Abstract
The reproductive histories of 41 adult bottlenose dolphin females were analysed using photo-identification data collected between 2006 and 2014 in four sub-areas of the eastern Ligurian Sea (northwest Mediterranean). The Rapallo sub-area revealed the highest (highly significant) frequency of encounters (per unit effort) of reproductive females in association with young individuals, therefore emerging as a candidate nursery area in the region. The estimated fertility rate of adult females ranged between 290 and 407 births per 1000 individuals per year, higher than that of other known bottlenose dolphin populations, with a calving interval between 2.45 and 3.5 years. These results will be useful for projecting future trends of this (sub)population.
Highlights
When variation in male abundance does not limit female reproduction, knowledge of female reproduction parameters is key to assessing population viability and formulating conservation plans (Caswell 2001; Fujiwara & Caswell 2001).Understanding the life history of long-lived species requires detailed information on fertility and mortality parameters (Caswell 2001; Stanton & Mann 2012)
37,477 km were covered throughout the entire area; a total of 286 adult dolphins were photo-identified, of which 41 fulfilled the strict requirements of the study design to be identified as reproductive females
Since 44 mothers were resighted during the year following their first sighting with a cub, of which only 33 were still in steady association with a young individual, the number of dead cubs was 11 and the estimated cub mortality was 25% (11/44), corresponding to a cub survival of 75% (Table III). This is a first study of the reproductive parameters of female bottlenose dolphins in the Mediterranean, based on a 9-year-long sighting-history data set and related photo-identification from the eastern Ligurian Sea
Summary
When variation in male abundance does not limit female reproduction (as for polygamous or promiscuous species), knowledge of female reproduction parameters is key to assessing population viability and formulating conservation plans (Caswell 2001; Fujiwara & Caswell 2001).Understanding the life history of long-lived species requires detailed information on fertility and mortality parameters (Caswell 2001; Stanton & Mann 2012). A first approach to investigating cetaceans’ life histories has been based on stranding data (Stolen & Barlow 2003; Arrigoni et al 2011) Another fruitful approach is based on data sets of sightings (possibly repeated over a number of years) of individuals permanently marked by photo-identification techniques (Würsig & Jefferson 1990). These data, typically documenting nursery areas, group composition, social behaviour, spatial patterns and female reproduction, may provide valuable information on the population structure (Fujiwara & Caswell 2001; Rossi et al 2014b; Fruet et al 2015). The only available demographic studies regard the population structure of the Mediterranean fin whale (Balaenoptera physalus), analysed by both stranding (Arrigoni et al 2011) and photo-identification data (Rossi et al 2014b), and the mortality of the Mediterranean bottlenose dolphin analysed by strandings along Italian and French Mediterranean coasts (Rossi et al 2014a)
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