Steller sea lions are large predators along rocky shores and beaches of the cold, north Pacific Ocean. Like all seals and sea lions, the steller sea lion feeds in the ocean but mates, gives birth to its pups, and rests on land.
Its preferred pupping areas include rocky shores and gravel beaches. Steller sea lions are generalist predators that eat a variety of large, marine fishes Pacific Cod, Pollack, salmons, flatfishes, etc. They are known to pester fishers by eating fishes out of their nets, bringing them into dangerous contact with humans. As they are some of the largest animals throughout their range, steller sea lions have few natural predators. In the water, the Steller sea lion pulls itself through the water using its front flippers.
Other marine animals such as seals, swim with their hind flippers using a body action that is more fishlike. Genetically, there are three distinct populations called the Russian population, Western population and Eastern population. These sites can be rock shelves, ledges, boulders, and gravel or sand beaches. Adult Steller sea lions eat a wide variety of fishes, including Pacific herring, capelin, sand lance, Atka mackerel, walleye pollock, salmon, Pacific cod, rockfishes, salmon, flatfishes, sculpins, squid, octopus and occasionally seal pups.
Most fish are swallowed whole. Large prey are torn apart and consumed at the surface. Sea lions sometimes feed in groups which may help to control the movement of large schools of fish and make them easier to catch. Diet appears to vary between regions and has also changed through time. The causes and consequences of these changes in diets are still under debate.
Young sea lions require twice this amount. Steller sea lions mate and give birth on land. On average, females give birth for the first time when they are 5 years old. A few mothers are as young as 3 years old. Births occur mid-May to mid-July and peak in June.
In May, dominant males 9 years and older establish their breeding territories on rookeries, and maintain them for approximately 40 days without eating. During this time, the males establish a harem and mate with females on their territories. On average, males successfully defend territories for only 2 breeding seasons. Mating occurs about 1 week following the birth of the pups.
Pups are able to crawl and swim soon after birth. Pups will approach other females, but are often bitten or thrown by females who have their own pups. Contaminants that might harm Steller sea lions can occur naturally in the environment and enter ocean waters from many sources, such as oil and gas activity tankering and pipeline transport, production, etc.
Once in the environment, some contaminants move up the food chain and accumulate in top predators. Certain pollutants that Steller sea lions are exposed to have been shown to damage the immune and reproductive systems of other mammals and to negatively impact their health and survival.
Of particular concern now is information showing that mercury contaminant loads of some western DPS Steller sea lion pups are relatively high in some parts of the range where declines are still occurring. Exposure to organochlorines known to affect health impacts in other species have been found in parts of the western and eastern DPSs, though impacts on Steller sea lions are not clear.
Emerging environmental contaminants, such as Polybrominated diphenyl ethers PBDEs are known to bioaccumulate in marine mammals and thus are also a concern, though Steller sea lion exposure to these compounds is not well understood.
Steller sea lions may be disturbed by humans in vessels power, kayak, etc. When disturbed, Steller sea lions may stampede into the water, which can injure or kill pups and juveniles when they are crushed by adults, and in extreme cases cause pup abandonment. Steller sea lions that are illegally fed can cause them to become habituated, aggressive, lead to more fisheries interactions, entanglements, and illegal shootings as a result of increased frustrations.
Historically, commercial fishing in the Bering Sea and the North Pacific Ocean incidentally killed many Steller sea lions. Changes in fishing techniques and areas and times fished are thought to have significantly reduced incidental take.
Amendments to the Marine Mammal Protection Act in and required observer programs to monitor marine mammal incidental take in some domestic fisheries and NOAA Fisheries provides estimates of mortality and serious injury of Steller sea lions due to US commercial fisheries in marine mammal stock assessments for the western and eastern DPSs.
These estimates are likely an underestimate of the actual levels, since large segments of the fishing industry, including fisheries near Steller sea lion rookeries, haulouts, and feeding areas, and fisheries with known past interaction with sea lions have either no or very limited observer coverage. Thus, we are highly uncertain about the impact of this threat. Steller sea lions may be disturbed by vessels power boats, kayaks, paddleboards, etc.
Disturbance to Steller sea lions on terrestrial haulout sites can lead to individuals fleeing toward the water, causing mass stampedes during which pups and juveniles may be injured or killed when crushed by adults.
Disturbance can also cause sea lions to flee from the tops of steep rocks or cliff faces, also causing injury or death. Disturbance can lead to interruption of important behaviors such as nursing, resting, breeding, and socializing. Repeated disturbances that cause lactating females to abandon rookeries or use them less often could impact the health and survival of pups by reducing normal nursing cycles. Steller sea lion feeding can also be disturbed by vessel traffic or underwater noise.
Steller sea lions can become entangled in marine debris or fishing gear, either swimming off with the gear attached or becoming anchored. Once entangled, sea lions may drag and swim with attached gear for long distances, ultimately suffering fatigue, compromised feeding ability, or severe injury that may lead to reduced reproductive success and death.
Entanglement rates to the west however are likely underestimated due to fewer observations in a less-populated area. Not all entangled animals strand e. This is true especially in the most remote parts of the range of this species. Illegal Feeding. Feeding of sea lions is illegal and can lead to close interactions between humans and sea lions that pose risks to both. Feeding-related problems include changes in sea lion behavior; habituation; aggression toward humans; negative impacts to fisheries; and entanglement, injury, and death of animals.
It is illegal to shoot Steller sea lions unless you are an Alaska Native and the take is for subsistence purposes food or handicraft and is not accomplished in a wasteful manner. Historical accounts, especially associated with fisheries, documented substantial mortality to the western DPS due to illegal shooting. Subsistence use stuck and lost Steller sea lion carcasses further complicate efforts to estimate illegal shooting.
Most parts of the range of the western DPS are not systematically monitored for carcasses, so there are no current studies evaluating levels of illegal shooting; large parts of the fishing industry, including fisheries near Steller sea lion rookeries, haulouts, and feeding areas, have either no or very limited observer coverage.
Inadvertent vessel strikes can injure or kill Steller sea lions. There have been four documented cases of Steller sea lions being injured or killed due to nearshore vessel strikes in Alaska since PDF: see Table Nearshore vessel strikes are most likely to occur in areas where Steller sea lions are concentrated for feeding or rafting, or near large haulouts or rookeries from which large numbers of animals will be in transit.
The primary predators of Steller sea lions are killer whales , sharks, and humans. Our work includes:. Our research has helped inform us about new aspects of Steller sea lion biology, behavior, and ecology and better understand the threats to Steller sea lion individuals and populations.
Continued research is especially important in recovering the endangered western DPS and sustaining the recovery of the delisted eastern DPS. Under the ESA, most western DPS rookeries are protected by no-entry buffer zones that prohibit entry, with some exceptions, by sea and on land.
A firearm is any weapon, such as a pistol or rifle, capable of firing a missile using an explosive charge as a propellant. Learn more about special protections for western DPS Steller sea lions.
Be responsible when viewing Steller sea lions in the wild. Steller sea lions can be injured or killed if they are disturbed when they are hauled out. Individuals may unexpectedly panic and flee to the water; a group may stampede and pups or juveniles can be crushed. Even adults can be injured or killed. Disturbing Steller sea lions that are resting, nursing, feeding, or engaged in other key behaviors can reduce the chance that they will survive or reproduce.
Their reaction to people is hard to predict. Play it safe —make sure not to disturb Steller sea lions that are hauled out on land or in the water. On the water, observe Steller sea lions from a safe distance of at least yards and limit your time spent observing to 30 minutes or less. If they are hauled out, do not approach close enough to disturb them. If they are rafting, do not approach. Do not enter no-entry buffer zones around specified rookeries. Steller sea lions are also vulnerable to disturbance by air and they have been observed to stampede in response to helicopters more than a mile away.
All aircraft need to ensure they do not disturb Steller sea lions. Learn more about our marine life viewing guidelines. In Alaska, report a sick, injured, entangled, stranded, or dead marine mammal to the Alaska Marine Mammal Stranding Hotline at to make sure professional responders and scientists know about it and can take appropriate action.
Numerous organizations around Alaska are trained to receive reports and respond when necessary. On the west coast of the U. Other reporting hotlines and resources:. This hotline is available 24 hours a day, 7 days a week for anyone in the United States. The decline in the abundance of Steller sea lions was first observed in Alaska in the s, and the rate of decline increased dramatically in the late s. Due to genetic, morphological, ecological, and population trend data supporting the overall distinctiveness, NOAA Fisheries recognized two distinct population segments DPS in Threats vary throughout the range of each DPS and vary over time.
Some of the threats that led to an Endangered Species Act listing are better controlled, but new threats may be present or emerging. Some of the most pressing threats are discussed under the Overview tab. While the western population has been increasing slowly overall since about , it continues to decline rapidly in large areas of its range central and western Aleutian Islands regions. Recent changes in counts in other areas that were showing signs of recovery eastern and central Gulf of Alaska regions are of high concern, and evidence as a whole indicates that there are multiple remaining threats to their existence.
Intentional killing, such as predator control and commercial harvests in large areas of the range of the eastern population, resulted in major reductions in abundance through much of the s. Culling and commercial harvests in Alaska prior to the Marine Mammal Protection Act , competition with fisheries for prey, incidental take in fisheries, entanglement, legal and illegal shooting, and possibly other factors also adversely affected Steller sea lions.
Intentional killing of Steller sea lions with certain exceptions non-wasteful take by coastal Alaska Natives for subsistence and the making of handicrafts , take authorized under a marine mammal research permit, take by a government official under select circumstances is illegal.
Deliberate killing by fishermen is still a threat throughout the species' range. There is also conflict with fish farms in Canada, 87 Steller sea lions being killed legally under predator control permits by the British Columbia fish farming industry in , mostly in the Vancouver Island area.
It is thought that other sea lions are also being killed illegally by fish farmers. Commercial hunting, which took large numbers of the sea lions until as recently as the s, no longer takes place. There is an average subsistence kill of Steller sea lions in Alaska each year, almost all from the western population and the majority taken by Aleut hunters in the Aleutian and Pribilof Islands. There is also some mortality of the western population of Steller sea lions in the U.
These two causes of mortality are significant given the precarious state of the western population. Steller sea lion numbers have been declining in recent years in the southern end of the species' range in central California where habitat concerns include reduced prey availability, contaminants and disease.
Steller sea lions in Alaska may have been affected by the El Nino although it is not known yet to what extent. Environmental changes in the Bering Sea ecosystem, such as warmer ocean temperatures, altered ocean currents and atmospheric conditions, may also be affecting the species. There is also a danger to Steller sea lions from vessels running aground in their habitat, although the species is not as vulnerable to oil-related injuries as sea otters or sea birds.
In May a metre fishing vessel ran aground on the rocks of Unimak Island in the Aleutian Islands, the coastguard saying that they expected the vessel to lose all 30, litres of diesel, lubricating and hydraulic oils which it was carrying.
In the same month a metre freighter carrying , litres of fuel oil ran aground at the entrance to Cold Bay, east of Unimak Island, leaking up to litres of lubricating oil.
A number of Steller sea lion haulout and rookery sites were affected by the Exxon Valdez oil spill in Prince William Sound, Alaska, in but inadequate data exists to determine the impact of the spill on the population. High levels of the antifouling paint tributyltin TBT have been found in Steller sea lions around Hokkaido. Photo: National Marine Mammal Laboratory Lifestyle The Steller sea lion breeding season is from mid-May to mid-July and individuals appear to have a high fidelity for their breeding rookery.
0コメント