I’m the Executive Director for the Hawaii Association for Marine Education and Research (HAMER)(www.hamerinhawaii.org), and I have been studying manta rays in the Pacific for the past decade. Using methods of photo-identification, paired-laser photogrammetry, genetics, acoustic and satellite tagging, we are learning what habitats are critical, how they use these habitats on a daily and seasonal basis, how quickly they grow and mature, how often females get pregnant, what mating strategies are used, and how much of a threat large sharks and humans have on the survival of these majestic, large-brained giants.

I've spent the last 10 years conducting long, arduous swims in full dive gear, battling howling winds, pounding surf, ripping currents, and even fighting off tiger sharks to save and protect Hawaii's majestic giant manta rays and the habitats they rely on for survival. I will do whatever it takes.

We recently launched a crowdsourcing campaign to help understand why 10% of Maui’s mantas are getting entangled in fishing line and what can we do to mitigate against this threat (www.savemauimantas.org). We have 4 days remaining in our campaign. I’m happy to answer all your questions about studying manta rays and all that is good, bad, inspiring and heartbreaking. Ask me anything.

Proof here

"UPDATE: Thank you for the awesome questions! I have to go now but I will be checking in periodically to see if there are anymore questions. Don't forget to check out our Save Maui Manta's Indiegogo Campaign and help us get to 100 supporters before our time runs out (1 DAY LEFT!). Even if you donate just $1 you will help us achieve our goal and that would be very, very cool. We only need 6 more supporters!! www.savemauimantas.org "

Comments: 102 • Responses: 44  • Date: 

andayy14 karma

Hello Dr. Mark,

I've always been in love with the ocean, and all the creatures in it. It's my dream to be a marine biologist. I've already become SCUBA certified, and am fluent in a few languages, which are all things that I have read will help when I finally enter the workforce.

My question is, what are some of the unique challenges facing young people that wish to pursue the field of marine biology?

Do you have any words of wisdom for me, and others, that hope to follow in your footsteps?

and, as a more fun question, where is your favorite place to dive, or just visit?

DrDeakos3 karma

Thank you for your question. You are very lucky to have such passion already, many people never really know what it is they want to do. My advice to you is to study hard and get as much experience as you can. In today's world, you not only have to have good grades but you need to have experience in the workforce. This may mean volunteering at first so you can start to build that experience. Also, be determined to succeed regardless of what people tell you, only you can stop you from what you want to do.

My favorite place to dive was Palymra Atoll, a small island about 800 miles south of Hawaii. The reefs are so beautiful that it almost does't seem real.

pinkseaglass8 karma

Whats the most amazing thing you've seen/your favorite moment from out in the field?

DrDeakos10 karma

Hard question to answer, the turtle that landed on my head as I was filming a manta ray or the tiger shark that gave me a kiss were both kind of cool



pinkseaglass3 karma

The fact that you have both of these things on video is really amazing. Thanks for the reply! That turtle made my day :)

DrDeakos2 karma

You are welcome, that turtle made my day as well :)

littlelobos2 karma

YIKES! How large of populations of sharks do you deal with? Are they aggressive? Are they usually seen within range of Manta Rays?

DrDeakos2 karma

In Maui, I almost never see a shark around the mantas but that doesn't mean they aren't there. When I studied manta rays in Palmyra, I had 2-8 sharks around me almost all the time, mostly black tip reef sharks and grey sharks, which are rarely a problem. On a healthy reef, you should see lots of sharks.

littlelobos6 karma

What is the bare minimum gear you use to study manta rays? How much gear/planning does it take to be a "Manta Ray specialist" in Maui?

DrDeakos8 karma

To do manta ray research at a basic level, you only need a snorkel and mask and a camera. If you can free dive and get a photograph of the manta ray's belly (each manta ray has a unique set of spots on their belly that identifies them), you can keep track of individuals each time you go snorkeling and over time you develop life histories of individuals (who hangs with whom, how often is she pregnant, etc.).

scubasnak5 karma

Do manta rays reproduce often and HOW do they reproduce? Do they lay eggs or have live babies?

DrDeakos9 karma

Manta rays only have one pup every 2-3 years on average in some populations and maybe every 5-7 years in other populations. The pups are born live and have a disc width of about 4 feet. Males have claspers (same as sharks), cigar shapped appendages by the genitals and while biting the female's pectoral fin (almost always on the left wing) from above, they bend their body so that they are almost belly to belly to insert one of the claspers into her cloaca. He pumps rapidly a few times and ejaculates, usually lasting less than a minute before they break apart and go their separate ways. https://www.youtube.com/watch?v=KZGT2uH7dho

scubasnak3 karma

So it sounds like they are pretty slow reproducers then? Does this mean they are also more vulnerable to rapid decline?

DrDeakos5 karma

Absolutely, we call these K strategists (slow maturation, small, infrequent litters, long lifespan), which means it takes a long time for a newborn to enter the reproductive pool. And so if you remove even a few individuals from the population, especially mature females, it takes a long time to replace that individual. In areas where they are hunted (e.g. Indonesia), small local populations could be wiped out in a matter of months.

darbyr4 karma

It sounds like you have spent quite a bit of time with the manta rays. Have they become accustom to you being around them and do they interact with you? Are they ever protective of their territory or do they constantly move around?

You mentioned 10% of Maui's manta rays show signs of entanglement. Does this number include those that have been killed by the fishing nets, or just those that have survived and have injuries?

I am also interested to hear about the acoustic tagging as previously asked. Thank you!

DrDeakos5 karma

I've spent about 10 years and over 500 dives. Some populations are more used to people than others. They are very curious animals, often investigating divers and boats (they have very large brains even compared to the size of their body). The 10% is only the survivors, I don't know how many are being killed from entanglement other than one in Maui and one in Kona that drowned after entangling in a mooring line, so the 10% is a conservative estimate.

MightyTaquito3 karma

Can you give us a really gnarly dive story?

DrDeakos4 karma

One time I went diving on the North Shore of Oahu, a place where there are lots of caves and connecting channels, spaces so tight that you can get in but can't always back back out. Before the dive I asked my dive buddy to check my air to make sure my tank was on. He turned it on and backed it off the threads a quarter turn. During my dive I felt very claustrophobic inside the caves, felt like I was breathing air through a straw, but kept telling myself that it was my mind racing and calming myself down. After 25 minutes I had to bail on the dive because I was getting headaches. Later I realize my dive buddy had shut my tank off and opened it only a quarter turn, thinking he turned it on all the way. Is that gnarly? Adam, if you are reading this, I have forgiven you...

KingOfDaCastle1 karma

I've never had my tank only a tiny bit open before, would you not detect that during your gear check?

DrDeakos2 karma

I would have but I trusted my dive buddy and he thought "on" was in the other direction so he accidentally turned it off, then came back a quarter turn to back-off the threads leaving me with a pinhole flow of air to survive on. Of course if you ever see your pressure gauge needle move when you take a breath, that is an indicator that your tank is not fully open.

dannywarbucks112 karma

Have you been haunted by the ghost of Steve Irwin?

On a serious note, what interesting facts about Manta Rays do you know, something that the layman wouldn't?

DrDeakos3 karma

Remora fish sometimes live inside the genitals of a manta ray. I couldn't believe it when I saw a manta ray poop and two remoras came out and then went back in. Crazy.

Moonsnail82 karma

What is your opinion on the organized manta ray night dives? Are they harmful to the rays?

How can I, as a diver, help mantas?

Thank you!

DrDeakos2 karma

Something interesting I learned in my limited work in Kona, where they do they famous manta night dive is there are some manta rays that choose to join in the light show and others that don't, but we don't know who benefits most. Most of those involved in those dives do an excellent job at educating their customers and minimizing the impact on the mantas so I applaud them. However it is getting more and more crowded each year, posing some safety issues, more so for the people than the mantas in my opinion, but they are working together at solutions.

Oh, and if you want to help the mantas in Maui you should visit www.savemauimantas.org.

DrDeakos2 karma

Thanks for all the awesome questions. I am signing off for now but will be checking back in periodically for any new questions. Please don't forget to check out our Indiegogo Campaign to Save Maui's Mantas at


Even if you donate just $1 you can get us over the 100 supporters goal our campaign ends in just 4 DAYS, and that would be really cool!

mark89922 karma

At what age do mantas rays become sexually mature? Also, there are a few aquariums (like the one here in Atlanta) who have captive manta rays. Do you care to share your opinion regarding keeping mantas in captivity? The artificial habitat here is the largest of its kind anywhere - over 6 million gallons, but clearly very small compared to their natural environment. It is wonderful to get to observe them up close (you can even sign up to dive with them if you are scuba certified) but I am unsure if the educational benefit of keeping them captive is greater than the sad fact of their loss of freedom. I would be happy to know your opinion about it.

DrDeakos2 karma

We don't really know at what age manta rays reach sexual maturity, at least in wild populations since you would need to know the birthdate of a manta ray and no manta births in the wild have been documented. Current thoughts are between 6 and 10 years old. Perhaps they know in captivity and this could be one of the benefits, learning some information about their life history that can help wild populations. Captivity is a controversial topic and I would say that benefits to wild populations (new information that can't be obtained in the wild, public awareness and education) would need to outweigh the costs of captivity (disruption of its wild population, the animals quality of life). How you measure and compare those two things is difficult and subjective.

littlelobos2 karma

As a young person interested in conservation practices, I am interested in how you become interested in Manta Rays? How did your research come to fruition?

DrDeakos3 karma

I always felt at home in nature and around animals so naturally studied biology for my undergrad. I also liked the ocean (competitive swimmer and waterpolo player) so I combined the two in marine biology. I came to Hawaii to study humpback whales (my master's degree) but while scuba diving on my free time, became interested in manta rays and decided to do this for my PhD research. The best advice I can tell you is to follow your passion no matter what. Many, many, many people will tell you that you are crazy but only YOU can stop yourself from living your dream.

Smellzlikefish2 karma

Hi Mark! I'm a manta-dive videographer over here in Kona and appreciate all you are doing to help mantas in south Maui. Your recent estimate for how many mantas are affected by fishing line is shocking and yet maybe an underestimation for the animals here. I just wanted you to know that you do not fight alone. Beyond picking of derelict fishing gear and raising awareness of mantas through education on the night manta dive, how can I help more?

DrDeakos1 karma

Glad to hear you are doing your part. The Kona mantas are pretty amazing and I'm always amazed when I hear the stories of hooks and line being removed from mantas. I think we need more discussion within communities about the state of our coral reefs. Here on Maui, Community Based Marine Managed Areas are becoming very popular where independent communities meet once per month and develop a management plan for their marine resources in their backyard. Starting a CMMA in your community could be very beneficial.

octobimpe2 karma

When did you know you wanted to be a marine biologist? How were you introduced into the field? Also, have you alwats been passionate about mantas? Have any other animals inspired your research?

Themanxyboy1 karma

Hey dr deakos! I want to become a marine biologist when im older (or more specifically, a shark biologist) my current grades are B for biology B for chemistry and C for physics, I wanna take a marine biology course at uni, but tell me, was it hard work for you? Did you struggle? (Oh and just a side note I am taking a scuba diving course too)


DrDeakos3 karma

Yes, I did find my classes challenging and had to study very hard. Something I didn't find out until my last year in college is to always go and talk to your teachers after class, or especially before an exam. I could never understand how some of my friends were doing so much better than I in the classes until I learned they got "extra" information by talking to the teachers. I wish I had known that in my first year. You don't have to have straight A's to be a good marine biologist but you do have to work hard. Enjoy your scuba diving class!

sheik_yerboutis1 karma

can i join you?

DrDeakos1 karma


scubasnak1 karma

How can people find out more about connecting with you and HAMER to volunteer or intern?

DrDeakos1 karma

You can visit our website at www.hamerinhawaii.org or email us at [email protected].

trainspotter11 karma

Did you have to have any diving experience or qualifications to get into your job in the first place?

DrDeakos2 karma

I've always been a water person, first a swimmer, then water polo player, then started scuba diving and I was hooked. There are a lot of marine biologists that don't know how to swim or scuba dive so it isn't necessary but depending on what type of career you want to pursue, it may be a requirement. To do the type of work that I do, you definitely have to be comfortable in the water and know how to scuba dive.

zakriboss1 karma

What do you think the best approach is to working to fix this problem?

DrDeakos1 karma

We first need to know what habitats are important to the mantas so we can protect those habitats. Satellite tags are the best way to get that information but tags are expensive. The tags would likely reveal areas that the manta rays spend a great deal of time in that overlap with high fishing pressure. Once we learn about those areas, we can make fishermen aware so they don't keep losing there fishing gear, which can be expensive. Perhaps there are ways to modify the gear to still catch their fish but that may be more safe for the manta ray.

h20bugz1 karma

I'm assuming mantas have ampulla of lorenzini, I heard it was used for mating, is this true?

DrDeakos1 karma

Since they are closely related to sharks, they likely do but they have become plankton feeders rather than searching for prey in the sand, so it is possible that the system is no longer well developed. I do know that if they don't know I'm above them, my hand needs to be about 1 foot away from them before they sense it. I am not aware of it being used for mating.

Geoffany1 karma

Dr. Mark, how does someone young and enthusiastic, like myself, without a bachelors degree in any scientific field (or at all) get involved with something like marine conservation? I think there are many people who are stuck in the office-job world to survive but only earning enough to do so and not ever really break out. I have a passion for marine conservation and would happily quit my job and leave tomorrow if I knew there was some kind of option available for this.

DrDeakos2 karma

Well, the world can always use more conservationists. You don't have to have a degree or be a scientist to help, many people do their part in other ways (participate in beach cleanups, support plastic bag ban, support a cigarette ban on the beaches, start or attend a Community Based Marine Managed Area, etc.). You don't have to quit your job to support marine conservation. i don't get paid to do manta ray research, i do it in my free time.

stevehokie1 karma

Do you feel that the targeting of manta rays in this manner is raysist?

DrDeakos1 karma

Ha, I understand your question now, ray-cist, very funny!

Currie691 karma

Is anybody a marine biologist?!?!?

DrDeakos1 karma

Anyone can get involved in marine conservation, you don't need to be a scientist.

awesterdam1 karma

Is there a purpose for their tails?

DrDeakos2 karma

Interesting question. They used to have a spine, much like stingrays for defense, but with their large size it was no longer naturally selected for, so all that remains is a vestige bone where the spine used to be. Given they still have a tail, I would suspect that it is still being selected for, otherwise I would think they would have lost it by now, much like the defensive spine. However, we have many mantas in our population that have lost their tail and they seem to function perfectly fine. Good question.

hofftrot1 karma

Is it bone or is it cartilage as it is with sharks?

DrDeakos1 karma

mantas have no bones, just cartilage like sharks

Begginstrip1 karma

Hi Dr. Deakos, as a person with Thalassophobia, I have to ask - does anything in the ocean actually scare you? Other than threatened ocean habitats, of course.

DrDeakos2 karma

I think like most things, the more exposure you get, the more comfortable you get, fear is mostly of the unknown. When I dive in new places and I don't know what to expect, I certainly have more anxiety so I in those situations, I would dive with someone who knows the area well. Most people's fear of the ocean is fear of sharks, which is a product of the movie Jaws and the media. If you look at the statistics of shark attack deaths, you have a better chance of getting hit by lightening. I would suggest getting more exposure to the ocean so it becomes familiar, either though videos, or shallow tide pools, and go with very experienced friends, it won't take long before you become addicted to the ocean.

MightyTaquito1 karma

How old were you when you decided to/started to pursue marine biology as a career?

DrDeakos1 karma

My third year at University, around 22 years old.

Galelao1 karma

How big of a problem is manta ray entanglement, and where is it worst in the world today?

DrDeakos2 karma

We know very little about the level of threat, entanglement in fishing line is having on manta rays. Although many mantas have been photographed with injuries that appear to be from entanglement, in populations all over the world, nobody has quantified the threat except in Maui. In Maui, one in ten manta rays among its 330+ individuals has evidence of entanglement, which to me, is unacceptable and needs to be mitigated.

littlelobos2 karma

When you say entanglement, I'm assuming you mean fishing net entanglement, correct? What practices are other fishing operations (in other unthreatened manta ray habitats) utilizing that could be effective to prevent this from happening?

DrDeakos2 karma

Regarding entanglement, I can speak mostly about the Maui population, and this is entanglement in monofilament line not nets (few nets around here, or at least it is illegal to leave them unattended). Since fishers don't want to loose their fishing gear (and guaranteed a 1000 lbs manta will spool their gear in no time), they would benefit from knowing where the manta rays spend most of their time and are more likely to get entangled. The fisher then has the choice of fishing somewhere else, where he can equally catch his prey. Another option would be gear modification but this would take some creative thinking, much like they do with false killer whales and turtles to allow fishing to continue while minimizing the threat.

22PoundHouseCat1 karma

You mentioned acoustic tagging, could you go into more detail about? What it is, and how you use it in your studies?

DrDeakos3 karma

Acoustic tagging involves a small tag, about the size of a Sharpie, that contains a battery, some sensors (usually measuring light, depth, and temperature), and emits a high frequency signature that can be heard by special, bottom mounted receivers. When attached to a manta ray, it will record light, depth, and temperature every few seconds and when it passes within 1 km or so of a receiver, it will transmit the information to the receiver. The signature will also tell the receiver, which manta ray this is. The scientist can then download the data from all his receivers and learn about which manta rays were in the area, how often they come to the area, and a bunch of information about how they spend their time diving throughout the day. We will use acoustic tags in the same way to get residency information and dive profile information from our mantas.

hofftrot1 karma

Dr. Mark, do tags hurt the manta rays?

DrDeakos2 karma

The tags are very small (the size of a sharpie pen) compared to the mantas (12 feet wingspans weighing more than 1000 lbs), so they appear to have very little impact on the manta ray and have stayed on some animals for over a year.

hofftrot1 karma

Whew! I was worried about animal cruelty....so if I want to contribute to your cause how do I do that?

DrDeakos1 karma

This is our Indiegogo Fundraiser (ONLY 4 DAYS LEFT!). Some cool videos and picks on there as well so you can learn all about what we are trying to do.

IamTori1 karma

Hello! My friend and I are both super interested in what you do- can you give us advice on how to achieve success in working in an area that you are both passionate about and highly interested in? Especially because it is both in the fields of science and conservation- sometimes these fields can work against each other I presume? Do you even find there are things you can not prevent?

DrDeakos1 karma

Conservation can be very challenging in the world we live in today because so many are disconnected with the natural world. My advice would be to surround yourself with like-minded people who are equally as passionate, they will give you strength, especially through the challenging times and don't forget to celebrate the wins. If you have passion about something, that in itself is a gift so follow it through.

"Never doubt that a small group of thoughtful, committed citizens can change the world; indeed, it's the only thing that ever has."

--Margaret Mead

scubasnak1 karma

Do you ever take volunteers to come work with you?

DrDeakos1 karma

Yes we do and not just marine scientists, we are always looking for people with expertise in accounting, marketing, fundraising, grant-writing, relational database management, website management, and public relations. We also need people to help match new photos to our manta ray catalog, a great tasks for kids. You can check out our website at www.hamerinhawaii.org or email us at [email protected].

h20bugz1 karma

So you obviously have a plan to help the Maui manta ray population avoid entanglement, but what if you don't get all the money you want from Indiegogo? Also, if I don't have a bunch of money are there other ways I can help?

DrDeakos1 karma

With the funds raised thus far and an additional tag that was donated, we can get some very good information already. There are also other ways to get good information and that is by using Citizen Science. Since most places that have manta rays living in and around their reefs usually have divers and snorkelers in the water with cameras almost every day, we can take advantage of those eyes on the reef. During your snorkel or dive, if you take a picture of the belly spots of the manta ray (manta ray's identification), you can submit that photograph to researchers with a date, time, and place where you got the photo. Over time, these photos can provide a lot of information about the behavior pattern of these manta rays. For example you can check out the Maui manta ray catalog here: http://hamerinhawaii.org/page30/page62/ to see if any of your Maui manta rays match and send the photo to me at [email protected]. If you don't live near the ocean, you can still help by looking for matches with other peoples photos and researchers are always looking for volunteers to help with matching.

seabassett1 karma

What is the safest way for fisherman to ensure that they do not tangle manta rays?

DrDeakos0 karma

I think making fishersaware of where manta rays spend a lot of their time, especially at night when in shallow waters. The tagging work we plan to do (www.savemauimantas.org) will help us learn that information. The last thing a fisher wants to do is loose all their fishing gear (expensive) when they get spooled by a large fish. Our research will help them make better decisions.

scubasnak1 karma

It there certain gear that is better or worse, or is it just a matter of position?

DrDeakos1 karma

This is great question and I don't yet know the answer but I'm confident that fishermen and scientists working together, we will find the answer to this question.

BolshevikPower1 karma

Hey guys!

Just wondering how much interaction you have with other organizations online. I'm familiar with MantaMatcher.Org or AquaticAlliance.Org with my dive time in Indonesia.

I know they have vast databases of individuals in the area they research, do you guys all share to try to track the pelagic movements of manta rays?

Side Note : What type of Mantas do you typically get in Hawaii?

DrDeakos1 karma

Yes, we work closely with other organizations studying manta rays like the Marine Megafauna Foundation, Manta Trust, Manta Pacific Research Foundation, Conservation Society of Pohnpei and Yap Divers and we are discussing ways of collaborating our manta catalogs in a way that benefits everyone and most importantly, the mantas.

We have two species of manta ray in Hawaii: 1)Manta birostris (pelagic mantas) and Manta alfredi (reef-associated mantas).

Raidenoid1 karma

You sound awesome! Also is it acceptable to call manta rays flap-flaps?

DrDeakos3 karma

Of course it is. Is it ok if I start calling them flap-flaps?

RandomRedPanda1 karma

I have a few questions if you don't mind. What fishing gears are the most problematic for manta ray bycatch? Is it a common gear? Have you seen any declines on the population? And where does the 10% number come from?


DrDeakos1 karma

With regards to fishing "bycatch", drift nets (illegal), gill nets, and tuna purse seine nets pose the biggest problem for manta rays. Gill and purse seine nets are very common in many parts of the world, here in Hawaii I don't believe they are an issue to the mantas. Determining the population size and trend is difficult and time consuming but we are close to gathering enough data to begin such analyses. As of know, we don't know what the trend is. A simple but not a very robust method of determining population size called a discovery curve. This involves take photo-identifications and plotting the number of new ID's against the number of total IDs. When that curve levels off, that means you have photographed all the individuals in the population (in theory). Currently we have over 330 individuals and although the curve has slowed down a lot, we still get a few new recruits on a regular basis, likely a reflection of new individuals. One out of ten of those individuals has evidence of entanglement. I should state that the Olowalu population is segregated, only animals great than 8 feet wingspans so we are still trying to find out where all the 4-8 foot individuals hang out.