Marine Megafauna: An Introduction to Marine Science and Conservation is a great Coursera MOOC led by Dr. David W. Johnston from Duke University. One writing assignment from the 2014 session requested students to choose and research a species of marine megafauna. For each student, the final output was a brief, original species profile that was later peer-reviewed by other students in the class.
Below is a copy of the species profile I wrote about Harbor Seals, adorable animals sighted here in California and on other Pacific and Atlantic coasts.
1. Key / Interesting facts [up to 3 points; 1 point per fact]
Harbor seals are examples of mammalian marine megafauna that inhabit the western, eastern, and northern coasts of the North American continent. Harbor seals, although docile, are capable underwater carnivores. (1) A harbor seal can dive for ~30 minutes, using oxygen reserves in its blood and muscles while underwater. (2) Furthermore, a harbor seal’s whiskers can sense pressure waves from prey and objects underwater, facilitating hunting and navigation. (3) The large eyes of harbor seals have a high number of rods and even a tapetum lucidum, which help the organism see in deep, dark waters. Each eye is covered by a clear mucus while the seal is underwater. (4) Harbor seals can sleep underwater and even surface to breathe without waking up.
2. Scientific name [1 point], Taxonomic information [1 point], Common name [1 point], Related species [1 point]
The scientific name of the harbor seal is Phoca vitulina. This name is derived from the Greek words: phoca (seal), vitula (calf), and inas (like). Harbor seals are specifically categorized under Kingdom Animalia, Phylum Chordata, Class Mammalia, Order Carnivora, Family Phocidae, Genus Phoca, and Species Phoca vitulina (Linnaeus, 1758). The harbor seal is but one of the 19 extant species under the family Phocidae. The phocids are referred often to as true seals, earless seals, or crawling seals. Common name of the species include “harbor seal” and “common seal.” However, unique common names exist for each of the five subspecies: Eastern Atlantic Harbor seal [Phoca vitulina vitulina (Linnaeus, 1758)], Western Atlantic Harbor seal [Phoca vitulina concolor (De Kay, 1842)], Ungava seal / Hudson Bay Harbor seal [Phoca vitulina mellonae (Doutt, 1942)], Eastern Pacific Harbor seal [Phoca vitulina richardii (Gray, 1864)], and Western Pacific Harbour seal / Kuril seal [Phoca vitulina stejnegeri (J. A. Allen, 1902)]. Out of the 19 phocid species, harbor seals are most closely related to the spotted seal, Phoca largha, with which it shares the same genus classification. The other true seals are found under one of 12 other genera.
3. Size (could include a number of possibilities, such as average adult mass, average adult length, maximum mass, or other size-related information) [1 point], Coloration [1 point], Range (describing where in the world you can find this species, for example, “the western coast of South America”) [1 point], Habitat (describing the general environment where you can find this species, for example, “coral reefs” or “silty estuaries”) [1 point], Population size estimate (either worldwide or within a specified area) [1 point]
In length, harbor seals are roughly as tall as humans. Adult male harbor seals are 1.5-2.1 meters in length and weigh 85-150 kilograms. Adult female harbor seals are 1.4-1.7 meters in length and weigh 65-115 kilograms. Newborns are usually less than a meter in length and weigh only about 8-12 kilograms. Harbor seals may have a white coat with dark spots or, alternatively, a dark brownish-black coat with white rings. Harbor seals also molt annually, sometime between May and October. The coat with old hair may be brownish in color, whereas the new coat may have a bluish color. Harbors seals in the San Francisco Bay may be fully or partially reddish in color, due to iron and selenium accumulation in the water or phenotypic changes in their hair follicles. A harbor seal can live in both freshwater and saltwater, but will usually remain within a fixed area of ~5 square miles for the entirety of its life. Harbor seals can be found in Arctic, sub-Arctic, and temperate zones of the Pacific and Atlantic Oceans. Harbor seals live in places such as northern Japan, Bristol Bay, Baja California, France, Norway, Greenland, Iceland, Canada, New Jersey and even Quebec, Canada Harbor seals inhabit shallow waters, sandbars, river mouths, island beaches, mudflats, bays, estuaries, reefs, and other coastal areas. Some harbor seals can even be found further inland near freshwater lakes. Worldwide, there are approximately 500,000 harbor seals.
4. [Up to 3 points maximum; with 1 point for any of the following elements]: Lifespan [1 point], Reproduction [1 point], Gestation time [1 point], Number of offspring [1 point], Age of sexual maturity [1 point]
Harbor seals usually live 25-30 years, though some sources state that the lifespan of harbor seals can extend to 40 years. In captivity, the oldest male and female harbor seals lived to be 32 and 26, respectively. Breeding harbor seal males each defend a group of females and perform courtship actions such as rolling, bubble-blowing, chasing, playful biting, mouthing partners’ necks, and embracing. Copulation occurs in the water. The expected gestation period is about 10 months. Adult female harbor seals usually mate and give birth to one new pup annually. Pups are usually born between February and September, and mostly in June. Male harbor seals reach sexual maturity upon weighing about 75 kilograms, which corresponds to 3-7 years of age. Female harbor seals reach sexual maturity upon weighing about 50 kilograms, which corresponds to 2-5 years of age.
5. Details on how the species forages [up to 2 points; 1 point per behavior detail], Two examples of food sources [up to 2 points; 1 point per food source]
Harbor seals are opportunistic feeders. Harbor seals may dive down to 650 feet from the surface, but usually dive to shallower depths where their food is concentrated. Harbor seals can detect prey by using their whiskers to sense changes in pressure conditions and vibrations in the water. Each day, a wild harbor seal may consume about 6-8% of its body weight in food. Juvenile harbor seals usually feed on shrimp. Adult harbor seals eat sole, flounder, sculpin, hake, cod, herring, octopus, squid, crustaceans, eels, and mollusks.
6. EXTRA CREDIT: Special characteristics – Description of a special characteristic of the species [1 point]
In addition to harbor seals’ impressive visual and tactile senses underwater (attributed to specially adapted eyes and whiskers), harbor seals also have a great sense of hearing. The seals’ hearing sense helps them avoid predators. Underwater, arbor seals can respond to sounds from 1 to 180 kHz underwater (especially those at 32 kHz). Human hearing ranges extend only from 0.02 to 20 kHz (in air). Out of the water, harbor seals respond to sounds from 1 to 22.5 kHz, with a peak sensitivity at 12 kHz.
7. Conservation status [1 point], Threat(s) faced by species [1 point], Management action being undertaken or proposed [1 point]
Collectively, harbor seals are considered a species of Least Concern (IUCN). However, certain subspecies have been considered as Threatened due to several reasons. Harbor seals are vulnerable to lethal threats other than natural predators such as killer whales, sharks, Steller sea lions, bears, coyotes, and eagles. These threats include Phocid Distemper virus, entanglement in fishing nets, water pollution, habitat loss (through land reclamation), and exploitation. Historically, harbor seals have been hunted for their fur. Harbor seals were also hunted because they were considered competition for commercial fisheries. Fortunately, the 1972 US Marine Mammal Protection Act made it illegal to kill any marine mammal in and around the United States; As a result, harbor seal populations have been recovering. (In other countries where it still remains legal to shoot harbor seals as a means of protecting fisheries and fish farms, certain periods of the year are made “closed seasons” for hunting.)
8. Biography of species expert [1 point]
Harbor Seal Expert: Don Bowen, PhD
Dr. Bowen’s research interests are on the life history patterns, foraging ecology, diet, population energetics, and population dynamics of pinnipeds. Dr. Bowen currently works with the Bedford Institute of Oceanography in order to conduct studies focused on the foregoing research interests. Dr. Bowen has published six papers with regard to harbor seals in particular, and many other papers about pinnipeds related to harbor seals.
The website of his pinniped laboratory can be found here: http://bowenlab.biology.dal.ca/index2.html
An old CV of his can be found here: http://www.msc.org/track-a-fishery/fisheries-in-the-program/certified/pacific/new-zealand-hoki/second_reassessment-downloads-1/Don_Bowen_CV_Sept_2010.pdf
An updated profile can be found here: http://www.meds-sdmm.dfo-mpo.gc.ca/sdb-bds/profile-profil.do?id=443&lang=eng
9. Three references to further readings, including for each reference the author’s name, the year published, the title of the reading, and a link to the reading [up to 3 points; 1 point per reference]
Wilson, S.C., Corpe, H.M., Scullion, R. and Singleton, T. (2007). Harbour seal pupping patterns, pup dispersal and stranding rates in Dundrum Bay, north-east Ireland. http://www.sealresearch.org/attachments/article/103/Minerstown%20and%20BK%20ms%202007%20.pdf
Brown, R. F., & Mate, B. R. (1983). Abundance, movements, and feeding habits of harbor seals, Phoca vitulina, at Netarts and Tillamook Bays, Oregon. http://ir.library.oregonstate.edu/xmlui/bitstream/handle/1957/21913/AbundanceMovementsFeedingHabits.pdf?sequence=1
Pitcher, K. W., & Calkins, D. G. (1979). Biology of the harbor seal, Phoca vitulina richardsi, in the Gulf of Alaska. Outer Continental Shelf Environmental Assessment Program, US Department of Interior, Bureau of Land Management. http://www.data.boem.gov/PI/PDFImages/ESPIS/0/313.pdf
Quick links to the sources read to produce this report: