The Pacific sharpnose shark, (Rhizoprionodon longurio, Jordan and Gilbert, 1882), migrates along the Pacific coast of Mexico. It is captured with gillnets and bottom long lines commonly used in the artisanal fishery of Mazatlan. From a sample of 3 464 individuals, R. longurio was observed to be a viviparous shark of small size, which is born at an average length of 31 cm total length (TL), after a gestation period of 10 to 11 months. The number of embryos showed no statistical relationship to the TL. The average number of embryos per female was 7.4 (σ = 2.01, n = 146) and sex ratio was 1:1. Observations on the growth of the claspers indicated that male maturity begins at 93 cm TL. The two smallest gravid females measured were 83 and 87 cm TL. The rest of the gravid females were at least 92 cm TL. Between 90 and 95 cm TL, the females exhibited an increase in the width of the oviducal gland and its size ranged from 5 to 12 mm. The statistical relationship between weight and length is presented in which females reach a larger size than males. The diet of R. longurio was composed principally of crustaceans and demersal teleost fishes.

There is a lack of basic biological information on the shark species caught in the region around the "Tres Smooth hammerhead Sphyrna zygaena (35%), silky shark Carcharhinus falciformis (27%) and blue shark Prionace glauca (25%) were the most important species of 2 004 sharks observed at La Cruz de Huanacaxtle. At Isabel Island, the most important species of 7 464 sharks sampled were S. lewini (49%) and Pacific sharpnose shark Rhizoprionodon longurio (45%). This paper describes the shark species caught at these islands, the catch per unit effort of the principal species throughout the fishing season, their length frequency distributions and percent mature, and gear selectivity issues.

We report on the proportion of maturity stages as a function of size of the Pacific sharpnose shark Rhizoprionodon longurio. Based on the development of internal and external organs, males and females were classified as immature or mature. A logistic model was fitted to develop a maturity curve to estimate the length at which 50% of the individuals are mature (L 50%). This species has an annual reproductive cycle and its birthing season is from April to July, with June as the main month. For males, L 50% = 100.61 cm total length (TL) and = 2.57, and for females, L 50% = 92.9 cm TL and = 1.08. For pregnant females, L 50% = 106.4 cm TL and = 6.11. The maturity curves obtained in the present study can be used in demographic studies to produce more accurate forecasts of the population reproductive rate and thus develop fishery management measures for this species.

We assessed the spatial pattern of genetic structure of smooth hammerhead shark Sphyrna zygaena in 10 localities from the Northern Mexican Pacific. A total of 35 haplotypes were identified in 129 sequences of the mtDNA control region. The results showed slight but significant genetic structure among localities (ΦST = 0.044, P < 0.001). In addition, the localities with highest number of juveniles were genetically different (ΦST = 0.058, P < 0.024), which may be representative of nursery areas. The genetic differentiation pattern can be associated to female philopatry and preference for particular birthing sites. Finally, historical demography shows that S. zygaena populations present a recent demographic expansion that occurred during glacial events in the late Pleistocene to early Holocene.

Defining species boundaries is important not only for the appropriate attribution of life history and ecological traits but also for sustainable fishery management and for the conservation of biodiversity. Problems arise from taxonomic uncertainty and incorrect species delineation leading to historical misidentification. This is the case of Pacific guitarfishes in the genus Zapteryx. We use a molecular phylogenetic approach combining mitochondrial and nuclear loci to investigate genetic variation in fish along the Mexican Pacific coast. Our analyses reveal a lack of nuclear and mitochondrial distinction between rays identified morphologically as banded guitarfish Z. exasperata and as southern banded guitarfish Z. xyster, casting doubts on the validity of their current systematics. However, we detected two mitochondrial lineages in accordance with the number of species described for the Pacific: a “northern” lineage corresponding to Z. exasperata and a “southern” lineage possibly attributable to Z. xyster. The poorly understood phenotypic plasticity in coloration and size of the evolutionary lineage of Z. exasperata and its apparently wider than currently thought geographic distribution (at least to Oaxaca) are the major sources of confusion regarding the taxonomic and geographic delineation of these nominal species. In light of our findings, eastern Pacific guitarfishes in the genus Zapteryx require a thorough taxonomic revision using morphological and genetic data to unveil what appears to be a complex pattern of diversification.