No abstract

Despite being one of the most abundant and highly exploited species in the Mexican Pacific Ocean, information on the biology of the silky shark, Carcharhinus falciformis is limited. The objective of the present study was to describe the reproductive biology of this species, based on 262 sharks (117 females and 145 males) caught from September 2004 to May 2006 in the Gulf of Tehuantepec, Mexico. The size of females ranged from 70 to 229 cm total length (TL); males measured from 69 to 220 cm TL. Female reproductive organ measurements showed that between 175 and 190 cm TL there was an increase in oviducal gland width (19–45 mm), as well as in uterus size (20–220 mm width). Mature males over 180 cm had calcified claspers, well-developed testes (184–282 mm) and presence of sperm in the seminal vesicles. The estimated length of males at first maturity was 180 cm, and that of females was 190 cm. Ovarian fecundity varied from 4 to 11 oocytes, and uterine fecundity varied from 2 to 14 embryos. We infer that mating occurs between May and June. We did not find sperm storage in the oviducal glands. Birth size was observed to be between 60 and 69 cm TL. No defined gestation period was observed.

The reproductive cycle of the scallop Argopecten circularis, an important resource of the fisheries in Baja California Sur, was studied in relation to exogenous factors such as temperature and photoperiod in Bahía Concepción. Monthly samples of adult specimens were used, and biometric data for the shell and soft body parts were recorded. The gonads were analysed histologically and five phases of gonadal maturation were described. This species was confirmed to be functionally hermaphroditic, with a reproductive pattern characterized by a period of maximum activity from December to March, when the dominant phases are maturity and spawning. The prevailing conditions during the main spawning peak were: water temperature between 16 and 22ºC, and photoperiod between 630 and 760 minutes of daily average illumination per month. The first maturation of the gonads, determined histologically, occurred when the organisms had an anteroposterior length of 35 mm. Spawning can occur at 47 mm. The minimum size for maturity and spawning in the general population was 58 mm. We determined that maximum reproductive potential starts at this size, and coincides with the lowest water temperature in the annual cycle. The annual variations in the spawning periods of this species, in different parts of Baja California Sur, suggest flexibility in the influence of exogenous factors and endogenous controls on the reproductive event.

The California butterfly ray Gymnura marmorata is frequently caught by artisanal fisheries in north‐western Mexico (Baja California Sur; BCS). The aim of this study was to estimate reproductive characteristics and describe the micro and macroscopic reproductive structures of female and male G. marmorata. Sampling was carried out at two fisheries landing sites located on the west coast BCS, from 2008 to 2012. The largest disc width (WD) ever recorded for this species was 131.0 cm and females were larger than males. The male sample was composed exclusively of adult specimens, with a median size at 50% maturity (WD50) estimated at 44.9 cm WD. For females, size at onset of maturity was estimated at 63.0 cm WD; WD50, at 64.7 cm WD; and size at pregnancy at 80.1 cm WD. Gonadal asymmetry was observed for the first time in this species. Indeed, in males only the left testis was functional (testicular asymmetry), while in females, only the left ovary was functional (ovarian asymmetry).

1. Devil rays of the genus Mobula are subject to fishing exploitation worldwide and are considered vulnerable to overexploitation due to population reduction, which is evidenced by a decline in the number of catches of these animals.2. Limited biological knowledge on these species has forced the use of precautionary conservation measures in countries where intensive fishing occurs. 3. This study aimed to describe biological data of interest for estimating the feasibility of the recovery of Mobula populations, emphasizing the reproductive activity of three endangered species of the genus Mobula (Mobula munkiana, Mobula thurstoni, and Mobula mobular) in the Gulf of California. 4. Reproductive organs were collected during 7 years of commercial fishing (2001)(2002)(2003)(2004)(2005)(2006)(2007), and data on population structure, sex ratio, gamete production, and the number of offspring per breeding period were obtained.