Data Information

Methodology

The survey area covers the Northwest Atlantic Fisheries Organization (NAFO) divisions 4R and 4S as well as the deep strata of 4T located north of the Magdalen Islands shelf. The total area is 118 587 km2. Sampling stations are selected using a random stratified methodology based on strata of predetermined depth. The number of fishing stations per stratum is proportional to its surface and includes a minimum of three stations per stratum in the case of smaller strata. A Rockhopper type Campelen 1800 shrimp trawl is used as fishing gear. The extension and codend come with a knotless mesh (12.7 mm) nylon lining. The duration of standard fishing tows is 15 minutes. To be considered valid tows must be at least 10 minutes and no more than 20 minutes long (±1/3 of the time). Ship speed must be 3 knots.

Throughout the years, as certain strata have not been sampled using two successful tows, a multiplicative model has been used to assess catch rates (numbers and weights). The predicted value is calculated from the current year data, if available, and those from the three previous years. Effort dedicated to species identification and taxonomy has also varied over the years. In order to be able to visualize species evolution over a long period taxonomic groupings have been implemented. DFO scientists use several taxonomy reference publications before deciding on the identification. They also use integrated taxonomic information systems or marine organism international catalogues. To assist with work while at-sea, Quebec Region makes use of an identification guide for fishes (Nozères et al. 2010) and a comparative portfolio for invertebrates (Nozères et al. 2014).

  • Number and biomass values that are made available are standardized for a 15 minutes tow. The “Methodology” section contains additional information on this aspect of the sampling protocol.
  • Positioning data correspond to the central point, in latitude and longitude, between the starting and ending position of each fishing set. They are expressed in a decimal format (i.e. 48.5000 equals 48° 30').
  • Data collected during those surveys primarily serve the needs of DFO in the achievement of its mandates including the provision of scientific advice on the status of fisheries resources. Data are made available on the SLGO portal after the publication of official advices, usually in the year following the survey.
  • Additional information can be obtained by sending a request to the following address: gddaiss-dmsaisb@dfo-mpo.gc.ca

Editor's Note
SLGO also has an identification guide.