Browsing by Author "Vasconcelos, Joana"
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- Age and growth of the Atlantic chub mackerel Scomber colias Gmelin, 1789 off Madeira IslandPublication . Vasconcelos, Joana; Dias, Manuel A.; Faria, GraçaThe Atlantic chub mackerel, Scomber colias Gmelin, 1789, is one of the main fisheries resources of Madeira Island. It is caught by a small and coastal purse-seine fleet that traditionally operates around the island. From January 2002 to December 2003, monthly samples of chub mackerel were collected from landings by this commercial fishing fleet. A total of 2212 sagitta otoliths were extracted for age readings from 1068 males (17.4-41.7 cm total length, TL), 1066 females (18.0-41.2 cm TL) and 78 undetermined (13.0-26.8 cm TL). A single reader aged the fishes using surface-read whole otoliths aiming to build annual age-length keys. Age readings precision and reader consistency were assessed by using the average percentage error index (APE ≤ 1.52). Ages were validated up to 4 years using marginal analyses. Estimated mean lengths at age and length von Bertalanffy growth curve parameters, estimated by non-linear methods, showed no significant differences (p>0.05) between sexes (L∞=50.08 cm TL, k=0.252 yr-1 and t0=-1.339 yr; males and females combined). Length-weight relationships were estimated aiming to convert growth in length to growth in weight. No differences between sexes were found in length-weight parameters (P>0.05). For sexes combined, total weight (TW, g) = 0.00218.LT 3.40 and the estimated asymptotic weight, W∞=1523.7 g.
- Age and growth of the blue jack mackerel, Trachurus picturatus Bowdich, 1825 (Pisces: Teleostei) off Madeira archipelago.Publication . Vasconcelos, Joana; Alves, Adriana; Gouveia, Elisabete; Faria, GraçaBetween 1984 and 1986, 630 pairs of sagitta otoliths were collected to determine the age and growth of the blue jack mackerel, Trachurus picturatus from Madeiran waters. The oldest specimen in this study was nine years old and the largest was 46 cm of total length (TL). The parameters of the von Bertalanffy growth curve were estimated for the whole period studied for all fish (L∞=42.32 cm, k=0.161 year-1, t0= -2.563 year; r2=0.743) for males (L∞=39.57 cm, k=0.194 year-1, t0=-2.282 year; r2=0.722) and for females (L∞=49.78 cm, k=0.114 year-1, t0=-3.052 year; r2 = 0.747). There was no significant differences in mean lengths (t–test, p>0,05) and in the von Bertalanffy growth curves (Ftest, p>0,05) between sexes. The validity of otolith readings for estimating age and growth was supported by results from backcalculation method. No significant differences were found in the Bertalanffy growth curves between direct reading of otoliths and backcalculation. Growth parameters estimated from backcalculated sizes-at-age were: for both sexes, L∞=48.28 cm, k=0.135 year-1, t0=-2.898 year and r2=0.999; for males, L∞=44.79 cm, k=0.143 year-1, t0=-3.207 year, r2=0.999; and females, L∞=44.63 cm, k=0.163 year-1, t0=-2.430 year, r2=0.999. The relationship between length and weight was calculated for all fish (Wt=0.00764Lt3.05746; r2=0.951), for males (Wt=0.01271Lt2.90807; r2=0.915) and for females (Wt=0.00604Lt3.12613; r2=0.948).
- Age and growth of the pink dentex Dentex gibbosus (Rafinesque, 1810) caught off the Madeira ArchipelagoPublication . Alves, Adriana; Vasconcelos, JoanaA total of 146 otoliths were extracted for age readings from 68 females (23.2-90.1 cm TL), 76 males (22.0-81.3 cm TL) and 2 undetermined (30.3-38.0 cm TL), between April 2004 and December 2007. The maximum age obtained from whole otoliths was 11 years. Differences in the growth rhythms were observed between the sexes (females: L∞=134.4, K=0.092 and t0=−0.406; males: L∞=135.9, K=0.078 and t0=−0.894; and all fish were: L∞=149.8, K=0.078 and t0=−0.784). Pink dentex attain 50% of their maximum theoretical length during their fourth year of life. The weight-length relationship (W = q Lfb) were determined separately for each sex and for all fish: for females q=0.01094 and b=3.033, for males q=0.10002 and b=3.047 and for all, q=0.01027 and b=3.046. According to the F-test, there were no significant differences between the weight-length relations obtained for females and males (F-test, F=2.2526, p=0.06646).
- Atlantic chub mackerel (Scomber colias) spawning season, size and age at first maturity in Madeira watersPublication . Vasconcelos, Joana; Afonso-Dias, Manuel; Faria, GraçaThe pelagic chub mackerel, Scomber colias Gmelin, 1789 is one of the most important fishery resources in the Madeira Archipelago. S. colias is caught by a small and coastal purse-seine fleet that traditionally operates around the islands. Monthly samples of chub mackerel were taken from commercial landings, between January 2002 and December 2005. Sex and maturity were assigned by visually inspecting the gonads of 1998 males (17.4-46.0 cm total length, TL; 0-5 yr) and 2108 females (18.0-41.2 cm TL; 0-4 yr) using a five-stages macroscopic maturity scale; 99 specimens with undetermined sex (13.0-26.8 cm TL; 0 yr) were also sampled. The analysis of monthly gonadosomatic indices and maturity stages proportions showed that gonad development started slowly in July-August and increased in October-December, for males and females. Spawning took place between January-April peaking in February-March. Maturity ogives were fitted to the observed proportions of mature males and females by using non-linear methods, to estimate size and age at first maturity: 22.12 cm TL at 1.05 yr for males and 21.55 cm TL at 0.82 yr for females.