DIVE DRY WITH DR. BILL #574: ELEPHANT SEALS: BACK FROM THE BRINK
Last week I introduced my readers to the northern elephant seal (Mirounga angustirostris), the largest true seal in the northern hemisphere. I also mentioned that I'm not an expert on "milk givers" (mammals) either in the sea or on land as my training is as a kelp forest ecologist and invertebrate biologist. Actually the only marine mammal I've shown a strong interest in is the mermaid, and NOAA keeps telling me they don't exist. I'm beginning to believe them. However, as a service to my readers and those who watch my cable TV show, I thoroughly researched these seals so I could entertain you with their exploits for a few weeks.
If this species is the largest true seal in the northern hemisphere, what is the largest one down under? Why, the southern elephant seal (Mirounga leonina) of course! Males of that species may typically reach five to nearly nine thousand pounds. These are the only two species of elephant seal in the world. Unlike me, these two seals are not particularly fond of life in the tropics and prefer the cold polar regions. Yet they are closely related and must have evolved from a common ancestor.
During the last Ice Age, beginning about 130,000 years ago, elephant seals were present in California. They were also found much further south because it was... well... cold. They don't call it an Ice Age because of warm sunshine! The tropical belt was much narrower and since these seals spend much of their time in the deep ocean, it was much easier for them to cross the equator and enter the southern oceans. Then when the glaciers retreated and the tropics and subtropics expanded, a barrier was created that prevented them from moving between the hemispheres.
Let's accelerate time a bit until we reach the historic period, say the early 1800s. This was before humans realized they could puncture the Earth's surface and pump oil out of the ground. Back then we relied on marine mammals for some of our energy needs. I'm sure all of you are familiar with the history of whaling. However, how many of my readers were aware that seals were also hunted for their oil so our ancestors could burn their lamps brightly after the sun went down?
"Sealing" (and not the one above your head) was a common pastime along the coast of North America and elsewhere in the world. Due to their massive size and high blubber content (up to 50% of their body), they were a prized catch. Notorious sealers Charles Scammon reported that an 18 ft bull taken on nearby Santa Barbara Island yielded 210 gallons of oil. That's more than my first car, a 1956 Ford, burned in a year. Fortunately it was more efficient with gasoline (which cost as little as 19 cents a gallon back in my youth).
It is reported that hunting elephant seals for oil began about 1818 and that by the 1860s about 250,000 of them had been converted into flame in your great-great-great-great grandparent's oil lamps. By 1884 our species was thought to be extinct. However, in 1892 an expedition from the Smithsonian led by Townsend and Anthony discovered eight or nine elephant seals on remote Guadalupe Island off Baja... and promptly killed seven of them! If there were only eight as frequently reported, I guess their understanding of reproductive biology was somewhat limited. Elephant seals do NOT reproduce by splitting in half like an amoeba. They require two to tango... or is it tangle?
Museum collectors continued to kill them through 1911. Fortunately in 1922 they were afforded protection when the Mexican government declared Guadalupe Island a biological reserve. It is estimated that as few as 20 individuals were alive at that time, and that the entire current day population of about 175,000 northern elephant seals derived from that small number. Those of you who understand genetics realize that this is a very limited population with a narrow range of genetic diversity. When a species passes through a stage where its numbers are so greatly diminished; through actions like hunting, fishing, disease or natural catastrophe; we say it had passed through a genetic bottleneck.
So why was Mexico ahead of the United States in protecting this species? Good question. Of course by 1922 they were all gone from U.S. waters so there was nothing to protect here. However, our government soon followed suit as a slowly increasing elephant seal population began to enter federal waters. By the 1930s they had reached the Channel Islands which became the center of the U.S. population since they prefer to breed on offshore islands to avoid land-based predators like grizzly bears. I guess they finally realized the Grizz had been vanquished from coastal waters and they began colonizing mainland sites as well.
Two of the best known mainland rookery sites are the mainland near Año Nuevo Island (where they first appeared in 1955) and the beaches near the Piedras Blancas lighthouse below Hearst Castle near San Simeon on Highway One where I was among the first to see them back in 1990 or 1991. Back in the late 1960s when I first arrived on Catalina to teach marine biology, I became aware of Dr. Burney LeBoeuf's groundbreaking research on this species as they colonized the area at Año Nuevo. He has followed that population and its dynamics from 1961 to today.
LeBoeuf noted that initial growth of the new colony was quite rapid. Many of the new arrivals were young females originally resident in the Channel Islands. They sought new breeding areas due to competition for space from older females. And, of course, where the girls are the boys will soon arrive! Pup production in this new colony reached a peak between 1995 and 2006 at 2,700 births per year. Following that period the number of pups born declined. New rookeries ar being established as the total population increases.
In many senses the story of the northern elephant seal is a remarkable one. It illustrates that a species may rebound from near extinction if appropriate protections are put in place. We have seen similar rebounds in our own Catalina Island fox population following the outbreak of canine distemper in the late 1990s, and in the giant sea bass population once protections were put in place following extreme fishing pressure. However, despite the numerical success, the limited genetic variation in this population could leave them more susceptible to disease outbreaks or natural disasters. Let's hope they don't face such threats.
Image caption: Extent of winter sea ice (light blue) in the northern hemisphere during Pleistocene Ice Age and cover of seal and whale hunter Charles Scammon's book on Marine Mammals; illustration of elephant seal by Scammon and five 42 gallon barrels (210 gallons) of oil from large male elephant seal.
Last week I introduced my readers to the northern elephant seal (Mirounga angustirostris), the largest true seal in the northern hemisphere. I also mentioned that I'm not an expert on "milk givers" (mammals) either in the sea or on land as my training is as a kelp forest ecologist and invertebrate biologist. Actually the only marine mammal I've shown a strong interest in is the mermaid, and NOAA keeps telling me they don't exist. I'm beginning to believe them. However, as a service to my readers and those who watch my cable TV show, I thoroughly researched these seals so I could entertain you with their exploits for a few weeks.
If this species is the largest true seal in the northern hemisphere, what is the largest one down under? Why, the southern elephant seal (Mirounga leonina) of course! Males of that species may typically reach five to nearly nine thousand pounds. These are the only two species of elephant seal in the world. Unlike me, these two seals are not particularly fond of life in the tropics and prefer the cold polar regions. Yet they are closely related and must have evolved from a common ancestor.
During the last Ice Age, beginning about 130,000 years ago, elephant seals were present in California. They were also found much further south because it was... well... cold. They don't call it an Ice Age because of warm sunshine! The tropical belt was much narrower and since these seals spend much of their time in the deep ocean, it was much easier for them to cross the equator and enter the southern oceans. Then when the glaciers retreated and the tropics and subtropics expanded, a barrier was created that prevented them from moving between the hemispheres.
Let's accelerate time a bit until we reach the historic period, say the early 1800s. This was before humans realized they could puncture the Earth's surface and pump oil out of the ground. Back then we relied on marine mammals for some of our energy needs. I'm sure all of you are familiar with the history of whaling. However, how many of my readers were aware that seals were also hunted for their oil so our ancestors could burn their lamps brightly after the sun went down?
"Sealing" (and not the one above your head) was a common pastime along the coast of North America and elsewhere in the world. Due to their massive size and high blubber content (up to 50% of their body), they were a prized catch. Notorious sealers Charles Scammon reported that an 18 ft bull taken on nearby Santa Barbara Island yielded 210 gallons of oil. That's more than my first car, a 1956 Ford, burned in a year. Fortunately it was more efficient with gasoline (which cost as little as 19 cents a gallon back in my youth).
It is reported that hunting elephant seals for oil began about 1818 and that by the 1860s about 250,000 of them had been converted into flame in your great-great-great-great grandparent's oil lamps. By 1884 our species was thought to be extinct. However, in 1892 an expedition from the Smithsonian led by Townsend and Anthony discovered eight or nine elephant seals on remote Guadalupe Island off Baja... and promptly killed seven of them! If there were only eight as frequently reported, I guess their understanding of reproductive biology was somewhat limited. Elephant seals do NOT reproduce by splitting in half like an amoeba. They require two to tango... or is it tangle?
Museum collectors continued to kill them through 1911. Fortunately in 1922 they were afforded protection when the Mexican government declared Guadalupe Island a biological reserve. It is estimated that as few as 20 individuals were alive at that time, and that the entire current day population of about 175,000 northern elephant seals derived from that small number. Those of you who understand genetics realize that this is a very limited population with a narrow range of genetic diversity. When a species passes through a stage where its numbers are so greatly diminished; through actions like hunting, fishing, disease or natural catastrophe; we say it had passed through a genetic bottleneck.
So why was Mexico ahead of the United States in protecting this species? Good question. Of course by 1922 they were all gone from U.S. waters so there was nothing to protect here. However, our government soon followed suit as a slowly increasing elephant seal population began to enter federal waters. By the 1930s they had reached the Channel Islands which became the center of the U.S. population since they prefer to breed on offshore islands to avoid land-based predators like grizzly bears. I guess they finally realized the Grizz had been vanquished from coastal waters and they began colonizing mainland sites as well.
Two of the best known mainland rookery sites are the mainland near Año Nuevo Island (where they first appeared in 1955) and the beaches near the Piedras Blancas lighthouse below Hearst Castle near San Simeon on Highway One where I was among the first to see them back in 1990 or 1991. Back in the late 1960s when I first arrived on Catalina to teach marine biology, I became aware of Dr. Burney LeBoeuf's groundbreaking research on this species as they colonized the area at Año Nuevo. He has followed that population and its dynamics from 1961 to today.
LeBoeuf noted that initial growth of the new colony was quite rapid. Many of the new arrivals were young females originally resident in the Channel Islands. They sought new breeding areas due to competition for space from older females. And, of course, where the girls are the boys will soon arrive! Pup production in this new colony reached a peak between 1995 and 2006 at 2,700 births per year. Following that period the number of pups born declined. New rookeries ar being established as the total population increases.
In many senses the story of the northern elephant seal is a remarkable one. It illustrates that a species may rebound from near extinction if appropriate protections are put in place. We have seen similar rebounds in our own Catalina Island fox population following the outbreak of canine distemper in the late 1990s, and in the giant sea bass population once protections were put in place following extreme fishing pressure. However, despite the numerical success, the limited genetic variation in this population could leave them more susceptible to disease outbreaks or natural disasters. Let's hope they don't face such threats.
Image caption: Extent of winter sea ice (light blue) in the northern hemisphere during Pleistocene Ice Age and cover of seal and whale hunter Charles Scammon's book on Marine Mammals; illustration of elephant seal by Scammon and five 42 gallon barrels (210 gallons) of oil from large male elephant seal.
