Stephanie Marie Sowa, ABSTRACT

Transcription

1 Sea Turtle Patrols of Playa Preciosa, Costa Rica and Marine Mammal and Sea Turtle Boat-Based Surveys of Gulfo Dulce, Costa Rica September to November 2016 Stephanie Marie Sowa, ABSTRACT The Osa Peninsula, Gulfo Dulce, Costa Rica holds the title of the highest biodiversity hot spot teeming with unique insects to gregarious humpback whales. This project surveyed Playa Preciosa and Golfo Dulce from September 2016 to November 2016 for animal population estimates, locations, nesting habitats and behaviors (sea turtles), and feeding habitats, and marine mammal behaviors. The animals of focus were olive ridley sea turtles (Lepidochelys olivacea), green sea turtles (Chelonia mydas), Pacific black green sea turtle (Chelonia agassizi), hawksbill sea turtles (Eretmochelys imbricata), leatherback sea turtles (Dermochelys coriacea), humpback whales (Megaptera novaengliae), pantropical spotted dolphins (Stenella attennata), and bottlenose dolphins (Tursiops truncatus). INTRODUCTION The Osa Peninsula is located on the southern Pacific side of Costa Rica. Its high levels of biological diversity coupled with its unique combination of 13 distinct tropical ecosystems classify it as a high global conservation priority. With a total area of only 121,500 hectares, the Osa Peninsula is home to 50% of species found in the entire country of Costa Rica, including many endemic species (Bessesen 2010). The Osa Peninsula possesses the greatest unharmed mangrove ecosystem in Pacific Mesoamerica, the most substantial remaining areas of lowland Pacific tropical rain forest, and one of only four tropical fjords on the planet, the Golfo Dulce (Osa Conservation 2016). These ecosystems provide habitat crucial for the Osa Peninsula's bounteous wildlife, including the sea turtles. Hawksbill sea turtles (Eretmochelys imbricata) may consume vegetation from mangroves and were a focus of this study during in water surveys (Abreu-Grobois 2000). The ecosystems of the Osa Peninsula and Golfo Dulce and provide rich diet sources for all marine life. Documented species that utilize the habitat of the Osa Peninsula are yellow-bellied sea snakes (Pelamis platurus), Caiman (Caiman crocodylus), and the American crocodile (Crocodylus acutus) (Bessesen 2010). Bird species that utilize the Golfo Dulce are brown boobies (Sula leucogaster), magnificent frigates (Fregata magnificens), osprey (Pandion haliaetus), brown pelicans (Pelecanus occidentalis), heron (Garceta), gulls (Laridae), turkey vultures (Cathartes aura), terns (Sternidae), and swallows (Hirundinidae) (Bessesen 2010). Fish species that are found in Golfo Dulce are manta rays (Manta birostiris), flying fish (Exocoetidae), needlefish (Belonidae), roosterfish (Nematistius pectoralis), parrotfish Page 1 of 24

2 (Scaridae), yellow fin tuna (Thunnus albacares), Pacific bonita (Sarda chiliensis), ballyhoo (Hemiramphus brasiliensis), snappers (Lutjanus), crevalle jack (Cannax hippos), sardines (Sardina pilchardus), hog mullet (Joturus pichardi), blue runners (Caranx crysos), mackerel (Scomber japonicus), eels (Anguilliformes), and puffer fish (Tetraodontidae) (Bessesen 2010). Professional sports fisherman report roosterfish, crevalle jack, Pacific bonita, blue runners, and mackerel as the most common fish in Gulfo Dulce (McGuinness 2016). Invertebrates found in Golfo Dulce are Portuguese Man of War (Physalia physalis), sea jellies (Cnidaria), mangrove crabs (Aratus pisonii), oysters (Ostreidae), and other mollusks (Bessesen 2010). Other species found in the Gulfo Dulce are: olive ridley sea turtles (Lepidochelys olivacea), green sea turtles (Chelonia mydas), Pacific black green sea turtle (Chelonia agassizi), hawksbill sea turtles (Eretmochelys imbricata), leatherback sea turtles (Dermochelys coriacea), humpback whales (Megaptera novaengliae), pantropical spotted dolphins (Stenella attennata), whale sharks (Rhinocodon typus), and bottlenose dolphins (Tursiops truncatus). Along with marine mammals, fish, invertebrates, and reptiles, the Golfo Dulce supports a unique vegetation system. The table below shows documented vegetation of the area (CNP 2001, Zuchowski 2007). Table 1: Vegetation Types on Playa Preciosa Common Name Scientific Name Coconut Palm Beach Grass Red Mangrove Manzanillo Sea Heart Sea Purse Tea Mangrove Beach Morning Glory Black Mangrove Buttonwood Beach Hibiscus Coco Plum Bombacopsis sessilis Terminalia catappa Chrysobalanus icaco Amphitecna latifolia Licania operculipetala Stachytarpheta jamaicensis Cocos nucifera Amophilla Rhizophora mangle Hippomane mancinella Entada gigas Dioclea reflexa Pelliciera rhizophorae Ipomoea pes-caprae Avicennia germinans Conocarpus erectus Hibiscus pernambuscensis Chrysobalanus icaco Bombacopsis sessilis Terminalia catappa Chrysobalanus icaco Amphitecna latifolia Licania operculipetala Stachytarpheta jamaicensis Past studies have been done in the Osa Peninsula. From 1998 to 2002, Efrain Mesen, a local living in Playa Preciosa, Costa Rica, ran a sea turtle hatchery and released 45,000 Page 2 of 24

3 sea turtle hatchlings over the period of four years (Waleksa 2016). In 2010, a pilot project studied Golfo Dulce extensively with boat surveys and interviews of local fisherman (Bessesen 2010). Fisherman documented a decline in all populations studied, presenting a need to preserve the area s habitat and marine life. Since 2010, no significant studies have been reported. This study provides an updated account of species in the Golfo Dulce and encourages further research on the area. Study Area MATERIALS AND METHODS Sea Turtle patrols were conducted on Playa Preciosa, Costa Rica. The map below shows the municipal location of Playa Preciosa in relation to the closest city, Puerto Jiménez, Costa Rica (Figure 1; Barquero 2016). Map Credit: Geinier Barquero Figure 1: Map of Playa Preciosa Page 3 of 24

4 The beach is partitioned into meter sectors. The study area extends 3700 km in length. Figure 2 shows the map of the study area, with Inicio de la Playa Estudio representing sector 1 and Final de la Playa Estudio representing sector 37 (Figure 2; Barquero 2016). Map Credit: Geinier Barquero Figure 2: Playa Preciosa Beach Map for Morning and Night Patrols Survey Methods: Morning Patrols and Night Patrols Morning patrols generally begun at 05:00 AM and night patrols begun at various times depending on tidal behavior. The depicted time of surveys occurred during middle point of low, rising to high tide. Locals called this time medio creciente, translating to the middle of the rising tides (Waleska 2016). Patrols extended from sector 19 to sector 37, from sector 37 to sector 1, or the entire beach from sector 37 to sector 1, and then sector 1 to 37 (Figure 2). Researchers and volunteers walked or biked Playa Preciosa, searching for sea turtle tracks and nests. If a track was found, the following data were recorded: track width, species, track symmetry, old or new track, present or absence of nest, and poaching and/or predation evidence, GPS (latitude/longitude), tide, moon phase, vegetation type and profile, and a photograph of the nesting area. If a nest was discovered after probing the sand for an egg chamber, the nest was initially marked with a stick with yellow string, with the date written three days before to deter poachers during the beginning surveys. Further sea turtle surveys did not include marking nests blatantly due to poachers finding and removing eggs. Nests were hidden with beach debris and secret systems to dissuade poachers from finding them. Page 4 of 24

5 Cayenne pepper was added to deter dog predators on the top layer of sand and covered with another layer of sand. Patrols encountered sea turtles in various phases during the nesting process. MINAE permitted scientists performed the following procedures during the egg laying phase (when the sea turtle is an a trance and is not disturbed): Flipper Tags, PIT tags, Curved Carapace Length (CCL) (Notch to Notch; Notch to Tip), Curved Carapace Width (CCW), temperature of sand and turtle (in later surveys), and body condition assessment. In-Water Surveys for Marine Mammals and Sea Turtles Surveys regularly begun at 09:00, leaving from and returning to the Corcovado Beach Lodge boat launch ( N, W) or the Puerto Jiménez dock (Muelle Público, Puerto Jiménez) ( N, W) for motorized surveys. For each survey, the following abiotic environmental data were collected: Date, Start, Time, End Time, Route, Boat, Researchers present, Tide, Cloud Cover, Beaufort Sea State, Weather, and Air Temperature. Surveys encompassed 2 hours on kayak and 6 or more hours on motorized boats, weather dependent. When an animal was sighted, the following data were recorded: Time of Sighting, GPS (Latitude/Longitude), Species of Animal, Number of animals sighted, Behaviors of animals, Tide, Beaufort Sea State, Altitude, Speed, Cloud Cover, Photos of dorsal fin (dolphin); fluke (whale), turtle (face); Additional notes, Vegetation presence, Fish presence, Presence of boats (or anything that would influence behavior), Weather (Rain, thunder, lightning etc.), and Beaufort Sea State. Photo-Identification When animals or reptiles were close enough for detailed photographs, pictures were captured to assist in the creation of a photo identification catalog of Golfo Dulce. The dorsal fins of dolphins are the focus to identify unique individuals. Flukes of humpback whales are the main focus of photo identification, with the ventral side of the animal being the secondary focus. Sea turtle heads are the focus of photo identification. Morning and Night Sea Turtle Patrols RESULTS For the month of September, 43 beach patrols were done on Playa Preciosa. A total of 16 olive ridley nests were laid and 5 olive ridley false crawls were seen. For the month of November, 95 beach patrols were done on Playa Preciosa. A total of 24 olive ridley nests were laid, 1 green sea turtle nest was laid, and 14 olive ridley sea turtle false crawls were seen. The figure below shows the number of nests that were poached versus non-poached and the types of poachers that ensued (Figure 3,4,5). Page 5 of 24

6 Figure 3: September 2016 Poaching Frequency Playa Preciosa (n=19 nests) 25% 50% 10% 10% 5% Human Ants Animal Dog Unpoached Figure 4: October 2016 Poaching Frequency Playa Preciosa (n=25 nests) 0% 19% 42% 39% Unpoached Human Dog Ants Page 6 of 24

7 Figure 5: September and October Poaching Frequency Playa Preciosa (n=44 nests) 45% 32% 4% 4% 15% Human Ants Animal Dog Unpoached Page 7 of 24

8 Figure 6 and 7 show the distance of the sea turtle nests to the closest vegetation during the months of September and October. Figure 6: Sea Turtle Nest Distance to Closest Vegetation September (cm) (n=19 nests) Distance (Cm) Page 8 of 24

9 Figure 7: Sea Turtle Nest Distance to Closest Vegetation October (cm) (n=25 nests) Distance (cm) The tidal range of Playa Preciosa spanned from 0.03 m to 3.20 m in September 2016, 0.1 m 3.3 m in October 2016, and -0.1 m to 3.3 m in November 2016 (Tablademareas.com 2016). Figure 8 and 9 show the amount of wrack (sticks, ocean debris, and detritus) around the circumference of the nest. This is important because sea turtles displace wrack materials when creating their body pit, during the nesting process. Page 9 of 24

10 Figures 8 and 9 show the percent coverage of sea turtle nests with wrack. Figure 8: Percent of Sea Turtle Nest Circumference covered by Wrack September 2016 (n=19 nests) Percent (%) Page 10 of 24

11 Figure 9: Percent of Sea Turtle Nest Circumference covered by Wrack October 2016 (n=25 nests) Percent (%) Page 11 of 24

12 Figure 10 shows the types of vegetation seen, in September 2016, in Playa Preciosa, closest to nests and false crawls. Figure 10: September to October 2016 Vegetation Types Closest to Nests and False Crawls Playa Preciosa October September Mango Tree Zacate Manzanillo Cocnut Palm Beach Hibuscius Beach Morning Glory Page 12 of 24

13 Figure 11 shows the map of all the false crawls and nests that occurred from September to November 2016 in Playa Preciosa, Costa Rica (ERSI 2016). Map Credit: Stephanie Sowa Figure 11 Page 13 of 24

14 Figure 12 compares moon phases to the nesting behaviors seen on Playa Preciosa. 18 Figure 12: Comparison of Moon Phase to Nesting Behaviors of Sea Turtles on Playa Preciosa Number of Nests or False Crawls Nest False Crawl 0 New Moon First Quarter Last Quarter Full Moon Phase Figure 13 compares tidal phases to the nesting behaviors seen on Playa Preciosa. 30 Figure 13: Comparison of Tide to Nesting Behaviors of Sea Turtles on Playa Preciosa Number of Nests or False Crawls Nest False Crawl 0 Low Medium High Tide Page 14 of 24

15 In-Water Surveys for Marine Mammals and Sea Turtles Six surveys were conducted monthly in Golfo Dulce. The graph below shows the total numbers of animals and reptiles sighted during in water surveys, conducted by boat and kayak (Figure 14). Figure 14: Marine Mammals Sighted in Golfo Dulce September to October 2016 Total Animals Sighted Megaptera novaeangliae Stenella attennata Tursiops truncatus Unidentified Sea Turtle Species September October Figure 15 shows the number of behaviors seen from Megapatera novaengliae, Stenella attennata, Tursiops Truncatus, and unidentified sea turtle species. Figure 15: Behaviors of Golfo Dulce Marine Mammals: September to October Number of Animals Exhibiting Behavior September Number of Animals Exhibiting Behavior October Page 15 of 24

16 Photo Identification Of all animals studied, dolphins exhibited bow-riding behaviors and allowed for the most opportunities to capture dorsal fin identification photos due to maximal proximity to the boats. Humpback whales tended to have larger distances from the boats and did not provide as many opportunities for photographs. Pantropical Spotted Dolphin Dorsal Fins (Stenella attennata) Photo Credit: Stephanie Sowa Photo Credit: Stephanie Sowa Photo Credit: Stephanie Sowa Bottlenose Dolphin Dorsal Fins (Tursiops truncatus) Photo Credit: Stephanie Sowa Humpback Whale Flukes (Megaptera novaengliae) Photo Credit: Stephanie Sowa Photo Credit: Stephanie Sowa Photo Credit: Stephanie Sowa Page 16 of 24

17 Photographed Humpback Whale Behaviors (Megaptera novaengliae) Breaching Photo Credit Noelle Mauri Page 17 of 24

18 Pectoral Fin Slapping (Pec Slapping) Photo Credit Stephanie Sowa Lob Tailing Photo Credit Stephanie Sowa Page 18 of 24

19 Figure 16 shows all animals and reptiles sighted using ERSI mapping tools online (ERSI 2016). Map Credit: Stephanie Sowa Figure 16 Page 19 of 24

20 DISCUSSION Golfo Dulce, Osa Peninsula, houses the most biodiversity in the world requiring much attention to maintain its title. This project shows a population survey and observational results from Golfo Dulce and Playa Preciosa. Future projects could focus on habitat use of marine mammals, mangrove vegetation being consumed by sea turtles, and animal and reptile behaviors of Golfo Dulce to preserve this crucial habitat. Sea turtle patrols faced challenges of poaching and weather. Poaching rates were 50 and 58 percent in September and October, respectively (Figure 3, 4). Humans and dogs represented the most common type of poachers. Most poachers traveled with dogs on the beach when nests were robbed. One night a group of poachers followed the patrol team and prevented them from completing the survey that night. To address the problem of poaching and keep the patrol team safe, poachers were avoided if seen and surveys were ended. Tranquility guards relocated nests near their property and protected them from poachers due to 24-hour security on their section of the beach. Other challenges of sea turtle patrols were weather-based. Rain, thunder and lightning storms were often too dangerous and prevented the team from patrolling for sea turtles. The wrack present on the beach and sea turtle nests did not appear to be correlated (Figure 8, 9). It is understood that when a sea turtle creates a body pit, she pushes away the debris on the sand with her flippers. Further, the tidal range of Playa Preciosa is large, and washes wrack onto nests after they are laid. The tidal range of Playa Preciosa spanned from 0.03 m to 3.20 m in September 2016, 0.1 m 3.3 m in October 2016, and -0.1 m to 3.3 m in November 2016 (Tablademareas.com 2016). Playa Preciosa wrack coverage data is not accurate unless recorded directly during the sea turtle nesting process. High tides can alter data of the condition of the nesting area on the beach. Figure 11 showed that nests occurred more frequently in the southern portion of Playa Preciosa and false crawls occurred more regularly in the northern portion of the beach. Fishermen are more prevalent in the northern section, possibly causing false crawls and scaring the turtles when they emerge to lay their eggs. The southern part of the beach is less inhabited and allows for more private, less disturbed nesting conditions for sea turtles. Sea turtle nests tended to be closer to vegetation in September. The farthest nest from vegetation was 1560 cm and the closest nest was 0 cm (directly on vegetation) (Figure 6,7). Nests had farther distances from vegetation in the month of October compared to September (Figure 6,7). Multiple nests displayed in and out crawls that overcame obstacles of vegetation debris. The most common type of vegetation was called Zacate. Zacate is a type of beach grass that prevents erosion (Table 1; Figure 10). Zacate was the most common plant on Playa Preciosa, followed by beach morning glory, and coconut palm (Figure 10). Playa Preciosa is a relatively uninhabited beach with fewer visitors than other Costa Rican beaches. Playa Preciosa is not developed and potentially shows a control group for vegetation and beach profiles. Page 20 of 24

21 Sea turtles nests and false crawls were compared to tidal and moon phases. The last quarter displayed the most nests and false crawls, succeeded by the full moon for both nests and false crawls (Figure 12). This behavior contradicts past sea turtle reports of behaviors in other locations (Law et al. 2010). However, locals of Playa Preciosa report that full moons tend to have more nesting event historically. Our data from 2016 also supports those reports of high turtle sightings during brighter moon phases (Figure 12). Tides were also studied and correlated with sea turtle nesting behaviors. The medio creciente tide (middle of rising low to high tide) showed the most turtle nesting events (Figure 13). According to 2016 nesting season data, sea turtles prefer medium tides (middle of low rising to high) and bright moon phases (last quarter and full moons). In-Water surveys showed that Megaptera novaeangliae had stable numbers in both months (7 animals in September and 6 animals in October) (Figure 14). High numbers of stenella attennata sightings (40 individuals) occurred in September followed by a drop in sightings in October (15 individuals) (Figure 14). Tursiops truncatus rose from 1 to 5 sightings in October (Figure 14). Only two sea turtles were sighted during in-water surveys in October (Figure 14). Sea turtles surface above water for a few seconds to breath and return below the water, explaining the lack of sightings. Nests on Playa Preciosa confirmed the presence of green and olive ridley sea turtles in Golfo Dulce waters. The behaviors of marine mammals showed trends. The most common behaviors were pectoral fin slapping and breaching in September (Figure 15). These behaviors correspond with communications of warning other animals nearby (Deakos 2002). Due to calving season, mothers may be more protective of their calves (Dulce 1995). Traveling, splashing, bow riding, following, chuffing, and spinning in air were the most common behaviors of the marine mammals in October (Figure 15). These tend to be play behaviors with no purpose (Deakos 2002). Also, October correlates with migrations of marine mammals out of the gulf (Dulce 1995). Further, marine mammal sightings were more prevalent north of Ojo de Agua and were more concentrated near waters of Puerto Jiménez (Figure 16). It is possible that the boat traffic is heavier near Puerto Jiménez, attracting marine mammals with engine sounds and vibrations (Van Parijs and Corkeron 2001). Increased boat traffic provokes possible harm to marine mammals and sea turtles, if commercial development continues in Puerto Jiménez. Future studies should assess the marine mammal behaviors and human interactions with boats. Future directions for the studies of the Golfo Dulce could have daily spatially and temporally aligned boat surveys to measure changes in marine mammal sightings and behaviors over time. Sea turtle nests could be measured for success rate of hatchlings. The temperature of nests could be measured to compare hatchling success with sand characteristics. Stable isotopes of sea turtles could be measured in conjunction with isotopes of vegetation and mangroves, to see if mangrove leaves are an alternate food source. Golfo Dulce and Playa Preciosa, Costa Rica hold potential for impactful and innovative studies on sea turtles, beach vegetation, and marine mammals. Page 21 of 24

22 ACKNOWELDGMENTS Thank you to the Disney Conservation Fund, Osa Turtles, Georgia Sea Turtle Center, Osa Turtles Volunteers, the Playa Preciosa Turtle Group, and the Corcovado Beach Lodge for helping with the project and promoting conservation of animals of the Osa Peninsula. Page 22 of 24

23 LITERATURE CITED Abreu-Grobois, F. A. et al "Hawksbill Turtle Feeding Habits in Cuban Waters." Eighteenth International Sea Turtle Symposium. Barquero, Geinier. Map of Playa Preciosa. MINAE Bessesen, B.L Project Report and Summary of Multi-Species Marine Sighting Survey in Golfo Dulce, Costa Rica, January-February CNP Corcovado National Park and Piedras Blancas National Park. An Introductory Field Guide to the Flowering Plants of Golfo Dulce Rain Forests, Costa Rica: Corcovado National Park and Piedras Blancas National Park ( Regenwald der Osterreicher ). Oberosterreichisches Landesmuseum Deakos, Mark H Humpback whale (Megaptera novaeangliae) communication: the context and potential functions of pec-slapping behavior on the Hawai ian wintering grounds. Dissertation. University of Hawai i, Dulce, I. C. A. G First records of humpback whales including calves at Golfo Dulce and Isla del Coco, Costa Rica, suggesting geographical overlap of northern and southern hemisphere populations. Marine Mammal Science, 11(4), ERSI ERSI. ArcGIS Online. Law, A., T. Clovis, G.R Lalsingh, and J.R Downie "The Influence of Lunar, Tidal and Nocturnal Phases on the Nesting Activity of Leatherbacks (Dermochelys Coriacea) in Tobago, West Indies." MTN 127:12-17 The Influence of Lunar, Tidal and Nocturnal Phases on the Nesting Activity of Leatherbacks (Dermochelys Coriacea) in Tobago, West Indies. Seaturtle.org, Web. 09 Dec Osa Conservation, Admin "The Osa Peninsula: A Unique Place for Research and Education." Osa Conservation. Osa Conservation, Web. 08 Dec Tablademareas.com Tides for September to November Mauri, Noelle. Photographer McGuinness, Tomas Personal Communication. October Van Parijs, S. M., & Corkeron, P. J Boat traffic affects the acoustic behaviour of Pacific humpback dolphins, Sousa chinensis. Journal of the Marine Biological Association of the UK, 81(03), Waleska Personal Communication. October Zuchowski, Willow A Guide to Tropical Plants of Costa Rica. Comstock Publishing Associates. Zona Tropical Publications Page 23 of 24

24 FIGURE AND TABLE INDEX Table 1: Vegetation Types on Playa Preciosa Figure 1: Map of Playa Preciosa Figure 2: Beach Map for Morning and Night Sea Turtle Patrols Figure 3: September 2016 Poaching Frequency Playa Preciosa (n=19 nests) Figure 4: October 2016 Poaching Frequency Playa Preciosa (n=25 nests) Figure 5: September and October Poaching Frequency Playa Preciosa (n=44 nests) Figure 6: Sea Turtle Nest Distance to Closest Vegetation September 2016 (cm) (n=19 nests) Figure 7: Sea Turtle Nest Distance to Closest Vegetation October 2016 (cm) (n=25 nests) Figure 8: Percent of Sea Turtle Nest Circumference covered by Wrack September 2016 (n=19 nests) Figure 9: Percent of Sea Turtle Nest Circumference covered by Wrack October 2016 (n=25 nests) Figure 10: September to October 2016 Vegetation Types Closest to Nests and False Crawls Playa Preciosa Figure 11: Map of all the false crawls and nests that occurred from September to November 2016 in Playa Preciosa, Costa Rica Figure 12: Comparison of Moon Phase to Nesting Behaviors of Sea Turtles on Playa Preciosa Figure 13: Comparison of Tide to Nesting Behaviors of Sea Turtles on Playa Preciosa Figure 14: Marine Mammals Sighted in Golfo Dulce September to October 2016 Figure 15: Behaviors of Golfo Dulce Marine Mammals: September to October 2016 Figure 16: Map of Marine Mammals and Sea Turtles Sighted during Boat Surveys Page 24 of 24