Using sightings of bottlenose dolphins to study spatial patterns

Where’s that dolphin?

Objectives• Learn about the ecology of bottlenose dolphins and

the research methods used to study dolphins • Plot points on a coordinate scale using latitude and

longitude• Learn about utilization areas • Calculate area of geometric shape and convert

measurements using a map scale • Think spatially: look at patterns in data related to

location

Dolphin surveys• Each group of dolphins is called a “sighting”• During each sighting, the scientists:– Use a GPS device to record position (latitude and

longitude)– Record the number and

behavior of dolphins– Record environmental

conditions– Take photos of each dolphin’s

dorsal fin to identify individual dolphins

Photo by C. Kovacs

Latitude and longitude The coordinate system

Where are you located?

Common bottlenose dolphins• Scientific name name is Tursiops truncatus• Are marine mammals; therefore, they need to go

to the surface to breathe air• Live in tropical and temperate waters worldwide • Primarily eat fish and squid

02Aug10 photo by R. Perrtree under permit #14219

Photo-identification• Scientists use nicks and notches to identify dorsal fins • Dolphins receive a number based on the location of

their nicks• Some dolphins receive names as well, for example

dolphin 80068 is also known as Fingers

70025 80068 – “Fingers” 1Aug09 photo by R. Perrtree under permit #14219 12Jul09 photos by R. Perrtree under permit #14219

Strand feeding• Behavior observed only in South Carolina and Georgia (Petricig 1995,

Hoese 1997)

• Dolphins rush towards the shore of a mudbank, and their wave causes fish to wash up on the bank

• The dolphins temporarily strand themselves on the bank to eat the fish, and then slide back into the water

• This behavior occurs mostly in shallow creeks at low tide (Bowen

2011), when mud banks are exposed

01Aug10 photo by R. Perrtree under permit #14219

For another activity in which students explore strand feeding, see Bowen-Stevens et al. 2011

Tides in Savannah, Georgia• Tides in Savannah are very large (ranging from 2 to 3 m) • Tides in Savannah are semidiurnal, meaning there are two high

tides and two low tides each day. • Fish can hide in the marsh plants at high tide, but at low tide

the fish move into the creeks and rivers

• Mud banks are exposed at low tide, as seen in the photos below

Low tideHigh tidePhoto by C. Kovacs Photo by C. Kovacs

Shrimp fishery • In Georgia, fishermen trawl for shrimp in the Atlantic Ocean just

outside of sounds and the mouths of rivers• The fishermen sometimes anchor in Wassaw Sound overnight • There are 3 major shrimp docks in Savannah, referenced here

by the stars

Shrimp docksShrimp docks

Wassaw SoundAtlantic Ocean

Atlantic Ocean

Dolphins feed in association with shrimp trawlers

• Dolphins near Savannah, Georgia feed in association with shrimp trawlers, either by swimming behind moving vessels and eating fish that are stirred up by the nets or by consuming bycatch that the fishermen push off the boat (Kovacs 2012)

• Bycatch is any species of animal that is caught by accident. Trawl nets catch many types of fish, jellyfish, and crustaceans

Dolphins following a shrimp trawl net

8Jun10 Photo by C. Kovacs under permit #14219

Begging• Some dolphins in Savannah also beg for food from humans in

recreational or fishing boats (Perrtree 2012)

• Begging usually occurs when boats are traveling slowly or stopped

27Aug09 photo by R. Perrtree under permit #14219 12Jun10 photo by K. Doyle under permit #14219

Begging• Begging is not a natural behavior• It is illegal to feed wild dolphins under the Marine Mammal Protection

Act• Feeding dolphins is potentially harmful to the animals and dangerous to

humans– Dolphins that become conditioned to

boats are more likely to get struck by a boat or propeller (Donaldson et al. 2010)

– Mother dolphins may not teach their calves to catch fish (Perrtree 2012)

– Dolphins have sharp teeth and sometimes bite people (Cunningham-Smith et al. 2006)

08Jul10 Photo by R. Perrtree under permit #14219

Calf with scars from a boat propeller

Other behaviors

• In addition to foraging, dolphins spend time traveling, resting, and socializing

08Jun10 Photos by C.Kovacs under permit #1421911Jun09 photo by P. Perrtree under permit #14219

Utilization area

• The area that a dolphin spends most of its time in is called a utilization area

• Some dolphins have a small utilization area and remain there, and other dolphins travel more and have a large utilization area

Utilization area:Minimum convex polygon (MCP)

• Connects the outside points of a group of points

Each of you has:

• A Sighting Summary Sheet with sighting information for two dolphins

• A Study Area Map

• A Student Report Sheet

You will:

• Plot the locations of the sightings for each of your dolphins using the coordinates provided

• Find the utilization area using a simplified minimum convex polygon

• Look for spatial relationships in the data

Real MCP vs a simplified MCP• In this activity, you will draw a simplified MCP around

the sightings you plot. The simplified MCP should be in a shape such that you can easily find the area of it.

• On the left is an example of a real MCP, on the right is a simplified MCP for the same sightings. There is more than 1 possible simplified MCP for each set of sightings.

Conclusions

• Where were your dolphins found?

• Based on what you learned about dolphin behavior, why do you think your dolphins were found in those areas?

• These data only cover one summer. If we had sighting information for the entire year, do you think it would look the same? Why or why not?

References

• Bowen, S.R. 2011. Diet of Bottlenose Dolphins Tursiops truncatus in the Northwest Panhandle and Foraging Behavior Near Savannah, Georgia. Masters thesis, Savannah State University, Savannah, Georgia, 162 pp.

• Bowen-Stevens, S.R., T.M. Cox, and M.C. Curran. 2011. What are bottlenose dolphins doing on land? An activity teaching the scientific method through the unique behaviors of strand feeding. The American Biology Teacher 73 (7): 407-411.

• Cunningham-Smith, P., D.E. Colbert, R.S. Wells, and T. Speakman. 2006. Evaluation of human interactions with a provisioned wild bottlenose dolphin (Tursiops truncatus) near Sarasota Bay, Florida, and efforts to curtail the interactions. Aquatic Mammals 32:346-356.

• Hoese, H.D. 1971. Dolphin feeding out of water in a salt marsh. Journal of Mammalogy 52 (1): 222-223.

• Kovacs, C.J. 2012. Interactions between common bottlenose dolphins (Tursiops truncatus) and shrimp trawlers in Savannah, Georgia. Masters thesis. Savannah State University, Savannah, Georgia, 155 pp.

• Donaldson, R., H. Finn, and M. Calver. 2010. Illegal feeding increases risk of boat-strike and entanglement in bottlenose dolphins in Perth, Western Australia. Pacific Conservation Biology 16:157-161.

• Perrtree, R.M. 2011. Begging behavior by the common bottlenose dolphin (Tursiops truncatus) near Savannah, Georgia: Prevalence, spatial distribution, and social structure. M.Sc. thesis, Savannah State University, 203 pp.

• Petricig, R.O. 1995. Bottlenose dolphins (Tursiops truncatus) in Bull Creek, South Carolina. Ph.D. dissertation, University of Rhode Island, Kingston, Rhode Island. 298 pp.