Spawning Grounds Research Articles

Analysis of reproductive traits reveals complex population dynamics on a small geographical scale in Atlantic herring

Atlantic herring (Clupea harengus) has a complex population structure and displays a variety of reproductive strategies. Differences in reproductive strategies among herring populations are linked to their time of spawning, as well as to their reproductive investment which can be an indicator for migratory vs. stationary behavior. These differences are reflected in the number of oocytes (fecundity) and the size of the oocytes prior spawning. We studied potential mixing of herring with different reproductive strategies during the spring spawning season on a coastal spawning ground. It has been hypothesized that both spring and autumn spawning herring co-occur on this specific spawning ground. Therefore, we investigated the reproductive traits oocyte size, fecundity, fertilization success as well as length of the hatching larvae during the spring spawning season from February to April. We used a set of 11 single nucleotide polymorphism markers (SNPs), which are associated with spawning season, to genetically identify autumn and spring spawning herring. Reproductive traits were investigated separately within these genetically distinct spawning types. Furthermore, we used multivariate analyses to identify groups with potentially different reproductive strategies within the genetic spring spawners. Our results indicate that mixing between ripe spring and autumn spawners occurs on the spawning ground during spring, with ripe autumn spawners being generally smaller but having larger oocytes than spring spawners. Within spring spawners, we found large variability in reproductive traits. A following multivariate cluster analysis indicated two groups with different reproductive investment. Comparisons with other herring populations along the Norwegian coastline suggest that the high variability can be explained by the co-occurrence of groups with different reproductive investments potentially resulting from stationary or migratory behavior. Fertilization success and the length of the hatching larvae decreased with progression of the spawning season, with strong inter-individual variation, supporting our findings. Incorporating such complex population dynamics into management strategies of this species will be essential to build its future population resilience.

Life Cycle Model Reveals Sensitive Life Stages and Evaluates Recovery Options for a Dwindling Pacific Salmon Population

AbstractPopulation models, using empirical survival rate estimates for different life stages, can help managers explore whether various management options could stabilize a declining population or restore it to former levels of abundance. Here we used two decades of data on five life stages of the population of Sockeye SalmonOncorhynchus nerkain the Cedar River to create and parameterize a life cycle model. This formerly large but unproductive population is now in steep decline despite hatchery enhancement. We gathered population‐specific data on survival during five stages: (1) egg to fry, (2) fry to presmolt, (3) presmolt to adult return from the ocean, (4) adult en route from the ocean to the spawning grounds, and (5) reproduction. We ground‐truthed the model to ensure its fit to the data, and then we modified survival and other parameters during various stages to examine future scenarios. Our analyses revealed that low survival of juveniles in Lake Washington (stage 2: averaging only 3% over the past 20 years), survival of adults returning to freshwater to spawn (stage 4), and survival of adults on spawning grounds to reproduce (stage 5) are likely limiting factors. Combined increases in these stages and others (specifically, the proportion of fish taken into the hatchery to be spawned) might also recover the population. As in other integrated hatchery populations, managers must weigh options relating to balancing the fraction of natural‐ and hatchery‐origin fish, and our results showed that increasing the fraction of fish taken into the hatchery alone will not recover the population. Our model brings together population‐specific data to help managers weigh conservation strategies and understand which stages and habitats are most limiting and how much survival must increase to achieve recovery targets. By extension, our analyses also reveal the utility of such models in other cases where stage‐specific data are available.

Fishing Enclosure as a Simple Approach to Stimulate Spawning Success of Tenualosa ilisha (Hamilton, 1822) in Bangladesh

The study was intended to assess the impact of fishing enclosure during the peak breeding time of hilsa, Tenualosa ilisha on its breeding success. During the last peak breeding season of hilsa (October 4-25, 2021) a comprehensive investigation was attempt to evaluate the impact of fishing enclosure by “MV Rupali Ilish” research vessel, speedboat and experimental fishing net were deployed to demeanor a rigorous investigation in and around the spawning grounds areas (about 7,000 sq km, including Moulvirchar, Monpura, Dhalchar and Kalirchar). Additionally, data were also assumed from landing stations (via terrestrial cruises) near the spawning ground areas and other hilsa prone region of Bangladesh. The percentage of spent hilsa (locally called pite) and oozing hilsa were monitored following a standard protocol. Among all the hilsa captured in and around the spawning grounds, the proportion of male and female were 16-41% and 85-97%, respectively of the total catch, suggesting a male and female sex ratio (1:2.3). The rate of breeding success in 2021 was 51.76% i.e., 51.7% hilsa successfully participated in the breeding process which was 103.52% higher than the base year (2001-02). The approximate number of fertilized eggs in 2021 was 7,86,314 kg. Increased production of hilsa eggs and jatka indicated a positive impact of twenty-two days fishing enclosure. Percentages of gravid and oozing hilsa were also found higher compared to previous years. Due to the prohibition of all types of fishing, the percentage of female hilsa in the breeding areas increased up to 83.96%. Overall, twenty-two days fishing enclosure was found very effective for successful spawning of hilsa.

Magnetic fields generated by submarine power cables have a negligible effect on the swimming behavior of Atlantic lumpfish (Cyclopterus lumpus) juveniles.

Submarine power cables carry electricity over long distances. Their geographic distribution, number, and areal coverage are increasing rapidly with the development of, for example, offshore wind facilities. The flow of current passing through these cables creates a magnetic field (MF) that can potentially affect marine organisms, particularly those that are magnetosensitive. The lumpfish (Cyclopterus lumpus) is a migratory species that is widely distributed in the North Atlantic Ocean and Barents Sea. It migrates between coastal spawning grounds and pelagic offshore feeding areas. We tested whether lumpfish respond to MFs of the same intensity as those emitted by high voltage direct current (HVDC) submarine power cables. Laboratory experiments were conducted by placing juvenile lumpfish in an artificial MF gradient generated by a Helmholtz coil system. The intensity of the artificial MF used (230 µT) corresponded to the field at 1 m from a high-power submarine cable. The fish were filmed for 30 min with the coil either on or off. Swimming speeds, and presence in the different parts of a raceway, were extracted from the videos and analyzed. Juvenile lumpfish activity, defined as the time that the fish spent swimming relative to stationary pauses (attached to the substrate), and the distance travelled, were unaffected by exposure to the artificial MF. The swimming speed of juvenile lumpfish was reduced (by 16%) when the coil was on indicating that the fish could either sense the MF or the induced electric field created by the movement of the fish through the magnetic field. However, it seems unlikely that a 16% decrease in swimming speed occurring within 1 m of HVDC cables would significantly affect Atlantic lumpfish migration or homing.

Can seamounts in the Gulf of Alaska be a spawning ground for sablefish settling in coastal nursery grounds?

In addition to their prevalence on the continental shelf, adult sablefish have been found over the chain of seamounts far offshore in the Gulf of Alaska (GOA). Many of the females that were observed had recently spawned or were ready to spawn. However, to date, it is not known what role the seamounts play in sablefish life history and there are no observations of sablefish eggs or larvae over the GOA seamounts. Due to their depth and remoteness, there are no suitable shallow nursery areas in the vicinity of the seamounts. For successful recruitment, individuals hatching from eggs spawned over seamounts would need to be transported hundreds of miles to suitable areas inshore. Using an individual-based model (IBM) of sablefish, we have demonstrated that if spawning occurs over any of the seamounts in the GOA seamount province it is likely that at least some individuals will be successfully transported to shallow inshore nursery areas in the coastal GOA. As our simulated individuals only exhibit vertical movement behavior this on-shore transport results from the prevailing currents to which they were subjected and not from any geographic or environmental homing capabilities. Our analysis indicates that the strength of the on-shelf velocity is not the primary factor in determining the likelihood of transport to nursery areas. We speculate that the size, strength, location, and direction of the eddies that populate the GOA in any given year could be important in determining transport success. This idea is reinforced by our path analysis which shows that there are markedly different pathways taken by successful individuals among years. Our findings suggest that it may be necessary to expand what is considered suitable habitat for young sablefish. With seamounts being a potentially important spawning site for sablefish, future research priorities should include ground-truthing with fishery or fishery-independent data collected from seamounts. Potential applications of this expanded sablefish IBM include testing for connectivity between seamount and slope spawning areas and the Aleutian Islands and Bering Sea and contributing to the development of spatially explicit assessment models of sablefish.

Pelagic connectivity of European sea bass between spawning and nursery grounds

The sea bass stock around the UK (northern stock) has declined rapidly over the past decade, likely due to a combination of both overfishing and low recruitment. Understanding mechanisms that drive the number of young reaching nursery grounds is important for explaining observed recruitment variability and therefore developing effective management strategies. An individual-based model (IBM) has been developed here to investigate factors affecting sea bass settlement on nursery grounds for the northern stock. Simulations considered seven years with varying environmental conditions and year class strength, and outputs were compared to empirical data from monitoring of nursery areas in the UK and Ireland. The IBM includes hydrodynamics to simulate the drift of eggs and larvae, temperature-dependent growth and mortality, and behavior affecting position in the water column. Comparison between the model and ICES assessment abundance of age class zero fish showed similar temporal variability, but with higher recruitment predicted for 2018, and a lower peak recruitment in 1997. The model reproduced general patterns of interannual variability for the Thames estuary, but performed less well for some other regions. Further investigation is needed to understand differences between modelled supply and observations, as these could be due to uncertainties in reproducing the physical environment (e.g., currents, temperature) or biology (e.g., spawning, behavior, mortality), as well as uncertainty in recruitment derived from stock assessments or data collected from nursery grounds. Nevertheless, the model provides a useful demonstration of connectivity between spawning and nursery grounds, showing spawning regions that are likely to have greatest influence on recruitment in different estuaries, and how these may vary interannually. For example, sources from western Channel and Celtic Sea can supply larvae to many areas, leading to connectivity across the Channel and Celtic Sea, and into the Irish Sea. However, other regions may depend on more local areas. For example, with the Solent estuary dependent on sources within the Channel each year. With the temperature-dependence on growth, and therefore duration of the pelagic stage, results show the potential influence of spawning timing, in relation to ocean temperatures, for connectivity between spawning and nursery grounds.

A first glimpse of larval ecology of halibut species in the Gulf of St. Lawrence, Canada.

Knowledge of the larval ecology of winter-spawning fish from the Estuary and Gulf of St. Lawrence, Canada, remains scarce due to the seasonal ice cover that prevents ichthyoplankton sampling using conventional methods. Two winter-spawning species, Atlantic halibut (AH, Hippoglossus hippoglossus) and Greenland halibut (GH, Reinhardtius hippoglossoides), support the most important groundfish fisheries of this area. In March 2020, the authors captured 10 halibut larvae ranging in size from 5 to 14 mm during an opportunistic survey in the GSL onboard an icebreaking vessel. Of these, eight were AH and two GH. Judging by their very small size, the larvae were only a few days old, suggesting that the spawning grounds are close to the capture sites. This effort constitutes a first step in validating the putative spawning areas for these two important GSL stocks. This knowledge is important for the conservation and sustainable management of these fisheries.

Genome-Wide Identification of the Odorant Receptor Gene Family and Revealing Key Genes Involved in Sexual Communication in Anoplophora glabripennis.

Insects use a powerful and complex olfactory recognition system to sense odor molecules in the external environment to guide behavior. A large family of odorant receptors (ORs) mediates the detection of pheromone compounds. Anoplophora glabripennis is a destructive pest that harms broad-leaved tree species. Although olfactory sensation is an important factor affecting the information exchange of A. glabripennis, little is known about the key ORs involved. Here, we identified ninety-eight AglaORs in the Agla2.0 genome and found that the AglaOR gene family had expanded with structural and functional diversity. RT-qPCR was used to analyze the expression of AglaORs in sex tissues and in adults at different developmental stages. Twenty-three AglaORs with antennal-biased expression were identified. Among these, eleven were male-biased and two were female-biased and were more significantly expressed in the sexual maturation stage than in the post-mating stage, suggesting that these genes play a role in sexual communication. Relatively, two female-biased AglaORs were overexpressed in females seeking spawning grounds after mating, indicating that these genes might be involved in the recognition of host plant volatiles that may regulate the selection of spawning grounds. Our study provides a theoretical basis for further studies into the molecular mechanism of A. glabripennis olfaction.

Spatial ecology of translocated American Eel (Anguilla rostrata) in a large freshwater lake

American Eel (Anguilla rostrata) undertake extensive migrations from their rearing grounds to spawn in the Sargasso Sea, and historically the upper St. Lawrence River and Lake Ontario provided an important source for large, fecund female eel. Following declines in the Lake Ontario population, glass eel were translocated from eastern Canada from 2006 to 2010. From 2016 to 2018, large, presumably translocated yellow eel (N = 230) with the potential to begin maturing and out-migrating within their year of capture were collected in spring and fall and tagged with acoustic transmitters. Eel were released into eastern Lake Ontario and tracked to better understand their movement patterns prior to and during migration, and the timing of migration. Most eels successfully migrated out of Lake Ontario (64%). Timing of migration was consistent regardless of year or tagging season and primarily occurred in late summer or fall, with cooling water temperatures and decreasing sky illumination associated with initiation for fall tagged eel. Eels were mostly detected in eastern Lake Ontario and those in western Lake Ontario were mostly detected in shallow waters (< 20 m) close to shore. Eels were detected on fewer receivers in the winter, suggesting reduced movements during this season. Finally, larger individuals spent less time in the system, particularly when tagged in the fall. These findings confirm that translocated eels can migrate out of Lake Ontario; however, the weeks when migration occurred were more aligned with timing in their natal range (i.e., eastern Canada) than with naturally recruited eels from Lake Ontario. This temporal mismatch requires further consideration, since it may influence arrival times of translocated eel to the spawning grounds and their recruitment potential. These results can be used to inform future assessments of eel translocation efficacy and can also aid in the design of future tracking studies to more completely explore the downstream migration success of eel translocated into the highly productive waters of Lake Ontario.

Application of artificial spawning substrates to support lacustrine fish recruitment and fisheries enhancement in a Chinese lake

Lake littoral zones with abundant submerged vegetation are considered to harbor diverse biotic communities and additionally serve as spawning grounds for important fishery resources. In recent decades, due to various human activities submerged vegetation in lakes have declined dramatically resulting in the function loss of spawning grounds. In order to enhance the recruitment of lacustrine fish (mainly Carassius auratus and Cyprinus carpio) and the proliferation of fishery resources, we explored a method of constructing artificial spawning ground based on artificial spawning substrate in lake. The results of present study indicate that the artificial substrates with complex and dense three-dimensional structure which have enough space to enable material exchange and oxygen circulation could be efficient to enhance fish recruitment. The water temperature of spawning peaks of artificial substrates were within the range of 20 ~ 25°C, and the water temperature provides a basis for the deployment period of artificial spawning grounds. The spawning substrate in the upper layer of water column was more attractive for fish to spawn. The above results provide guidance for the deployment of artificial spawning grounds from both temporal and spatial scales. Observations on the behavior of aggregations found that spawning activities mainly occurred at night and in the early morning. The abundance of larger individuals (&amp;gt;20 cm), as potential spawning groups, increased during this period. The above findings are informative to the construction and management of artificial spawning ground in lakes.

First record of gray rockcod Lepidonotothen squamifrons larvae in the Amundsen Sea, Antarctic: implication for a new spawning ground and early life characteristics

First record of gray rockcod Lepidonotothen squamifrons larvae in the Amundsen Sea, Antarctic: implication for a new spawning ground and early life characteristics

Modifications of unmanned aerial survey on spawners of pacific salmons in the rivers of Sakhalin and Khabarovsk Regions

Two modifications of unmanned aerial vehicle (UAV) survey on spawners of pacific salmons are examined for certain rivers in Sakhalin and Khabarovsk Regions. The route survey along the rivers was tested to evaluate its applicability for the salmons counting in prespawning and spawning aggregations. Poor suitability of such approach was found for some of surveyed rivers. For these rivers, an alternative approach was proposed, as a localized UAV survey with shooting video over contrast background, like tower videocounts widely used in North America. This kind of survey can be easy adopted for many rivers of southern Sakhalin due to their spatial proximity, transport accessibility, and rather dense population in this area. Detailed technical recommendations for the UAV counting on observation transects are provided and limitations for this approach are shown. The route UAV survey allows to make inventory of the salmon spawning grounds and to evaluate the spawning efficiency, whereas the local UAV survey solves a narrower task for operative fishery regulation as counting the spawners escapement to rivers.

Fish resources of the early life history stages in the Fuling section of the Three Gorges Reservoir and their responses to hydrological and thermal characteristics

三峡水库调度运行改变了库区江段的水文情势,影响漂流性卵苗在库区江段内的时空分布特征。在水库低水位运行时,具有流水生境特征的库中和库尾江段是产漂流性卵鱼类在整个三峡库区内重要的产卵江段。了解三峡库中和库尾江段产漂流性卵鱼类的早期资源状况及其对水文和水温特征的响应关系,对于采取适宜的保护措施促进鱼类早期资源的恢复具有重要的意义。本文通过2017-2020年5-7月在库中涪陵断面进行的逐日早期资源监测,了解三峡库中和库尾江段产漂流性卵鱼类早期资源的种类组成、产卵规模、产卵场分布及其年际变动特征,并采用随机森林(RF)模型,分析鱼类逐日产卵规模变动与水文、水温格局及其过程的关系,辨识影响不同种类产卵规模变动的关键水文及水温要素。结果表明:2017-2020年共采集到漂流性鱼卵21种,包括长江上游特有鱼类鱼卵3种;以圆筒吻鮈Rhinogobio cylindricus、蒙古鲌Chanodichthys mongolicus、贝氏Hemiculter bleekeri等6种鱼类的鱼卵为主,占总采集鱼卵数的88.76%;各年的鱼卵规模分别为83.04×10⁸、14.29×10⁸、20.43×10⁸和22.83×10⁸ 粒;涪陵以上干流江段分布有6个鱼类的集中产卵场,是圆筒吻鮈、长鳍吻鮈R. ventralis、长薄鳅Leptobotia elongata等长江上游特有鱼类重要的产卵场所;逐日产卵规模主要受产卵时透明度及流量大小、产卵前流量或水位上涨过程以及产卵前积温大小的影响,且影响不同鱼类自然繁殖的关键水温、水文因素在不同种类间存在差异。研究结果可为三峡库区鱼类资源保护措施特别是生态调度措施的实施提供科学依据。;Reservoir operation resulting from river damming has altered the flow regimes of the river sections of reservoirs, inducing profound impacts on the spatiotemporal distribution of the early resources of fish species that spawn drifting eggs (FSDE) in the river sections of reservoirs. During the period of low water-level operation stage of the reservoir, the river section with flowing-water habitats is an important spawning river section compared those other sections of the reservoir. Fully understanding the status of early resource of FSDE and their response to hydrological and thermal characteristics in a reservoir's middle and tail reaches is of great significance for the restoration and promotion the scale of early resource. This paper intended to reveal the inter-annual variation in the species composition of eggs and larvae collected, as well as the spawning scale and distribution of fish spawning grounds in the middle and tail reaches of the Three Gorges Reservoir (TGR), through the daily sampling for eggs and larvae being conducted at the Fuling section from May to July in 2017-2020. The random forest model was further performed to clarify the relationships between the variations in the daily spawning scales and the hydrological, thermal patterns and process conditions, aiming to identify the key hydrological and thermal factors affecting the variations of spawning scales of different species. The results showed that: 1) 21 species of eggs were collected, including 3 species of fish eggs that endemic to the upper reaches of the Yangtze River, and the amounts of eggs of 6 fish species, including Rhinogobio cylindricus, Chanodichthys mongolicus, and Hemiculter bleekeri, etc., were dominant, which accounted for 88.76% of total number of eggs collected. 2) The scale of fish eggs each year was 83.04×10⁸ ind., 14.29×10⁸ ind., 20.43×10⁸ ind., and 22.83×10⁸ ind., respectively. 3) There were 6 main spawning grounds distributed in the upstream of Fuling sampling site in the TGR, where is an important spawning place for endemic fish species (e.g. R. cylindricus, R. ventralis, and Leptobotia elongata) in the upper reaches of the Yangtze River. 4) The daily spawning scales were mainly affected by the amounts of transparency and flow discharge during spawning, as well as flow or water level rising rate and accumulated water temperature before spawning, and the key hydrological and thermal factors that affect the natural reproduction were different among different species. This research provides data support for the implementation of fish resource protection measures, especially ecological regulation measures, in the TGR.

Современное состояние и условия функционирования Усть-Манычских рыбоходных каналов

Purpose: to assess the state and operating conditions of the fish passage channels of the Ust-Manych waterworks on the river Western Manych. Materials and methods. The factual basis for assessing the state and operating conditions of the Ust-Manych fish passage channels was the materials of the author’s survey and field studies performed at the given facility in 2022. The studies were carried out according to generally accepted methods for conducting hydrometric measurements of flow rate parameters and geometric dimensions of channels and network (“canal”) hydraulic structures. Results and discussion. The survey data of structures and elements of two fish passage and spawning channels operating as part of the Ust-Manych waterworks, designated for passing semi-anadromous fish from its tail race to the head race - from the mouth of the river Western Manych to the Ust-Manych flood plain which is a potentially highly productive spawning ground for phytophils (bream, pike perch, carp and ram). The channel hydrometric parameters are given, a description of the structures included in their composition, ensuring the functioning of structures and structural elements or influencing it is given. The characteristics of the water flow on the structures and along the canal tract, as well as on the site of the conjugation of the canal mouth with the river are given. Estimated qualitative and quantitative indicators of the conditions for fish channel functioning are given. Conclusions. The survey data of the current state of structures and structural elements of two fish passage channels arranged around the Ust-Manych waterworks retaining structures were obtained. The hydrometric (flow-rate and geometric) channel parameters are given, and an assessment of the quality of their operating conditions on spawning-migratory fish passage from the river Western Manych to the spawning grounds located in the channel basin of the Ust-Manych waterworks is made.

Гидравлический расчёт регулирующего сооружения, расположенного в ильменной части Прикаспийской низменности

Purpose: to solve the problem of conservation and reproduction of fish stocks of valuable commercial fish species in natural reservoirs, on the example of performing one of the tasks of developing a facility for regulating water regime of the ilmen part of the Volga delta. Using the well-known formulas of hydraulics, scientific developments of scientists in the field of hydraulic engineering and a priori information, it is necessary to determine the main parameters of a control structure located on a fishery reservoir in Astrakhan region. Materials and methods: a stage-by-stage hydraulic calculation of a tubular control structure that performs the functions of a water outlet was performed: the carrying capacity of the facility during operation in a pressure mode was determined; the main loads influencing the structure underground contour were determined by filtration calculation; a strength calculation of the floor for shear was performed. Results. A facility to regulate the water regime of the ilmen area of the Volga delta, ilmen, which are places of natural spawning grounds for commercial fish in Astrakhan region has been developed. The task of hydraulic calculation is to determine the conditions for the advancement of the filtration flow under the structure determining the pressure at characteristic points and to define the minimum dimensions of the floor that perceive stably the loads created by this flow. Conclusions. The calculation determined the main dimensions of the floor (length, width of the structure – 46.0; 4.65 m; length, thickness of the apron – 4.54; 0.3 m; length, thickness of the water apron – 4.8; 0.9 m; depth, water apron teeth width – 1.19; 0.40 m; length, thickness of the rear apron – 20.36; 0.6 m; length of the tubular part of the regulator – 16.3 m) taking into account the placement of gates, service and road bridges. The shear stability of the floor and the structure as a whole was determined.

Dynamics of fish larvae recruitment in the hydrographic basin of the Paraguay River in western Brazil

Abstract The conservation of fish assemblages depends on the longitudinal and lateral connectivity between riverine habitats, in particular during the breeding season and the initial development. This study investigated the composition and spatio-temporal structure in the ichthyoplankton of the hydrographic basin of the Paraguay River in western Brazil to identify the local spawning grounds and the importance of the longitudinal connectivity of economically valuable migratory species. Data were collected at 10 sites between two breeding seasons (2017/2018 and 2018/2019). Were collected 8,635 larvae, representing 55 taxa in 25 families, including the migratory species Brycon hilarii, Hemisorubim platyrhynchos, Piaractus mesopotamicus, Prochilodus lineatus, Pseudoplatystoma spp., Salminus brasiliensis, Sorubim lima, and Zungaro jahu, which are important fishery resources, with the highest larval densities being recorded between November and January. The Sepotuba, Paraguay, Jauru, and Cabaçal rivers were the areas of greatest connectance, and should thus be considered critical for the conservation of the longitudinal connectivity of this fluvial system, indicating that the migratory species spawn upriver. More efficient fisheries management mechanisms are needed, respecting the spawning period of migratory species, maintaining quality and longitudinal connectivity between habitats, and characteristics necessary for successful larval recruitment.

РЕТРОСПЕКТИВНЫЙ АНАЛИЗ ИХТИОФАУНЫ РЕКИ ТОМЬ В ПРЕДДВЕРИИ СТРОИТЕЛЬСТВА КРАПИВИНСКОГО ВОДОХРАНИЛИЩА

The resumption of design and survey work for the construction of the Krapivinsky Hydroelectric Power Plant on the Tom River has necessitated the assessment of the current state of its fish resources and called for making the prediction of their transformation in the event of the hydroelectric complex being put into operation. In the early 20th century, the Tom River was classified as a salmonid habitat. At that time, such valuable commercial species as the Siberian taimen Hucho taimen, blunt-snouted lenok Brachymystax tumensis , tugun Coregonus tugun, humpback whitefish Coregonus pidschian, Nickolsky’s grayling Thymallus nikolskyi , nelma Stenodus leucichthys nelma, muksun Coregonus muksun, and peled Coregonus peled were permanent residents. Sturgeons, such as the Siberian sturgeon Acipenser baerii and sterlet Acipenser ruthenus, were also abundant. Currently, out of these species, grayling, occasionally taimen and lenok are caught in the Tom River; the common roach Rutilus rutilus , European perch Perca fluviatilis, Siberian dace Leuciscus baicalensis and Eurasian ruffe Gymnocephalus cernuus comprise 95 % of all fish caught. If construction of the Krapivinsky Reservoir on the Tom River is completed and it is put into operation, a deep-water, slow-flowing “lake-type” water body will be created. The river bed will be blocked, so semi-anadromous fish species, many of which are listed in the Red Data Book-such as Siberian sturgeon, sterlet and nelma,-will disappear. A decrease in the abundance of grayling, taimen and lenok, already low in number, should also be expected. These fish species winter in the pits, some of them migrate to the Ob River, so, after passing the spillway, they will not be able to return upstream to the spawning grounds. The abundance of lake and lake-river species is expected to increase, among them the common roach, dace Leuciscus leuciscus , European perch, Prussian carp Carassius gibelio (introduced locally, subsequently self-dispersed), as well as common bleak Alburnus alburnus and sunbleak Leucaspius delineates (accidental invaders). In the future, it is possible to make an attempt to introduce peled to the upper basin of the Krapivinsky Reservoir. There is a prospective threat of the Chinese sleeper Perccottus glenii spreading in the upcoming reservoir, which can severely undermine its fish stocks.

On survival of the larvae of marine parasitic nematode &lt;i&gt;Anisakis simplex&lt;/i&gt; sensu lato (Rudolphi, 1809) in the fresh waters

Survival of the larvae of marine parasitic nematode Anisakis simplex sensu lato (Rudolphi, 1809) in the fresh waters was monitored. In total, 37 live larvae of A. simplex s.l. were sampled from charr Salvelinus malma caught in the lower reaches of the Kamchatka River. The larvae were kept in the freshwater refreshed everyday, without food, their viability was examined daily at 9 a.m. All larvae were still alive in the 4 th day (100 %); 2.7 % were alive after 9 days in freshwater, but all of them were died after 10 days. Dependence of the number of dead larvae on the time of their exposition in the freshwater is well approximated by von Bertalanffy equation (R 2 = 0.996). Besides, viability of A. simplex s.l. larvae in the bodies of dead sockeye spawners was examined at the spawning grounds in Lake Azabachye: the larvae were alive in the body cavity of fish that died at least 3–5 days ago and remained alive at least 3 days more being placed in the freshwater. The larvae of marine nematode A. simplex s.l. are able to enter to the fresh waters with migratory fish. Following to our results, they can survive there for several days. So, measures for disinfecting against A. simplex s.l. are recommended for the freshwater fish caught in the water bodies connected with the marine environment.

Chum salmon Oncorhynchus keta (Walbaum) on the continental coast of the Okhotsk Sea. Communication 2. The juveniles

Long-term data on downstream migration, qualitative and quantitative characteristics and feeding of juvenile chum salmon are generalized for the continental coast of the Okhotsk Sea. The downstream migration begins in conditions of certain heating of river waters; its dynamics depends on the rate of water flow and other environmental factors. The juveniles migrate from rivers to the coastal waters both in the daytime and at night. Their qualitative characteristics change in correspondence with escapement of either summer or autumn races of chum salmon progeny from the spawning grounds. The juveniles stay in the coastal waters until September. Their food spectrum is determined by the inhabited biotope.

Factors controlling the year-classes strength for chum salmon &lt;i&gt;Oncorhynchus keta&lt;/i&gt; in the Okhotsk district

A quasi-cyclicity associated with variability of environmental conditions is detected for the regression residuals of the stock-recruitment model for chum salmon Oncorhynchus keta in the Okhotsk district, described by Ricker’s equation. The main factors influenced on the chum progeny abundance were the number of spawners and the amount of precipitation in the spawning grounds area in certain months. A mathematical model has been developed that simulates satisfactorily the dynamics of progeny, which can be used for forecasting. Role of the freshwater and marine periods of chum salmon life in formation of the year-classes strength is discussed.