The effects of cage-diving activities on the fine-scale swimming behaviour and space use of white sharks

Wildlife tourism has become increasingly popular and is one of the fastest growing sectors of the tourism industry. A radio-acoustic positioning system was deployed to monitor the fine-scale movements of 21 white sharks (Carcharodon carcharias) and investigate the effects of shark cage-diving activities on their swimming behaviour and space use. This study contributes towards improving our understanding of the complex relationship between wildlife tourism and its effects on sharks, and assesses how tourism targeting sharks affects behaviour at a finer spatial scale than previously investigated. Our study demonstrated that shark cage-diving operators (SCDO) influenced the fine-scale three-dimensional spatial distribution and the rate of movement of white sharks at the Neptune Islands. White sharks stayed more than 30 m away from the SCDO on 21 % of the days detected, but spent a significant amount of time in close proximity to the SCDO on the remaining days. Individual variation was detected, with some sharks behaviourally responding to SCDO more than others. The degree of variation between individual sharks and the different levels of interaction (e.g. presence, proximity to SCDO, and consumption of tethered bait) highlights the complexity of the relationships between SCDO and the effects on sharks. To improve our understanding of these relationships, future monitoring of shark cage-diving operations requires proximity to SCDO to be recorded in addition to the presence within the area. Further work is needed to assess whether the observed behavioural changes would affect individual fitness and ultimately population viability, which are critical information to unambiguously assess the potential impacts of wildlife tourism targeting sharks.     

Informationsübermittlung mit Hilfe neurosekretorischer Peptide als Mediatoren

The Science of Nature - Morphological indications and new experimental results demonstrate that neurosecretory peptides or low-molecular proteins, respectively, appear to effect as mediators in...     

Behavioral evidence for eavesdropping on prey song in two Palearctic sibling bat species

Eavesdropping on prey communication signals has never before been reported for a Palearctic bat species. In this study, we investigated whether lesser and greater mouse-eared bats, Myotis blythii oxygnathus and Myotis myotis, find tettigoniid bushcrickets (Tettigoniidae) by eavesdropping on their mate-attraction song. Tettigoniids are known to be the most important prey item for M. blythii oxygnathus, while carabid beetles and other epigaeic arthropods are the most important prey for its sibling species, M. myotis, in many places in Europe. M. myotis locates walking beetles by listening for their rustling sounds. We compared these two species’ response to four acoustic prey cues: calling song of two tettigoniid species, the rustling sound made by walking carabid beetles, and a control tone. Individuals of both bat species attacked the speaker playing tettigoniid song, which clearly indicates that both species eavesdrop on prey-generated advertisement signals. There were, however, species differences in response. M. blythii oxygnathus exhibited stronger predatory responses to the calling song of two species of tettigoniid than to the beetle rustling sound or the control. M. myotis, in contrast, exhibited stronger predatory responses to the beetle rustling and to one tettigoniid species but not the other tettigoniid or the control. Our study (1) for the first time demonstrates eavesdropping on prey communication signals for Palearctic bats and (2) gives preliminary evidence for sensory niche partitioning between these two sympatric sibling bat species.     

Do cormorants injure fish without eating them? An underwater video study

The populations of European great cormorants (Phalacrocorax carbo) and North American double-crested cormorants (Phalacrocorax auritus) have increased sharply over the last decades and these piscivorous birds are suspected to deplete valuable fish stocks and compete with human fisheries. Beyond direct consumption of fish, cormorants are accused of injuring vast numbers of prey without eating them. Using underwater video systems, one of them mounted onto the back of tame Chinese cormorants, we evaluated the proportion of successful pursuits of cormorants on live fish. Trials were conducted with 6 great cormorants and 9 double-crested cormorants and involved a total of 676 prey pursuits. We show that, although they are regarded as highly efficient predators, cormorants aborted about half of their pursuits. However, detailed analysis of prey-capture behaviour in double-crested cormorants revealed that only 0.4% of the prey pursued was injured without being ingested. Further studies using miniature video systems deployed on free-ranging cormorants are required to complement our knowledge of their hunting tactics.