MEPS 283:255-268 (2004)  -  doi:10.3354/meps283255

Age and growth of larval cod and haddock on Georges Bank during 1995 and 1996

J. Green*, R. Jones, S. Brownell

National Oceanic and Atmospheric Administration, National Marine Fisheries Service, Northeast Fisheries Science Center, 28 Tarzwell Drive, Narragansett, Rhode Island 02882-1199, USA

ABSTRACT: Growth rates of larval cod Gadus morhua and haddock Melanogrammus aeglefinus were estimated based on collections in winter and spring of 1995 and 1996 during the US Global Ocean Ecosystem Dynamics (GLOBEC) Georges Bank Program. Growth was determined using length-at-age data derived from otolith increments to indicate age in days from hatching. Growth varied significantly among months and between 1995 and 1996. In general, cod growth exceeded 0.2 mm d-1 and reached a maximum growth rate of 0.7 mm d-1 in May 1996. Haddock growth was also greater than 0.2 mm d-1 with a peak of 0.5 mm d-1 in June 1995. For cod, instantaneous growth rates of 3.3 to 3.5% d-1 were higher than those published previously for the Georges Bank region. Haddock growth was comparable to that of cod in 1995 (3.3% d-1), but a higher growth rate for haddock (3.5% d-1) in 1996 was probably due to an under-representation of larger sizes in the data available. Increased size-at-age was associated with higher temperatures for both species; however, the effect of temperature on growth appears to have decreased in May as temperatures exceeded 6°C and approached 8°C. Insufficient numbers of larvae of either species were available in May of 1996 for a similar analysis; however, cod growth during May 1996 was the most rapid observed in this study (0.7 mm d-1). This corresponded to a period of high production of suitable food organisms, early stage Calanus finmarchicus, in May 1996 resulting from cooler winter temperatures and late warming after the winter of 1996, suggesting that cooler temperatures favor a prolonged period of food production for larvae and better conditions for growth late in the larval period.

KEY WORDS: Cod larvae · Haddock larvae · Temperature variability · Growth · Otolith

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