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Jůza T, Blabolil P, Čech M, Draštík V, Holubová M, Kočvara L, Kubečka J, Malinovskyi O, Policar T, Rychtecký P, Říha M, Sajdlová Z, Tušer M, Vašek M. 2024. Assessing the efficacy of spring stocking of pikeperch (Sander lucioperca) into a eutrophic reservoir. Lake Reserv Manage. 40:196–204. The survival of stocked fish is one of the crucial problems of management measures. In April 2023, approximately ten thousand 1-yr-old pond-reared pikeperch fry were marked and stocked into the small, eutrophic Hubenov Reservoir in the Czech Republic. Later that year, in August, the abundance of the stocked pond-reared pikeperch in the reservoir was estimated through beach seining, electrofishing, and gillnetting. Gillnet results showed that pikeperch avoided pelagic and deeper benthic habitats. Consequently, the most quantitative results were obtained by night beach seining. Our captures indicated that approximately 688 stocked pikeperch individuals were present in the entire reservoir in August, representing 6.5% of the stocked fish. These pikeperch displayed good growth and condition, primarily feeding on European perch fry, the most abundant 0+ fish in the reservoir. Our findings elucidate a relatively high mortality of 1-yr-old pond-reared pikeperch in the reservoir after spring stocking. Despite this mortality, the stocked pikeperch represented 85% of all 1-yr-old pikeperch in the reservoir. This highlights the effectiveness of spring stocking as a valuable tool for supporting the pikeperch population in reservoirs, emphasizing the stocking of an adequate quantity of pond-reared fish to compensate for the observed mortality. [ABSTRACT FROM AUTHOR]

Raiding seals pose a big problem to gillnet fishers in areas with high seal abundances. As moving to active gears could be a potential solution for that problem, one gear of particular interest in areas with relatively flat sea bed structure is the so-called “MiniSeine” – a demersal seine that is reduced in size so it can be operated from small vessels. Besides its ability to catch most of the species targeted by gillnet fishers, it offers various advantages compared to other active gears. To reduce the gear in size to fit on a small vessel, the present study assessed how seine rope length (4 coils vs 8 coils), seine rope diameter (18 mm vs. 22 mm) and seine net configurations of different sizes and shapes (three different designs) affect the catch efficiency and the ratio of fish below minimum conservation reference size (MCRS). In general, shorter seine ropes (4 coils) resulted in significantly lower catches than longer ones (8 coils), except for the smallest seine configuration. Larger seine net configurations and longer seine ropes caught generally less fish below MCRS, both up to around 10 %. The seine rope diameter did not affect catches significantly. As potential “adjusting screw” to counteract lower catches due to shorter seine ropes, the effect of different layout patterns of the seine ropes on the catch efficiency was assessed. Laying out the second seine rope perpendicular to the first one can increase the fishing area to more than three times while CPUE showed a tendency to be increased compared to the standard layout pattern. Besides its importance for a successful development of the MiniSeine, these findings are of equal interest for the large-scale demersal seine fishery.

As a commercial fish, bullet tuna is constantly caught in purse seine fisheries to provide economic benefits for coastal communities. Biological information such as food preference has to be known due to their sustainability in the future. This research aims to figure out the food composition and preference of bullet tuna (Auxis rochei Risso, 1810) in Prigi Coast, Trenggalek Regency East Java. A total of 294 fish landed by purse seine fishermen have been collected from March up to May 2018. Each individual was measured in its total length and weight, then was dissected for sex determination, measured the length of intestine, and analyse the stomach content. The data analysis encompasses frequency distribution of total length, relative gut length, frequency of occurrence, index of preponderance, trophic level, niche breadth, and food overlapping. The research result indicates that the main foods of Auxis rochei are fish and crustacean, while the complementary and additional foods were copepod, mollusc, annelid, and debris. Bullet tuna was a carnivorous fish with the trophic level of 3.7 and shows the existence of competition for food resources. Overlapping of feeding occurred in the 19-20 cm long group against the 23-24 cm long group in male fish and the 19-20 cm size group against the 21-22 cm length group in female fish. Bullet tuna use the same feed resources among the size groups of fish, where females use feed over a wider area than males. [ABSTRACT FROM AUTHOR]

Raiding seals pose a big problem to gillnet fishers in areas with high seal abundances. As moving to active gears could be a potential solution for that problem, one gear of particular interest in areas with relatively flat sea bed structure is the so-called "MiniSeine" - a demersal seine that is reduced in size so it can be operated from small vessels. Besides its ability to catch most of the species targeted by gillnet fishers, it offers various advantages compared to other active gears. To reduce the gear in size to fit on a small vessel, the present study assessed how seine rope length (4 coils vs 8 coils), seine rope diameter (18 mm vs. 22 mm) and seine net configurations of different sizes and shapes (three different designs) affect the catch efficiency and the ratio of fish below minimum conservation reference size (MCRS). In general, shorter seine ropes (4 coils) resulted in significantly lower catches than longer ones (8 coils), except for the smallest seine configuration. Larger seine net configurations and longer seine ropes caught generally less fish below MCRS, both up to around 10 %. The seine rope diameter did not affect catches significantly. As potential "adjusting screw" to counteract lower catches due to shorter seine ropes, the effect of different layout patterns of the seine ropes on the catch efficiency was assessed. Laying out the second seine rope perpendicular to the first one can increase the fishing area to more than three times while CPUE showed a tendency to be increased compared to the standard layout pattern. Besides its importance for a successful development of the MiniSeine, these findings are of equal interest for the large-scale demersal seine fishery., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2024 The Authors.)

Aquatic ecosystems are deteriorating, with the most impacted species and populations having insufficient data to inform conservation and management. Monitoring aquatic biodiversity and evaluating anthropogenic impacts typically rely on time-consuming, logistically challenging, and invasive methods (e.g., seining, trawling or electrofishing). Environmental DNA (eDNA) methods have been touted as an important advancement, especially in fish biodiversity assessment. We compare eDNA metabarcoding and seining methods along a 350 km section of the Upper St. Lawrence River (Canada) for: i) mapping the distribution of invasive and threatened fish species, ii) describing species richness and fish community structure, and iii) assessing the effect of habitat type and anthropogenic degradation of riparian zones on fish community composition and richness. eDNA detected more fish species (n = 67) than seining (n = 38) and revealed higher fish diversity in samples adjacent to intact, natural riparian zones. Fish assemblages were influenced by habitat type according to analyses using eDNA, while no effect of any environmental predictor on fish community composition was found using seining. Altogether, our results support eDNA metabarcoding as a powerful, complementary tool in fish monitoring and testing for the impacts of anthropogenic disturbances. [ABSTRACT FROM AUTHOR]

Flyshooting or Scottish seining is a relatively new but fast growing seining technique. In the English Channel and the North Sea, the main targets are species without Total Allowable Catch (TAC), but whiting (Merlangius merlangus) is a quota-regulated species that is often landed as bycatch. This could make whiting a potential choke species under the current landing obligation. The goal of this study was to evaluate the effectivity of a square mesh panel (SMP) in releasing (undersized) whiting. A catch analysis was done to assess the loss of fish through the SMP. This revealed that over 40% of the undersized and 20% of the marketable whiting escaped through the SMP and was retained in the 55 mm SMP cover. The commercial loss of other species was limited to minor quantities of small red mullet (Mullus surmuletus). We conclude that this SMP can be an effective net adaptation to significantly reduce the bycatch of whiting in the flyshooting fishery with only a marginal commercial loss of other species. • SMPs reduce bycatch of undersized whiting in the flyshooting fishery. • SMPs have only a marginal loss of commercial species in the flyshooting fishery. • SMPs can be useful for technical regulations and management in flyshooting fishery. [ABSTRACT FROM AUTHOR]

Data Envelopment Analysis (DEA) studies of fisheries usually apply output oriented capacity utilization based on physical measures. Although physical measures capture important input factors employed in fishing activities (such as boat size, engine power), economic measures directly reflect the cost of inputs employed. This case study investigates whether economic measures are vital or whether capacity efficiency is sufficiently well reflected solely by the use of physical measures. The analysis makes use of a double bootstrap DEA technique and compares input oriented capacity utilization based on physical versus economic measures. The double bootstrap technique was chosen as it allows statistical inference based on the estimated capacity utilization. The results show that economic measures give a lower capacity utilization than that obtained by physical measures. However, no significant difference was found in the capacity utilizations between the two measures. Truncated regression models indicated that factors such as skipper experience and family size did not significantly affect these two measures of capacity utilization at the 5% level. This study concludes that physical variables are capable of capturing the essential economic differences between vessels. [ABSTRACT FROM AUTHOR]