Research Document - 2001/062
Overview of 2000 Hydrographic Sampling Effort and Near-Bottom Water Temperature and Salinity Conditions During the Canadian Research Vessel Groundfish Summer Surveys Conducted on the Scotian Shelf and in the Bay of Fundy (4VWX)
By R. Losier, F. Page, P. McCurdy, J. McRuer
Abstract
The Canadian Department of Fisheries and Oceans conducts bottom trawl surveys on an annual basis within NAFO subdivisions 4VWX as part of its approach for developing scientific advice on the status of groundfish resources. Vertical profiles of water temperatures and salinities are measured during these surveys. The sampling locations are randomly allocated as part of the stratified random design of the survey. Each year the most recent sampling effort and associated temperature and salinity data are summarized and compared to the historical data from the survey. The summary presents strata specific analyses of the data so fisheries assessment biologists can easily scan the overview for conditions of interest to their species areas. In the present overview, we present a summary of sampling effort and the resulting estimates of water temperatures and salinities during the 1970-2000 summer surveys conducted within NAFO subdivisions 4VWX. The focus is on the near-bottom conditions in the year 2000 and how these compare to conditions encountered throughout the history of the survey series. In 2000, sampling was conducted from 4 July (consecutive day 187) to 28 July (consecutive day 210). CTD profiles were obtained from all 48 strata. The analyses indicate that in the year 2000 near-bottom temperatures throughout NAFO subdivisions 4VWX area were greater than those in most of the previous years and above the 1980-90 baseline mean. This was due mainly to a relative lack of low temperature water. Salinities in the year 2000 within 4VW were lower than most previous years. However, relative to the 1980-90 strata means, the 2000 strata specific anomalies varied between positive and negative. In NAFO subdivision 4X, the salinities were greater than most previous years and the strata mean salinities for 2000 were generally above the 1980-90 means. This was mainly due to a relative lack of low salinity (<~32.5) water.
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