The spatial distribution of brown sole Pseudopleuronectes herzensteini eggs and larvae, and their food organisms were examined to elucidate the early life history of this species in Mutsu Bay. In April 1990 1997, pelagic larvae were widely distributed in the bay. Vertical distributions of eggs and larvae were investigated at two sam-

Abstract:To clarify the feeding strategy of pelagic larvae of the stone flounder in Mutsu Bay, the dietary composition and prey size was investigated from February to April during 1989April during -1999 Diets were compared with the numerical and volumetric compositions and frequency of occurrence of each prey species. Mensuration formulae were applied to estimate individual prey volume in the diet, while the length of planktonic species was measured from net and water samples. Prey shapes were assumed as sphere, cylinder, ellipsoid, pyramid, two elliptical cones, or a combination of ellipsoid and cylinder. Prey-size range increased as the larvae grew.Pre-flexion larvae fed mainly on copepod nauplii. Flexion and post-flexion larvae ingested primarily appendicularians, with a suggestion that these larvae might depend on some parts of the microbial food web. Low frequencies of flexion and post-flexion larvae with empty guts (1.7 and 1.4%, respectively) might be derived from feeding on slow-swimming appendicularians.From a size comparison between "house"-like organ length and trunk length of the appendicularian Oikopleura sp., almost all house-like organs with trunks in the larval diet were non-expanded "house rudiments", not expanded "houses". Thus, stone flounder larvae may not chew the houses, but swallow the house rudiments with trunks.

To clarify the recruitment process of sand lance Ammodytes sp., we investigated larval condition factor, relative gut fullness (%GF), prey abundance and oceanographic structure in Mutsu Bay, Japan, in 1999-2001. Ammodytes sp. larvae, which were collected by horizontal hauls of Motoda nets and a ring net at 1, 10, 20, 30 and 40 m depths, were mainly distributed at 10-30 m. Larvae at the first feeding time until 12 mm in body length (BL) fed predominantly on copepod nauplii, whereas large larvae of 12.1-14.0 mm BL fed on a mixture of copepod nauplii, copepodites and appendicularians from late February to April. A path analysis showed that difference in water density between 35-and 5-m depths negatively affected naupliar abundance at 10-30-m depth (standardised path coefficient β=−0.71, p=0.005 for 3.3-8.0-mm body length (BL) larvae and β=−0.78, p<0.001 for 8.1-12.0-mm BL larvae). Naupliar abundance positively affected %GF of Ammodytes sp. larvae (β=0.75, p<0.001 for 3.3-8.0-mm BL larvae and β=0.66, p<0.001 for 8.1-12.0-mm BL larvae), whereas it was negatively affected by water temperature (β=−0.45, p=0.008 for 3.3-8.0-mm BL larvae and β=−0.56, p=0.002 for 8.1-12.0 mm BL larvae) and temperature effect was weak compared with that of naupliar abundance. In turn, %GF positively affected larval somatic weight (β=0.91, p<0.001 for 6.0-mm BL larvae and β=0.70, p=0.005 for 10.0-mm BL larvae). The recruitment failure in 1999 was likely caused by a reduced condition factor, which resulted from low naupliar abundance. In contrast, the abundances of nauplii and Oithona similis copepodites were high in 2000 and 2001. It is possible that the higher recruitment success in 2001 was because of the higher water temperatures in Mutsu Bay sustaining faster growth of the larvae than in 2000 under the high prey abundance conditions.

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