Age and growth of the small Mediterranean endemic skate, Raja polystigma Regan 1923 were studied through the annuli counts in vertebral centra. During the period between 2012 and 2013 a total of 183 speckled rays (97 females, ranging from 115 to 590 mm in TL and 87 males with TL among 118 and 521 mm) were caught through experimental (MED.I.T.S.) and commercial trawl surveys. From each individual total length (TL in mm) total mass (TM in g) in addition to the gender and maturity stage were recorded, then vertebral centra were extracted from the thoracic cavit. Annuli counts were made by two readers through the observation of vertebral sections stained in Alizarin Red. Readings showed a good reproducibility (Percent of Agreement = 86.8, %Cv = 7.0, Index of Average Percent Error = 5.177). The oldest skate observed was a female estimated at age 11 (TL = 590 mm) while the oldest male was aged 8 (TL = 521 mm). Four different models were applied on length at age data: the common von Bertalanffy growth function, the Exponential, and finally the Gompertz and the Logistic functions. According to the Akaike’s Information Criterion values the Logistic model (L∞ = 691.49 mm ± 10.21; K = 0.26 ± 0.008; point of inflection = 4.03 y-1 ± 0.147), followed by Gompertz function, provided the best fitting curve, showing a higher growth rate and consequently a lower L∞ value than what obtained with the VBGF (L∞ = 784.49 mm ± 12.2; K = 0.11 ± 0.004; t0 = -1.718). This result was obtained also for females and males separately. Given the best fitting results achieved with the Gompertz and the Logistic functions, R. polystigma seems to grow relatively faster during the first few years as previously reported for other batoid species.
A multiple models investigation on age and growth of the speckled ray (Raja polystigma) from Sardinian seas
BELLODI, ANDREA;ALVITO, ANDREA;FOIS, MAURIZIO;SOLDOVILLA, GIUDITTA;VITTORI, STEFANIA;MULAS, ANTONELLO
2014-01-01
Abstract
Age and growth of the small Mediterranean endemic skate, Raja polystigma Regan 1923 were studied through the annuli counts in vertebral centra. During the period between 2012 and 2013 a total of 183 speckled rays (97 females, ranging from 115 to 590 mm in TL and 87 males with TL among 118 and 521 mm) were caught through experimental (MED.I.T.S.) and commercial trawl surveys. From each individual total length (TL in mm) total mass (TM in g) in addition to the gender and maturity stage were recorded, then vertebral centra were extracted from the thoracic cavit. Annuli counts were made by two readers through the observation of vertebral sections stained in Alizarin Red. Readings showed a good reproducibility (Percent of Agreement = 86.8, %Cv = 7.0, Index of Average Percent Error = 5.177). The oldest skate observed was a female estimated at age 11 (TL = 590 mm) while the oldest male was aged 8 (TL = 521 mm). Four different models were applied on length at age data: the common von Bertalanffy growth function, the Exponential, and finally the Gompertz and the Logistic functions. According to the Akaike’s Information Criterion values the Logistic model (L∞ = 691.49 mm ± 10.21; K = 0.26 ± 0.008; point of inflection = 4.03 y-1 ± 0.147), followed by Gompertz function, provided the best fitting curve, showing a higher growth rate and consequently a lower L∞ value than what obtained with the VBGF (L∞ = 784.49 mm ± 12.2; K = 0.11 ± 0.004; t0 = -1.718). This result was obtained also for females and males separately. Given the best fitting results achieved with the Gompertz and the Logistic functions, R. polystigma seems to grow relatively faster during the first few years as previously reported for other batoid species.
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