Listening to wild bottlenose dolphins

Transcription

1 Listening to wild bottlenose dolphins Article by Ylenia Vimercati Molano, photos by Bottlenose Dolphin Research Institute BDRI A fter have been searching through the web for a research center where to pursue my master s thesis in biodiversity and evolutionary biology, I luckily bumped into the Bottlenose Dolphin Research Institute BDRI. The Center, located in O Grove, a small town in the north-western coast of Galicia (Spain), sounded like the perfect place where to work on a scientific project suitable for my student career. Among all the internship projects available I decided to focus my thesis on bottlenose dolphins (Tursiops truncatus) communication, and in particular on the vocalization characteristics of two non-adjacent populations. Students and volunteers collaborating with the BDRI live for the entire duration of their stay in an apartment less than 5 minutes walk from the lab and close to the city center which makes it extremely easy to reach all the facilities needed by the interns. Sharing the accommodation with your coworkers means to get to know them, to help each other with research, and to learn what it is like to live with several people with different backgrounds and from various cultures under the same roof. It isn t always easy to share everything with other people of course, but it is such a precious life lesson because it makes you realize what adaptation means and, when you look back at your experience and the people you have met, you will have a big smile on your face because you will feel enriched as a person. During my 5 months internship I got to meet many people from different countries. Some people came and some people left making the BDRI students group very dynamic. This turnover let me encounter many people and relate myself with different attitudes and cultures. The daily work at the BDRI entirely depended on the weather conditions. If the wind was too strong, or it was raining too hard, or the visibility was poor we wouldn t go at sea with the boat to collect data, but we would stay in the lab analyzing data or taking part to lectures on cetaceans biology led by the BDRI s director Bruno Díaz López and the marine ecologist Séverine Methion.

2 Speaking of biology, the bottlenose dolphin, which it owes its name to his bottled-shape rostrum, belongs to the genus Tursiops and it is one if the best known cetacean species. Being a cosmopolitan animal, the bottlenose dolphin is found in temperate and tropical marine waters along the continental shelf of the Atlantic, Pacific, and Indian Oceans. Their spindle-shaped body is grey in color with a darker tone laterally and lighter ventrally. Considering I had never seen wild bottlenose dolphins previous to this experience I didn t expect them to be so large. They are quite impressive with their average body length of 260 cm, so every time they would jump next to our boat or swim below, it was always spectacular and touching looking at those majestic animals full of energy and life. For what concerns its diet, T.truncatus is an opportunistic predator which feeds on a high variety of preys with various feeding techniques. It usually feeds on fish, cephalopods, mussels and crustaceans that often catches from fishing nets and cages used by fishing boats or for aquaculture. The bottlenose dolphin is an extremely vocal mammalian species and much knowledge has been acquired on its advanced and complex communication system which plays a fundamental role in social interactions. T.truncatus lives in dynamic groups which means that composition is highly variable. Groups are usually made of 2 to 15 animals but it is not rare to encounter more than 100 individuals in the same group. Animals are usually observed busy in one of the following behavioral displays: feeding, travelling, socializing, and resting.

3 My master s thesis focused on investigating the characteristics of particular vocal sounds, called whistles, produced by two bottlenose dolphin populations, one from O Grove (where the BDRI is located) and one from Sardinia Island in Italy, where the BDRI was originally based before moving to Spain. T.truncatus produces whistles along with other sounds known as burst-pulsed and clicks. The first are used in social contexts as whistle do and can be produced simultaneously to whistles. Clicks are instead mostly used for echolocation allowing dolphins to scan the surrounding environment. The sounds are produced in the forehead inside the blowhole in the region of the socalled nasal sacs and reflected by the curved bone of the head and focused into the melon, a low density tissue full of lipids. The melon works as a lens to focus and emit sounds rostrally. A typical day at sea usually would begin very early in the morning in order to maximize data collection as long as weather and sea conditions were favorable. During our boat trips we would take part to different duties depending on our position on the boat. People in front were busy spotting the dolphins and communicating positions, numbers, and possible IDs to the people on the top. There the staff members and students were involved in collecting data for surveys and sightings. Surveys were accomplished every 20 minutes by filling out a table with data mostly regarding environmental conditions, anthropogenic presence, and animals presence in the area. Whenever in presence of dolphins we had to collect data for the sightings table and repeat the same process every 5 minutes. During these time intervals information regarding behavioral displays or any valuable detail for scientific research was annotated. Students in the back of the boat were engaged both in spotting dolphins both in collecting data every 5 minutes for vessel intermediate positions. When a group of T.truncatus was encountered and sea and environmental conditions were good, acoustic recordings were collected. The engine of the boat had to be off and the distance from the animals had to range from 2 to 50 meters. We would lower a hydrophone connected to a digital recorder and monitor the sounds through headphones. Once at the BDRI center my work mainly consisted in analyzing the recordings on the computer through a visual and acoustic examination. Vocal sounds were classified on the basis of their shape, and acoustic parameters were measured for subsequent analysis.

4 When working in the lab, I was also involved in other activities that are essential for the research carried out by the BDRI. For example I spent some time working on the photo-identification, which is the use of photos to identify individuals thanks to the presence of natural marks and unique pigmentation on the dorsal fins. Photos were also used to create digital silhouettes of each known individual s dorsal fin and put them in the catalogue for the current year. Another important task was to transcribe data collected at sea; these would have been later inserted into the BDRI database. One day during winter season we received a call saying that two common dolphins (Delphinus delphis) were found stranded on a beach. Unfortunately the two individuals were found dead, and thanks to necropsy it turned out that the animals had died because of humans. One had its caudal fin cut probably because it got entangled in a fishing net and was subsequently removed by fishermen, and the other had water in its lungs meaning that he drowned for the same reason. It was very frustrating to see in first person that bycatch kills animals every year, and realize that our activities and the daily choices we make are responsible for this loss. Another unexpected experience, but this time extremely rewarding, happened when two bottlenose dolphins, a mother and her calf, found themselves trapped in shallow waters right in front of the BDRI, an area subjected to tides. The dolphins were not able to move because their bellies were stuck on the seabed and the situation was getting worse as the tide was lowering. Thanks to the incessant effort everybody put and the precious help of other organizations, the two dolphins were safely released into deeper waters. It was very touching to hear the calls emitted by the dolphins. The mother wouldn t stop whistling at the young male when the two were separated to be carried to the right place for the release. The strong bond that exists between a mother and her baby is something powerful that doesn t only belong to our species, and it is something we don t often take into account.

5 My experience at the BDRI made me realize how impressive is the amount of work needed to lead a research center that focuses on wild animals. Data have to be collected throughout the year no matter the temperature and weather conditions are not ideal for our bodies or mood. Bottlenose dolphins are aquatic mammals which makes it even more difficult to spot and study them. This means that everybody has to put a lot of effort in this job and give the best contribution possible despite the difficulties we can go through. Sometimes it can be frustrating to go at sea and come back without having spotted a single dolphin, but patience and perseverance are the key when dealing with wild species. Only by understanding what field research means and the sense of gratification you feel after such an experience, every struggle you face will surely be defeated. The information provided by this article is the outcome of the non-stop research conducted by the BDRI. To learn more about the Bottlenose Dolphin Research Institute BDRI visit the website: Visit: for LWA