Siquan Tian

Age, maturation, and population structure of the Humboldt squid Dosidicus gigas off the Peruvian Exclusive Economic Zones

Age, maturation and population structure of the Humboldt squid Dosidicus gigas were studied based on random sampling of the Chinese jigging fishery off the Peruvian Exclusive Economic Zones (EEZ) during 2008–2010. Estimated ages ranged from 144 to 633 days, confirming that the squid is a short-lived species with longevity no longer than 2 years. Occurrence of mature females and hatching in each month indicated that Humboldt squid spawned year-round. Back-calculated hatching dates for the samples were from January 22nd, 2008 to April 22nd, 2010 with a peak between January and March. Two size-based and two hatching date-based populations could be defined from mantle length (ML) at maturity and back-calculated hatching dates, respectively. Females matured at a larger size than males, and there was a significant difference in ML at maturity between the two hatching groups (P <0.05). The waters adjacent to 11°S off the Peruvian EEZ may be a potential spawning ground. This study shows the complexity of the population structure and large variability in key life history parameters in the Humboldt squid off the Peruvian EEZ, which should be considered in the assessment and management of this important resource.

Impacts of spatial scales of fisheries and environmental data on catch per unit effort standardisation

Spatial scale is an important factor that needs to be considered in data collection and analysis in ecological studies. Studies focusing on the quantitative evaluation of impacts of spatial scales are, however, limited in fisheries. Using the Chinese squid-jigging fishery in the north-western Pacific Ocean as an example, we evaluated impacts of spatial scale used in grouping fisheries and environmental data on the standardisation of fisheries catch per unit effort (CPUE). We developed 18 scenarios of different spatial scales with a combination of three latitudinal levels (0.5°, 1° and 2°) and six longitudinal levels (0.5°, 1°, 2°, 3°, 4° and 5°) to aggregate the data. We then applied generalised additive models to analyse the 18 scenarios of data for the CPUE standardisation, and quantified differences among the scenarios. This study shows that longitudinal and latitudinal spatial scale and size of the spatial area for data aggregation can greatly influence the standardisation of CPUE. We recommend that similar studies be undertaken whenever possible to evaluate the roles of spatial scales and to identify the optimal spatial scale for data aggregations in the standardisation of CPUE and fisheries stock assessment.

A comparison between two GAM models in quantifying relationships of environmental variables with fish richness and diversity indices

Various regression methods can be used to quantify the relationships between fish populations and their environment. Strong correlations often existing between environmental variables, however, can cause multicollinearity, resulting in overfitting in modeling. This study compares the performance of a regular generalized additive model (GAM) with raw environmental variables as explanatory variables (regular GAM) and a GAM based on principal component analysis (PCA-based GAM) in modeling the relationship between fish richness and diversity indices and environmental variables. The PCA-based GAM tended to perform better than the regular GAM in cross-validation tests, showing a higher prediction precision. The variables identified being significant in modeling differed between the two models, and differences between the two models were also found in the scope and range of predicted richness and diversity indices for demersal fish community. This implies that choices between these two statistical modeling approaches can lead to different ecological interpretations of the relationships between fish communities and their habitats. This study suggests that the PCA-based GAM is a better approach than the original GAM in quantifying the relationship between fish richness and diversity indices and environmental variables if the environmental variables are highly correlated.

Reconstructing cephalopod migration with statolith elemental signatures: a case study using Dosidicus gigas

Cephalopods exhibit a variety of movement patterns during their lifespan, from the passive drifting of eggs and paralarvae to the active long-distance migrations of adults between feeding and spawning grounds. However, it is difficult to observe directly the movements of cephalopods at these different stages of development. An alternative approach is the use of elemental signatures recorded in statoliths to gain valuable insight into cephalopod movement. Dosidicus gigas is an economically important squid that undertakes large-scale migrations over its lifespan to satisfy its habitat requirements at different life history stages. In this study we used D. gigas as an example to illustrate a new approach to reconstructing cephalopod migration patterns using the relationship between sea surface temperature and elemental signature analyses of statoliths. We found that statolith elemental signatures are a useful natural tag to ascertain D. gigas migration routes from juvenile to adult stages. This approach is not applicable to embryonic and paralarval stages during which movement is more likely passive and determined by ocean currents. The conclusions which can be drawn from this study improve our knowledge of the distribution and migration of juvenile and adult cephalopods. Supplementary trophic analyses using stable isotopes would further benefit the reconstruction of cephalopod migration pathways.

The effect of sea surface temperature increase on the potential habitat of Ommastrephes bartramii in the Northwest Pacific Ocean

In the Northwest Pacific Ocean, the squid jigging fisheries from China, Japan and other countries and regions have targeted the west winter-spring cohort of neon flying squid (Ommastrephes bartramii) from August to November since the 1970s. This squid is a short-lived ecological opportunist with a life-span of about one year, and its population is labile and recruitment variability is driven by the environment or climate change. This variability provides a challenge for ones to forecast the key habitats affected by climate change. The catch data of O. bartramii from Chinese squid jigging fishery and the satellite-derived sea surface temperature (SST) data are used in the Northwest Pacific Ocean from August to November of 1998 to 2004, the SST preferences of O. bartramii corresponding to high values of catch per fishing day (CPUE) are determined and monthly potential habitats are predicted using a histogram analysis of the SST data. The possible changes in the potential habitats of O. bartramii in the Northwest Pacific Ocean are estimated under four climate change scenarios based on the Fourth Assessment Report (AR4) of the Intergovernmental Panel on Climate Change, i.e., 0.5, 1, 2 and 4°C increases in the SST because of the climate change. The results reveal an obvious poleward shift of the potential habitats of O. bartramii in the Northwest Pacific Ocean.

Effects of El Nino/La Nina on distribution of fishing ground ofDosidicus gigasoff Peru waters

Jumbo flying squid,Dosidicus gigas,which is distributed in the waters off Peru,and is an important economic squid,has been caugth by many countries in the world.The study on large-scale environmental change on distribution of D.gigas is important for scientifically fishing and mastering the changing regularity.In this study,the fishing data from Chinese squid jigging fleets,sea surface temperature(SST) and the water temperatures data from 0 to 200 m(sea temperature at 15 meters layer,T15;sea temperature at 50 meters layer,T50;sea temperature at 100 meters layer,T100;sea temperature at 200 meters layer,T200) are used to analyze the large-scale environmental changes on distribution of D.gigas under the different conditions of El Nio and La Nia.The result indicated that under El Nio,the fishing ground was around 79° 84°W and 10° 17°S with the optimal SST range of 19 22 ℃ during October to December in 2006 and 2009,while under La Nia during October to December in 2007,the fishing ground was located around 81° 85°W and 10° 14°S with the optimal SST range of 17 20 ℃.The main fishing ground in the year of La Nia moved to further northward for 1 2° latitude and its average SST decreased 2 ℃ compared with that in the years of El Nio.The distribution of water layers temperature indicated that T15 and T50 in 2007 was significantly higher than that in 2006 with the maximum temperature difference of 6~9 ℃,and but T100 and T200 in 2007 was little higher than that in 2006 with the maximum temperature difference of 1 ℃.The vertical temperature structure indicated that the upwelling is not formed in fishing ground from October to December in 2006,and the fishing ground was distributed at the mixed region between oceanic water and coastal water.But the strong upwelling is formed in coastal waters from October to December in 2007,and the fishing ground was distributed at the intensive isotherm around the upwelling area.Moreover,the strong upwelling will lead to producing more nutrients in the squid habitat layer,which will be useful for squid to feed and make change of the distribution of D.gigas.It is concluded that El Nio/La Nia events are closely related to the change of distribution of fishing ground of D.gigas.

Impacts of fish aggregation devices on size structures of skipjack tuna Katsuwonus pelamis

Tuna purse seine fisheries target fish aggregated in schools, including free schools that are formed naturally based on fish biology and aggregations associated with natural and/or artificial drifting objects. Using data collected from skipjack tuna (Katsuwonus pelamis) fisheries, we evaluated differences in size structures between drifting-floating-object-associated schools and unassociated schools. We developed a generalized linear model to remove impacts of environmental variables on skipjack size composition. This study indicates that the drifting-floating-object-associated schools tended to have significantly wider size ranges than the unassociated schools. This suggests that unassociated schools were likely formed based on similarity in sizes among individuals within a school while drifting-floating-object-associated schools were probably composed of individuals of large size ranges and their formation was not based on the “size selection” rule. We concluded that the unassociated schools and the drifting-floating-object-associated schools were formed through different mechanisms, and drifting floating objects could aggregate unassociated schools of different size structures. Thus, a large scale of deployment of man-made floating objects might disrupt the spatial aggregation pattern of fish that otherwise tended to school based on their sizes in the absence of floating objects.

Genetic differentiation in blue shark, Prionace glauca, from the central Pacific Ocean, as inferred by mitochondrial cytochrome b region.

Abstract Six hundred and ninety-seven base pairs of cytochrome b gene of mtDNA was sequenced and analyzed for 78 blue shark Prionace glauca individuals from three sampled locations in the central Pacific Ocean (CPO). In total, three polymorphic sites were detected which defined four haplotypes. The haplotype diversity (h) ranged from 0.517 to 0.768, and nucleotide diversity (π) was between 0.0007 and 0.0011. Analysis of molecular variance indicated a non-significant differentiation among subpopulations. Furthermore, pairwise FST score analysis revealed a non-significant differentiation among three sampled regions. Generally, low genetic differences were found between different geographic locations in the CPO. This study suggests a single panmictic population of P. glauca in the CPO.

Complete mitochondrial genome of the Taractes rubescens (Perciformes: Bramidae)

Abstract Taractes rubescens is a high vulnerable species which widely distributes in tropical and subtropical water in Pacific and Atlantic Ocean. The complete mitogenome sequence of T. rubescens was determined in this study. The complete mitogenome of T. rubescensis 16 720 bp in length, which contains 13 protein-coding genes, 22 transfer RNAs, 2 ribosomal RNAs and a control region (D-loop). Furthermore, base composition of A, C, G and T is estimated to be 27.6%, 30.9%, 15.8% and 25.7%, respectively. The complete mtDNA sequence of T. rubescens provides a useful data for studying on the molecular systematic, stock assessment and conservation genetics.

Complete mitochondrial genome of Hemiculter bleekeri bleekeri

Abstract Hemiculter bleekeri bleekeri is a typical freshwater species that are mainly distributed in the river basins in China. The biological information of this species is very limited. In this study, we determined the complete mitogenome sequence of H. bleekeri bleekeri. The complete mitogenome of H. bleekeri bleekeri is 16 6173 bp in length, which contains 22 transfer RNAs, 2 ribosomal RNAs, 13 protein-coding genes and 2 non-coding region, a rep region (33 bp) and a control region (D-loop). This work provides new information which is helpful for comprehending the molecular systematic, taxonomic status and evolutionary biology of this species.