512 
Fishery Bulletin 99(3) 
Table 2 
Ovalipes punctatus caught in the swash zone of Koshirahama Beach, Otsuchi Bay, during the summers of 1994 and 1995. The 
numbers of each developmental stage and of papershell crabs caught during the day and at night are shown. No softshell and 
premolt crabs were collected. 
Number of papershell crabs 
Total number of 
Day or night 
Developmental stage of crabs (CW) 
crabs collected 
Early papershell 
Late papershell 
Day 
Juvenile (12-30 mm) 
7 
6 

Immature (31-50 mm) 
1 
1 
— 
Adult (51-80 mm) 
— 
— 
— 
Night 
Juvenile (12-30 mm) 
35 
4 
1 
Immature (31-50 mm) 
39 
4 
1 
Adult (51-80 mm) 
14 
3 
6 
Table 3 
Percentage occurrence, points, and percentage points for the 12 categories of foregut content in 69 Ovalipes punctatus from Koshi- 
rahama Beach, Otsuchi Bay. The points express the dietary contribution in terms of foregut fullness and estimated volume of food 
items in the foregut (see text). Sand was excluded from the calculation of the percentage points. 
Food item 
Percentage occurrence 
Points 
Percentage points 
Crustaceans 
Haustorioides japonicus 
59 
1437.5 
26.1 
Archaeomysis kokuboi 
54 
1287.5 
23.4 
Excirolana chiltoni 
30 
528.7 
9.6 
Crangon sp. 
14 
540.0 
9.8 
Crustacean fragments 
42 
1115.6 
20.3 
Other crustaceans 
4 
62.5 
1.1 
Mollusks 
Bivalves 
6 
41.3 
0.7 
Gastropods 
1 
25.0 
0.5 
Fishes 
Unidentified fish 
3 
5.0 
0.1 
Other items 
Unidentified organic matter 
19 
456.3 
8.3 
Algae 
3 
3.8 
0.1 
Sand 
94 
970.6 
— 
foreguts examined were more than half full (classes 3-5) 
and 7% had empty foreguts, which suggests that the crabs 
fed actively in the swash zone at night (Fig. 2). 
When describing the diet of portunid crabs, Williams 
(1981) recommended including only individuals with fore- 
guts more than 50% full (i.e. classes 3-5). Applying this 
criterion, we found 69 crabs (39 females, 30 males) for the 
diet analysis, 66 of which were collected at night. Because 
there was no significant difference in the diets by sex (chi- 
square test, P>0.5), the male and female data were com- 
bined. Forguts contained 11 prey categories plus sand; 
percent frequency of occurrence, total points, and the rela- 
tive proportions of the diet components in terms of points 
are listed in Table 3. Although sand is not considered a 
part of the diet, it contributed more than 14% to the total 
points of the foregut contents. 
Small crustaceans were frequent and predominant in the 
foreguts of O. punctatus (Table 3). The sand-burrowing am- 
phipod Haustorioides japonicus was the most frequent prey, 
contributing 26.1% of the total points. Second most frequent 
prey was the sand-burrowing mysid Archaeomysis kokuboi 
(23.3% of the total points), followed by the sand-burrowing 
isopod Excirolana chiltoni (9.6%) and sand shrimps Cran- 
gon sp. (9.8%). Fragments that probably came from these 
crustaceans produced 20.3% of the total points (Table 3). 
The results show 90.2% of the total diet volume of O. punc- 
tatus consisted of crustacean prey. Mollusks and fish were 
not important in the diet (1.3% collectively). 
