The distribution of blue whiting eggs and larvae on Porcupine Bank in relation to hydrography and currents

In March/April, and again in May 1994, the Porcupine Bank area was surveyed to determine the distribution of eggs and larvae of blue whiting (Micromesistius poutassou) in relation to hydrographic conditions. In March/April high concentrations of blue whiting eggs were found in a rather restricted area above the western slope of the Bank. The eggs were abundant in waters cooler than 10°C, either to the east of a thermal front on the bank or in deeper layers below the thermocline (400-600 m) off the Bank. In contrast, the larvae distribution of blue whiting was not restricted by the frontal structure but was generally found along the western slope of the bank in both warmer off-bank, and the cooler bank waters. In May only very few older larvae were found, the majority occurring in the northeastern corner of Porcupine Bank. Larvae hatching over the northwestern slope of Porcupine Bank were transported southeastwards onto Porcupine Bank. Under moderate wind conditions, larvae were retained above the bank by a Taylor Column circulation associated with cold, and relatively low saline, water. The circulation above Porcupine Bank may support the existence of a self-sustaining spawning population due to the high retention potential of the Taylor Column circulation. In 1994, however, strong westerly to southwesterly winds prevented the persistence of the Taylor Column circulation, so that blue whiting larvae were not retained above the bank for any length of time. Instead, a southeastward transport can be inferred, probably mixing the larvae with the offspring of other blue whiting populations.