Population CharacteristicsPopulation Density British Columbia Sea Otters are typically found in close proximity of each other, covering the coast of British Columbia. As seen in the population page, the sea otters tend to be spread out along the beaches but are very social animals that are non-competitive for space. Sea Otters, just like specific birds, return to the same area for feeding, and living space and they share this space with other otters to be more intimidating to prey. When Sea Otters sleep, they hold hands with other otters to ensure that they do not get lost or float away from the rest of the pack (3). |
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Population Distribution
The population increase in B.C. has slowed in recent years as because some parts of the population appear to be at equilibrium. Sea Otters were extirpated from British Columbia by 1929 and a total of 89 Sea Otters were reintroduced to Checleset Bay, British Columbia from Amchitka Island and Prince William Sound in 1969, 1970 and 1972 (1). During this time Sea Otters were also reintroduced to parts of Southeast Alaska, Washington and Oregon and but the Oregon reintroduction were successful in establishing population. In British Columbia, following the reintroductions to Checleset Bay, Sea Otters occupied two locations along the west coast of Vancouver Island, an area of Checleset Bay as well as Bajo Reef off of Nootka Island. By 2008, Sea Otters along Vancouver Island ranged from Vargas Island, in Clayoquot Sound, northward to Cape Scott and eastward into Queen Charlotte Straight. In 2008, Sea Otters on the central British Columbia coast ranged continuously from the southern end of the Goose Group, northward through Queens Sound to Cape Mark at the edge of Milbanke Sound and also in an area off Aristazabal Island (3).
Single Sea Otters are periodically reported outside the continuous range. Throughout the North Pacific, the Sea Otter presently occupies about one half to two thirds of its historical range. It is estimated that by 2004 the Sea Otter occupied 25-33% of its historical range within British Columbia (1). Reintroduced Sea Otter populations extend through Southeast Alaska, British Columbia and Washington (see Figure 1). Along the North American coast south of Alaska, the sea otter's range is discontinuous. A remnant population survived off Vancouver Island into the 20th century, but it died out despite the 1911 international protection treaty, with the last sea otter taken near Kyuquot in 1929 (1). The status of the sea otters has improved since 2004 with a report of 4,700 in 2008 that improved their status in Canada.They currently occupy much of the exposed west coast of Vancouver Island and parts of the central mainland BC coast. These Sea Otters tend to occupy the same space every year in a uniformed way. Although the sea otters tend to live in clumped families, they travel to the same spaces for hunting, nesting and swimming.
The population increase in B.C. has slowed in recent years as because some parts of the population appear to be at equilibrium. Sea Otters were extirpated from British Columbia by 1929 and a total of 89 Sea Otters were reintroduced to Checleset Bay, British Columbia from Amchitka Island and Prince William Sound in 1969, 1970 and 1972 (1). During this time Sea Otters were also reintroduced to parts of Southeast Alaska, Washington and Oregon and but the Oregon reintroduction were successful in establishing population. In British Columbia, following the reintroductions to Checleset Bay, Sea Otters occupied two locations along the west coast of Vancouver Island, an area of Checleset Bay as well as Bajo Reef off of Nootka Island. By 2008, Sea Otters along Vancouver Island ranged from Vargas Island, in Clayoquot Sound, northward to Cape Scott and eastward into Queen Charlotte Straight. In 2008, Sea Otters on the central British Columbia coast ranged continuously from the southern end of the Goose Group, northward through Queens Sound to Cape Mark at the edge of Milbanke Sound and also in an area off Aristazabal Island (3).
Single Sea Otters are periodically reported outside the continuous range. Throughout the North Pacific, the Sea Otter presently occupies about one half to two thirds of its historical range. It is estimated that by 2004 the Sea Otter occupied 25-33% of its historical range within British Columbia (1). Reintroduced Sea Otter populations extend through Southeast Alaska, British Columbia and Washington (see Figure 1). Along the North American coast south of Alaska, the sea otter's range is discontinuous. A remnant population survived off Vancouver Island into the 20th century, but it died out despite the 1911 international protection treaty, with the last sea otter taken near Kyuquot in 1929 (1). The status of the sea otters has improved since 2004 with a report of 4,700 in 2008 that improved their status in Canada.They currently occupy much of the exposed west coast of Vancouver Island and parts of the central mainland BC coast. These Sea Otters tend to occupy the same space every year in a uniformed way. Although the sea otters tend to live in clumped families, they travel to the same spaces for hunting, nesting and swimming.
Population Dispersion
Historical accounts from explorers and maritime fur traders indicate that the west coast of Vancouver Island, Haida Gwaii and the central and northern mainland coast were important trading destinations, implying an abundance of Sea Otters (5). Genetic Diversity Genetic diversity is of concern to conservation of species that have been reduced to a small size and then allowed to increase; a phenomenon called a bottleneck. The loss of genetic diversity through inbreeding in small populations will reveal deleterious recessive alleles, resulting in lower fecundity, higher rates of mortality and an overall reduction in population growth rate. Furthermore loss of diversity reduces a population’s ability to respond to unexpected environmental or biological events. A recent genetic study shows that current sea otter populations have significantly less genetic variation than did their pre-fur trade ancestors. This is attributed to the severe population bottleneck that resulted from the fur trade (5). |
Figure 1: Historical and current global range of all three subspecies of Sea Otters.
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Among current populations there are no significant differences in genetic variation between remnant and translocated populations, even though translocated populations experienced two bottlenecks. However, found that among current populations, mitochondrial DNA haplotype diversity was inversely correlated with the amount of time remnant and translocated populations spent at their small founding population sizes, and that haplotype diversity was positively correlated with the size of the founding population (5). Several other studies have also assessed genetic diversity and stock delineation of sea otters that reduced genetic diversity is apparent in extant populations compared to pre-fur trade ancestors indicates genetic diversity should remain of concern in the long-term as it increases the risk of extinction from random events.
Environments Carrying Capacity
The Wildlife Management calculated a linear, coast-wide carrying capacity of 52,459 sea otters which is a more realistic upper limit to sea otters in British Columbia. Our carrying capacity estimates are helping set population recovery targets for sea otters in Canada, and our habitat predictions represent a first step in Critical Habitat identification. This habitat-based approach to estimating carrying capacity is likely suitable for other nonmigratory, density-dependent species.
Environments Carrying Capacity
The Wildlife Management calculated a linear, coast-wide carrying capacity of 52,459 sea otters which is a more realistic upper limit to sea otters in British Columbia. Our carrying capacity estimates are helping set population recovery targets for sea otters in Canada, and our habitat predictions represent a first step in Critical Habitat identification. This habitat-based approach to estimating carrying capacity is likely suitable for other nonmigratory, density-dependent species.
Population Growth
Historical Data
Prior to the maritime fur trade of the 18th and 19th centuries, Sea Otters ranged from northern Japan to central Baja California, Mexico but commercial exploitation commencing in the 1740’s led to near extinction of the species (3). By 1911, when Sea Otters were protected under the International Fur Seal Treaty, only 13 remnant groups were known to exist (1). Sea Otters were likely widely distributed along the coast of British Columbia. Historical accounts from explorers and maritime fur traders indicate that the west coast of Vancouver Island, the central and northern mainland coast were important trading destinations, implying an abundance of Sea Otters (3). Unfortunately the Sea Otters were extirpated from British Columbia by 1929. A total of 89 Sea Otters were reintroduced to Checleset Bay, British Columbia from Amchitka Island and Prince William Sound in 1969, 1970 and 1972 (1) This eventually began the reintroducing of sea otters to Canada in hopes to further the reproduction of more Sea Otters.
Prior to the maritime fur trade of the 18th and 19th centuries, Sea Otters ranged from northern Japan to central Baja California, Mexico but commercial exploitation commencing in the 1740’s led to near extinction of the species (3). By 1911, when Sea Otters were protected under the International Fur Seal Treaty, only 13 remnant groups were known to exist (1). Sea Otters were likely widely distributed along the coast of British Columbia. Historical accounts from explorers and maritime fur traders indicate that the west coast of Vancouver Island, the central and northern mainland coast were important trading destinations, implying an abundance of Sea Otters (3). Unfortunately the Sea Otters were extirpated from British Columbia by 1929. A total of 89 Sea Otters were reintroduced to Checleset Bay, British Columbia from Amchitka Island and Prince William Sound in 1969, 1970 and 1972 (1) This eventually began the reintroducing of sea otters to Canada in hopes to further the reproduction of more Sea Otters.
In British Columbia, following the reintroductions to Checleset Bay, Sea Otters occupied two locations along the west coast of Vancouver Island, an area of Checleset Bay as well as Bajo Reef off of Nootka Island, (as seen in Figure 2). In 1989, females with pups were reported near the Goose Islands on the central British Columbia coast indicating establishment of Sea Otters in the area (3). By 2008, Sea Otters were located along Vancouver Island ranged from Clayoquot Sound, northward to Cape Scott and eastward into Queen Charlotte Strait but, single Sea Otters are periodically reported outside the continuous range. (3).
Sea Otter populations that have re-established naturally after exploitation extend through Southeast Alaska, British Columbia and Washington. In Washington State the Sea Otter population may be approaching equilibrium density on the outer coast (2). The Sea Otters in Canada are beginning to multiply exponentially and will hopefully be removed from the species at risk list, (as seen in Figure 3). Unfortunately, the number of sea otters in Canada specifically are still fairly low at this point but with help, the Sea Otters population will keep growing. |
Figure 2: Range of Sea Otters in British Columbia (red shaded area) as of 2008,
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Figure 3: The Population of Sea Otters in British Columbia of Independent Sea Otters and Sea Otter Pups Over Time
Limiting Factors
The Sea Otter is a density-dependent species and population growth is ultimately regulated by resource availability. The abundance of prey affects primary survival, whereas female reproductive rates in the population remain relatively constant regardless of the population. Female reproductive rates are estimated to be 0.83 to 0.94 pups per year and as the number of Sea Otters in an area increases and food becomes limiting (3), Sea Otter density in the area is maintained at equilibrium through mortality and emigration. Pre-weaning survival ranges from 22- 40% in populations near equilibrium to 85% in growing populations (2). Survival post-weaning to one year of age tends also to be lower in populations near equilibrium but, Sea Otters older than two years of age generally have high rates of annual survival, approaching 90% regardless of population status (3).
Other limiting factors that may impact population growth are disease and predation. Disease is a threat because of the potential interaction between human influences from contaminant exposure and introduction of novel infectious diseases in Sea Otters and their habitat. Predation is a limiting factor that contributes to demography. Pup carcasses found at eagle nests suggest eagles may be a source of pup mortality in British Columbia (3). In the Aleutian Islands, Sea Otter pups comprise five to 20% (by frequency) of the eagle diet during the Sea Otter pupping season (4). Killer Whales are not thought to be a significant source of mortality in British Columbia, although there is one anecdotal account of Killer Whales pursuing Sea Otters in Kyuquot Sound (3). White Shark predation is a significant cause of mortality in the southern Sea Otter population and has increased through time, particularly during the current and recent period of the southern Sea Otter population decline (3). However, White Sharks occur rarely in Canadian waters and shark attack is not considered a source of predation in British Columbia.
Separate limiting factors consist of ingestion of marine biotoxins. The toxin responsible for Paralytic Shellfish Poisoning (PSP), produced by certain dinoflagellate species, can accumulate to toxic levels in Butter Clams, which form an important component of the Sea Otter diet (3). A large die-off of Sea Otters in the Kodiak Archipelago in the summer of 1987 was in part attributed to PSP poisoning, suggesting Sea Otters are susceptible to this natural phenomenon (3). One study, however, suggests that Sea Otters may be able to detect PSP and avoid clams with lethal concentrations so the contribution of this limiting factor to population regulation is not known (2). Recently, the incidence of myocarditis and dilated cardiomyopathy in southern Sea Otters, found to be the cause of death in 13% of beach cast carcasses between 1998 and 2001 (2). Although the occurrence of toxic phytoplankton is a natural phenomenon, the problem of harmful algae blooms appears to have increased over the past two decades. Coastal pollution in particular, increased levels of nitrogen and phosphorus abundant in sewage and coastal runoff, is at least partly to blame and in this way a natural phenomenon such as marine biotoxins and its impact on Sea Otter mortality may be influenced by human activity (3).
The Sea Otter is a density-dependent species and population growth is ultimately regulated by resource availability. The abundance of prey affects primary survival, whereas female reproductive rates in the population remain relatively constant regardless of the population. Female reproductive rates are estimated to be 0.83 to 0.94 pups per year and as the number of Sea Otters in an area increases and food becomes limiting (3), Sea Otter density in the area is maintained at equilibrium through mortality and emigration. Pre-weaning survival ranges from 22- 40% in populations near equilibrium to 85% in growing populations (2). Survival post-weaning to one year of age tends also to be lower in populations near equilibrium but, Sea Otters older than two years of age generally have high rates of annual survival, approaching 90% regardless of population status (3).
Other limiting factors that may impact population growth are disease and predation. Disease is a threat because of the potential interaction between human influences from contaminant exposure and introduction of novel infectious diseases in Sea Otters and their habitat. Predation is a limiting factor that contributes to demography. Pup carcasses found at eagle nests suggest eagles may be a source of pup mortality in British Columbia (3). In the Aleutian Islands, Sea Otter pups comprise five to 20% (by frequency) of the eagle diet during the Sea Otter pupping season (4). Killer Whales are not thought to be a significant source of mortality in British Columbia, although there is one anecdotal account of Killer Whales pursuing Sea Otters in Kyuquot Sound (3). White Shark predation is a significant cause of mortality in the southern Sea Otter population and has increased through time, particularly during the current and recent period of the southern Sea Otter population decline (3). However, White Sharks occur rarely in Canadian waters and shark attack is not considered a source of predation in British Columbia.
Separate limiting factors consist of ingestion of marine biotoxins. The toxin responsible for Paralytic Shellfish Poisoning (PSP), produced by certain dinoflagellate species, can accumulate to toxic levels in Butter Clams, which form an important component of the Sea Otter diet (3). A large die-off of Sea Otters in the Kodiak Archipelago in the summer of 1987 was in part attributed to PSP poisoning, suggesting Sea Otters are susceptible to this natural phenomenon (3). One study, however, suggests that Sea Otters may be able to detect PSP and avoid clams with lethal concentrations so the contribution of this limiting factor to population regulation is not known (2). Recently, the incidence of myocarditis and dilated cardiomyopathy in southern Sea Otters, found to be the cause of death in 13% of beach cast carcasses between 1998 and 2001 (2). Although the occurrence of toxic phytoplankton is a natural phenomenon, the problem of harmful algae blooms appears to have increased over the past two decades. Coastal pollution in particular, increased levels of nitrogen and phosphorus abundant in sewage and coastal runoff, is at least partly to blame and in this way a natural phenomenon such as marine biotoxins and its impact on Sea Otter mortality may be influenced by human activity (3).