Abstract
Heavy vessel traffic can negatively affect dolphins by increasing the risk of habitat disruption, emigration, or physical harm by boat propellers.1 It is important to assess the behaviors of the resident population of bottlenose dolphins (Tursiops truncatus) in the Galveston Ship Channel, near the entrance to the second busiest port in the USA, as a 5.2 billion dollar expansion of the Panama Canal is to be completed in 2014 that will bring more and larger ships to Galveston Bay.2 Hour-long surveys were conducted from a shore-based station along the Galveston Ship Channel in the morning, mid-afternoon, and late-afternoon from August through December 2012. Group size, number of boats, and predominant behavior of dolphin groups were recorded during each survey. We predicted a decrease in social behavior and an increase in travelling behavior as vessel traffic increased, as noted in previous studies of short-term behavioral shifts of dolphins during periods of heavy vessel traffic.3 A X2 contingency test showed that the behaviors of dolphins varied significantly from chance expectations relative to the number of boats (X2 = 9.72, d.f. = 4 at p = 0.05). However, contrary to our predictions, socializing behavior did not change inversely proportionately to vessel traffic nor did travelling behavior increase with increasing traffic. We tested alternative hypotheses for changes in dolphin behavior including the number of dolphins in a group and the time of day. X2 contingency tests showed that dolphin behaviors varied relative to group size (X2 = 9.51, d.f. = 4 at p = 0.05), but not to the time of day (X2 = 9.02, d.f.= 4 at p = 0.05). Our results suggest that several factors influence behavioral decisions of socially complex dolphins. Further studies are necessary to better understand potential effects of increased ship traffic on the local dolphin population and to establish effective mitigation protocols. Ongoing data analysis will determine if the dolphins demonstrate different behavioral responses based on the type, size, speeds, and noises of approaching vessels, and to what degree and how they alter their habitat use when vessels approach.
Acknowledgements
I would like to thank Ashley Zander and Sarah Piwetz for their assistance with data collection.
* Presenting author
+ Student presenter
Literature Cited
1. Nowacek SM, Wells RS. 2001. Short-term effects of boat traffic on bottlenose dolphins, Tursiops truncatus, in Sarasota Bay, Florida. Mar Mamm Sci 17(4): 673–688.
2. Overview [Internet]. [PHA] Port of Houston Authority; c2012 [cited 2013 Jan 10]. Available from: www.portofhouston.com/about-us/overview/
3. Wells RS. 1993. The marine mammals of Sarasota Bay. In: Roat P, Ciciccolella C, Smith H, Tomasko D, editors. 1992 Framework for Action. Sarasota Bay (FL): Sarasota National Estuary Program. p 9.1–9.23.