Spawning Grounds Research Articles

Study on the spawning habitat suitability of four major Chinese carps in the fluctuating backwater area of the Three Gorges Reservoir

The upstream of the Yangtze River has abundant fish resources and is home to the four major Chinese carps (FMCCs), which are economically important fish in the Yangtze River that reside in the fluctuating backwater area (FBA) of the Three Gorges Reservoir (TGR). Their spawning habitat has been influenced by the Three Gorges Dam (TGD) operations. This study investigated the effects of dam operation on spawning habitat suitability and the potential spawning sites of FMCCs, using a physical habitat suitability model combined with a two-dimensional (2D) hydrodynamic numerical model. The habitat model was verified by field measurements of the fish egg density in the FBA, illustrating the capability of predicting the spawning availability of FMCC by comparing the habitat suitability index (HSI) distribution and the weighted usable area (WUA) with the simulation scenarios before and after the TGD construction. The habitat model was then applied to evaluate the effects of TGD operation on spawning habitat suitability and potential spawning grounds in the FBA. These results implied that the TGD operation had negative effects on spawning habitat suitability and produced temporal changes in the available WUA in the FBA. The predictions revealed that impoundment of the TGD decreased the suitability of the hydrodynamic factors. The main spawning period was delayed from April to May, and the variation in the water level induced by the reservoir operation scheme was likely the main factor. The HSI distribution in the FBA showed that the potential spawning grounds decreased to one site located in the Mudong-Luoqi River section. Furthermore, there was a rapid reduction in WUAs, accounting for approximately 18% of that seen in 2001 (before the TGD operation). The results of this study can aid in the management of the spawning grounds of FMCCs in the TGR and provide efficient methods for improving spawning habitat suitability, such as adjusting the pool level of the TGD during the falling stage.

Climate-induced habitat suitability changes intensify fishing impacts on the life history of large yellow croaker (Larimichthys crocea).

Intense fishing pressure and climate change are major threats to the fish population and coastal fisheries. Larimichthys crocea (large yellow croaker) is a long‐lived fish, which performs seasonal migrations from its spawning and nursery grounds along the coast of the East China Sea (ECS) to overwintering grounds offshore. This study used length‐based analysis and habitat suitability index (HSI) model to evaluate the current life‐history parameters and overwintering habitat suitability of L. crocea, respectively. We compared recent (2019) and historical (1971–1982) life‐history parameters and overwintering HSI to analyze the fishing pressure and climate change effects on the overall population and overwintering phase of L. crocea. The length‐based analysis indicated serious overfishing of L. crocea, characterized by reduced catch, size truncation, constrained distribution, and advanced maturation causing a recruitment bottleneck. The overwintering HSI modeling results indicated that climate change has led to decreased sea surface temperature during L. crocea overwintering phase over the last half‐century, which in turn led to area decrease and an offshore‐oriented shifting of optimal overwintering habitat of L. crocea. The fishing‐caused size truncation may have constrained the migratory ability, and distribution of L. crocea subsequently led to the mismatch of the optimal overwintering habitat against climate change background, namely habitat bottleneck. Hence, while heavy fishing was the major cause of L. crocea collapse, climate‐induced overwintering habitat suitability may have intensified the fishery collapse of L. crocea population. It is important for management to consider both overfishing and climate change issues when developing stock enhancement activities and policy regulations, particularly for migratory long‐lived fish that share a similar life history to L. crocea. Combined with China's current restocking and stock enhancement initiatives, we propose recommendations for the future restocking of L. crocea in China.

Impact of the construction of a dam and spur dikes on the hydraulic habitat of Megalobrama terminalis spawning sites: A case study in the Beijiang River (China)

• A 2D hydrodynamic model was coupled with habitat suitability curves to simulate the hydraulic habitat of Megalobrama terminalis spawning sites. • The usable habitat area decreased by 35.5%, and the habitat quality and diversity decreased because of the barrage. • The usable habitat area increased by 13.9%, and the habitat quality and diversity increased because of the spur dikes. • The barrage and spur dikes together resulted more improvement for the hydraulic habitat than the spur dikes alone. Water conservancy projects may result in considerable economic and social benefits, though there is widespread concern about how their impact on aquatic ecosystems. However, there is no study about the combined effects of typical hydraulic structures (a dam and numerous spur dikes) on hydraulic habitat conditions. This is why the impacts of the construction of a dam and spur dikes in a reach of the Beijiang River between the Feilaixia and the Qingyuan on fish hydraulic habitat conditions are assessed. A habitat suitability model was established by coupling a two-dimensional (2-D) hydrodynamic model with habitat suitability curves. The coupled model then was used to simulate the spawning sites of Megalobrama terminalis ( M. terminalis ), calculate the usable habitat area (UHA), identify the spatial distribution of suitable spawning ground in the river reach, and analyze the habitat quality and hydraulic habitat diversity. The results show that the dam alone would negatively impact fish habitat, and cause the UHA to decrease by 35.5 % on average. The high-quality habitat area and the hydraulic habitat diversity decreased because of the dam. The spur dikes had positive effects and increased the UHA by 13.9 % on average. In addition, spur dikes increased the high-quality habitat area and enhanced the hydraulic habitat diversity. The lateral discontinuity resulting from spur dikes (the rate of UHA change, RC = 13.9 %) had less impact on the fish hydraulic habitat than the longitudinal discontinuity impact resulting from the dam construction (RC = − 35.5 %). The spur dikes and a dam (RC = 21.94 %) resulted in a more significant improvement effect on the habitat conditions than the spur dikes without a dam (RC = 5.84 %). The dam and spur dikes in combination resulted in better outcomes regarding hydraulic habitat conditions than spur dikes alone, and the spur dikes reduce the ecological stress caused by the dam. The insight from this study can serve as a reference for engineers and scientists who are considering similar river regulation and ecological restoration initiatives aimed at a steady flow pattern that are advantageous for a specific fish species and lifestage.

Benthic Macroinvertebrates in fish spawning grounds, diversity and spatial distribution, Buyo lake dam (Côte d'ivoire)

This work focuses on the diversity and spatial distribution of benthic macroinvertebrates in the ichthyological spawning grounds of Lake Buyo. Sampling took place from June 2018 to May 2019 on 11 spawning grounds using a Van Veen grab, a dip net and a dip net. A total of 19,940 individuals grouped into 28 Families, 13 Orders, 6 Classes and 4 Branches were identified. The most abundant Families with a percentage higher than 20 in the study area are Thiaridae (63.33%) and Chironomidae (22.88%). The Insects class is the most diversified with 17 families followed by Gastropods with 8 families. The values of the Shannon-Weaver indices and the Pielou equitability calculated are low, which reflects a low taxonomic diversity and an imbalance in the spatial distribution of benthic macroinvertebrates in the different ichthyological spawning grounds.

A no-take zone and partially protected areas are not enough to save the Kattegat cod, but enhance biomass and abundance of the local fish assemblage

Abstract To supplement catch and effort regulations with the purpose to rebuild the cod (Gadus morhua) stock in Kattegat, Sweden and Denmark established a large (426 km2) year-round no-take zone (NTZ) surrounded by partially protected areas (PPAs) in 2009. The purpose of these spatial regulations was to prohibit cod fishing on the spawning grounds and to displace fisheries bycatch of cod from areas where mature cod aggregate in the Kattegat. The aim of this study is to evaluate the effects of the established NTZ and PPAs on the local fish assemblage, including cod. Based on a spatially high-resolution bottom trawl survey in the Kattegat (covering 2008–2021), multivariate analyses revealed significant shifts in the fish assemblage. A closer analysis indicated that six to seven fish species, including cod increased in the NTZ relative to control areas depending on if abundance or biomass was used as dependent variable. Univariate analysis showed that two flatfish species dab (Limanda limanda) and lemon sole (Microstomus kitt), and Norway lobster (Nephrops norvegicus) significantly increased in biomass in the NTZ, and turbot (Scophthalmus maximus) in the PPA relative to the control areas. These results suggest that the NTZ protected even relatively mobile species in an open sea system, such as the Kattegat. However, neither cod abundance nor biomass showed a significant increase as an effect of the NTZ and PPA despite two relatively strong year classes in 2012 and 2013, which possibly would have helped the recovery of the cod stock. As assessed by the International Council for the Exploration of the Sea in 2022, Kattegat cod continuously suffer from being severely overfished with low recruitment, and high discard rates in the mixed N. norvegicus fishery, is considered the major driver behind the reinforced depletion of the stock.

Unraveling the Drifting Larval Fish Community in a Large Spawning Ground in the Middle Pearl River Using DNA Barcoding

Simple SummaryDNA barcoding identified 28 species from larvae collected from the Dongta spawning ground. Six invasive species were identified in the larval pool, implying that these species had successfully colonized the middle Pearl River. Several migratory species common in the lower Pearl River were rare or absent in the Dongta spawning ground, suggesting that adverse effects of dam construction posed on these migratory species. Our study provided important reference data for fishery management and conservation in the Pearl River.Resolving the species composition of a larval pool in a spawning ground can provide novel insights into regional fish stocks and can support the development of effective monitoring and conservation policies. However, it is challenging to identify fish larvae to species due to their high diversity and dramatic phenotypic changes over development. In this study, we collected fish larvae in the Dongta spawning ground (Guiping City, Guangxi Province, China) in the middle reaches of the Pearl River between May and August 2018. We used a DNA barcoding approach to determine the species composition of the larval pool. A total of 905 larvae were chosen for molecular identification, of which 750 yielded high-quality barcoding sequences. Of these, 597 (≈79.6%), 151 (≈20.1%)/and 2 (≈0.3%) were assigned to 28 species, 8 genera, and 1 subfamily using the Barcode of Life Data System and GenBank nucleotide databases, respectively. Among the 28 identified species, 21 were cyprinids. Two species (Mugilogobius myxodermus and Pseudolaubuca engraulis) that were present only infrequently in previous adult surveys were abundant in the larval pool. Six invasive species were identified in the larval pool, implying that these species had successfully colonized the studied river section. Several migratory species common in the lower Pearl River were rare or absent in the investigated region, suggesting that dam construction in the Pearl River has had adverse effects on these migratory species. In summary, our study confirmed the applicability of DNA barcoding to studies of fish larval ecology and provided important reference data for fishery management and conservation in the Pearl River.

Spatial suitability evaluation of spawning reach revealing the location preference for fish producing drifting eggs

Hydrologic (water temperature) and hydrodynamic (water depth, flow velocity, and Froude number) factors affect fish spawning activities, and spawning grounds provide suitable hydrologic and hydrodynamic conditions for fish spawning to occur. However, locating fish spawning grounds is encumbered by uncertainty, particularly for pelagic spawners. This may be because such fish species have unique hydrologic and hydrodynamic requirements during their spawning periods, resulting in the wide-ranging approaches used to locate their spawning grounds. Accordingly, this study was designed to accurately locate fish spawning grounds through means of spatial suitability evaluation. For this experiment, the four major “Asian carp” target species were selected in the Dongta spawning reach, a tributary of the Pearl River. First, we investigated the historical information on the location of the spawning reaches. An acoustic doppler current profiler (ADCP) was used to measure topographic and hydrodynamic data of the spawning reaches during the spawning period. Then, based on the spatial clustering method, cluster analysis on spatial attributes (water depth, flow velocity, water temperature, and Froude number) was conducted on potential spawning grounds. The cluster analysis method uses k-means clustering; a method often employed to classify large amounts of data. Finally, we analyzed and evaluated the spatial suitability of spawning reaches by combining fish spawning suitability curves to obtain spatial preferences associated with fish spawning activities. Proportionally, results revealed a high suitability (>0.4) area (60.86%). Moreover, spawning suitability in curved river sections and deep pools in straight river sections were significantly higher than bifurcated sections. Furthermore, areas near the riverbanks were more suitable than mid-course sections of the river. Finally, the locations of six potential Asian carp spawning grounds were determined according to their spatial suitability. This study provides technical support to accurately locate spawning grounds for the fish that produce drifting eggs.

The importance of sound to the Atlantic cod, Gadus morhua, and the Atlantic haddock, Melanogrammus aeglefinus.

The gadoid fishes, including the Atlantic cod and haddock, are currently being exploited close to their safe biological limits, requiring restrictions upon the human activities that may harm them. This has prompted interest in the biology of such fishes. Studies of the cod and haddock have shown highly complex behavior, involving prolonged and energetic visual and acoustic displays. Different sounds are produced in different behavioral contexts and are emitted almost continuously by cod and haddock, especially throughout the spawning season (February to May). The distinctive characteristics of these sounds make it possible to locate spawning cod and haddock at their marine spawning grounds. Human activities in these areas may affect their spawning adversely and have deleterious effects upon their stocks. Man-made sounds in water do have an adverse effect upon cod and haddock, and other fishes. Listening for the cod and haddock sounds provides a reliable, non-invasive technique for detecting their locations, and especially their spawning areas, and enables them to be protected well.

Habitat suitability evaluation of Harpadon nehereus in nearshore of Zhejiang province, China

Coastal waters provide an important spawning and nursery ground for offshore marine organisms. To understand the suitable habitat and distribution of Harpadon nehereus, a key nearshore species, this study assessed the survey data of fishery resources and environment in Zhejiang’s nearshore fishery in Spring of 2017 to 2020. We used the generalized additive model (GAM) and random forests model (RF) to analyze the environmental factors affecting the selection of spawning habitats by H. nehereus and analyzed the suitable habitat characteristics of H. nehereus in nearshore fisheries. Our results indicate that H. nehereus is widely distributed in Zhejiang’s nearshore and that its density is higher in waters near islands and reefs. Among the relative importance scores of predictors calculated based on RF, seawater salinity is an important environmental factor affecting the distribution of H. nehereus in April (surface seawater salinity was 38.67% and bottom seawater salinity was 34.5%), followed by depth (34.19%), whereas the change in water temperature had no obvious effect on H. nehereus distribution. The suitable habitat characteristics of H. nehereus mainly include high salinity near a water depth of 40 m and a water area with sea bottom dissolved oxygen levels < 6 mg/L. The prediction results of the model indicate that the suitable habitat of H. nehereus is mainly located in the region near Zhoushan Islands in the north of the fishing grounds. Overall, these results may serve as a basis for determining the protection strategies of key nearshore species and enhancing fishery management units.

Coastal aquaculture farms for the sea cucumber Apostichopus japonicus provide spawning and first-year nursery grounds for wild black rockfish, Sebastes schlegelii: A case study from the Luanhe River estuary, Bohai bay, the Bohai Sea, China

Aquaculture farms are known to attract wild organisms from nearby areas. Sea cucumber Apostichopus japonicus aquaculture farms in Bohai Bay, the Bohai Sea, China, might provide spawning and nursery grounds for wild black rockfish Sebastes schlegelii populations. To identify the above, we studied the variation in the numbers of S. schlegelii larvae (and length-categories as a percentage of the natural population) via ichthyoplankton surveys by months from January to October 2020, and assessed the food web structure and energy flow distribution of the farm and trophic links of S. schlegelii natural stock by using Ecopath modeling in July 2016 to August 2017. Larvae with a length between 3.90-5.80 mm were observed in the farm in May 2020, the juveniles with an estimated trophic level of 4.31. Juveniles used the farms as first-year nursery ground, and then they swam into deeper waters in August of the following year. MTI analysis showed increasing biomass of S. schlegelii might result in a decrease in the biomass of crustacea, and had positive and negative impacts on mollusk and Hexagrammos otakii biomass. We argued that aquacultural infrastructures constructed by artificial reefs could be used as a fisheries management tool to enhance S. schlegelii stocks and that monitoring of other marine organisms, such as oysters, Rapana venosa, Charybdis japonica, and Asterias spp. etc., was necessary to maintain sustainable exploitations of aquacultural farm ecosystems. A paucity of knowledge surrounding the interactions between aquaculture farms and wild organisms needs furthermore researches.

Empirical support for sequential imprinting during downstream migration in Atlantic salmon (Salmo salar) smolts

The precise homing of Atlantic salmon to their natal river and spawning grounds is the foundation for locally adapted genetically differentiated populations across rivers or across river sections. A sequential imprinting hypothesis states that salmon smolts may imprint on environmental clues along the outward migration route and then use this in reverse order to direct the spawning migration later in life. In this study, we provide empirical support for this hypothesis. PIT-tagged wild Atlantic salmon using a 2 km hydropower tunnel as downstream migrating smolts had a 18% (1SW) and 23% (2SW) lower probability of successfully migrating through the parallel river stretch as adult spawners compared to spawners that migrated through the same river stretch as smolts. These findings highlight how a fine-scale riverine migration route may be imprinted in wild Atlantic salmon smolts. From an applied perspective, these results stress the importance of not depriving smolts from parts of their migration route to ensure successful return of adults to their natal spawning grounds.

Review of tagging studies on Atlantic herring (Clupea harengus) in relation to transboundary movement in the Bay of Fundy/Gulf of Maine/Scotian Shelf region of the Northwest Atlantic

The management of Atlantic herring in the Bay of Fundy/Gulf of Maine/Scotian Shelf region of the Northwest Atlantic (NAFO areas 4WX5YZ) assumes separate stocks in Canadian and US waters; however, herring landed in the weir fishery in southwest New Brunswick (SWNB) are assumed to be of US origin for management purposes. The present study is a review of tagging studies that have been conducted on herring since the 1950s in NAFO areas 4WX5YZ. The tagging data show consistent patterns over time. Juvenile herring in the coastal Gulf of Maine and SWNB nursery areas generally show only movements between these two areas. These nursery areas are believed to include herring that hatched from the US and Canadian spawning grounds, contrary to the current management assumption for the weir fishery in SWNB. As herring mature, they are understood to primarily return to their natal spawning area. The tagging data show mixing of adults from different spawning grounds (including transboundary mixing) during the summer feeding and overwintering seasons. Canadian spawners have been observed to overwinter in New England and US spawners have been observed to overwinter in Nova Scotia. Herring tagged on Canadian spawning grounds have been recaptured in the SWNB weir fishery, refuting the assumption that all herring landed in this fishery are of US origin. The tagging data suggest that the weir fishery comprises a mix of herring hatched from spawning grounds in Canada and the US. The biases associated with recapture data from tagging programs precludes estimation of any proportions of stock mixing. Alternative methods for evaluating stock structure in NAFO areas 4WX5YZ are recommended.

Structural and Functional Characterization of Orcokinin B-like Neuropeptides in the Cuttlefish (Sepia officinalis)

The cuttlefish (Sepia officinalis) is a Cephalopod mollusk that lives in the English Channel and breeds in coastal spawning grounds in spring. A previous work showed that the control of egg-laying is monitored by different types of regulators, among which neuropeptides play a major role. They are involved in the integration of environmental cues, and participate in the transport of oocytes in the genital tract and in the secretion of capsular products. This study addresses a family of neuropeptides recently identified and suspected to be involved in the control of the reproduction processes. Detected by mass spectrometry and immunocytochemistry in the nerve endings of the accessory sex glands of the females and ovary, these neuropeptides are also identified in the hemolymph of egg-laying females demonstrating that they also have a hormone-like role. Released in the hemolymph by the sub-esophageal mass, a region that innervates the genital tract and the neurohemal area of the vena cava, in in vitro conditions these neuropeptides modulated oocyte transport and capsular secretion. Finally, in silico analyses indicated that these neuropeptides, initially called FLGamide, had extensive structural homology with orcokinin B, which motivated their name change.

In-river behaviour and freshwater return rates of sea trout, Salmo trutta L., from two coastal river populations.

The effective management of anadromous Salmo trutta resources is challenging because long-term data on life history, phenology and survival are sparse and most stocks across the range are highly diverse and data-limited. The current study employed acoustic telemetry to tag 448 sea trout across three life stages, to describe the phenology, spawning behaviour and return rates of smolts, finnock (0+ sea age) and adult (≥1+ sea age) sea trout in two Irish river systems during 2018-2021. Tagged smolts (n=206) exhibited river to sea transition rates of 78%-92% and a number of surviving smolts returned to their natal river as 0+ sea age finnock, exhibiting overall smolt to finnock return rates of between 6% and 17%. Short-term vagrancy occurred among smolts, and 14 individuals were detected in adjacent non-natal rivers. Finnock tagged during the late summer (n=205) exhibited a range of behaviours with a minority (<30%) ascending upstream to spawning areas. Tagged adult sea trout (n=37) ascended upstream to the spawning grounds and between 50% and 80% successfully returned to sea as kelts after spawning. Subsequent return rates of kelts back to the river in the following year ranged from 9% to 40%. The current study indicated that body size was an influential predictor of behaviour and survival across all three life stages. Increased body size was positively associated with marine transition success in smolts, long-term marine survival in kelts and spawning behaviour in finnock. This work further demonstrates the complexity of sea trout life-history dynamics and provides a comparative perspective across different age classes. An understanding of life-history variation, behaviour and survival is fundamental for the successful management and conservation of sea trout stocks.

HSI model for early life stages of anchovy considering transport processes in Laizhou Bay

Marine fishes are sensitive to the environment during their early life stages. This study adopts a habitat suitability index (HSI) model to evaluate the environmental suitability for early stages of anchovy (Engraulis japonicus) in Laizhou Bay. Instead of calculating the suitability of spawning grounds and nursery grounds independently or the simple average of the two, an individual-based model is used to simulate the drifting trajectories of anchovy eggs to establish the link between a spawning ground and its corresponding nursery ground. The HSI of early life habitat is determined by averaging the HSI value of the paired two grounds. The model results suggest that a small patch at eastern Laizhou Bay (near 120.1 E°, 37.6 N°) is the most critical and suitable area for anchovy in early life stages. It can provide an appropriate habitat for anchovy eggs and allow the eggs to migrate to the inside of the bay with plenty of plankton, which would benefit the newly hatching larvae. The results indicate the significant impact of hydrodynamic transport on fishery recruitment process, which should not be neglected in habitat quality evaluation. The model adopted in this study is applied to anchovy as a case study, but it is also exportable to other species of commercial interest.

Features of exploitation of high-number industrial chum salmon &lt;i&gt;Oncorhynchus keta&lt;/i&gt; on the example of Lake Tunaicha (south-eastern Sakhalin): problems and proposed solutions

In Lake Tunaicha mainly artificial reproduction of chum salmon is carried out. The escapement is at a high level — more than 1 million fish. Significant pre-settlement mortality of chum salmon has been regularly observed in the lake basin over the last three years (2019–2021). The scale of fish mortality was estimated based on the results of surveys of the lake, including those carried out with the help of UAVs. The data of fishing statistics, the filling of natural spawning grounds and the features of spawning chum salmon migration were analyzed. The sea surface temperature (SST) data was used. To assess the hydrochemical conditions in Lake Tunaicha during the period of mass entry of chum salmon spawners in 2019–2021, water samples were taken in the coastal area of Lake Tunaicha and in the estuarine sections of the rivers of its basin. The coastal marine fishery cannot keep up with the withdrawal of the commercial part of chum salmon return (no more than 10 %), and most of the fish migrate from the sea to the lake through the Krasnoarmeisky Strait. Before entering the rivers the chum salmon spends a long time in the lake (average of 11 days), and significant accumulations of chum salmon create a danger of fish mortality due to unfavorable hydrological conditions (low oxygen content, high water temperature), especially in shallow areas with an abundance of aquatic vegetation. It is necessary to organize the withdrawal of chum salmon brood stock surplus in the basin of Lake Tunaicha. Taking into account the nature protection status of the lake, this is only possible to implement in the Krasnoarmeisky Strait at the Okhotsk salmon fish farm fish accounting barrier. It is recommended to remove 50 % of the spawning chum salmon there from the beginning of its mass migration in the strait — from September 11.

Spatiotemporal Characteristics of Fish Larvae and Juveniles in the Waters around Taiwan from 2007 to 2019.

Simple SummaryFish larvae and juveniles are necessary fishery recruitment resources. As climate change and natural climate events continue to impact marine ecology, it may become difficult to determine the characteristics of changes in fish larvae and juveniles. Using samples and data from long-term marine experimental monitoring, we found a high diversity of fish larvae and juveniles in the waters around Taiwan, and the abundance of different fish species varied spatially and seasonally. We also found that distance from the coastline and topography were the key factors affecting the community of fish larvae and juveniles. By presenting these data as times series, we confirmed that 2009 was a critical year for regime change between fish larvae and juveniles in different depth zones. The year also happened to include Taiwan’s worst typhoon on record. These results emphasize the need to conduct more detailed research to prevent predictable and unpredictable shocks.Taiwan is located at the intersection of tropical and subtropical islands in the western Pacific Ocean. This area is an important spawning and breeding ground for many economic and noneconomic species; however, little is known about the long-term dynamics of fish larvae and juveniles in these waters. In this study, we conducted an in-depth exploration of their spatial characteristics using 2007–2019 field survey samples. Our results demonstrated the seasonality and spatiality of the larvae and juveniles of different fish species. We also found that the continental shelf and offshore distance were key factors affecting fish larvae and juveniles. Changes in community structure were temporally correlated with the extreme rainfall of Typhoon Morakot (the worst typhoon ever recorded in Taiwan). These data can be used as a management reference for fisheries’ policymaking and provide key insights into nearby marine ecosystems and the early life history of fish.

Catches, size and age composition of the spawning stock muksun Coregonus muksun in the Middle Ob (Tomsk region)

Muksun Coregonus muksun is one of the most valuable whitefish species. It lives in large rivers of Siberia. This is a typical semi-anadromous species. There are presents data on the catches of muksun in the Middle Ob (on spawning grounds and migration routes to them), which generally reflects the number of spawning stock of this species rising to spawn. It is shown that in the middle of the 20th century the catches of muksun averaged 47 tons per year. In the early 1970s, there was a sharp short-term increase in its catches to an average of 215 tons per year, which may be caused by the start of intensive work on collecting whitefish caviar in the area of their spawning run for obtain fish stock for pasture aquaculture in the lakes of Western Siberia. Since the early 1980s, muksun catches have fallen catastrophically, and its fishing is currently prohibited. On the spawning grounds of the Middle Ob, specimens under the age of 16+ were noted. Until the end of the 1990s, the age and size composition of the Muksun spawning stock remained relatively stable. In recent years, there has been an increase of younger fish and, accordingly, a decrease in the average size of fish in the catches. At present (2017–2019), specimens with a fishing length from 392 to 523 mm (on average 457 mm) and a weight of 747 to 1915 g (on average 1233 g) have been noted in the catches of muksun.

Exploitation of striped snakehead (Channa striata) in Sempor Reservoir, Central Java, Indonesia: A proposed conservation strategy

Abstract. Setyaningrum N, Lestari W, Krismono, Nuryanto A. 2022. Exploitation of striped snakehead (Channa striata) in Sempor Reservoir, Central Java, Indonesia: A proposed conservation strategy. Biodiversitas 23: 3584-3592. Striped snakehead (Channa striata) has important economic value in freshwater systems, including Sempor Reservoir in Indonesia, where increases in catch sizes have resulted in a declining population. In this study, we determined its population size based on abundance and distribution of length and assessed the rate of exploitation based on estimated growth and mortality rates to determine a conservation strategy in Sempor Reservoir. The study was undertaken from March to October 2020. The method used was a purposive random sampling survey. Fish samples were taken from five stations with different land uses. The estimated growth, mortality, and exploitation rates were analyzed by Pauly's model using FISAT II. Channa striata abundance data were analyzed using a Kruskal-Wallis test. The results showed that the highest abundance of C. striata at the KW station was almost three times higher than at the BK station. The average size of the gonads at first maturity was 277.4 mm in females and 284 mm in males. The estimated growth parameters indicated an asymptotic length (L?) of 409.5 mm. An exploitation rate of 0.74 was classified as overfishing. The proposed conservation strategy is to limit the number of catches by as much as 44% and prohibit the catching of individuals with a length of 230-349 mm. Kedungwringin Station was defined as a reference area with the largest abundance and complete size distribution, namely, the pre-reproduction, reproduction, and post-reproduction stages. Bangkong Station was defined as a spawning ground because there were many fish in the reproductive stage and Sempor River Station was the nursery ground with mostly juvenile fish. These two sites must be protected for sustainable striped snakehead populations in the river and reservoir.

Spatial and temporal variability of spawning and nursery grounds of Loligo forbesii and Loligo vulgaris squids in ecoregions of Celtic Seas and Greater North Sea

Abstract The inshore commercial squids, Loligo vulgaris and L. forbesii, co-occur in the ecoregions of Celtic Seas and Greater North Sea but the spatio-temporal structure of their spawning ranges is poorly understood. To help solve the problem, data sets collected during the last 30 years by British, German, French, and Irish scientists, as well as observations from multinational Citizen Science, were combined. Spawning grounds of L. forbesii were found to form an external semi-circle around the spawning grounds of L. vulgaris, with the latter being centred on the English Channel and southernmost North Sea. The nursery grounds of both species appear to coincide with the respective spawning grounds, though L. forbesii makes much wider use of the North Sea. Seasonally, the position of the spawning grounds of both species is driven by the local temperature regime, although this is possibly subject to interannual variability. Spawning of both species begins around November and gradually progresses eastward following favourable currents and increasing water temperatures. Spawning in both species is mostly over by July, though some egg masses persist until August–November. Nursery grounds follow the same seasonal shift from west to east, at least in L. forbesii.