Commercial Catch Research Articles

Past and present sawfish (Pristidae) records from India

Overfishing, as well as habitat loss and degradation, has led to major population declines and local extinctions of sawfishes (Pristidae) globally. Four sawfish species reportedly occur in India; however, records have been limited to opportunistic commercial catch and landing reports. Here, we provide the first comprehensive review of published and grey literature on sawfish records from India, including opportunistic observations of sawfish rostra offerings to religious places, highlighting the cultural significance of these species locally. In total, 223 recorded capture events were compiled between 1794 and 2022, with largetooth sawfish Pristis pristis (n = 82), followed by narrow sawfish Anoxypristis cuspidata (n = 32), being the dominant species reported. In addition to marine fisheries, 8 reports of sawfish were reported from freshwater systems. The wide range of rostra sizes and total lengths recorded also suggests that India’s waters harbour various life history stages of sawfish. When caught, sawfish livers were utilised to produce oil, meat was locally consumed, and fins were exported. Despite being legally protected in India since 2001, 63 incidental captures were recorded from landings, suggesting various levels of awareness and enforcement of catch bans across the country. To avoid extinction of these species in India, we emphasise the need to conduct culturally associated awareness programs with coastal communities, encourage safe release and improve handling practices with fishers, identify critical habitats, and strengthen enforcement for mandatory live release.

Dynamics of fishery and distribution of aggregations for saffron cod Eleginus gracilis (Tilesius) at northern Kuril Islands

The fishery on winter-spring accumulations of saffron cod in the area of northern Kuril Islands has a long history with varying intensity, though this species is not abundant both in the Pacific and Okhotsk Sea waters of this area. The annual catch ranged from 1.8 to 167.4 t in 2003–2022, on average 40.8 t/yr. The fish with length of 24–56 cm were presented in commercial catches of Danish seine, with prevalence of the 36–48 cm size group. The average length of saffron cod in the catches was changed from 35.4 cm in summer to 43.2 cm in winter that coincided with the fishing depth increasing in winter. The main commercial concentrations of the species had formed between the islands of Paramushir and Shumshu and in the area of the First Kuril Strait.

What bycatch tells us about the diet of harbor and gray seals and overlap with commercial fishermen

Northwest Atlantic harbor (Phoca vitulina vitulina) and gray (Halichoerus grypus atlantica) seal populations are recovering from early to mid-20th century exploitation, increasing their biological interactions and bycatch in Northeastern US commercial fisheries. We evaluated the seals’ diet composition and compared their prey to commercial catches to assess trophic overlap and potential competition with commercial fisherman target catches. We obtained 148 harbor and 178 gray seal stomach samples from bycatch events that occurred between 2004 and 2018. We learned from the hard part remains that the majority of seals bycaught are young-of-the-year (≤12 months old) that consume a wide breadth of prey across three trophic groups. There was a general dichotomy in extrinsic factors associated with seal diet in which 45% trophic niche separation was explained by non-overlapping harbor and gray seal phenology and pup haul-out locations that are adjacent to active fishing areas. Prey size estimated from fish otoliths and squid beaks recovered from stomach contents showed that gray seals consumed larger prey than harbor seals and prey sizes from both seals showed limited overlap with prey sizes caught by commercial gillnet fishermen. The most important prey to both seals included large (>20 cm) and small (≤20 cm) silver hake (Merluccius bilinearis), (≤40 cm) red hake (Urophycis chuss), gulf stream flounder (Citharichthys arctifrons), medium (21–40 cm) white hake (Urophycis tenuis), and (<50 cm) Atlantic cod (Gadus morhua). Important prey to harbor seals that did not overlap with gray seals were Acadian redfish (Sebastes fasciatus), Atlantic herring (Clupea harengus), longfin (Doryteuthis pealeii), and shortfin squid (Illex illecebrosus). They contrasted with prey important to gray seals that did not overlap with harbor seals: yellowtail flounder (Limanda ferruginea), sand lance (Ammodytes spp.), Urophycis spp., and fourspot flounder (Hippoglossina oblonga). Despite the potential bias associated with opportunistic bycatch sampling, this study demonstrates the importance and value of utilizing carcasses retained from bycatch events, is complimentary to newer methodologies (i.e., DNA meta-barcoding), and fills data gaps in our understanding of the role recovering harbor and gray seal populations have on Northeastern US regional food webs.

Unveiling the reproductive and migrative behavior of Trichiurus lepturus in a tropical environment: Insights and implications.

This study aimed to understand the reproductive biology and migrative behavior of the largehead hairtail Trichiurus lepturus in a tropical area, specifically off Pernambuco coast, northeastern Brazil. Commercial catches from fish corrals provided samples for analysis, including measurements, weight recording, and examination of gonads to determine its maturation stage. Reproductive analyses were performed, such as sex ratio, gonado-somatic index, and sizes at first maturity. There was a slightly higher proportion of females among the 141 largehead hairtail specimens analysed. No significant differences were observed in length distributions between males and females. However, during the winter, significant differences were observed in length distributions for grouped sexes. The species exhibited a seasonal migratory pattern, with a higher presence on the continental shelf during the winter. The study identified strategic allocation of energy in feeding activities and temporal spacing of reproductive cycles, as indicated by the sex ratio and abundance of individuals during different seasons. Fish corrals probably do not harm largehead hairtail population off the southwestern Atlantic tropical coast, with minimal capture of individuals below the size of first maturity. The insights of the study into reproductive and migration patterns contribute to future assessments and management strategies for this species and corral fisheries.

Fishery, population dynamics and stock assessment of flat needlefish Ablennes hians (Valenciennes, 1846) from the south-eastern Arabian Sea off Kerala coast, India

The age, growth, mortality parameters and stock status of Ablennes hians(Valenciennes, 1846) were assessed by using length frequency, catch, and effort datacollected from the commercial catches along the coast of Kerala (south-eastern ArabianSea) during 2015-2017. The growth parameters, L∞, K and t0 were estimated at 133.9 cm TL,0.72 yr-1 and -0.0026 yr, respectively. The instantaneous natural mortality (M), total mortality(Z), fishing mortality (F) and current exploitation rate (Ecur) were estimated as 0.95 yr-1,2.78 yr-1, 1.83 yr-1 and 0.66, respectively. Length at capture (Lc50) was estimated at 77.58cm TL, which is greater than Lm50. Beverton and Holt yield per recruit analysis, indicated thatmaximum Y/R could be obtained at an exploitation rate (Emax) of 0.75, suggesting scope foran increase in exploitation. In this analysis, spawning stock biomass (SSB) was not takeninto consideration, which is essential for maintaining recruitment in the future. In the presentstudy, E0.1 (0.61) and Ecur (0.66) were nearly equal, indicating that the fishery is running atan economic reference point i.e., maximum economic yield (MEY). Thompson and Bellprediction model showed that at the current level of exploitation, the SSB was reduced by20.49% and hence, there is no scope for further increase in fishing efforts to maintain the SSBat a relatively safe and sustainable level. The analysis revealed the maximum sustainableyield (MSY) of this species as 90.26 t, which can be obtained by increasing the present levelof fishing effort by 1.3 times but would result in the depletion of the SSB to a critically lowlevel of 15.65%. Therefore, a precautionary safe level of exploitation (E0.1), estimated at 0.61for the species, is recommended. Keywords:Belonidae, Fishery management, Population dynamics,Spawning stock biomass, Stock status

Challenges in collecting age composition data from commercial catches of the Barents sea bottom fishes

The paper presents the rationale for collecting information on the structure of catches and the distribution of bottom fish species (and in particular North-East Arctic cod) on fishing vessels in the Barents Sea and adjacent waters by observers of the Polar Branch of FSBSI «VNIRO» («PINRO» named after N.M. Knipovich). The problems that arise during the work of a scientific observer are described. Possible solutions to solve the problems of collecting materials on commercial catches are proposed. Increase of the scientific observers number on bottom fish fisheries and elevation of their legal status is recommended. A fundamentally new scheme for collecting information on the size distribution of fish in commercial catches by the crews of fishing vessels has been proposed.

Another One Bites the Net: Assessing the Economic Impacts of Lagocephalus sceleratus on Small-Scale Fisheries in Greece

The assessment of the economic impacts of marine invasive species is fundamental for adopting mitigation measures, yet such impacts have been underreported in the Mediterranean Sea. The silver-cheeked toadfish (Lagocephalus sceleratus) is a toxic pufferfish that since its introduction has seriously disturbed small-scale fisheries along the eastern Mediterranean coast. This species depredates on fishing gears, causing damage to nets, longlines and commercial catches. To quantify its economic impact on small-scale fisheries, we interviewed 141 fishers from Crete (Cretan and Libyan Sea) and the Ionian Sea (Greece) during May 2020–December 2022. The mean annual economic cost resulting from L. sceleratus depredation was estimated at EUR 6315 ± 2620 per vessel in Crete and EUR 258 ± 120 in the Ionian Sea. Additionally, observer surveys carried out on board small-scale fishing vessels in Crete showed that depredation probability was significantly influenced by fishing depth, sea surface temperature, gear type (nets, longlines) and region (Cretan, Libyan Sea). L. sceleratus was caught more frequently and in higher numbers in the Libyan Sea. In response to depredation, fishers in Crete have altered their fishing tactics in terms of fishing in deeper waters, reducing fishing time and changing the technical characteristics of fishing gears. Our results underscore the adverse impacts of L. sceleratus on Greek small-scale fishers, emphasizing the need for region-specific management plans where the species establishes large populations.

Investigating temporal variability and influence of condition on fecundity and spawning of spotted wolffish (Anarhichas minor) in Icelandic waters

Spotted wolffish (Anarhichas minor) is a poorly understood species which is often captured as part of mixed demersal fisheries across its range. Abundance has declined in many regions and there is a need for greater knowledge on its biology. To improve our understanding of reproduction of A. minor, we investigated inter- and intra- annual differences in fecundity, the influence of condition on fecundity and time scale of ovary development. From 2006 to 2021, 150 females A. minor were sampled in Icelandic waters. Of these females, 73 were also used to estimate spawning time together with an additional 334 females from commercial catch and surveys from 2006 to 2023. Backwards extrapolation of oocyte size indicates that vitellogenesis begins in December and is likely completed after 8–10 months. There was no evidence of either intra- or inter-annual differences in fecundity, indicating that downregulation is minimal and that fecundity of A. minor is stable between years. A positive relationship between oocytes size and fish length was detected, while body condition and hepatosomatic index had only a small influence on fecundity in comparison with weight. There was a negative relationship between length and relative fecundity and the exponent of the fecundity–length relationship was lower than exponent of the weight–length relationship. Therefore, total egg production is likely not proportional to the spawning stock biomass of A. minor, and unusually, total egg production would decrease with increasing proportion of larger fish in the population. The spawning season was estimated to be from middle of August to middle of October with peak of spawning in September.

Network of nearshore protected areas provides important benefits to lake whitefish in the Apostle Islands region of Lake Superior

Aquatic protected areas are commonly used for fish conservation, restoration, and management and a spectrum of protection levels exist in the Great Lakes. Using fishery-independent survey data over 43 years, we evaluated whether lake whitefish (Coregonus clupeaformis) population dynamics differed among nearshore partially protected areas (PPAs; commercial fishing prohibited or severely limited), offshore no-take refuges, and unprotected areas in the Apostle Islands region of Lake Superior. Lake whitefish biomass and recruitment to the spawning stock increased at faster rates in nearshore PPAs and offshore refuges than unprotected areas during the initial phase after protected areas were established (1980–2000). Recruitment and biomass stabilized in all management areas in the post-rebuild phase (2002–2022), and mortality was lower in the nearshore PPAs. Mean size of adults decreased within protected areas as abundance increased but not in unprotected areas, suggesting a density-dependent growth response and spillover to the fishing grounds, which was reflected in commercial catch rates. However, nearshore PPAs still harbored larger, faster-growing, and earlier-maturing lake whitefish, likely due to underlying habitat differences. Tag recaptures indicated greater minimum distances traveled near an offshore refuge compared to a nearshore PPA, suggesting habitat gradients may influence boundary porosity. PPAs provided protection and benefits for lake whitefish in areas of higher vulnerability where ceasing all fishing was not reasonable. Great Lakes managers should consider implementing networks of protected areas across multiple habitats as tools for conserving spawning biomass, maintaining diverse population demographics, and preserving portfolio effects to enhance recruitment and population stability.

Re-assessment of a blackfoot abalone (Haliotis iris) population in Peraki Bay, New Zealand, after 45 years

ABSTRACT Marine species are facing an increasing number of stressors and some species once thought to be resilient to change are now threatened. It is important to understand how species populations have changed through time so that management can be adjusted accordingly, and so that achievable restoration goals can be set. However, many species lack population data at multidecadal or longer time scales. Using historical data from the 1970s, this study investigates how the dynamics of a New Zealand abalone (Haliotis iris), or pāua, population at Peraki Bay changed over a 45-year period. No commercial fishing of the population occurred prior to the initial survey and limited commercial catch has been reported between surveys. Repeat monitoring of the H. iris population at a 45-year interval indicates that a large change in population size and structure had occurred. Since 1976, there has been an 84% decrease in estimated population size. The remaining population is restricted to where juveniles were found in the original survey. These findings are consistent with conclusions, made from modelling in the 1970s, that the population seen in the 1970s was not stable and that a possible cause was temporal variability in population recruitment.

Consumption of Post-Larval Swordfish (Xiphias gladius) by Dolphinfish (Coryphaena hippurus): New Ecological Insights into Both Species in the Tyrrhenian Sea

Knowledge of post-larval swordfish (Xiphias gladius) ecology in the world’s oceans is incomplete as they are rarely found in ichthyoplankton samplings or commercial catches and individuals are difficult to observe in the marine ecosystem. Analyses of stomach contents of apex predators can provide otherwise unobtainable ecological insights. Two well-preserved bills of post-larval swordfish were identified among the partially digested stomach contents of an adult male dolphinfish (Coryphaena hippurus) caught in the northern Tyrrhenian Sea. The lower jaw to fork lengths of the two predated swordfish were estimated at, respectively, 18 and 22 cm, corresponding to 81- and 99-day-old swordfish hatched in the 2022 spawning season. This analysis and recent information on the reproductive dynamics of swordfish in the same area reported in the literature shed light not only on the early stages of swordfish growth but also on dolphinfish ecology in the Tyrrhenian Sea. The two species share the same habitat and are both caught with commercial pelagic surface longlines. Environmental shifts associated with climate change could unpredictably modify the reproduction dynamics, growth, recruitment and distribution of both species. This knowledge is important for the sustainable management of regional fisheries.

Evidence from interpretable machine learning to inform spatial management of Palau's tuna fisheries

AbstractStatic and dynamic area‐based management tools hold substantial potential to balance socioeconomic benefits derived from fisheries and costs from bycatch mortality of at‐risk species. Palau longline fisheries have high bycatch of at‐risk species including the olive ridley marine turtle and silky and blue sharks. This study analyzed a two decades‐long time series of observer and electronic monitoring datasets from the Palau distant‐water and locally‐based pelagic longline fisheries. An interpretable or explainable machine learning‐based modeling approach was used to derive spatially resolved species‐specific catch rate predictions. These models were conditioned on a suite of potentially informative environmental, bathymetric, ocean‐climate metric, vessel, monitoring system, and set‐specific operational predictors. Overall, there would be limited ecological tradeoffs from focusing fishing effort within primary catch rate hotspots for target bigeye and yellowfin tunas. Mean field prediction surfaces also defined catch rate hotspots for at‐risk species of silky and blue sharks, olive ridley turtle, and pelagic stingray, which did not overlap the hotspots for target species. The predicted target species hotspots, however, overlap olive ridley and pelagic stingray warmspots. Results also identify opportunities for temporally dynamic spatial management to control catch rates of target and bycatch species. Management of fishery operational predictors of fishing depth and soak duration present additional opportunities to balance catch rates of at‐risk bycatch and target species. A transition to employing fleetwide or vessel‐based output controls that effectively constrain the fishery would alter the spatial management strategy to focus on zones with the lowest ratio of at‐risk bycatch to commercial catch. Our findings support evidence‐informed evaluation of spatial management strategies and complementary measures to meet objectives for balancing socioeconomic benefits derived from target species catch with costs to threatened species.

Возраст и рост обыкновенного судака Sander lucioperca в разнотипных водоемах юга Западной Сибири

The age and growth of fish are the most important characteristics underlying the assessment of the state of fish stocks and the forecasting of future catches. The pike-perch Sander lucioperca (Linnaeus, 1758) is an alien fish species in Western Siberia. It was first introduced into the Ob basin in 1956. The introduction of this species into the Novosibirsk reservoir was carried out in 1959-1964, and into Lake Chany in 1964-1966. Currently, pike-perch is spread throughout the Ob basin and is an important fishery target. This study summarizes long-term data from the Novosibirsk branch of Russian Federal Research Institute of Fisheries and Oceanography ("VNIRO") about the growth of different-aged individuals of the pike-perch, collected during monitoring of aquatic biological resources in the Novosibirsk reservoir (54°20' N, 81°57'E) and Lake Chany (54°55'N, 77°31'E) over the last 10 years (2013-2022). These water bodies are of different types: the Novosibirsk reservoir was formed on the Ob River, the maximum depth reaches 25 m, the average depth is 8 m. The area of the reservoir is 1.07 thousand km^. Lake Chany is located in the Ob-Irtysh interfluve, drainless, filled due to the runoff of the Kargat and Chulym rivers, atmospheric precipitation and groundwater. The maximum depth is up to 8 m, average depth is 2 m. The area of the lake fluctuates greatly from year to year depending on the water level, in the long-term aspect it has tends to decrease, currently amounting to about 2 thousand km. The lake water has increased mineralization in most of the reaches. Fish collection for analysis of size characteristics is carried out annually from commercial catches. The total volume of material for this study was 2953 individuals from Lake Chany and 1102 individuals from the Novosibirsk reservoir. As a result of this work, it was found that in commercial catches in different types of water bodies in the south of Western Siberia, pike-perch has been known at the age of up to 14+ years over the last 10 years. In Lake Chany, there were mostly individuals of age groups 2+-4+, and in the Novosibirsk Reservoir - 3+-6+ (See Fig. 1). The pike-perch size of the same age from commercial catches varies greatly from one year to the next in Lake Chany, and in the Novosibirsk reservoir (See Fig. 2). It confirms the data on significant variability in growth rates of this species and indicating the need for a cautious approach to comparing the length and weight of pike perch in different observation periods. On average, over the last decade, pike-perch in Lake Chany is characterized by a slightly shorter standard length and greater weight than in the Novosibirsk Reservoir, however, the differences reach statistical significance (p < 0.001) only when comparing fish aged 2+ by standard length (See Fig. 3). The analysis of the relationship between the growth rate of pike-perch and environmental temperature showed that the absolute increase per year of standard length and weight of younger age groups fish in the Novosibirsk Reservoir has a statistically significant positive correlation with the temperature in April (r = 0.6110.775), and in Lake Chany - in May (r = 0.633-0.737) (See Tables 1, 2). Considering that the average April temperature in the area of the Novosibirsk reservoir is 1.9°C higher than in the area of Lake Chany, probably, in the latter, juvenile pike-perch begins to actively feeding a little later. It may explain the smaller sizes of pike-perch of younger age groups in Lake Chany compared to the Novosibirsk reservoir. The article contains 4 Figures, 2 Tables and 28 References. The authors express their gratitude to all colleagues - employees of the Novosibirsk Branch of "VNIRO", who over in different years took part in collecting the material. The Authors declare no conflict of interest.

Fishing profile and commercial landings of shark and batoids in a global elasmobranchs conservation hotspot.

This paper describes the fishing profile and the temporal variation in the commercial landings of elasmobranchs in a global hotspot for their conservation and investigates the variables that influenced the landings. Census data on commercial catches were obtained between April 2008 and October 2010 from nine landing sites in Bragança (Pará, northern Brazil). Five vessel types, four fishing gears, and eight fishing techniques engaged with elasmobranch capture were identified. A total of 2,357 landings were recorded, with a total production of 354 t. The highest yields were recorded in 2009, with sharks being harvested mostly by small and medium-sized vessels, and batoids, by small vessels and canoes. Drifting nets and longlines played a prominent role in elasmobranch fisheries. The results show that the landings were influenced by days at sea, which is common in tropical fisheries. The elasmobranch data series is discontinuous as statistics are absent for most fishing sites albeit imperative for proper management, as well as relevant for decision-makers focusing on their conservation.

Size at sexual maturity estimation for 36 species captured by bottom and mid-water trawls from the marine habitat of Balochistan and Sindh in the Arabian Sea, Pakistan, using maximum length (Lmax) and logistic (L50) models.

The aim of this study was to estimate the size at first sexual maturity (Lm) for 36 species belonging to 24 families from the marine habitat of Balochistan and Sindh in Arabian Sea, Pakistan through maximum length based an empirical and logistic model using commercial catch during June 2020 to May 2021. Individual total length (TL) was noted up to 0.1 cm using measuring broad. The Lm was calculated using two formulae; (i) log (Lm) = - 0.1246 + 0.9924 * log (Lmax) for Elasmobranchs and (ii) log (Lm) = -0.1189 + 0.9157* log (Lmax) for ray-finned fishes. The minimum Lm was recorded as 10.27 cm TL for Caranx malabaricus and 108.38 cm TL for Isurus oxyrinchus, respectively. Around Lm with 58.33% species were ranges from 19.00 cm to 25.00 cm TL. This study was estimated 16 newly Lm which is globally absent and rest 20 Lm are absent in the Arabian Sea (Pakistan coastal habitats). Therefore, the results will be helpful for the sustainable management and conservation of these marine fishes through the establishment of mesh size of trawl nets based on the size at sexual maturity (Lm).

К ВОПРОСУ ОБ ОПРЕДЕЛЕНИИ ПРОМЫСЛОВОГО ЗАПАСА АНТАРКТИЧЕСКОГО КРИЛЯ EUPHAUSIA SUPERBA В РАЙОНЕ АНТАРКТИЧЕСКОГО ПОЛУОСТРОВА ПО ДАННЫМ ТРАЛОВЫХ УЛОВОВ КОММЕРЧЕСКИХ СУДОВ

Background. The assessment of the density and total biomass of the Antarctic krill aggregations has been conducted based on the commercial catches by the fishing and krill harvesting trawlers (supertrawlers) “Konstruktor Koshkin” (“Design Engineer Koshkin”) in 2006 and “More Sodruzhestva” (“Commonwealth Sea”) in 2017 in the Bransfield Strait (FAO Subarea 48.1). Relevance. Recommencement of the Russian krill harvesting necessitates timely strategical characterization of the krill aggregations with regard to their prospective exploitation. This work is aimed at the identification of the density and biomass of the Antarctic krill aggregations in 2006 and 2017, which have been calculated by the volumetric (net) method based on the catches by the commercial vessels in the Bransfield Strait. Methods. A midwater rope trawl of the 74/600 m design with the mesh size 20 mm in the krill-targeting insertion was used as a fishing gear. Estimation of the biomass was done using the isoline method. The catchability coefficient was considered to be 1. Mapping of the biomass density values was conducted with Golden Software Surfer 9 and QGIS 2.18.16. Confidence intervals for the average variation were calculated with 95 % probability. Results. The decrease in the average density of the krill biomass at the harvesting sites in the Bransfield Strait in 2017 (18.0±0.23 g/m3) as compared to 2006 (32.5±0.40 g/m3) has been identified; it resulted from the krill aggregations scattering over the increased area. The total krill biomass in the aggregations in 2006 and 2017 was 2678.3±65.07 thousand t and 2743.1±68.70 thousand t, respectively. Conclusion. Based on the commercial trawl catches, the volumetric method allows for the expedient estimation of the density and biomass of the krill aggregations with the size composition optimal for their exploitation. Taking into consideration that the commercial trawls capture the relatively large-sized krill preferred by the krill-dependent predators, the volumetric method makes it possible to estimate the volume of their food reserves. Exploitable krill stock in the aggregations in the Bransfield Strait in 2017 remained virtually unchanged as compared to that of 2006 and amounted to 2.7 million t.

Characterization of microbiota and histology of cultured sea cucumber Isostichopus badionotus juveniles during an outbreak of skin ulceration syndrome.

Due to the dramatic reduction of sea cucumber Isostichopus badionotus populations in the Yucatan Peninsula by overfishing and poaching, aquaculture has been encouraged as an alternative to commercial catching and restoring wild populations. However, the scarcity of broodstock, the emergence of a new disease in the auricularia larvae stage, and the development of skin ulceration syndrome (SUS) in the culture have limited aquaculture development. This study presents the changes in the intestine and skin microbiota observed in early and advanced stages of SUS disease in cultured juvenile I. badionotus obtained during an outbreak in experimental culture through 16S rRNA gene sequencing and histological evidence. Our results showed inflammation in the intestines of juveniles at both stages of SUS. However, more severe tissue damage and the presence of bacterial clusters were detected only in the advanced stages of SUS. Differences in the composition and structure of the intestinal and skin bacterial community from early and advanced stages of SUS were detected, with more evident changes in the intestinal microbial communities. These findings suggest that SUS was not induced by a single pathogenic bacterium. Nevertheless, a decrease in the abundance of Vibrio and an increase in Halarcobacter (syn. Arcobacter) was observed, suggesting that these two bacterial groups could be keystone genera involved in SUS disease.

DNA Barcoding and Phylogenetic Study as a Modern Taxonomical Tool for Identifying Commercial Catch along the Egyptian Mediterranean Coast, Alexandria

DNA Barcoding and Phylogenetic Study as a Modern Taxonomical Tool for Identifying Commercial Catch along the Egyptian Mediterranean Coast, Alexandria

Влияние промысла на биологическую структуру популяции щуки Esox lucius (L.) авандельты р. Волги

The main area of pike habitat and fishing is the avandelta of the Volga River. Pike fishing is conducted by passive fishing gear - mainly by secrets, to a lesser extent by nets. The main part of the pike catch traditionally falls in the spring period, when it forms pre-spawning and spawning clusters. Since 2010, official pike catches have been declining in March and April, due to an increase in illegal seizures. Pike caviar, due to its high nutritional qualities and demand among the population, has a high cost, which contributes to the massive concealment of commercial catches and poaching. Over the past two decades, the biological indicators of pike in the Volga River delta have undergone changes. Based on long-term data, there was a decrease in the age range, an increase in the proportion of younger age groups, a decrease in the proportion of females in the sexual structure of the population, average age, length and weight of pike. At the same time, the size and weight indicators of the same-aged pike individuals are quite stable. The main reason for the ongoing negative changes is the purposeful high commercial withdrawal of females in the pre-breeding and spawning periods. The scale of the total pressure of illegal industrial, poaching and amateur fishing, according to expert estimates, is comparable to the amount of official catch recorded by fishing statistics. To reduce the catch of spawning females for the first time, it is recommended to increase the minimum fishing length of the pike.

Структурні показники та динаміка промислових уловів риб дніпровських водосховищ

Purpose: to establish and analyze the dynamics of the species composition and amounts of commercial fish catches over the past 10 years in the context of assessing the overall efficiency of the fishery exploitation of Dnieper reservoirs. Methodology. As primary materials, data from official commercial fishery statistics and the results of field monitoring studies carried out by the Institute of Fisheries of the National Academy of Sciences on Dnieper reservoirs in the period of 2012‒2022 were used. The intensity of commercial fish harvest was assessed by the annual fishing mortality rate, which was defined as the difference between the total and natural mortality. The total mortality rate was determined graphically by the natural logarithms of the number of age groups in catches; natural mortality — based on the parameters of the von Bertalanffy equation. Statistical data processing was carried out in MS Excel. Findings. The dynamics of commercial catches in the cascade of Dnieper reservoirs in the last 10 years has been characterized by instability with a minimum of 8.9 thousand tons in 2013 and a maximum of 14.0 thousand tons in 2019. The majority of commercial catches was Prussian carp (28.2% of the total catch), common bream (21.1%), roach (20.5%) and silver bream (8.3%). The catch dynamics of all limited species had the same features — a growth in the period 2014‒2016, stabilization until 2019 and a further decrease, which was due to the determining influence of organizational factors. The distribution of fishing pressure by the objects of fishing does not fully correspond to the quantitative parameters of their ichthyomass; the average (2019‒2021) coefficients of annual fishing mortality were: pikeperch — 32.0%, common bream — 22.8%, roach — 24.2%, silver bream — 22.7%, Prussian carp — 19.0%. The maximum catches per unit effort of the gill net in the studied period were recorded for the Kamianske reservoir (348.9±73.4 kg), the lowest (152.0±44.5 kg) — for the Kaniv reservoir. The average fish catch per one gill net per cascade was 245.1±36.3 kg; a trend towards its growth during 2012‒2021 was observed. Originality. Original data on the modern dynamics of the amount and structure of commercial fish catches as a component of scientific support for fisheries exploitation of the Dnieper reservoirs were obtained. Practical value. It has been found that the fluctuations of fish catches in Dnieper reservoirs are largely determined by the influence of external (organizational) factors, which makes it possible to effectively manage the use of fish stocks. It is shown that for some species (in particular, pikeperch), the intensity of fishery exploitation exceeds the optimum, for others (Prussian carp, Black Sea sprat), on the contrary, an increase in the fishing pressure is possible.