What Happens When A Species Disappears?

“My big fish must be somewhere.”

Ernest Hemmingway, The Old Man and the Sea

In the US Virgin Islands, the parrotfish once made a delicious and frequent appearance on the dinner table. They were plentiful, easy to catch and their big scales made them easy to clean.
It was a thrill to snorkel with them and admire the amazing rainbow of colors they shamelessly displayed. They were everywhere.
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Parrotfish have been a highly favored food source throughout the Caribbean. This has lead directly to their significant population decline.

Tragically however, larger parrotfish like the Blue, Rainbow and Midnight, have been completely removed from the USVI coral reef ecosystem and indeed the marine food chain due to fishing. These popular species were easy targets for spearfishing, pot fishing and hand line fishing.

The consequence of the loss of a major player in the coral reef environment is unknown. What we do know is that the largest parrotfish species are effective at controlling large algae on reefs. This is the algae that can smother corals and cause reef degradation. What happens on coral reefs when these fish disappear?

Coral reef fish Scarus 2
Species like the Queen Parrotfish seen here, and the Stoplight Parrotfish can still be found in USVI waters, although to a much lesser extent than before. However, it is the loss of the larger species that has caused alarm. *Notice the beak-like teeth used to scrap the reef clean.

In stark contrast, parrotfish populations in Bermuda are significantly more robust; their population rebounded rapidly following a ban on pot fishing in 1990. Because of their vibrant numbers, University of the Virgin Islands researchers are investigating The Effects Of Herbivory By Large Parrotfish Species On Coral Reef Ecosystems Along A Latitudinal Gradient, or, more simply, comparing the parrotfish’s impact (or lack of) on the ecosystems in Bermuda vs. the USVI.  Scientists are trying to determine the role large species of parrotfish had in maintaining ecosystem health.

Why Is This Important?

Well, there is the obvious tourism-related bonus of having these gorgeous multi-colored fish swimming around close to shore. But more significantly, their importance to the health of coral reefs cannot be understated. The parrotfish eat algae growing on coral as well as small organisms which may be hiding in its crevices. Their huge, fused, beak-like teeth are uniquely suited for this task as they simultaneously grind coral into soft white sand. By removing the algae, in essence “tidying-up” the reef in aquatic Marie Kondo style, the coral stays clean, less susceptible to disease, and prepared for new corals to attach and grow.

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Researchers have travelled to Bermuda to study their more vibrant parrotfish populations. Here they tag and measure the fish before returning it unharmed to the ocean.

With funding from VI-EPSCoR, Drs. Rick Nemeth, Marilyn Brandt and Tyler Smith are working collaboratively to compare populations and ecosystems in Bermuda (high parrotfish density and diversity) and the USVI (low parrotfish density and few to no larger species). One of the key questions they would like to answer is how much algae do parrotfish actually eat, and does the size of the fish matter?

Methodology

Two methods can be used to answer this question. One is to actually follow a parrotfish for a period of time and count how many times it takes a bite. This method is limited because we don’t know how long a parrotfish feeds or how far it swims each day.

Another and more effective method used to gather this information is acoustic telemetry.

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Dr. Rick Nemeth surgically inserts an acoustic tracker into the belly of a fish. After a little bit of antibiotic is applied the fish is stitched up and returned to the sea. There is little to no mortality to the fish as a result of this procedure.
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Seen here, a hydrophone is attached to the ocean floor.

Using acoustic telemetry, tags surgically implanted into the fish send out unique pings every minute. These pings deliver information to strategically placed hydrophones or receivers which record the fish’s identification code, date and time. Scientists turn this information into maps of the fish’s movements over weeks and months.

The area of study in Bermuda is Hungry Bay where researchers track the fish’s movements and its habits. To date, three Rainbow and one Blue Parrotfish were tagged in July, 2015 and four Rainbow Parrotfish were tagged in August, 2016. Scientists have been able to observe so far that the parrotfish are active swimmers from approximately 7am – 7pm and stay loyal to their home territory (Hungry Bay). This helps us to understand how long a fish may be feeding each day. They appear to leave the bay about two weeks every month during the winter (December thru March). We are not sure where they are going when they leave the bay or if they continue to feed, but that is another mystery we would like to solve in the future to better understand these important species.

Meaningful Partnerships Have Been Forged

This project has been possible only with the help of many individuals in Bermuda who have worked closely with our team. In particular we wish to recognize the support of Drs. Tammy Trott, Thad Murdoch and Robbie Smith, and Hugh A.C. Davidson, Andreas Ratteray and the residents of Hungry Bay.


Postscript

In response to comments received, we note that our intention is not to blame fishermen for the loss of these species but to bring attention to the issue and to the hope research efforts bring to this discussion.

It is important to note however that overfishing caused the original decline in populations of these large parrotfishes. Subsequent recovery may have likely been slow due to habitat loss and possibly pollution and sedimentation. Because they disappeared before there was research done on these species, little is known about their early life history habitat requirements and nothing is known about how they reproduce. It’s also possible that recreational fishing pressure has continued to suppress populations since no real outreach/education programs are informing the general public about local and federal regulations.
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