Environmental influences on the distribution and transport of Atlantic cod, Gadus morhua, eggs and larvae in coastal Newfoundland

Abstract

This study examines spatial and temporal variability in distribution of Atlantic cod (Gadus morhua L.) eggs and larvae in Placentia Bay, Newfoundland, from three directions. The first chapter reviews the literature regarding the roles of transport and behavior in planktonic egg and larval pattern for benthic marine invertebrates and fish. This review suggests that the processes affecting each group are very similar, acknowledging that differences may be found in the capacity to contribute actively to dispersal and habitat selection. The second chapter provides evidence that variation in location and timing of spawning of Atlantic cod has a major impact on occurrence, distribution and development of eggs and larvae in Placentia Bay. Repeated ichthyoplankton surveys of the bay during the spawning and post-spawning periods indicate that eggs spawned early in the year (March - May) are lost from the bay. By contrast, elevated egg production late in summer of 1998 (July) resulted in a dramatic increase in larval densities. The third chapter combines modeling and field examination of the relationships between mortality, transport, and temperature during the egg stage, and demonstrates that consistent transport out of the bay may limit numbers hatching within the bay. Thus, the appearance of larvae is confined to summer months when development times are shortest. This thesis demonstrates the importance of cod spawning timing and location, as well as temperature and hydrographic influences on the transport and development of planktonic eggs and larvae in coastal Newfoundland.