Research Document - 2001/021

Status of witch flounder in NAFO Division 4RST, February 2001.

By Swain, D., Poirier, G.A.

Abstract

Throughout the 1990s and most of the 1980s, landings of witch flounder in NAFO Divisions 4RST have been mostly by seiners directing for witch flounder between May and October in St. George's Bay, Newfoundland (4Rd) and off the west coast of Cape Breton Island (4Tf and 4Tg). Landings declined in the 1990s, reaching historical lows between 1994 and 1997, but increased to the TAC (800-1000 t) in 1998-2000. The low landings in 1994-1997 reflected a sharp decline in effort in 4R during this period (when a high incidence of crab gear interfered with the fishery for witch flounder in 4R). A biomass index for witch flounder over the entire 4RST area was calculated by combining data from annual research vessel surveys conducted in the northern Gulf of St. Lawrence each August and in the southern Gulf each September. A sharp decline in the biomass of commercial sizes (=30 cm in length) occurred from 1990 to 1993. The biomass index remained at a low but steady level from 1993 to 1998. It increased sharply in 1999 and remained at this relatively high level in 2000. Changes in biomass were not uniform throughout the stock area. The decline in biomass occurred in 4R, 4S and western 4T, but was not evident in eastern 4T. The large increase in the biomass index in 1999 was confined to eastern 4T, but increases in survey catch rates in 4R, 4S and western 4T also contributed to the relatively high biomass index in 2000.Sentinel surveys conducted in the northern Gulf (mainly 4R and 4S) in July and October indicated that biomass in this area changed little from 1995 to 1999. The October sentinel survey indicated an increase in biomass in 2000 but the July survey did not. Pre-recruit abundance (witch flounder 16-29 cm in length) in the research surveys fluctuated without trend between 1990 and 1999 but increased markedly in 2000. This sharp increase in 2000 reflects a strong year-class, likely the 1995 year-class, that has been evident in the northern Gulf survey each year since 1997. Stock structure is a major source of uncertainty for this resource.

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