Aquatic Urbanites: Examining presence and group size of bottlenose dolphins (Tursiops truncatus) in the Western New York Bight Kristi A. Collom 1, Paul Sieswerda 2, Eric A. Ramos 1,3, Catherine Granton 2, Merryl Kafka 2, & Diana Reiss 1,3 1 Hunter College, City University of New York, NY, 2 Gotham Whale, Staten Island, NY, 3 The Graduate Center, City University of New York, NY
Goals
Introduction Bottlenose dolphins (Tursiops truncatus) are commonly reported in the New York and New Jersey Bight yet there is limited data on their distribution to confirm their annual presence in this specific habitat. Several decades of annual surveys across the Atlantic Ocean support year-round occurrence of Bottlenose dolphins in the coastal and offshore waters of the Western New York Bight (WNYB) but a lack of site-specific study effort and fine-scale examinations of populations specific to the New York and New Jersey metropolitan area may hinder efforts to manage and conserve these populations. (Roberts et al. 2016).
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• To document the occurrence of bottlenose dolphins in in WNYB region. • To illustrate the spatial relationships between bottlenose dolphin distribution and vessel activity
Results • 410 boat-based surveys from 2011-2017; 1,640 hr of survey effort. (Tt = 42.44%, Mn = 75.94%) • Sightings spiked by 45% from 2016 to 2017 (Fig. 3), disproportionate to an increase in survey effort (6%) (Fig. 5). • Group size was a mean of 49.04 (SD 56.38) and ranged from 1-150 dolphins. • Sightings increased over time and in later years dolphins were found in previously undocumented habitats. Most sightings occurred near shore. Sightings spiked from 45% from 2016-2017, disproportionate to an increase in survey effort (6%).
Seasonal Occurrence and Anthropogenic Impact
Figure 5. Number of surveys and sighting occurrences of bottlenose dolphins from 2011 to 2017.
Discussion • In our study, we document a steady increase in the number and geographic extent of dolphin occurrence, regardless of reduced survey effort (Fig 5). • Submarine canyons like the New York and New Jersey Bight drive warmer waters that may be drawing in both the dolphins and their prey.
Fig. 1. Vessel and aerial surveys of the Atlantic. 1-50 individuals/km. Roberts et al. (2016) Toth-Brown et al. (2011) documented presence in adjacent coastal habitats of New Jersey, identifying 205 individuals including similar seasonal peaks (May to September) 47% of which were within the Jacques Cousteau National Estuarine Research Reserve, suggesting the value of managed marine reserves. Photo-identification suggests that populations are small, possibly resident, and vary seasonally in occurrence.
Figure 3. Distribution of sightings, organized by annual occurrence. A) 2011-2012, B) 2013-2014, C) 2015-2016 (A sand assessment survey was conducted using seismic activity during this time in overlapping regions) D) 2017 . All surveys began at Fort Tilden, Riis Landing along the Rockaway peninsula. The vessel would begin each survey from the middle apex of the bight to the end of the survey area and then follow along the coastline for sightings or reports. Sightings from 2017 were noticeably dispersed.
• Numerous commercial shipping lanes overlap with regions where dolphins are regularly sighted (Fig. 4). • High levels of year-round recreational activities (boating, fishing, water sports) and commercial activities may threaten local marine mammal populations.
The goal of our study was to gather information on the occurrence of dolphins in the region and investigate the influence of environmental and anthropogenic factors on group size and sighting location to provide critical information for coastal managing authorities
• Future research efforts including yearround surveys and passive acoustic monitoring are optimal in assessing yearround distribution patterns in this region. • Recent accounts of marine mammals entering nearby rivers and estuaries suggest a need for monitoring across shipping lanes and channels, focusing studies on coastal regions (e.g., rivers, harbors, estuaries). Fig 2. Bottlenose dolphins in WNYB. Sightings ranged from 1-150+ individuals/encounter.
• Future studies should investigate impact from recent seismic activity in 2015-2016 which may account a change in their distribution.
Methods •
Boat-based surveys aboard a 34 m commercial whale watching vessel (American Princess Cruises, New York) were conducted from May to October in 2011-2017 in the New York/New Jersey metropolitan region inclusively within an 84 km coastline survey area within water depths of 5-50 m and water temperatures from 58-67 F˚.
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Sightings were logged at the beginning of every encounter, documenting vessel heading (˚), surface and water temperature (˚C), depth (m), species type, group size, and Ad libitum observations on animal behavioral activity.
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Efforts were made to photograph and video document all of the animals in each sighting. Group size was estimated based on surface counts by experienced individuals and verified by media when possible.
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Dorsal fins and distinct features were organized to develop a catalog of dolphins using standard methodology.
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Using ArcMap, all sightings were plotted to define seasonal and annual presence as well as proximity to track lines showing commercial and recreational vessel activity in an effort to examine risk to marine mammal populations.
• We plan to deploy recorders in 2018 to develop a method of monitoring dolphin presence along the coastline of New York and in nearby rivers.
Figure 4. A) Distribution of all sightings from 2011-2017 across track lines from passenger vessels and recreational boating areas, B) Distribution across commercial shipping lanes reserved for cargo vessels and container ships. It is evident that the majority of sightings seem to avoid the areas of highest anthropogenic activity with larger groups sighted along tracklines. C) Distribution along tracklines for Spring 2011-2017 indicating that sightings in colder months were closer to shore. D) Highest rate of occurrence was in the Summer months with greater dispersion across areas of consistent vessel activity. E) Sightings in the Fall were sparse and included occurrences in the shallower bays and closer to the apex where warmer water may increase the presence of prey in the winter months. References 1. Toth, J. L., Hohn, A. A., Able, K. W., & Gorgone, A. M. (2011). Patterns of seasonal occurrence, distribution, and site fidelity of coastal bottlenose dolphins (Tursiops truncatus) in southern New Jersey, USA. Marine Mammal Science, 27(1), 94-110. 2. Toth-Brown, J., & Hohn, A. A. (2007). Occurrence of the barnacle, Xenobalanus globicipitis, on coastal bottlenose dolphins (Tursiops truncatus) in New Jersey. CRUSTACEANA-INTERNATIONAL JOURNAL OF CRUSTACEAN RESEARCH-, 80(10), 1271. 3. Roberts, J. J., Best, B. D., Mannocci, L., Fujioka, E., Halpin, P. N., Palka, D. L., ... & McLellan, W. A. (2016). Habitat-based cetacean density models for the US Atlantic and Gulf of Mexico. Scientific reports, 6, 22615.
Acknowledgements Thanks to Gotham Whale, American Princess Cruises, and their volunteers for facilitating this research. Special thanks to Artie Raslich, Celia Ackerman, Yadira Blanco, Danielle Mognahan Brown, Jacklyn Sullivan, Arthur Kopelman, Jochen Albrecht, John & Patricia Collom, Joseph & Marilyn Schwartz, Sheila Chase and various mentors at the American Museum of Natural History for their invaluable insight and support! This research was supported in part by a student research grant from the Animal Behavior and Conservation Biology masters program committee and the generosity of Tom Palladino and Frank deSantis for letting me scour the high seas on these seasonal whale watching excursions aboard American Princess Cruises.
