21 March 2011

How many dolphins in the Gulf of Corinth? Pictures can tell

The following article has become available online:

Giovanni Bearzi, Silvia Bonizzoni, Stefano Agazzi, Joan Gonzalvo, Rohan J.C. Currey
Striped dolphins and short-beaked common dolphins in the Gulf of Corinth, Greece: abundance estimates from dorsal fin photographs
Marine Mammal Science (2011), doi: 10.1111/j.1748-7692.2010.00448.x

Capture-recapture methods relying on dorsal fin natural markings have never been applied successfully to striped dolphins, Stenella coeruleoalba, and were rarely used to assess abundance of short-beaked common dolphins, Delphinus delphis. We used digital photo-identification to obtain abundance estimates of striped and common dolphins living in mixed groups in the Gulf of Corinth, Greece. The proportion of either species was calculated based on the relative number of photographs of adult animals showing relevant portions of their body during conspicuous surfacings. Striped dolphins and common dolphins averaged 95.0% and 3.2% of all individuals, respectively. Animals showing intermediate pigmentation accounted for another 1.8%. Striped dolphin numbers were relatively high, with a point estimate of 835 animals (95% CI = 631-1,106). Common dolphins numbers were low (point estimate 28 animals; 95% CI = 11-73) and individuals were scattered within striped dolphin groups, indicating that this common dolphin population may be nonviable. Within a semiclosed Gulf exposed to considerable anthropogenic impact, the future of both dolphin species is of concern due to their suspected geographic isolation and restricted extent of occurrence. Information provided here can be used to inform timely conservation efforts.

A pdf copy can be obtained from the journal's web site (subscribers only).

ITALIANO: il metodo della cattura-ricattura mediante foto-identificazione è stato applicato a gruppi di stenelle e delfini comuni nel golfo di Corinto, in Grecia. Se ne è ottenuta una stima numerica puntuale, che per le stenelle è risultata relativamente alta (835); mentre appare nettamente inferiore per i delfini comuni (28), una specie che in Mediterraneo è quasi ovunque in forte declino.

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