Abstract
The recruitment process for Brazilian sardine ( Sardinella brasiliensis ) from 1977 to 1993 was investigated by taking into account the effects of spawning stock biomass (SSB), the intensity of the wind and the sea surface temperature (SST). Nonparametric models were applied. Best fits resulted from relating recruitment to a combination of SSB and Ekman transport. Transformation of Ekman transport is nearly dome-shaped, with lower and upper limits of 520 and 700 kg s -1 m -1 respectively. Fitting explained 94% of recruitment variability. Regions of maximum values in the transformations were for predictors related to wind, such as wind stress and turbulence index, whose limits were respectively 0.035-0.045 N m -2 and 30-45 m 3 s -3 . These values correspond approximately to winds of 3.0-4.5 m s -1 . SST transformations also follow an apparent dome-shaped curve optimising around 24.75 and 25.5oC. Inclusion of SST as a third predictor variable led to the loss of the dome-shaped relationship, as shown by the transformations with two predictor variables. Biomass curves are almost logarithmic, their critical point oscillating around 200,000-250,000 t, below which value the stock becomes more dependent on recruitment. The biomass range is greater than previous estimates.
Highlights
The Brazilian sardine (Sardinella brasiliensis) supports a commercially important fishery in the southeastern Brazilian Bight (Fig. 1)
We believe that we have shown that the wind and upwelling-based system in the southeastern Brazilian Bight, despite generally light winds in summer, reveals an optimal environmental window for wind intensities between 3.0 and 4.5 m s–1
The evidence leads us to believe that even the limited turbulence arising from winds stronger than 4.5 m s–1 can disrupt the plankton distribution pattern that is crucial for survival of sardine larvae in the Bight
Summary
The Brazilian sardine (Sardinella brasiliensis) supports a commercially important fishery in the southeastern Brazilian Bight (Fig. 1). 000 t, but since catches have declined, first to an annual mean of some 140,000 tons from 1977 to 1980 and to some 125,000 t from 1983 to (IBAMA, 2000). 32,000 t, but they recovered somewhat to 115,000 t in 1997 before falling again to just 17,000 t in 2000. For 2001, partial data indicate a slight recovery, to some 25,000 t. It is probable that recruitment is influenced by environmental factors related to meteorological and oceanographic conditions of a regional nature, and to the increase in fishing mortality. According to Matsuura (1996, 1999), limited intrusion of South
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