Baby boom in The Bottlenose Dolphin Capital of the World
By Lloyd Edwards

1. News

Female Bottlenose dolphins reach sexual maturity three years before males at around ten years. Calves are born at an average of 1 metre and nearly 14kg, after a gestation period of a year. Although they can be born throughout the year, the peak is in spring and summer.

During our 23 years of running cruises we have seen an ever increasing number of calves and also an increase in the school size. One just can’t help wonder if the depletion of our shark populations by the demersal shark long liners has been the cause. Less sharks, less predation, more dolphins.

A newborn calf sticks close to its mother while she monitors the breathing and gets it into the knack of keeping up with the school. Have a look at the fetal folds on the new-born calf in the photo. The concentric rings will fade with time. Suckling alone sustains the calf for six months, after which time this will be supplemented with solid food. Suckling can last for three years, although nine years has also been recorded, the ultimate big babies! Mothers and calves usually feed closer to the shore and eat the similar sized prey which indicates substantial parental guidance.

The calves are also susceptible to agricultural (DDT) and industrial (PCB) pollutants that are washed down rivers. They increase from birth and in males keep on increasing. In females however they drop after nursing, which means they are passed onto the calf in her milk. It is thought that firstborns can “inherit” 80% of their mother’s pollutants. One group of scientists we had on the boat told us they had found DDT in penguin eggs on Bird Island that originated in Tzaneen, which is over a thousand km away and far inland from the coast. It is obviously carried into the sea by rivers.

We have never missed seeing dolphins on our morning cruises since their resumption after lockdown. Seeing as up to 30 000 dollies make use of Algoa Bay, this is not surprising!