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Monk Seal Fact Files

Mediterranean Monk Seal

(Monachus monachus)

Threats

Alarmed by the species’ dwindling numbers, scientists meeting in Rhodes, Greece in 1978 drew up a comprehensive list of threats facing the Mediterranean monk seal — as well as a raft of measures to combat them (Ronald & Duguy eds. 1979, Israëls 1992, Johnson & Lavigne 1999b).

Although their significance or intensity may vary from region to region, a consensus of scientific opinion holds that these – often inter-relating – factors continue to constitute a serious threat to the species’ survival:


  • Habitat loss and deterioration (including increased pup mortality caused by pupping in unsuitable locations).
  • Deliberate killing (mostly by fishermen).
  • Accidental killing through entanglement in fishing gear.
  • Lack of food and depressed physical condition as a result of overfishing.
  • Lack of international coordination and funding of conservation and management actions (Marine Mammal Commission, in prep.).
  • Disease epidemics, cave collapses, oil spills, toxic algae blooms or other stochastic events.
  • Pollution.
  • Inbreeding depression resulting in reduced fecundity and pup survival.


Habitat loss and deterioration

Over centuries, human disturbance and persecution has driven the Mediterranean monk seal into increasingly marginal habitat — and continues to do so.

Sources from the ancient world, including Homer, Aristotle and Oppian, speak of herds of Mediterranean seals congregating on open sandy beaches, shoreline rocks and also “great arching caverns” – most easily accessible to humans.

More recent accounts from the Mediterranean, however, portray seals as solitary and reclusive, shying away from human contact and seeking refuge in small, inaccessible caves, often along remote, cliff-bound coasts. This erroneous view of the monk seal – as shy and reclusive – also gave rise to the modern myth that its name was inspired precisely because of its monastic nature (e.g. Attenborough 1987).

A recent review (Johnson & Lavigne 1999a) records various phases in this habitat deterioration:

  1. Monk seals were driven or eradicated from the sandy beaches, shoreline rocks and promontories that offered habitat to relatively large colonies of seals in ancient times.
  2. Easily-accessible ‘arching caverns’, with extensive sand or shingle haul-out areas, and capable of accommodating small colonies of seals, eventually proved too vulnerable to hunting pressures and in modern times to tourism disturbance (Bareham & Furreddu 1975, Johnson 1998).
  3. Seals were then progressively displaced from smaller caves capable of accommodating small family units. Typically, these incorporated a beach for sleeping, giving birth and the nursing of young, a barrier against storm surges, and possibly a ‘nursery pool’ for pups (Mursaloglu 1984, IUCN/UNEP 1988).
  4. With a boom in pleasure boating, diving, and mass tourism, human disturbance reached caves of inferior characteristics that could offer only limited protection from storm surges. While shelters of this type may sometimes incorporate underwater entrances cutting deep into rock faces – thus providing greater security from human harassment – they may also lack other essential characteristics (e.g. offering only a limited haul-out area or none at all).

The risks to the species are potentially far-reaching. Habitat deterioration has acted selectively against colony formation, in favour of individuals or mothers with pups (Sergeant et al. 1978, Johnson & Lavigne 1999a). By severely limiting social interaction, mating and breeding success has presumably been compromised (Johnson & Lavigne 1999a, b). In addition, storm surges may cause breakers to funnel into caves, washing nursing pups into the sea to be swept away and killed (Anderson 1979). As a result, annual pup survival rates in certain areas, such as the Cabo Blanco region, are extremely low – amongst the lowest to be recorded amongst pinnipeds (Gazo et al. 1999, 2000a).

By the late 1970s, it was concluded that the cave habitat occupied by the monk seal may not be adequate for the survival of the species, and that some return to sandy beaches might be essential to promote recovery (Ronald & Duguy eds. 1979, Sergeant et al. 1978).

Habitat conservation efforts appear to confirm that Mediterranean monk seals will return to open beaches to rest, nurse their pups and perhaps even breed if human disturbance in marine protected area core zones is eliminated. Such behaviour is now being observed consistently in Madeira’s Desertas Islands Nature Reserve (Pires & Neves 2000, Pires 2004).

Elsewhere, however, with human disturbance and harassment increasing dramatically since the 1970s, there is evidence to suggest that the suitability of available cave habitat may be continuing to deteriorate below even the most marginal standards.

Certified divers and researchers in Turkey have recently discovered monk seals occupying underwater entrance caves that can only be accessed through narrow tunnels cutting almost a hundred meters into cliff faces (Cem Kiraç, pers. comm. 1998). In some areas, seals have been discovered inhabiting caves that are, in reality, little more than water-filled crevices. With no internal beach or haul out area, the animals rest or sleep while floating in the water  (IUCN/UNEP 1988, Johnson & Lavigne 1999a, 1999b, Güçlüsoy & Savas 2003a, Johnson 2004).

It appears unlikely that caves of this type can meet the essential biological needs of the species. The same conclusion might also apply to less extreme forms of marginal monk seal habitat, where breeding viability is severely compromised by a number of factors associated with the characteristics and constraints of the habitat in question. These include reduction in gregarious behaviour (for which the species was so famed in antiquity), fecundity and pup survival (Anderson 1978 & 1979, Anon. 1990, Johnson & Lavigne 1999a &1999b, Güçlüsoy & Savas 2003a, Güçlüsoy et al. 2004a).

Deliberate killing

Although the Mediterranean monk seal was hunted commercially for its oil and skin until the late Middle Ages, population collapse eventually brought an end to such exploitation.

Deliberate killing of surviving individuals continued by fishermen, angered over damaged nets and ‘stolen fish’. As had been the case since at least Roman times, fishermen would club to death seals dragged ashore in their nets (Johnson & Lavigne 1999a, Johnson 2004). In poor communities, fishermen would continue to convert such opportunistic killings into fur, oil and meat. Elsewhere, fishermen angered by repeated net attacks would sometimes take the offensive, shooting seals in their shelters, or even dynamiting caves (Goedicke 1981, Johnson 1988). More recently, fish farm operators have also come into conflict with monk seals that raid their facilities, particularly where adequate protective netting has not been installed (Güçlüsoy & Savas 2003b).

Modern day research in Greece suggests that deliberate killing remains the monk seal’s main source of mortality, accounting for 43% of the deaths of adult/juvenile animals (Androukaki et al. 1999). A study in Turkey, by contrast, indicated that only 5 out of 22 dead seals had been deliberately killed (Güçlüsoy et al. 2004a).

Although most scientific papers have ranked direct killing by fishers as the single most important mortality factor affecting the species, it is important to distinguish between causes of adult mortality and causes of species decline (Johnson & Lavigne 1999b). Although the two are interrelated, field research is better able to record specific instances of direct killing than to quantify decline due to factors such as disturbance, habitat deterioration and unsuccessful breeding (Berkes et al. 1979). As a result, direct killing (mortality) has often been mistakenly cited as – or implied to be – the major threat to the species, regardless of the fact that the limited available data do not allow a comparative evaluation between this and other causes of species decline (e.g. UNEP/MAP 1987, Dendrinos 1998).

In a 1999 study (Androukaki et al. 1999), for example, Greek researchers found “natural mortality” in pups to be high, accounting for 91% of those found dead. With few telltale signs available for autopsy, however, such ‘natural’ causes might equally be attributable to the effects of disturbance and habitat deterioration.

Entanglement in fishing gear

Although there is some debate about its severity today, in the recent past accidental entanglement in fishing gear has posed a major threat to the Mediterranean monk seal. As a mortality factor, it has even played a significant role in the extirpation of Monachus monachus from several parts of the species’ former range (Johnson & Karamanlidis 2000).

Entanglement is not restricted to a specific type of fishing gear. Unlike pelagic species, however, monk seals appear to be most vulnerable to entrapment in static gear and discarded nets in coastal areas (Israëls 1992).

Entanglement involving different types of gear appears to have been widespread throughout the species’ former range, including baited hooks and trammel nets. In the Balearic Islands of Spain, it was reported that most losses occurred in tuna nets and that entanglement was second only to shooting as a source of mortality (Sergeant et al. 1978).

A similar picture emerges from the species’ current range. In Algeria, eight drownings were recorded between 1987 and 1990 on the west central coast (Boutiba 1996).

Research conducted in the Ionian islands of Greece has shown that accidental entanglement accounted for 23% of all recorded monk seal deaths (Panou et al. 1993). In a 1999 study incorporating data from both Aegean and Ionian Greece, researchers found that accidental deaths in fishing gear accounted for 12% of the total deaths recorded (Androukaki et al. 1999).

Prior to the establishment of a protected area, the extensive use of gill nets constituted a major threat to the survival of the small surviving monk seal colony in the Desertas Islands of Madeira. Animals had been dying frequently by entanglement in abandoned ‘ghost’ nets (Anselin & van der Elst eds. 1988). A major clean-up operation, coupled with an initiative to have fishermen convert from net gear to long line effectively solved the problem (Neves 1991).

From 1975 to 1987, the monk seal colony inhabiting the Côte des Phoques at Cabo Blanco in Mauritania and the Western Sahara were largely shielded from the effects of incidental entanglement because of warfare. With the resumption of both industrial and artisanal fishing, however, the risk of entrapment returned in force, together with a possible reduction in food availability for the colony. Although no deaths have been directly linked to fishery interactions, there is concern that some seals – most notably weaned pups or juveniles – may fall victim to entanglement (Anon. 1990, Francour et al. 1990, Manel Gazo pers. comm. 2000, González et al. 2002).

In Morocco, 27 out of 40 dead seals reported to Avella between 1980 and 1990 had died entangled in nets (Anon. 1990).

Research along the southern Aegean and western Mediterranean coasts of Turkey in the mid-1970s found that entanglement could almost rival shooting as a cause of mortality. Out of 7 known seal deaths, 4 could be attributed to direct killing, and three to drowning by entanglement (Berkes et al. 1979). More recently, entrapment in fishing nets has been blamed for several monk seal deaths in the Foça Specially Protected Area and environs, effectively wiping out a new generation of individuals that the SPA had been established to protect (Veryeri et al. 2001).

Despite the earlier belief that no age or sex category was particularly vulnerable (Anon. 1990), consistent monitoring in Greece and Turkey indicates that monk seal pups and juveniles may be particularly prone to entanglement (Mursaloglu 1984, Androukaki 2000, Veryeri et al. 2001). The Greek survey found that most drownings were juveniles ranging from 1.5 - 4 years of age. The researchers speculated that such individuals might be less cautious and less experienced than adults when approaching nets (Androukaki et al. 1999, Androukaki 2000).

Two separate theories have been advanced to explain the seal’s habit of raiding fishermen’s nets. The first relates to the innate tendency of every species to conserve energy and seek food at the most convenient of places. The second, however, implicates over fishing of coastal areas within the species’ distribution range (Johnson & Karamanlidis 2000).

Overfishing

According to the IUCN Seal Specialist Group “poor condition due to lack of food as a result of over fishing” threatens the survival of the Mediterranean monk seal. The possible effects of over fishing, such as malnourishment and susceptibility towards pathogens, may affect growth, reproduction, juvenile survival and mortality rate and cause the animals to disperse (Israëls 1992).

Although research on the cause and effect of this threat has not been carried out systematically, and consequently, only circumstantial evidence is available, overfishing has been implicated in the decrease of monk seal populations in Algeria (Boudouresque & Lefevre 1988), and certain areas in Greece (Marchessaux 1979), where it has also been linked to an apparent increase in the frequency of attacks by seals on fishing nets (Jacobs & Panou 1988, Anon. 1990). It has also been implicated in the low population of cetaceans and the change in dietary preferences of monk seals in the Cabo Blanco region (Forcada et al. 1999), as well as abnormal feeding incidents recorded in Greece (Margaritoulis et al. 1996), Turkey (Salman et al. 2001) and elsewhere (Güçlüsoy et al. 2002). Osteoporosis in a dead female monk seal, discovered on the north Aegean coast of Turkey in 1999, was also linked to chronic insufficient dietary calcium intake (Kompanje et al. 2000).

In certain areas, lack of sufficient fish resources may have led individual animals to become dependent on fishermen for food. Research indicates that some seals seek out fishing boats laying their nets, ‘stealing’ fish and damaging nets in the process (Johnson & Karamanlidis 2000). The losses inflicted by seals in terms of reduced catches and damaged gear (Karavellas 1994, Johnson (ed) 1998) – including fish farm installations (Glain et al. 2001, Guçlusoy & Savas 2003) – may be considerable in certain areas, exacerbating economic hardship, particularly among artisanal fishermen.

Stochastic events

Stochastic events (also known as “chance” events) can have a detrimental impact on the survival chances of endangered species (Soulé 1987). Because the entire Mediterranean monk seal population is so reduced in size, a severe stochastic event could wipe out entire colonies and thus jeopardise the survival of the species.

Just how serious a threat such stochastic events can pose was vividly demonstrated in the summer of 1997, when a sudden mass die-off struck the Mediterranean monk seal’s largest surviving colony at Cabo Blanco in Mauritania/Western Sahara, eliminating two thirds of the entire population (Blackmann 1997, Aguilar et al. 1998, CNROP/SRRC 2000). The event affected the adult section of the population almost exclusively (Samaranch et al. 1998), with conflicting scientific theories implicating both a morbillivirus (Osterhaus et al. 1997, 1998, Osterhaus 2002, van de Bildt et al. 1999) and a toxic “red tide” caused by a dinoflagellate bloom (Costas & Lopez-Rodas 1998, Hernandez et al. 1998, Reyero et al. 2000).

Other stochastic events that have affected the species, though to a lesser degree, include rockslides and cave collapses in Cabo Blanco (González et al. 1997) and in the Ionian Islands (Panou et al. 2002), and a severe winter cold in the mid-1950s at the Black Sea (Berkes et al. 1979).

According to a population viability analysis performed in 2002 (González et al. 2002) a catastrophic event, such as the one that struck Cabo Blanco in 1997, increases the extinction risk from 1-2% to nearly 20% over a simulation timeframe of 50 years.

Pollution

Pollution has been viewed as a potentially serious threat to the Mediterranean monk seal ever since the advent of efforts to protect the species in the late 1970s (Ronald & Duguy eds. 1979). Despite a lack of conclusive field data, various researchers have continued to hold pollution at least partly responsible for the reduction in monk seal population numbers in various regions.

These include the Marmara and Black Seas (Berkes et al. 1979) and the Gulf of Antalya in Turkey (Berkes 1982), and the coast of Oran in Algeria (Boutiba 1996). Other authors have claimed that the accumulation of pelagic oil and debris has rendered sea caves uninhabitable for the species in Libya (Ronald & Healey 1976), Lebanon (Baccar 1975 in Sergeant et al. 1978), some areas in the Ionian Sea (Sergeant et al. 1979) and the southern part of the Aegean island of Evia in Greece (Koukouras et al. 1992), as well as stretches of the Bodrum Peninsula in Turkey (Kiraç 1998).

The recent discovery of oil in Mauritanian waters, and the bulk transport of crude along the coast, is likely to increase the oil spill risk to the Cabo Blanco monk seal colony as well as other critical areas, such as the Banc D’Arguin National Park (Kloff & van Spanje 2004, Oilwatch 2005).

More detailed scientific research on the effects of pollution upon marine mammals in general and pinnipeds in particular (O’Shea 1999), has also furthered understanding of its possible impacts upon Monachus monachus (Yediler et al. 1993, Henderson et al. 1994, Georgakopoulou-Gregoriadou et al. 1995, Dosi 2000, Dosi et al. 2002). A particular focus of concern has been the effects of organochlorine compounds used in pesticides. These compounds have been consistently identified as a primary environmental factor affecting the reproductive fitness and general health of many other pinniped populations (Olson et al. 1992 in Borrell et al. 1997).

The effects of these pollutants in the Cabo Blanco population are considered to be negligible (Borrell et al. 1997). In contrast, organochlorine levels detected in monk seals living in the Mediterranean are considered high (Duguy & Marchessaux 1992, Cebrian et al. 1994, Borrell et al. 1997). Although sparse, some evidence also suggests that heavy metal compounds may be higher in the Mediterranean seal populations than in the Atlantic (Sergeant et al. 1978, Duguy & Marchessaux 1992). However, a recent study that analysed monk seal blubber and skin samples from Greece was unable to draw firm conclusions on the significance of heavy metal presence (Dosi 2000, Dosi et al. 2002).

Inbreeding depression

Inbreeding depression is not currently linked to any Mediterranean monk seal population, and is not expected to pose a significant threat to the species in the short term (Israëls 1992). As a risk factor common to small populations of highly endangered species, however, inbreeding is considered to be a potential future threat to the survival of Monachus monachus.

Loss of genetic variability and subsequent inbreeding depression is known to cause reduced fertility, increased infant mortality and a distorted sex ratio, which in turn can limit the response of an endangered species to environmental change (Anon. 1990).

To date, suggestions of possible inbreeding in the monk seal have been based on sparse and highly circumstantial evidence. The discovery of aborted monk seal foetuses in a well-known monk seal cave in Sardinia, for example, might well have had more plausible causes than the possibility of inbreeding raised by researchers, including intense tourism disturbance (Bareham & Furreddu 1975).

Other seal species, such as the Northern elephant seal (Mirounga angustirostris) or the Cape fur seal (Arctocephalus pusillus), have recovered from improbably low population levels, (the Northern elephant seal from a single herd possibly numbering fewer than 20 animals in 1890, to 48,000 in 1976) (King 1983, Gerber & Hilborn 2001), leading some authorities to speculate that pinnipeds might be less vulnerable to the inbreeding threat than other mammalian species (Harwood et al. 1984 in Scoullos et al. 1994). The ability of Mediterranean monk seals to travel great distances (Adamantopoulou et al. 1999), also potentially enhances genetic exchange.

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