All authors contributed to data analysis and manuscript preparation. All authors read and approved the final manuscript. Correspondence to Emma Hayes. Permissions to conduct seismic surveying, from which this data resulted were acquired from relevant authorities by the data owners.
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Search all BMC articles Search. Download PDF. Abstract This study reports observations of basking sharks Cetorhinus maximus sighted during an offshore geophysical survey conducted in July and August , west of Shetland, UK. Background The basking shark Cetorhinus maximus is the largest fish in UK waters and the second largest fish globally, reaching 12 m in length and weighing up to 4 t Sims, Full size image.
Methods Marine wildlife observations were conducted by experienced Marine Mammal Observers MMOs on an 80 m long seismic source vessel from July 2nd to August 9th in an area to the west of Shetland during hours of daylight. Basking shark breaching a and surface behaviour b observed west of Shetland. Discussion Breaching has been proposed as a male-male competitive behaviour during courtship displays and female basking sharks may breach to signal their readiness for mating Sims et al.
Conclusions Taking into consideration the number of sightings of basking sharks recorded during this survey, the breaching behaviour, the presence of young individuals as well as the suitability of the region in terms of oceanographic features, it is possible to suggest that this area west of Shetland may be an important habitat for basking sharks. Article Google Scholar Download references. Acknowledgements We thank BP for permission to use data collected during the west of Shetland seismic survey campaign and for endorsing the publication of this work.
Funding The authors declare that no funding was received for this study. Availability of data and materials All data made accessible during this study are included in this published article. Witt Authors Emma Hayes View author publications. View author publications.
The shark cleared the water for one second, and its leap peaked at a height of 1. To achieve this breach, the basking shark exhibited a six-fold increase in tail beat frequency and attained a top speed of approximately 5. The videos from boats and the land of both basking sharks and great whites breaching showed similar speeds of breaching in other individuals. Breaching was more energetically demanding than routine swimming breaching VeDBA 7.
During multiple breaching events, the ascent rate, swimming speed and acceleration were similar for every subsequent breach, although the ascent starting depth was often shallower than for the initial breach. The relatively low field metabolic rate that comes with being ectothermic makes energetically demanding behaviour relatively more expensive for sharks. Therefore, the costs of performing multiple breaches may accumulate more rapidly compared to endothermic whales, such as humpback whales Megaptera novaeangliae , which have been recorded breaching 17 times in a 6.
On average, sharks required an estimated Comparatively, the energetic cost of breaching for an 8 m basking shark weighing kg was estimated six times greater 63 to 72 kJ These differences may be attributed to the sharks in the present study being smaller, with the cost of breaching found to increase with increasing body mass A breach likely constitutes approximately 0. For comparison, the relative cost of performing a single breach in a 7. The question remains what the function of breaching is for basking sharks.
We are still far from certain what the function of breaching is for many aquatic species, but spinner dolphins, blacktip sharks and humpback whales are known to breach to dislodge epiparasites Gore et al.
Breaching may be used to visually signal between spinner dolphins, and between humpback whales Basking sharks breached during the night-time as well as the daytime, and have small eyes, suggesting that breaching is unlikely to be a visual signal. However, breaching may play a role in acoustic communication between distant groups of sharks. Basking sharks can apparently detect weak electric signals produced by zooplankton 18 , and some elasmobranchs use electro-sensory cues during courtship 19 , suggesting that breaching could convey readiness to mate.
It thus seems possible that the acoustic signal of breaching could be detectable and useful to basking sharks. We have no information in the present study about the presence of other sharks during breaching, although future work using animal-borne acoustic proximity receivers on large numbers of sharks, or aerial drones, could provide insight into the social networks of basking sharks, and whether they breach in proximity to conspecifics.
We propose that in the absence of a better explanation and given the predictable and persistent aggregations of basking sharks in Scottish waters, that breaching may be more likely to be related to intra-specific signalling, than anything else yet described.
We show using repeated direct measurements from three individuals, that the mechanical forces required for basking sharks to breach are considerable, but that basking sharks can breach repeatedly in quick succession. The role of breaching seems most likely to be related to intra-specific signalling and may add to a weight of evidence suggesting that Scottish waters may be an important site for breeding for the species.
Based on body length maturity estimates 3 , these two female sharks were juveniles. DD tags recorded accelerometry at 8 Hz on three orthogonal planes corresponding to the dorso-ventral, anterior—posterior and lateral axes of the animal.
Accelerometry data are comprised of i static low-frequency acceleration obtained by smoothing each of the acceleration measurements of acceleration in the X,Y and Z dimensions respectively with a running mean of three seconds [S1, S2], and ii dynamic high-frequency acceleration, obtained by subtracting the static acceleration from the raw data for the corresponding X, Y and Z axes and used to calculate the Vectorial Body Dynamic Acceleration VeDBA, see also Supplementary Materials.
Data were individually inspected, looking for rapid depth changes coinciding with peaks in dynamic acceleration to identify breaching events. For each breach, the ascent and descent phases of breaching events were described by changes in depth, VeDBA, speed and tail beat amplitude, including the maximum and absolute mean pitch and roll angles, the ascent and descent depths and duration.
See also Supplementary Materials. Cooke, S. Remote bioenergetics measurements in wild fish: opportunities and challenges. Part A Mol. Hussey, N. Aquatic animal telemetry: a panoramic window into the underwater world. Science , Sims, D. Sieving a living: a review of the biology, ecology and conservation status of the plankton-feeding basking shark Cetorhinus maximus. Article Google Scholar. Doherty, P. Testing the boundaries: seasonal residency and inter-annual site fidelity of basking sharks in a proposed Marine Protected Area.
Dolton, H. Assessing the importance of Isle of Man waters for the basking shark Cetorhinus maximus. Species Res. Gore, M. Transatlantic migration and deep mid-ocean diving by basking shark. Bren Whelan, another member of the team, also filmed the breaching behaviours of 20 basking sharks from the shore. The footage showed giant basking sharks leaping near vertically to about 1. Houghton estimates the sharks must have accelerated to a speed of 18 kilometres per hour for breaching — the same speed reached by white sharks.
The entire breaching event, from bursting to recovery, would cost an 8-metre-long basking shark 45 to 51 kilocalories — a greater energy expenditure than white sharks incur when they breach.
He points out that great white and basking sharks have very different cardiovascular capacities for their divergent lifestyles.
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