Research Document - 2015/039
Trends in the abundance and distribution of sea otters (Enhydra lutris) in British Columbia updated with 2013 survey results
By L. M. Nichol, J.C. Watson, R. Abernethy, E. Rechsteiner, and J. Towers
Abstract
In 2013 the BC sea otter population had a minimum of 6,754 sea otters: 5,612 sea otters were counted in the Vancouver Island region and 1,142 sea otters in the central mainland coast region. The population has continued to grow and expand its range since the last survey, demonstrating population growth patterns that are typical among recovering sea otter populations. In the Vancouver Island region, which encompasses the west and north coast of Vancouver Island as well as Queen Charlotte Strait, annual growth was estimated regionally to have been 6.8% year-1 Standard Error (SE) = 1.20) during 2004 to 2008 and 7.2% year-1 (SE = 1.05) from 2009 to 2013. These rates are similar but slightly lower than previous estimates for the period 1995 to 2008. They reflect density dependent growth along some parts of Vancouver Island where the sea otter population is approaching carrying capacity. This trend was detected in this assessment by fitting growth models to sub-regional data sets and estimating growth rates over shorter time intervals than has been done previously. On the central BC mainland coast, growth averaged 4.2% year-1 (SE = 1.62) during 2004 to 2008 reflecting density dependent growth in the longest occupied sub-region. However the contribution of exponential growth in sub-regions where range expansion was first noted in 2007 and 2008 contributed to a much higher regional rate of 12.6% year-1 (SE= 1.65) for the most recent five-years 2009 to 2013.
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