Human Disturbance and the decline of Steller sea lions
Steller sea lions are easily scared off their rookery and haulout sites by humans. While animals commonly return after having been disturbed, it is not clear what the effect of prolonged or repeated human disturbances might be on Steller sea lions. Human disturbance (fishing vessels, visitors, scientists) might therefore be a contributing factor to the population decline.

Scientists are looking at whether prolonged or repeated human disturbances at rookeries and haulout sites might be a contributing factor to the Steller sea lion's population decline.

Laura Kucey and Andrew Trites sought to determine if there were measurable short-term effects of human disturbance on the numbers of Steller sea lions using terrestrial sites. They documented numbers and composition of sea lions for 1 – 2 weeks before — and for 1 – 2 weeks after a predetermined research disturbance at six sites in summer, and four sites during winter / spring in southeast Alaska and British Columbia. 

Disturbances resulted in significantly fewer sea lions using the haulouts, and an increase in variation in daily numbers at nine of the ten disturbed sites.  Rates of animals joining and leaving the haulouts were not significantly different throughout the study.  However, sea lion numbers did not return to pre-disturbance levels at four sites — suggesting a departure of animals at the time of the disturbance.  At the remaining six sites, the daily mean numbers of sea lions took 1.1 days to reach 50% of the pre-disturbance grand mean, 2.1 days to reach 75% and 4.3 days to reach 100% recovery.  Other disturbances from both natural (birds and sea lions) and unnatural events (boats and aircraft) appeared to occur frequently and typically resulted in up to 20% of the animals leaving the haulouts.  Responses of sea lions to different disturbances were site-specific and indicated varying degrees of sensitivity.

RELATED PUBLICATIONS:

A review of the potential effects of disturbance on sea lions: assessing response and recovery. Kucey, L., and A.W. Trites. 2006. In A.W. Trites, S. Atkinson, D.P. DeMaster, L.W. Fritz, T.S. Gelatt, L.D. Rea and K. Wynne (eds), Sea Lions of the World. Alaska Sea Grant College Program, University of Alaska, Fairbanks. pp. 581-589. abstract Human intrusion within areas of sea lion habitat is increasing worldwide, leading to concerns about disruption of distribution and daily activities of sea lions. Sea lion responses to disturbance can be quantified by recording changes in behavioural patterns, documenting numbers of animals on shore before, during and after the disturbance, or by measuring physiological stress of individual animals. However, assessing recovery is not so straightforward, as highlighted by an example from a study of the short-term effects of disturbance on Steller sea lions. Recovery is generally recognized as a return to an original state or normal condition, but is often operationally defined as a percent-return to pre-disturbance numbers or behaviours. Simple interpretation of disturbance effects can be easily confounded by concurrent natural seasonal changes in behaviours or haulout patterns, or by daily variability in numbers that can be attributed to weather, tidal cycle stage and other factors. Overall, a range of recovery criteria needs to be simultaneously applied when assessing the effects of human disturbance on sea lion populations. Insights gained from research on the effects of disturbance on Steller sea lions may help guide the development of studies undertaken on other species of sea lions.
Human disturbance and the haulout out behaviour of Steller sea lions (Eumetopias jubatus). Kucey, L. 2005. Graduate Thesis, University of British Columbia, Vancouver. 75 pages abstract There is considerable interest in assessing and mitigating disruptive effects of humans on the behaviour of marine mammals, especially for species with uncertain or decreasing population trends. Steller sea lions (Eumetopias jubatus) have been under intensive study throughout their range over the past few decades in an attempt to identify the causes of a large population decline in the Gulf of Alaska and Aleutian Islands. Consequently, disturbance due to scientific research has also increased at rookeries and haulouts. The purpose of my study was to determine if there were measurable short-term effects of human disturbance on the numbers of Steller sea lions using terrestrial sites. Numbers and composition of sea lions were documented for 2 – 3 week periods in southeast Alaska and British Columbia during summer (n = 8 sites) and winter / spring (n = 6 sites). They revealed considerable daily variation in numbers of sea lions hauled out within and among study sites that was related in part to prevailing environmental conditions. However, counts could not be corrected to account for environmental influences on the total numbers of sea lions using haulouts. Hauling out trends were examined for pre- and post-disturbance periods across multiple sites over two seasons. Predetermined research disturbances occurred to collect scats at the haulouts, and to brand pups at the rookery. Three methods were explored to assess local population recovery that addressed both quantitative and temporal aspects of sea lions returning to the study locations. Disturbances resulted in significantly fewer sea lions using haulouts during the post-disturbance period. Variation in the numbers of animals using the haulouts increased following the disturbance, but rates of change in daily numbers did not differ significantly between periods. Six of ten disturbed sites reached full recovery (100% of the pre-disturbance mean) on average 4.3 days after the research disturbance. To determine if individual behaviour was affected by disturbance, sea lions arriving on shore were followed to determine normal patterns of interactions and behaviour. Significant differences were noted in hauling out behaviour between animals that remained on land and those that returned to the water. Sea lions that returned to the water exhibited higher rates of behaviour and interactions with other animals during the week that followed the disturbance. Seasonal differences were also noted in the rates of behaviour and interactions that may be indicative of certain times of the year when sea lions are more sensitive to human presence and disturbance. Increasing levels of human–sea lion contact are expected as more and more people visit the remote coastal habitat of Steller sea lions. Future studies are needed to assess the influence of disturbance on sea lion redistribution within a critical recovery period, as well as to determine the physiological effects that sea lions experience with repeated human disturbance. Disturbance studies are an important aspect of conservation initiatives because they can help guide policies and establish restrictions to protect wild populations from human intrusion.

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Last updated 16 June 2006