Sea Otter Status-Year End 2008
March 2009
                                 

“How are the sea otters doing?” We get asked this A LOT! It would be easier if we could say the California sea otter population was increasing or decreasing, healthy or not.  But we use several measures to determine the status of the population and these measures often give conflicting messages about how the population is doing as a whole. In 2008, three measures were down, pointing towards a population decline. One measure improved. 

In Summary

The Otter Project considers four factors when evaluating population status. For 2008 the factors indicated the following:

• Spring survey: Negative—points towards decline The spring 2007 count was a new record, but the spring 2008 count was strongly down. The fall 2008 count was also down.
• Dead strandings: Positive-does not point towards decline. Through December 2008, the number of dead otters recovered was down.
• Mortality by age-class: Negative—points towards decline.  The fall count showed increased mortality in pup and reproductive adult age classes.
• Pup to independent ratio: Negative—points towards decline. From 2003 through 2007 the pup ratio modestly improved. In 2008 the pup ratio declined.

The Otter Project is concerned that the California sea otter population is less healthy than recent years and could be headed into decline.

Sea Otter Survey

The sea otter population is surveyed twice a year. There is consensus that the spring survey is more accurate than the fall survey due to better viewing conditions and less surface kelp. There is some statistical uncertainty inherent to the count. The survey does not include “replicate surveys” which might give a measure of statistical error. Most likely, not every otter is counted, so the survey may represent a minimum number. We don’t know what percentage of the population is surveyed, how the survey is influenced by conditions, or if a different percentage is counted every year. 

The spring 2008 survey found 2760 sea otters, down 8.8-percent from the record 2007 spring survey.

To dampen the statistical impact of an unusual dip or spike, the US Geologic Survey-Biological Resources Division, uses a three year running average. 

The 3-year running average also serves as the measure for considering de-listing of the southern sea otter from the Endangered Species list. The 2006-2008 average is 2826; the southern sea otter could be considered for delisting if the average reaches 3090 for three consecutive years. The current running average could indicate a plateau in population growth. 

The fall 2008 survey found 2144 sea otters, down 7.3-percent from the fall 2007 survey. Fewer otters were found in many coastal segments but the sharpest decline was found in Monterey Bay (Capitola to Seaside coastal segment). Fewer otters were also found in the far northern (north of Pigeon Point, San Mateo County) and southern (SE of Point Conception, Santa Barbara County) portions of the range.

February-March 2009 Update: Sea otters have returned to Coal Oil Point (near UC Santa Barbara), Santa Barbara County. In the summer of 2008 the Coal Oil Point sea otter raft grew to over 25 otters and then declined to zero in the fall. So far in 2009 the maximum count has been 7 otters. A lone sea otter has been spotted in Oregon. Biologists believe the Oregon otter may have come from California. This is the first ‘wild’ sighting of otters in Oregon for 103 years. 

Dead strandings

The number of dead otters found on the beach is another measure of population status; an unusual number of carcasses could indicate a serious problem. Through December, the number of dead otters found (237) was near equal to the 10-year average (230), 21-percent lower than last year’s record dead stranding year (299), and is the lowest number of otters found dead since 2002.

2009 update: Eleven sea otters were found dead in January (February numbers have yet to be released); fewer than 2008 (16) and about equal to the 10-year average.

It makes intuitive sense that as the sea otter population grows, the number of dead sea otters found on the beach will increase.

To compensate for the impact of population increase, we look at the percentage of the spring count found stranded. For the past four years the percentage of the spring count found dead stranded was stable at 9.9 percent. In 2008 the percentage found dead dropped to 8.6 percent. 

Mortality by age class

Every sea otter found dead on the beach has a tooth pulled and aged. The sample size is very large, with data on well over 4000 otters. While there is no consensus on how to look at this factor, The Otter Project averages all previous years and then compares the most current year against that average. Intuitively, we would expect otters live to old age – mortality in all early age classes would go down, and mortality in “aged adults” would correspondingly go up. In 2008 the opposite was true: even fewer otters were living to old age.

There is some discussion whether we should look at all otters or just females (demographically, the more important sex). A recent doctoral thesis indicated persistent high mortality of reproductive females.

The Otter Project has only a few years of sex specific data. These data should be considered inconclusive. Again, there may be a pattern of early and prime-age mortality.

Generally, more male sea otters are found dead than female. It isn’t known if the population is dominated by males, male mortality is disproportionate, or if the areas where most carcasses are recovered are dominated by males .  In 2008 more females stranded (106) than males (96).  

Pup to independent ratio:

Fewer reproducing adults could lead to a reduction in the number of pups born each year. From 2003 through 2007 the pup ratio modestly improved. In 2008 the pup ratio declined. The overall trend continues to slope downwards. 

Our Interpretation: What The Otter Project thinks is happening

We are concerned with the low 2008 spring count, reinforced by the low fall count. Given the year to year variability of the count, it is difficult to know if the decline is truly a trend.    The number of spring pups (pup to independent ratio) is also worrisome. Otters dying before reproductive age is very worrisome and possibly a prime factor in the sluggish population growth.  

Because of the lack of statistical rigor in the annual surveys, we tend to discount small year to year changes. We believe increased measures should be taken to ensure statistical accuracy. The Otter Project would support – with volunteers and financial contributions – any effort to increase the reliability of the survey or statistical analysis.  

Biologists estimate that 50% of all mortality is recovered dead on the beach. Approximately 15% of all sea otter mortality is recovered ‘fresh dead’ and studied down to the cellular level to determine cause of death. Fifteen percent is a very significant sample size; as such, we would hope to see a more concrete understanding of the causes of sea otter death and population stagnation from the ongoing studies of sea otter mortality. While there will always be some inherent uncertainty to statistical analysis, we believe that scientists have reliable enough data to offer tangible policy advice. As of yet, researchers have not been forthcoming. We are becoming increasingly frustrated that scientists in pursuit of funding are unwilling to offer policy advice on saving the sea otter. 

Why are California sea otters dying?  Sea otters die from a long list of causes including gun shot, boat strike, and shark bite. But, the largest and most unusual cause of death is ‘disease.’ Thirty to fifty percent of all mortality is due to a variety of diseases. Otters are being inflicted with diseases that come from land; pathogens and chemical pollutants are being washed into the ocean from sewage, urban, and agricultural sources. Sea otters have huge chemical contaminant loads (DDT, PCB, PBDE and butyltins) and many researchers believe the otter’s immune system is weakened, leaving them susceptible to opportunistic diseases. So, immunodeficient, weakened sea otters are swimming in a thickening soup of disease ridden water.

What can be done?

• We can stop polluted sewage and runoff from reaching the ocean.
• We must tolerate fewer municipal sewage spills by requiring cities to maintain and update their sanitary sewer systems to a high tertiary standard.
• We can develop updated municipal storm water plans that are restrictive of pollutants entering the ocean.
• We can tackle legacy chemicals such as butyltins, DDT, and PCB by:
• Cleaning chemicals  out of our harbors (i.e., Butyltin hotspots)
• Minimizing the ‘down watershed’ transport of chemicals by improving farm practices and irrigated agricultural discharge
• We can lift restrictions on sea otter range expansion by getting rid of the no-otter zone in Southern California, a federally mandated zone that restricts sea otters to northern California. The US Fish and Wildlife Service should discontinue the zone.
• We can complete work on a California statewide network of no-take marine reserves, parks, and conservation areas. No-take marine reserves offer benefits to sea otters by:
• Eliminating conflicts with fisheries
• Reducing boat disturbance
• Enhancing the forage base available to sea otters and other wildlife
• We can take aggressive action to reduce the possibility of a catastrophic oil spill from offshore oil development or a tanker collision.

Why save the California sea otter?

• Sea otters increase the primary productivity of their environment. By eating herbivores, the otter increases kelp production which supports fish populations (sea otters do not eat fish). Healthy kelp forests are critical to fin-fish fisheries.
• Sea otters increase biodiversity. The coastal environment is three times more diverse with sea otters than without. A healthy kelp forest supports fish, crabs, lobster, shellfish, etc. Diverse ecosystems are more stable in the face of environmental change.
• According to a 2001 study, each sea otter per California county can bring between $170,100 to $589,100 in tourism revenues to that county each year. Tourism revenue is far greater than any shellfish fisheries displaced.
• The sea otter is especially sensitive to chemical and pathogen pollution. Listening to what sea otters are telling us about ocean pollution will benefit the entire nearshore ecosystem, including humans.

Notes

The above status report was compiled from agency and peer reviewed data. Data tables to support the graphs and citations are available on request to: Steve Shimek, The Otter Project, 831/646-8837, steve@otterproject.org. More information at: www.otterproject.org.