Izurde marradunaren [Stenella coeruleoalba (Meyen, 1833)] banaketa eta habitat-erabilera euskal kostaldean

Abstract

[EUS] Ikerketa honetarako, AMBAR elkarteak zetazeoen azterketarako jarraipen programan 2013tik 2018ra bildutako datu-basea erabili da, eta helburu nagusia, euskal kostaldean zehar aurkitzen den izurde marradunaren [Stenella coeruleoalba (Meyen, 1833)] inguruko ezagumendua emendatzea da, lehen lan zientifiko bat idatziaz. Izurde marraduna Delphinidae familiako bigarren zetazeorik begiztatuena izan da [delfinidoen begiztatzeen % 22, izurde arruntaren (Delphinus delphis) ostean] eta haren batimetriaren araberako banaketa 200 eta 2073 metro bitartean kokatu dugu. Izurde marraduna eta haren kumeak udan agertzen dira gehien, eta gainerako urtaroetan begiztatzeak murriztu egiten dira. Horren arrazoia irteera kopuru altuagoa da, korrelazioa baitago irteera-kopuru eta begiztatze-kopuruen artean. Begiztatze-portzentajeak behatzean berriz, maiatzean eta ekainean ditugu baliorik altuenak kume zein helduetan, eta hori, antxoaren ugaritasunaren ondoriotzat hartzen da. Urtez urtez, hauen populazioak konstante mantendu dira. Udako hilabeteetan kostaldera asko gerturatzen direla behatu da, sardinaz elikatzeko gehienbat, eta beste urtaroetan ur sakonagoetan mugitzen dira, nagusiki miktofideetan oinarritutako dieta jarraitzeko, salbuespenak salbuespen. Taldeak 11-50 indibiduoz osatuta egongo dira nagusiki, nahiz eta hau talde osoaren portzentaje bat besterik ez dela uste den.

[EN] The data base compiled by the AMBAR organization between the years 2013 and 2018 has been used as a resource for this investigation, and the main goal is to amend the knowledge of the stripped dolphin [Stenella coeruleoalba(Meyen, 1833)] through the Basque Coastwith the first research about it . Following the short-beaked common dolphin (Delphinus delphis), the stripped dolphin is the second most extensively sighted dolphin of the Delphinidae family, with 22 % of sightings. Its bathymetry has been set between 200 and 2073 metres. The stripped dolphin and the offspring’saremostly spotted in the summertime, and there are fewer sightings along our coasts the rest of the year. The reason for such difference between seasons is the number of outings which take place. There is an interrelationship between the number of outings and the sightings. So if we focus on the sighting frequency, the month with the highest ones of the stripped dolphin is May and the offspring’shighest sighting frequency is during the month ofJune. During the winter seasons the number of sightings is null,the sightings are null due to the bad weather conditions which impede the outings. Year after year and season after season, the number of these mammals has kept stable, even if it is easier to come across them closer to the coast during the summer. As a matter of fact, these dolphins come close to the shore during the months of summer, especially to feed fromsardines, whereas the rest of the seasons they swim in deeper waters to be able to base their diet on myctophids. Nevertheless, sighting frequency ishigh in May because anchovy presence is abundant. They travel in groups of 11-50 dolphins; however, this is thought to be only a percentage of the whole group.