Tiger Report and Dive Recommendations for National Park January 2017

Todd Steiner, Island Restoration Network and MigraMar, [email protected] Mark Stabb, Turtle Island Restoration Network Cocos Team, [email protected]

On November 30, 2017, two divers had a serious encounter with a shark at the Manuelita-Channel dive site in the Costa Rica National Park at Cocos Island, resulting in the death of one recreational diver, a park guest, and serious injury to the other diver, a dive master with the UnderSea Hunter group. This was the first known attack on a diver by a tiger shark at Cocos Island, which has been a popular recreational diving spot for nearly thirty years, and only the fourth recorded anywhere in Costa Rica1.

The Circumstances: A recreational diver and her dive buddy (in this case, one of two divemaster’s with the group) surfaced early and not with the rest of the group. This is the normal dive practice when a group member is running low on air or bottom time. Near the surface, the divers were attacked by a single tiger shark. According to second-hand reports (I did not directly interview the injured divemaster), the divemaster placed himself between the shark and the other diver, was bitten, pushed aside and the shark went after the other diver who suffered a fatal bite. Both were pulled out of the water and were rushed to a mother ship that coincidentally had two medical doctors onboard. The dive master’s bite was successfully treated; however, the recreational diver’s injuries proved too severe for treatment, and she died due to loss of blood.

At the time of the incident, an “abort dive” signal was relayed to the rest of the divers, they surfaced without incidence and were transported back to the mother ship by a second skiff sent to the scene.

Earlier in the dive, the rest of the group, led by divemaster Rodrigo Roersch, reported seeing a large female tiger shark approach the group while they were near the bottom in at least 20 m of water. The shark made several close passes to the group, causing them to retreat towards nearby rocks, before the shark swam away – presumably to then encounter the victims closer to the surface. Divemaster Roersch, reported the shark’s behavior was very unusual in his [extensive] dive experience at Cocos Island. (“YoYo” Rodrigo Roersch, pers. comm with M. Stabb). We have requested to UnderSea Hunter personnel to know if any photos or video of this shark encounter are available, and we await a response. If there are such images, it may be possible to determine if this individual was the same shark that caused an aborted dive on our expedition the following week (see below). 1

Tiger : Tiger Sharks ( cuvier) are large top-level predators as adults. Tiger sharks are generally considered solitary hunters that feed primarily at night near the bottom or diurnally at the surface2. However, their mottled color pattern suggests that they may at times swim near the bottom, where they may remain unseen due to color pattern matching the background. They may then, like white sharks, dash upward to strike an object as the surface such as the red-footed boobies that form ‘rafts’ on the surface around the island (Peter Klimley, pres. comm. w/T. Steiner). No general schooling behavior has been recorded; however, they are known to aggregate around concentrated sources of food including carcasses, rookeries during fledgling periods, and at nesting site concentrations3. In some locations, tiger sharks are known to make regular, seasonal migrations to coincide with aggregations of large prey.

Tiger shark diets are extremely varied and includes , sea , seabirds, marine and terrestrial mammals, carrion and human flotsam. A study on tiger shark stomach content in HI4 indicated ontogenic shifts in diet with prey diversity and frequency of large prey items increasing in larger sharks including more sea turtles, marine mammals and . Large (human-sized prey) were found in sharks at >230cm. Yet even large sharks continued to eat bony fish, elasmobranchs (primarily sharks) and .

The occurrence of these various species do not necessarily reflect the importance of these prey to total caloric impact and may underestimate the importance large prey plays in the diet of medium and large size tiger sharks. In a large study of tiger shark diets in South Africa (n= 628), mammals and birds became an increasingly important functional part of the diet, which included humans (Homo sapiens) recorded from the stomachs of two tiger different tiger sharks (2.1 and 2.3 m).5 This study also indicated seasonal shifts in diets between and mammals depending on availability of mammalian prey, and it suggested tiger sharks undergo asymmetric feeding behavior indicating larger eat larger prey, yet small prey (fishes) remains common in their diet.

Tiger Sharks and Humans: Tiger sharks (Galeocerdo cuvier) are curious when in contact with humans6 and often approach divers closely but do not linger and then move on (pers. obs., T. Steiner).

Tigers sharks are second only to white sharks (Carcharidon ) in recorded attacks on humans with 111 (32 fatal) recorded worldwide7. In Costa Rica (1907-present) only four shark attacks of any species have been recorded8.

Tiger Sharks Agonistic Behavior: An aggregation of as many as 16 different tiger sharks have been recorded feeding on a blue carcass in New Caledonia9 in the South Pacific. Here, several agonistic behaviors between sharks were recorded for the first time, including ‘”Give way,” “Stand back,” and “Tail slapping” behavior, as well as “feeding frenzy” behavior (see Table 1 for description of behaviors). During these observations, agonistic behavior was also sometimes directed at the vessels observing the shark feeding.

“On several occasions, some of the largest sharks came straight to the platform of the main research vessel or the motor of the small tender, showing some ‘jaw gapping’ and ‘flank displaying’ (Video clip 6) as an agonistic behaviour toward the boat and people on board,” and “Most of the time, they would then ‘ram with their snout’ before backing off either with a ‘rapid withdrawal’ (Table 1, 2 Video clip 7) or by violently ‘slapping’ the boat or the motor with their tail (Table 1, Video clip 8). “

Tiger Sharks at Cocos Island: Tiger shark observations at Cocos were rare before 2007 and their numbers seem to be increasing yearly (Figure 1). Though not recorded in the primary reference on the fishes of Cocos Island10, we know of one early mention of a tiger shark in Chatham Bay from the 192511, and a second report by Hans Haas in 195412.

Since 2011, Cocos Island Research program of Turtle Island/CREMA, in association with MigraMar, have acoustically tagged 8 tiger sharks. The majority of visual observations and acoustic recordings have been around the “Manuelita-Channel” and “Manuelita-Out” dive sites, but tiger sharks have been recorded at most of the regularly frequented dives sites at Cocos Island (Figure 2). Furthermore, one individual tagged shark, moved between as many as four different dive sites on the same day and visited six different dives sites over a <7-month period, (Figure 3). With longer time-series records, the number of individual sharks using multiple dive sites would likely increase.

In recent months, anecdotal information from long-time divemasters at Cocos has included seeing tiger shark aggregations at Cocos,: six sharks together at Manuelita Channel (Geovanny Castro, pers. comm with T. Steiner), seeing three tiger sharks consume a sea turtle near Silverado (“YoYo” Rodrigo Roersch, pers. comm.) though no accompanying whale or other carcasses.

Diving Cocos after the incident: The Park Service immediately closed the Manuelita- Channel and adjacent dive sites Manuelita-Out and Manuelita-Coral Garden and also cancelled all night dives. Our research team arrived at Cocos a few days later and was granted permission to dive these sites during daylight hours. We limited our diving at these sites to four total, allowing us to collect/service and redeploy two acoustic receivers at Manuelita-Channel and Manuelita-Out, and attempt to tag hammerhead sharks (primary species planned in advance for this mission). We dove these sites without incident, including observing one tiger shark at Manuelita-Out, near the sandy bottom that did not approach the research dive team.

On the first day of diving, while the research team was servicing equipment at the Manuelita-Out dive site, the other skiff completed a dive at the Pajara islet a few hundred meters to the southwest. Upon return toward the mother ship anchored at Manuelita island, the skiff was approached by a large tiger shark at the surface. The shark circled the boat – somewhat unusual behavior – and was photographed. A unique, characteristic ‘white spot’ was observed on the front of the of this shark.

On the afternoon dive on Day 3 (12/7/17, at ~1515 hrs) a dive team made up of a divemaster and a combination of eight research permitees and recreational diver assistants, dove Ulloa (the islet just to the north west of the “Lobster Rock” dive site shown on many maps), located approximately 2 km ESE of the closed dive sites. On this dive, a large tiger shark was first sighted near the surface when the dive team was at about 20 m deep. The shark rapidly descended to the depth of the divers, approaching the group multiple times getting closer with each pass, eventually approaching within 3-4 meters. The dive group tightened formation, retreated to the rocky slope of Ulloa, and exited the water as quickly as was safely possible. After all divers were aboard the skiff, the shark was observed near the surface in close proximity to the skiff. 3

After the dive, the divers and divemaster all agreed that the behavior shown by the shark on this dive was unusual both in terms of the curiosity shown by the shark (in the frequent, repeated passes) as well as the nearness of the shark to the group. It should be noted, the shark did not display any characteristic agonistic or threatening behavior, however the unusual nature of the encounter, coupled with the knowledge of the recent attack led the dive group to take extremely cautious behavior.

Video footage taken of the encounter verified the characteristic white spot was seen on the dorsal fin of this shark, leading to the likely conclusion it was the same shark observed two days earlier at the surface, which had also exhibited some unusually curious behavior.

Of note, this encounter has a number of similarities to that of the fatal accident – with the critical exceptions that no divers were “mid water” when the shark arrived, and the entire group stayed together throughout the encounter.

After this episode, some members of the research team returned in the skiff to Ulloa and Manuelita-Channel on three different days during the afternoon to see if they could see the tiger shark from the vessel. Each time, a tiger shark approached the vessel, but did not linger. None of the observed sharks appeared to match the animal from the “Ulloa dive” in size, and none had the characteristic “white spot” observed on its dorsal fin.

Discussion: The data suggests tiger sharks have become more abundant. Observations include occasional aggregations, though not necessarily in association with carrion or recently dead carcasses as have been reported in the scientific literature. Nonetheless, tiger shark-human encounters remain rare at Cocos and in Costa Rican waters.

There were no unusual occurrences at Cocos we are aware of leading up to the tragic incident. There were no reports of marine mammal carcasses in the area prior to the shark attack. During our expedition in December, it did not appear to be a time of significant fledging for boobies that nest at Manuelita or around Chatham Bay.

Sea turtle (primarily Chelonia mydas) observations at Cocos have dropped precipitously since the arrival of tiger sharks (Figure 1). This is probably the result of predation and changes in sea turtle habitat use to avoid predation, and some shark and ray populations have also shown some decrease over longer time periods13, leading to speculation that limited food resources may be to blame. While turtles are less frequently seen, other food sources that are found in the diet of large tiger sharks (bony fish, sharks and seabirds) appear to remain abundant.

The behavior of the divers who were attacked was not out of the ordinary. Second-hand accounts suggest the tiger shark was specifically interested in the woman diver, leading to speculation about possible perfumes she may have been wearing, or whether she was menstruating. Sharks ability to detect minute quantities of scents and organic materials are well known14. Yet there is no data to suggest that menstrual fluids would elicit a shark attack. The male:female shark attack ratio reported by the International Shark File is 9.2:1, not because tiger sharks prefer males, but likely reflecting a historic pattern of more males engaged in marine aquatic activities, such as and diving15

4 Recommendations for Safer Diving at Cocos: Temporarily closing dive sites near the incident seemed prudent, and this area (Manuelita dive sites) definitely seems to be the highest used area by tiger sharks.

However, the data suggests that tiger sharks are using multiple dive sites and have been seen hunting recently at other sites such as Silverado (Rodrigo Roersch, pers. comm.), and the encounter of a tiger shark situation that caused an aborted dive on December 7th, was at the site of Ulloa. Furthermore, all of these dives sites surround Chatham Bay, the most common location for “check-out” dives, when divers are most likely to be involved in adjusting gear and paying less attention to their surroundings. Closing all of these dives to recreation is likely untenable with current dive operations.

Removing all risk of tiger shark attacks is impossible and contrary to the very reason people travel to Cocos Island and other wild areas to view top predators. Thus ultimately, the best recommendations we can make are to improve vigilance, and create better, quicker and safer ways to abort dives and get divers to safety when danger is sensed or is imminent. Improved medical help available at the Island is also recommended.

1. Improve Vigilance – Controlling the encounters between divers and tiger sharks, starts with early awareness of an approaching shark, so the dive group has time to make an assessment of the potential threat and act accordingly.

A) Requiring two divemasters with each group of divers is a way to provide additional vigilance and safety. This would also allow divers who must end the dive early due to low air or bottom time to surface with an experienced divemaster. (Although this did not prevent the current tragedy, it seems likely to be safer than a solo ascent).

B) Skiff drivers should remain alert to tiger sharks near the surface and develop a communications method to alert divemasters underwater if necessary. Currently skiff drivers signal divemasters to abort the dive by constant revving of the engine. An improvement to this approach would be to use diver recall equipment that uses a hydrophone to alert divers within range with either voice, solid or intermittent tones, (see http://decadiving.com/product/diver-recall/). Another simple way to impove communication would be to implement a modified engine revving pattern should it be necessary to alert divemasters of possible tiger shark danger. If necessary, the skiff driver should call for additional skiffs to come to the site to speed getting divers out of the water and to safety.

C) Divemasters should consider carrying blunt-ended pole spears or other mechanical means to keep tiger sharks at bay when they approach too closely.

2. Institute a Reporting System

A) All tiger shark observations should be reported to a single entity to collate and make available to the park and other interested researchers/parties. This should include more than just “unusual” encounters – every encounter should be documented for time, dive site and if possible size and gender of 5 shark – to help establish a baseline of what is “normal” or “usual” behavior and abundance. The recent encounters have all been reported as “unusual” by divers and divemasters with significant experience at Cocos, but such observations are anecdotal, and without a better understanding of shark/diver encounters, it is hard to accurately judge if there are underlying trends in behavior.

In addition to documenting all encounters, any behavior deemed noteworthy should definitely be noted, including reports of tiger shark aggregations, “aggressive” or “unusually curious” behavior toward divers, etc. All collected data should be collated by Cocos Island Park personnel or possibly MigraMar researchers and made available to park managers and researchers. This is unlikely to occur in a systematic fashion unless divemasters are regularly interviewed after each trip to Cocos Island, and they are required to log tiger shark encounters/observations after any dive on which one occurred. Additionally, it would be useful to interview all dive masters who worked at Cocos in October and November 2017 to see if there were other “signs” of behavioral changes in tiger sharks that may have alerted managers before the incident occurred.

3. Improve speed of getting divers out of the water - Hanging on a line waiting one’s turn to climb the ladder onto the skiff seems like an especially vulnerable time in a tiger shark attack emergency.

A) Skiffs should be equipped with a second ladder to double the speed of exiting the water.

B) Divers should be instructed on how to remove their dive tanks in the water and how to assist pulling other divers over the transom in the skiff. Ropes with quick release clips could be suspended over the side to allow divers to “clip off” their BCD or other gear to facilitate a faster exit from the water at times tanks are removed before boarding the boat. Ropes with clips would aid in recovery of gear that was “ditched” in order to exit the water faster, and as such might encourage divers to jettison their equipment in a situation where such action might not be required, but still be prudent.

4. Improved Medical Care on the Island and Communication with Nearby Ships- Improved access to medical care at this remote site would have multiple health and safety benefits for visitors and park personnel under many medical circumstances.

A) Park Service should consider having a trauma nurse with necessary equipment available on the island for park personnel and visitors.

B) Communication with US Coast Guard should be developed. Currently the US Coast Guard has a significance presence in Costa Rican waters primarily for drug interdiction. The ability of this resource to assist medical emergencies of US citizens and others should be developed. Other large ships such as industrial tuna purse seiners are also located in the region and these vessels often have helicopters and may have additional medical equipment available 6 that could be useful in an emergency. Efforts should be made to quickly communicate medical emergencies to these vessels and seek their help in the case of trauma emergencies.

5. Practice Cautious Diving in the Presence of Tiger Sharks - If a tiger shark is sighted, remain calm and maintain your position in as quiet a manner as possible. Tiger sharks are curious and will most likely will leave on their own accord. If a shark begins to get too interested in you by coming closer and closer, the best strategy is to bring the group closely together and leave the water, maintaining eye contact with the shark at all times. Keep eye contact with the animal at all times and do not swim with your back to the shark. Minimize time at the surface and avoid bright or contrasting colors. Wearing full length black wetsuits and black dive hoods and black gloves are recommended.

Figures and Tables

Figure 1. Recorded number of tiger sharks by UnderSea Hunter Group indicating an increase in tiger shark and a decrease in turtle observations. (Note that data is available to update this figure in the future, but we believe the general trend continues.)

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Figure 2. Data from 8 tiger sharks tagged with acoustic transmitters between 2011 – 2016. While we believe this is a relative accurate reflection of occurrence, the number of detections is partially a reflection of how long the transmitters have been in place, as malfunctions, lost receivers, etc. have resulted in uneven coverage.

14000 12871 12000

10000 8206 8000

6000 5241

4000

2000 Number of Detections 575 101 119 269 386 21 0

Sites

Figure 3. A single tiger shark tagged with an acoustic tag moved between six different dive sites over the course of several months.

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Table. 1. A screen shot of new agonistic behavior described for tiger sharks for the first time in 2013 (in: [9])

Acknowledgments We thank Peter Klimley, Neil Hammerschlag, and Alex Hearn for reviewing this document and providing suggestions for improvement. This document was also improved by conversations we had with Geovanny Castro, Rodrigo Roersch, Shmulik Bloom, Genna Marie Davis and other members of the UnderSea Hunter Group. We also appreciate the panel held on this subject at the recent Migramar Assembly in Panama. The data on tiger sharks in Figures 2 and 3 are based on an on-going collaboration with Randall Arauz (Pretoma, Crema, Turtle Island Restoration Network and FinsAttached). Figure 1 was prepared from long term data provided by UnderSea Hunter Group and Figure 3 was modified from a figure produced by Elpis Joan.

References

1 International Shark Attack File. 2017 https://www.floridamuseum.ufl.edu/fish/isaf/shark-attacks-maps- data/central-america/

2 Lowe, C.G., M.M. Wetherbee, G.L. Crow, and A.L. Tester. 1996. Otogenetic dietary shifts and feeding behavior of the tiger shark, Galeocerdo cuvier, in Hawaiian waters. Environmental Biology of Fishes. 47:203-211. and see International Shark Attack File. 2017. https://www.floridamuseum.ufl.edu/fish/discover/species- profiles/galeocerdo-cuvier/

3 Behavioural patterns of a Tiger Shark (Galeocerdo cuvier) feeding aggregation at a blue whale carcass in Prony Bay, New Caledonia, Marine and Freshwater Behaviour and Physiology, DOI:10.1080/10236244.2013.773127 9

4 Lowe, C.G., M.M. Wetherbee, G.L. Crow, and A.L. Tester. 1996. Otogenetic dietary shifts and feeding behavior of the tiger shark, Galeocerdo cuvier, in Hawaiian waters. Environmental Biology of Fishes. 47:203-211

5 Dicken ML, Hussey NE, Christiansen HM, Smale MJ, Nkabi N, Cliff G, et al. (2017). Diet and trophic ecology of the tiger shark (Galeocerdo cuvier) from South African waters. PLoS ONE 12(6): e0177897.

6 International Shark Attack File. 2017. https://www.floridamuseum.ufl.edu/fish/discover/species- profiles/galeocerdo-cuvier/

7 International Shark Attack File. https://www.floridamuseum.ufl.edu/fish/isaf/contributing- factors/species-implicated-attacks/

8 International Shark Attack File. January 23, 2017. https://www.floridamuseum.ufl.edu/fish/isaf/shark- attacks-maps-data/central-america/

9 Eric Clua , Claude Chauvet , Tyffen Read , Jonathan M. Werry & Shing Y. Lee (2013): Behavioural patterns of a Tiger Shark (Galeocerdo cuvier) feeding aggregation at a blue whale carcass in Prony Bay, New Caledonia, Marine and Freshwater Behaviour and Physiology, DOI:10.1080/10236244.2013.773127

10 Garrison, G. 2005. Peces de la Isla del Coco. Instituo Nacional de Biodiversidad. Second edition, 2005. 429 p. 11 Beebe, W. 1926. The Arcturus adventure : an account of the New York Zoological Society's first oceanographic expedition. GP Putnam & sons, New York. 436 pp.

12 As reported in: Weston, C. 1992. La Isla del Coco (Cocos Island) (Spanish and English Edition) (Spanish) Hardcover – 1992. The Mario Sotela Pacheco Foundation (1992)

13 Easton R. W., M. C. Myers, J. M. Flemming, and J. K. Baum. 2015. Shifting elasmobranch community assemblage at Cocos Island—an isolated marine protected area . Conserv Biol. 2015 Aug;29(4):1186-97

14 International Shark Attack File. https://www.floridamuseum.ufl.edu/fish/isaf/reducing- risk/menstruation/ Also see http://www.motherjones.com/politics/2012/08/do-menstruating-women- attract-shark-attacks/

15 https://www.floridamuseum.ufl.edu/fish/isaf/reducing-risk/menstruation/

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