Monk Seal Fact Files
Mediterranean Monk Seal
Sexual dimorphism [Glossary], site fidelity [Glossary] of breeding females (Gazo et al. 1999, Gücü et al. 2004) and defence of aquatic territories by adult males, suggests that Monachus monachus is moderately polygynous [Glossary] in its breeding structure (Sergeant et al. 1978, Cebrian 1994, Matono & Pires 1998, Pastor et al. 1998, Forcada et al. 1999, Güçlüsoy and Savas 2003a).
Little is known about the age at which Mediterranean monk seals reach sexual maturity. Early reports associated the attainment of sexual maturity with animal body size (Sergeant et al. 1978, Ronald & Yeroulanos 1984), in contrast to more recent studies that link it to the age of the animal.
The earliest estimate of attainment of sexual maturity for a Mediterranean monk seal was first reported to be 5-6 years (King 1983). Over the years, this was revised downwards, to 5 (Marchessaux & Pergent-Martini 1991), 4 (Marchessaux 1989), and 3-4 (Cebrian 1993).
The earliest sexual maturity ever observed was of a female at the Cabo Blanco colony (Mauritania/Western Sahara) aged 2.5 years, which corresponds to the lowest age band recorded for any phocid species (Gazo et al. 2000b). Male Mediterranean monk seals are estimated to mate for the first time in their 7th year. Mating occurs in the sea (Pastor et al. 1998).
Throughout the species’ distribution range, reproductive events are seasonal and show their highest concentration during the months of October and November (Duguy & Marchessaux 1992, González et al. 1994, Pastor et al. 1998, Dendrinos et al. 1999, Gazo et al. 1999, Pires & Neves 2001, Güçlüsoy and Savas 2003a, Gücü et al. 2004). At the monk seal colony at Cabo Blanco, births have been recorded throughout the entire year (Gazo et al. 1999), although there appears to be a shift towards September as the month with most births. This protracted pupping season may be attributed to the location of the colony in subtropical latitudes and its particular ecological parameters (Pastor & Aguilar 2003).
The highest pup production has been recorded at the Cabo Blanco colony, which averaged approximately 50 pups per year prior to the 1997 mass die-off (Pastor et al. 1998), and today, approximately 28. The sex ratio does not differ significantly from 1:1 (Gazo et al. 1999). Births in smaller colonies, such as the one at the Northern Sporades Islands, Greece, average approximately 8 pups per year (Dendrinos et al. 1998). At the Desertas Islands of Madeira, pup productivity has increased from 1 to 3 pups per year (Pires, unpublished data).
After a gestation lasting approximately 9 to 11 months (Marchessaux & Pergent-Martini 1991, Pastor & Aguilar 2003), one pup is born (King 1956).
Before giving birth, females will often retreat to isolated areas within caves, which they actively defend against other approaching seals (Layna et al. 1999, Dendrinos et al., in prep.).
Despite an earlier assumption that Mediterranean monk seals reproduce every other year (Troitzky 1953, Ronald 1973, Scoullos et al. 1994), it is now generally accepted that females can give birth in consecutive years (Panou et al. 1993, Pires & Neves 2001, Güçlüsoy and Savas 2003a, Pastor & Aguilar 2003).
The duration of suckling may be subject to various environmental and health factors and thus also partially responsible for apparently contradictory reports. These have ranged from just 6 weeks (Troitzky 1953, Ronald and Healey 1976, Sergeant et al. 1978), to 5 months (Mursaloglu 1984). More comprehensive field research at Cabo Blanco (Mauritania/Western Sahara) (Pastor & Aguilar 2003) and Madeira has suggested that lactation extends over the first 3 to 4 months of a pup’s life. During this time the mother does not fast, but regularly leaves the pup in order to forage (Dendrinos et al. 1999, Pastor & Aguilar 2003, Gazo & Aguilar 2005). Thereafter, weaning appears to occur gradually, in contrast to the typical phocid pattern which is characterized by an abrupt interruption of suckling (Riedman 1990, Trillmich 1996, Gazo, Lydersen & Aguilar 2006).
Pupping sites that are close to feeding areas and offer protection from predators and storms encourage the tendency of female pinnipeds to aggregate (Boness 1991, Güçlüsoy and Savas 2003a). This might also explain why female Mediterranean monk seals show a strong site fidelity to specific pupping sites throughout their distribution range (Gazo et al. 1999).
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