With an adult size of up to 33 feet long, basking sharks (Cetorhinus maximus) might look intimidating, but they're really gentle giants. These huge filter feeders open their mouths wide and swim along, feeding on plankton they extract from the water. They live in both the Atlantic and Pacific oceans, in subpolar and temperate regions. Preferring open water, they only move closer inland to breed.
Summer is breeding season for basking sharks. These creatures are usually solitary -- although groups and pairs are sometimes spotted -- but males and females of the species come together when it's time to mate. Not much is known about the mating habits of this species, but they use internal fertilization when mating, meaning the male releases his sperm inside the female, where it travels to meet and fertilize her eggs.
With a gestation period of 3 1/2 years, basking sharks have the longest gestation of any vertebrate. Females are ovoviviperous, which means that, although they lay eggs, these eggs hatch within their wombs and they give birth to live young. While developing in the womb, the young feed on unfertilized eggs. This explains why basking sharks have a row of small teeth in their mouths, which seem to serve no purpose for adults of the species.
Juvenile Basking Sharks
When female basking sharks give birth to their young, the juveniles swim off right away. There's no maternal involvement in their raising. However, since newborns are already 5 1/2 feet long, they're more than large enough to look after themselves. These are the largest of all shark pups, and they're already larger at birth than many fully grown sharks. Juvenile basking sharks have elongated snouts -- not unlike a short trunk -- which was possibly used in the womb to help them ingest the yolky soup of unfertilized eggs they used to sustain themselves.
It takes a long time for basking sharks to reach adulthood and their full potential length. On average, males are fully mature at between 12 and 16 years of age and reach a length of 13 to 16 feet. Females are usually between 25 and 29 feet when they reach full maturity -- although they can be larger -- but it's unclear at exactly what age they become full grown. Despite taking this long to reach their full sizes, it's thought they become sexually mature at between 2 and 4 years of age. They can live to be about 32 years old.