Cephalopod beak identification and biomass estimation techniques: tools for dietary studies of southern Australian finfishes
Museum Victoria Science Reports: No. 6 pp 1-65 (2002)
Abstract
Need for this research. Squid, octopus and cuttlefish (cephalopods) are known to be an important food source for many marine animals including whales, porpoise, seals, seabirds, tuna, sharks and swordfish. The hard beaks (chitinous mandibles) of these preys are frequently encountered in predator stomachs. Cephalopod beaks can be used to identify the prey species and to calculate prey size and biomass consumed. Such hard parts from fishes (i.e. otoliths and vertebrae) have long been used for these purposes. Cephalopod species in the northern hemisphere have also had such tools available, but until now little information has been available on this aspect of the cephalopod fauna of our region.
Results and conclusions. A key of cephalopod beaks of 75 southern Australian species is available to identify samples taken from predators in this region for the first time, along with the formulae required to calculate prey size and biomass.
Production of this key required the analysis of 1596 specimens, involving detailed measurements of various parts of the whole animal (mantle length, animal weight) and the beaks. Statistical analysis of the data then allowed the description of the relationship between beak measurements and the size and weight of animals, providing formulae to back calculate prey size and biomass.
A table provides details of the species examined, classified to order and family, with information on the size and weight range of whole animals. Most complete beaks can be easily identified to the order level and a key is provided for this. Further keys are provided to allow identification to genus/species level within each of the four orders. Detailed descriptions of beaks are provided for each species, supplemented by further tables providing ranges, ratios and means of various beak characters.
Further work. Collection and analysis of further cephalopod beak material would allow the formulae developed here to be further refined. A similar project with a scope that included the tropical cephalopod fauna of Australia would be valuable to workers in northern Australia and nearby regions.
Citation
Lu, C. C., and Ickeringill, R. 2002. Cephalopod beak identification and biomass estimation techniques: tools for dietary studies of southern Australian finfishes. Museum Victoria Science Reports 6: 1–65.