Friday, April 4, 2014

The Manta Rays of Guam

Mantas are like really, really big flat vegetarian sharks
We had the chance to meet up with Julie Hartup of the Manta Trust in Guam this week.  After a short dip in the ocean, she agreed to an interview for our blog.

Shark Defenders: What attracted you to study mantas and where can you find them in the Micronesia region?

Julie: While diving in Yap I had some incredible interactions with reef mantas. At the time I was trying to decide if I wanted to return back to school to obtain my Master’s degree and what marine animal I would want to spend the rest of my life studying. I was surprised to learn that no one was studying the Yap mantas, and no one knew about any of the manta populations throughout Micronesia. I decided to start studying manta rays, right here in my own backyard, here in Guam through the Master’s Program at the University of Guam Marine Lab. We knew from snorkeler’s and divers that Guam had a population of manta rays but knew little to nothing about them. It has taken a lot of hard work but we have been learning a tremendous amount about Guam manta rays and manta rays throughout Micronesia, more then I expected. It has personally been rewarding.

Angelo, Julie Hartup of the Manta Trust, Elise, and Joni Kerr from Guam Community College
SD: What are you learning about the mantas in Guam? Is there something unique about them?

Julie: Mantas can tell you a lot about themselves, just by looking at them. Each manta has unique spot patterns on their belly’s that enables you to tell one individual from another. The size of the manta gives you an idea if it is young or a more mature individual. Presence or lack of reproduction appendages tells you if it’s male or female. Scars can tell you if the mantas are mating or what natural or anthropogenic pressures they might be experiencing. For instance, in Mozambique mantas have more shark bites, Maui mantas have higher number of missing cephalic lobs (those paddle like appendages coming off the side of their mouth region) from getting tangled in long fishing gear. Guam mantas have cuts and slashes in them, most likely from boats and wave runners.

To date we have found a unique in behavior in our Guam mantas. I had heard of two different times in 2010 people had seen mantas feeding where fish were spawning. It was thought the mantas were feeding off the fish spawn since mantas eat zooplankton. I figured that if mantas were targeting these events to feed, I would need to find out where and when these spawning events were taking place. The idea was that the spawning aggregation of fish would lead me to the mantas. In 2012 I had two predicted spawning dates I had transposed from the 2010 dates and moon phases, a site, two species of fish thought to spawn, and two different daylight times. I was hoping the mantas would show up. Sure enough on my first predicted event, my snorkeling partner Paul Carlson and I went over the reef where we actually had two species of fish spawning (one of those species was unexpected), hundreds if not thousands of fish and 12 mantas were feeding off the fish spawn. Several months later we had the second predicted event of a different fish species, and sure enough we had a huge aggregation of fish spawning and again at least 12 manta feeding. It was the biggest thrill I’ve ever had. I just couldn’t believe my hypothesis, theory, and methods all worked. It had been documented that whale sharks, a relative of manta rays, targets fish spawning aggregations to feed, but this was the first every documented event of manta rays targeting fish spawn as a food source. Our Guam mantas created scientific history, it shows how important studying new things in new areas matters, adding to the overall scientific understanding from other regions. I have been learning so much about mantas and fish spawning aggregations at these events.

SD: The manta rays you are seeing in Guam are just outside the marine protected area in Tumon, which up until the reserve was created a few years ago was full of jet skis, banana boats, and dinner cruises. Do you know if the creation of the protected area is responsible for the appearance of the mantas?

Julie: It would be great to have previously collected data, or information prior to when the MPA was established but unfortunately we didn't. What came first, the fish spawning, mantas, or the MPA? I would love to answer that question. I’m assuming we can’t prove this, but I know the MPA has had a huge positive effect on the number of spawning fish. If the MPA were not there, those fish numbers would be dramatically lower, if not completely gone. Fishing at fish spawning aggregations is an easy way to get a high volume of fish with the least amount of time expended, however this can radically increase the potential to overfish a population if not regulated. It’s no secret Guam has been overfished, and if the MPA weren’t there, I believe all the fish and healthy corals starting to thrive there would not be there as well. We would mostly have intermittent live and dead coral, limited fish, low diversity, and algae, which isn’t too attractive to tourists. By creating the MPA the fish population was able to naturally increase. More fish in a spawning aggregation make more noise and emit natural chemicals into the water probably attracting the mantas.

Additionally, manta rays are shy creatures. Loud noises from boats, or waver runner traffic are not a draw for manta rays. Local residents have noticed that in another area where mantas regularly were sighted in the past have decreased. This area, over the years has had increased boat and wave runner action. I wonder if we limited boat and waver runner activity in certain areas if the mantas would return to those habitats? We could have areas where tourists and locals could enjoy wave running and habitat areas unobstructed for the manta rays.

Wouldn’t it be great to build up sites where mantas rays are frequenting? We could have a potential of creating areas tourist and locals could see these magnificent animals without chasing them off. Manta rays currently bring in $140 million dollars worldwide annually for ecotourism. If we were able to do this in a correct and controlled manner, as not to affect the mantas or other interest groups, it’s a win-win for everyone. By creating the MPA and limiting the boat and wave runner activity it allowed an area for manta rays and fish to naturally flourish. Just like in society we need different roles for a thriving community. We need MPAs or Community Based Managed Area for us to have healthy reefs and “good” fishing. I’m a believer in sustainable management. However, there are some fish or marine animals due to their life history that cannot and should not be fished. Manta rays and sharks can’t support sustainable fishing. Living on an island, fish is a major proponent of the communities diet, social interactions, businesses, and cultural history. I just want to make sure all these things can be around for the next generation.

SD: Some of the places you work, including Palau, Yap, and Guam, have legislation protecting manta rays. What is the reason behind doing that?

Julie: Manta rays, just like thier relatives the sharks live long, mature late, and have a limited number of offspring. Mantas are thought to live at least live 50 years and maybe even on up to 100 years. However, we only have documentation of mantas living 30 years since we just started studying them in the last several decades. Marine animals that have life histories such as manta rays need protection. Luckily our Island of Guam and several other Micronesian islands know how important they are and have protected manta rays along with sharks. Yap and Palau have seen the benefits of manta ray ecotourism making them even more important to these regions to protect. These animals are magical. I’ve spent hours diving next to these creatures and every time I come away in awe of their beauty. I’m very concerned about the recent proposed Shark fishing in the Mariana Archipelago. Our Guam law would be dissolved leaving Guam sharks and manta rays unprotected. These magnificent animals could be fished out for their gill rakers ending up in a Chinese medicine store or as a supplement ingredient for shark fin soup. We would never know if Guam could have actually set up dive ecotours around our manta population.

SD: Thanks, Julie.
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