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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. [ABSTRACT FROM AUTHOR]

Chub mackerel (Scomber japonicus) in the Northwest Pacific is an important pelagic fishery resource and a significant target species in purse seine fisheries. However, the catch of chub mackerel fluctuates greatly from year to year, and recent studies have shown that the Tsushima stock may be overfished. Therefore, research on the biology and population dynamics of this species is required to provide sufficient scientific support for the development of reasonable management and recovery plans and for the increased sustainable use of resource fisheries. In this study, a dynamic energy budget (DEB) model was constructed based on DEB theory for the complete life cycle of chub mackerel in the Northwest Pacific by using biological data to simulate processes, including growth, reproduction, and death. The key results were as follows. 1) The DEB model accurately simulated the complete life cycle of chub mackerel, with a good fit for the relationships between age and length as well as length and weight, while accurately estimating annual absolute fecundity, aging, and death and predicting the metamorphosis time of larval fish. 2) The DEB model can incorporate the effects of temperature and food to describe the effects of marine environmental conditions on chub mackerel growth. 3) The DEB model involved multiple interrelated parameters; however, owing to a lack of observational data, there was a certain degree of uncertainty in estimated parameter values. The DEB model provides a basis for establishing correlations and intrinsically unifying biological processes, including growth, sexual maturation, reproduction, aging, and death, thereby guiding studies of growth, reproduction, and population dynamics of chub mackerel in the Northwest Pacific. • Chub mackerel in the Northwest Pacific is an important fishery species. • A dynamic energy budget (DEB) model for its complete life cycle was constructed. • DEB model accurately simulated the complete life cycle processes of chub mackerel. • The model also established a temperature and food-related growth pattern. • Reasonable species management plans can be derived from the constructed model. [ABSTRACT FROM AUTHOR]

Fish populations and fishing efforts in most fisheries exhibit spatial heterogeneity. However, spatial considerations are generally ignored in fishery stock assessment and management because of a lack of spatially explicit data and poor understanding of the spatial dynamics of most fisheries. This study uses a simulation approach to evaluate the consequences of misspecifying spatial structure and migration during the assessment process. We developed an operating model to simulate a fishery using US Atlantic herring ( Clupea harengus) as our model species. This population consists of two well-defined spawning substocks distributed and mixed in four management areas. Simulations were done for three alternative 'true' populations, each having a different spatial structure both biologically and with regard to the geographic distribution of fishing effort. Stock assessments were then performed for the three simulated 'true' populations using standard methodologies and assumptions currently used. Management-area-based assessments lead to overestimation of spawning stock biomass and underestimation of fishing mortality because of the interaction within the management area between the spatial structure of the population and that of the spatially heterogeneous fishery removals. In contrast, when fishing is spatially homogeneous, movement across management boundaries may not be relevant to modeling population dynamics. Such an idealized situation does not typically hold, however. [ABSTRACT FROM AUTHOR]

Catch per unit of effort (CPUE) data can display spatial autocorrelation. However, most of the CPUE standardization methods developed so far assumes independency of observations for the dependent variable, which is often invalid. In this study, we collected data of two fisheries, squid jigging fishery and mackerel trawl fishery. We used standard generalized linear model (GLM) and spatial GLMs to compare the impact of spatial autocorrelation on CPUE standardization for different fisheries. We found that spatial- GLMs perform better than standard-GLM for both fisheries. The overestimation of precision of CPUE estimates was observed in both fisheries. Moran's I was used to quantify the level of autocorrelation for the two fisheries. The results show that autocorrelation in mackerel trawl fishery was much stronger than that in squid jigging fishery. According to the results of this paper, we highly recommend to account for spatial autocorrelation when using GLM to standardize CPUE data derived from commercial fisheries. [ABSTRACT FROM AUTHOR]

Sustainable use of fishery resources requires the effective monitoring and managing of fish stocks and fish habitats. Chub mackerel (Scomber japonicus), distributed in the East China Sea and Yellow Sea, are mainly caught by purse seine fishing fleets from China, Japan, and South Korea. This study used fishery data from Chinese large lighting–purse seine fleets and environmental data including sea surface height (SSH), sea surface temperature (SST) from remote sensing, and temperature gradient derived from SST (GSST) during 1998–2010 to develop habitat suitability index (HSI) models. The HSI models were then used to identify hotspots for chub mackerel for each month. HSI models were developed separately for each of the three distribution areas defined for chub mackerel. According to the frequency distribution of the fishing effort with respect to three environmental variables, suitability index (SI) values were calculated and SI models for each environmental variable were established. The three SI models were combined into two different empirical HSI models: the arithmetic mean model (AMM) and the geometric mean model (GMM). The results showed that the AMM was more suitable than the GMM to estimate the HSI for chub mackerel. The monthly latitudinal variation trend of hotspots was consistent with that of the gravity centres of fishing effort in almost all months. Hotspot maps based on the predicted HSI values were validated by fishery data in 2011. This result indicates that the HSI model based on the AMM can reliably predict hotspots for chub mackerel in the coastal waters of China. [ABSTRACT FROM AUTHOR]

Fish aggregation devices (FADs) have been used extensively in the tuna purse seine fishery since the 1980s. This long-term modification of natural habitat has generated discussions as to whether FADs impact movement patterns of tuna species. We examined this question using data collected from the skipjack tuna (Katsuwonus pelamis) fishery. We used the longitudinal gravitational center of catch (G) to examine temporal variability in skipjack movement in the Western and Central Pacific Ocean, and related this to El Niño Southern Oscillation (ENSO) events. We found that in most cases G for free-swimming school sets changed with the onset of ENSO events, while G for floating-object-associated school sets remained relatively constant. This suggests that skipjack exhibit distinguishable behavioral strategies in response to ENSO events: they either react by moving long distances or they associate with floating objects. There has been no previous attempt to evaluate the interaction between FADs and the environmentally-determined movement of skipjack; this study shows evidence of an interaction, which should be considered when managing skipjack populations. [ABSTRACT FROM AUTHOR]