Early life history affects fish size mainly by indirectly regulating the growth during each stage:a case study in a demersal fish

The complex life histories of demersal fishes are artificially separated into multiple stages along with changes in morphology and habitat.It is worth exploring whether the phenotypes expressed earlier and later during the life cycle are related or decoupled.The life stages of first year Pacific cod(Gadus macrocephalus)were tracked over different hatch years and regions to test whether the early life history had a long-lasting effect on subsequent growth.We further explored the contribution of growth in the early and subsequent life history stages to body size at the end of each stage.In addition to the accessory growth centre and the first annual ring,the other two checks on the otolith possibly related to settlement and entering deeper waters were identified in 75 Pacific cod individuals.The direct and indirect relationships among the life history stages was interpreted based on path analysis.The results showed that growth prior to the formation of the accessory growth centre had a significant effect on the absolute growth of the fish before and after settlement and migration to deep water.However,there was no or moderate evidence that early growth affected the body size at each stage,which was mainly regulated by growth during the stage.This study supports the lasting effect of early growth and clarifies that it affects size mainly by indirectly regulating staged growth.Quantifying the phenotype relationships and identifying the internal mechanisms form the basis for assessing population dynamics and understanding the processes behind the changes.

Simulation of the distribution,growth,and survival rate of chub mackerel larvae and juveniles in the East China Sea

In the East China Sea(ECS),chub mackerel Scomber japonicus constitutes an important coastal-pelagic fishery resource that is mainly exploited by Chinese,Japanese,and Korean light-purse seine fisheries.Because the early life history of chub mackerel plays a significant role in its recruitment,we developed an individual-based model to study the distribution,growth,and survival rate of chub mackerel larvae and juveniles in the ECS to improve our understanding of the chub mackerel population structure and recruitment.Our results show that as body length rapidly increases,the swimming capacity of chub mackerel larvae and juveniles improves quickly,and their spatial distribution depends more on their habitat conditions than the ocean currents.Correspondingly,the juveniles from the central and southern ECS spawning ground are scarcely recruited into the Japan/East Sea(JES)or the western Pacific Ocean,but a significant proportion of juveniles from the northern ECS spawning ground still enter the JES and there are exchanges between the stocks in the ECS and JES.Thus,it seems more reasonable to assess and manage the chub mackerels in the ECS and JES as a stock.The water temperature and ocean primary production in the ECS are two important factors influencing the chub mackerel habitat conditions and their spatial and temporal distribution are significantly different as the spawning time changes.Therefore,the spawning time and location play an important role in the growth and survival rate of the larvae and juveniles.Generally,when chub mackerel spawns at the southern ECS spawning ground in March,the larva and juvenile growth and survival rate is relatively high;as spawning time moves forward,higher growth and survival rates would be expected for the chub mackerel spawned coastward or northward.For specific spawning sites,early or delayed spawning will reduce the survival rate.

A Review of Interaction Between Neon Flying Squid(Ommastrephes bartramii) and Oceanographic Variability in the North Pacific Ocean

The neon flying squid （Ommastrephes bartramii） is a short-lived opporttmistic species widely distributed in subtropical and temperate waters in the North Pacific Ocean. The life cycle of O. bartramii from planktonic eggs to nektonic adults is closely linked to oceanographic conditions. The fluctuations in O. bartramii abundance and distribution tend to increase and widen continu- ously due to the heavy influences of ocean-climate events on various spatio-temporal scales. In this study, we reviewed the interac- tion between O. bartramii and oceanography variability in the North Pacific with respect to large-scale climatic-oceanic phenomena including E1 Nifio, La Nifia, Kuroshio, Oyashio and Pacific Decadal Oscillation （PDO）, as well as regional environmental variables such as sea surface temperature （SST）, sea surface height （SSH）, sea surface salinity （SSS）, chlorophyll-a （Chl-a） concentration, and plankton density. The population dynamics of O. bartramii is mediated mainly by meso- and large-scale climatic-oceanic events （e.g., Kuroshio and Oyashio Currents） rather than other local environmental conditions （e.g., SST and Chl-a concentration）, because all of the oceanographic influences are imposed on the context of large-scale climate changes （e.g., PDO）. An unstructured-grid finite- volume coastal ocean model coupled with an individual-based model is proposed to simulate relevant physical-biological oceano- graphic processes for identifying ocean-climate influence and predicting O. bartramii distribution and abundance in the North Pacific. Future research needs to be focused on improving the knowledge about early life history of O. bartramii and evaluating the relation- ship between marine physical environment and two separate passive drifting life stages of O. bartramii including free-floating eggs and planktonic paralarvae.