Jaime Otero

Contemporary ocean warming and freshwater conditions are related to later sea age at maturity in Atlantic salmon spawning in Norwegian rivers

Atlantic salmon populations are reported to be declining throughout its range, raising major management concerns. Variation in adult fish abundance may be due to variation in survival, growth, and timing of life history decisions. Given the complex life history, utilizing highly divergent habitats, the reasons for declines may be multiple and difficult to disentangle. Using recreational angling data of two sea age groups, one-sea-winter (1SW) and two-sea-winter (2SW) fish originated from the same smolt year class, we show that sea age at maturity of the returns has increased in 59 Norwegian rivers over the cohorts 1991–2005. By means of linear mixed-effects models we found that the proportion of 1SW fish spawning in Norway has decreased concomitant with the increasing sea surface temperature experienced by the fish in autumn during their first year at sea. Furthermore, the decrease in the proportion of 1SW fish was influenced by freshwater conditions as measured by water discharge during summer months 1 year ahead of seaward migration. These results suggest that part of the variability in age at maturity can be explained by the large-scale changes occurring in the north-eastern Atlantic pelagic food web affecting postsmolt growth, and by differences in river conditions influencing presmolt growth rate and later upstream migration.

Erratum to: Histomorphological study of ovarian atresia over the reproductive cycle of Octopus vulgaris from Galician waters (NW Spain)

Atresia has been poorly examined in cephalopods. We here provide a histological description of this process along the whole ovary development for Octopus vulgaris. Additionally, we related its occurrence to morphometric parameters, and its seasonal cycle was further analysed. Atresia occurred all year round in immature and mature females and in previtellogenic and vitellogenic oocytes. However, more mature females were more prone of being atretic. This occurred mainly in spring when females had atretic previtellogenic oocytes in mature macrostages. By contrast, vitellogenic atresia occurred mainly from spawning to post-spawning females. Furthermore, two types of phagocytic cells were identified as responsible for the reabsorption during atresia. The phagocytic follicle cells only occurred in yolk-bearing oocytes; and within the two haemocyte populations only the smaller ones seemed to be involved in engulfing atretic oocytes. Additionally, advanced atresia in post-spawning females showed yellow–brown bodies as a possible result of follicle cell apoptosis and highlighting the end of the reproductive cycle. Given the pattern of atresia, the reproductive strategy of this species is based on an asynchronic ovary development and a synchronous ovulation during spawning. We further suggest that potential fecundity for this species should be measured on late vitellogenic oocytes in pre-spawning females.