Contents of the third stomach of sperm whale caught off Hokkaido. (Photo by T. Tamura, Research Institute of Cetacea)

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　Animals can be identified to species using external characters during the undigested to 2^nd digestion stages only. During stages 3-5 species can be identified using beaks only. In stages 6-7 species identification is very difficult except with beaks that have very specific characters. Lower beaks are typically used for species identification therefore beaks should be removed from buccal masses collected at digestion stages 3-4.

　Most specimens collected from stomach contents are fragile due to the effects of digestion. This is especially true for the head-mantle connection in cephalopods so care is required when removing specimens from the stomach to avoid breaking them apart. During preliminary sorting it is better to sort each of the digestion stages individually and record the stage. Based on that data you can estimate feeding intervals, the number of times they feed, and how much they feed during each event. For reference, stages of digestion will be shown below.

Undigested: almost no effects from digestion except parts that were already damaged

Stage 1: general shape is maintained but epidermis is lost; fins and arm tips partially digested.

Stage 2: fins and arms separated from mantle; armature of arms and tentacles remain.

Stage 3: viscera is digested and arm and tentacle armature falls off

Stage 4: buccal mass separates from arms

Stage 5: beaks separate from buccal mass and separate into upper and lower beaks (buccal mass muscle is completely digested)

Stage 6: marginal parts of beaks are destroyed; only solid parts remain

Stage 7: beaks break into fragments

Baird`s Beaked Whale stomach contents showing stages 5-6; spheres are cephalopod or fish lenses,
lenses that have separated into two hemispheres are cephalopods. (Photo by Toshiaki Kuramochi).

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