Distribution and Food Availability of Fish Larvae in the Vicinity of a Thermohaline Front at the Entrance of Ise Bay

Abstract

Distributions of fish larvae and their prey were simultaneously observed on February 11 and 12, 1995 in the vicinity of a thermohaline front at the entrance of Ise Bay, Japan. The front was about 0.5km in width, where a marked change in temperature (about 4°C) was detected. Most of the larvae were Japanese sand lance and greenlings fish. The densities of the larvae were appreciably higher inshore and at the front than those outside of the front; few larvae were collected in the offshore. On the other hand, copepod densities were relatively high at the front and lowered toward the offshore and inshore. The number of copepodite copepods in the gut contents of greenlings larvae was significantly larger at the front than that of the larvae collected from the inshore. The difference in the number of nauplii in the gut contents was not significant between the front and the inshore; this was probably because the greenlings larvae mainly fed on copepodite copepods. The thermohaline front possibly functions as a barrier to the larvae transported from Ise Bay, and enhances their food availability by increasing copepod densities at the front surface.