John G. Shedd Aquarium, Chicago, Illinois USA
Last week, you learned about how Shedd Aquarium’s long-term citizen science research program is helping to save endangered iguanas in the Bahamas. This week, we’ll explore another facet of our 2013 trip: an effort to understand whether the Andros iguana can swim, and what their behavior would mean for conservation.
You may be familiar with marine iguanas on Galapagos that can scull through the water searching for food. Or perhaps you’ve seen green iguanas drop from trees into rivers to swim away from disturbances. Can all 44 species of iguanas swim? Why does it matter to us? Does this knowledge impact how we manage endangered species?
On the move
On Andros, this question has particular importance as we work to develop management plans for a recently expanded national park that protects critical iguana habitat. Andros is actually a mini-archipelago of three main islands separated by “bights” or waterways. In addition to the main islands, hundreds of islets and small cays (pronounced “keys”) dot the landscape, connected by mangrove estuaries and tidal swamplands.
This network of small islands raises questions about how to approach population management for the species. Do the myriad waterways restrict iguana movements and thus isolate populations? If the Andros iguana can swim, how far can it travel? Some islands are separated by only a few feet of water, but other waterways on Andros are over two miles wide. How successful are iguanas in making their crossings? On a few occasions, I have observed iguanas swimming while predatory fish snap at their tails. If we can better understand the ability of these endangered animals to swim successfully between islands, that knowledge could help us determine whether to manage the Andros iguana as a single large population or many smaller populations.
On our most recent research expedition aboard Shedd’s vessel, the Coral Reef II, a team of Shedd biologists, citizen scientists, Bahamas National Trust representatives, and Giuliano Colosimo, a Mississippi State University graduate student working with Dr. Mark Welch, took up this question. This year, we explored a rarely visited region to search for iguanas on small cays so we could better understand their distribution across Andros. We also wanted to collect DNA samples throughout their range to better understand gene flow across the fragmented island landscape. On Andros, gene flow depends on the ability of iguanas to swim across water barriers. Isolated populations can potentially experience reduced genetic variability and subsequent inbreeding complications. It’s also important to identify isolated iguana populations with high levels of genetic variability, since these individuals may be good candidates for potential relocation efforts.
Searching for specimens
New technology makes it easier to identify potential sites than in years past, and we were armed with GPS coordinates and high hopes. Unfortunately, high hopes have a tendency to deflate after spending hours on a small boat in bumpy, wet conditions, followed by hours of walking on unforgiving terrain with little signs of iguanas. Luckily, the excitement of the chase and the camaraderie shared by team members made our adventure worthwhile and fun.
For three days we searched cays in the North and Middle Bights. Our efforts paid off as we discovered four new populations and increased sample sizes from areas visited in the past. More data helps us better understand the true genetic diversity from specific parts of Andros, and learn whether there are genetic similarities or differences between populations at different sites. The samples are so precious for our conservation efforts that you learn to get creative when confronted with new challenges. After an iguana slipped away from us into a limestone hole, I found that we could still collect a sample if I lay on my side with an arm down the hole to draw blood from the ventral side of the tail. It worked: I was dusty but happy, and the iguana was none the wiser.
By the end of the expedition, we collected 36 blood samples. It may not sound like much, but they will be combined with previous samples collected over the years that can help inform management plans to save this incredible lizard. It’s a lot of work for each iguana but well worth it. If you are interested in participating in the next research expedition, please contact us at IguanaResearch@sheddaquarium.org. Don’t just take my word for it—stay tuned for posts from our trip assistant, who will share her perspective as a citizen scientist on our program.