Since February of 2006, the 10,000 Island Dolphin Survey Team has been monitoring the activity of the bottlenose dolphin population in the Marco River and surrounding areas on board the Dolphin Explorer. They track the social behavior, movement, activity, travel range and genealogy of these amazing cetaceans.
Just a few weeks ago a summary report was released and sent to agencies around the world in hopes that the data collected in this area can be shared and studied, providing a better understanding of these mammals. Here are some highlights from that report.
In 2019, the team comprised of Captain Michael Tateo, Captain Ed Farr, Naturalist Kent Morse and Naturalist Bob McConville, recorded more than 500 trips in the Marco River area, collecting data and transferring that info into their database for research purposes.
A base population of approximately 110 dolphins was noted and seen on a regular basis throughout the calendar year. These dolphins do not migrate away from this region; thus, the repeated sightings give a clearer and more accurate overview of their behavior, habits and travel range.
Since the Fall of 2017, 23 calves have been born with 19 surviving. This represents nearly 20% of the total dolphin population here. Two adult males that appeared to be aging have not been seen in the past year and one adult female and her calf have not been seen since Hurricane Irma passed over the area.
With the exception of two, all of our adult females have produced at least one new calf since 2016. 20% of these females are first–time mothers and all of their calves are surviving.
The population classified as sub-adults are those that have left their mother’s care, usually at 3-4 years old in this habitat, but not yet reached physical maturity—that happens about ages 8 through 12. These youngsters comprise about 25% of the local population. In the Fall of 2019, 6 claves left their moms’ sides and are now considered sub-adults. At least 4 of the adult females of these new sub-adults produced a new calf.
Not all of the young survive, however. Predation by Bull Sharks and Hammerhead Sharks is always a threat and there has been a loss of life. We do have at least 2 sub-adults that bear scars from shark attacks but have survived. Skipper is now over 6 years old and was attacked at 8 months old. Parton is now over 3 years old and was attacked about 2 years ago. Both are doing well on their own. Also, adult males will sometimes try to eliminate the young in their society. This will free the adult female of motherly responsibility and she would more open to mating. The taking of a young life by an adult male is called “Infanticide.”
Birthing season in the north Marco River tends to be in the Fall. Although males and females will mate all year long, the females tend to become pregnant in the Fall months. The pregnancy period is 12 months; thus, the birthing season is also in the Fall. With the exception of two, all of our calves have been born in August, September, October or November.
Our local bottlenose dolphin population does not have a “pod” structure as it might be experienced in other habitats; no consistent grouping of dolphins for protection and feeding purposes. Our dolphins tend to feed independently of one another, not working in large groups, as is common in other habitats.
In conclusion, our area population in the north Marco River and the surrounding area has increased by nearly 20% in recent years. The survival rate of the young is in the 80% range, with primary predators of these young being bull sharks and hammerhead sharks. The natural occurrences of tropical storms, hurricanes and algal blooms have had little effect on the overall population.
Results might be different in other area habitats, such as south Marco Island and south Naples but this report, because of the daily sighting information gathered by the team, indicates that all information is very accurate.
To read the full 2019 Annual Dolphin Report regarding the north Marco Island area, you can go to dolphin-study.com. The Dolphin Explorer program is proud to be a member of this community and looks forward to sharing more important data in the years to come.
Bob is a Naturalist on board the Dolphin Explorer, a dolphin study program and eco-tour. He is the author of two books and an award-winning columnist for Coastal Breeze News. Bob loves his wife very much!