New information on the biology of the bizarre Goblin shark has been revealed in a recent study by Japanese researchers.
The study, published in the most recent edition of Ichthyological Research, examined 171 specimens of the Goblin shark, Mitsukurina owstoni, collected off the Pacific coast of Japan over a 30-year period.
The sharks, collected using bottom gillnets from Sagami Bay, Suruga Bay, the Enshu-nada Sea and from the steep slope of the Tokyo Submarine Canyon (100-350m depth), were used to obtain basic information about the morphology, distribution, diet and reproduction of this poorly know and rarely collected shark.
Catch recordsSpecimens ranging in size from 82 to 348 cm in length (from the tip of the snout to the tip of the upper lobe of the caudal fin) were examined.
Though previous studies had examined larger specimens (the largest specimen on recorded is a male 384 cm in length), the Japanese researchers were able to examine both the smallest male (81.7 cm) and female (82.8 cm) specimens of the Goblin shark recorded to date.
Diet of Goblin sharksOf the 110 stomachs examined 29% were empty. Stomach content analysis of filled stomachs confirmed that teleost fishes of the families Macrouridae and Melanostomiidae formed the bulk of the Goblin shark s diet.
Other prey items found in smaller quantities included squid, decapods and isopods. Human refuse was also recovered from the stomachs of a small percentage of sharks.
No difference in diet preference with increasing body size was discovered during the study, suggesting that teleost fishes are the most important prey item of M. oswstoni for all size classes examined.
Goblin shark reproductionStrangely, all of the Goblin sharks examined were found to be immature, including the largest male (208.5 cm) and female (348 cm) specimens examined.
Though sexually mature goblin sharks have been captured before, gravid females of this species have yet to reported and many questions about the reproduction of M. owstoni remain unanswered.
In addition to Japan, M. owstoni has been collected in bottom trawls off the coasts of Australia, France, French Guiana, Guinea, New Zealand, Portugal, Senegal, South Africa, Suriname, Taiwan and the US.
Despite its wide distribution very few specimens of the Goblin shark have been available for examination by previous researchers interested in its biology.
Though many questions about its biology remain to be answered, the large number of specimens examined recently by Japanese scientists has significantly furthered our understanding of the natural history of this strangest of shark species.
For more details see the paper: Yano, K., Miya, M., Aizawa, M. and Noichi, T (2007) - Some aspects of the biology of the Goblin shark, Mitsukurina owstoni, collected from the Tokyo Submarine Canyon and adjacent waters, Japan. Ichthyological Research, 54: 388-398.