Frequency And Correlation Of Surface Observed Behaviors Of The Bottlenose Dolphin (Tursiops Truncatus) In Cape May, New Jersey.

Credit to Cape May Whale Watch and Research Center Database

Introduction

Collection of opportunistic  data during  whale watching trips can offer a wide range of insights into cetacean behavior.  In addition  to spatial information and long term tracking of individuals through photographic methods, notable short-term behaviors of individuals are recorded during sightings (Hauser 2007). Feeding and mating are two essential behaviors often observed at the surface in the bottlenose dolphin (Tursiops truncatus). Breaching is a spectacular behavior  which is easily recorded  due to its dramatic nature.  Observing the occurrence of these three behaviors may lend insight into  how various behaviors are related as well as the data collection process.

Methods

Data collected during the 2014 field season was utilized in this work. Data was segregated according to trip times to avoid unnecessary variables associated with time of day. Unless otherwise noted, listings  of behavior occurrence are the percentages of total particular behavior listings out of the total sightings for a particular time of day.  For time ranges, AM indicates 10:00-12:00, PM 13:00-16:00, and SS 18:00-20:00.  incomplete datasets were not included in this analysis .

Results

Figure 1: percent occurrence of behaviors.

Figure 2. Breach occurrence in relation to feeding

Discussion

Figure 1. demonstrates that the most commonly observed of the three selected behaviors is feeding, which was uniformly observed  during roughly 58% of the trips regardless of time of day. Feeding  therefore  seems  equally likely to occur during any of the three trip times. Breaching  and mating, while somewhat less predictable, also demonstrate similar occurrence across  time periods. Breaching decreases slightly from morning to evening, but it is debatable whether this indicates a legitimate trend.  Altogether the data indicates surprising  stability of behavior regardless of the time of day.

Figure 2. represents an attempt to correlate breach occurrence with feeding behavior.  Column A demonstrates that out of the total number of breaches during a given time period, a large proportion were observed  along  with feeding behavior.  An average of roughly 70% of the total breaching  observations occurred during feeding behavior.  Even during feeding, however, breaching is relatively uncommon. Column B demonstrates that the number of feeding observations which include breaching out of the total number of feeding observations.  While higher than breaching percentage with all sightings pooled,  the average  occurrence  of roughly 27% is still relatively low. Therefore, while breaching is most likely to occur during feeding behavior,  it  clearly does not occur of necessity, and appears to apply only to certain feeding circumstances.  There is the possibility that other variables must be explored to further investigate this relationship.  

Reasons for a potential correlation of breaching and feeding behavior  relate to issues of communication and prey capture (Perrin 2008). Breaching may produce long ranging, low  frequency sounds which provide information to individuals about pod movement and structure useful during feeding. It has been suggested that breaching may function as a signal to  the approach and surrounding of prey items (Thomas 1990).  In addition, it has been theorized that the underwater shock caused by breaching may disorient prey items in the  same way as fluke slapping  (Perrin 2008). Finally, some breaching may be a result of high speed prey capture; on at least one occasion a dolphin was observed breaching vertically through a bubble net in an attempt to seize fish concentrated at the surface (personal observation). The fact that breaching may apply to feeding in only certain social or behavioral  contexts may explain its apparently infrequent or irregular occurrence.

    Further development of this study would involve analysis of wind speed and breaching to assess whether breaching may be an attempt to communicate more easily at the surface during times when more sound interference is present due to wind.

Michael A. Denk, Intern at Cape May Whale Watch & Research Center 

 
REFERENCES
.Thomas, Jeanette A,. Kastelein , Ronald A   Sensory Abilities of Cetaceans: Laboratory and Field Evidence   Plenum Press 1990 pg 527
  Perrin ,William F., Wursig, Bernd, Thewissen, J.G.M. “Hans”    Encyclopedia of Marine Mammals Academic Press; 2nd edition (December 8, 2008) pgs.  6-8
http://faculty.washington.edu/eeholmes/Files/Hauseretal2007.pdf
http://www.dolphincommunicationproject.org/index.php/about-dolphins/current-research