Original Paper
Title Distribution and migration of age-0 juvenile walleye pollock, Theragra chalcogramma, along the Pacific coast of Hokkaido based on reports from fishermen
Authers Satoshi HONDA*
Citation Bull. Fish. Res. Agen. No.2, 1-22, 2002
For detecting the distribution and migration patterns of age-0 walleye pollock along the Pacific coast of Hokkaido including the Nemuro Straight, reports of pollock juveniles from fishermen were analyzed with previous information collected through various surveys. In the waters along Donan to Cape Erimo, pollock juveniles initially appear in April around Funka Bay, a major spawning ground. The distribution of the juveniles expands eastward and reaches to Cape Erimo in September. This observation suggests that some of the juveniles originating in Funka Bay move to Cape Erimo. In the Nemuro Straight, juveniles spawned in this area appear in the southern part of the Straight from April to July, and they move to the northern part of the Straight in summer and autumn. In the waters of Doto(from Cape Erimo to the Nemuro Peninsula), pollock juveniles mainly appear from September to next April, and they are widely distributed on the continental shelf areas. It is suggested that most of the juveniles migrate from the east of Cape Erimo, because pollock spawning occurs on a very small scale in this area.

Accepted on September 26, 2001
Contribution No.A 7 from Fisheries Research Agency
* Hokkaido National Fisheries Research Institute, 116 Katsurakoi, Kushiro, Hokkaido 085-0802, Japan

Title Some observations on the spawning depth of the Japanese sardine, Sardinops melanostictus, and the Japanese anchovy, Engraulis japonicus, off southern Kyushu, Japan
Authers Masanobu MATSUOKA*1, Kuniaki MIYAJI*2 and Osamu KATOH*3
Keywords Sardinops melanostictus, Japanese sardine, Engraulis japonicus, Japanese anchovy, spawning depth, vertical distribution
Citation Bull. Fish. Res. Agen. No.2, 15-23, 2002
The vertical distribution of eggs of the Japanese sardine, Sardinops melanostictus, and the eggs of the Japanese anchovy, Engraulis japonicus, was investigated to clarify their respective spawning depths. Net sampling was made at the station of N35°55′, E130°29′. Vertical tows using a 45cm diameter net from 150m depth were done every two hours 15 times from 18:00, March 1 to 6:00, March 3, 1992. Horizontal tows using 60cm diameter nets with net closing apparatus were simultaneously conducted at five layers of approximately 1m, 20m, 40m, 60m and 80m, for 15 minutes, and carried out 15 times such as vertical tows. AA stage eggs (from fertilization to beginning of enlargement of perivitelline space)of Japanese sardine were mostly collected at 40m depth at 22:00, March 1, at 40m depth at 20:00 and 22:00, March 2, and at 60m depth at 0:00, March 3. This means that the spawning depth of this species was approximately 40~60m. Unfertilized and disintegrating eggs were largely collected at 80m depth at 0:00, March 2 and at 40m depth at 22:00, March 2. These eggs seem to sink rapidly after spawning. Although A stage eggs (from end of AA stage to closing of blastopore)distributed from the surface to the 80m layter, a lot of eggs were collected at 20~60m depth at 4:00 and 6:00, March 2. A few AA stage eggs(from fertilization to cleavage)of Japanese anchovy were collected at 22:00, March 1 to 2:00, March 2. Many AA stage eggs were caught at 22:00, March 2 to 2:00, March 3. Most eggs distributed at the surface and the 20m depth layer. Therefore,it is considered that the spawning depth of this species was approximately 0~20m. In this species,the unfertilized and disintegrating eggs as collected in Japanese sardine were not recognized. A stage eggs(to the attainment of blastoderm to 1/2 of yolk length)were mainly caught at 18:00, March 1 and from 2:00 to 6:00,March 3. On March 3, A stage eggs were mostly distributed from the surface to the 20m depth layer such as AA stage eggs. This result shows that the spawning depth of these two species does not overlap,in the case where the two species coexist.

Accepted on September 26, 2001
Contribution No.A 8 from Fisheries Research Agency
*1 National Research Institute of Fisheries and Environment of Inland Sea, Ohno, Hiroshima 739-0452, Japan
*2 National Research Institute of Far Seas Fisheries, Orido, Shimizu 424- 8633, Japan
*3 Japan Sea National Fisheries Research Institute, Suido, Niigata 951-8121, Japan

Title Comparison between Conventional and Bayesian Statistics in Interval Estimation for Quadrat Method and Petersen Method
Authers Tatsuro AKAMINE*
Keywords Bayesian, binomial distribution, hypergeometric distribution, interval estimation, Petersen method, quadrat method
Citation Bull. Fish. Res. Agen. No.2, 25-34, 2002
The quadrat method and the Petersen method are basic techniques for the investigation of stock size. The binomial distribution or the hypergeometric distribution is used for these methods in statistics. The comparison between the conventional and Bayesian statistics for these models makes it easy to understand the meaning of the confidence interval. Several numerical examples show that the approximation to the normal distribution corrected by half integer is the most useful method for these models. The classical Bayesian method in which a uniform distribution is used for prior distribution of n or p is most adequate,because its confidence interval is proven to be almost equal to that of the conventional statistics.

Accepted on September 26, 2001
Contribution No.A 9 from Fisheries Research Agency
* National Research Institute of Fisheries Science, Fukuura, Kanazawa, Yokohama 236-8648, Japan

General Remarks
Title Bivalves as a possible sentinel marine organism to monitor metal pollution in coastal waters―A review―
Authers Kazufumi TAKAYANAGI* and Tomoko SAKAMI*
Citation Bull. Fish. Res. Agen. No.2, 35-46, 2002
In order to evaluate three bivalve species : Mytilus edulis, Perna viridis and Crassostrea gigas as a possible sentinel organism to monitor metal pollution in coastal waters, related literatures have been reviewed. The special attention was given to five requirements to use a sentinel organism:(1) ability to accumulate metals, (2) representative of coastal waters, (3) easily sampled year around, (4) easy to obtain a large amount and (5)wide distribution to cover all the continents. The metal concentrations (Mn, Cd, Cu, Ni, Pb and As) in transplanted Mytilus galloprovincialis ( closely related species of M. edulis)and P. viridis into Tokyo Bay and Aburatsubo Bay were also monitored for 8 weeks to check accumulation patterns of the metals space. The literature review indicates that the combination of three species is necessary to meet the above requirements. Although all three species can accumulate metals efficiently (more than 106)and all are representative organisms of the intertidal zone, the geographical coverage of each species is limited. In order to cover world wide, the combination of the three is required. The transplanted bivalve studies indicate that these three species can be used interchangeably as a sentinel organism at least for Cd, Ni, Pb and As.

Accepted on September 26, 2001
Contribution No.A 10 from Fisheries Research Agency
* National Research Institute of Aquaculture, Fisheries Research Agency, 422-1 Nakatsuhamaura, Nansei, Mie 516-0193, Japan

Doctoral thesis
Title Study on the Precise Estimation of the Target Strength of Fish
Authers Kouichi SAWADA*
Keywords echo sounder, target strength, reverberation volume, split-beam, echo trace analysis
Citation Bull. Fish. Res. Agen. No.2, 47-122, 2002
Fish target strength is very important as a scale factor to estimate fish abundance from echo integration results in an acoustic survey, as information to estimate fish length and species, and as a parameter to design echo sounders.
 In Chapter 2, several methods of target strength estimation are enumerated and the principal of fish length estimation method is presented. This chapter is the starting point of the following chapters.
 In Chapter 3, the precise fish target strength pattern measurement system is developed in a tank. Both the preciseness and accuracy of this system are confirmed by the comparison between the target strength pattern measurements of the artificial targets and their exact theoretical calculations. The dorsal target strengths of five species are measured in this system and the precise target strengths available for the abundance estimation are shown.
 In Chapter 4, the validity of the theoretical calculations based on the deformed cylinder model is confirmed. The model calculations based on the swimbladder shape obtained by a conventional soft X-ray system or a computed tomography imaging system agree well with the measurements.
 In Chapter 5, the indexes for the preciseness of the target strength measurement in situ are proposed and the validity of these indexes is confirmed by measurements and computer simulations.
 In Chapter 6, the estimation method of fish length and behavior is developed by combining the split-beam method with the echo trace analysis method. The validity of this method is confirmed by the computer simulation and the measurements in a tank and at sea. The effect of the motion of the transducer at sea is considered using a computer simulation.
 In the last chapter, Chapter 7, a software for the analysis of the target strength is developed. It can analyze the target strength in situ with the proposed indexes and can estimate individual fish length and behavior, seeing the echograms and selecting the arbitrary area. The actual data obtained at sea is used and the estimation results by this software agree well to the fishing results.
 This paper is a slightly modified version of the doctoral dissertation proposed to Tokyo University of Fisheries.

Accepted on September 26, 2001
Contribution No.A 11 from Fisheries Research Agency
*National Research Institute of Fisheries Engineering, Ebidai, Hasaki, Kashima, Ibaraki, 314-0421, Japan