Following the classic lines of evidence of Hunter et al. (Hunter, J. R., Macewicz, B., Lo, N. C. H., and Kimbrell, A. 1992. Fecundity, spawning, and maturity of female Dover sole Microstomus pacificus, with an evaluation of assumptions and precision. Fishery Bulletin US, 90: 101–128.) on the fecundity type of fishes (determinate vs. indeterminate), the stock of horse mackerel (Trachurus trachurus) in Atlantic Iberian waters (ICES Division IXa) was shown to exhibit a mixed picture. Total fecundity, the total number of secondary growth (SG) oocytes dropped during the spawning season and there were reproductively active individuals with a distinct size hiatus between primary growth (PG) oocytes and SG oocytes, while no massive atresia was observed in late-season spawners. All of these characteristics matched with evidence for determinate fecundity. However, daily decrease rate of total fecundity was lower than daily specific fecundity (i.e. the number of eggs produced daily per unit weight) by orders of magnitude which suggested that the stock of SG oocytes was replenished during the spawning period through de novo oocyte recruitment. In addition, the maximum number of batches in reproductively active females was lower than the predicted annual number of spawnings, while total fecundity in recent spawners—those containing post-ovulatory follicles—was not lower than the fecundity of the remaining reproductively active females. All of these results suggest that, despite the aforementioned mixed lines of evidence, the fecundity of horse mackerel is clearly indeterminate. We attribute these mixed characteristics to the fact that, unlike most typical indeterminate spawners, horse mackerel ceases to recruit new SG oocytes during the latter part of its spawning season.
Weight/length relationships, condition factor, gonadosomatic and hepatosomatic indices, conversion factor for gutted to total weight and spawning season of hake in the Portuguese Coast (36.92 to 42.22 degrees latitude N; 9.61 to 6.07 degrees longitude W) were investigated for the first time, aiming to fill the lack of information on the biology of hake of the Portuguese waters. Data were obtained from commercial samples collected between 2005 and 2010 and pooled by month. Sex ratio observed in fish below 40 cm was close to 1:1; females were always dominant above 50 cm length. All the parameters were analysed by month and by sex and by combined sexes. The relationships obtained for combined sexes for the entire period concerning the growth in length and weight were: total length-total weight = 0.0038L 3.172 , total length-gutted weight = 0.0052L 3.059 . The relationship total weight-gutted weight was W t = 15.8112 + 0.8480W g and the conversion factor was of 1.1524. The growth rate is similar for both sexes but different when based on total weight or gutted weight. The analysis of the condition factor, gonadosomatic index, hepatosomatic index and the monthly distribution of the maturity stages seem to indicate that hake from the Portuguese Coast has a long spawning season, with three spawning peaks in March, May and August but the start of the spawning season seems independent of the fish length.
Costa, A. M. 2009. Macroscopic vs. microscopic identification of the maturity stages of female horse mackerel. – ICES Journal of Marine Science, 66: 509–516. The consequences to fisheries management of erroneous macroscopic identification of maturity stages are evaluated. The percentage error in macroscopic identification of maturity stages of female horse mackerel (Trachurus trachurus) from the Portuguese coast was determined and analysed by maturity stage, between the periods January–June and July–December, between research surveys and commercial landings, and between per year and month and by length class, to assess its implications in determination of spawning season, maturity ogives, and spawning-stock biomass. The highest percentage errors in macroscopic identification were between late ripening and partly spent stages, in fish >30 cm, and for all fish collected in 1998 and 2005. Late ripening was generally macroscopically underestimated, and the partly spent stage overestimated. The implications for the information provided to the ICES assessment working group are analysed.
Gonçalves, P., Costa, A. M., and Murta, A. G. 2009. Estimates of batch fecundity, and spawning fraction for the southern stock of horse mackerel (Trachurus trachurus) in ICES Division IXa. – ICES Journal of Marine Science, 66: 617–622. Since 1995 the annual egg production method has been applied triennially to the southern stock of horse mackerel (Trachurus trachurus) in the Northeast Atlantic (ICES Division IXa). This method assumes that fecundity is determinate, but increasing evidence indicates that horse mackerel are indeterminate spawners. The daily egg production method (DEPM) does not rely on the assumption of determinate fecundity, making it the appropriate method for this species. Therefore, we reanalysed samples collected from previous surveys (2002, 2004, 2005, and 2007) to obtain estimates for batch fecundity and spawning fraction, which are important DEPM parameters. The estimates of batch fecundity are around 200 oocytes g−1 of female (total ovary-free weight). Several criteria were used to estimate spawning fraction (migratory nucleus stage, hydrated oocytes, and post-ovulatory follicles) and all showed the same trend among years, varying between 0.10 and 0.30 d−1. The estimates were significantly different among methods, but those differences were similar across surveys, indicating that a consistent bias would be reflected in the final spawning-stock biomass (SSB) estimates obtained from the DEPM. Until further information is available regarding the accuracy of the criteria used to estimate spawning fraction, the southern horse mackerel SSB estimates from the DEPM should only be taken as indicative of trends rather than measures of absolute abundance.
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