Guoping Zhu

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.

Upper trophic structure in the Atlantic Patagonian shelf break as inferred from stable isotope analysis

The Patagonian Shelf is a very productive region with different ecosystem structures. A long history of fishing in the Southwestern Atlantic Ocean combined with a complex hydrographic structure, with a permanent front over the shelf-break and different coastal frontal regions, and a wide non-frontal area in between have made the food web in this area more complex and have resulted in changes to the spatialtemporal scale. Stable isotopes of carbon and nitrogen were used to determine the trophic structure of the Patagonian shelf break which was previously poorly understood. The results indicated that the average δ15N value of pelagic guild (Illex argentinus) was remarkable lower than those of the other guilds. The δ13C values of almost all species ranged from -17‰ to -18‰, but Stromateus brasiliensis had a significant lower δ13C value. Compared with the southern Patagonian shelf, short food chain length also occurred. The impact of complex oceanographic structures has resulted in food web structure change to the temporal-spatial scale on the Patagonian shelf. The Patagonian shelf break can be considered as a separated ecosystem structure with lower δ13C values.

Inferring trophic variation for Antarctic krill (Euphausia superba) in the Antarctic Peninsula from the austral fall to early winter using stable isotope analysis

The Antarctic krill (Euphausia superba) is a key species in the Southern Ocean ecosystem and an important link in the food web of the Antarctic ecosystem. The trophic information for this species during the transition from the austral fall to the winter is important to understand its poorly known overwintering mechanisms. However, the few studies on the topic differ in their results, in terms of both spatial and temporal variables. We investigated the size dependence and monthly and regional variation in δ13C and δ15N values of adult krill in the Antarctic Peninsula, in the austral fall (April to May) and the early winter (June). We aimed to examine the trophic variations of krill occurred during this period, and the relationship between krill and their feeding environment in the Antarctic marine ecosystem. The following results were obtained: (1) no significant relationship was observed between size and the δ13C value of krill, but the δ15N value of krill presented a remarkable association with size; (2) the δ13C values of krill increased during the austral fall, but no remarkable variation existed at the onset of winter, and the δ15N values were not significant different during this period; (3) mean δ15N values of krill differed significantly between the Bransfield Strait and the South Shetland Islands. Our data imply that adult krill present size-, season-, and region-dependent trophic variation during the transition from austral fall to early winter in the Antarctic Peninsula.

Application of Pocket PC in Marine Fishery Survey

At present, during marine fishery survey, the field work heavily depends on the traditional recording fashion, i.e. recording data on paper sheets by hand. Obviously, it is very inefficient and easily lead to bad data quality. To address this problem, a solution of marine fishery survey which is based on Pocket PC is put forward. This solution, making use of mobile devices, records the field data in electronic form directly. It can assure the data consistency, improve the efficiency of field staff and make them more productive. The electronic collected data can transfer to desktop computers or database servers directly over the wired or wireless network outdoors, or by direct connection indoors, and so the indoor workload is reduced. Finally, a prototype system is designed and developed for squid survey data collection. Its test result shows that the system can make up the shortages of the traditional work mode obviously, and improve the efficiency of field work. It also proves that the solution of marine fishery survey based on Pocket PC is feasible.

Dynamical Simulation of a Knotless Netting Based on Explicit Method

Based on finite element analysis and explicit Euler method, the present study visualized the dynamical simulation of a knotless netting in R environment. In the physical models, the linking between knot and twine were considered as a mass-spring system. Vector algebra methods were applied to analyze the hydrodynamic forces and tensile forces of the spring. To solve the equations numerically, explicit Euler method was introduced for the mechanical system to achieve the stable solutions. A package of scatterplot3d in R program was transferred to realize the visualization of the knotless netting in three-dimensional space. The results of dynamical simulation were displayed distinctly to show the sinking processes and equibibrium state of the knotless netting in the sea water.