Original Paper
Title Allometry and development of caudal skeleton of hatchery-reared yellowfin tuna Thunnus albacares
Authers Hirofumi SHIMIZU*1 and Satoshi SHIOZAWA*2
Keywords Thunnus albacares, Yellowfin Tuna, growth, caudal skeletonation
Citation Bull. Fish. Res. Agen. No.10, 1-7, 2004
Yellowfin Tuna Thunnus albacares reared at Ishigaki Station, Japan Sea-Farming Association in May and June 1997 were examined to clarify the allometry and the developmental osteology of the caudal skeleton on 298 specimens. Fishes ranged in length from 3.1 to 40.8mm TL and in age from two to 30 days after hatching. A total of 73 wild juveniles were measured allometry in eight characters.
A growth winding point in allometry of hatchery-reared Yellowfin Tuna was observed in fishes from 10 to 15mm TL. Significant differences were found between wild and hatchery-reared fishes regarding allometry in eight characters measured.
The components of the caudal skeleton first appeared in fishes at 5.75mm TL. Ossification began at 11.30mm TL at the point of neural and haemal spines of pleural centrum 4. All the components of the caudal skeleton appeared at 31.50mm TL and half of them were ossified by that time.

Received on February 6, 2004
Contribution No.A 48 from Fisheries Research Agency
*1 Ishigaki Tropical Station, Seikai National Fisheries Research Institute, 148-446 Fukai Ohta, Ishigaki 907-0451, Japan
*2 Obama Station, Japan Sea-Farming Association,Matsumae 26 Tomari, Obama 917-0117, Japan

Technical Report
Title Development of a method for numbering the knots and bars of netting
Authers Satoshi KUBO*
Keywords Cauchy's formula, automatic numbering, netting movement, computer simulation
Citation Bull. Fish. Res. Agen. No.10, 8-14, 2004

In the field of fishing, there have been several traditional uses of netting (fishing nets) seen over the years . To achieve further development and improvement, experimentation using a field survey or tank test is required. Recently, some attempts at numerical simulation to determine netting movement have taken place. In numerical simulations of this type, each knot and twine(bar) of the netting must be numbered. Generally, when a net texture is laid flat, the knots and bars of the net are placed in orderly rows. Therefore, in the case of simple net-texture shapes, this work is not too difficult and can even be done manually.

However, if this work could be done with a computer, the task of numbering various net shapes would become easier and faster.

This document is a report on a method for numbering the knots and bars of variously shaped net textures with a computer by applying Cauchy's integral formula in a complex number field. After numbering is completed using this method, the data is processed in order to obtain a form that can be used for numerical simulation. Also, one example of seasurface crawl-netting moored by ropes is shown in the first paragraph of the computer simulation.

Received on December 15, 2003
Contribution No.A 46 from Fisheries Research Agency
* National Research Institute of Fisheries Engineering. Ebidai 7620-1, Hasaki, Kashima, Ibaraki, 314-0421, Japan

Short Paper
Title Time series changes in gillnets abandoned at shallow water
Authers Yoshiki MATSUSHITA*, Naoto HONDA*, Kaoru FUJITA*, and Toshihiro WATANABE*
Keywords sink gillnet, ghost fishing, diving observation, net configuration
Citation Bull. Fish. Res. Agen. No.10, 15-17, 2004
Sink gillnets of different 3 designs were set for 20-37 days in Tateyamabay, Chiba. Gilled/entangled organisms and net configurations were recorded by diving observations. Total 27 individuals of fish and crustaceans were observed on the gillnets within 14 days after deployments for all gillnets. Net areas, which keep proper mesh openings between sinker and float lines decreased gradually, and finally whole float lines contacted with the seafloor for all gillnets. These changes in net area imply degradations of two capture functions, interception of fish paths and enmeshment, but not for entanglement.

Received on December 5, 2003
Contribution No.A 45 from Fisheries Research Agency
* National Research Institute of Fisheries Engineering. Ebidai 7620-1, Hasaki, Kashima, Ibaraki, 314-0421, Japan

Doctoral Thesis
Title A statistical study for ecosystem modeling focused on marine mammals
Authers Hiroshi OKAMURA*
Keywords abundance estimation, ecosystem modeling, marine mammals, prey preference, stock structure
Citation Bull. Fish. Res. Agen. No.10, 18-100, 2004

Most of cetacean species are highly migratory and difficult to keep in captivity so that it is not easy to grasp precise status of the populations. On the other hand, the limitation of the management based on single species has been recognized and the demand on the ecosystem-based population assessment and management has been increasing over the world. It is important to know the status of the population precisely and accurately as far as we can in ecosystem-based approach. To extract information efficiently from the data in which a lot of uncertainty exist and grasp the status of the population precisely and accurately, the use of statistical models is essential. This paper focuses on population assessment of marine mammals and develops some statistical models. Furthermore, the competition between marine mammals and fishery is investigated using an ecosystem model.

Marine mammals are one of the important top-predators in an offshore ecosystem. The information on the distribution, migration, and stock structure is therefore indispensable to the construction of the offshore ecosystem model. In addition, the degree that the biological resource is affected by the catch greatly varies with the assumption of the stock structure in the procedure developed by the International Whaling Commission (IWC) for the management of large baleen whales. The regression analyses based on the generalized linear and additive models are useful for modeling the complicated phenomena such as the temporal-spatial structure of biological resources. In this paper, the spatial distribution and seasonal changes of the density of the western North Pacific minke whales was estimated using the generalized additive model so that there was no evidence that multiple stocks exist in the western North Pacific. On the other hand, the seasonal change of the density reproduced the aspect of migration of the minke whales well. The investigation of temporal-spatial distribution of biological resources using the regression models can be extensively useful for other species other than marine mammals.

Line transect sampling is a standard method for estimating the population size of marine mammals. One of the important assumptions in standard line transect sampling is that all animals on the trackline are detected without fail. However, the surfacing-diving behavior of marine mammals for respiration and feeding can lead to failures in detection even if they are on the trackline. As a result, the population size tends to be underestimated. Although the underestimation of the population size brings conservative effect on single-species management, it leads to another problem in ecosystem approach because the impact by consumption of predator is underestimated. Conventional methods for estimating the detection probability on the trackline have several problems. The flexible method developed in this paper modified and improved such problems. Simulation studies showed that the method is promising. In addition, it was confirmed that the present method is able to be applied to real data sets using Antarctic minke whales data.

The prey-predator interaction is extremely important in ecosystem modeling. If we can know preference of animals in laboratory, we can estimate diet composition of animals non-lethally by putting the information on the preference and the availability of animals obtained from sighting survey together. Preference for multiple food items can be measured in the laboratory by choice tests like cafeteria trials, in which an animal is initially offered a variety of foods that are equally available at the same time. However, the results of the multiple-choice experiments can be affected by many factors such as placement, amounts of foods, and the length of time that the experimental animal is permitted to eat. An alternative way to determine multiple-preference is to repeat a series of paired comparisons. The paired comparisons have an advantage over the multiple-choice tests because the design of each trial is simpler so that the conditions of the experiment can be easily controlled. The data collected from paired comparisons can be analyzed with the Bradley-Terry model. However, conventional Bradley-Terry model has some defects; for instance, it is not able to deal with the amount of consumption. This paper proposes a modification of the estimation method used in the Bradley-terry model. The maximum likelihood estimation based on a binomial distribution in the original model is replaced with the nonlinear least squares method. Furthermore, some simple methods to estimate the precision of parameters and to test several hypotheses on preferences are provided. The methods were applied to the analysis of food preference of a captive northern fur seal. The comparison between the method and the conventional Bradley-Terry model indicated that the statistical power of the method can be higher than the conventional one.

Finally, the ecosystem model off Sanriku area using Ecopath was constructed and the competition between consumption of whales and fishery was investigated by Ecosim. The strong competition was found under the setting of a certain parameter. The precise estimation of parameters and the appropriate incorporation of uncertainty are extremely important because the results are sensitive to the input parameters. The statistical models developed in this paper gave improvements upon the previous ones in some ways. The population trajectory predicted from the ecosystem model tends to depend much on input parameter estimates. Therefore, the importance of estimation of the parameters used in ecosystem models will be increasing in the future. In the problems such as wildlife and ecosystem conservation, and a food shortage, reasonable assessment and management of aquatic resources is still more important. To construct ecosystem models incorporating uncertainty appropriately and making the best use of information the data have at the maximum is a big theme to be attained in the twenty one century.

Received on September 16, 2003
Contribution No.A 43 from Fisheries Research Agency
* National Research Institute of Far Seas Fisheries, 5-7-1, Shimizu-Orido, Shizuoka, Shizuoka, 424-8633, Japan