Current Threats

Oil Spills: 

Oil covered Sea Otters

Source: http://www.alaska-in-pictures.com/sea-otter-death-3199-pictures.htm

       Currently the most prominate threat  facing sea otters is oil spills, this is because they are extremely sensitive to them. Sea otters depend on their coats to keep warm, they have extremely thick coats that trap air providing an insulated layer around their bodies. When they come in contact with oil it saturates their fur, causing them to lose the barrier needed to stay warm. This coupled with problems from ingestion leads to death. In 1989 the Exxon Valdez oil spill in Prince William Sound, greatly affected the sea otter population (IUNC Red List).

This map shows the range of the spill along the Alaskan coast
 

Exxon Valdez oil spill
Source: http://www.pwsrcac.org/about/index.html

    

    
    

       The number of sea otter deaths due to the Exxon Valdez oil spill was originally estimated to be very high, with an upper  limit around 5,000 individuals which represented complete population elimination. It was later found that this estimate was far too high and that the actual mortality rate was  around 750 individuals. This was estimated using the number of sea otter carcasses recovered after the spill and estimates of the number of carcasses not discovered. This process also took into account otters that were found alive but later died. To maintain accuracy the number of carcasses discovered for which the oil spill wasn't the cause of death were removed from the calculations. This estimate of 750 individuals was an average of many different scenarios dealing with the uncertainty of the aforementioned factors.  Even though this number was much smaller than was once thought it doesn't make this any less of a catastrophe. Accurate reporting on numbers of lost individuals is crucial for conservation efforts and to understand the true consequences of an event like this (Garshelis 1997). 

      Both the Northern and Southern sea otter are still listed as threatened under the Endangered Species Act. Threatened means that,  "A species is likely to become endangered within the foreseeable future throughout all or a significant portion of its range"(U.S. Fish and Wildlife Service). When considering delisting the southern sea  otter as threatened, the main factors  that need to be considered are population size and resilience to an oil spill. Meaning that the population has to be large enough to be able to withstand an oil spill; and not fall below the  numbered that would cause it be considered endangered. Resilience to oil spills has been taken into account in recovery plans. The Exxon Valdez oil spill was used to approximate  the mortality rate of oil spills, and many simulations were run to determine how many individuals would likely parish with different size spills. This also illustrates that it was critical to get the real number of individuals effected by such an event, to allow good planning for the future. This should also illustrate how difficult it is to decide when a population should be delisted.   The delisting of a species increases its vulnerability because it is no longer specially protected under the Endangered Species Act. This makes it extremely important for survival of the species that there is accurate data and possible reasons for decline were considered (Ralls 1996). 

Disease: 

The Malformed brain of a sea otter pup that got infected
with Toxoplasma gondii from its mother

Source: 

Miller, M, P Conrad, ER James, A Packham, S Toy-Choutka, MJ Murray, 
D Jessup, and M Grigg. "Transplacental Toxoplasmosis in a 
Wild Southern Sea Otter (enhydra Lutris Nereis)." 
Veterinary Parasitology. 153 (2008): 1-2. Print.

     There is a fairly new problem emerging in Southern Sea Otters (sea otters that live along the California coast). This is the identification of the presence of a protozoa parasite Toxoplasma gondii which causes Toxoplasmosis, which can lead to death. Toxoplasmosis has been observed before in sea otters, but transmission during gustation was only recently observed.  This gestational transmission is the passing on of the parasite from mother to pup during pregnancy. If it is passed on during gustation it can lead to a pup born with birth defects, which will probably result in death of the pup. This can also cause the pup to be stillborn, or aborted. This mother to pup transmission was first documented in  southern sea otters in 2004, through the examination of a abandon pup found in Monterey Bay, California. Toxoplasmosis is common in many marine mammal species, but documentation of transmission from mother to offspring is rare. It is currently unclear how much of a threat this poses to sea otter populations, but it does account for some mortality within the population (Miller et al. 2008).  

Predation: 

     
      The problem of predation is mostly affecting sea otter populations in Alaska. Sea Otter populations have declined due to predation by killer whales, this is possibly a result of decreased availability of other killer whale prey. This has caused an extreme decrease in the sea otter population. As a result of this decrease in sea otters, one of sea otters prey species sea urchins has had an explosive increase in numbers. This may perpetuate the increased mortality rate of sea otters by leading to a destruction of their habitat. Sea urchins feed on kelp forests which are one of the preferred habitats by sea otters This increase in sea urchins has led to a decrease in the habitat quality for the remaining otters. This problem is greatly impacting sea otter numbers and has led to smaller populations, which unfortunately will lead to even more problems for the sea otter. To put killer whale predation in perspective a killer whale could eat 1,825 sea otters in one year. This relationship was established by looking at the number of killer whale attacks observed on sea otters and comparing this to the rate of decline in sea otter population. These two variables seem to match indicating that killer whale predation is the likely cause of decline in sea otter populations in Alaska. This also showed the impact of adding a predator above sea otters on the trophic cascade (Estes et al. 1998). Refer to the trophic cascades tab for more information on how decrease in sea otter population could influence the ecosystem in which it lives.

Source: www.sodahead.com

Source: www.3news.co.nz

Sources: 

1. Katherine Ralls, Douglas P. Demaster and James A. Estes. “Developing a Criterion for Delisting the Southern Sea Otter under the U.S. Endangered Species Act.” Conservation Biology , Vol. 10, No. 6, Special Issue: Festschrift for Michael E. Soule (Dec., 1996), pp. 1528-1537

2. Garshelis, David L. "Sea Otter Mortality Estimated from Carcasses Collected After the Exxon Valdez Oil Spill." Conservation Biology. 11.4 (1997): 905-916. Print.

3. Miller, M, P Conrad, ER James, A Packham, S Toy-Choutka, MJ Murray, D Jessup, and M Grigg. "Transplacental Toxoplasmosis in a Wild Southern Sea Otter (enhydra Lutris Nereis)." Veterinary Parasitology. 153 (2008): 1-2. Print.

4. Estes, J A, M T. Tinker, T M. Williams, and D F. Doak. "Killer Whale Predation on Sea Otters Linking Oceanic and Nearshore Ecosystems." Science. 282.5388 (1998): 473-476. Print.

5. "Enhydra Lutris." (Sea Otter). N.p., n.d. Web. 24 Feb. 2013. 

<http://www.iucnredlist.org/details/7750/0>.

6."Species Reports." U.S. Fish and Wildlife Service. N.p., 10 Mar. 2013. Web. 10 Mar. 2013. <http://ecos.fws.gov/tess_public/SpeciesReport.do>.