Methods • Boat based surveys conducted around Savannah Georgia (Figure 1); surveys

extended 3 km seaward past set transects in Wassaw Sound only during the first week of 2010 shrimp season.

• 16 April to 4 August 2009 and from 11 May to 24 August 2010.

• Community division by modularity was determined with SocProg 2.6 Compiled using all non-calf individuals seen ≥ 6 times.

• Sightings of social clusters were mapped in ArcGIS 9.3 and kernel isopleths were created using Home Range Tools for ArcGIS.

Figure 1. Study area, located near Savannah, Georgia

Are common bottlenose dolphin (Tursiops truncatus) interactions with shrimp trawlers resulting in social segregation in Savannah, Georgia?

Carolyn Kovacs, Robin Perrtree, and Tara Cox Marine Sciences Program, Savannah State University

Abstract Foraging specializations can often lead to social segregation of animal groups. In bottlenose dolphins (Tursiops sp.), foraging in association with shrimp trawlers has been correlated with social segregation. In Savannah, Georgia, common bottlenose dolphins (Tursiops truncatus) associate with the shrimp fishery during trawling in nearshore coastal waters as well as during discard of bycatch inside estuaries. Many dolphins also engage in begging from both commercial and recreational vessels. We used boat-based surveys in May-August 2009 and 2010 to determine if there was social segregation of dolphins that associate with trawlers and those that do not. We hypothesized, based on other areas of the world, that there would be clear social segregation based on foraging in association with shrimp trawlers. Photo-identification was used to distinguish individuals that associated with shrimp trawlers. Community division by modularity was used to determine social clusters for animals seen ≥ 6 times. Out of the 5 social clusters identified, 4 were mixed, although 2 of these were predominantly comprised of dolphins known to associate with shrimp trawlers and the other 2 were mostly dolphins that no not associate with shrimp trawlers. Clusters appear to be segregated by associations with shrimp trawlers more than by begging behavior. Clusters comprised of mostly trawler-associated dolphins had a core utilization area in Wassaw Sound whereas non-trawler dolphins were found mostly in rivers further inshore. On the first day of the 2010 shrimp season, 96 dolphins were observed associating with shrimp trawlers, 33 (34%) of which were only seen during the first week of the shrimp season. In the estuaries and coastal waters near Savannah, associating with shrimp trawlers has resulted in some social segregation, although it is less extreme than that seen in other areas of the world. In fact, shrimp trawler associations may result in social integration between estuarine and coastal or offshore stocks mixing at the mouths of estuaries where shrimp trawlers operate, as demonstrated by the previously unseen animals sighted during the first week of shrimp season.

Introduction • Dolphins associate with shrimp trawlers for food by following behind

actively trawling vessels and feeding on fish that pass through the net, by consuming discarded bycatch, or by foraging around non-active vessels (Leatherwood, 1975; Fertl and Leatherwood, 1997).

• Dolphins near Savannah, Georgia exhibit the highest recorded rate of begging behavior in the world. Begging is mixed throughout the population and has not resulted in social segregation (see poster by R. Perrtree 14:12).

• The high rate of begging in Savannah may be related to dolphins associating with shrimp trawlers, especially during the discard of bycatch.

• In other areas of the world, associating with shrimp trawlers has led to extreme social segregation with no interaction between trawler and non-trawler dolphins (Chilvers and Corkeron, 2001; Fleming 2004).

Bottlenose dolphins foraging behind a shrimp trawler hauling in its nets

Literature Cited

Chilvers, B.L. and P.J. Corkeron. 2001. Trawling and bottlenose dolphins' social structure. Proceedings: Biological Sciences 268(1479): 1901-1905.

Fertl, D. and S. Leatherwood. 1997. Cetacean interaction with trawls: A preliminary review. Journal of Northwest Atlantic Fisheries Science 22:219-248.

Fleming, K.H. 2004. The social structure, behavior, and occurrence of bottlenose dolphins in relation to shrimp trawlers in Southport, North Carolina. M.Sc. thesis, University of North Carolina at Wilmington, 52 pp. Leatherwood, S. 1975. Some observations of feeding behavior of bottle-nosed dolphins (Tursiops truncatus in the northern Gulf of Mexico and Tursiops cf. T. gilli) off southern California, Baja California, and Nayarit, Mexico. Marine Fisheries Review 37(9):10-16.

Results continued

On the first day of shrimp season in 2010, 96 dolphins were observed associating with shrimp trawlers • 48 (50%) had been seen at another time in our study area • 33 (34%) were only seen on the first 3 survey days (June 8, 9, and 12)

at the start of the shrimp season, always with trawlers • 15 (16%) were clean, calves, or did not have good enough photo

quality to match

Discussion

• Over a third of the catalog is known to associate with shrimp trawlers, and this may increase with more field effort around shrimp trawlers.

• The same percent of confirmed beggars and non-beggars associate with shrimp trawlers, indicating that shrimp trawlers are not the sole source of the begging problem.

• Social clusters are mostly separated by dolphins that associate with shrimp trawlers versus dolphins that do not.

• Social segregation from trawler associations is not as extreme as in other areas (Chilvers and Corkeron, 2001; Fleming, 2004).

• Dolphins that associate with shrimp trawlers are more likely to be found near Wassaw Sound, just inshore of where trawling occurs.

• There is much spatial overlap of utilization areas, although core areas differ.

• There may be mixing of stocks as a result of estuarine and coastal or offshore dolphins coming to the mouths of sounds to forage in association with shrimp trawlers.

Acknowledgements Thank you to the members of the Savannah State University Dolphin Science Lab and interns who assisted in the collection of sighting information and photo-identification. This work was supported by NOAA LMRCSC and the NSF GK-12 program (NSF award number 0841372). Photos of dolphins were taken in accordance with the Marine Mammal Protection Act under NMFS Letter of Confirmation # 14219.

17Jul10 Photo by C. Kovacs

Objectives

• Determine the extent of shrimp trawler associations in Savannah, Georgia.

• Determine if shrimp trawler associations have resulted in social segregation.

• Examine the utilization areas of social clusters.

8Jun10 Photo by C. Kovacs

50%

34%

16% Previouslyseen

Only seen in 3day span

Unidentifiable

Results

Trawler associated groups Cluster 1 Cluster 2 20 trawler dolphins / 22 total dolphins 26 trawler dolphins / 27 total dolphins

• Clusters with mostly trawler dolphins had a core 50% area primarily in Wassaw Sound.

Non-trawler associated groups Cluster 3 Cluster 4 0 trawler dolphin / 2 total dolphins 1 trawler dolphin / 25 total dolphins

• Clusters with non-trawler dolphins were found more in rivers further inland or smaller creeks.

Mixed group Cluster 5 6 trawler dolphins / 27 total dolphins

Conducting surveys around a shrimp trawler

Definitions of dolphin categories: • Trawler – dolphin seen at least 1 time associating with a shrimp trawler by:

foraging behind the vessel while trawling, begging from a vessel, or swimming non-directionally within 50 feet of the vessel.

• Non-trawler – dolphin with 6+ sightings never seen associating with a trawler.

• Beggar – dolphin with 6+ sightings seen ≥1 time begging (see poster by R. Perrfree).

• Non-beggar – dolphin with 6+ sightings and never observed begging.

Results

• 110 out of the 294 (37%) of all cataloged dolphins associated with shrimp trawlers

• 23 out of 42 (55%) confirmed beggars associated with shrimp trawlers

• 28 out of 55 (51%) confirmed non-beggars associated with shrimp trawlers

• The mixed cluster had a core area in a different large river as well as small creeks, including one that houses shrimp docks and has easy access to the ocean.

• There is overlap in the utilization areas of all clusters.

• Modularity of the social clusters was 0.303.