The 10,000 Island Dolphin Survey Program is an ongoing study of the wild, bottlenose dolphin population in the waters on the north end of Marco Island, Florida. Conceived in February 2006 the program concentrates its attention on the Marco River and surrounding inland waterways including the 10,000 Islands and Rookery Bay Reserve. The dolphins here do not migrate, giving the team year-round access to study the social patterns, movement, range and genealogy of these mammals. They are considered “coastal” bottlenose dolphins.
The program is funded by the public by combining the gathering of dolphin information with an in-depth ecotour that educates guests about our cetaceans, other marine life, bird life and the importance of the pristine estuary found in this region, mainly the mangrove forest. In 2019 more than 500 tours were conducted, educating more than 10,000 guests on our vessel named Dolphin Explorer.
Dolphin identification is made possible by examination of markings on each dolphin dorsal fin which occur when 1 dolphin rakes its teeth across another’s fin, causing permanent nicks, notches and marks to appear. There is no tagging or branding of these dorsal fins.
Here is the 2019 report:
Population: The overall bottlenose dolphin population has increased dramatically in recent years. In 2017, shortly after Hurricane Irma made landfall in the Marco Island area, 4 calves were born, and all have survived. In 2018 10 new calves were recorded and 9 have survived. In 2019 9 new calves were recorded and 7 have survived.
These 20 calves represent nearly 20% of the everyday population in our catalog. In previous years of the study an average of 4-5 calves were recorded each year. 2 adult males, that appeared to be aging, have not been seen in over a year. 1 mom and calf disappeared after Hurricane Irma passed through and 2 sub-adults have not been seen in over a year. Several first-time moms have been recorded, so a third generation, grandmothers, are now in our files.
Adult Males: 3 dominant male pair bonds command the area. A Male Pair Bond occurs when 2 mature males pair with one another. This results in more successful competition for mating rites with females. These bonds can last a lifetime. The dominant male pair bonds are Hatchet and Capri, Captain Jack and Trixie, Bangle and Finch. More than a dozen other males call the area home and are more independent and solo of the pairs. Simon has matured and has been moved from sub-adult to adult male status. Males Flag and Marco have not been seen in 2019 and are presumed deceased. The solo males tend to spend a lot of time on their own but will fish and socialize with other dolphins on occasion.
Adult Females: With the exception of 2, all of our other females have produced a calf since 2016. Several females have matured to produce their first offspring in 2018 and 2019. Those moms are Jing Jing, Nadine, Kaya, Destiny and Orange. With the exception of Destiny, the mothers of the other first-time moms are still in the area, giving us a third generation, grandmothers. They are Sydney (mom of Jing Jing),
Tess (Nadine), Halfway (Kaya) and Sparky (Orange). Sydney, Halfway and Sparky have all produced new calves in the last 3 years. Several mothers have had calves in this period that did not survive. They will be addressed in the “Predation” section of this report.
Sub-adults: These are the younger dolphins that are old enough and educated enough by their mothers to be out on their own. This will occur in our area at about 3 to 4 years of age, with some young staying by mom’s side a bit longer. Maturity occurs at about 8 to 12 years of age. This population sector comprises nearly 25% of the total number of dolphins cataloged in our survey area. In the Fall of 2019, 6 young of year left their mother’s sides at about 34-36 months old and are experiencing their first 6 months on their own. They are Parton, 360, Tigertail, Ollie, Wyatt and Popcorn. At least 4 of the mothers of these 6 sub-adults produced a new calf, just months after the young left mom’s side. Although a new calf was not seen by the adult females’ side it is possible that the other 2 mothers of these 6 young did give birth. That will be addressed in the “Predation” section.
Calves: These are the young of year, still by the mother’s side. 7 new calves were recorded in 2016, 5 in 2017, 10 in 2018 and 9 in 2019 in our survey area, a total of 31 calves still under the age of 4 with at least 26 surviving. All of the 3 year old ( born in 2016 ) have left their respective mothers’ sides.
Predation: Not all of our calves survive. There are sharks in the area and attacks by Bull sharks and Hammerheads have surely cost some young their lives. There are success stories of young being attacked and surviving. Now over 6 years old, Skipper was bitten in the torso at 8 months old and will bear a lifetime scar but is doing well. The daughter of one of our most reproductive females, it is anticipated that Skipper may be a very productive female when she reaches maturity. Now over 3 years old, Parton was bitten by a Bull shark on the back and around the right eye when young but is now on its own and doing well. The eyesight does not seem to be affected.
Predation 2: Infanticide: This is the occurrence of an adult male eliminating a young calf from the population by drowning it. A tour operator on the south end of Marco Island recently witnessed a mother trying to shield its calf along the mangrove trees, protecting it from a large male. The male was too strong, and the last sighting of the calf was in the mouth of the male. The calf was not seen again. In our survey area, 2 of our newborn disappeared shortly after birth. The adult females were immediately stalked by our male pair bonds and it could be assumed that these males eliminated the young in order to mate with the adult females. In addition, even though no new calf was seen, another adult female that was expected to give birth in the Fall of 2019 was never seen with a calf but was stalked by a male pair bond in the same fashion that the females that lost their calves were stalked.
One last note about the lack of survival of young… Karenia Brevis, a naturally occurring phenomenon known as Red Tide is a harmful, toxic algal bloom that killed hundreds of dolphins, manatees and sea turtles from northern Collier County all the way to the Tampa Bay region. Marco Island only suffered minor bouts of this bloom, but it could, in theory, enter the bloodstream of the adult females who have breathed the air during the bloom or eaten fish contaminated with the toxin. In theory, if the dolphin mother’s milk was tainted, and passed on to its young during nursing, the immune system of the new calves might not be strong enough to combat the toxins, possibly causing an end of life for the calf.
Birthing “Season”: Although adult males and females will mate all year long it is typical to see new calves in our survey area in late Summer and Fall. There are very few exceptions to this event. Since the gestation period of an adult female is about 12 months, the primary time of year for conception is also late Summer and Fall. One of our females, Sintas, gave birth in September of 2018 and the calf did not survive. She gave birth again in November of 2019, so she conceived almost immediately after the 2018 calf died.
Association Patterns: For “coastal” bottlenose dolphins in our survey area there is no pod structure, no consistent grouping of dolphins for the purpose of protection and feeding. The eco-system in our area is very shallow and our population will typically feed independent of each other. The female sub-adults are consistently seen in the company of other sub-adults or adult females and their calves. The males not in a pair bond relationship seem to be independent of one another as well, with occasional gathering of just a few for feeding and traveling.
Conclusion: Our survey area population has increased by nearly 20% in recent years. The survival rate of our calves is in the 80% range. The primary predators for the young are bull sharks, hammerhead sharks and the adult males ( infanticide ). The natural occurrences of tropical storms, hurricanes and the algal bloom known as Red Tide have had little effect on the overall population count in our survey area.
Please contact dolphin-study.com, firstname.lastname@example.org or contact Florida Master Naturalist Bob McConville at 239-642-6899 for any inquiries into our program or if you desire additional information about our study.
Thank you for your interest in reading this report. We are anxious to share any of our findings with any organization, team, media or professionals that may want to report and compare their findings in an effort to learn more about these special mammals, bottlenose dolphins.
Prepared by Florida Master Naturalist Bob McConville, naturalist on board the dolphin study vessel Dolphin Explorer, Owner / partner Dolphin Explorer LLC