Fecundity and reproductive behaviour of Atlantic cod (gadus morhua) using active and passive acoustics

Fudge, Susan B. (Susan Beth) (2009) Fecundity and reproductive behaviour of Atlantic cod (gadus morhua) using active and passive acoustics. Masters thesis, Memorial University of Newfoundland.

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Abstract

Fecundity-size-age relationships in Atlantic cod (Gadus morhua) for the late 1990s and early 2000s off Newfoundland and Labrador were compared with historical data and with similar relationships from cod stocks in Icelandic and Norwegian waters and in the, Baltic and the North Seas. For southern Newfoundland stocks that have fared relatively well in the 1990s and early 2000s, fecundity-size relationships did not differ from historical norms, although age at maturity was lower. In the highly stressed northern stock off Labrador, however, age at maturity was much lower than historical norms or in southern stocks, and fecundity much higher in small and young fish. Mortality rates were higher in the northern fish. These changes are explored in the context of changed life histories and the potential for rebuilding in stressed gadoid stocks. -- For the behavioural component of the study, passive and active acoustic properties of an Atlantic cod spawning aggregation were observed at depths of 40-50 m at the Bar Haven grounds in Placentia Bay, Newfoundland in April 2003. Sounds recorded by hydrophone were identical to those recorded from captive spawning cod of the same stock, but heard less often. From a surface-mounted transducer (EK500; 38kHz), cod were observed to undertake relatively rapid periodic vertical migrations approximately half way to the surface (20-25 m) which resulted in the formation of cod columns. This work is the first to demonstrate the simultaneous incidence of cod sounding and vertical behaviours resulting in column formations during spawning.

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