Mediterranean Monk Seal
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IUCN STATUS (2010) CRITICALLY ENDANGERED
Distribution and Numbers
The Mediterranean monk seal is the most endangered pinniped species worldwide and is currently on the brink of extinction. Although formerly found all over the Mediterranean Sea, Black Sea and northwest African coast, the species' numbers have now been reduced to perhaps less than 600. Whereas the former distribution was continuous throughout its range, the present distribution is discontinuous, with probably little exhange between the separated populations (Johnson et al., 2006). The remaining seals are found in remote and undisturbed areas around the north-east Mediterranean Sea (Greece and Turkey) and northwest African coast (Mauritania), with a few individuals along the Mediterranean coast of Morocco and the Portuguese Desertas Islands of Madeira (Johnson et al., 2006).
Photo: Matthias Schnellmann,
The Monachus Guardian
For centuries Mediterranean monk seals have been killed by fishermen who see the seals as competitors or accuse them of destroying their fishing gear. In the past the seals were also killed by those who believed that sealskin and seal parts were able to provide protection from a variety of medical problems. When European explorers discovered the monk seal colonies off the NW coast of Africa, they made short work of them to lucrative advantage. In the Mediterranean, sustained persecution coupled with disturbance and habitat degradation appears to have suppressed colony formation and led to fragmentation of relict populations. A 'naturally gregarious and beach-dwelling species' became transformed into 'a less social and reclusive inhabiter of caves' (Johnson et al., 2006). The final demise of the monk seal in the Black Sea may have been accelerated by the repeated capture of individuals for zoos and outdoor fairs in the 1970s (Öztürk, 1993). The mortality of monk seals by entanglement in fishing gear is still a problem, while over-fishing has also resulted in a general lack of food resources. The continually increasing use of motor vessels, expansion of fishing effort and areas, coastal construction and increased tourism have all contributed to difficulty in protecting monk seal habitat and preventing recovery of monk seal colonies.
The colony of monk seals on the Cap Blanc peninsula in Mauritania, NW Africa numbered ~270 individuals, incuding ~50% adults and 50% subadults, juveniles and pups (Jiddou et al., 1997). It was therefore the largest surviving population of Mediterranean monk seals by the mid 1990s and the only one to possess the actual social and numerical structure of a colony. However, in May-June 1997 there was a mass mortality of seals at this important colony. The mortality was first noted on May 05, and ended ~02 June. 47% of the population died, including 74% of adults. An initial diagnosis based on 4 of 17 of the dead seals and from blood samples taken from five live seals suggested the presence of a morbillivirus infection, probably from a small cetacean carrier (Osterhaus et al., 1997). However, there was also strong evidence for a toxic algae bloom in the Cape Blanc region at this time, and the dead seals were exposed to this, and the conclusion was that the algae bloom was probably the main cause of the mortality (Harwood et al., 1998). Fortunately the colony is now recovering, and believed to number about 200 individuals as of 2011 (Monachus Guardian, personal comunication).
Four pups whose mothers were presumed to have died durng the 1997 mortality were taken from caves on May 24–25, rehabilitated and released again, fitted with satellite tags, on September 20 and December 23 (Jiddou et al., 1997). They were apparently released some distance from the colony. The signal from one of the first two pups was lost after two days, while the other pup did not return to the coony but remained some 50 km suth of the release point (Harwood et al., 1998). The development of a protocol for rescue, rehabilitation and release of monk seals, in conjunction with the IUCN Re-introduction Specialist Group, was therefore recommended (Harwood et al., 1998).
|The species is listed as Critically Endangered on the IUCN Red List (Aguilar and Lowry, 2008) and as an Appendix I species under CITES. It is also listed as an Appendix II species under the Bern Convention, as an Appendix I and Appendix II species under the Bonn Convention, and as an Annex II and Annex IV species under the European Community's Habitats Directive. In Greece the Meditereanean monk seal was given complete protection in law in 1981, and a Strategy for the protection of the monk seal in Greece was published by Mom (the Hellenic Socity for the study and protection of the monk seal) in 1996 and revised in 2009.
Pup - photo : Cem O. Kiraç, SAD-AFAG
Pup - Photo: Alexandros Karamanlidis, MOm
Photo : Cem O. Kiraç, SAD-AFAG
Various protected areas have been created by diferent countries with the aim of protecting the Mediterranean monk seal within its present limited range. The difficulty of creating protected areas with boundaries is that the present distribution of monk seals is highly fragmented and discontinuous, and a protected area should be large enough to contain a Minimum Viable Population (MVP) (Durant and Harwood, 1992). To date, Marine Protected Areas for monk seals have been established at the Desertas Islands in Madeira, the National Marine Park of Alonnissos Northern Sporades in Greece, on the Aegean (at Foça and Yalikavak) and the Mediterranean cost of Turkey, and along the Côte des Phoques (Cap Blanc) in Mauritania/Western Sahara. In addition, Special Areas of Conservation (SACs) under the EU Habitats Directive have been proposed to initiate a wider network of protected areas. Conservation measures within each of these protected areas differ according to national laws and programmes (e.g. Wilson et al., 2001). Along the Turkish Mediterranean coast the establishent of several no-fishing zones has reduced entanglement and thus improved pup survival (Johnson et al., 2006). In March 2001, Mauritania announced a ban on all fishing, except traditional non-motorised fishing by local communities, along the Cap Blanc coast, and also strict protection of the caves used by the colony and surrounding beaches. Until then, the beaches had only been used by a few adult males.Since 2006 the beaches have been used by all classes of seals, including mothers and pups, and this important population is now believed to be recovering from its low point following the 1997 mortality. Nevertheless, the practices of artisanal fishermen continue to pose a threat to the seals (Johnson et al., 2006; Monachus Guardian, 2007, and seals are still being deliberately shot by fishermen, especially in parts of the Greek Aegean sea. Because the relict populations in each of the protected areas is so small, and probably well below the MVP, the potential survival of the population will depend heavily on variation in the inherent properties of individuals, eg fecundity, foraging ability, behavioural adaptibility etc, and also on environmental factors, including disease outbreaks, pollution events or hunting/fishing mortality (Durant and Harwood, 1992).
A computer simulation study of the extinction risks for monk seals suggests that population size within a reserve should be monitored by means of analysis of the number of sightings of identifiable animals, which should be observed directly on beaches or by using 'camera traps' placed at resting sites, including cave entrances (Durant and Harwod, 1992). Where there is a predictor of extinction (these are defined for small populatons of different sizes, and include measures such as zero pups born, low % of breeding adults, low % juveniles observed in a population), then every effort should be made to increase both juvenile and adult survival. Juvenile survival may be increased by rescue of abandoned pups and of seals entangled in fishing gear (Durant and Harwood, 1992).
Pups are nursed for a period now known to be about four months - a study of 9 pups at Cap Blanc found lactation lasted 103–149 days (Pastor and Aguilar, 2003; Aguilar et al., 2007), which is almost twice as long as any other phocid seal, and more than twice as long as the 5–6 week lactation of the Hawaiian monk seal. Pups sometimes suckle from females other than their mothers, and fostering - long term or short term -may sometimes occur (Aguilar et al., 2007). After the first week, the mothers of two pairs observed, along with a few other seals, in a Turkish cave (Mursaloglu, 1986) left the pup for some hours at a time to go fishing. When the mother was away, the pup mostly slept, and if hungry, would start to bleat, eventually producing a wailing cry if the mother did not soon return. Mother and pup communicated vocally and by close physical contact when reunited (Mursaloglu, 1986). While the mother was away, the pup was often washed to and fro by the sea flooding the cave, and the pup often responded by curling into an 'egg' shape, thus floating passively for some hours. The pup also learned to swim in quiet water, gradually gaining sufficient motor control. The pup showed no interest in fish swimming in the waters of the cave. About two months after moulting, the pup followed its mother out of the cave. Soon after the pup moulted, all the seals deserted the cave, including the mother and pup (Mursaloglu, 1986). More recent observations of a cave containing a mother-pup pair, three other adult females and a juvenile were achieved using a surveillance infrared camera system (Dendrinos et al., 2007). The mother and pup always occupied one section of the beach, while the other seals occupied the other section; the juvenile twice tried to approach the newborn pup, but was aggressively repelled by the mother. The surveillance system also recorded the date and hour of each seal's entry and exit to and from the cave. Using this monitoring system, two births were recorded in the cave in 2007 (Karamandilis et al., 2010). In both cases the birth was immediately followed by a period of intense nuzzling and vocalisations. The pup remained in close body contact for ~5h after birth before moving ~1adult body length away. The first suckling occurred ~6hr post-partum, and thereafter about every 4h for the next 4–5 days, after which the mother left the pup for the first time. A storm occurred when the pup was two days old, and the mother manoeuvred it back to the beach and placed herself between the pup and the waves. The 2nd mother simlarly stayed with her pup for 4–5 days before leaving it for the first time. In a study in Madeira, a mother was observed to protect a neighbouring pup from being swept away by the waves while its own mother was away fishing (Pires, 2004).The 2nd mother in the Greek study was scared away by a human intruder into the cave and did not return for 7h. The authors point out that the disturbance might have led to permanent separation and death of the pup (although in this case mother and pup were successfully reunited). Effective protection of pupping sites against disturbance is considered to be one of the outstanding conservation prioriities for the monk seal.
The principal mating season of the Mediterranean monk seal is from October to November. At Cap Blanc, several adult males display underwater territorial behaviour, with the apparent aim of gaining and maintaining access to females (Johnson et al., 2006).
Studies of diving, both by means of time depth recorders (TDRs) attached to the seals' backs and by direct observation, have identified two distinct types of dives, i.e. 'spot feeding dives' where the seal dives continuously, perhaps for several hours, in the same spot, and 'transit feeding dives' where the seals cover some distance along the shoreline (Kiraç et al., 2002). Monk seal dives recorded have been relatively shallow, with most dives of one adult male being <8m and only 5% exceeding 50m (Gazo, 1997). Pups develop their divng capacity while still nursing, but increase their diving activity after weaning. Nearly half the dives of newly weaned pups were U-shaped, with a mean depth of 11m, maximum depth of just over 20m and mean duration 150s. The long bottom times (mean 100s) suggested the pups were feeding. Older pups had a higher proportion of u-shaped dives in deeper water up to 40m (Gazo et al, 2006). One rehabilitated female pup (Artemis) aged about 5 months was recorded diving to 117m (Monachus Guardian 2009) while a male rehabilitated pup (Dimitris) was recorded diving to 180m (Monachus Guardian 2004). However, these were maximum dives, and the diving behaviour of rehabilitated pups may not be typical of the species.
Mediterranean monk seals are opportunistic feeders, mainly foraging close to the shore near shallow reefs. They seem to prefer bony fish such as mullet and sea bream, but also take benthic cephalopods (such as octopus) and crustaceans (such as lobster). Usually monk seals are considered to be relatively sedentary, with adult males having a home range of up to ~50km (Johnson et al., 2006). When facing a food scarcity, however, adults may travel considerable distances, 65–159nm Adamantopoulos et al., 1999), and these longer-range movements need to be considered when designing conservation measures (Wilson et al., 2001).
Mediterranean monk seals are relatively large seals, with an adult nose-to-tail length of ~280cm and weighing up to about 300kg or more, with adult males being slightly larger than females (King, 1983; Johnson, et al., 2006). The breeding season is not well defined, but most pups in the current distribution range are born in the autumn (Johnson et al., 2006). Pups are born measuring 88-103cm in length and weighing ~15-20kg. Nutritional weaning age is uncertain, being given at about 6 weeks (King, 1983), which would be similar to Hawaiian monk seals. More recently it has been observed that pups may be nursed for as long as 16–17 weeks. This is much longer than in any other phocid seal (Pastor and Aguilar, 2003; Aguilar et al., 2007). Weaning weight seems not to be known. Sexual maturity is usually reached at the age of 5-6 years, and it is thought that individuals can live up to 20-30 years of age (Johnson et al., 2006).
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