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