Evidence for inshore spawning of Atlantic cod (Gadus morhua) in Trinity Bay, Newfoundland, from 1991 to 1993

Abstract

The objective of this thesis was to determine if northern Atlantic cod (Gadus morhua) spawn in Trinity Bay, Newfoundland. Prior to this study, only indirect evidence existed for inshore spawning by cod along the northeast coast of Newfoundland. Research reported here confirms that Atlantic cod spawn in Trinity Bay, Newfoundland, during the early summer on an annual basis. This conclusion is supported by evidence from three lines of investigation. These are 1) the observed progressive maturation of inshore cod from spawning to spent condition, 2) direct observation of a spawning aggregation of cod in Trinity Bay, and 3) the presence of recently spawned cod eggs (≤ 10 days old) in the bay. A spawning "window" in Trinity Bay from mid-June to early July is estimated for the period of 1991-1993. This timing of spawning was delayed relative to offshore spawning components of Atlantic cod at similar latitudes. A simple model was proposed to explain this delay based upon the temperature to which inshore cod were exposed during the winter. Predictions of oocyte development times in female Atlantic cod were in phase with observed spawning times. Predictions using cumulative degree-days calculated from monthly seawater temperature profiles were less able to explain the temporal component of the spawning window in Trinity Bay.