Pupping season, perinatal sex ratio and natality rates of the Mediterranean monk seal (Monachus monachus) from the Cabo Blanco colony

Abstract

Pupping seasonality, annual pup production, reproductive rate and sex ratio at birth were determined for the Mediterranean monk seal Monachus monachus colony at Cabo Blanco, the only surviving population of the species which still shows a colony structure. Data were collected by means of a monitoring programme that operated continuously in the main reproductive areas of the population during the period March 1993±May 1997. Most (84%) of the pups observed were born in two caves separated by a short distance. Although both caves were used by females to bear the pups, preferences greatly¯uctuated from season to season with no apparent trend. Reproduction occurred throughout the year with a small peak of births in October. This unusual lack of seasonality is associated with the low latitudinal location of the colony and the effect of the upwelling that provides constant food throughout the year. The neonatal sex ratio did not differ signi®cantly from 1 : 1 and the estimated annual productivity ranged from 44±58 pups. Taking into account population numbers, the annual birth rates were estimated to range from 0.3 to 0.43 pups per reproductive female, an extremely low rate when compared to other pinniped populations, particularly those of a similar size. Such low rates may be either an evolutionary determined characteristic of the species or a demographic consequence of the low population density over the last few centuries. Coupled with high pup mortality rates, this may account for the observed non-recovery of the population.

Diving behaviour of Mediterranean monk seal pups during lactation and post weaning

“…Births in Mediterranean monk seals are recorded throughout the year, and a small peak occurs in October (Gazo et al 1999). This non-seasonal breeding activity may be related to the stable weather conditions and relatively constant productivity of the area inhabited by these seals (Tilot 1993, Gazo et al 1999.…”

“…Births in Mediterranean monk seals are recorded throughout the year, and a small peak occurs in October (Gazo et al 1999). This non-seasonal breeding activity may be related to the stable weather conditions and relatively constant productivity of the area inhabited by these seals (Tilot 1993, Gazo et al 1999. The nursing behaviour of the Mediterranean monk seal also differs from the phocid norm in that lactation is protracted, moult is not associated with weaning, females feed during the nursing period and pups remain unattended while females feed at sea (Gazo & Aguilar 2005, Pastor & Aguilar 2003.…”

“…Bearded seal pups, which are born with lanugo that is already moulting (Kovacs et al 1996), enter the sea on the very day they are born (Lydersen et al 1994), but their blubber layer is already well developed (Kovacs et al 1996). In contrast, Mediterranean monk seal pups are born with a lanugo that molts at 50 d (Gazo et al 1999). Both this species and the congeneric Hawaiian monk seal spend a lot of time in water long before moulting (Boness 1990).…”

“…This area is inhabited by the only large aggregation of Mediterranean monk seals that exists today, with a total population estimated at 109 individuals (CV = 0.14; 95% CI: 86 to 145) (Forcada et al 1999). Many individuals, including most lactating females and their pups, haul out onto the beaches and inside 2 caves, where they can be monitored easily (Gazo et al 1999).Seals were captured using a net mounted on a metal frame (2.0 × 1.3 m) . The frame was submerged horizontally in a natural channel (1 m deep) located near the entrance of the main breeding cave.…”

“…The plastic base-plate then remained glued to the back of the seal until the next moult. We recovered 3 TDRs; another was lost because of the accidental breaking of the zip ties 6 d after attachment.We made daily observations on the nursing behaviour of the tracked seals with a remote-control video camera which was installed on the roof of the breeding caves (Gazo et al 1999). We then assessed behaviour at the end of the lactation period through observations conducted by scan sampling every 30 to 60 min and ad libitum sampling between scanning sessions (Altman 1974).…”