Life-history traits of an exploited skate: The short-tail yellownose skate Zearaja brevicaudata (Chondrichthyes: Rajiformes).

The short-tail yellownose skate, Zearaja brevicaudata, occurs off southern Brazil and along the Argentine continental shelf, including waters surrounding the Islas Malvinas and the upper slope, and is very frequently caught by trawl fisheries throughout its range. The age, growth, and maturity of Z. brevicaudata were investigated using 204 individuals collected by commercial fishing vessels from northern Argentina, between March 2016 and September 2019. Age was determined on a sample comprising vertebrae from 151 individuals, 60 males, ranging in size from 391 to 956 mm total length (TL), and 91 females, ranging in size from 324 to 1060 mm TL. Maximum ages determined for males and females were 22 and 29 years, respectively. A Bayesian framework was employed with a set of three candidate models to estimate growth parameters (von Bertalanffy, Gompertz, and Logistic). The von Bertalanffy model had the best fit, and the sexes showed undistinguishable growth parameters. For sexes combined, derived growth mean parameters (± S.D.) were L∞ = 1081 mm ± 64.34 mm, k = 0.09 ± 0.01 years-1 , and L0 = 248 mm ± 23.52 mm. The age at maturity was estimated at 13.15 and 14.66 years for males and females, respectively.

Age, growth, maturity and extinction risk of an exploited and endangered skate, Atlantoraja castelnaui, from off Uruguay and northern Argentina.

The spotback skate Atlantoraja castelnaui (Arhynchobatidae) is a large and threatened skate species subjected to fishing pressure, endemic to the Southwest Atlantic that occurs from Rio de Janeiro, Brazil, to San Jorge Gulf, Argentina. The age, growth, age at maturity and the maximum intrinsic rate of population increase rmax of A. castelnaui were studied using 152 specimens collected from off Uruguay and north Argentina (35°-42° S), between June 2013 and February 2020. Vertebrae from 143 individuals were used for ageing (females: n = 83, size range 404-1300 mm total length, TL; males: n = 60, size range 400-1270 mm TL). Maximum ages determined for females and males were 30 and 28 years, respectively. To fit growth models, non-linear and Bayesian estimation approaches were considered. For the first approach, a set of four candidate growth (size-at-age) models were fitted: three-parameter von Bertalanffy, two-parameter von Bertalanffy with fixed L0 , Gompertz and Logistic. In the second approach, von Bertalanffy, Gompertz and Logistic were fitted. For non-linear estimation, model selection indicated that the entire set of candidate growth models were supported by the data. The von Bertalanffy was selected as the best model for Bayesian estimation. There were no differences in growth between sexes. For the sexes combined, the von Bertalanffy growth model by Bayesian method was considered the most adequate to describe the growth of A. castelnaui (growth mean parameters ± S.D.: L∞  = 1210.29 ± 40.68 mm; k = 0.12 ± 0.01 years-1 ; L0  = 179.20 ± 11.62 mm). The age at maturity was estimated at 16.21 and 14.04 years for females and males, respectively. The maximum intrinsic rate of population increase rmax was estimated as 0.252 years-1 . Life-history traits and rmax provided in the present study suggest that this species has a relatively low productivity and may be vulnerable to an intense fishing pressure.

Feeding habits of the cockfish, Callorhinchus callorynchus (Holocephali: Callorhinchidae) from off northern Argentina

The feeding habits of Callorhinchus callorynchus were investigated in coastal waters off northern Argentina. The effect of body size, seasons and regions was evaluated on female diet composition using a multiple-hypothesis modelling approach. Callorhinchus callorynchus fed mainly on bivalves (55.61% PSIRI), followed by brachyuran crabs (10.62% PSIRI) and isopods (10.13% PSIRI). Callorhinchus callorynchus females showed changes in the diet composition with increasing body size and also between seasons and regions. Further, this species is able to consume larger bivalves as it grows. Trophic level was 3.15, characterizing it as a secondary consumer. We conclude that C. callorynchus showed a behavior of crushing hard prey, mainly on bivalves, brachyuran, gastropods and anomuran crabs. Females of this species shift their diet with increasing body size and in response to seasonal and regional changes in prey abundance or distribution.(AU)

RESUMEN Los hábitos alimentarios de Callorhinchus callorynchus fueron investigados en las aguas costeras del norte de Argentina. Se evaluó el efecto del tamaño del cuerpo, la temporada y la región sobre la composición de la dieta de las hembras mediante un enfoque de modelado de múltiples hipótesis. Callorhinchus callorynchus se alimentó principalmente de bivalvos (55,61% PSIRI), seguido de cangrejos brachyuras (10,62% PSIRI) y de isópodos (10,13% PSIRI). Las hembras de C. callorynchus presentaron cambios en la dieta con incremento del tamaño del cuerpo, la temporada y la región. Además, esta especie es capaz de consumir bivalvos de mayor tamaño a medida que incrementa el tamaño del cuerpo. El nivel trófico fue calculado en 3,15, caracterizando a esta especie como un consumidor secundario. Concluimos que C. callorynchus presentó un comportamiento de triturador de presas duras, principalmente bivalvos, cangrejos y gasterópodos. Las hembras de esta especie cambian su dieta con el incremento del tamaño del cuerpo y en respuesta a cambios temporales y regionales en la abundancia y distribución de sus presas.(AU)

Diet composition and feeding habits of the eyespot skate, Atlantoraja cyclophora (Elasmobranchii: Arhynchobatidae), off Uruguay and northern Argentina

The eyespot skate, Atlantoraja cyclophora, is an endemic species from the southwestern Atlantic, occurring from Rio de Janeiro, Brazil, to northern Patagonia, Argentina. The feeding habits of this species, from off Uruguay and north Argentina, were evaluated using a multiple hypothesis modelling approach. In general, the diet was composed mainly of decapod crustaceans, followed by teleost fishes. Molluscs, mysidaceans, amphipods, isopods, lancelets and elasmobranchs were consumed in lower proportion. The consumption of shrimps drecreased with increasing body size of A. cyclophora. On the other hand, the consumption of teleosts increased with body size. Mature individuals preyed more heavily on crabs than immature individuals. Teleosts were consumed more in the south region (34º - 38ºS) and crabs in the north region (38º - 41ºS). Shrimps were eaten more in the warm season than in the cold season. Prey size increased with increasing body size of A. cyclophora , but large individuals also consumed small teleosts and crabs. Atlantoraja cyclophora has demersal-benthic feeding habits, shifts its diet with increasing body size and in response to seasonal and regional changes in prey availability and distribution.(AU)

La raya de círculos, Atlantoraja cyclophora , es una especie endémica del Atlántico Sudoccidental, que se distribuye desde Río de Janeiro, Brasil, hasta el norte de la Patagonia, Argentina. Los hábitos alimentarios de esta especie fueron evaluados frente a la costa de Uruguay y norte de Argentina, utilizando un enfoque de modelado de múltiples hipótesis. En general, la dieta estuvo compuesta principalmente por crustáceos decápodos (71,37 %IRI), seguido de peces teleósteos (28,54 %IRI). En menor proporción fueron consumidos moluscos, misidáceos, anfípodos, isópodos, anfioxos y elasmobranquios. El consumo de decápodos Natantia disminuyó con el incremento del tamaño del cuerpo de A. cyclophora . Por otro lado, el consumo de teleósteos se incrementó con el incremento del tamaño del cuerpo. Individuos maduros consumieron cangrejos en mayor proporción que individuos inmaduros. Los teleósteos fueron consumidos mayormente en la región sur (34º - 38ºS) y los cangrejos en la región norte (38º - 41ºS). Los decápodos Natantia fueron más consumidos en la estación cálida que en la estación fría. El tamaño de las presas consumidas se incrementó con el aumento del tamaño corporal de A. cyclophora , pero individuos de mayor tamaño no abandonadon el consumo de pequeños cangrejos y teleósteos. Atlantoraja cyclophora presenta hábitos alimentarios demersal-bentónicos, cambia su dieta con el incremento del tamaño corporal y en respuesta a cambios estacionales y regionales en la disponibilidad y distribución de las presas.(AU)