Velvet Belly Lanternshark - Biology and Ecology

Biology and Ecology

Along with the blackmouth catshark (Galeus melastomus) and the Portuguese dogfish (Centroscymnus coelolepis), the velvet belly is one of the most abundant deep-sea sharks in the northeastern Atlantic. It is found individually or in small shoals. Samplings in the Mediterranean have found females outnumbering males across all ages; this imbalance increases in the older age classes. In the Rockall Trough and the Catalan Sea, large adults are found in deeper waters than juveniles, which may serve to reduce competition between the two groups. However, this pattern has not been observed at other sites in the eastern Mediterranean.

The velvet belly's liver accounts for 17% of its body mass, three-quarters of which is oil, making it nearly neutrally buoyant. To deal with the higher concentrations of heavy metals in the deep sea, the velvet belly has T-cells in its bloodstream that can identify and mark toxic compounds for elimination. These T-cells are produced by a lymphomyeloid gland in its esophagus called a "Leydig's organ", which is also found in some other sharks and rays. In its liver, specialized proteins are also capable of detoxifying cadmium, copper, mercury, zinc, and other toxic contaminants. The velvet belly's bioluminescence is thought to function in counter-illumination, which eliminates the shark's silhouette and camouflages it from upward-looking predators. Its bioluminescence may also serve a social function, such as finding mates or co-ordinating groups, as the pattern is species-specific. The velvet belly is an important food of larger fishes such as other sharks; a major predator of this species is the longnosed skate (Dipturus oxyrinchus).

Numerous parasites are known for this species, and both juveniles and adults often carry heavy parasite loads. Known internal parasites include the monogenean Squalonchocotyle spinacis, the tapeworms Aporhynchus norvegicus, Lacistorhynchus tenuis, and Phyllobothrium squali, and the nematodes Anisakis simplex and Hysterothylacium aduncum. Some of these parasites use the velvet belly's prey as intermediate hosts and are acquired via ingestion, while others use the shark itself as an intermediate host. The barnacle Anelasma squalicola, an external parasite, attaches to the shark's dorsal spine socket and penetrates deeply into the muscle, in the process often providing an attachment site for a second (and rarely a third) barnacle. Infestation by this barnacle reduces its host's fecundity by impairing the development of the reproductive organs.