Photo 1. The boat of “Dezinsekcija” towed the carcass of a basking shark away from the beach at Kantrida. (Photo by Patrik Krstinić)
Basking shark in Rijeka Bay
The carcass of a large fish was found on the beach in front of the Children’s Hospital Kantrida on Tuesday, 2 February. Because of health considerations, the carcass was towed out into the open Rijeka Bay by the boat of “Dezinsekcija”. All relevant institutions were informed about the beached fish, as there was a possibility that it might be a strictly protected marine animal. For cases such as this, a protocol has been developed for reporting on and taking action concerning strictly protected marine animals (marine mammals, sea turtles and cartilaginous fish) found dead, ill or injured. Despite the fact that PI “Priroda” is not listed as an operational participant in any segment of the protocol, the County Department for the Maritime Domain, Traffic and Communication asked us for our professional assistance in disposing of the carcass. Upon consulting with the Croatian Environment Agency, it was decided we try to sink it.
Upon viewing the carcass, we established that the fish was a basking shark (Cetorhinus maximus), a species of cartilaginous fish, listed in Appendix 1 of the Regulation on strictly protected species (Official Gazette no. 144/13). The six-metre-long carcass was found in a state of advanced decomposition. Skin was missing from all parts of its body and in places its internal organs were protruding through tears in the connective tissue and muscles. On the surface of the sea, a fatty smear was spreading from the carcass. The trunk of the fish was bent sideways, so that its head and tail were below the water with the central part of the trunk floating on the surface. The part of the head up to the first gill slit was missing.
A visual examination of the carcass established that a rope, about 1.5 cm thick, was wrapped around both pectoral fins and the entire trunk in the region of the fins. The rope had largely cut into the decaying flesh and tiny pieces of connective tissue were embedded in the rope fibres. From this we can assume that the rope became wrapped around the animal’s trunk before it began to decompose. The rope or net that entangled the basking shark limited its movements as well as its breathing, this being one of the likely causes of death. As cartilaginous fish do not have a swim bladder but maintain buoyancy thanks to high quantities of oil in their large livers, it was necessary for us to remove the shark’s liver from the abdominal cavity in order to sink the carcass.
The basking shark grows to an average length of 10 metres and can weight up to about four tons, making it the second largest fish in the world after the whale shark. It can be found in all temperate and cold seas. Since 1822 it has been reported more than 30 times in the Adriatic Sea, usually in the northern part. The longest specimen recorded was 8.5 metres long and weighed 2.5 tons (Blitvenica 2000). The basking shark is a migratory species, usually staying in schools and feeding on planktonic organisms which it filters through its long and dense gill rakers. It is the only fish that seasonally regenerates its gill rakes and during that time it probably rests on the floor of the continental shelf. The greatest threat to the basking shark is accidental entanglement in fishing nets. Occasionally fishermen find it caught in ropes or nets in a catatonic* state. In such cases they should free the shark completely of all pieces of rope or nets instead of just severing the excess rope and leaving the animal to die, wrapped in the remaining rope. That’s why it is the duty of every Croatian citizen to report any such situations by calling 112 to ensure that a rescue operation is organized in as short a time as possible to save these rare and threatened giants of the sea.
*A CATATONIC STATE ensues when an organism is almost completely torpid and does not move.
Photo 3. As cartilaginous fish do not have a swim bladder but maintain buoyancy thanks to high quantities of oil in their large livers, it was necessary to remove the shark’s liver from the abdominal cavity in order to sink the carcass. (Photo by Patrik Krstinić)
Photo 4. Growing to an average length of 10 metres and weighting up to about four tons, the basking shark (Cetorhinus maximus) is the second largest fish in the world, after the whale shark (Rhincodon typus) (Drawing by M. Randić)