Test Fishing Research Articles

Imagination, Reality, and Reproduction: Comparing Perceptions of Coastal Sea Trout Anglers, Real Catches, and Sea Trout Spawning Activity

ABSTRACTSustainable management of recreational fisheries requires balancing angler attitudes and behaviour with fisheries' biological potential. Herein, we investigated the balance in the sea‐run brown trout (Salmo trutta) fishery around the Swedish island of Gotland using data collected through a creel survey, test fishing, and spawning returns to selected streams. Anglers accurately anticipated catches of large fish but underestimated the role of natural reproduction in supporting the stock. Female sea trout entering spawning streams and post‐spawn sea trout caught on the coast were significantly larger than spawning males and non‐spawned fish, and were particularly important for the fishery. Larger sea trout also faced a higher level of harvest pressure than other sizes. Small changes to angler preferences, harvest rates, or regulations could significantly influence characteristics and sustainability of this fishery. The scale and direction of these changes merit further investigation.

Cellular composition of the kidneys of the common carp after the use of cellobacterin-T under conditions of anthropogenic pressure

The study presents the data on the cellular composition of the kidneys of the common carp against the background of the use of the probiotic Celloblacterin-T. The experiment was planned and carried out at a specialized fish farm in Voronezh region. Specimens of the common carp aged 1 year and weighing in the range of 250-300 grams were selected for the experiment. As part of the baseline study, kidneys were taken from fish (n=5) for cytological studies. After that, the fish were divided into 2 groups: carps from the control (n=8000) and experimental (n=8000) ponds. The fish from the control pond received the main diet, and the fish from the experimental pond received the probiotic drug Cellobacterin-T (with the main diet), calculated at a dose of 2 kg/t of feed. Then a test fishing was carried out, during which kidneys were taken from the specimens of both ponds (n=8 from each) for cytological studies. They were conducted 14 days after the beginning of using the probiotic and 42 days after the beginning (12 days after the end of using the probiotic). In the baseline study, we revealed inhibition of the lymphoid lineage of the anterior kidney, an inflammatory neutrophilic reaction caused by the effect of heavy metals, as evidenced by a low number of lymphocytes (16.5%) and a high number of neutrophils and their precursors (10.5%). Against the background of the use of Cellobacterin-T, activation of lymphocytes was observed, their number increased by 1.9 times relative to the baseline study. The number of neutrophils and their precursors was reduced by 3 times. After discontinuation of the drug, the results of the experimental group were close to the results of the baseline study.

Adult Sockeye Salmon Assessment in a Tidal, Turbid River: A Comparison of Sonar and Test Fishing Methods

AbstractThe feasibility of using sonar in Alaska's lower Kvichak River, a region with a 3.8 m tidal flux, to assess the abundance of adult Sockeye Salmon Oncorhynchus nerka was evaluated as a replacement for an in‐river gill‐net test fishery. Test fish indices are one tool that is used to manage commercial and subsistence fisheries in Bristol Bay. On this river, an observation tower project near the clear headwaters provides accurate abundance estimates for this species, but fishery managers require timelier estimates for in‐season daily management. The lower‐river test fish index is timelier, but it is less precise than tower estimates are. We had to determine whether to replace the test fish project with sonar based on how well each compared with tower estimates and an assessment of their cost and effort. Two dual‐frequency identification sonars (DIDSONs) were deployed along one bank of the lower river (one pointed toward shore and one away from shore) to assess salmon passage across all tidal stages in an attempt to produce an index with higher precision. Compared with the tower estimates, the test fish index showed a slightly stronger correlation in each of the three study years than the sonar index did, despite the stronger sampling power of the sonar. The test fish and sonar indices were strongly correlated. In the lower river, upriver salmon migration (85–98%) occurred primarily during ebb tides and downriver passage (97–100%) during flood tides, indicating that salmon do not use selective tidal stream transport to minimize their energy expenditures in this river. We were able to successfully use fixed‐location sonar in a tidal nearshore region to produce an index of fish abundance. Our recommendation was to continue the test fishing project rather than to replace it with sonar because of the similarity between their indices and the higher cost of the sonar project.

Responses of the fish community in a eutrophicated lake to long-term food web management assessed by multiple sampling methods

Fish community responses to long-term mass removal of planktivorous fish from eutrophicated Lake Tuusulanjärvi were examined during 1996–2018 by gill net test fishing, hydroacoustics with simultaneous trawling, virtual population analysis (VPA) and fish growth measurements. The gillnet catches of white bream and roach increased first while bream and bleak decreased but recovered in the early 2000s. Perch and pikeperch increased but ruffe decreased and remained low. According to hydroacoustics, pelagic fish biomass decreased. Smelt was the most abundant species at the beginning and the end of the monitoring period but bream dominated the fish biomass in most years. VPA calculations indicated a five- and threefold increase in the biomass of bream and white bream, respectively, during 2005–2011. Significant increases appeared in the growth of perch, bream and roach. Overall, the responses in the fish community structure and fish abundance to the food web management were slight and mostly masked by changes in reproduction and growth of fish and annual variability in environmental conditions such as temperature and water turbidity. Gillnet test fishing and echo sounding complemented each other well in monitoring the effects of management fishing. Where bream is one of the dominant species VPA is also recommended.

First records of the non-indigenous signal crayfish (Pacifastacus leniusculus) and its threat to noble crayfish (Astacus astacus) populations in Estonia

This study gives an overview of status and distribution of signal crayfish (Pacifastacus leniusculus), the first NICS in Estonia and its influence on native noble crayfish (Astacus astacus) populations. The first specimen of signal crayfish was caught during the monitoring of noble crayfish in North Estonia in 2008. The signal crayfish has since been found in three additional sites. Test fishing has indicated that the abundance of signal crayfish has been fluctuating between years and among localities. It has had strong negative impact on abundance of one noble crayfish population. The disconnected distribution of signal crayfish strongly suggests that these populations are the result of human-assisted introductions. Real-time PCR analyses proved that signal crayfish carry the causative agent of the crayfish plague, an oomycete Aphanomyces astaci, thus contributing to its spread. Mortalities in noble crayfish populations had been caused by A. astaci strains from A, B and E genotype group.

Recruitment of sympatric vendace (Coregonus albula) and whitefish (C. lavaretus) is affected by different environmental factors

AbstractVendace and whitefish in Lake Osensjøen (boreal south‐east Norway) were studied by means of gillnet test fishing (1976–2013) and hydro acoustic acquisition (1986–2011). Vendace increased in number between 1998 and 2009 while growth and size at maturity decreased. The relative density of whitefish decreased in the pelagic habitat, whereas growth and size remained the same. Both species exhibited varying year‐class strength. Whereas strong year‐classes of both species became less frequent after 1980 than before this, this seemed to change after 2000, especially for vendace. Generalised additive models suggested a strong positive relationship between July/August mean air temperature and year‐class strength of both vendace and whitefish. Whitefish recruitment was also negatively affected by the new regulation regime implemented since 1981, and positively correlated with water level after hatching and by late ice off. The reason for the diverging impacts of environmental factors on the two species may be that vendace spawn in deeper waters that whitefish do. The results indicate that increasing summer temperatures benefit recruitment of both species, whereas low water level and early ice off will harm whitefish recruitment. Both trends are caused by climate warming. It may be speculated that increased density of the specialised plankton feeding vendace may affect the algal community through increased predation on herbivorous zooplankton and potentially affect the trophic state of the lake.

거제연안 새우조망 조업구역과 비 조업구역에서의 어획물 특성

Experimental fishing was carried out to compare and analyze catch characteristics of shrimp beam trawl in a fishing area and a non-fishing area during the period of fishing season and off-fishing season in the coastal waters of Geoje. A commercial fishing boat (4.99 tons) was used for the test fishing. The amount of total catches were 14,654g in the fishing area and 12,359g in the non-fishing area, shrimp catches of non-fishing area were much greater than that of the fishing area during the period of off-fishing season (June and August). However, total catches were 27,670g in the fishing area and 33,004g in the non-fishing area, shrimp catches of fishing area were bigger than that of non-fishing area during the period of fishing season (October and December). On the results of the study, catches characteristics between fishing area and non-fishing area showed the reversed results for the period of fishing season and off-fishing season.

Fish‐based assessment of ecological status of Finnish lakes loaded by diffuse nutrient pollution from agriculture

Abstract The European Union Water Framework Directive stipulates that pressures on surface waters due to diffuse loading of nutrients have to be taken into account in determination of their ecological status. A Finnish data set of fish communities in 178 lakes was used to assess the effects of agriculture‐induced nutrient loads on the ecological status of lakes. The lakes were divided to reference (n = 100) and impacted sites (n = 78) based on water quality, land use and nutrient load data. Fish sampling was conducted by standardised gill net test fishing. A fish‐based classification tool of the four parameters (EQR4) was applied to assess the ecological status of lakes. The parameters included were: mean total biomass of fish per gill net night, number of fish individuals per gill net night, biomass proportion of cyprinid fishes and the presence of indicator species. The analysis resulted in a median EQR4 value of 0.78 (good status) for reference lakes and 0.56 (moderate status) for affected lakes. Thus, the classification tool gave an acceptable output for different nutrient‐loaded lakes.

Biomanipulating the drinking water reservoir of Estonia's capital city: Prospects for success

The possibility of utilizing biomanipulation to improve the water quality of Tallinn's drinking water reservoir (Lake Ulemiste) was analysed on the basis of water quality data, test fishing by different methods, and earlier studies on aquatic plants, light climate and sediments. Eutrophic, polymictic Lake Ulemiste is characterized by a prevalence of high filamentous cyanobacteria biomass, rotifers in the zooplankton community, mature bream in the fish biomass, and a high density of planktivores (YOY perch). Several prerequisites for being a potential target for biomanipulation were identified, including (i) decreased external total phosphorus (TP) loading; and (ii) a sufficient stock of piscivorous fish in the lake. Prohibition of fishing should favour biomanipulation efforts. The potential for recolonization of macrophytes and large Daphnia species in Lake Ulemiste could be judged from historical data. The in-lake TP concentrations are within the limits that facilitate successful restoration. As phytoplankton biomass was significantly limited by phosphorus in Lake Ulemiste, its water quality improvement will be driven primarily by reduced nutrient concentrations, and then by zooplankton grazing. Internal TP loading and a new phytoplankton species community were assessed as major challenges for successful implementation of biomanipulation as a means of improving the water quality of Lake Ulemiste.

Assessing shifts in fish assemblages of German large lakes by literature data and commercial catch statistics

To assess the ecological integrity of lakes according to the European Water Framework Directive, the present status of fish assemblages has to be compared to a type-specific reference status. Monitoring fish assemblages by standardized fish sampling surveys as recommended for smaller lakes can be performed in large lakes only by an extraordinarily high effort and with severe doubts in terms of representative sampling. As an alternative, we present the evaluation of fisheries data from historic and present catch statistics and literature for the 26 lakes > 10 km 2 surface area in Germany. Documented species-specific fish catches were classified into four abundance classes for both the historic and the present situations. Cluster analyses of the historic and the present fish abundance matrices revealed that fish assemblages mainly differed between ecoregions and watersheds. Local species extinctions and abundance declines were frequent in some lakes and most often occurred in the fish families Core-gonidae and Salmonidae. However, in almost 60 % of all species present, no changes in abundance classes were found. Lake-specific changes in fish assemblage composition were correlated to present trophic situation, natural shore structure and human use intensity, but the correlations differed between ecoregions and watersheds. Shifts in relative species abundances were only partially correlated to species turnover rates, based on presence/absence lists. Accordingly, human impacts on lakes predominantly modified the relative species abundances rather than resulted in massive species extinctions or a dominant establishment of invaders. Extensive literature data may be a valuable source of information to fulfil the demands of the WFD for a fish-based assessment of the ecological state of large lakes for which comprehensive data sets exist and thereby offer a cost-effective alternative to effort-intensive test fishing.

북서태평양 공해의 원양오징어채낚기 어획조사

To investigate the catches of squid jigging fishery, a series of fishing experiments was conducted in the high seas of the Northwest Pacific(<TEX>$40^{\circ}-43^{\circ}N$</TEX>, <TEX>$150^{\circ}-155^{\circ}E$</TEX>) during the period of 1 August to 22 October 2005 by commercial fishing vessel. The number of 142 test fishing was carried out in the Northwest Pacific during 83days. The total catch were 47,524kg as 4 squid species and CPUE was <TEX>$8.9kg/line{\cdot}day$</TEX>. CPUE showed high values in the frontal zone during the survey. Main squid species caught from the experimental fishing were the neon flying squid, Ommastrephes bartrami(96.8%) and the boreopacific gonate squid, Gonatopsis borealis(3.2%). Dorsal mantle length of the neon flying squid were increased by the time and increasing of the hook size. Loss rate of the neon flying squid in the water showed the highest values in 28.2% compare to the others. And the loss rate of the front roller and in the air were 1.1% and 1.0%, respectively.

북태평양 중부 해산어장에 있어서 저층 트롤의 어획실태

This study was conducted in order to the experiment of bottom trawl fisheries in the sea mount of central northern pacific(, ), during the period of July 1 to August 25, 2004 by commercial trawl ship. Fishing experiment was carried out by bottom trawl, with the codend of 110mm mesh size. The number of 101 test fishing was done in the sea mount of central northern pacific during 56 days and the total catches were 198,593kg as 18 fish species, and CPUE/day and catches/day were 8.3 hours towing time and 3,546kg. Catch ratio according to each fishing ground was higher with the order of B, C, and E, and catches for B was 7,171.0kg during the towing time of 13.2 hours. Main target species were Pseudopentaceros richardsoni and Beryx splendens, there was 14.9% of damage ratio for fishing gears on catching the target fishes inhabiting on the rough sea bottom. Catches by water depth was the order of 300m below, 301-350m, 451-500m and 351-400m. It is thought that there was no problem on the mesh size because most of fishes caught from the experimental fishing was 30cm over.

북태평양 중부 해산어장에 있어서 저층 선주낙의 어획실태

This study was conducted to survey the catches of vertical bottom longline fisheries in the sea mount of central northern Pacific(<TEX>$30^{\circ}-42^{\circ}N$</TEX>, <TEX>$170^{\circ}-175^{\circ}E$</TEX>), during the period of July 1 to August 25,2004 by commercial fishing vessel. The number of 57 test fishing was carried out in the central northern Pacific during 43 days and the total catches were 21,092.4kg as 19 fish species, CPUE/day and catches/day were 185 baskets and 490.5kg, respectively. Main fish species caught from the experimental fishing were Squalus mitsukurii (66.3%), Coelorhyrchus asperocephaius (11.7%) and Helicolenus avius (9.8%) and, average inside diameter for fish mouth was 4.0cm over. Catch ratio according to each fishing ground was the order of F, D, J, B and C. Catch ratio fur water depth was the order of 450-500m, 350-400m, 300-350m, 400-450m, 1000-1100m and 500-550m and, main species by water depth was Squalus mitsukurii for 300-400m, Etmopterus lucifer for 300-550m, Coelorhyrchus asperocephaius far 1,000m over. Catch ratio according to the kind of hooks was higher at the hook no.6 for Squalus mitsukurii and no. 5 for Etmopterus lucifer and, catch ratio by baits was higher at squid for Squalus mitsukurii, saury and eel for Helicolemus avius and saury for Etmopterus lucifer. Accordingly, it is thought that the extension of fishing hours is needed with the reduction of damage and loss for fishing gears during fishing operation.

Habitat utilisation by fish community in a short-term regulated river reservoir

Short-term streamflow regulation (hydropeaking) affects the ecology of regulated rivers. We examined the longitudinal and temporal changes occurring in fish assemblages in a hydropeaking single river reservoir between two power plants by using electrofishing along the shoreline, hydroacoustics and test fishing in the open water. A longitudinally changing fish community was found among bottom-dwelling fish in the fast-flowing and highly disturbed upstream part of the reservoir progressing to generalists and pelagic fish in the lentic and most stable environment at the downstream end. The fish assemblage showed temporal patterns as fish density increased during night-time darkness and also towards autumn. Our work provides evidence for gradient effects of flow regulation and contributes to awareness of the effects of disturbance (flow/habitat variability) on biological systems.

Population responses of perch (Perca fluviatilis) and roach (Rutilus rutilus) to recovery from acidification in small Finnish lakes

Decreasing trends in atmospheric emissions and acidic deposition during the 1990s have resulted in chemical recovery from acidification in the sensitive surface water systems of southern Finland. Responses of perch and roach populations to the improved water quality were studied in 30 small lakes with the aid of water chemistry monitoring data gathered in 1987–2002 and the data collected from two consecutive periods of gillnet test fishing, 1985–1988 and 2001–2002. In the most acidified lakes, alkalinity and ANC have increased and sulphate and labile aluminium concentrations decreasaeed markedly. The response of perch populations to the improved water quality is seen in improved reproduction success, indicated by a higher CPUE in numbers and a lower mean weight. The growth rate of perch has declined as the population density has increased. Roach populations have not recovered in the same way as perch, there being no major changes in NPUE or mean weight. Lower growth rates were, however, observed in the roach populations of all study lakes. The increased perch population density as an obstacle to the recovery of roach populations is discussed. Despite the chemical and biological recovery of the study lakes, the buffer capacity of many headwater lakes is low and the lakes will be sensitive to any increases in acidic deposition in the future.

플라스틱 붕장어 통발어업에 있어서 침지 시간과 어획과의 관계

Test fishing was carried out utilizing a coastal pot-fishing boat from IS March to 7 April 2002 and the results obtained are summarized as follows ; 1. Mean catches(Number of sea eels) according to the soak time of 3 hours, 6 hours and 12 hours were 44.6, 60.0 and 83.3, and CPUE(Number of catch / 10pots·hour) were 2.5, 1.7 and 1.1 respectively 2. Catch difference between over 24 hours and 48 hours was 11.3% and 3.3% between over 48 hours and 72 hours. 3. In the test fishing, by-catches were so low(1.5∼3%) until 12 hours of soaking time passed By-catches were increased according to the soaking time addition on the over 24 hours of soaking time. The bait effect for sea-eel seems to be diminished as soon as the casting started and there was big difference in proportion to bait size and freshness

유실된 플라스틱 붕장어 통발에 어획된 붕장어의 위내용물 분석

Ghost fishing으로 추정되는 유실된 플라스틱 붕장어 통발에 어획된 붕장어의 섭이 상태와 개체의 성장에 대해 조사하기 위하여, 통발 조업선에 어획된 붕장어와 트롤 그물에 어획된 붕장어를 이용하여 비교 분석하였다. 어획된 붕장어의 평균 전장은 연안 통발 조업선과 시험 조업에서 어획된 것이 33.6cm, 트롤 그물에 어획된 것이 48.9cm 그리고 수거된 유실 통발에 어획된 것이 45.6cm이었다. 이러한 체장의 분포는 붕장어가 성장하면서 연안에서 외양으로 나간다는 사실과 일치한다. 위내용물 조사에서 먹이를 섭이하지 못해 위내용물이 전혀 없었던 붕장어의 비율은 통발 조업선 5.0%, 트롤 4.2% 그리고 유실 통발 87.6%로 유실 통발에서 17～20배 높게 나타났다. 먹이로써 어류를 섭이한 붕장어의 비율은 통발 조업선이 98.7%, 트롤이 78.8% 그리고 유실 통발이 63.3%로 나타났으며, 그 외의 먹이 생물은 갑각류와 두족류 등이었다. 순체중과 전장을 이용하여 계산한 비만도는 트롤 어획물이 1.514이고, 유실 통발 어획물이 1.292로서 약 15%의 차이가 있었으며, 이들 자료에 대한 공 분산분석에서 실시한 t검정 결과 5% 유의수준에서 위치의 차이가 있는 것으로 나타났다. Sea-eels caught by fishing boat and trawl were analyzed to investigate feeding status and individual growth of sea-eels caught from the lost plastic sea-eel Pot which is estimated at the ghost fishing Average length of sea-eel caught from fishing boat and test fishing was 33.6cm, 48.9cm for trawl and 45.6cm for the lost plastic sea-eel pot, respectively. The length frequency distribution is the same as the fact that sea-eel goes to the offshore from the coastal waters according to the getting growth. Sea-eel rate having empty stomach were 5.0% for fishing boat, 4.2% for trawl and the empty stomach rate of sea-eel was the highest as 87.6% in the lost pot. Sea-eel rate feeding fish as prey were 98.7% for fishing boat, 78.8% for trawl and 63.3% for the lost pot, respectively and other preys were crustacean and cephalopod. Fatness index calculated using weight and length were 1.514 for trawl catches and 1.292 for the lost pot and the difference was 15% between trawl catches and the lost pot. There also was difference at the 5% significance level in the result of t-test of Covariance Analysis.

Chenderoh Reservoir, Malaysia: a characterization of a small-scale, multigear and multispecies artisanal fishery in the tropics

A study on the artisanal fishery of Chenderoh Reservoir, Perak River, Malaysia, was conducted from April 1988 to May 1989 using creel survey, rapid rural appraisal (RRA) and test fishing. The main landing site, used by 30 fishers and controlled by a middleman, was identified. The fishers indicated fishing as a secondary occupation supplementing income from farming or rubber tapping. The fishery was not regulated and most of the catch (30–94%) was landed with multifilament gill-nets (stretched-mesh 5.7, 10.2 and 11.4 cm), whereas long lines (30–40 m long) contributed 6.2–55.0% of the catch. Each fisher used a wooden boat (4–6 m long, 1.0–1.5 m wide) fitted with a 5 hp gasoline engine and utilized either 15–20 sets of gill-nets each 3 m deep and 30–40 m long or one or two sets of long lines. The daily catch per unit of effort (CPUE) was low (2.7–12.8 kg per fisher-day) and the daily income ranged from Malaysian Ringgit (M$) 4.94 to 32.43 per fisher-day. The total annual catch and income generated by the fishery was 25713.0 kg and M$63179.74, respectively. Even with declining catches the fishery is still important in providing supplementary incomes. In the absence of ‘official’ regulations and management, the fishing community imposed their own rules and regulations which were enforced by the middleman.

Multi‐mesh gillnets to estimate species composition and catch per unit effort of fish in a small water body in Zambia

A standard method comprising multi‐mesh monofilament nylon gillnets and depth stratification, the Drottningholm method, was employed in test fishing of a small Zambian reservoir (32 ha) on eight occasions over 1 year. The catch per unit effort (cpue) from the 0–3 and 3–6 m zone was timated with benthic and pelagic nets, while in the 6–12 m zone only benthic nets were used. Results include species caught and cpue with coefficients of variation and confidence intervals, for net types and depth zones. A total of 11 species were caught, of which Burbus paludinosus, B. marequensis, Laheo cylindricus, and Oreochromis sp. dominated. Coefficients of variation did not indicate a preferable season for test fishing. During the cold season some species were not caught. The applicability of the method in estimation of species composition and cpue is discussed.

Computation of Migratory Timing Statistics for Adult Chinook Salmon in the Yukon River, Alaska, and Their Relevance to Fisheries Management

Abstract An objective definition of migratory timing is applied to commercial and test fishing catch data for chinook salmon (Oncorhynchus tshawytscha) from the Yukon delta, 1961-1980. On the average, 91% of all the commercial catch is taken before the end of June, with one-half of the catch being taken by June 21. The middle part of the migration (25-75%) usually is available for harvest only over a span of 11 days. However, the length of the central span has varied from 8 to 13 days, depending on timing. Mean dates of migration based on catch and CPUE data were nearly identical (about June 21), with range limits of June 12-30. Test fishing and commercial catch data for 1963-1978 showed no significant difference (α = 0.05) for the mean date of migration. The spread of the migration (variance) appears to be inversely proportional to the mean date of migration for early and late migrations. Timing of migration may be dependent on factors related to air temperature.