Bottlenose dolphins are widely recognized marine mammals, known for their intelligence and social behaviors. This article explores their typical lifespan, the factors influencing their longevity, and how scientists determine their age.
Understanding Bottlenose Dolphin Lifespans
In the wild, bottlenose dolphins can live for at least 40 years, with some females reaching 60 years or longer. Median lifespans for wild populations range between 8.3 and 17.4 years, highlighting population differences. Females typically outlive males.
The oldest recorded bottlenose dolphin, Nicklo, was a female from Sarasota Bay sighted at 67 years old in 2017. In human care, some bottlenose dolphins have lived to 61 years, such as Nellie and Qarik. However, captive bottlenose dolphins generally have a shorter average lifespan, around 28 to 29 years.
Factors Affecting Longevity
Both natural and human-influenced factors impact a bottlenose dolphin’s lifespan. Natural factors include food availability, which directly affects their ability to thrive, and large predatory sharks like tiger, dusky, bull, and great white sharks. Diseases, often exacerbated by biotoxins, also reduce lifespan, as seen in mass mortality events linked to morbillivirus.
Human activities introduce substantial risks. Entanglement in fishing gear (gillnets, seines, trawls, recreational lines) is a leading cause of injury and death.
Pollution from toxins (polychlorinated biphenyls, mercury), chemical discharges, and oil spills can severely compromise immune systems, leading to disease and reproductive issues through biomagnification. Vessel strikes cause injuries and fatalities.
Habitat degradation, including noise pollution from shipping, disrupts crucial behaviors and displaces dolphins from vital areas, impacting their survival. Illegal feeding and harassment alter dolphin behavior, making them dependent on handouts and less wary, which can lead to injury.
Scientific Methods for Age Determination
Scientists primarily determine bottlenose dolphin age by analyzing growth layers in their teeth, similar to counting tree rings. A tooth is carefully removed, sectioned into thin slices, stained, and examined under a microscope.
These visible layers, called Growth Layer Groups (GLGs), generally represent one year of growth. While effective, this technique requires tooth extraction, an invasive procedure for live animals. Challenges can arise from tooth wear or accessory layers, which can complicate accurate counting, particularly in older individuals. Ongoing research explores less invasive methods, such as using epigenetic markers from DNA in small skin or blood samples, to estimate dolphin age.