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A report of the 37th Northeast Regional Stock Assessment Workshop : assessment of the Gulf of Maine and Georges Bank witch flounder stock for 2003
  • Published Date:
    2003
Filetype[PDF - 2.56 MB]


Details:
  • Corporate Authors:
    Northeast Fisheries Science Center (U.S.)
  • Series:
    Northeast Fisheries Science Center reference document ; 03-14
  • Document Type:
  • Description:
    The 2003 analytical assessment for witch flounder in USA waters, covering the period 1982-2002, estimates 2002 fishing mortality and spawning stock biomass for stock status, and provides short-term projections of median landings, discards and spawning stock biomass for various fishing mortality scenarios. USA commercial landings increased during the 1960's from 1,200 mt to about 3,000 mt, then fluctuated between 2,000 and 3,000 mt until 1983 through 1985 when landings abruptly increased to about 6,000 mt. Landings subsequently declined to 1,500 mt in 1990. Since the early 1990s, landings have fluctuated between 2,000 and 3,000 mt. In 2002, USA commercial landings totaled 3,186 mt, a 5% increase over 2001; and 117% higher than in 1990, the lowest value since 1964. Research survey indices of abundance and biomass remained fairly stable from 1963 until the late 1970s; autumn indices declined during the early and mid 1980s, reaching record low levels in late 1980s and early 1990s. Abundance sharply increased in 1993 and has continued to increased to near record high levels in 2002; however, the age composition still remains truncated. The VPA indicates that fishing mortality (ages 8-9, unweighted) increased from 0.26 in 1982 to 0.67 in 1985, declined to 0.22 in 1992, increased to 1.13 in 1996, then declined to 0.41 in 2002. Spawning stock biomass declined from 16,897 mt in 1982 to about 3,800 mt in 1996. With recent increases in recruitment and declines in fishing mortality, SSB has increased to 18,296 mt in 2002 . Since 1982 recruitment of age 3 has ranged from approximately 3 million fish (1984 year class) to 67.6 million fish (1997 year class). Over the 1982-2002 period, average recruitment of age 3 fish (the 1979-2000 year classes) was 19.6 million (the geometric mean equaled 14.4 million fish). The 1995-1999 year classes appear to be above average, and the 1997 year class is the largest in the VPA time series. In addition to the VPA, an alternative model, a statistical catch at age model (SCAA) was also conducted. The SCAA generally confirmed trends in the VPA results. The biological reference points were updated by applying the approach used to estimate MSY proxies for witch flounder. Fmsy is approximated as F40% (0.23), the SSBmsy proxy is 25,248 mt, the product of 40%MSP (1.2882 kg spawning biomass) and average long-term recruitment (19.6 million). The MSY proxy is 4,375 mt, the product of yield per recruit at F40% ( 0.2232 kg) and average recruitment. Based on the ADAPT VPA, the witch flounder stock was not overfished, but overfishing was occurring in 2002. Fully recruited fishing mortality in 2002 was 0.41, nearly double Fmsy (0.23), and spawning stock biomass was estimated to be 18,296 mt in 2002, 72% of SSBmsy (25,248 mt). Recent year classes appear to be above average. Although the spawning stock biomass has increased, the age structure still remains truncated. Fishing mortality should be reduced to Fmsy or below to allow the age structure to rebuild.