Age and growth of Zapteryx brevirostris (Elasmobranchii: Rhinobatidae) in southern Brazil

Age and growth studies are fundamental to successful fisheries management. Zapteryx brevirostris (Müller & Henle, 1841) is distributed off the Brazilian continental shelf and this species is assessed as "Vulnerable" in the Red List of the International Union for the Conservation of Nature (IUCN). Thus, the objective of this study was to present previously unknown information about the age and growth of Z. brevirostris that can be used for its management, conservation, and fisheries. A total of 162 specimens were sampled, with total lengths (TL) varying between 35.7 cm and 56 cm. The vertebrae were embedded in resin, sectioned in cuts with 0.5 mm thickness and the growth bands of the vertebrae were read under a light microscope. In the studied area, Z. brevirostris ages were estimated from 4 to 10 years according to vertebrae patterns. The species reaches its maximum asymptotic size (Linf) around 56 cm (56 cm for females and 50.37 cm for males). This is the first estimate of age and growth for a species of the Zapteryx genus, and the results support the hypothesis that this ray requires future management conservation, particularly due to its slow growth rate and consequent susceptibility to overexploitation.(AU)

Estudos de idade e crescimento são fundamentais para o sucesso da gestão pesqueira. Zapteryx brevirostris (Müller & Henle, 1841) distribui-se pela plataforma continental brasileira, sendo classificada como "Vulnerável" no livro vermelho da IUCN (International Union for the Conservation of Nature). Assim, o objetivo deste estudo foi apresentar informações previamente desconhecidas sobre a idade e o crescimento de Z. brevirostris que podem ser utilizados para sua gestão, conservação e pescas. No total foram amostrados 162 espécimes, com comprimento total (CT) variando de 35.7 cm a 56 cm. As vértebras foram incluídas em resina e seccionadas num corte com cerca de 0.5 mm de espessura, e as bandas de crescimento das vértebras foram lidas com microscópio de luz transmitida branca. Na área estudada, Z. brevirostris possui idades estimadas entre os 4 a 10 anos de idade, de acordo com seu padrão de vértebras. A espécie atinge seu Linf (comprimento máximo assintótico) em torno dos 56 cm (56 cm para fêmeas e 50.37 cm para machos). Essa é a primeira estimativa dos parâmetros de idade e crescimento para uma espécie do gênero Zapteryx, e os resultados obtidos corroboram a hipótese de que a espécie requer uma gestão de conservação adequada, devido sobretudo à sua lenta taxa de crescimento e consequente suscetibilidade à sobre-exploração.(AU)

Comparative age and growth of common snook Centropomus undecimalis (Pisces: Centropomidae) from coastal and riverine areas in Southern Mexico

Common snook Centropomus unidecimalis is an important commercial and fishery species in Southern Mexico, however the high exploitation rates have resulted in a strong reduction of its abundances. Since, the information about its population structure is scarce, the objective of the present research was to determine and compare the age structure in four important fishery sites. For this, age and growth of common snook were determined from specimens collected monthly, from July 2006 to March 2008, from two coastal (Barra Bosque and Barra San Pedro) and two riverine (San Pedro and Tres Brazos) commercial fishery sites in Tabasco, Mexico. Age was determined using sectioned saggitae otoliths and data analyzed by von Bertalanffy and Levenberg-Marquardt among others. Estimated ages ranged from 2 to 17 years. Monthly patterns of marginal increment formation and the percentage of otoliths with opaque rings on the outer edge demonstrated that a single annulus was formed each year. The von Bertalanffy parameters were calculated for males and females using linear adjustment and the non-linear method of Levenberg-Marquardt. The von Bertalanffy growth equations were FLt=109.21(1-e-0.21(t+0.57)) for Barra Bosque, FLt=94.56(1-e-0.27(t+0.48)) for Barra San Pedro, FLt=97.15(1-e-0.17(t+1.32)) for San Pedro and FLt=83.77(1-e-0.26(t+0.49)) for Tres Brazos. According to (Hotelling’s T², p<0.05) test growth was significantly greater for females than for males. Based on the Chen test, von Bertalanffy growth curves were different among the study sites (RSS, p<0.05). Based on the observed differences in growth parameters among sampling sites (coastal and riverine environments) future research need to be conducted on migration and population genetics, in order to delineate the stock structure of this population and support management programs.

El robalo blanco Centropomus undecimalis representa un ingreso monetario significativo y un recurso alimentario para todas las comunidades rurales cercanas a su distribución. Se determinó la edad y crecimiento de esta especie. Los organismos se recolectaron mensualmente en los desembarcos de la pesca artesanal de las cooperativas de mayor contribución en la zona costera (Barra Bosque y San Pedro) y ribereña (San Pedro y Tres Brazos) entre julio 2006 y marzo 2008. La edad se determinó mediante otolitos seccionados. La edad estimada fue de 2 a 17 años. Mensualmente se estableció la formación anillos opacos y traslúcidos. Para ambas zonas de estudio agrupadas, se validó el retrocálculo por comparación de tres métodos (Fraser-Lee, Dahl-Lea y Whitney-Carlander), se encontraron diferencias significativas (ANCOVA, p<0.05) entre el promedio de la longitud observada y la longitud retrocalculada. Las constantes de la ecuación de von Bertalanffy fueron calculadas para cada sexo y combinados, se empleó el método no lineal de Levenberg-Marquardt’s. La edad estimada para el robalo blanco fue de 2 a 17 años. Se encontraron diferencias significativas en el crecimiento entre sexos (T² Hotelling, p<0.05). Los parámetros de crecimiento para ambos sexos fueron, zona costera: Barra Bosque Lf t=109.21(1-e-0.21(t+0.57)), Barra San Pedro Lf t=94.56(1-e-0.27(t+0.48)), y para la zona ribereña: San Pedro Lf t=97.15(1-e-0.17(t+1.32)) y Tres Brazos Lf t=83.77(1- e-0.26(t+0.49)). Se encontraron diferencias significativas en las curvas de crecimiento de von Bertalanffy entre las poblaciones comparadas (RSS, p<0.05).