Study ID 288

DFO Maritimes Research Vessel Trawl Surveys Fish Observations (OBIS Canada)

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Realm: Marine
Climate: Temperate
Biome: Temperate shelf and seas ecoregions
Central latitude: 43.977389
Central longitude: -63.682015
Duration: 34 years, from 1970 to 2006

19074 records

195 distinct species

Across the time series Illex illecebrosus is the most frequently occurring species

Citation(s):

Clark, D. & Branton, B. (2007) DFO Maritimes Research Vessel Trawl Surveys, OBIS Canada Digital Collections. Bedford Institute of Oceanography, Dartmouth, Nova Scotia, Canada, OBIS Canada,

Methods

The DFO summer Scotian Shelf and Bay of Fundy research vessel (RV) survey. hereafter referred to as the summer RV survey. has been conducted annually in Northwest Atlantic Fisheries Organization (NAFO) Divisions 4VWX5Y since 1970. The summer RV survey follows a stratified random sampling design (Halliday and Kohler 1971). and includes both hydrographic sampling and sampling of fish and invertebrates using a bottom otter trawl.The bottom trawl survey was originally planned to provide biomass and abundance trends for groundfish residing at depths from about 50 m to 400 m. and was extended to cover depths down to 750 m in 1999.There were changes to the net used and the vessel conducting the survey in 1982 and 1983. From 1970 ? 1981 the RV A.T. Cameron. a side-trawler using the Yankee 36 trawl. was used for the survey. In 1982. the RV Lady Hammond was used. towing a Western IIA trawl. Since 1983. the Alfred Needler has been the primary survey vessel. and the Western IIA trawl has been used in all years. Conversion factors were calculated for net and vessel changes (Fanning 1985).For long-term averages. the most appropriate starting point has been selected for each species. In the case of white hake. biomass plots start in 1970 but the abundance index data only go back to 1982. For silver hake. biomass plots and abundance index data are used starting in 1982. This is in conjunction with the change in the type of trawl. from a Yankee 36 to a Western IIA. as well as more consistent identification of white hake and red hake.In 2010. additional survey tows were completed in deeper water off the shelf edge (750 ? 1.800 m) to investigate species composition and biomass in deeper waters. Catches from these stations are not included in the biomass index estimates. to ensure that comparability with other years is maintained. Distribution plots are included here only for the most abundant species noted at these depths. Tables of the entire catches at these depths are also presented.The survey area has been divided into three zones. based on oceanography and biogeography. Trends are shown for the entire shelf survey area. and also for three separate regions: eastern Scotian Shelf (4VW; strata 440 - 466). western Scotian Shelf (4X East; strata 470 - 481). and Gulf of Maine/Bay of Fundy (4X West; strata 482 - 495). Differences in patterns of fish abundance and species composition are apparent for these regions during the survey. Strata 496 - 498 (the shelf edge; 350 m ? 750 m) have been sampled in most years since 1996. while strata 501 - 505 (750 m ? 1.800 m) have not previously been sampled as part of the stratified random survey series. These depths are considered separate biogeographic zones and since they have not been sampled in all years. are not included in the long-term biomass index estimates.Plots of the size and distribution of catches are provided for selected species and stratified average catches are compared with past results to provide a general overview of trends in abundance and biomass. For select commercial species where individual fish weights have been collected throughout most of the time series. trends in condition (Fulton?s K: weight/length3) are also included (Ricker 1975).Data are presented for the major commercial species. for species that comprise a large part of the survey catch. and for species where the 2010 catch was either unusually high or low (see also DFO 2011a). The set of species examined to determine if catches in 2010 were unusual was restricted to those where the area occupied exceeded 7.000 square nautical miles (approximately 1/7th of the surveyed area) in 2010. or averaged greater 2 than this in the 1970s. the 1980s or the 1990s. The species examined were restricted in this manner to avoid rare species for which catches display high inter-annual variability.Comparisons of stratified length frequencies for 2009 and 2010 to the long-term mean are also included for major commercial fish species. These data were summarized to assist in reviewing trends in abundance that are directly relevant to fisheries management when they are developing advice on allowable catch; hence. these data are grouped by the applicable stock management areas for each species. Unit of abundance = IndCountInt, Unit of biomass = NA