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Monk Seal Fact Files

Mediterranean Monk Seal

(Monachus monachus)

Biology

Ethology – Behaviour

Behaviour of pups and juveniles

The behaviour of Mediterranean monk seal pups appears to be greatly influenced by two overriding factors: the presence of the nursing mother and the need to move with confidence in their aquatic habitat as early as possible.

The first two months of a pup’s life are particularly important for their subsequent development. During this period, pups build up a strong bond and spend considerable time with their mothers. This strong relationship is expressed through frequent physical contact and loud vocalisations between them (Mursaloglu 1984, 1986). Any disruption of this bond may have severe consequences, and it has often been suggested that increased human presence near pupping sites has led to abortions or to lactating mothers abandoning their pups (Ronald & Yeroulanos 1984, Johnson & Lavigne 1999a, 1999b).

In contrast to past reports (Troitzky 1953, Ronald & Healy 1974, Mursaloglu 1984) Mediterranean monk seal pups have been observed to enter the sea within their cave shelters during their first week of life, even in the absence of their mothers, while pups have also been observed to leave their shelter and swim in the vicinity alone in the second week of life. Their swimming and diving skills are developed progressively and by the age of one and a half months they swim and dive with ease (Mursaloglu 1986, Dendrinos 1998, Dendrinos et al. 2000). Soon after, they are even capable of travelling distances of up to 1 km or more together with their mothers (Dendrinos et al. 2000, Fernandez de Larrinoa pers. observation). Confidence in moving independently about their aquatic environment is an essential skill since, even from the first weeks of life, mothers tend to leave their pups alone for hours in order to search for food (Mursaloglu 1984, 1986, Dendrinos et al. 2000, Gazo & Aguilar 2005).

This increases the probability of an inexperienced pup being swept away by a strong swell or storm surge, becoming separated from its mother and dying as a result (Gazo et al. 1999). Storm surges have been blamed for increased neonatal mortality observed throughout the species’ distribution, but particularly at Cabo Blanco, in Mauritania/Western Sahara (González et al. 2002). When present, mothers try to protect their pups from being washed away by taking them by the neck and carrying them to the upper zone of the beach, or by interposing their bodies between the pup and the waves (Pires 2004). In Madeira, Pires (2004) observed that a second female monk seal would consistently look over and protect a monk seal pup from breaking waves while its mother was at sea feeding. Such duties would revert to the mother as soon as she returned to the beach. Pires likened such behaviour to the roles played by “aunties” in elephant social structure.

In case of imminent danger, monk seal mothers have been observed to warn their pups by nipping them (Kouroutos 1987, Neves 1998).


Social behaviour

Although little understood, the social behaviour of Mediterranean monk seals appears to be influenced by the moderate polygyny [Glossary] that is characteristic of the species (Cebrian 1994, Matono et al. 1998, Gücü et al. 2004). As a consequence, in the Cabo Blanco region of Mauritania/Western Sahara, the only place where the species has managed to maintain the social and demographic structure of a colony, several adult black males display territorial behaviour, both in the area of the breeding caves and in other areas as far as 30 km away. Social interactions between adult males mainly occur underwater while defending these aquatic territories (Marchessaux & Muller 1987, González et al. 1997). During the mating season, these males may also intrude into other territories in an effort to displace dominant males and gain access to females (Chalkidiki, Greece: Cebrian 1993 cited in Cebrian 1994, Kephalonia, Greece: Panou et al. 1993, Chafarinas Islands, Spain: Manez, pers comm. to Cebrian 1994). Anecdotal accounts from the Turkish coast also suggest territorial fights among males (Güçlüsoy et al. 2002).


Feeding behaviour and diet

Mediterranean monk seals have often been described as opportunistic predators (Marchessaux & Duguy 1977, Jacobs & Panou 1988, Boutiba & Abdelghani 1997) because of their ability to easily exploit a wide variety of food resources, though mainly those that are in abundance and thus easy prey.

What little data have been collected and analysed through scat and stomach content samples, as well as anecdotal evidence obtained from fishermen, appear to show a preference for bone fishes, such as mullet, sea bream and bogue (Cebrian et al. 1990, Scoullos et al. 1994 for Greece, Salman et al. 2001 for Turkey, Sergeant et al. 1978, Neves 1998 for Madeira). However, the varied menu of Monachus monachus also includes such diverse items as cephalopods (octopus, squid, cuttlefish), lobsters and seaweed (Ronald 1973, Boulva 1979, Salman et al. 2001). In certain locations, and when food resources are abundant, the species even tends to focus on particular prey species, such as lobsters (Marchessaux & Muller 1985).

Despite reports from geographically diverse areas, there is no conclusive evidence that monk seals raid vineyards to feed on the ripening grapes or other crops located near the seashore (Kuehn 1930, Anonymous 1975, Boutiba & Abdelghani 1997). Conceivably, the phenomenon may be linked to seals seeking shelter from the summer sun, and to the long-held tendency of coastal dwellers to regard the seal as a pest (Güçlüsoy et al. 2002, Johnson 2004).

In one single, and possibly exceptional case in Zakynthos, monk seals were observed to attack and feed on loggerhead turtles (Margaritoulis et al. 1996).

Average prey size is thought to be 2.5 kg, although prey up to 10 kg have been recorded (Duguy & Marchessaux 1992, Dendrinos unpubl. data). Studies of captive Mediterranean monk seals indicate a daily food intake ranging between 5 and 10% of the total body weight; or a daily intake of between 12.5 and 25 kg for an animal weighing 250 kg (Jacobs & Panou 1988 in Scoullos et al. 1994, Caltagirone 1995).

When searching for food, Mediterranean monk seals usually stay close to shore and prefer shallow reefs where the currents and productive seabed provide the best foraging conditions. When facing food scarcity, however, they are capable of covering extensive distances in order to find new feeding grounds (Kiortsis & Veriopoulos 1984, Marchessaux 1989, Gazo et al. 1998 in Mo 1999). Although no definitive migration of the species is known (Boulva 1979, Duguy & Marchessaux 1992), seasonal movements, possibly following the migration routes of fish, have been frequently reported in the past (Maigret 1976 in Scoullos et al. 1994, Avella and González 1984 in Scoullos et al. 1994, Matsakis ed. 1985, Jacobs & Panou 1988). Reports from the Black Sea suggest that monk seals regularly visited the fish-rich area of the Danube delta in search of food (Sergeant et al. 1978) and used to pursue schools of bluefish tuna during their migration (Berkes et al. 1979).

Little is known about the feeding techniques and behaviour of Monachus monachus. The species has been observed to employ two different hunting techniques. The first, “spot feeding”, involves diving against the surface current and parallel to the coast, emerging at the same spot (Marchessaux 1989, Neves 1998, Kiraç et al. 2002) – a feeding technique often exercised for many hours at a time. In contrast, while “transit feeding”, monk seals cover relatively large areas close to the shore, usually remaining in shallow waters, preferring to look for prey in 2-25 meters’ depth (Neves 1998, Güçlüsoy and Savas 2003a). When a fish is caught, the prey is often first eviscerated by violent sideways movements of the head, and then ingested headfirst (Duguy & Marchessaux 1992, CBD Habitat 2004).


Swimming and diving

Although conclusive evidence is rare, average dive depths for Mediterranean monk seals have been described as being within 50 m (Ronald & Duguy eds. 1979). Average dive duration, a more reliable figure that, in the case of spot feeding, can be recorded by observers on land, has been put at 6-12 minutes (Duguy & Marchessaux 1992, Gazo 1996, Neves 1998). The longest dive recorded has been 18 minutes (Kiraç et al. 2002) and the greatest depth 75m (Ronald et al. 1978).

However, recent satellite tracking data obtained from a 10 month old rehabilitated orphaned monk seal, released into the Northern Sporades Marine Park of Greece, registered a maximum dive of 123 meters, effectively rewriting current scientific knowledge of the species (Dendrinos et al. in prep.).

Fully developed diving capacity is gradually acquired during the early stages of neonatal development (Mursaloglu 1986). As weaning occurs, pups spend less time resting or swimming at the surface, and diving activity and duration increases (Reijnders & Ries 1989, Gazo, Lydersen & Aguilar 2006).

At Cabo Blanco, pups were observed entering the water during their first week of life and their diving performance increase progressively with age. Pups spent most of their time at sea (55-74%) and their swimming activity is greater at nighttime compared with daytime. In pups from the Cabo Blanco colony of Mauritania/Western Sahara, three dive types were found: one V-shaped and two U-shaped. The most common type was U1-dives, mainly used by older pups during 44-48 % of their total dive time. These dives were relatively deep and long (mean depth = 11.6 ± 9.5 m, mean duration = 149.1 ± 80.6 s). They had long bottom times (100 ± 67 s) suggesting that pups were foraging, coinciding with the end of lactation (Gazo, Lydersen & Aguilar, 2006).


Movements and migration

With a current distribution range stretching from the eastern Mediterranean to the Atlantic Ocean, and including vast stretches of open sea, the question of how far monk seals can travel or whether they migrate has long been a matter of both scientific and conservation debate.

With the precarious status of the species ruling out extensive radio or satellite tracking experiments, however, knowledge on movements and migration remains incomplete and largely circumstantial. Although Monachus monachus is generally considered sedentary (Boulva 1979), with adult males having an estimated home range of 40-50 km (Berkes et al. 1979, Gücü et al. 2004) and daily movements mainly consisting of local feeding forays, the species is capable of travelling extensive distances in relatively short periods of time (Mursaloglu 1992, Lopez-Jurado et al. 1998, Mozetich et al. 2002, CBD-Habitat 2004).

In three cases of photo-identified individuals in Greece (Adamantopoulou et al. 1999), one monk seal travelled a direct distance of 59 nautical miles between two study areas, while another covered a total of 159 n.m. within a three month period.

The theory that increased nutritional demands or the need to locate suitable pupping sites encourages a marginally greater activity range in female Mediterranean monk seals (Schnapp et al. 1962, Boulva 1979) has yet to be substantiated.

Following a common pattern in pinnipeds, juvenile monk seals seeking new territories have often been sighted far outside their normal distribution range (Baudouin-Bodin 1964, Maigret et al. 1976, van Bree & Duguy 1977).

Movement behaviour of monk seals has significant implications for the conservation of the species. Taking possible daily movements into account, Berkes (1978) suggested the existence of an interbreeding monk seal population between Greece’s eastern Aegean islands and Turkey. More recently, it has been postulated that sightings of monk seals in parts of southern Italy, in Sardinia and Sicily, where they were previously considered extinct, may be the result of movements from other areas, including North Africa and the Ionian Islands of Greece (Coppola 2003, Gruppo Foca Monaca 2002, Mo 2002).


Activity patterns

Tide appears to be one of the principal factors affecting the activity of Mediterranean monk seals living in the Atlantic. During low or rising tide, monk seals usually haul-out or take care of their young on the beaches within caves (Marchessaux 1989, Aguilar et al. 1995, González et al. 1997). During mid and high tide, in contrast, monk seals are usually observed at sea, feeding and interacting (Trotignon 1982, Marchessaux & Muller 1987, Neves 1998, Neves & Pires 1998, Pires & Neves 1998). Within the Mediterranean basin, however, where tides are negligible, effects on monk seal activity are correspondingly small. Refuting early reports (Bareham & Furreddu 1975, Boulva 1975, Hiby et al. 1987, Jacobs & Panou 1990), extensive research in the eastern Mediterranean indicates that monk seals are active during the day and that they use the caves during the night (Dendrinos et al. 1994, Karamanlidis 2000, Güçlüsoy & Savas 2003, Gücü et al. 2004).

In terms of seasonal patterns, evidence suggests a shift in activity during winter. During this time of the year seals appear to visit caves more often and stay there for longer periods (Bareham & Furreddu 1975, Jacobs & Panou 1988, Dendrinos et al. 1994). Several factors, such as moulting, weather, the breeding season, and a reduction in human disturbance, may influence this pattern.

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