Abstract
The Chilean jack mackerel Trachurus murphyi support an important fishery in the South-eastern Pacific Ocean and has declined considerably over time. T. murphyi have asynchronous ovarian development with an oceanic spawning (September to January). Despite the economic importance of this resource critical issue such as characteristics and dynamics of atresia, which affect the reproductive output, are unknown. Females of T. murphyi caught in different spawning seasons were analysed to describe patterns of prevalence and intensity of atresia. General linear models (GLM) were performed by using prevalence and intensity atresia as response variables and gonadosomatic index, condition factor, sea surface temperature, postovulatory follicles and month/year as explanatory variables. The batch fecundity and relative fecundity were compared between females showing atresia, postovulatory follicles and non-atretic females. The stages of atresia identified were alpha, beta and gamma. The GLM showed that variations in the prevalence and intensity of atresia were explained for all variables, except condition factor for prevalence, and gonadosomatic index for intensity of atresia. According to our results, the dynamic of alpha and beta atresia could be considered a potential proxy for any disruption of spawning season. The batch fecundity and relative fecundity were lowest compared with other Trachurus spp. This is the first assessment comparing fecundity between atretic and not atretic females for this species.
Highlights
In the South-eastern Pacific Ocean (SEP), industrial fisheries for the highly migratory Chilean jack mackerel Trachurus murphyi Nichols, 1920
Ethical approval was not required for this study, due all specimens were collected as part of research cruises that are performed for the evaluation of spawning biomass (DEPM) in the Chilean jack mackerel, Trachurus murphyi from oceanic spawning area off central Chile (Table 1)
Trachurus murphyi showed three mains sequential atretic stages (Alpha, Beta and Gamma), like others Trachurus species (Macewicz & Hunter 1993, Karlou-Riga & Economidis 1997, Gordo et al 2008); being prevalence and intensity of atresia influenced by months/years of spawning seasons
Summary
In the South-eastern Pacific Ocean (SEP), industrial fisheries for the highly migratory Chilean jack mackerel Trachurus murphyi Nichols, 1920. In the SEP, Chilean jack mackerel conform a single large population (Poulin et al 2004, Cárdenas et al 2009) that can be found in three different habitats (Arcos et al 2001) according to its life history: a) nursery ground area, b) coastal feeding area and c) a large, main oceanic spawning area off central Chile (Bertrand et al 2004, Cubillos et al 2008, Vásquez et al 2013). For T. murphyi, is not easy to find females harbouring hydrated oocytes during the spawning season (George 1995, Leal et al 2013), vitellogenic oocytes could be counted, and in this case, atresia must be quantified (Saborido-Rey & Kjesbu 2005). The main objectives were (1) to describe the phases of atresia in T. murphyi caught during the post-migration spawning period in order to evaluate the spawning history, (2) to determine the prevalence and intensity of atresia in different spawning periods and its relation with physiological conditions and environmental factors and (3) to determine the impact of atresia in the fecundity
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