Tuesday, March 21, 2017

Sharks of Rangiroa

The lab's first trip to Rangiroa

For the past several years, the lab has been working on sharks and rays in French Polynesia using a variety of methods and tools, including drones and remote underwater cameras.  Our goal is to better understand the behavior of these animals on reefs and how they interact with other species. Ultimately, we want to figure out how important sharks are to the health of reefs.  Our work started on Moorea (you can read about our first trip in the October and November, 2013 blog posts) and expanded to Tetiaroa in collaboration with Dr. Aaron Wirsing at University of Washington.
Rangiroa is the world's second largest atoll.

At Blue Lagoon with Jeremy (center) and Eric (right).
This year, we have greatly expanded our work in French Polynesia.  Along with Dr. Eric Clua and CRIOBE we have started sampling multiple islands – both high islands and atolls – using baited remote underwater video systems (BRUVs).  This work will help us understand what drives patterns of shark abundance and the species inhabiting a particular island or reef type. The 1,000 camera drops (each 90-min long) that we plan to make are part of the Global FinPrint Project that will survey more than 400 reefs around the world!  PhD student Frances Farabaugh is leading the shark and ray analyses for the lab in French Polynesia.  Even though 1,000 drops and 1,500 hours of footage seems like a lot it is really just scratching the surface of French Polynesia, which covers a huge area of the Pacific Ocean! The more than 100 islands of French Polynesia are spread across about 2,000 miles!

Frances preparing to set BRUVs
In February, Jeremy Kiszka, Frances, and I made our first trip to Rangiroa to meet Eric to continue sampling for FinPrint and to begin other studies.  Rangiroa is found northwest of Moorea and Tahiti and is the world’s second largest atoll.  The lagoon in the middle of the atoll is about 70 km across from east to west and 40 km from north to south.  While Frances worked on FinPrint sampling, Jeremy, Eric and I started projects on nursery habitats of the lagoon and the movements and feeding behavior of bigger sharks on the reef that lines the outside of the atoll (the forereef). 

The blacktip reef shark nursery at Blue Lagoon
On our first day, we headed to Blue Lagoon – a small, shallow lagoon within the larger lagoon of the atoll.  Think of a (very small) hot tub in a (very large) swimming pool.  Pulling to the edge of Blue Lagoon on our first day, we were greeted by dozens of mostly full-grown blacktip reef sharks at the mooring.  Blacktip reef sharks can be found from the forereef to the lagoon and don’t get particularly big – only about 4-5 feet on average.  But we were interested in the younger sharks that call the shallow flats of Blue Lagoon home.  We hadn’t been there long before we were watching 20 small sharks – from newborns (about 1.5’ or 50 cm long) to animals that are around 3 years old.  For the youngest sharks, they need to stay in these shallow areas to stay safe from predators, particularly large lemon sharks that are found in the deeper waters of the lagoons.  We had a magnificent morning, capturing sharks and getting samples to help us learn where they are feeding and to get an idea of what their favorite foods might be.  Once we finished in the lagoon, we headed back to the mooring to test out a 360 degree dome camera system!  This system lets us see sharks all around the camera stand instead of just in one direction.  We are using the 360 cameras to get a better understanding of just how many sharks might be around when we do our standard counts for FinPrint that use one camera and to get a better view of their behavior.  PhD student Jimmy Kilfoil, who has been working in Tetiaroa, has been leading these studies but we took the opportunity to collect data since there were so many sharks around.  During the trial, we even had some big sicklefin lemon sharks show up.  With impressive predators like these just outside Blue Lagoon it is easy to see why the babies stick to the shallows!
Larger blacktip reef sharks outside Blue Lagoon
Sicklefin lemon shark
Another project that we worked on was to understand the movements and feeding behavior of the large shark species found on the forereef.  To do this, we captured and collected blood from gray reef sharks and silvertip sharks.  Because we didn’t want to catch great hammerhead sharks (they can be very sensitive), we got help from a professional free diver, Francis, who can hold his breath long enough to dive 60 meters!  The idea was for him to use a modified spear to take a small sample of skin.  The blood and skin samples help us understand where the different species might be feeding – in the lagoon, along the reef, or out in deeper water.  Knowing this might help us figure out how so many species are able to coexist!

Out in blue water off the reef, we waited by a baited canister for hammerheads.  We didn’t see any during my time there but Francis got several samples of silky sharks and tiger sharks!  One tiger shark was about 4m long! With any luck we will get those hammerhead samples eventually! We also were able to deploy a satellite tag on a silvertip shark which will help us determine its movements.  Silvertips are usually thought of as the largest resident sharks on reefs, but the satellite tag will tell us just how far the silvertip goes.  The tag will stay on the shark for three months and then pop off and float to the surface to download its data.  Hopefully, we will have results to share soon!
We couldn't have done it without the amazing people at the Rangiroa Diving Center!!

And Miki Miki Lodge
We saw bottlenose dolphins in the pass every day.

Sunday, March 12, 2017

Intern research on display

By: Elizabeth Whitman

Our work is made possible by the help of our interns and assistants! Laura Thornton and Ryley Parent, and Liberty Boyd took on individual projects while assisting me with my dissertation research in Abaco, Bahamas during the summer of 2016.  Earlier this year, Laura and Ryley presented their work at FIU’s Biosymposium.

Laura (top left) and Ryley (bottom left) posing next to their posters after presenting them at FIU's Biosymposium
Laura took the lead on a project to assess the foraging preferences of the variegated urchin, Lytechinus variegatus, and to provide a better picture of their role in seagrass ecosystem dynamics. This echinoderm is commonly found in tropical seagrass meadows; however, little is known about the feeding preferences of these urchins. We conducted cafeteria (food options provided with equal probability of encounter) and natural (naturally growing food options) feeding experiments in a shallow coastal seagrass meadow near Marsh Harbour, Abaco. In both experiments the urchins appeared to first choose and consume turtle grass (Thalassia testudinum) before moving on to consume other seagrass and algae species. We are now awaiting the results of nutrient content analysis on the seagrass and algae to see if the urchins prioritize food with higher nutrient content.

Ryley developed an outreach campaign to encourage restaurants to stop serving turtle meat, which currently is against the law. The Bahamian law, passed in 2009, prohibits the taking of turtles or disturbing of nests; however, despite enforcement by local Abaco fisheries officers, there is still demand for turtle meat. Her goal is to educate the public about the laws and encourage the community to support them. Ryley speaks with restaurant owners about the campaign, asks them to hang “Turtle Free Restaurant” signs in visible areas, and in return publishes the names of participating restaurants in local publications. She is currently pursuing additional support to continue the campaign in Abaco and eventually expand it to other Caribbean locations.

Ryley will be presenting this project and Liberty will be presenting her study on the effects of burrowing sea cucumbers on green turtle foraging habitat at this year’s International Sea Turtle Symposium
This team of Abaco Global FinPrint volunteers were reunited at the Biosymposium! 
From left to right: Valeria Paz, Riki Bonnema, Ryley Parent, Elizabeth Whitman, Liberty Boyd and Laura Thornton 

Friday, September 16, 2016

Turtles of Abaco

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Facebook page: Bahamas Sea Turtle Network
As of August 1st, the Facebook page has received 48 observations. We have had reports of significant nesting in Grand Bahama and Abaco, several strandings, slaughtered turtles in Abaco and San Salvador, and two brave rescues of turtles captured by local fishermen in Sandy Point Abaco. It has been very encouraging to have so many new people involved in turtle conservation.


Since the Loyalist days in the 18th century, the Abacos have been famous for turtles. Years ago Harold Albury, an old friend from Cherokee, told us stories of the days when he was a boy fishing on a sailing smack boat with his uncle who harpooned turtles. There are excellent turtle habitats all through the Abacos, and the people ate them regularly right up until the ban in 2009. Now we are learning that there is considerable illegal harvest, especially in Sandy Point and the northern Abacos.
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Kranston Simms with green turtles in Jean’s Bay, Eleuthera

On June 12th Kranston Simms, a BNT volunteer, joined me in Spanish Wells to tag a few turtles and then run up to the Abacos. Kranston is volunteering for BNT while he is waiting to go to sea for 18 months as part of his training at LJM Maritime Academy in Nassau. On the 13th we tagged seven green turtles around Spanish Wells, then got up early the next morning and cleared Ridley’s Head at “day clean” for the trip up to Abaco. We went through the cut by Little Harbour and still had time to run another 15 miles to Marsh Harbour. I had reserved a mooring from the Harbour View Marina, and that turned out to be a blessing.
I also called Beth Williams who is a PhD. Candidate at the Heithaus Lab at Florida International University (http://faculty.fiu.edu/~heithaus/). Beth and her three interns were living at the Kenyon Centre for Research at Friends of the Environment while she conducts her research. Her main project is studying sea grass, but she is also conducting BRUV (baited remote underwater video) surveys for Global FinPrint (https://globalfinprint.org/). These surveys consist of setting baited video cameras in 15-25 feet to film sharks on the reefs on the eastern side of the Abaco cays. This is part of a global survey.
The day after Kranston and I arrived in Marsh Harbour we went out to follow Beth and her crew to help set and retrieve 12 BRUV rigs. As it turned out, Beth was fine without us, so we lent some moral support and took photos of the operation.

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Setting a BRUV
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Reef shark filmed by the BRUV. Notice the bait in the background.
By noon Kranston and I were getting restless, so we took two of the interns, Liberty and Ryley, into the cut north of Scotland Cay where I had tagged turtles several years ago. We caught two green turtles then rejoined Beth, dropped off Liberty and Ryley and picked up Laura. Beth agreed to meet us near Scotland Cay when she was finished retrieving her last BRUV. By then we had caught one more turtle and were happy for the help measuring and tagging. The Scotland Cay habitat is beautiful with clear water, plenty of grass, healthy turtles, and winter residents to protect them.
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Kranston, Beth Whitman, and her interns at Scotland Cay
As we entered the channel into Marsh Harbour our outboard made some ugly noises and shut down. I checked all the usual suspects, but found nothing wrong. After we fiddled for several minutes the engine decided it would start, and we idled back to FOXY LADY with Beth following us in her whaler. By then I was pretty well convinced that it was a stripped gear in the lower unit.
The next morning I talked to Jamie Malone, the Suzuki dealer in Marsh Harbour, who did not have parts, so I called Ron Pinder in Spanish Wells who arranged to send a used lower unit that I could use for the rest of the season. Between Ron, Portia Sweeting handling transport in Nassau, and Jamie installing the gear I was up and running again in three days. Good to know people who will take care of you.
On the 18th I carried Beth’s interns to Snake Creek for a really good day of tagging. After some time figuring out the creek we tagged eight turtles. Unfortunately 5 turtles had fibropapilloma tumors.

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Ryley and Liberty dive up a small green in Snake Creek

After three days at the mooring in bad weather I went up to Hills Creek with Keith Bishop’s daughter-in-law and grandchildren. It was cloudy but we caught six green turtles. Five of the six had tumors. The turtling was fun, but it was tough for the kids to deal with the tumors, and I was afraid that they would lose interest. But they started asking very good questions about the disease. I was impressed. Maybe someday one of the students we carry will solve the mysteries of fibropapillomatosis.

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Jack Bishop in Hills Creek
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Hills Creek turtle with tumor on right shoulder

The next day interns Ryley and Laura helped me move FOXY LADY down to the anchorage off Tilloo Cay. From there it was an easy run in the speed boat to Snake Creek, and I would be ready to move down to Cherokee the next day. We were in the creek looking for turtles by 1000. Brian Higgs who had worked with me several years ago joined us for the day. Brian lives in Abaco and is college bound at the end of the summer. The tide was high so we were able to chase the small turtles in the flats near the boat ramp. We caught three, one of which was kyphotic. That is the second kyphotic we have caught in 10 years (approximately one kyphotic turtle per 1,000 green turtles). The hump reduces the individual’s hydrodynamic efficiency, but otherwise the turtles are fine. They are even said to be able to reproduce successfully.
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Kyphotic turtle in Snake Creek

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Kyphotic turtle from 2010 in Crooked Island

The ladies could only work with us until Beth arrived at 1130, then Brian and I were on our own. Not a problem. Brian is the son of a commercial fisherman and runs eco tours in Snake Creek. He took me to new places in the creek with plenty of turtles. We caught 10 turtles on the day and none had tumors. Obviously we need to spend a lot more time in Snake Creek.
Ryley Parent, one of Beth’s interns, is giving turtle conservation a boost by starting a turtle-free restaurant program. Restaurants that commit to never serving turtle will post a turtle-free sign and get their name listed in the press. Ryley has already had success with the tourist restaurants. Now she will brave the restaurants that serve a more exclusively local population. It is rumored that some of these restaurants still serve turtle meat despite the ban.
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Ryley at a Marsh Harbour restaurant
The next morning I picked up Brian who would pilot FOXY LADY up the shallow channel to the small anchorage off Cherokee. Unfortunately, the bottom is like a concrete slab, so we set two anchors in patches of grass, and I dove to set them, but there was no way they would hold in a breeze of wind.
Cherokee Sound is a very special place with miles and miles of flats. The boys in Cherokee understand shallow water, and their definition of a channel is any place that has two or three inches of extra water.
Cherokee is a beautiful loyalist settlement that, “one time ago,” was a major fishing and boat building community with close ties to Spanish Wells. The settlement is small and remote though there is now a good road that reaches the settlement. Cherokee Sound has been badly overfished, so there are only a few men who still fish commercially.
Before he left for the day, Brian introduced me to his friend, Tim Sands, who talked to his cousin who would loan me his mooring. The next morning I picked up Tim and his son, Branden. Branden swam around, dove up the mooring and we moved FOXY LADY. We only had inches under us at low tide, but the mooring was heavy and secure.
Then we took off to find some turtles. We scouted around a bit at low tide and wound up spending most of our time in Big Mangroves where we caught a good selection of green turtles, and all the turtles were tumor-free.
Tim Sands was ready to go with his whole family after church on Sunday, and I was happy to have the morning to rest up. What a lovely family! We went to a new area, and everyone caught a turtle, and again, no papillomas.

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Tim Sands with son Branden and daughter Rachel
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Julie Sands lands a turtle

Soon after I dropped off the Sands, David Knowles, the head BNT Warden in Abaco, drove Elijah Sands (no relation) down to Cherokee from the Marsh Harbour airport. Elijah was going to start work at BNT in ten days, so he had time to work with me in Cherokee and then make the trip back to Spanish Wells.
In the early evening Elijah and I went ashore to attend a town meeting that would discuss the proposed marina in Little Harbour. The representatives of the developer, the Abaco Club in Winding Bay, were prepared and persuasive; but many of the foreign residents of Little Harbour were angry. They want their harbour to keep its funky feel. It was a classic conflict. My guess is that the developers will get their marina, but not easily.

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Josh, Branden, Rachel, and Elijah
Monday was one of those magical days. Branden and Rachel Sands brought their friend, Josh, to go along with Elijah and me. All the kids were enthusiastic and good in the water. Branden guided us around in the northeastern part of Cherokee Sound and we caught 13 turtles, all healthy. I knew it was a really good day for the kids when I heard from Tim Sands that Branden had admitted when he got home, “I THOUGHT I knew a lot about turtles.”

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Elijah Sands with green turtle in Cherokee Sound
On our last day we had to wait for the afternoon tide, so after checking the engine and tying down all the gear, Elijah and I went out to look for a manatee in Casuarina creek. We saw a huge school of bonefish but no manatee. The locals said they had not seen it for a long time. I reported that to Diane Claridge, and then Elijah and I went off to tag two turtles before we had to get back to the boat.
We made it out the channel by 1500 and had an easy run down to Egg Island. In the Egg Island channel we almost ran into a small barge on stilts that was taking core samples for the proposed Disney project to develop Egg Island as a cruise ship destination. Spanish Wells is gearing up to fight tooth and nail against the project.
We anchored for the night and the next day off the Bluff and moved into Muddy Hole on Thursday. Elijah took the fast ferry that afternoon saying, “I will be back,” and I stayed on for a couple of days to lay the boat up for the summer.
The Abaco trip made a very successful finish to the season. We tagged 58 green turtles, surveyed three areas for fibropapillomas, spent time with the Fisheries Officer for Abaco, helped Ryley Plant with her turtle outreach project, and made a lot of good contacts.

On July 22 the “Nassau Tribune” printed a statement from Disney saying that they would not develop Egg Island. Disney said that the project would cause too much damage to the environment. I would bet that the outcry in Spanish Wells influenced the decision.
Not sure what the future holds for Egg Island but hopefully a Spanish Wells group will get a 99-year lease on the cay or it will become a national park.

Tuesday, June 28, 2016

Sharks vs Dolphin

With the Premiere of Shark vs. Dolphin: Face Off on Shark Week, I thought it would be a good time to write a little bit about the current state of the science.  I've been studying shark-dolphin interactions for about 20 years.  Most of my work has been in Shark Bay, Western Australia (www.sberp.org) where I investigated how often tiger sharks attacked Indo-Pacific bottlenose dolphins and how dolphins changed their behavior to reduce their chances of being attacked.  This led to studies of the influence of tiger sharks on the whole ecosystem.  You can learn more about that at the Shark Bay Ecosystem Research Project webpage.  We put together a video-based lesson for K-12 classrooms that lets students join the work that you can get here. Below are answers to a couple of the most common questions I get.

Do sharks really eat dolphins?  How do we know sharks attack dolphins?

The threat that sharks pose to dolphins is greater than we once thought. Most shark species won’t attack dolphins, but there are some species that do! Although it is very rare, people have seen and filmed dolphins being attacked by sharks.  That means that we have to use other methods to figure out how big a threat sharks are to dolphins.  We can see if particular shark species have dolphins in their stomachs or use chemical markers in the blood or muscle of sharks to see if they have eaten dolphins. 

A scar on the back of a dolphin in Shark Bay
These methods don’t tell us if the sharks attacked a living dolphin or if they ate one that had died already.  By using the scars on the bodies of dolphins that are left behind after an attack, we get an idea of how many dolphins are attacked and, sometimes, what species of shark attacked the dolphin.  In our work in Shark Bay, we found that more than 70% of Indo-Pacific bottlenose dolphins have scars from shark attacks and probably 10% of the population is attacked (but escape) every year!  Around 20% of spotted dolphins in Bimini, Bahamas has shark-inflicted scars and around 30% of common bottlenose dolphins have evidence of shark bites in Sarasota, Florida and Morteon Bay, Australia.  In many locations, shark attacks are very rare.  This could be because populations of large predatory sharks have declined in many parts of the world.

What sharks are a threat to dolphins?

A tiger shark cruises the shallows
Not all sharks are a threat to dolphins and only a few species are probably a regular risk to them.  Within these species, only large individuals will attack dolphins.  Tiger sharks, bull sharks, and white sharks are at the top of the list. Sixgill and sevengill sharks also are likely to take dolphins. Hammerhead sharks, oceanic whitetip sharks, dusky sharks, and mako sharks might occasionally attack and kill dolphins, but it is likely rare and only very large individuals that do so.  The cookie cutter shark is a species that attacks dolphins, but won’t kill them.  Instead it scoops out small bites of blubber and skin, leaving a mark that looks like a cookie cutter made it.

How do dolphins avoid being attacked?

Even for shark species that are major threats to dolphins, it is unlikely that they go too far out of their way to try to eat dolphins.  But, dolphins will make major changes to their behavior in order to reduce the chances that they are attacked!  The success of these anti-predator behaviors is probably one reason that dolphins aren't found in diets of sharks very often. 

A dolphin in the shallows when tiger sharks are not around
The best way for dolphins to avoid an encounter with a shark is to spend their time in the safest places.  This is what we found for dolphins in Shark Bay.  When there are very few large tiger sharks around, many dolphins feed in shallow waters where most of their food (fish) is found.  When the number of tiger sharks increases, these sharks concentrate their foraging in shallow habitats, where there is a lot of prey (other than dolphins).  In response, dolphins shift to feeding more in deep waters that may have less fish but are safer.   In Hawaii, Hawaiian spinner dolphins feed offshore at night and then come into shallow bays with white
Spotted dolphin with two scars
sandy bottoms to rest during the day.  This minimizes the chances that the spinner dolphins run into sharks.  Many dolphins live in large groups, which likely help to increase the chances that predators, like sharks, are detected.  Living in groups can also help reduce the risk to a particular individual because groups can confuse attacking predators.   Some species of dolphins form big groups with other species of dolphins.  These "mixed-species groups" probably help further reduce the risk of predation without greatly increasing competition for food since the species in such groups generally have different favorite foods.

If a dolphin does run into a shark, their best defense is speed and maneuverability.  Dolphins are much more maneuverable than most sharks so they are able to keep out of the way once they see a shark. Dolphins also are faster over the long haul. In Shark Bay, we saw a white shark approach a group of dolphins that didn’t see the shark until the last second.  Even though the shark didn’t attack, the dolphins scattered and leapt away from the shark for a long time before slowing down!  Sometimes, dolphins may group together to “mob” a shark, much like small birds will do to a hawk.  They harass the shark until it swims away.  This behavior has been observed in several locations around the world.

Can a dolphin kill a shark?

They can. Smaller dolphins - like the well-known bottlenose dolphin - will attack and kill small sharks occasionally, but sharks are not a part of their diets.  Accounts of dolphins killing large and dangerous sharks by ramming them in the gills have not been verified. 

Some populations of killer whales (yes, they are dolphins), eat sharks, and can even kill a great white shark.  Off New Zealand, killer whales eat many rays and sharks.  Off the western coast of North America, there are several types of killer whales.  "Resident" whales eat fish like salmon while "transient" killer whales eat marine mammals including seals and sea lions, dolphins, porpoises, and whales.  The "offshore" whales are not as well known and appear to eat a large number of sharks, especially Pacific sleeper sharks which live in fairly deep water. 

False killer whales also have been observed taking dolphins. 

Heithaus lab publications on shark-dolphin interactions:

Connor, R. C. and M. R. Heithaus.  1996.  Approach by great white shark elicits flight response in bottlenose dolphins.  Marine Mammal Science 12: 602-606.

Heithaus, M. R.  2001. Shark attacks on bottlenose dolphins (Tursiops aduncus) in Shark Bay, Western Australia: attack rate, bite scar frequencies, and attack seasonality.  Marine Mammal Science 17: 526-539.

Heithaus, M. R.  2001.  Predator-prey and competitive interactions between sharks (order Selachii) and dolphins (suborder Odontoceti): a review. Journal of Zoology (London) 253:53-68.

Heithaus, M. R. and L. M. Dill. 2002. Food availability and tiger shark predation risk influence bottlenose dolphin habitat use. Ecology 83: 480-491.

Heithaus, M. R. and L. M. Dill.  2006. Does tiger shark predation risk influence foraging habitat use by bottlenose dolphins at multiple spatial scales? Oikos 114:257-264.

Heithaus, M. R., J. J. Kiszka, A. Cadinouche, V. Dulau-Drouot, V. Boucaud, S. Perez-Jorge, and I. Webster. In press. Spatial variation in shark-inflicted injuries to Indo-Pacific bottlenose dolphins (Tursiops aduncus) of the southwestern Indian Ocean. Marine Mammal Science

Selected other publications on shark-dolphin interactions:

Cockcroft, V. G., Cliff, G. and G. J. B. Ross. 1989. Shark predation on Indian Ocean bottlenose dolphins Tursiops truncatus off Natal, South Africa. South African Journal of Zoology 24:305-310.

Corkeron, P. J., R. J. Morris and M. M. Bryden. 1987. Interactions between bottlenose dolphins and sharks in Moreton Bay, Queensland. Aquatic Mammals 13:109-113.

Ford, J. K. B., G. M. Ellis, C. O Matkin, M. H. Wetklo, L. G. Barrett-Lennard, R. E. Withler. 2011. Shark predation and tooth wear in a population of northeastern Pacific killer whales.  Aquatic Biology 11: 213-224.

Kiszka, J., Perrin, W. F., Pusineri, C. and V. Ridoux. 2011. What drives island-associated tropical dolphins to form mixed-species associations in the southwest Indian Ocean? Journal of Mammalogy 92:1105-1111.

Melillo‐Sweeting, K., Turnbull, S. D. and T. L. Guttridge. 2014. Evidence of shark attacks on Atlantic spotted dolphins (Stenella frontalis) off Bimini, The Bahamas. Marine Mammal Science 30:1158-1164.

Norris, K. S. and T. P. Dohl. 1980. Behavior of the Hawaiian spinner dolphin, Stenella longirostris. Fishery Bulletin 77:821-849.

Pyle, P., M. J. Schramm, C. Keiper, and D. Anderson. 1999. Predation on a white shark (Carcharodon carcharias) by a killer whale (Orcinus orca) and a possible case of competitive displacement. Marine Mammal Science 15: 563-568.