fish that we don’t typically see on the reef either. For example, two of the divers saw a school of blackfin tuna near the surface! This species is typically found far offshore in the blue ocean, not on the reef. Researchers think that the Nassau grouper possibly chose this particular spot off Little Cayman because the currents tend to push inward and down, to possibly keep the Nassau grouper eggs close to their home reef in Little Cayman, instead of using the currents to get some place else, like sea turtle hatchlings do. The researchers have special scientific instruments near the aggregation site to measure the currents and how the currents change. There are many questions about the Nassau grouper that the Grouper Moon Project team have and are researching. This is yet another reason why it’s important to stay curious and always ask questions about the world around you. Do you have any questions for the Grouper Moon Project team? If so, post them as a comment on the blog, and the team will try to answer them for you.

 

This evening, January 31st, marked three evenings since the Winter Full Moon on January 28th. Any guesses for whether the Grouper Moon Project research team on this evening’s dive saw any Nassau grouper spawning?

Today at the Nassau grouper spawning aggregation site, we sadly found a large plastic bag floating in the ocean. Paul Chin from the Grouper Moon Team was able to remove the bag from the ocean.

Plastic pollution is an ever growing problem around the world. Seeing large plastic bags like this in the ocean is devastating as sea turtles, fish, or other marine life could easily become entangled or ingest the plastic.

It is estimated that eight million tons of plastic enters our ocean every year, which is in addition to the estimated 5.25 trillion pieces of plastic already in the ocean.

You can help to reduce plastic pollution in our oceans by refusing items that come in single-use plastic packaging, recycling, participating in beach cleanups, and educating others about plastic pollution. Together, we can make a difference.

I arrived in Little Cayman to join the Department of Environment Grouper Moon Team Friday after school. So today was my first official day with the team and underwater with the Nassau grouper! The seas were a bit rough today, but what a day we had! Each day there are three dives – a morning dive that leaves the dock at 8 am, an afternoon dive at noon, and an evening dive at 4:30 pm. 

There are three main tasks for the team of divers on each dive. The first is a research method called ‘Fish Faces.’ This year instead of physically tagging the grouper to obtain an estimate of the population size, researchers are obtaining images of individual grouper ‘faces’ or the sides of the grouper. Each grouper has a pattern that is unique to only him or her, sort of like our fingerprints! Using a GoPro on a long selfie stick, we take videos of as many fish as we can so that the researchers can use AI software to identify each fish. Today there were many fish, in the thousands! Some were up in the water column against the edge of the coral reef wall. Other grouper were resting at the bottom of the reef along the sea floor. Today we had three buddy teams, so a total of six divers, doing ‘Fish Faces.’

The second task that a buddy team of divers is assigned to is ‘Stereo Video.’ The Stereo Video is a specially designed device to take length measurements of the grouper. It is essentially a long stick with a GoPro on each end. This device is used to measure the length of different Nassau grouper at the spawning aggregation site. Length data is important because the larger the fish are, the more eggs the fish will have. Also, the fish get bigger as they get older, so this is one way to determine how the population of fish is growing.

The third research method that we are using is a ‘Video Pan.’ This is probably the most exciting! Two divers are propelled through the water on underwater scooters and dive the entire length of the band of fish, sometimes this can be longer than 100 yards, the length of a football field! 

We are expecting the peak spawning to either be on Sunday or Monday, so stay tuned for tomorrow’s post!

Hi Everyone! My name is Amanda Brown, and I will be joining the Cayman Islands Department of Environment (DoE) and Reef Environmental Education Foundation on this year’s Grouper Moon Project in Little Cayman.

I am a grade two teacher at Cayman International School on Grand Cayman. In Grade 2, my students do a Project Based Learning Unit on the ocean, and our driving question is, “How are we connected to the sea?” Engaging students in the Grouper Moon Project each year is one of the many ways that we develop their understanding about how we affect and are affected by our ocean.

Outside of the classroom, you will find me scuba diving our coral reefs in Grand Cayman, volunteering with the Department of Environment’s sea turtle monitoring program and Stony Coral Tissue Loss Disease project, and helping with the Guy Harvey Ocean Foundation’s conservation efforts and surveys at Stingray City Sandbar. I absolutely love the ocean, and it brings me joy to share all of the ocean’s wonders with my students!

This year I am incredibly excited to join the Grouper Moon Project’s research team, and to bring the project to life for my students in a way that I’ve only dreamed of.

I’ll be updating this blog daily, so check here for updates, exciting videos, and a behind the scenes look at this year’s Grouper Moon Project!

Hi Everyone!

I hope you all enjoyed today’s livestream from Bloody Bay!!  We saw so many amazing things and you had absolutely fantastic questions! Thank you all so much for being awesome audience members.

Today, I’m posting a short video clip taken at the spawning aggregation site. Look very closely and see how many different color phases you can identify.  Please leave any comments or questions below.

Enjoy!

Todd