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					Movement patterns of Atlantic spotted
dolphins (Stenella frontalis) and bottlenose
dolphins (Tursiops truncatus) in relation to
oceanographic fronts




      R.B. Griffin,* C. Hu+, and N.J. Griffin*
             *Mote Marine Laboratory
             + University of South Florida
                                        Study Area
               28


              27.8


              27.6


              27.4
Latitude oN




              27.2


               27


              26.8


              26.6

                     83.4   83.2   83      82.8     82.6   82.4   82.2   82
                                         Longitude oW
                     Atlantic spotted dolphin
                     Stenella frontalis




Bottlenose dolphin
Tursiops truncatus
                                  Methods
One-day surveys approximately 140 km in length
                 27.5


                 27.4
   Latitude oN




                 27.3


                 27.2


                 27.1


                 27.0
                    83.1   83.0   82.9   82.8     82.7   82.6   82.5   82.4
                                         Longitude oW
          Data Collected
Location and abundance
Digital photography for photo-identification
Initial behavioral state
Group follows
               Group Follows
Periodic locations of animals when in vicinity of vessel
Continuous documentation of behavioral events
Sequential data—3 min intervals
Continuous underway surface oceanography
Some radio-tagging data
S. frontalis dive data
                       Sea Surface Temperature 21 Feb 2000

               28




              27.5
Latitude oN




               27




              26.5



                84.5       84     83.5        83   82.5      82
                                   Longitude oW
                         Data Histogram for 19-21 March 2000
# of pixels                      and 11-15 June 2002


                                                        19-21 March 2000
              1000
                                                        11-15 June 2002




               100



               10
                     0             50                 100                 150
                                        Image value
                       Ocean Color (Chl) 25 Jan 2002

               28



              27.5
Latitude oN




               27



              26.5


                84.5   84      83.5       83    82.5   82
                               Longitude oW
                                               Underway SST: 12 April 2004
                                               Sighting 6—S. frontalis
Temperature oC



                 19.4
                 19.2
                  19
                 18.8
                        -5      -4        -3      -2    -1        0          1     2    3    4          5
                                                         km from sighting
Temperature oC




                 19.4
                 19.2
                  19
                 18.8
                         10.8        11          11.2   11.4          11.6       11.8   12       12.2
                                                             Decimal Hours
Surface manifestation of thermal front
                         Follow track with SST: 12 April 2004
              27.25
                         Sighting 6—S. frontalis
Latitude oN




               27.2




              27.15
                  82.9                   82.85                  82.8
                                      Longitude oW
                       Follow track with Chl: 12 April 2004
              27.3
                       Sighting 6—S. frontalis

Latitude oN




              27.2




              27.1
                  83                     82.9                 82.8
                                     Longitude oW
              27.22     Follow track with Chl: 12 April 2004
                        Sighting 6—S. frontalis

              27.21
Latitude oN




               27.2           A


              27.19
                            dLat




              27.18
                            C      dLon                B
                 82.9      82.89   82.88       82.87       82.86   82.85
                                     Longitude oW
Km/deg Lon vary as a function of cos(Lat)
1o Lat = 111.12 km
1o Lon = 99.01 km at 27o Lat

tan angle CBA=(AC km/BC km)
arctan CBA then converted to 360o reference

       A
     dLat




     C        dLon            B
Circular statistics using Oriana (Kovach Computing Services)
    Rayleigh test
    Watson-Williams F-test
    Fronts and travel directions treated as axial data
 Tested hypothesis of uniform distribution
 of travel vectors, frontal vectors
 Tested equality of travel vectors, frontal vectors.
 Tested differences in travel vectors between:
 1) Possible feeding behavior
 2) Season
       S. frontalis follows
Ocean Color                   SST
       T. truncatus follows
Ocean Color                   SST
         S. frontalis follows
November-May             June-October
         T. truncatus follows
November-May            June-October
Griffin and Griffin 2003, 2004

       S. frontalis in highest density between 20-30 m isobaths in
       winter months, lowest densities in summer, while
       T. truncatus did not differ by season.



No seasonal variation in T. truncatus movement patterns,
consistent with our earlier work.
During winter months in the eastern Gulf of Mexico, S. frontalis
travels primarily in a north/south direction, in same trend as
frontal location. During summer, animals travel primarily in
east/west direction.

Hypothesis: During winter, animals are foraging along fronts,
which are better defined during this time of year. In summer,
lower abundance and general east/west trend of movements
suggest dolphins may be at higher densities farther from coast,
with some animals making short-term foraging runs into
shallower water.
More work on frontal definition is needed.



Continued group follows and photo-identification
are planned to understand movement patterns and behavior
of continental shelf dolphins in the eastern Gulf of Mexico.
Harbor Branch Oceanographic Institution “Protect Wild Dolphins” Program
                           Private donors
              Mote Marine Laboratory student interns

				
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posted:5/24/2013
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