Basking shark Cetorhinus maximus, (Lamniformes:
Cetorhinidae), at northern and western Iberian Peninsula waters (NE Atlantic)
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1
Oceanographic Center of Vigo, Spanish Institute of Oceanography, Spain
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2
Coordinadora para o Estudo dos Mamíferos Mariños (CEMMA), Spain
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3
Sociedade Portuguesa de Vida Selvagem, Portugal
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4
AMBAR Elkartea, Spain
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5
Coordinator for the Study and Protection of Marine Species (CEPESMA), Spain
The basking shark Cetorhinus maximus is a plankton feeding shark (Lamniformes: Cetorhinidae) distributed worldwide in boreal to warm temperature waters. The presence in Spanish and Portuguese Iberian waters is poor documented although this species occurs and it is well-known by fishermen. In this work we present data on basking shark presence in 30 year in Atlantic Iberian waters from monitoring data by involved organizations, also including records from monitoring data collected by the organizations involved, including records known by people, social networks and media
We record sightings off shore (31%), strandings (17%) and incidental fishing captures (52%). Incidental catch occurs mainly in fishing net used by artisanal fleet all along the continental shelf. Some of stranding records could be dead or injured sharks discarded at sea due to large size, low economic value and to comply with the legislation that prohibits its commercialization.
The presence of basking sharks concentrates mainly at north-western coast and data suggest a seasonality of abundance in the study area. 73% of the basking sharks appeared between the months of February and April. These results indicate a temporal pattern in the abundance which coincides with the scientific data of recent years with satellite telemetry indicating migratory movements of the species. In the Bay of Biscay, most registrations take place between May and July, and in Ireland and the United Kingdom, the highest density occurs in spring and summer. The decline in records after spring may be due to the movements of the species during summer and autumn to other waters, perhaps to northern areas that are rich in zooplankton at that time of the year. This recording pattern could be influenced (1) oceanographic conditions and the abundance of food resources are a key factor in the distribution and appearance of this plankton feeder, (2) displacement of the species to far pelagic areas where the observation and capture is less frequent by the shortage of human activity and (3) spatio-temporal changes in fishing effort throughout the year, and therefore in accidental catches. Although the records of the species are mainly concentrated in Galicia, the net fisheries work throughout the coast in all the area. The knowledge of species occurrence and mentioned factors will allow clarifying the presence and working on conservation problems in the study area.
Acknowledgements
Authors wish to thank the volunteers of the Marine Mammals Stranding Networks of Galicia (CEMMA). We would like to thank skippers and crew of fishing vessels for kindly share their knowledge, observations and incidental captures.
Keywords:
Basking shark,
bycatch and discards,
Shark ecology,
Fisheries,
Fish migration
Conference:
XX Iberian Symposium on Marine Biology Studies (SIEBM XX) , Braga, Portugal, 9 Sep - 12 Sep, 2019.
Presentation Type:
Poster Presentation
Topic:
Ecology, Biodiversity and Vulnerable Ecosystems
Citation:
Valeiras
J,
Covelo
P,
Ferreira
M,
Ruiz
L,
Cermeño
P,
Laria
L,
Eira
C and
López
A
(2019). Basking shark Cetorhinus maximus, (Lamniformes:
Cetorhinidae), at northern and western Iberian Peninsula waters (NE Atlantic).
Front. Mar. Sci.
Conference Abstract:
XX Iberian Symposium on Marine Biology Studies (SIEBM XX) .
doi: 10.3389/conf.fmars.2019.08.00144
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Received:
19 May 2019;
Published Online:
27 Sep 2019.
*
Correspondence:
Dr. Julio Valeiras, Oceanographic Center of Vigo, Spanish Institute of Oceanography, Vigo, Spain, julio.valeiras@ieo.csic.es