Seals and sea lions were hunted extensively during the 1800s and early 1900s for their blubber, fur, and meat. They continue to be imperiled by human encroachment of haul-out beaches, entanglement in marine debris and fishing nets, incidental catches, disease, and lack of food due to competition from humans for prey species.
Imperiled Seal and Sea Lion Populations
As of February 2006 there were four U.S. species and two foreign species of seals and sea lions listed under the ESA as shown in Table 5.1. The species are Caribbean monk seal, Guadalupe fur seal, Hawaiian monk seal, Mediterranean monk seal, Saimaa seal, and Steller sea lion. However, the Caribbean monk seal has not been sighted since 1952 and is presumed by the NMFS to be extinct.
GUADALUPE FUR SEALS
The Guadalupe fur seal breeds along the eastern coast of Isla de Guadalupe, Mexico. The island is approximately 400 miles west of Baja California. Although populations once included as many as 20,000 to 100,000 individuals, decline and endangerment resulted from extensive fur hunting in the 1700s and 1800s. The species was believed extinct in the early twentieth century, but a small population was discovered in 1954. NMFS scientists believe that the population is now on the increase.
HAWAIIAN MONK SEALS
Hawaiian monk seals are the only pinnipeds found on Hawaii and are endemic to those islands—that is, they occur nowhere else on Earth. Hunting was the primary cause of population decline. Hawaiian monk seals are also extremely sensitive to human activity and disturbance and now breed exclusively on the remote northwestern Hawaiian Islands, which are not inhabited by humans. Most females give birth to a single pup every two years, a reproductive rate lower than other pinniped species. The seals also fall prey to shark attacks and mobbing, violent mating acts perpetuated by adult male seals on females and pups of both sexes. Mobbing can result in fatal wounds or drowning. Scientists monitoring seal populations have relocated males guilty of repeated mobbing. The National Marine Fisheries Service Web site (http://www.nmfs.noaa.gov/) estimates the species population at around 1,400 animals.
MEDITERRANEAN MONK SEALS
Mediterranean monk seals inhabit remote areas around the Mediterranean Sea and northwest African coast. Most are found off the coasts of Mauritania/Western Sahara, Greece, and Turkey. According to the Seal Conservation Society there are only about 300 of the seals believed to be in existence. Mediterranean monk seals are very sensitive to disturbance. As humans have encroached on beaches and coastal areas, the seals have retreated to isolated caves.
In 1997 there was a massive die-off in a colony of the seals near Mauritania. The exact cause is not known; however, a virus or "red tide" event is generally blamed. This was a severe blow to the seal population. The animals are also purposely killed by fishermen, who consider them a nuisance and competition for limited fish stocks. Scientists fear that Mediterranean monk seals could become extinct with a few decades.
SAIMAA SEALS
Saimaa seals are found only in the cold waters of the Saimaa Lake system in eastern Finland. Their numbers were decimated by hunting over the centuries to the point of extinction. However, protection measures and fishing restrictions allowed some measure of recovery. In 2005 the World Wildlife Fund estimated that there were approximately 250 Saimaa seals remaining, making them one of the most endangered species in the world. Although the number of seals has been slowly increasing, they are still imperiled by entanglement in fishing nets when they leave protected areas of the lake.
STELLER SEA LIONS
Steller sea lions are large animals, with males reaching a length of about eleven feet and weight of 2,500 pounds. Females are significantly smaller. Steller sea lions are found in Pacific waters from Japan to central California, but most populations breed near Alaska and the Aleutian Islands. The breeding season is from May through July. The species was named after George Wilhelm Steller, a German scientist who studied the animals when he accompanied Russian explorer Vitus Bering on an expedition to Alaska in 1741.
The Steller sea lion population is divided into two stocks as shown in Figure 5.5. The eastern stock inhabits the area east of Cape Suckling, Alaska, and extends down the west coast of Canada and the U.S. mainland. The western stock is found west of Cape Suckling and extends across the Aleutian Islands to Russia and Japan.
According to the National Marine Fisheries Service, the western stock declined by 75% between 1976 and 1990. In April 1990 the Steller sea lion was listed under
FIGURE 5.5 Distribution of the Steller sea lion, 2004
Steller sea lion populations have declined for a variety of reasons including bycatch, illegal and legal hunting, predation, and disease. In addition, scientists believe that the animal has experienced reduced productivity due to the indirect effects of climate change and competition from humans for prey species (food fish).
In February 2004 the North Pacific Universities Marine Mammal Consortium reported that population declines may be explained by the fact that Steller sea lions had switched from eating fatty fish to fish with low fat content. In particular, their diet now consists primarily of pollock and flatfish, rather than herring. The low fat content of the new diet prevents Steller sea lions from building up enough blubber to survive and reproduce in their cold aquatic habitat.
The NMFS has conducted surveys of Steller sea lion populations since 1985. These surveys are primarily aerial. The most popular rookeries and haul-outs are photographed from the air, and the animals are counted from examination of detailed photographs. During the summer of 2005 the first Alaska-wide aerial pup count was conducted. The results are shown in Figure 5.7 for target rookeries in the Gulf of Alaska and the Aleutian Islands. Pup populations have declined dramatically since the 1980s. However, the numbers appeared to level off during the early 2000s.
As shown in Table 5.2 species-specific expenditures under the ESA for Steller sea lions totaled $42.6 million in fiscal year 2004, accounting for 60% of expenditures on all marine mammals. The Steller sea lion ranked third in spending among all species covered by the ESA. (See Table 2.8 in Chapter 2.)
FIGURE 5.6 Trends in Steller sea lion populations, through 2005
Recovery Plans for Seals and Sea Lions
Table 5.4 shows the status of recovery plans for endangered seal and sea lion species as of February 2006. No plans have been developed for Caribbean monk seals (which are believed to be extinct) or Guadalupe fur seals. A recovery plan published in 1983 for the Hawaiian monk seal is currently being revised. Likewise, a plan published in 1992 for the eastern and western stocks of the Steller sea lion is also being revised.
Table 5.4 also shows the recovery priority numbers assigned by the NMFS to each endangered seal and sea lion species. Priority numbers can range from a value of 1 (highest priority) to 12 (lowest priority). The Hawaiian monk seal has a priority level of 1, indicating strong concern about its abundance and chances for survival as a species.
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