A demographic approach to cetacean conservation based on photo-identification and stranding data

The preservation of the biodiversity is nowadays one of the most difficult challenges for conservation biologists, as an increased number of species has been threatened or overexploited in the last years. Demography, “the science of the populations”, can furnish useful tools to improve natural population management and conservation. The knowledge of life-history traits and demographic parameters is needed to develop demographic models; these models, based on life-history tables and transition matrices, are essential to foster population conservation, as they allow to assess population performance, project population trends overtime and then suggest specific measures for their protection. This is mostly meaningful with long-lived and slow reproducing species, as cetaceans, threatened by many sources of mortality and environment stress. Nevertheless, few studies deal with the demography of these marine mammals because of the difficulty in collecting this kind of data, thus the main cetacean life-history traits are still largely unknown, especially in the Mediterranean Sea. The aim of my PhD thesis is to improve the demographic knowledge on Mediterranean fin whale (Balaenoptera physalus Linneaus 1758) and bottlenose dolphin (Tursiops truncatus Montagu, 1821), analyzing stranding and photo-identification data. The most exhaustive long-term photo-identification dataset available for the Mediterranean fin whale, recorded by Tethys Research Institute in the Pelagos Sanctuary over 1990-2007, was analyzed in order to obtain demographic information on the only mysticete regularly occurring in our basin. The analysis of the annual encounter rate revealed an uneven occurrence of the fin whale across the years and months: an anomalous reduction between 2001 and 2004 and a higher abundance of the target species in the Corso-Ligurian Basin in late-spring and summer were observed. Using the photo-identification technique, 431 different fin whales were recognized, 318 of known size: 6 calves (≤10 meters), 33 immatures (10-15 m), 261 adolescents-adults (>15 15 m over 1990-1999 was 539 (95% CI = 345-732), using the capture-mark-recapture POPAN model. After correcting the number of calves by a mathematical approach, a static-life history table was set out for the period 1990-2007. The highest survival was between calf and immature (61.1%), while the minimum between adolescent-adult and old (2.5%) vital stages. The overall life expectancy was 6.3 years and 14.3 years at entry in the adolescent-adult stage. Stranding data are a valuable and quite inexpensive source of information on demography of marine mammals. The analysis of 1105 bottlenose dolphins stranded along Italian and French Mediterranean coasts between 1986-2011 highlighted a not homogeneous spatio-temporal distribution. The highest number of specimens/coastal km were recorded along Italian Adriatic Sea and a significantly higher number and homogeneous distribution of strandings were found over 1999-2011. The finding of newborns throughout the year revealed a continuos reproduction of the target species in the Mediterranean. The sex ratio of strandings was significantly biased toward males (1.38:1). A mortality table was set out sharing female of known size (n=308) into 4 vital stages: cub (≥90 <180 cm, 0-1 yr), calf (≥180 <220 cm, ≥1 <3 yr), juvenile (≥220 <270 cm, ≥3 <7 yr), adult (≥270 cm, ≥7