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Fishery Bulletin 11 6(1) 
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35 
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14 16 18 20 22 24 26 28 30 32 34 36 
Length (cm) 
□ Madeira m Canary Islands ■ Portugal mainland 
Figure 3 
Length-frequency distribution per sampling area for blue jack mackerel (Trachurus 
picturatus ) sampled in 2015 for this study in 3 areas: off Peniche, a city on the 
coast of Portugal, off the Madeira archipelago, and off the Canary Islands 
purse seine fishing off both Madeira and the Canary 
Islands; and trawling off Peniche. 
Samples from waters off Peniche and off the Canary 
Islands were stored frozen (-20 e C) until just before 
they were measured at the laboratory, and all steps 
were taken to maintain fish shape. Fish from Madeira 
were analyzed fresh. From each specimen, total length 
was measured and, after being photographed for body 
shape analysis, sex was determined macroscopically. 
Both sagittal otoliths (hereafter referred to as otoliths) 
were extracted, rinsed, and stored dry in labeled vials 
for later otolith shape analysis. 
Body shape analysis 
A total of 300 fish equally distributed among the areas 
were sampled (Fig. 3): Peniche, 22-37 cm total length 
(TL), 40 females and 60 males; Madeira, 14-27 cm TL, 
48 females and 52 males; Canaries, 16-23 cm TL, 46 
females and 54 males. 
Twelve anatomical landmarks (e.g., fin insertion 
point) were defined and used mainly along the left side 
of the body contour (Fig. 4), in order to be meaning¬ 
ful as systematic terms (Cadrin, 2000; Cadrin et al., 
2014), and were based on the 11 anatomical landmarks 
selected for horse mackerel in a similar study (Murta 
et al., 2008a). 
Each of the 100 fish was then photographed with 
the left side upwards, by using a Canon 6 EOS 700D 
digital camera (Canon, Inc., Ohta-ku, Tokyo) with 
6 Mention of trade names or commercial companies is for iden¬ 
tification purposes only and does not imply endorsement by 
the National Marine Fisheries Service, NOAA. 
a Canon EF-S 18-55 mm lens that was placed on a 
firm support to maintain a right angle and adequate 
height to stabilize and avoid image distortion. From 
each digital image, a digital TPS (thin-plane spline) 
file was generated with x and y coordinates for each 
homologous point with tpsDig software, vers. 2.10 
(Rohlf, 2006). 
Subsequent methodological procedures followed 
those of Sequeira et al. (2011) and Porrini et al. (2015). 
The tpsDig software (Rohlf, 2006) was used to acquire 
x and y coordinates of the landmarks previously not¬ 
ed, and a generalized least squares Procrustes super¬ 
imposition (Rohlf, 1990) was used to adjust them. In 
order to calculate and eliminate the effect of size on 
shape (allometry), a multivariate (total) regression of 
the Procrustes coordinates on centroid size was carried 
out with MorphoJ software, vers. 1.05c (Klingenberg, 
2011) and the residuals of this regression were used 
as ‘size-free’ variables. To test the null hypothesis of 
independence between shape and size, a permutation 
test with 10,000 runs was applied (Good, 1994). Pos¬ 
sible sexual dimorphism among study areas was tested 
by using IBM SPSS, vers. 23 (IBM Corp., Armonk, NY) 
and a multivariate analysis of variance (MANOVA). To 
detect possible morphometric differences in the body 
shape of T. picturatus among the 3 study areas, a ca¬ 
nonical variate analysis was performed with MorphoJ. 
A canonical discriminant analysis with jackknife cross- 
validation procedures was carried out with IBM SPSS 
software to calculate an unbiased estimation of clas¬ 
sification success. 
A significance level of 0.05 was set for all statistical 
analyses. 
