Blog Posts

How many Charleston individuals? 

Based on our mark-recapture estimates from 2004-06, between 300-400 for CES stock (Charleston Estuarine Stock).

What is their range? 

Depends on sex and area affiliation.  Most females tend to have smaller ranges encompassing a couple rivers and the smaller associated creeks.  Some males can be seen throughout most of stock, from Charleston Harbor to North Edisto.  

Which river(s) are most popular, why?

Stono appears to be the most popular, followed by the Folly and North Edisto. The Ashley, Cooper, and Wando Rivers are popular depending on the time of year. The popular areas are probably due to amount or prey, fewer boats, and proximity to coast.

Male/female ratio? 

According to biopsies, the estimate is around 186 males to 107 females (biased since biopsies always favor males).  According to sightings and research, the estimate is 217 males to 411 females (biased since females are easier to detect (presence of calf) vs males).

Approximately how many births per year? 

Good consistent records from 2005-2009 indicate an average of 35 births/year.

Oldest individuals? 

Animal FB864 was recently spotted in the harbor and is recorded as 36 yrs old. His age was confirmed because he was captured and tagged in the early 2000’s. A tooth was pulled to age him. Oldest known CES dolphins (assuming he is still alive, last seen in 2009) is FB894 who would be 42.  Oldest female (assuming she is still alive, last seen in 2009) is FB805 who would be 41.

Alliances? Male/male? Females/females and calves? 

Yes, male pairs are prevalent.  We’ve noted dozens of them here.  Possibly had a three male “alliance” but not seen together with same frequency as pairs.  Likely a pair and a wanna-be male.  Females tend to stick together especially with calves. Females are known to “babysit” other female calves.

How do they use the harbor-spatially and behaviorally? 

Can be seen throughout the harbor with hot spot behind Fort Sumter.

Main source of food in Charleston Harbor? 

Based on Pate and McFee from 2012, Star Drum was the most abundant prey species for SC dolphins, with Brief Squid the most frequently observed prey item (all from stranded dolphins throughout the state).

What threats do the bottlenose dolphins in the Charleston Harbor face?

There are documented reports of fishery-related mortality and serious injury to the population related to the blue crab pot fishery. During a review of bottlenose dolphin strandings in South Carolina from 1992 to 2003, it was found that 24% of the 42 entanglements of dolphins were associated with crab pots and 19% of entanglements deemed probable to be from interactions with crab pots. Between 2003 and 2007, 12 bottlenose dolphins displayed evidence of being entangled in crab pots. In addition, standings in South Carolina have been greater near urban areas and agricultural input, suggesting negative health effects to bottlenose dolphins in these areas. Reduced immune response has been reported due to an increase in concentrations of several containments, such as mercury, copper, manganese, lead, uranium, and zinc.
Some of the highest concentrations of polychlorinated biphenyls (PCBs) and DDT reported for cetaceans have been founded in the blubber of bottlenose dolphins from the Charleston area.
https://www.nefsc.noaa.gov/publications/tm/tm219/441_BODO_CES.pdf

Do they interact with crab pots a lot? 

Based on strandings and entanglements, they appear to. Dolphins have been seen tugging on crab pot lines.

What makes them unique? 

Strand feeding is probably the most unique feature of CES dolphins, which is seen mostly in SRE (Stono River Estuary). Strand feeding is a unique feeding behavior where dolphins corral fish near sandy shores then create a large wave to push the fish and themselves onto shore to eat the fish before returning to the water. Strand feeding has only been documented in South Carolina and Georgia in the USA. It occurs in several rivers around Charleston. Not all dolphins strand feed and those that do use strand feeding as a secondary feeding behavior. It’s a learned behavior from mom. Dolphins only strand on their right side and typically in small groups (1-3 animals).

Here are some general questions and their answers to help the outreach learn more about Bottlenose Dolphins.

How long is their gestation period?

12 months. The calf will nurse for more than a year and then typically stays with their mother for three to six years.

How fast can they swim?

They can reach speeds of over 30km/hour and dive as deep as 250m.

How much do they weigh? How long are they?

An average of 660 pounds. They can reach a length of just over 13 feet.

What are their different fins used for?

The fluke (tail fin) is used to propel through the water and the pectoral fins (on each side) provide the direction control and the dorsal fin (on top) provides stability.

Do dolphins travel in groups?

Yes. They travel in groups, called ‘pods’. Although, adult males mostly travel alone or with smaller groups and then join the pod for a short time.

What is echolocation?

Bottlenose dolphins produce high-pitched clicks to navigate and find food. When the clicking sound hits an object, it bounces back to the dolphin as echoes, which allows the dolphins to determine the location, size, shape of the object.

What do bottlenose dolphins eat?

They are carnivores so they feed on mostly fish, but can also eat shrimp, crab, or squid. Locally, they eat Star Drum, Menhaden and Mullet.

How long can a dolphin hold its breath for?

10-15 minutes. Dolphins breathe through their blowhole; a muscular flap covers their blowhole while they are underwater.

How do dolphins sleep?

They float just beneath the surface of the water and small movements of their tail flukes propel them to the surface so they can take breaths while sleeping.

Do dolphins mate for life?

Dolphins do not mate for life. Dolphins mate for reasons other than reproductions, similar to humans and when food is scarce, they may not mate at all to focus on survival.

How long do bottlenose dolphins live?

Typically between 30 and 50 years. Dolphins in captivity live much shorter lives than wild dolphins.

What protections are in place to protect them?

Dolphins face various threats around the world, including direct kills, entanglements in fishing gear, live captures for captivity, habitat alteration, boat collisions, and the negative effects of pollution. Fortunately, bottlenose dolphins are protected in U.S. waters under the Marine Mammal Protection Act, which makes it illegal to “take” marine mammals without a permit. A “take” includes harassment, feeding, hunting, capturing, collection, or killing any marine mammal.