A report of the 21st Northeast Regional Stock Assessment Workshop. The Lorenz curve method applied to NEFSC bottom trawl survey data

The Lorenz curve method was applied to Northeast Fisheries Science Center (NEFSC) research vessel survey data to determine changes in the concentration of haddock (Melanogrammus aeglejinus) and witch flounder (Glyptocephalus cynoglossus) in the Georges Bank - Gulf of Maine region over a 32 year period. Estimated biomass for each species within a strata set area was examined. Since the survey strata area vary in size, a modification to the method was explored and a comparison of methods conducted. Lorenz curves (ordered by mean weight per tow) were calculated for each NEFSC autumn bottom trawl survey between 1963 and 1994. Haddock distribution on Georges Bank has become more concentrated over the study period and there appears to be two phases of increasing concentration, with the later phase higher in concentration than the first. Although changes in concentration of witch flounder biomass have occurred, there is no apparent trend over time. by Susan E. Wigley. "July 1996." System requirements: Adobe Acrobat Reader. Includes bibliographical references (page 4). 1996 NMFS (National Marine Fisheries Service) NEFSC (Northeast Fisheries Science Center) Library Public Domain 1863