Disturbance at seal haul-out at breeding sites due to human activities has been increasing over the past 30 years.

A review of studies of the effects of seal disturbance at pinniped colonies world-wide may be downloaded from the link below. Many studies dating from the 1970s have focused on phocids, mainly harbour seals, and most have concerned recreational disturbance. Since 2000 disturbance of other phocid species have received more attention and there has also been a growing literature on recreational disturbance of otariids (fur seals and sea lions).  

The types of disturbance described here include tour boats, paddle boats (kayaks and canoes), speed boats and jet-skis and recreational ‘swim-with’ activities, including snorkelling and scuba diving, and also aircraft over haul-pouts, icebreaking vessels and snowmobile activity. Pinniped haul-out groups considered include non-breeding animals, moulting groups and breeding groups with suckling pups.

Overt signs of seal response to disturbance grade from increased alertness and sometimes threat displays to moving towards the water and flushing into the water. Impact on pupping groups includes temporary or permanent pup separation, disruption of suckling, energetic costs and energetic deficit to pups, physiological stress and sometimes enforced move to distant or suboptimal habitat. Impact on moulting groups includes energy loss and stress, while impact on other haul-out groups causes loss of resting and digestion time and stress. Speed powercraft in the vicinity of seal haul-outs create the risk of physical trauma to animals in the water.

A distinction is made between pinniped species which are inherently ‘tame’ and readily allow very close human approach often to less than 20m with little overt response (most fur seals, sea lions and southern phocid seals) and those which are generally wary of human approach and flush to the water when boats may be at a distance of 200m or more (grey and harbour seals). A distinction is made between positive human-seal interaction in the water (as with juvenile grey and monk seals) and tolerance or mild avoidance of human swimmers (as with most otariids). Further distinction is made between seal species habituation to sensitive human activity, allowing for non-intrusive tour boat visits or pedestrian visits from behind a barrier, allowing for pinniped co-existence on the same coastline and conditioning, where initially positive interaction between seals and people can become a problem for either people or seals (as has occurred with monk seals in particular).  

Disturbance is considered to occur if the human activity disrupts or alters the animals’ normal behaviour. This includes increased alertness or movement on haul-out sites and flushing to the water, which are generally not understood by tourists to be a problem.  From a strictly conservation perspective disturbance is only important if it results in decreased survival, reproductive rate or population shift or decline. Such effects have been recorded, eg for Hawaiian monk seals, California sea lions in the Gulf of California and harbour seals in Alaska – but are generally not immediately obvious and may require long term monitoring.

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