In order to investigate the cannibalistic mortality of larval Japanese sand eel Ammodytes personatus by adults, the stomach contents of 352 adults collected from Ise Bay in central Japan in March 1995 and February 1996 were observed. Sand eel larvae were found in the stomachs of 22.4% of adults. The average weight of larvae in stomach/adult weight was 0.5%. The relationship between standard length (SL) of adult (SLa in cm) and the maximum SL of larvae (SLmax in mm) was expressed as SLmax=5.1•SLa-22.9. The daily predation rate on the larvae by an adult sand eel was estimated to be 2.1% of its body weight, using the observed weight of the larvae in a stomach and the gastric evacuation rate (0.313h-1) obtained from a laboratory experiment. The total number of larvae which could be preyed on by a pair of 8cm, 10cm, and 12cm SL adults was estimated to be 2, 000, 3, 800, and 6, 400 individuals, respectively, assuming that the period when the spacial distribution of the adults and the hatched larvae in the mouth of Ise Bay are overlaping is ten days. These values were equivalent to 62%, 44%, and 34% of the fecundity of an adult female of 8cm, 10cm, and 12cm SL, respectively.
