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Here I report observations over three years (2001-2003) at Argostoli harbour, Kefalonia, Greece, (38º 10´N 020º 29´E) during which loggerhead turtles were observed feeding on discarded fish, thrown overboard during net-cleaning operations by professional fishermen. To avoid having to capture and tag animals at sea (and in public view), individual turtles were identified instead by using carapacial epibiotic distribution (i.e. recording which scutes had been parasitised by barnacles), physical damage and scarring, and the number and shape of facial scales.
Between 5 and 10 caiques are still used to fish commercially in local waters, often with gill-nets. These boats have 1-3 crew and normally fish overnight, returning to Argostoli at mid-morning to sell their catch directly to passers-by at the quayside. The quay extends about 400 metres and forms part of a public promenade; the water depth is 3-6 metres. The boats are normally moored elsewhere, and depart as soon as fishermen have sold their catch. Fish are usually disentangled from the nets in harbour, although this work may have commenced at sea, and unwanted species and debris are thrown overboard. Loggerhead turtles began to appear regularly near to the harbour wall when the boats came alongside, apparently for opportunistic scavenging; usually just a single turtle was foraging at the fish-quay at any one time. At least four individuals demonstrated some level of fidelity to the site; a large adult male (estimated CCL 100 cm), a large (estimated CCL 87 cm) untagged short-tailed turtle, a juvenile (estimated CCL 40 cm), and a large tagged turtle presumed female (estimated CCL 85 cm). The serial number on the red ‘Rototag’ could not be read from a distance due to barnacle encrustation; no attempt was made to capture the turtle during this behavioural study.
When fish were thrown overboard, a foraging loggerhead would manoeuvre itself so that the prey, which was usually immobile, was approached, often from underneath, and taken with the beak. During a typical approach the turtle’s body was angled downwards at about 45 degrees, head uppermost, the front flippers were used to propel the animal into position; the rear flippers were used as brakes – either together or in opposition and often directed anteriorly. If a discarded fish was sinking, a turtle would often take it during descent. The turtle’s fore-flippers were used solely for propulsion and played no part in prey manipulation, as had been observed by Davenport and Clough (1985) for small juveniles, which had been obtained from Cyprus. Smaller fish were usually swallowed whole, while larger fish were often taken laterally (sideways) and crushed between the jaws before being swallowed. Larger prey items were retained in the mouth between successive bites and swallowed progressively. Excess water was forcibly ejected from the external nares (nostrils) following prey capture, probably indicating that the throat was blocked off by the glottis to reduce seawater intake. Fish scales and small portions of flesh escaping from the turtle’s beak were rapidly consumed by small scavenging fish, which the loggerheads ignored.
The fish species discarded varied between fishermen, but different identifiable turtles were observed eating most of the discards, which included: electric rays Torpedo nobiliana; damselfish Chromis chromis; saddled seabream Oblada melanura; red mullet Mullus surmuletus; grey mullet Mugil cephalus; long-nosed wrasse Symphodus rostratus; round sardinella Sardinella aurita; and salema Sarpa salpa. Some wrasse [Labridae] and scorpionfish [Scorpaenidae] species were only occasionally discarded. All turtles ignored holothurians, mainly Holothuria tubulosa and Stichopus regalis.
There appeared to be no preferential prey selection between individual turtles and they ate whatever was available at the time. The most notable single observation was of a loggerhead eating a large discarded piece of cow-nosed ray Rhinoptera marginata, which took several minutes to swallow; the two-metre wide ray was being filleted on a fishing boat.
No attempt was made to quantify prey consumption by turtles for several reasons: the size of discard varied each day (hundreds of sardines but perhaps only ten wrasse or mullet); the author could only observe one or two turtles closely at the same time; the number of boats along the quayside varied between none and eight; sometimes turtles ate everything and remained by the boats, but on other occasions they departed leaving some discarded fish uneaten.
Several pieces of evidence were gathered demonstrating marked habituation to humans. On 16th September 2002, a loggerhead was observed trying to get fish, (flat-headed mullet Mugil cephalus) out of the submersed keep-net of a local angler. The turtle approached slowly, gliding vertically up the wall from underneath, and attempted to bite the catch through the mesh; providing more evidence of the attractiveness of immobile fish. When the net was lifted out of reach, the turtle rested her front flippers against the wall and raised the anterior part of her body out of the water, following the food. For about 30 minutes, each time the net was re-immersed, the turtle attempted to access the catch; it was eventually enticed away by a fish (Mugil cephalus) that the fisherman threw out to sea.
On 30th July 2002, an elderly fisherman was observed hand-feeding a loggerhead turtle. The man held a small fish (Oblada melanura) over the stern of his boat, the turtle approached and, using its mouth, took the fish very gently from his hand (repeated six times). A considerable level of trust was apparent between man and animal, the fisherman could stroke the turtle’s head even without offering a fish. People on the quayside were within 1.5 m, chattering and taking photographs. Once local fishermen recognised that feeding turtles attracted tourists, they would deliberately throw fish overboard when loggerheads were close by. This had an unexpected educational role, in that many tourists visited the quay to photograph turtles, and then became interested in learning more about marine animals and their habitat threats. In 2003, different fishermen were observed on several occasions handfeeding and stroking other turtles; some students also bought fish and hand-fed loggerheads on a number of days.
On one occasion when hand feeding was being observed one turtle was taking a fish from the man when a second short-tailed turtle, similar in size, swam quickly from beneath the fishing boat and attacked the original animal, trying to bite its face and neck. The defending turtle retaliated and pursued the attacker rapidly downwards, where they could be seen chasing each other around in tight circles (head to tail) at a depth of 1.5-2 m below the surface. The defender drove off the unidentified intruder, and returned to feed at the boat. [Water depth 3-4 m, seawater temperature 25.7ºC, high turbidity].
On several further occasions in 2003, different loggerheads were observed fighting. Every conflict involved one turtle chasing another, rapid circling, nose-to-tail, trying to bite the opponent’s head and face. Conflict behaviour (attack and avoidance) took place in three dimensions (i.e. not just in the horizontal plane), and often occurred in the confined space between a fishing boat’s hull, the harbour wall, and the seabed (depth 4 m). One juvenile turtle did not initiate any attack but, even after being chased off by a larger turtle, remained nearby ready to exploit a further food opportunity (sneaking). The smaller turtle was much more agile than its larger conspecifics, particularly in confined spaces, and usually managed to escape unhurt. No adult males were observed fighting but these animals were comparatively rare, since most turtles encountered during this study were short-tailed.
Competition was only observed when fish boats were present at the quay, so the resource being protected seemed to be the location (perhaps even a boat or fisherman) rather than a food item, as fighting also occurred in the absence of fish discards. These fighting incidents were clear examples of resource contesting and protection and were the first observed incidences of aggression between loggerheads during seven years’ study at this site. Under normal conditions, such as during benthic foraging, there was no conspecific competition; individual turtles rarely approached one another.
These observations confirm that loggerheads do eat fish, especially when the prey is less able to escape, for instance following the trauma of being captured in a net. The fact that different turtles identified the boats as a regular source of food, and exhibited foraging site-fidelity, shows that bycatch discarded by a fishery does attract loggerhead turtles. The likelihood of turtles being accidentally captured would be increased in areas where boats were actively engaged in fishing, whilst discarding unwanted catch overboard (Shoop & Ruckdeschel 1982; Tomas et al. 2001).
Each year more turtles were observed feeding on fish discards in Argostoli, with loggerheads mainly ignoring the abundant mussel beds (Mytilus galloprovincialis) along the harbour wall; a further example of the opportunistic nature of loggerheads. Furthermore, this study reports several examples of very close encounters (including stroking) between loggerheads and people, suggesting that humans are not necessarily perceived as a threat by turtles.
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