Maturation of Squalus mitsukurii and Cirrhigaleus asper (Squalidae, Squaliformes) in the southwestern equatorial Atlantic Ocean

Abstract

Summary Specimens of Squalus mitsukurii (n = 206) and Cirrhigaleus asper (n = 93) were opportunistically collected from the catches of a research vessel using traps and benthic longlines off the coast of northeastern Brazil between March 1997 and August 2002. For both species, larger females than males were captured. Catches of S. mitsukurii were biased toward females (1 : 4.6), while no significant disequilibrium in sexes was detected for C. asper (1 : 0.86). Common regressions for total length (TL) and eviscerated weight (EW) were calculated as LnEW = 3.13LnTL − 6.217 (S. mitsukurii) and LnEW = 3.22LnTL − 7.01 (C. asper). Based on changes to the reproductive tract, females and males of each species were categorized into several stages of maturation. Sizes at sexual maturity for female (n = 169) and male (n = 37) S. mitsukurii were 77.8 and 65.0 cm TL, respectively. Gravid S. mitsukurii had between 3 and 11 embryos that ranged in size from 2.0 to 22.5 cm TL (n = 262). No significant bias in the sex ratio of embryos was detected. A clear relationship between embryonic development and maturation of the ovary demonstrated that female S. mitsukurii are ready to ovulate immediately after parturition. Female (n = 43) and male (n = 50) C. asper approached sexual maturity at 110.0 and 91.0 cm TL, respectively. Uterine fecundity in gravid C. asper ranged from 12 to 19 embryos that varied in size between 4.0 and 21.9 cm TL. Unlike S. mitsukurii, there was no concurrent development of the ovary and embryos. The results are discussed in terms of the reproductive plasticity of S. mitsukurii and the need for further life history studies on both species.

Deep-Water Sharks, Rays, and Chimaeras of Brazil

“…Deep-water Chondrichthyes of Brazil. These large captures suggest that it is likely that these species will become commercially exploited in the near future [45].…”

“…The chartered boat program was reviewed in 2002; mainly because of the influence and research on the monkfish fishery by the scientific crew of the Universidade do Vale do Itajaí-UNIVALI. However, this fishery continues and tends to expand toward the continental slope of the north and northeast coasts of Brazil [45], that brings concern on how fast local researchers will be able to follow fisheries growth and trends.…”

Is multiple mating beneficial or unavoidable? Low multiple paternity and genetic diversity in the shortspine spurdog Squalus mitsukurii

“…S. mitsukurii gestate their young for 24 mo (Compagno et al 2005) and give birth to average of 6 pups per litter (Table 1). Every mature female S. mitsukurii caught for the present study had either fertilized ova or embryos; like the congener S. acanthias, S. mitsukurii appears to have little or no quiescent period between pregnancies (Fischer et al 2006, T. S. Daly-Engel & R. D. Grubbs unpubl. data), such that successful copulation most likely occurs very soon following parturition.…”

Proporción sexual, relación talla-peso y distribución geográfico-batimétrica de Squalus cubensis (SQUALIFORMES: SQUALIDAE) en la costa Caribe de Centroamérica

“…Dicho análisis de sexos no se hizo por área ni por profundidad, sino sobre la población total, caso contrario al estudio con trampas y líneas bentónicas hecho por Fischer et al (2006), donde se encontró una proporción de sexos mayor para hembras que para machos de Squalus mitsukurii. Por lo tanto, por las condiciones de nuestro muestreo, no podría sugerirse que exista una vulnerabilidad a las faenas de pesca en función del sexo, ni tampoco una predominancia por sexo en las poblaciones asociadas a una posible segregación sexual por área o profundidad como lo reportaron en un estudio reproductivo para Squalus megalops en el Atlántico sur.…”

“…Este autor indica que frecuentemente se observa un dimorfismo sexual en la talla de tiburones y que, además, es más evidente en especies vivíparas, pues las hembras necesitan mucha más energía para ser empleada en el proceso reproductivo (útero, gónadas y embriones) y, por ende, existe una fuerte presión de selección hacia una talla más grande. Así mismo Fischer et al (2006), reportaron tallas mayores para hembras con respecto a los machos en Squalus mitsukurii.…”