Research Document - 2002/001
Recent trends in bottom temperatures and distribution and abundance of cod (Gadus morhua) in NAFO Subdivisions 3Pn and 3Ps from the winter/spring multi-species surveys
By E. Colbourne and E. F. Murphy
Abstract
An analysis of near-bottom temperatures in NAFO Division 3P during winter and spring surveys are presented in relation to the spatial distributions and abundance of cod (Gadus morhua) for the years 1983 to 2001. Interannual variations in the near-bottom thermal habitat were examined by calculating the areal extent of the bottom covered with water in 1oC temperature bins. The analysis revealed a significant shift in the thermal habitat in the region with the areal extent of subzero oC bottom water covering the banks increasing dramatically from the mid-1980s to the mid-1990s. During this time period zero catch rates dominated on St Pierre Bank and in the eastern regions of 3Ps. Beginning in 1996 the area of 0oC water on the banks decreased significantly reaching very low values in 1998 and a complete disappearance in 1999 and 2000. The areal extent of bottom water with temperatures >1oC on the banks was about 50% of the total area during 1998 the first significant amount since 1984 and it increased further to about 70% during 1999 and to 85% during 2000. During 1999 and 2000 larger catches of cod became more wide spread over St. Pierre Bank region as the cold sub-zero oC water disappeared from the area. There were many zero catches in the eastern areas during 2001 as colder water returned to the region. During all surveys most of the larger catches occurred in the warmer waters (>2-3oC) along the slopes of St. Pierre Bank and areas to the west of St. Pierre Bank. An examination of the cumulative distributions of temperature and catch indicates that cod are associated with the warmer portion of the available temperature range, with a slightly warmer preference based on weight than numbers.
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