Seals, marine mammals known for their sleek bodies, inhabit diverse aquatic environments across the globe. These agile creatures, belonging to the Pinniped suborder, exhibit a wide range of adaptations to their watery homes, from icy polar regions to temperate coastlines. Understanding how long seals live and the various factors that influence their longevity offers valuable insights into their biology and the health of marine ecosystems.
Seal Lifespan Across Species
The lifespan of seals varies considerably among different species, reflecting their unique evolutionary paths and ecological niches. Harp seals, recognized for their striking markings, typically live between 25 to 40 years. Ringed seals, the smallest and most widespread Arctic seal, generally live for 15 to 20 years.
Elephant seals, the largest pinnipeds, display a notable difference in longevity between sexes and species. Northern elephant seal males typically live up to 13-15 years, while females can reach 19-23 years. Southern elephant seals, found in the colder waters of the Southern Hemisphere, have an average wild lifespan of 21 years.
Fur seals, characterized by their visible external ear flaps, also show varied lifespans. Their average longevity ranges from 12 to 30 years across different species, with females often living longer than males. For instance, male northern fur seals can live up to 18 years, whereas females may reach 27 years. Harbor seals, commonly found in coastal waters, generally live for 20 to 25 years. Female harbor seals tend to outlive males, often reaching 30-35 years compared to males’ 20-25 years.
Factors Influencing Longevity
A seal’s lifespan is shaped by a complex interplay of environmental, biological, and human-related factors. Natural predators represent a threat, with killer whales (orcas), sharks, and polar bears being primary hunters of seals across various species. For example, orcas hunt seals using coordinated tactics, making escape difficult for their prey.
Disease and health conditions also impact survival rates, with infectious diseases being a leading cause of mortality for seals, accounting for over 60% of deaths across all age groups. Seals are susceptible to various viral and bacterial infections, and warmer ocean temperatures can facilitate the spread of these pathogens. Parasitic infestations can compromise a seal’s health and reduce its ability to thrive.
Human activities profoundly influence seal longevity. Fishing bycatch, where seals become accidentally entangled in fishing nets and drown, poses a significant threat. In some regions, such as the Falkland Islands, there has been an increase in fur seal bycatch, prompting the development of mitigation strategies like escape panels in fishing nets. Marine pollution, including plastic debris and toxic chemicals like PCBs and DDTs, leads to entanglement, ingestion, and immune system dysfunction in seals.
Climate change presents a growing challenge to seal populations and their lifespans. The reduction of sea ice, which many ice-dependent species like harp and ringed seals rely on for breeding, resting, and raising their pups, leads to habitat loss and increased pup mortality. Warmer ocean temperatures disrupt food availability, as seals depend on cool currents that bring abundant prey. An increase in the frequency and severity of extreme storms, driven by climate change, sweeps young pups away from their nursery sites, particularly for species that give birth on open shores.
Unlocking a Seal’s Age
Scientists employ several methods to determine the age of seals, providing data for conservation and management efforts. One of the most common and reliable techniques involves examining the growth layers found in their teeth, similar to how tree rings indicate a tree’s age. These layers, known as growth layer groups (GLGs), are deposited annually in the dentine and cementum of teeth.
Researchers typically use canine teeth for this analysis because they are large and exhibit clear growth layers. Incisors and post-canine teeth are also utilized, especially when aging living seals without causing harm. Each pair of light and dark bands observed in a sliced tooth section corresponds to approximately one year of growth, allowing scientists to determine a seal’s precise age.
Bone analysis offers another method to estimate age, particularly when teeth are unavailable or for corroborating tooth-based assessments. Long-term studies involving the tagging and recapture of individual seals contribute to understanding their lifespans. This approach provides data on survival rates and helps validate the accuracy of other age determination techniques, offering a picture of seal longevity in the wild.