Telling one dol­phin from an­other

The Northland Age - - Local News -

Iden­ti­fy­ing in­di­vid­ual dol­phins us­ing pho­tos of the unique pig­ment pat­terns on their fins can help in the man­age­ment of the species ac­cord­ing to Niwa sci­en­tist Dr Krista Hup­man.

Ce­tacean bi­ol­o­gist Dr Hup­man, lead au­thor of two new sci­en­tific papers out­lin­ing an ac­cu­rate method of count­ing dol­phins by us­ing photo iden­ti­fi­ca­tion, said in­di­vid­ual an­i­mals’ dor­sal fins had been pho­tographed to es­tab­lish a cat­a­logue of dol­phins that could be dif­fer­en­ti­ated by dif­fer­ences in their mark­ings and pig­men­ta­tion pat­terns.

Sci­en­tists used cat­a­logues to de­ter­mine how many an­i­mals oc­cu­pied a re­gion and whether the pop­u­la­tion is in de­cline, but some dol­phins could be hard to count as they oc­curred in large pop­u­la­tions over vast ar­eas, and may lack dis­tinc­tive mark­ings.

For those rea­sons many sci­en­tists shied away from us­ing photo-iden­ti­fi­ca­tion to es­ti­mate pop­u­la­tions, us­ing aerial or ship­board sur­veys in­stead, meth­ods Dr Hup­man said may not be the best, and lim­ited the abil­ity to learn about in­di­vid­ual an­i­mals.

There was a way to use pho­toiden­ti­fi­ca­tion to es­ti­mate the num­ber of poor­ly­marked dol­phins, but it in­volved es­tab­lish­ing new meth­ods such as us­ing dor­sal fin pig­men­ta­tion pat­terns for in­di­vid­ual iden­ti­fi­ca­tion.

Over 2010-13 Dr Hup­man and a team of re­searchers col­lected more than 240,000 im­ages of dol­phins in the Hau­raki Gulf at dif­fer­ent times of the year. Al­most 31,000 of those pho­tos were deemed of suf­fi­cient qual­ity to use in the iden­ti­fi­ca­tion process.

They were com­pared man­u­ally, us­ing nicks, notches and pig­men­ta­tion pat­terns, re­sult­ing in 2083 in­di­vid­u­als be­ing iden­ti­fied.

“This study formed the largest cat­a­logue of com­mon dol­phins world­wide, which is a sig­nif­i­cant achieve­ment for ev­ery­one in­volved in this project,” she said.

“This is also the first study us­ing pho­toiden­ti­fi­ca­tion to de­ter­mine the abun­dance of a large pop­u­la­tion of dol­phins, and demon­strates that it is pos­si­ble for species with [few] dis­tinc­tive mark­ings. The com­bi­na­tion of dor­sal fin edge mark­ings and pig­men­ta­tion pat­terns pro­vided a ro­bust method for in­di­vid­ual iden­ti­fi­ca­tion.”

Iden­ti­fy­ing dol­phins solely by the pig­men­ta­tion on their dor­sal fins had been thought to be un­re­li­able, be­cause the pig­men­ta­tion changed over time and was not al­ways vis­i­ble, but it had been found on more than 95 per cent of adult com­mon dol­phins in the Hau­raki Gulf. They also ex­am­ined dol­phins with pho­to­graphic records span­ning more than 10 years, and found no sig­nif­i­cant changes in the pig­men­ta­tion pat­tern.

Now the team wanted to cre­ate a fully com­puter-au­to­mated sys­tem for iden­ti­fi­ca­tion whales and dol­phins from pho­to­graphs and video taken in the field.

The first step was ap­ply­ing an al­go­rithm to clas­sify in­di­vid­u­als on pig­men­ta­tion pat­terns alone.

“It used to take up to an hour to com­pare one dol­phin im­age to the en­tire cat­a­logue of in­di­vid­u­als. How­ever, by us­ing th­ese al­go­rithms, we can match an im­age to the cat­a­logue in a mat­ter of sec­onds,” she added.

PIC­TURE / KRISTA HUP­MAN

Pig­ment pat­terns on their fins make every dol­phin a recog­nis­able in­di­vid­ual.

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