Measuring the effect of human activity on Weddell seals (Leptonychotes weddellii) in Antarctica

Although guidelines exist for approaches to, and vehicle use (over-snow vehicles, aircraft and watercraft) in the vicinity of, Weddell seals (Leptonychotes weddellii), there has been no scientific assessment of the effectiveness of these guidelines in minimising disturbance to the seals. This study examined tqe response of Weddell seals to various forms of human activity that the seals are currently exposed to. A series of controlled experiments were conducted to measure, (i) the immediate behavioural and physiological responses of lactating W ~ddell seals (and their pups) to approaches on foot, and the factors affecting the seals' respons~, (ii) the temporal ( - nature of the seals' response to repeated pedestrian activity fil?.d (iii) the immediate behavioural response oflactating cows to over-snow vehicle operations, and the factors that affect their response. In addition, sound/distance profiles were developed for commonly used Antarctic vehicles ~d the assumed detection threshold of Weddell seals was determined to investigate whether the noise generated by a range of vehicles had the potential to affect Weddell seals. Most lactating Weddell seals and lone pups responded to visits on foot {from 20- 5 m from the seals) by becoming alert. The separation distance at which the cows became alert was dependent upon the approach type (a single person or group of people), the distance a cow was from the water, the distance she was from a conspeci:fic, and whether her pup was exposed (i.e. whether the pup was between the approachers and the cow). The relative importance of these factors indicated that the - seals perceived pedestrians to be a threat, but that the level of threat was low. Regular and frequent approaches by a single person to lactating Weddell seals over a short time period(< 2 hours) produced evidence of rapid habituation. However, irregular approaches over a longer time period (~3 weeks), did not result in seals showing any sign of having habituated. The results suggested that the cows may have already become sensitised to human activity prior to the experiment and that pups became sensitised to pedestrian activity. Onshore heart rate of the seals in the absence of people revealed a daily periodicity in rate as well as three distinct heart rate patterns during resting behaviour and when the seal was looking in the water, i.e. the seal has its head immersed in water. Intra seal variation in heart rate highlighted the importance of obtaining baseline data at a fine scale (e.g. hourly) before heart rate can be used as a proxy for stress in human-wildlife interactions studies. Pedestrian approaches to a lactating seal did not elicit a heart rate response, suggesting that the approaches were not considered to be negative stimuli. Most lactating Weddell seals responded to the operation of over-snow vehicles by becoming alert. Response was dependent upon the distance at which the vehicles were driven, the position of the pups in relation to the cow and the distance the cow was from the water. The relative importance of these factors indicated that the seals perceived the vehicles to be a threat, but that the level of threat was low. Quantifying the effect of noise on the vocal behaviour of Weddell seals required the development of an assumed detection threshold of the species and sound/distance profiles of the commonly used vehicles in Antarctica. Much of the noise generated by these vehicles at the tested distances and speeds was barely audible to seals. However, there were some instances where the noise would have been cl~arly audible to seals both hauled out on ice and underwater. These higher noise levels were, however, still below the noise levels generated by the animals themselves and were therefore not expected to cause physical damage to the seals.- Manipulative experiments did indicate th~t the underwater vocal behaviour of Weddell seals could be affected by continuous Hagglund noise, manifest as a decrease in the calling rate of seals. This study has shown that the existing guidelines used in the Australian Antarctic Territory could be improved ifthe goal of management is to minimise disturbance to Weddell seals. Furthermore, the study has shown that the responses of the seals were influenced by a number of factors and that these co_uld be incorporated into visitor and operational guidelines in order to increase their effectiveness and sensitivity.