Publication Date:
2021-10-13
Description:
Object of this study was to gather further information on the influence ofhuman activities on gray whales (Eschrichtius robustus) in San lgnacio lagoon, with special emphasis on the potential impact of whale-watching tourism. Beyond that, 1 evaluated the possible consequences of the proposed development of a salt production facility at San lgnacio lagoon. The investigations were made on undisturbed and disturbed animals to assess the behavioral responses of gray whales. 1 recorded diving behavior, behavior during an interaction with boats and whale movements within the lagoon. The dependence of the behavioral responses on the quality of the human impact was determined as well. 1 also examined the applicability of digital photography as an aid for behavioral observations and photoidentification of gray whales. Human impact caused the investigated gray whales to dive longer and to significantly reduce respiration rates. These reactions to disturbance were observed in calves as well as in mothers and adults without calf. Gray whales who were participating in an interaction with boats changed significantly more often in swimming direction and accelerated significantly more frequently in swimming velocity opposed to undisturbed animals. Besides, adults without calf showed a significant increase in steep dives. Reactions of gray whale mothers and adults without calf seemed to be more dependent on the degree of the human impact than those of gray whale calves. Adults tended towards a more distinct avoiding reaction with increasing boat noise and increasing boat speed. Observations of whale movements showed that the animals do not avoid the whale-watching area but moved more frequently into this spacious region when boat numbers increased. In contrast to that observation, boat traffic in a relatively narrow channel of San Ignacio lagoon affected the behavior, especially of mother-calf pairs, very strongly. The presence of boat traffic in this channel resulted to a displacement of mother-calf pairs into an alternative, perhaps sub-optimal channel. The observed behavioral responses of gray whales were predominantly of relative short durations and were therefore classified as short-term disturbance. Possible long-term effects of these anthropogenic impacts could not be evaluated. The frequency of human impacts is undoubtedly decisive for a single animal. Repeated disturbance could have negative effects on the energy budget of the whales. Because of the long migration to the arctic feeding grounds subsequent to the stay in San Ignacio lagoon, a decreasing in energy reserves could lead to a considerable 〈langer especially for the new bom calves. Human activities in San Ignacio lagoon should therefore not be allowed to increase and the existing whale-watching tourism should be regulated through additional restrictions and a more accurate econsideration. lt was not possible to use digital photography as an aid for behavioral observations since no recorded whale was identified twice over the season. However, the method itself proved quite applicable. Also, the digital technique could be used for the photoidentification of gray whales, despite the lower resolution of the pictures in opposite to the analogue photography.
Type:
Thesis
,
NonPeerReviewed
Format:
text
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