Effects of current velocity on development and survival of lingcod,Ophiodon elongatus,embryos

Synopsis The influence of current velocity on the survival and development of lingcod embryos was investigated in the field and laboratory. Examination of egg masses at five lingcod spawning sites indicated that embryo mortalities were high (up to 95%) at low-current sites because of inadequate ventilation and resulting hypoxia. Development of embryos near the center of poorly ventilated egg masses was retarded relative to development of embryos near the periphery. Hatching of embryos from poorly ventilated eggs was protracted; embryos from the interior of egg masses hatched later and were significantly smaller than embryos from eggs near the periphery. Oxygen levels measured in egg masses at low-current velocity sites during tidal flow average 16% air saturation, corresponding to a Median Tolerance Limit (LT₅₀) of about 73 h. Oxygen levels measured in egg masses at high-current velocity sites during slack water average 69% air saturation, a level that did not adversely affect the embryos. Current velocities of 10–15 cm s^–1 were needed to maintain interstitial oxygen levels in egg masses near that of the ambient water. Water movement may be an important stimulus for spawning site selection by lingcod. In areas where tidal currents were weak, spawn deposition occurred in shallow water where waves and vertical tide motion created water movement. In areas where tidal currents were strong, spawns were consistently deposited in deeper water.