lOGO Undergraduate Research Experience in Ocean and Marine Science
Dolphin Presence/Absence Probabilities on the Virginia and North Carolina Coasts as Correlated with Sea Surface Temperature and Chlorophyll-A Levels

The Tursiops truncatus or bottlenose dolphins can be migratory or resident with some animals passing through and others remaining for the duration of the summer. Along the Mid-Atlantic coast there are four different stocks that may be observed: the residential populations, the off-shore populations, the on-shore populations and the north migratory stock. The Virginia population is estimated at several hundred areas. In 1987 and 1988 there was an estimated decrease of 50% in the population because the Tursiops were subjected to biomagnifications of toxin. While conducting research on the Tursiops, special attention was given to the Elizabeth River where the species socially interacted in this unique habitat. The Elizabeth River is a shallow low tidal area with a developed shoreline for the majority of the river, sand beaches and salt marshes. Sediments from ship repairs since colonial era have settled in the southern branch of the river and tend to linger in the habitat.

Because the species are at the top of the trophic level and are migratory we hypothesize that there is a strong correlation between the dolphin behavior and sea surface temperature. The distribution of migratory Tursiops truncatus along Mid-Atlantic Bight as correlated to sea surface temperature and chlorophyll alpha was determined using remotely sensed data from using Advanced Very High Resolution Radiometer and Sea viewing Wide Field-of-view Sensor. It is suggested that the presence of the species can be correlated to the sea surface temperature and chlorophyll alpha levels as Tursiops migratory location may be dependent on these variables. Sightings of the Tursiops can be compared with the remotely sensed data to determine a correlation between the sea surface temperature, chlorophyll alpha and the movement of the species.

With the sea surface temperatures, 17° Celsius was the critical temperature in determining the probability of sighting dolphins. Using the T-test, a significant difference was found between the chance of a dolphin sighting above and below 17° Celsius. The p value needed to show a significant difference has to be less than 0.05. The p value yielded from the T-test for sea surface temperatures was 0.032. The number of sightings above 17° amounted to 268 and the amount seen below 17° was 2. For the actual number of animals, the archival data has documented 2265 dolphins seen above 17° and 2 dolphins were seen below 17°. The chlorophyll alpha data shows no pattern of correlation. The p value from the T-test for the chlorophyll alpha was 0.83, showing no significance difference between the data. Sea surface temperature is related to the migrations of prey which in turn influence the dolphins to follow them. Another relation of sea surface temperatures to the dolphins is to their tolerance of the heat and the cold. A major reason why chlorophyll alpha is not a good indicator is because of a delay from the change of color. With the chlorophyll alpha, it takes time to attract the prey of dolphins before the dolphins themselves will show up. It is clear that sea surface temperatures is a better indicator than chlorophyll alpha in determining the level of presence or the level of absence of dolphins.