Original Paper
Title The present condition of recreational fisheries in the Yukawa River surveyed by a questionnaire to anglers
Authers Shoji KITAMURA*1,2, Kazumasa IKUTA*1,2, Toshio SHIKAMA*1,2 and Hidefumi NAKAMURA*1,2
Keywords recreational fishing, brook trout, questionnaire, catch-and-release
Citation Bull. Fish. Res. Agen. No.12, 2004
 In order to survey the present condition of recreational fisheries in the Yukawa River, Nikko, Japan, where sportfishing in Japan originated more than 100 years ago, we conducted a questionnaire to the anglers in 2001. Of the 3,574 anglers who visited the Yukawa River during the fishing season in the year, total of 259 anglers answered the questionnaire (response rate: 7.25%). Among 3 angling methods (fly, lure and bait fishing), the ratio of fly-fishing was the highest at 63.3%. Catch rates (number of fish caught/angler-hour) of brook trout (Salvelinus fontinalis) by fly, lure and bait fishing were 0.92, 1.12 and 1.39, respectively. There was a significant difference in the catch rate between fly and bait fishing (p<0.01). Anchor-tagged brook trout (mean body weight: 230g) stocked at 4 different areas were reported to be caught with recapture rate of 27.5- 77.5%. The trout stocked at the exclusive area for fly-fishing, where the anglers supposedly practiced catch-and-release, were caught with the highest recapture rate (77.5%) for about a month after release. In contrast, those stocked at 3 other areas were caught almost within 2 days after release with recapture rate of 27.5, 37.5 and 50%. Catch-and-release regulation would be effective to sustain brook trout stocks and acceptable to the anglers in the Yukawa River.

Received on May 13, 2004
*1 Nikko Branch, National Research Institute of Aquaculture, 2482-3 Chugushi, Nikko, Tochigi 321-1661, Japan
*2 National Research Institute of Fisheries Science, Freshwater Fisheries Research Division, 2482-3 Chugushi, Nikko, Tochigi 321-1661, Japan

Title A review on the black bass problem referring to the historical background in Japan
Authers Taiga YODO*1 and Kei'ichiro IGUCHI*2
Keywords Black basses, Recreational fishing, Invasive alien species, Commercialism
Citation Bull. Fish. Res. Agen. No.12, 2004
At present, Japan's inland waters face to an unique but serious topic so called black bass problem. The current problem grows so complicatedly involving social conflicts as well as ecological issue. One part grieves the crisis of biodiversity, while the other part appeals the right to take pleasure, showing no agreement. In the 1970s, insufficiency of legal control about alien species transplantation facilities anonymous transplantation with black basses without any local consensus. Extending of black bass distribution accelerated bass fishing which became popular in the 1980s. Commercialism in bass-related macro-industries during from the late 1980s to the early 1990s transformed the bass fishing from one of the fishing to one of the popular recreations. In Japan, those who receive the benefit from lakes and rivers have been under an obligation of stock enhancement for sustainable yield. On the other hand, newly introduced bass fishing is just a play or game and thereby dose not adapt to the traditional way of utilizing inland waters, which may lay to the outbreak of the bass problem.

Received on May 23, 2004
*1 Japan Society for Promotion of Science Domestic Research Fellow : Fish Culture Laboratory, Faculty of Bioresources, Mie University, 1515 Kamihama, Tsu, Mie 514-8507, Japan
*2 National Research Institute of Fisheries Science Ueda Station, 1088 Komaki, Ueda, Nagano 386-0031, Japan

Doctoral Thesis
Title Abundance estimation of the young cohorts of the Japanese Pacific population of walleye pollock (Theragra chalcogramma ) by acoustic surveys
Authers Satoshi HONDA*
Keywords walleye pollock, Theragra chalcogramma, Japanese Pacific population, acoustic survey, abundance estimation
Citation Bull. Fish. Res. Agen. No.12, 2004

 The Japanese Pacific population of walleye pollock (Theragra chalcogramma), which is distributed widely along the Pacific coast of Hokkaido and Tohoku, is one of the most important fishery resources in Japan. One of the features of this population in recent years is the occasional occurrence of dominant year classes. Once a strong year class occurs, this cohort accounts for the greater part of the age composition in this population and subsequently sustains good catches for several years. Recognizing the sign of the occurrence of a strong year class as soon as possible before its recruitment is an effective measure to assess the consequent quantitative situation of this population in the years ahead. Quantitative echo sounder has been well developed as one of the oceanographic observation equipments during last few decades; it is widely used for direct stock estimations of marine organisms at present. In this study, hydroacoustic surveys were applied for the quantitative evaluation of young cohorts of the Japanese Pacific population of walleye pollock, which had not evaluated by the orthodox method of stock analysis because of their pre-recruitment size.

 Optimum conditions and the seasons to accomplish the acoustic survey are presented from the viewpoint of the features of the survey equipment and other conditions to conduct the surveys. The attenuation of acoustic energy due to the effects of sailing was measured on the R/V Kaiyo-maru No. 3, which was used for the acoustic survey cruises. The attenuation by sailing appeared with the increase of the ship speed. In particular, the attenuation was apparent under the head sea condition of sailing; maximum attenuation was attained 1.3dB at 38kHz, 0.7dB at 120kHz. Furthermore, the attenuation by sailing occurred at slower sailing speeds than that at which the apparent attenuation was recognized on the echogram. This means that the attenuation by sailing exerted an influence upon the acoustic data without the operator being aware of it. On the planning of the acoustic survey by the R/V Kaiyo-maru No. 3, setting the sailing direction in a following sea will prevent the underestimation of the acoustic biomass index caused by the attenuation by sailing. Considering the weather conditions, various kinds of fisheries activities that would obstruct the grid surveys or trawl towing, and the overall schedule of the stock assessment of this population, early summer (June till July) was proposed as the optimal season for the acoustic survey aimed at juvenile pollock in the Pacific coast of Hokkaido.

 Distribution, ecology and the estimation of the standing stock at age of walleye pollock was described by the combined acoustic and trawl surveys conducted on the continental shelf and slope area in the Pacific side of Hokkaido from Jun. 1996 to Jan. 2002. The shoals of the young cohort of walleye pollock often occurred on the continental shelf area of the offshore southeastern Hokkaido. Apparent diel vertical migration of pollock appeared in every season and whole age groups. The range of the vertical migration varied with age/- size and season. Since the echo sounder has acoustical invisible zones both in the surface and the off bottom area, diel or seasonal variation of the swimming layer would cause the fluctuation of the stock estimation. Seasonal variation of the abundance estimation was wider than the diurnal variation; estimated standing stock in early summer was always larger than the results based on the data taken in winter. Emigration of the fish shoals from the survey area, underestimation caused by the bottom acoustic deadzone, increasing of the acoustic attenuation by sailing under rough weather, were assumed as the potential causes for the decrease of estimated abundance in winter. For young cohorts of pollock in early summer, acoustically estimated abundances based on the daytime survey were always larger than those based on nighttime survey. Surfacing of fish shoals toward the undetectable surface layer by echosounder in nighttime was considered as the main cause of the more conservative abundance estimation.

 Correspondence of the structure of walleye pollock shoals to the habitat conditions was investigated. In the present procedure of the allocation of acoustic energy from the pollock shoals to each age group, both age composition and the average sizes at age of each pollock shoal, taken from the trawl operations, are indispensable parameters. If we estimate both parameters of pollock shoal structure using the information of their habitat location instead of the numbers of trawl tows, we could reduce the effort for conducting trawl operation. The same as other demersal fishes, an age-dependent bathymetric pattern was observed; age composition biased younger in shallower coastal area, then gradually become older with the depth increasing. Furthermore, average sizes at same cohort also tended to be larger in proportion to the increasing depth. Using these relationships as regression functions, the age/size structures of walleye pollock shoals were estimated from their distribution depth and the area was then compared to the real structures of pollock shoals taken by trawl tows. Although the average size at age in the pollock shoal was well reproduced and matched with the real data, the age-composition ratio could not be reproduced from the regression function of the depth. Particularly, since the age-1 cohort appeared patchily on the shallower half of the continental shelf, a simple regression function explained by the depth and area could not well describe their elusive distribution pattern. This negative result consequently confirmed the need of direct biological sampling with the acoustic survey simultaneously for interpretation of the acoustically detected fish shoals.

 Geostatistics was applied to evaluate the precision of the abundance estimation and the optimal transect interval for the acoustic surveys. By applying geostatistics, standard error of mean (SEM) of the estimator was extensively reduced. This was caused by the existence of the autocorrelation among the data taken from the neighboring transects. If applying the orthodox statistics into the systematic parallel transects survey design, it neglects the autocorrelation among the neighboring data and regards them as mutually independent. Therefore, applying orthodox statistics into the systematic parallel transects survey design overestimated the variance of the abundance consequently. Although the point estimator itself was not varied regardless of the statistical method, applying geostatistics could show the correct level of variance of the estimator. Results of the simulation of varying the transect interval showed that narrowing the intertransect distance would improve the precision of the abundance estimation of young cohorts of pollock. However, narrowing the transect interval increased the total survey distance and therefore the necessary time to run. Considering the expansion of the survey area and the allowable shiptime, the present transect distance of 8 nautical miles was regarded as practical to accomplish the whole survey with an acceptable level of precision.

 In the case of young cohorts of pollock such as age-1 to-3, significant positive regression line was fitted on the correspondence between the acoustically estimated standing stock at age off southeastern Hokkaido (the Doto area) and the total abundance at correspondent cohort derived by VPA analysis a few years later. These results meant that the acoustically estimated standing stock of young cohorts of walleye pollock in the Doto area well reflected the total magnitude of these cohorts in the whole distribution, despite the Doto area is just a part of the whole distributional area of this population. By applying these regression functions, the total abundance of the young cohorts those have not been recruited or have just recruited recently can be forecast immediately. That is, the acoustic survey for young cohorts of pollock well complement the weak point of VPA on the process of the fish stock evaluation.

Received on May 24, 2004
* Hokkaido National Fisheries Research Institute 116 Katsurakoi, Kushiro, Hokkaido, 085-0802, Japan