Biochemical changes, specifically in hemocyanin and glucose concentrations in hemolymph, glycogen in the digestive gland, were studied throughout the

Age and growth of bull shark, Carcharhinus leucas, was investigated in the southern Gulf of Mexico (Veracruz and Campeche, Mexico) from December 1993 through June 1997. Ninety-five specimens were obtained from commercial fishery catches, and vertebrae were examined from 20 males, 61 females and 14 individuals unidentified to sex. Vertebrae were examined using five different techniques to enhance the visibility of growth rings: i) alizarin red stain, ii) crystal violet stain, iii) X-ray, iv) silver nitrate stain, and v) without staining. Verification of temporal growth ring forma - tion was done by the indirect method of marginal increment analysis. An isometric relationship was found between growth and length of centrum, is described by a linear equation. Age-at-maturity was 10 years (204 cm total length, TL) for females and 9-10 years (190-200 cm TL) for males. The old- est female was 28 (256.0 cm TL), and the oldest male was 23 (243.0 cm TL). The von Bertalanffy growth parameters were estimated for the species (L∞ = 256.4 cm TL, k = 0.1397 per year and to = -1.935), for males (L∞ = 248.4 cm TL, k = 0.1692 per year and to = -1.03), and for females (L∞ = 262.1 cm TL, k = 0.1235 per year and to = -2.44). Sexual differences for each particular growth curve were found, L∞ being the parameter that showed the greatest difference between males and females; females attain a larger size.

Climate change is currently considered one of the main phenomena affecting marine species through expansion or contraction of their distribution. Being ectothermic organisms, sharks of the family Carcharhinidae could be highly susceptible to the effects of climate change. These sharks are of great ecological importance, which is reflected in their role in the integrity of coastal and oceanic ecosystems as top predators that act to maintain the stability of the food chain, as well as providing economic value through fishing, consumption, and ecotourism. Currently, their populations are threatened by fishing pressure and anthropogenic activities, including meeting the demand for shark fins. Despite the ecological and economical importance of carcharhinid sharks, knowledge regarding how they are impacted by climate change remains scarce. Ecological niche modeling is a tool that allows analysis of future potential distributions under different climate change scenarios and could contribute to future planning activities and improved conservation outcomes for sharks. We generated models in Maxent in order to predict the potential geographic distribution of 25 carcharhinid sharks that inhabit Mexican waters, projecting this onto future climate change scenarios (RCP2.6, RCP4.5, RCP6.0, and RCP8.5) to calculate the potential losses and gains in their distribution areas by the year 2050. The greatest shifts in suitable areas were observed for the sharksTriaenodon obesus(gained area) andCarcharhinus porosus(lost area). Overall, under all four RCP future scenarios, six species presented gains in suitable area and 19 species presented losses. The greatest loss of suitable area for carcharhinid sharks was found with RCP8.5; however, under this high-emissions global warming scenario, seven species actually showed an increase in distribution area. Our results therefore indicate that climate change could reduce suitable areas for most of the species by 2050. Assessment of the distribution of shark species under climate change is urgently required in order to prioritize conservation efforts toward the most vulnerable species and to ensure the natural function of marine ecosystems, thus maintaining the important ecosystem services they provide to human society.