Changes in abundance and certain population parameters of American plaice Hippoglossoides platessoides in Northwest Atlantic Fisheries Organization (NAFO) subdivision 3Ps, south of Newfoundland, were examined over the period 1972–1994. During these years, there has been a substantial reduction in population size and in more recent years, there has been a redistribution of the remaining population to deeper, warmer water than previously observed. Despite the substantial changes in stock size and distribution, there is no clear evidence that growth patterns have changed nor has there been any truncation of the age structure of the population, both of which commonly occur if overexploitation takes place. On the other hand, age and size at 50% sexual maturity for both males and females declined over the same period. This stock has been managed through quota regulation since 1974; however, the quota rarely restricted the fishery. During the 1980s, when the greatest declines in stock abundance occurred, the commercial exploitation rate was far too low to have been an important contributor to the observed decrease in population size, It is concluded that management measures during this period were ineffective in maintaining stock size at the target level because the stock decline was not the result of fishing. The reasons for such substantial reductions in the stock remain unknown. During the 1990s, however, as this and other groundfish stocks were declining rapidly, a substantial increase in fishing effort was directed towards this stock in an attempt to fully utilize existing quotas. Annual catches thus were maintained at a moderate level despite a rapidly declining population, producing exploitation rates much higher than those of the 1980s. By 1995, the stock was estimated to be so reduced that a total fishing moratorium was introduced for American plaice in NAFO subdivision 3Ps. The result of this measure is yet to be evaluated.
A total of 5478 fishes were sampled between 2009 and 2020 to assess length–weight, length–length and weight–weight relationships in 39 marine species from 10 families caught in the Seychelles waters by the artisanal fishery. Two types of length (total length TL, fork length FL) and three types of weight (whole weight WT, gutted weight GW and gilled-gutted weight GGW) were measured. The parameters of the relationships were estimated using the log-transformed allometric model with bias correction. Our results include length–weight, length–length and weight–weight relationships for 39, 20 and 18 species, respectively. Our length–weight data and resulting relationships were compared against FishBase database for 36 species and were in the Bayesian 95% confidence interval of the relationships available for 33 species and above for Gnathanodon speciosus, Lutjanus gibbus and Variola louti. Finally, for five abundant and widely dispersed species we tested for spatial differences in morphometric relationships between the Mahé Plateau and three southern atoll groups. Significant differences were found for two species only, but their magnitude was small. We thus argue for the regression relationships based on pooled data to be used for most types of population and community analyses. The availability of these morphometric relationships will support the application of accurate size-based analyses for Seychelles fisheries survey data, and so enhance understanding of the ecology of the reef-associated fish component of marine ecosystems and food webs, and improve fisheries research management.
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