Aspects of the reproductive biology of two pelagic sharks in the eastern Atlantic Ocean

This study used data provided by the Chinese Longline Fishery Scientific Observer Programme from the tropical eastern Atlantic Ocean to estimate the reproductive parameters of the blue shark (Prionace glauca) and crocodile shark (Pseudocarcharias kamoharai). Sizes ranged from 80 to 298 cm fork length (FL) for blue sharks and from 48 to 99 cm FL for crocodile sharks. Sexual segregation was observed during different months for both sharks. The sex ratio for blue sharks was 1.38 F:1 M, and 1 F:2.79 M for crocodile sharks. The size of adult blue sharks ranged from 144 to 280 cm for males and from 174 to 298 cm for females; and that of crocodile sharks from 63 to 97 cm for males and 78-99 cm for females. The size at 50% of maturity for blue sharks was estimated at 191.7 cm FL for females and 197.5 cm FL for males, and that of crocodile sharks was assessed at 84.9 cm FL for females and 78.5 cm FL for males. Most sexually matured females were pregnant; their means were 207.2 ± 16.4 cm FL for blue sharks and 89.4 ± 4.3 cm FL for crocodile sharks. Mature sizes for both species were significantly different among months. Embryonic sizes also varied widely among months for crocodile sharks, but a slight change was recorded for those of blue sharks. The observed mean size at birth and litter size were 34.5 cm FL and 37 ± 12 for the blue sharks, and that of the crocodile sharks, 39.5 cm FL and a dominant four embryos in the uterus. Due to the observed increasing catch trend of blue sharks and the slow reproductive cycle of crocodile sharks, this study presents the need of implementing conservation measures to ensure the sustainability of both species in their habitat.

[Relationship between the environmental factors and the CPUE (catch per unit effort) of Pseudocarcharias kamoharai in tropical Atlantic Ocean based on the GAM-Tweedie model]

Crocodile shark (Pseudocarcharias kamoharai) is an important by-catch species of tropical Atlantic tuna longline fishery. The research on the relationship between the CPUE (catch per unit effort) and environmental factors can provide basic data for resource protection and management of this important species. Based on the Tweedie distribution theory, and the data of 1085 croco-dile sharks collected by the national observers of longline fishery from 2009 to 2015 in the tropical Atlantic Ocean (6.38° S-14.92° N, 42.03°-18.53° W), theGAM-Tweedie model was established, and the temporal and spatial effects of CPUE as well as the relationship with environmental factors were analyzed. The results showed the explained cumulative deviance of the crocodile shark's CPUE to be 40.2%. The spatio-temporal factors (year, month, longitude, latitude) all hadsignificant effects (P<0.05) on the crocodile shark CPUE. The environmental factors such as sea surface height, chlorophyll a concentration, weather code, sea surface salinity and sea level pressure all had significant effects on CPUE (P<0.05). However, the Beaufort wind force and lunar calendar did not have significant effects on theCPUE (P>0.05). Significant correlation (P<0.05) was observed at different latitudes and in months between the sea surface temperature and CPUE. The standardized CPUE of the crocodile shark in 2009-2015 showed a fluctuating increase trend.

Complete mitochondrial genome of the crocodile shark Pseudocarcharias kamoharai (Lamniformes: Pseudocarchariidae)

In this study, we determined the complete mitogenome sequence of Pseudocarcharias kamoharai. The complete mitogenome of P. kamoharai is 16,694 bp in length, which contains 13 protein-coding genes, 22 transfer RNAs, 2 ribosomal RNAs and 2 non-coding regions: control region (D-loop) and origin of light-strand replication (OL). Overall, base composition of mitogenome is estimated to be 32.06% for A, 23.63% for C, 13.21% for G and 31.10% for T. The complete mtDNA sequence of P. kamoharai provides a useful data for the studies on the molecular systematic phylogeography and population genetics.

The complete mitochondrial genome of the crocodile shark, Pseudocarcharias kamoharai (Chondrichthyes, Lamnidae)

The complete mitochondrial genome of the crocodile shark consists of 16,688 bp and includes 13 protein-coding genes, 2 ribosomal RNA genes, 22 transfer RNA genes, 1 replication origin region, and 1 control region. The mitochondrial gene arrangement of the crocodile shark is the same as that of most vertebrates. Base composition of the genome is A (32.0%), T (31.0%), C (23.7%) and G (13.3%).