Original Paper
Title Estimation of standard errors and confidence intervals in small samples
Authers Kazuhiko HIRAMATSU* and Hiroshi OKAMURA*
Keywords bootstrap, confidence interval, standard error, small sample
Citation Bull. Fish. Res. Agen. No.6, 1-8, 2003
The standard errors and confidence intervals have been used as a measure of the accuracy of estimators. However, it is known that the estimates of standard error using the standard procedures based on the unbiased estimate of variance and the bootstrap method are biased and the bootstrap confidence intervals based on the percentile method are too short when the sample size is small. The amounts and causes of these biases are examined and the corrections of these biases are discussed. The results indicate that the biases in the standard error using the standard procedures would be negligible. However, our Monte Carlo simulations show that the biases in the bootstrap estimate of standard error and cofidence intervals would not be negligible when sample size is equal to or less than 10 or the ratio of the number of parameters estimated to the sample size is larger than 0.1. We therefore recommend that researchers carefully consider the effective sample size when applying the bootstrap method. In particular, since the result of hypothesis test can be affected by the bias, bias corrected bootstrap method such as calibration or other method should be used when the effective sample size is small.

Accepted on July 22, 2002
Contribution No.A 27 from Fisheries Research Agency
* National Research Institute of Far Seas Fisheries, 5-7-1, Orido, Shimizu, Shizuoka, 424-8633, Japan

Title Spawning ecology of captive bluefin tuna (Thunnus thynnus orientalis) inferred by mitochondrial DNA analysis
Authers Shukei MASUMA*1, Nobuhiro TEZUKA*1, Hiroyuki OBANA*1, Nobuaki SUZUKI*2, Kenji NOHARA*2 and Seine CHOW*2
Keywords nouthern bluefin tuna, genotype of eggs, spawning ecology
Citation Bull. Fish. Res. Agen. No.6, 9-14, 2003
Sixty-three individuals of mature bluefin tuna (Thunnus thynnus orientalis) have been maintained in a 14-ha cove of Amami Island, Japan. Spawning activity was observed on 22 days during May 28 through November 10 in 2001. In order to investigate spawning frequency, period and number of spawning female per day, mtDNA genotypes of spawned eggs were analyzed. MtDNA Dloop region was amplified via PCR and the genotypes of 23 to 64 eggs collected per day were determined by RFLP analysis. Ten genotypes were detected among 691 eggs in total. Forty percent of the eggs belonged to genotype 3, which was observed on 20 out of 22 spawning days. Occurrence of genotypes 6, 7 and 10 were also frequent and observed on 9 to 11 days. Occurrence of the other genotypes was much less frequent. In June, eggs having genotype 3 were observed almost every day for a whole week. Occurrence of certain genotypes for 2 to 3 consecutive days was not unusual. Substantial spawning with such consecutive spawning was observed by mid November. These results differed from general presumption that individual female of natural population spawns intermittently for only a few times durling April to August.

Received on August 7, 2002
Contribution No.A 29 from the Fisheries Research Agency
*1 Japan Sea Farming Association Amami Station, 955-5 Hyosakiyamahara, Setouchi, Ooshima, Kagoshima 894-2323, Japan
*2 National Research Institute of Far Seas Fisheries, 5-7-1 Orido, Shimizu, Shizuoka 424-8633, Japan

Short Paper
Title Kink in the Cd-PO4 plot near Okinawa Island observed in the summer of 2001
Authers Kazuo ABE*
Keywords Cd, PO4, Kink, Okinawa Island
Citation Bull. Fish. Res. Agen. No.6, 15-17, 2003
The relationship between cadmium (Cd) and phosphate (PO4) was investigated in an area near the Okinawa Island in June 2001. A plot of these constituents showed two straight lines with a clear deviation (kink) at a PO4 concentration of around 0.4μM. The forces that caused the existence of the kink in the plot are not clear; however, the discontinuity of the water mass across this layer, as deduced from the T-S diagram, seems to be at least partially responsible.

Received on August 15, 2002
Contribution No.A 30 from Fisheries Research Agency
* Ishigaki Tropical Station, Seikai National Fisheries Research Institute, 148-446 Fukai-Ota, Ishigaki, Okinawa 907-0451,Japan

Title Synopsis of biological data on the blue shark, Prionace glauca Linnaeus
Authers Hideki NAKANO*1 and Michael P. SEKI*2
Keywords blue shark, synopsis, biology, life history, population
Citation Bull. Fish. Res. Agen. No.6, 18-55, 2003
Blue sharks, Prionace glauca, are wide ranging oceanic sharks found worldwide in tropical and temperate waters and the most abundant pelagic shark species. Blue shark is the most successful elasmobranch in the pelagic waters and frequently major by-catch species into the fisheries operating in high seas. Occupation of the pelagic niche in the temperate waters may be one of the key components of its domination in the pelagic ecosystem. The systematics, biology, life history, population, exploitation, and utilization on blue shark were reviewed based on more than eighty scientific publications during the past five decades. Over the years, numerous studies describing the biology, ecology and fisheries of blue sharks have been published, however, the information are more often than not patchy and local in scope. The synopsis thus compiles available information pertaining to blue sharks to establish what is known, where gaps in our knowledge exists, and identifies where additional and future research efforts should be focused. Although a comprehensive stock assessment of blue shark in the North Pacific is still lacking, no overly deviant fluctuations are obvious in the various CPUE series, and no evidence currently exists to suggest that tha stock status of North Pacific blue sharks is in a critical state. Nevertheless, further research is needed to assess the true catch levels in each fishery and their impacts on the population. Our mutual interests leads us to focus our efforts on the population of blue sharks inhabiting the North Pacific Ocean, although where relevant, information from the other oceans of the world are also reviewed and presented for comparison.

Received on October 2, 2002
Contribution No.A 31 from the Fisheries Research Agency
*1 National Research Institute of Far Seas Fisheries, Orido, Shimizu, Shizuoka 424-8633, Japan *2 National Marine Fisheries Service, NOAA Southwest Fisheries Science Center Honolulu Laboratory 2570 Dole St., Honolulu, HI96822-2396, USA

Title Present status on the development of alternative tributyltin-free antifouling paints and toxicity of new biocides to aquatic organisms -Review-
Authers Hisashi YAMADA* and Akira KAKUNO*
Keywords TBT compound, antifouling paint, biocide, aquatic organisms, toxicity, risk assessment
Citation Bull. Fish. Res. Agen. No.6, 56-72, 2003
The present status on the development of an alternative tributyltin(TBT) -free antifouling paints was reviewed in order to consider the hazardous effects of new biocides to aquatic organisms. Although 15 organic chemicals and cuprous oxide were selected for a biocide in the alternative organotion-free antifouling paints and the antifouling agents for fishing net, bis-(1-hydroxy-2(H) -pyridine thionate-O,S) zinc(zinc pyrithion;ZnPT) and bis-(1-hydroxy-2(H)-pyridine thionate-O,S) copper(copper pyrithion;CuPT), 4,5-dichloro-2-n-octy1-3-isothiazolone(Seanine-211), pyridinetripehnylboron(PyB), and 2-methylthio-4-t-butylamino-6-cyclopropylamino-s-triazine(Irgarol 1051) were mainly used in the newly developed anti-fouling paint. These organic chemicals were used with cuprous oxide in order to improve the anti-fouling efficiency. Irgarol 1051 was detected in water collected at several regions of Japan and Europe, however, other chemicals were not detected in the aquatic environment. Acute toxicity of ZnPT, CuPT, Seanine-211, PyB, and Irgarol 1051 on aquatic organisms was 2~1,780μg/L, 4.3~43.6μg/L, 2.7~1,312μg/L, 2.15~242μg/L, and 0.1~12,000μg/L, respectively. These chemicals showed the almost same acute toxicity as TBT. As these chemicals are not stable and persistent, it is suggested that the risk of alternative biocides to aquatic organisms is smaller than TBT.

Received on October 3, 2002
Contribution No.A 32 from Fisheries Research Agency
* National Research Institute of Fisheries and Environment of Inland Sea, Maruishi 2-17-5, Ohno, Hiroshima 739-0452, Japan

Doctoral thesis
Title Fishery biological studies on penaeid shrimps in Tosa Bay, Pacific coast of Japan
Authers Hideo SAKAJI*
Keywords penaeid shrimp, fauna, life history, stock diagnosis, beam trawler
Citation Bull. Fish. Res. Agen. No.6, 73-127, 2003
Penaeid shrimps are mainly distributed in shallow and inshore tropical and subtoropical waters. Worldwide, they support fisheries of significant importance and are important for the small-scale trawl fishery of southwestern Japan. The annual catch of penaeid shrimps in Japanese waters has decreased with the decrease in the number of small-scale trawlers in recent years. The decline in coastal fisheries such as the small-scale trawler is not desirable for the maintenance of regional industries and the diversity of food for the nation. For the sustainable running of small-scale trawlers, management of resources of penaeid shrimps is important, although there have been few studies on the life history of penaeid shrimps in the Japanese waters especially on small-sized species. In this study, the penaeid shrimps in the Japanese waters especially on small-sized species. In this study, the penaeid fauna, the vertical distribution of the penaeid shrimp assemblage on the continental shelf and the life histories of the major four species on the continental shelf are described and discussed for the sea areas around Tosa Bay 33゜N, 133゜E), Pacific coast of Japan, an area influenced by the warm Kuroshio stream. Further, the management of penaeid shrimp resources for the small-scale trawler in Tosa Bay is discussed.
 Many specimens were collected from 1994 to 1999 using bottom trawls of small-scale trawlers(<5 GT) from the 0~80m in depth in nighttime operations and of the R/V Kotaka-maruⅢ(49GT) and Ⅳ(59GT) from the 50 to 1,000m in depths in daytime operations in Tosa Bay, or using a push net from a small boat with an outboard motor in the river-mouth estuary area in Urado Bay, which in semi-enclosed and connected to Tosa Bay. A total of 35 species of penaeid shrimps were collected from Urado Bay and from 0~400m in depth in Tosa Bay. No penaeid shrimps were collected from the waters deeper than 400m in depth. The distribution patterns after settlement of the penaeid shrimps around Tosa Bay were classified into the following five types. (1)Estuary type(one species); juveniles and adults are distributed only in Urado Bay; Metapenaeus moyebi. (2)Estuary-upper cotinental shelf type (six species); juveniles are distributed in estuaries and semi-enclosed areas and migrate to the upper cotinental shelf (<80m depth) of Tosa Bay with growth; Marsupenaeus japonicus, Melicertus latisulcatus, Metapenaeus ensis, Penaeus monodon, P.semisulcatus, and maybe Metapenaeus intermedius. (3)Continental shelf type (twenty-three species); juveniles and adults are distributed on the continental shelf(<140m depth) of Tosa Bay; Atypopenaeus stenodactylus, Melicertus marginatus, Metapenaeopsis acclivis, M.barbata, M.aegyptia, M. dalei, M. dura, M. gallensis, M. lamellata, M. mogiensis mogiensis, M. palmensis, M. sinica, M. toloensis, Parapenaeopsis cornuta, P. tenella, Parapenaeus fissuroides, P. lanceolatus, P. longipes, Trachypenaeopsis richtersii, Trachysalambria albicoma, T. curvirostris, T. longipes, T. sp. (4)Continental shelf-continental slope type(three species); juveniles and adults are distributed on the cotinental shelf and the continental slope(≧140m depth and ≦400m depth) of Tosa Bay, mainly on the continental slope; Metapenaeopsis lata, M. provocatria owstoni and Parapenaeus sextuberculatus. (5)Continental slope type(two species); juveniles and adults are distributed on the continental slope of Tosa Bay; Parapenaeus fissurus and Penaeopsis eduardoi. The penaeid fauna in Tosa Bay is the richest compared to other reported Japanese waters. The warm environment in winter(>15℃) due to the effects of the Kuroshio are important for the rich penaeid fauna in Tosa Bay in addition to the varied habitats from estuary to continental slope in this area.
 The density of all penaeid shrimps in each depth class on the upper continental shelf was largest in 45m in depth and smallest in 5m and 75m in depths, the distribution patern looked like a normal or binomial distribution. The species composition of penaeid shrimps changed successively in relation to depth. Each distribution pattern of the main nine species also looked like a normal or binomial distribution each with a different mode and range, althougth some of the distributions partially overlapped one another. The depth range of the distribution of each species had seasonal stability, although the density of each species changed seasonally. On the other hand, on the grain size composition of the bottom, fine classes dominated in the deeper area and the change of the penaeid species composition by depth corresponded to the change of the grain size composition of the bottom by depth. Successive changes of the species composition is important for the richness of the number of penaeid species on the upper continental shelf of Tosa Bay.
 Ovaries were observed histlogically to make clear the maturing processes and the spawning seasons of the main four species on the upper continental shelf of Tosa Bay; namely Metapenaeopsis aegyptia, M. barbata, M. dalei and M. sinica. Seven stages were distinguished in the oocyte development. The cortical crypts, which have been generally reported to occur in the pre-maturation stage of oocytes in penaeid shrimps, did not occur even in the ovulated oocytes. Since ovulated or the late phase of the pre-maturation stage oocytes co-occurred with earlier stage oocytes in the same section of the ovary, each species was concluded to be a multiple spawner which have short spawning intervals. Monthly changes of the occurrence of each developmental stage indicated that the spawning season was throughout the year in M. dalei and in early summer to autumn in the other three species. Such a long spawning season confirmed in M. dalei has not been recorded in other penaeid shrimps in temperate waters including Japanese waters. 
 Seasonal changes in the carapace length (CL) composition and gonad somatic index (GSI) were observed to clarify the structure of the populations of the above four Metapenaeopsis species. In M. dalei, there were several generations a year, a large body (maximum size CL 17mm) and long life (about six month) generation from winter to spring and a small body (maximum size CL 14mm) and short life generations (of several months) from summer to autumn. Links of the spawning season of each generation made the spawning season of the population long. One generation a year with a short spawning season in summer in M. dalei is reported from other waters colder than Tosa Bay in winter and spring. It seems that the smaller maturation size and prolonged spawning season in the warm environment leads to shortened generation periods and an increase in the number of generations a year in M. dalei. In the other three species, there was one generation a year, a generation spawned in the current year appeared in autumn, grew even in winter and lived to the preceding autumn. On the other hand, their body sizes were different from each other, M.barbata is the largest (maximum size CL 26mm), M.sinica is next in size (maximum size CL 22mm) and M. aegyptia is the smallest (maximum size CL 18mm). Spawning was made mainly by the generation spawned in the preceding year, but it was confirmed histologically that some part of the generation spawned in the current year matured at a small size and spawned in autumn after they had just recruited. In M. barbata, it is reported that the generation period is two years with a stagnation of growth in winter and spring, when the water temperature falls lower than 15℃ in the inshore waters in Japan such as in the Inland Sea. It seems that the generation period is shortened by the rapid attainment to the maximum body size by the continuous growth throughout the year in warm waters such as in Tosa Bay. Based on this, the generation period of the Metapenaeopsis species is concluded to be changeable with the effects of the ambient water temperature. Two patterns of the life history of Metapenaeopsis were observed, one was observed in M.dalei and the other was observed in the other three species. In tropical waters these two life history patterns are potentially interchangeable, if almost all the individuals spawn within the first year and the generation period is shortened. On the other hand, such interchangeablity of the two life history patterns may not occur, if each life history pattern is specific to each species group, which is classified by the presence or absence of the stridulating organ on the carapace. The stridulating organ is absent in M. dalei but present in the other three species suggesting that the life history pattern may be inheritably different. In order to clarify the life history patterns of Metapenaeopsis, more species in different environmental conditions require examination.
 For the diagnosis of the stock of penaeid shrimps on the upper continental shelf of Tosa Bay, data of catch of shrimps and fishing effort (number of boat day) of the beam trawlers in Mimase Fisheries Cooperative Association from 1970 to 2000 were analyzed. Fishing period was from April to December. Monthly CPUE (catch number per unit effort) increased from April to May and decreased from May to September in most of the years. Monthly Z (total mortality coefficient) and qN0 in each year were estimated by the regression analysis to the following formula; ln(CPUE)=ln(qN0)-Z(i+1/2); then, q is a catchability coefficient, N0 is an initial stock number in May and i is a whole number which increases monthly from May to September. M (natural mortality coefficient) was estimated to be 0.208 by Tanaka's low (2.5/life span, which was twelve months in the shrimps) and 0.270, which was the same value of the smallest Z estimated above and was a too large estimation, was also used. Z was estimated to be between 0.270 and 0.749. N0 after 1980 were smaller than those of the 1970's. The rate of exploitation from May to September was gradually increasing from 1970's, each value in 1998 and 1999 showed almost 0.7~0.8. The present stock level of penaeid shrimps in Tosa Bay is estimated to be low comparing the past thirty years. The relationships of biomass of parent and abundance of progeny tended to go near the origin with the passage of time, although those after 1974, when the biomass of parent were less than 400 ton, were not significant. Judging from such relationships after 1974, it is not expected that the biomass of parent make sure the abundance of progeny in penaeid shrimps of Tosa Bay. Then, it is important to make YPR (yield per recruitment) largest, together with maintaining the biomass of parent. Here, delay of the starting of the fishing period was discussed, because the shrimps grew up until autumn. For Z in April, 0.1, 0, -0.2, -0.4 and -1.0, which were included in the range observed from 1970 to 2000, and for Z from May to September, 0.725, 0.575 and 0.412, which were the largest, the average and the smallest values in the 1990's, were used. For M, 0.208 and 0.270 were used as described above. In the result, it was expected that closing the fishing period in April made the total catch weight in the fishing period to increase, maximum 1.1 times larger. Biomass of the parent was estimated to be 1.07 ~1.47 times larger. It was estimated that closing the fishing period in April and May did not necessarily made the total catch weight to increase. In conclusion, it is necessary to close the fishing period of small beam trawlers in April for increasing total catch weight and maintaining parent biomass of penaeid shrimps in Tosa Bay.

Received on October 16, 2002
Contribution No.A 34 from the Fisheries Research Agency
* Kuroshio Research Devision, National Research Institute of Fisheries Science, 6-1-21, Sanbashidori, Kochi, Kochi 780-8010, Japan