Interannual variability of distribution, abundance and population dynamics of the smooth hammerheadSphyrna zygaena(Linnaeus, 1758) in the central‐southeast Pacific Ocean

Abstract

This study provides information on the population dynamics of the smooth hammerhead shark Sphyrna zygaena in the central-southeast Pacific Ocean. The samples were obtained from artisanal fisheries from 2008 to 2013 to analyse cohorts, growth, mortality, abundance and recruitment using methods based on length and relative age and an inference multi-model. According to the von Bertalanffy growth model, the results indicated that the species showed from three to seven cohorts annually and slow growth (W i = 57.20%): L ∞ = 292.86 cm, K = 0.141 per year and t 0 = −2.26. Length of sexual maturity was 239.30 and 209.10 cm at first capture; the average natural mortality value was 0.231 per year, by fishing 0.051 per year with a total mortality of 0.26 1 per year and exploitation rate of 0.15. Interannual variability was recorded in biomass with an average of 7367.24 tonnes, as well as a spatial permanence pattern. The results suggest that the La Niña event biologically favours the population in the area. The information from this study is essential for better understanding the species population and serves as a basis for future actions of management and conservation of S. zygaena.

Catch Composition, Seasonality and Biological Aspects of Sharks Caught in the Ecuadorian Pacific

“…and between 2007 and 2012 (263.7 cm TL) [97]. According to the maturity size of this study, 89.80% of the landed male individuals were immature, while 97.67% of the females had not reached sexual maturity, taking as a reference the maturity size estimated by López-Martínez et al (239.3 cm TL) [97].…”

“…Therefore, a greater vigilance and the application of stricter laws are needed [95,96]. Regarding the sexual proportion, no significant differences were found, disagreeing with what was reported in the Ecuadorian Pacific, between 2003 and 2006, where the sexual proportion was biased towards males [15], while another study carried out between 2007 and 2012 in the same region registered bias towards females [97]. The maturity size for males in this study (200.81 cm Tl) was higher than that reported in the Gulf of California, between 1995 and 2000 (193.7 cm TL) [46], but lower than reported in the Ecuadorian Pacific, between 2003 and 2006 (215 cm TL) [98],…”

“…and between 2007 and 2012 (263.7 cm TL) [97]. According to the maturity size of this study, 89.80% of the landed male individuals were immature, while 97.67% of the females had not reached sexual maturity, taking as a reference the maturity size estimated by López-Martínez et al (239.3 cm TL) [97]. These results are consistent with other studies conducted in the Ecuadorian Pacific [16,19], where most of the individuals landed were immature.…”

Population Dynamics and Exploitation Level of Stolothrissa tanganicae Regan, 1917 and Limnothrissa miodon (Boulenger, 1906), Two Clupeid Fish Species of Commercial Interest of Burundian Waters Northeast of Lake Tanganyika

“…The fish total length, which is most frequently used [19][20][21][22][23][24], was used to study the following parameters: size frequency, growth parameters, mortality, and recruitment pattern. Data processing was carried out using FiSAT II, the FAO software [25].…”