Harbor Seal: Phoca vitulina

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Haul-Out Sites
Phoca vitulina are gregarious- meeting in the same location every season to breed.  They gather on reefs, gravel beached sand bars, and an array of otherHarbor seals at a moss covered haul out site. Photo credit: Dave Withrow coastal habitats. Known as “haul-out” sites, these gatherings all have one common theme- they are all land based (Seal Conservation Society, 2011). Haul-out sites are inhabited by scattered small groups of seals, instead of a single collective entity (Boness et al., 2006). These areas provide numerous benefits for the seals including protection from predators and rough environmental conditions; they also put P. vitulina in close proximity to food sources. P. vitulina cling to these safe havens during reproductive seasons deriving their name: the harbor seal (Seal Conservation Society, 2011).

                                                                                                                    Harbor seals at a moss covered haul out site. Photo credit: Dave Withrow


Premating Season
During the premating season- before females enter estrus (heat) and prior to pupping season- males decrease their foraging efforts, their primary offshore activity, while increasing the time spent competing for females on the shore (Boness et al., 2006). This coincides with rising evidence that Phoca vitulina have a lek based reproductive system- a system in which females choose the males while males, attempt to, impress possible mates (Boness et al., 2006). Some premating tactics include visual displays, vocalizations (under- and above- water), and even fighting against other males in order to impress females (Boness et al., 2006).


Mating Season
During the mating season- when females are in estrus (following pupping season) - the tactics change. Males increase their underwater vocalizations, which are now believed to be a part of their mating behavior (SeaWorld, 2005). This idea arises from the fact that male harbor seals vocalize more often when females are likely to be present. Males also chase, bite the neck and flipper of (a playful activity), and embrace the females more (SeaWorld, 2005). Even though they compete for females on land, they mate nearby in the shallow waters (in order to reduce possible predation that arises in deeper waters) (Boness et al., 2006). The male is not limited to one female per season though, as males will mate with several females per year. Multiple births are extremely rare (never more than two), limiting the mothers to one pup annually (SeaWorld, 2005). This could be one of the factors into why some populations of harbor seals are declining, such as the colony surrounding Britain (Seal Conservation Society, 2011).

Pup Development
Giving birth at the haul-out site, the pups come into the world with most of the abilities that an adult is capable of. Since Phoca vitulina belongs to class Photo Credit: Robin Riggs, © Aquarium of the PacificMammalia, the young will acquire necessary nutrients from the mother’s milk. Her milk is primarily fat- giving rise to the immense weight gain pups undergo before weaning (occurring about six weeks after birth) (SeaWorld, 2005). They nurse both on land and in water, requiring a constant source of nourishment every three to four hours.  The pups are very social animals when they are young, but as the pup ages they become more and more isolated (SeaWorld, 2005).


Photo Credit: Robin Riggs, © Aquarium of the Pacific

Photo Credit: Robin Riggs, © Aquarium of the Pacific                    Mother Shelby and her newborn pup. Photo credit: Hugh Ryono, © Aquarium of the PacificPhoto Credit: Robin Riggs, © Aquarium of the Pacific                                              Photo Credit: Hugh Ryono, © Aquarium of the Pacific

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