Dol­phins whis­tle for a share of the catch

Sunday Star-Times - - WORLD -

Dol­phins that reg­u­larly in­ter­act with hu­mans have de­vel­oped a distinc­tive whis­tle to iden­tify their spe­cial­ist role within the pod, re­searchers have found.

The dis­cov­ery was made fol­low­ing ob­ser­va­tions of dol­phin be­hav­iour in the town of La­guna, in the south­ern Brazil­ian state of Santa Cata­rina. Since the mid-19th cen­tury, the town’s pris­tine shal­low waters have been the set­ting for a re­mark­able ex­am­ple of co­op­er­a­tion be­tween hu­mans and wild an­i­mals.

For sev­eral weeks ev­ery au­tumn, fish­er­men can be seen stand­ing in knee-deep wa­ter, close to the beach, nets in hand. They are wait­ing for a group of bot­tlenose dol­phins, 200 me­tres out to sea, to chase mul­let fish to­wards the shore.

When a shoal ap­proaches, the dol­phins give a clear sig­nal – an abrupt dive or tail slap. At that pre­cise mo­ment, the fish­er­men cast their nets.

With­out the help of the dol­phins, the hu­mans would never see the ap­proach­ing fish. The perk for the dol­phins is an easy catch: in­di­vid­ual fish flee the nets and head straight for their mouths.

The fish­er­men have long no­ticed that only a small el­e­ment of the lo­cal dol­phin pop­u­la­tion par­tic­i­pates in the joint hunt, and even have names for those in­di­vid­u­als who co-op­er­ate. Now a team of marine bi­ol­o­gists from the Fed­eral Uni­ver­sity of Santa Cata­rina has found that th­ese dol­phins also emit a no­tably dif­fer­ent whis­tle, fea­tur­ing fewer ris­ing notes.

Mauri­cio Can­tor, the lead scientist be­hind the re­search, told New Scientist mag­a­zine that the vari­a­tion was most prob­a­bly a way for the dol­phins to iden­tify them­selves as mem­bers of a par­tic­u­lar group within their pod.

‘‘It is as if they speak the same lan­guage but use some ‘ex­pres­sions’ that are ex­clu­sive to their so­cial com­mu­nity,’’ he said.

Dol­phin so­ci­eties are known to be com­plex, with spe­cific ‘‘net­works’’ within fam­i­lies ful­fill­ing dif­fer­ent tasks. The vari­a­tion in lan­guage is per­haps a way of in­di­cat­ing who does what.

The sci­en­tists be­lieve the co­op­er­a­tive trait, and the dis­tinct di­alect, is passed from gen­er­a­tion to gen­er­a­tion as mother dol­phins pass the knowl­edge by ex­am­ple to their calves.

REUTERS

Dol­phins that reg­u­larly in­ter­act with hu­mans can be iden­ti­fied by a distinc­tive whis­tle, sci­en­tists say.

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