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Research Document - 2003/093

Physical oceanographic conditions in NAFO Division 3P during 2003 - possible influences on the distribution and abundance of Atlantic cod
(Gadus morhua)

By Colbourne, E.B., and Murphy, E.F.

Abstract

Oceanographic data from NAFO Division 3P during the spring of 2003 are examined and compared to the previous year and the long-term (1971-2000) average. Temperature measurements on St. Pierre Bank show anomalous cold periods in the mid-1970s and from the mid-1980s to mid-1990s. Beginning in 1996 however, temperatures started to moderate, decreased again during the spring of 1997 and returned to more normal like values during 1998. During 1999 and 2000 temperatures continued to increase, reaching the highest values observed since the late 1970s in some regions. During the past 3 years however, temperatures have cooled significantly to values observed during the mid-1990s by the spring of 2003. In fact, the average temperature for NAFO Division 3P during the spring of 2003 was the coldest observed in about 13 years. The areal extent of <0°C bottom water increased significantly from the mid-1980s to mid-1990s, but decreased to very low values during 1998-2000. During 2001 to 2003 however, this area increased to values observed during the cold years of the early 1990s. Since 1995, the areal extent of bottom waters with temperatures <1°C has been increasing reaching pre-1985 values during 1999-2000, but during 2001-2003 this area decreased by 25%. On St. Pierre Bank <0°C water completely disappeared during the warm years of 1999 and 2000. It has since increased to between 20-30% areal coverage during 2001 and 2002 and to over 90% during 2003. In general, temperatures during the spring of 2003 decreased significantly over values observed during the past several years. The most evident trend in the numbers of cod caught per set during the multi-species surveys was the high number of zero catches in the <0°C water on St. Pierre Bank and regions to the east of the Bank, mainly from 1985 to 1998 but also from 2001 to 2003. During 1999 and 2000 larger catches became more wide spread over St. Pierre Bank as cold (<0°C) water disappeared from the area. In general, during all surveys most of the larger catches occurred in the warmer waters (2°-6°C) along the slopes and areas to the west of St. Pierre Bank. In addition, variations in the estimated abundance and biomass of cod from the RV surveys in strata with water depths <92 m are significantly correlated with bottom temperatures for that depth range.

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