Sarasota Dolphin Research Program Note Record Births in 2021

Posted By : The Animal Facts Editorial Team

Date: December 13, 2021 11:15 pm

Dolphin Mom-F167-Calf1676-on-2021-08-23: F167 was observed with her sixth calf on Aug. 23, 2021. Her previous calf, 1675, was born in 2017 and was last observed on July 9, 2021.

Photo Credit: Chicago Zoological Society’s SDRP/NMFS Permit #20455

The Chicago Zoological Society’s Sarasota Dolphin Research Program has experienced a record number of births among the resident dolphin population. This year 22 births have been documented to the long-term resident bottlenose dolphin.

Forty-four year old squarenotch gave birth to the most recently recorded calf on December 2nd 2021. “It’s great to see the continuing productivity of the Bay’s dolphins, and really interesting that it was one of our older females that put us over the top,” said Dr. Randy Wells, vice president of marine mammal conservation for the Chicago Zoological Society (CZS) and director of the Sarasota Dolphin Research Program (SDRP), which is based at Mote Marine Laboratory.

466 dolphins have been documented by Wells as part of his University of California, Santa Cruz Ph.D. dissertation “Structural Aspects of Dolphin Societies,” which he completed in 1986. 

The Sarasota dolphin population have been the subject of the world’s longest-running study of a wild dolphin population. By finding that identifiable dolphins could be studied over an extended period of time has allowed researchers to gain insights in to dolphin biology and physiology.

“It’s exciting to document new calves each year as one measure of the health of the Bay’s dolphin population and the health of the Bay itself,” Wells said. “But the long-term nature of our research allows us to drill deeper and consider the question of why we had a record number of births. It appears that the red tide that reached Sarasota Bay in 2018 may have played a role.”

The red tide entered Sarasota Bay in the summer of 2018 and lasted through the winter of 2018-19. SDRP have been conducting catch and release surveys on dolphin prey and these have provided evidence that dolphin prey is in abundance in the bay.

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Unfortunately the red tide has not brought all upsides for the dolphin population. 45% of all females which gave birth to a calf in 2021 had lost a dependent calf during or after the red tide. On average 31% of calves born in Sarasota bay do not survive for over 2 years.

Shark numbers also increased during 2019 and 2020 with more bites seen on dolphins.

Over half the number of stingrays were recorded during studies in this period.

“Adding these facts together allows us to make some tentative inferences,” Wells said. “We know that stingrays are a primary prey item for sharks. When a preferred prey is unavailable, they’ll look to alternatives. The loss of typical shark prey may have led to the increased interactions we documented between sharks and dolphins as alternative prey, which allows us to infer that increased shark predation accounts for at least some of the losses of dependent calves during that period. When we document decreased ray catches, we tend to see increased disappearances of young dolphin calves.”

The larger number of calves is likely brought about as dolphins typically raise their calves for four years. The increased loss meant more females were available to breed.

“The record number of births is a wonderful story in itself, but thanks to our long-term data, we’re able to develop hypotheses about some of the factors that may have led to this result, which should lead to a better understanding of what can happen to an animal population when an environmental anomaly occurs,” Wells said.

Learn more about Bottlenose Dolphins here – Bottlenose Dolphins Fact File | The Animal Facts

Learn more about the Chicago Zoological Society’s Sarasota Dolphin Research Program on their website – Chicago Zoological Society’s Sarasota Dolphin Research Program

Sarasota Dolphin Research Program staff observed F233’s second calf on July 11, 2021. Her previous calf was born in 2019 and disappeared that same year.

Photo Credit: Chicago Zoological Society’s SDRP/NMFS Permit #20455