For researchers on feeding habits of marine mammals, sea birds and fishes

Created by Tsunemi KUBODERA: National Science Museum, Tokyo
Assisted by Hiroshi OIZUMI andTomohito IMAIZUMI
English proofreader: Elaina M. JORGENSEN, Univ. of Washington

　Cephalopods are known to be one of the important prey animals for higher predators such as marine mammals, sea birds and large fishes in the marine food-web. Cephalopods are digested more rapidly than fish and crustaceans because they lack protective scales or chitinous carapace.

Initially, digestion effects the surface of body and the junctions between the head and mantle, and between the fins and mantle. This causes scission of head-arms and fins, from the mantle . Then, viscera and external organs, such as suckers, are digested so only muscular tissues of the mantle and arms are left. At this stage, it is difficult to identify species using external characters. As digestion advances the buccul mass separates from the head finally, only the upper and lower chitinous mandibles (beaks), which are hardly digested, remain in the stomach .

Marine biologists who have an interest in the feeding habits of marine mammals, sea-birds and large fishes study prey species of their target animals by means of examining those beaks remaining in the stomach. Knowledge and techniques for the identification of cephalopod beaks have been summarized by M. R. Clarke (1986) in "A Handbook for the Identification of Cephalopod Beaks". Kubodera and Furuhashi (1987) have offered "Manual for the identification of cephalopods and myctophids in the stomach of higher predators in the western North Pacific". However both of these resources ara a little bit older and have become difficult to obtain.

 This manual includes 100 species of cephalopod distributed in the waters adjacent to Japan and the western North Pacific and is based on the reference beak collections from the Kubodera and Furuhashi (1987) work as well as beak collections that have been made since that time. This manual is offered as a reference book for young biologists who intend to examine stomach contents of marine mammals and large fishes as well as for the experienced feeding habits researchers through the inter-net. This manual consists of three parts, “Key for identification of lower beaks”, “Data sheets for species” and “Estimation of body size and weight”. Users may be able to identify the lower beak into species or the nearest genera with “Key for identification of lower beaks”, and then compare the lower beak in detail with “Data sheets for species” of possible species for accurate identification. From the lower beak size, intact body size and weight can be estimated using the regression formulae given in “Estimation of body size and weight”, which includes about 20 species. In addition, general recommendations on the study of stomach contents are summarized as a side menu for beginners.

This manual does not include all the cephalopod species known in the North Pacific. Thus, depending on the predators, there might be a considerable number of unidentifiable lower beaks found in the stomach contents. Concerning those unidentifiable beaks, we are going to update the manual when we obtain new information.

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