Fluctuations In Catch Research Articles

Factors affecting purse seine catches: an observer-based analysis

A total of 72 fi shing trips were carried out by fi shery scientists onboard a purse seiner in the Pagasitikos Gulf (Greece) in an attempt to identify factors affecting total and individual species’ catches. As trawling is completely banned in the study area, purse seining is the main fi shing method. It was found that month, water depth and fi shing area affected total and Trachurus spp. catches of the purse seine fi shery, with month and water depth alone explaining 77.8% and 6.4% respectively of the total variation of the data. Signifi cant interactions observed indicate that the fl uctuations in total catches differed by month and fi shing area as well as fi shing area and water depth. Fishing area and water depth interaction were found to affect Trachurus spp. catches signifi cantly. Results also suggested that generalized linear modelling of the purse seine catches can be used to obtain representative abundance indices by reducing the observed variability. Fishery scientists’ onboard observations alongside fi sh market recordings during the same period confi rmed that each fi sher has developed an individual decision-making fi shing process. Fisher’s trip choice behaviour was found to be modulated by several factors, such as distance of fi shing grounds from the port, market demands (both in terms of species and market prices), weather conditions, alternative fi shing strategies, previously gathered information, economic pressure and personal skills. These fi ndings are discussed in the light of the need to incorporate additional quantitative information to stock abundance estimates if improved fi sheries management scenarios are to be advanced.

Relationship between sea-surface temperature and catch fluctuations in the Pacific stock of walleye pollock in Japan

This paper investigates the relationship between sea-surface temperature (SST) and catch fluctuations in the Pacific stock of walleye pollock Theragra chalcogramma in Japan. Incorporating time lags between years of birth and harvest, the correlation coefficients between the catch and SST in two regions off the east coast of Hokkaido were calculated. The catch in year t had a high negative correlation with the SST during January-April and November-December of the years t-2 and t-3 in the spawning area. These results coincided well with the correlation observed in the northern ‘Sea of Japan’ stock. Both analyses suggested that the long-term catch fluctuations of the two stocks could be explained by the same mechanism, that is, the fluctuations would be explained by the SST in their spawning are a during the spawning season using 2–3 or 3–5 years time lags, which corresponded to the dominant age of the catch within these two stocks.

The use of historical catch data to trace the influence of climate on fish populations: examples from the White and Barents Sea fisheries in the 17th and 18th centuries

Abstract We analysed catch records of Atlantic salmon (Salmo salar), cod (Gadus morhua), and halibut (Hippoglossus hippoglossus and Reinhardtius hippoglossoides) from the 17th and 18th centuries from several locations of the Barents and White Seas areas. Historical records, found in Russian archives, allow analysis of long-term series of catches, and sometimes of the average weight of the fish. In total, we obtained data on catches of salmon for 51 years (for the period from 1615 to 1772) and of cod and halibut for 33 years (for the period from 1710 to 1793). These data are comparable with respect to fishing effort within the series. The data on Atlantic salmon are also comparable with statistical data for the period 1875–1915. We found notable fluctuations in catches and sometimes in the average weight of salmon. There was also fluctuation in catches of cod and halibut. Both observational comparison of catch series and temperature data and formal statistical analysis showed that catches tended to decrease during relatively colder periods.

Catch fluctuations of the diamond squid Thysanoteuthis rhombus in the Sea of Japan and models to forecast CPUE based on analysis of environmental factors

Abstract This paper describes recent catch fluctuations of the diamond squid Thysanoteuthis rhombus in the Sea of Japan and the development of models used to forecast catch per unit effort (CPUE) off Hyogo Prefecture based on statistical analyses of environmental indices measured 600 km upstream in the Tsushima Current. Annual catches during 1989–2002 fluctuated widely, and prefectural annual catches were closely related to each other, especially among the western prefectures. Four indices in June were closely related with CPUE during the fishing season (September–November) off Hyogo: (1) water temperature in the Tsushima Strait, (2) salinity in the Tsushima Strait, (3) sea level at Izuhara (Tsushima Island) and (4) sea level difference between Izuhara and Hakata (Kyushu Island). Using these indices as independent variables, simple and multiple regression analyses were conducted, and CPUE was accurately estimated by both regression and extrapolation, indicating that the CPUE off Hyogo can be forecasted 2 months before the fishery starts using the described models. The strong correlation among catches in different prefectures suggests the indices discussed here affect the catches over a large area.

Are the long‐term fluctuations in Atlantic bluefin tuna (Thunnus thynnus) population related to environmental changes?

AbstractWe tested whether synchronous, long‐term fluctuations in Atlantic bluefin tuna (Thunnus thynnus) trap catches, collected from the ancestral Mediterranean and Atlantic trap fishery, might be related to large‐scale environmental change. Nine time series of trap catches of more than 80 yr long were compared with long time series of three preselected environmental variables, i.e. the North Atlantic Oscillation (NAO), the Length of the Day Index (LOD, a proxy of the atmospheric circulation index) and the temperature. Spectral analyses of trap catches, LOD and temperature displayed similar spectra with peaks at low frequencies, whereas those of the NAO exhibited a broad band spectrum. Regression analyses and tests of correlation did not reveal any clear relationship between trap catches on the one hand and NAO and LOD on the other hand. In contrast, long‐term fluctuations in trap catches appear to be closely and negatively related to long‐term trends in temperature. Underlying processes that could explain such a relationship are discussed, with special focus on changes in migration patterns of the Atlantic bluefin tuna.

Fluctuation in stock properties of north‐east Arctic cod related to long‐term environmental changes

AbstractFrom a historic perspective, the north‐east Arctic cod stock, which is found in the Barents Sea–Svalbard region, has been the most productive gadoid stock in the Atlantic. Variation in catch has always been large, but during the last 10–15 years catch and stock abundance have reached the lowest level on record. Three major causes of variation have been discussed: (i) stock reduction through exploitation; (ii) environmental influences on recruitment; and (iii) species interaction effects on maturation, growth and mortality. In addition, interactions among these three sources might be important. The influence of each specific factor is difficult to evaluate from incidental observations and short‐term time series. In this respect, the time series on catches and on biological and environmental information of this stock, which partly extend back to the 19th century, occupy a unique position in comparison to data on most other stocks. In this paper, fluctuations in catch and stock abundance are compared with changes in recruitment, size/age and growth. This information is discussed in view of historic variation in ecology and environment. The stock has been under particularly high exploitation pressure since the mid‐1970s. Further, large changes in growth rates and poor recruitment to the commercially exploited stock are characteristic of late 1980s and throughout the 1990s. The analysis shows that substantial long‐term variation might underlie short‐term variability, and more importantly, that long‐term changes roughly coincide with similar fluctuations in the environment. Such factors might substantially affect the relationship between spawning stock and recruitment, which is also apparent from the difference in conclusions reached by various published studies. Consequently, it is suggested that using a steady‐state perspective for the population dynamics may lead to mismanagement and to a reduction of the long‐term yield from this stock.

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Relationships between seasonal fluctuations in pheromone trap catches of Spodoptera litura F. (Lepidoptera: Noctuidae) and the number of soybean leaves newly injured by young larvae of this species were examined in soybean fields from 1999 to 2002 in Saga Pref., Japan. In soybean fields sown in July, a small peak of injured leaves occurred in mid to late August and a large peak occurred in mid to late September. In most cases, the pheromone trap catches and occurrence of injured leaves exhibited similar trends with both peaks occurring almost simultaneously (±3 days) in mid to late September. This suggests that not only a prominent increase in soybean leaves injured by young larvae, but also a prominent increase in pheromone trap catches are useful information to determine a precise timing of control. On the other hand, the timing of control seems to be difficult to predict using the effective accumulative temperature of this species.

한국 연근해 방어 어획량 변동 및 분포특성에 관한 연구

방어의 자원동태를 규명하기 위하여 한국 연근해에서 어획되는 방어 어획량의 31년간(1970∼2000년)의 통계청 년별어업생산량자료와 최근 10년간(1991∼2000년)의 지역별, 수협별, 어획량 자료 등을 이용하여 장기 어획량변동 경향, 어업에 따른 지방별, 어업별, 연도별, 월별 어획량과 그 변화 경향을 비교 분석한 결과를 요약하면 다음과 같다. 1. 한국의 31년간(1970∼2000년) 방어의 자원량 변동은 19/70∼1985년까지는 31년간의 평균어획량보다 낮은 저조한 어획량이 유지되었으며, 그 후 연간어획량의 증감은 있지만 전체적으로 증가경향을 나타내고 있으면서 평균 어획량 보다 높은 어획량이 유지되었다. 이 기간중 방어 자원량은 5∼6년 주기로 변동하는 경향을 나타냈고, 특히, 1995년부터 1998년까지 어획량이 크게 증가했다. 2. 어업별로는 대형선망의 경우 한국 전역에서 조업이 이루어져 어획량도 가장 높았고, 다음으로 정치망, 채낚기 등의 순이며, 대형선망을 제외한 지역별 조업특성을 보면 동해안에서는 정치망, 남해안에서는 저인망, 정치망, 채낚기, 서해안에서는 안강망, 제주도에서는 채낚기에 의해 주로 어획되었다. 3. 정치망에 의해 지방별로 어획되는 경향을 보면, 강원도와 경상북도는 6∼6월과 10월의 어획량이 많고, 그중 10월에 최고 어획이 나타나며, 경상남도는 5월과 12월에 어획량이 많고, 그중 5월에 최고어획량, 전라남도는 4∼5월과 8월에 어획량이 많고, 그중 8월에 최고어획량이 나타났다. 4. 한국 주변해역의 방어회유양상은 제주도 남쪽 및 대마난류역의 월동장내지는 산란장으로부터 3∼4월부터 황해 및 한국남 ·동해쪽으로 북상하기 시작하여 9∼10월까지 이 회유가 지속되다가 10월 이후 남하하기 시작하여 11∼12월에 양해역으로부터 제주도 주변해역까지 이동해와 2∼3월까지 월동장 및 산란장에서 체류하고 있다. 그러므로, 마라도 주변해역의 추·동계 방어채낚기 어장은 월동장내지는 산란장으로 이동하는 남하기의 방어군을 대상으로 하는 어장이다. We studied the characteristics of catch fluctuation and distribution of yellow tail resources in Korean Waters from 1991 to 2000. The obtained results are summarized as follow, The distribution of yellow tail resources in Korean Waters was showed by mooving north-ward groups from Spring to Autumn and south-ward groups from Autumn to Winter with they passed Winter and spawned from the south of Jeju Island and Tsushima current. Therefore, the fishing ground of yellow tail by handline fishing around Marado targets a school of yellow tails which migrate south-ward so as to winter and spawn.

Growth and Abundance of Burbot in the Curonian Lagoon and Determinatives of Burbot Abundance

Growth and nutrition peculiarities as well as puberty age of burbot juveniles were investigated in the lower Nemunas. According to the investigation data, the mean length and weight of burbot juveniles range from 20.1 cm and 44.6 g of 1+ year-old individuals, to 26.1 cm and 106.1 g of 2+ yearold individuals and to 38.9 cm and 277.4 g of the 3+ year-old fish respectively. Burbot males can reach maturity at the age of 2+ with their body length measuring 20 cm, whereas females maturate at the age of 3+ with the body length of 36 cm. The analysis of commercial burbot catches in the Kaliningrad Region and in Lithuania over the last 50 years was carried out with the reasons of fluctuations in catches specified. It was established that the main reason of decrease in burbot resources and catches is the impact of climate warming on their reproduction. The sequence of four–six cold winters may be followed by a 3–5-fold increase in burbot catches which lately has been prevented by winter floods and thaws and the res...

Long-term fluctuations in the eastern Atlantic and Mediterranean bluefin tuna population

Long-term time-series of bluefin tuna catches from ancestral Mediterranean and Atlantic trap fisheries are presented and analysed. The trap is a passive gear, little modified for centuries, that catches bluefin tuna Thunnus thynnus during their annual spawning migration. These features, together with preliminary analyses, lead us to suggest that long-term fluctuations in trap catches could reflect those in true abundance if they vary in the same manner all around the western Mediterranean and adjacent Atlantic. To test this hypothesis, we investigated 54 time-series more than 20 years long (the longest ones spanning four centuries) of trap catches along the western Mediterranean coasts of Italy, Sicily, Sardinia, Tunisia, Spain, and Morocco, and the adjacent Atlantic coasts of Spain, Portugal, and Morocco. Trends and cycles were identified using Eigen Vector Filtering and spectral analysis, and the synchrony between short- and long-term fluctuations in trap catches was studied with the modified correlogram of Koenig and Knops. The magnitude of fluctuations in trap catches is large, periods of great abundance being up to seven times bigger than those when abundance was low. More interesting was the occurrence of 100-year-long periodic fluctuations as well as 20-year cycles. These medium- to long-term fluctuations, representing more than 50% of the total variability in the time-series, were synchronous all around the western Mediterranean and adjacent North Atlantic. In contrast, short-term variability was synchronous at a local scale only. It is argued that long-term fluctuations in trap catches could be considered as a proxy for those of true abundance, and a synthetic time-series has been computed to depict them. Biological and ecological processes that could cause such long-term fluctuations are also discussed.

The Relationship between Red Cod, Pseudophycis Bachus, Recruitment and Environmental Variables in New Zealand

This paper examines the relationship between red cod, Pseudophycis bachus, recruitment and selected environmental variables. Commercial catch data of red cod were used as indices of relative recruitment strength for New Zealand fish stocks (east coast South Island, RCO 3; west coast South Island, RCO 7). Analysis of catch per unit effort (CPUE) supports the assumption that fluctuations in commercial catches reflect changes in abundance resulting from variable recruitment. Catch was assessed against 34 environmental variables that included the Southern Oscillation index, sea surface temperature, weather types, wind speed and direction, and river flows. Lagged correlations were calculated between annual commercial catch and averaged environmental data. Variables most strongly correlated with commercial catch were included in regression analyses. Regression models were calculated using all available data in its raw form, and after application of a logarithmic transformation. Robustness, and forecast skill was tested using a repeated leave-one-out procedure. The strongest correlations between commercial catch and explanatory variables for both RCO 3 and RCO 7 were consistently with sea surface temperature over a wide range of time lags followed by frequencies of southwest and northeast flow patterns. The correlations generally operated in the sense that ‘colder is better’: negative correlations (∼−0.75) with sea surface temperature, positive with the occurrence of cool southwest weather types, negative with the occurrence of warm northeast weather types. The maximum magnitude of the correlation occurs at 14-month lag for both fisheries, corresponding to the late spring/summer of the year prior to the catch year. There were often secondary maxima in the magnitude of the correlations two or three years prior to the catch year. The commercial fishery is made up largely of two and three-year-old fish, implying that juvenile fish (age ∼ one year) are most sensitive to environmental conditions, but egg, embryo and larva periods may also be affected. Regression analyses suggest that two-predictor regressions were unstable, with often large decreases in explained variance when applied to the independent years, however, at the lags when relationships are strongest (around 14 months), the explained variance on the left-out years remains high. Fluctuations in red cod landings are dependent on sea surface temperature, controlled largely by climatic variability, including El Nino and La Nina events. For short-lived species such as red cod, fluctuations in annual landings are commonplace and analyses of environmental data may be useful in predicting catches in subsequent years.

Stomach analyses of Baltic salmon from 1959–1962 and 1994–1997: possible relations between diet and yolk‐sac‐fry mortality (M74)

In recent years, Baltic Sea salmon Salmo salar have suffered high larval mortality (M74) which can be cured by thiamine treatment. Analyses of long term mortality records (1928–1998) from two salmon hatcheries suggest that before the 1970s M74 did not occur, or was less frequent. This indicates that varying M74 did not cause the long‐term fluctuations of Baltic salmon catches in this period. The frequency of M74 has been correlated positively to the abundance of the salmon's primary prey, sprat Sprattus sprattus. Sprat, herring Clupea harengus and three‐spined stickleback Gasterosteus aculeatus dominated the diet in both the periods of study, 1959–1962 and 1994–1997. The mean size of consumed sprat was significantly smaller in 1994–1997 compared with 1959–1962. Herring and, to a lesser extent, three‐spined stickleback increased in the diet of salmon, while sprat appeared to constitute a smaller part of the diet in 1994–1997. The cause of M74 and the thiamine deficiency involved remains unknown, but is thought to be related to changes in thiamine or thiaminase content in forage fish, winter‐feeding of salmon or general changes in the pelagic food web, caused by overfishing or eutrophication.

The Influence of Hydroregime on Catch, Abundance And Recruitment of the Catfish, Chrysichthys Nigrodigitatus (Bagridae) and the Bonga, Ethmalosa Fimbriata (Clupeidae) of Southeastern Nigeria's Inshore Waters

This paper investigates the relationship between the hydroclimatic parameters (rainfall and flood index) and the catch, stock abundance and recruitment of the catfish, Chrysichthys nigrodigitatus (Bagridae) and the bonga, Ethmalosa fimbriata (Clupeidae) of southeastern Nigeria's inshore waters. For C. nigrodigitatus, most peaks in the mean biomass \((\Delta \% {\bar B})\) and recruitment \((\Delta \% {\bar R(n)})\) curves occurred during the 'wet' years, i.e., years for which the percentage deviations of rainfall \((\Delta \% \overline {{RF}} )\) and flood index \((\Delta \% \overline {{FI}} - 1)\) from their means remained above their averages. Catch and abundance respectively showed good positive linear correlation with the flood index. E. fimbriata behaved differently; some peaks in the \(\Delta \% {\bar B}\) and \(\Delta \% {\bar R(n)}\) curves occurred in the 'wet' and some in the 'dry' years; and there was no correlation between the annual catch of bonga and either the rainfall or the flood index. The hypothesis, that linear relationships exist between the interannual variations in the hydroregime and the yearly fluctuations in the catch and population structure of some coastal and estuarine fishes, holds true for the catfish, C. nigrodigitatus, but not for bonga, E. fimbriata.

Plant succession in perennial grass strips and effects on the diversity of leafhoppers (Homoptera, Auchenorrhyncha)

The biodiversity of agroecosystems may be enhanced by increasing species richness and structural diversity of vegetation by creating perennial strips. Aims of the study were (1) to describe the plant succession of perennial strips in northern conditions; (2) to clarify the difference in insect fauna between cereal fields and perennial strips; (3) to determine the effect of succession on leafhoppers in perennial strips; and (4) to compare the leafhopper fauna of perennial strips with that of other uncultivated biotopes. Three perennial grass strips (12 m wide, 420 m long) were sown in the middle of cereal fields (15 ha) in 1991 with a seed mixture of timothy ( Phleum pratense), meadow fescue ( Festuca pratensis), red clover ( Trifolium pratense) and white clover ( Trifolium repens). The perennial strips were not mown or renewed after the establishment. In 1992 and 1993 barley and in 1994 spring wheat were grown in the surrounding fields. The composition of plant cover in the grass strips changed over four seasons. The total number of plant species decreased from 23 species in 1992 to 10 in 1995. The change resulted from the dramatic decrease of annual weeds after the first year. Furthermore, the total plant cover declined slightly. The cover of P. pratense increased, whereas that of T. pratense and T. repens decreased. The plant species typical of early succession were annual weeds including Tripleurospermum inodorum and Thlaspi arvense. In the last year, perennial weeds such as Cirsium arvense and Elymus repens became common. Leafhopper abundance and species number were higher in perennial grass strips than in cereal fields. Furthermore, the species composition varied between habitats. Year-to-year fluctuations in leafhopper catches were large. Leafhopper abundance and diversity (Shannon index) were highest in 1993 when 192 sweep net samples contained a total 4680 specimens belonging to 37 species. The plant species richness of the grass strips did not correlate with the abundance and species richness of leafhoppers, which seemed to be more dependent on other factors. Although the plant species number in grass strips decreased clearly during succession, changes in species richness of leafhoppers were not so great. Factors affecting the leafhopper community are discussed.

What problems do local habitat change represent for the constant effort site ringing scheme?

A mist‐netting site at Cow Lane Gravel Pits, Cambridgeshire, contributes to the British Trust for Ornithology's (BTO) Constant Effort Site (CES) ringing scheme. Standard net sites are located in relatively stable osier scrub Salix, but the nearby habitat is subject to rapid change which has resulted from the restoration of a gravel pit. This study addresses the question of whether this local habitat change results in fluctuations in the CES catch at Cow Lane which deviate from the national trends. CES catches of passerines in mist‐nets from 1989 to 1996 at Cow Lane are compared to the national trends as identified by the BTO. Most species have experienced increases and decreases at Cow Lane in accordance with the national trends, and appear to be relatively insensitive to local habitat changes. Sedge Warblers Acrocephalus schoenobaenus and Reed Warblers A. scirpaceus are the notable exceptions. Mist‐netting with additional nets in the adjacent habitat suggests that these species are responding to local expansion of wetland vegetation, and changes in the catch reflect localized changes in habitat use.

Population dynamics and fishery of dolphinfish (<i>Coryphaena hippurus</i>) in the western Mediterranean

SUMMARY: The dolphinfish (Coryphaena hippurus) fishery based on the island of Mallorca (western Mediterranean) and the population dynamics of the species were studied between 1995 and 1996. Fishing effort, landings and length composition of the catches during the sampling period, as well as the historic catch data series and fleet were analysed. Virtual Population Analysis (VPA), taking as the time unit the week in 1995 and the fortnight in 1996, were also carried out. Dolphinfish is fished from August to December, with main catches in September-October, using anchored fish aggregation devices (FADs) and surrounding net. The mooring areas, placed from 70 to 1200 m depth, are distributed among the boats registered for the year’s fishery. A total of 46 boats took part in this fishery in 1995 and 37 in 1996, with a catch of 128 and 52 metric tons respectively. These wide fluctuations are also shown in the annual catches of the 16year series, which ranged from 2 to more than 120 metric tons, showing a slightly increasing trend (4 tons per year). The comparison of different measures of effort (FADs, days and hours) showed similar values of CPUE, although the number of FADs showed the lowest variation, with normal variances and average values not significantly different between harbours. The length composition of the catches ranged from 20 to 64 cm fork length, which corresponds to juveniles between 2 and 6 months of age. The main results of the VPA, which must be regarded in relative rather than absolute values, showed that the available population and the recruitment in 1995 are greater (around one order of magnitude) than in 1996. For both years, the number of individuals declined in the course of the fishing season, while biomass increased during the first 5 weeks. The fact that the exploited fraction of the dolphinfish population is composed of 0-age class suggests that catch fluctuations might be related to environmental parameters and to the migratory behaviour pattern of the species. These two interrelated factors can produce failures of its annual spawning in the western Mediterranean, and/or of the recruitment of the species to the fishery.

Harvesting and economic patterns in the artisanal Octopus mimus (Cephalopoda) fishery in a northern Chile cove

We analyze intra- and inter-annual harvesting and economic patterns of the cephalopod Octopus mimus (pulpo) artisanal fishery at Caleta Coloso cove, Antofagasta, northern Chile, between 1991 and 1996. Information was collected daily, from 25 hookah divers that manually harvest pulpo in the subtidal along 29 km of coastline. Inter-annual fluctuations in catch, fishing effort, unit price and economic revenues increased from 1993 to 1996, when O. mimus landing and total revenues at Coloso were over 77 t and US$ 190 000, respectively. Contrary to the observed annual trend, the inverse intra-annual correlation between catch/fishing effort and price indicated short-term changes in price according to resource availability. A monotonic decreasing function between CPUE and price suggested a threshold catch rate economically feasible for harvesting. Inter-annual changes in the slope of the price–CPUE function indicated a marked increase in the demand of pulpo, jointly with warnings of stock depletion. We conclude that the O. mimus temporal fishery patterns at Coloso are scale-dependent. Our results and general fishery patterns in the Chilean pulpo fishery suggest that a precautionary management scheme is urgently needed to prevent overfishing.

ペットボトルを用いたスクミリンゴガイのトラップ

Seven types of plastic soft drink bottles were utilized as traps for the golden apple snail, Pomacea canaliculata (LAMARCK). The number of snails caught using the bottle traps were compared with the number of snails caught using the box type trap manufactured by Kyushu Sankyo Co. Ltd. The traps were installed 14 times in a paddy rice field in Koushi, Kyushu, southern Japan from June to July 1997. A total of 424 snails were trapped. The FRIEDMAN statistical test showed no significant difference in the number of snails caught using the two types of trap. Incidentally, there is a wide fluctuation in daily snail catch. The number of snails caught in plastic bottle traps were greater than those caught in box type trap. Moreover, the bottle type trap was simpler than the box type trap. Hence, the bottle trap may be recommended as a practical means of trapping snails in the field.

相模湾西湘地区定置網漁場における漁獲物組成からみた漁場区分の年変化

The similarities appearing in species composition of set-net catch was examined to explicate the mechanism of catch fluctuation by using the cluster analysis on the six fishing grounds in the Seisyou region of Sagami Bay. The Seisyou region is located in the Western Sagami Bay.As a result of similarities in species composition by cluster analysis, there is characterized for the tendency of dominant species catches, and then the similarities of set-net fishing grounds are classified by the five patterns. The yearly fluctuations of similarities varies in a short span of several years, influenced by species composition for each year. Further, the trend of Seisyou region is generally classified by Koyawata and Umezawa fishing grounds.

Relationship between temperature and fluctuations in sandfish catch (Arctoscopus japonicus) in the coastal waters off Akita Prefecture

The sandfish (Arctoscopus japonicus) catch in the coastal water off Akita Prefecture have fluctuated greatly over the period 1962–1990. The difference between the maximum and minimum catches over those years is more than 200 times. The aim of this paper was to investigate the relationships between water temperature and the fluctuations of the catch. Using the fuzzy logic approach, the water temperatures measured in the different points off the Prefecture were summarized as an index which would indicate the variation of water temperatures. In this study, the sensitivity tests showed that the index inferred using the water temperatures observed in 100–150 and 200–300 m depth at 9 and 65 km off the coast with time lags 1, 2, 3 and 4 years could explain the fluctuation of sandfish catch. That is, large changes in catch can be simply explained by the fluctuation of water temperatures.