SGS Product & Process Certification - Marine Stewardship Council

Size and Age data
Analytical assessment methods usually rely on data on the length and/or age distributions of fish
in the landed catch. In the UK, a biological sampling programme for sea bass has been run in
conjunction with the CEFAS logbook scheme, in which length data are collected either from the
whole landing from small vessels, often at fish merchants, or from markets by size category,
against targets set by gear group (i.e. demersal trawls, gillnets, lines, and pelagic trawls). Sea
bass are easily aged using scales (Kelley, 1988), and length-stratified ―all gears‖ scale samples
of at least 150 fish are used to provide corresponding half-yearly age-length keys for each stock
area. Sex ratio, maturity, and length-weight conversion factors are derived from biological
sampling carried out between 1982 and 1990 (Pawson and Pickett, 1996).
Recruitment
A robust time-series of data on year-class strength of pre-recruit bass has been provided by a
trawl survey in the Solent nursery areas (central English Channel), where a standard grid of 35
stations has been fished over a 4-day period at the same part of the tidal cycle (falling Springs)
in May and September each year since 1984 (Pickett et al., 2002). Numbers of each year
class caught at ages 2, 3, and 4 in up to 6 successive surveys are used to derive abundance
indices (Pawson, 1992), which have been shown to correlate well with model-derived
recruitment patterns to the bass fishery in Division VIId (Pawson et al., 2007b).
A similar fishery-independent trawl survey of bass has taken place across a standard grid of 35
stations in the Thames Estuary in November each year since 1995, from which indices of yearclass
strength of the bass population in the southern North Sea are available, Figure 3 (source
CEFAS). This index of recruitment is not used in the stock assessment, but acts as a fisheryindependent
validation. It becomes more robust as each year class is caught at ages 0,1,2,3
and 4, hence the provisional estimates for 2006 onwards. Both these surveys were
discontinued in 2010, due to cost cutting.
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