The social structure, behavior, and occurrence of bottlenose dolphins in relation to shrimp trawlers in Southport, North Carolina

UNCW Author/Contributor (non-UNCW co-authors, if there are any, appear on document)
Kimberly Hoover Fleming (Creator)
The University of North Carolina Wilmington (UNCW )
Web Site:
Laela Sayigh

Abstract: Bottlenose dolphins use a wide diversity of feeding tactics, and can be quite flexible in their use. Numerous researchers have described associations of dolphins with shrimp trawlers. Trawler foraging is characterized by bottlenose dolphins feeding on organisms stirred up by an actively trawling shrimp boat, bycatch, and/or fish attracted to non-working shrimp trawlers. This study analyzed data collected from boat-based photo-identification surveys conducted from 1998-2003 in the Southport, North Carolina area, where there is an active shrimp fishery in the summer and fall. Based on findings from two recent studies, the following hypotheses were tested: (1) separate, non-interacting communities of trawler and non-trawler dolphins occur, (2) trawler dolphins spend more time socializing and less time feeding than do non-trawler dolphins, (3) trawler dolphins are seasonal in their occurrence and (4) trawler dolphins occur in larger group sizes than non-trawler dolphins. Data from 99 sightings were analyzed (40 trawler sightings and 59 non-trawler sightings). Trawler dolphins were defined as any dolphin seen at least once with a trawler, and non-trawler dolphins were those never seen with a trawler. Of 51 dolphins sighted three or more times in the Southport area, 45 were trawler dolphins and 6 were non-trawler dolphins. Associations between trawler (T) and non-trawler (NT) dolphins were significantly different from those within both NT and T groups (p<0.0001), and within group associations (T-T and NT-NT) were significantly higher than between group associations (NT-T; p<0.0001). T animals had significantly different activity budgets than NT animals (p<0.0001); when not with trawlers, T dolphins spent more time socializing than did NT dolphins. In addition, NT dolphins spent more time traveling than did T dolphins, which could be at least partially due to their increased need to search for food. Sightings of trawler dolphins were highly seasonal, occurring only in the summer and fall (p=0.0033), and larger group sizes (p=0.0020, F=10.07) occurred with trawlers. Non-trawler dolphin sightings occurred primarily in winter in Southport, but year round in other portions of the Wilmington study area. Results support the hypotheses that separate, non-interacting groups of trawler and non-trawler dolphins occur in Southport, NC and that these groups differ in their activity budgets and seasonal patterns of occurrence.

Additional Information

A Thesis Submitted to the University of North Carolina at Wilmington in Partial Fulfillment Of the Requirements for the Degree of Master of Science
Language: English
Date: 2009
Bottlenose dolphin--Behavior, Bottlenose dolphin--North Carolina--Southport, Bottlenose dolphin--Research, Dolphins--Feeding and feeds--North Carolina--Southport
Dolphins -- Feeding and feeds -- North Carolina -- Southport
Bottlenose dolphin -- North Carolina -- Southport
Bottlenose dolphin -- Research
Bottlenose dolphin -- Behavior

Email this document to