Research Document - 2008/027

Physical oceanographic conditions in NAFO Division 3P during 2007-potential influences on the distribution and abundance of Atlantic cod (Gadus morhua)

By E.B. Colbourne and E.F. Murphy

Abstract

Oceanographic data from NAFO Div. 3P during the spring of 2007 are examined and compared to previous years and the long-term (1971-2000) average. The data show anomalous cold periods in the mid-1970s and from the mid-1980s to the mid-to-late-1990s with temperatures up to 1°C below average and up to 2°C below the warmer values of the late 1970s and early 1980s. Temperatures in deeper water off the banks during all years show significant variations, but remained relatively warm with values in the 3°-6°C range, compared to much colder values (often <0°C) on St. Pierre Bank. Beginning around 1996 temperatures on St. Pierre Bank begin to moderate and by 2000 they reached the highest values since the late 1970s. During 2001-03 however, temperatures cooled significantly to values observed during the mid-1990s with the average temperature during the spring of 2003 the coldest in about 13 years. Temperatures during both 2004 and 2005 warmed considerably over 2003 values to 1°C above normal in some areas. On St. Pierre Bank bottom water with temperatures <0°C covered <10% of the total area during the warm years of 1999, 2000, 2004 and 2005. During the spring of 2007 however, near-bottom temperatures decreased to below normal values in many areas particularly on St. Pierre Bank, where the area of <0°C water increased to more than 50% of the total area. 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, cod tend to prefer the warmer (2°-6°C) portion of the available habitat with a slightly warmer preference based on weight than on total numbers. Finally, variations in the estimated abundance and biomass of cod from the RV surveys in strata with water depths generally <100 m are significantly correlated with bottom temperatures, indicating a potential climate effect on cod distribution in this area.

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