Spawning Population Research Articles

Multiple-batch spawning as a bet-hedging strategy in highly stochastic environments: An exploratory analysis of Atlantic cod.

Stochastic environments shape life‐history traits and can promote selection for risk‐spreading strategies, such as bet‐hedging. Although the strategy has often been hypothesized to exist for various species, empirical tests providing firm evidence have been rare, mainly due to the challenge in tracking fitness across generations. Here, we take a ‘proof of principle’ approach to explore whether the reproductive strategy of multiple‐batch spawning constitutes a bet‐hedging. We used Atlantic cod (Gadus morhua) as the study species and parameterized an eco‐evolutionary model, using empirical data on size‐related reproductive and survival traits. To evaluate the fitness benefits of multiple‐batch spawning (within a single breeding period), the mechanistic model separately simulated multiple‐batch and single‐batch spawning populations under temporally varying environments. We followed the arithmetic and geometric mean fitness associated with both strategies and quantified the mean changes in fitness under several environmental stochasticity levels. We found that, by spreading the environmental risk among batches, multiple‐batch spawning increases fitness under fluctuating environmental conditions. The multiple‐batch spawning trait is, thus, advantageous and acts as a bet‐hedging strategy when the environment is exceptionally unpredictable. Our research identifies an analytically flexible, stochastic, life‐history modelling approach to explore the fitness consequences of a risk‐spreading strategy and elucidates the importance of evolutionary applications to life‐history diversity.

Drift diving: A quick and accurate method for assessment of anadromous salmonid spawning populations

AbstractThe accuracy of drift diving surveys of Atlantic salmon, Salmo salar L. and sea trout, Salmo trutta L., was evaluated by comparing the abundance and size distribution with catches in a fish trap over 6 years in the River Etneelva, western Norway. The population count from drift diving accounted for on average 96.3% of the salmon in the trap after accounting for the catches during fishing. Size structure registered during drift diving corresponded with trap catches of salmon, but the number of small salmon (<3 kg) appeared to be somewhat underestimated, while large salmon (>7 kg) were overestimated in drift diving. For sea trout, the match between drift diving counts and trap registrations was poorer (average 76.3%), but may have been affected by the surveys being performed too late with regards to sea trout spawning time. The study illustrates the utility of drift counting for estimating the entire population of anadromous salmonids in a river.

Mixed-stock analysis using Rapture genotyping to evaluate stock-specific exploitation of a walleye population despite weak genetic structure.

Mixed‐stock analyses using genetic markers have informed fisheries management in cases where strong genetic differentiation occurs among local spawning populations, yet many fisheries are supported by multiple, weakly differentiated stocks. Freshwater fisheries exemplify this problem, with many populations supported by multiple stocks of young evolutionary age and isolated across small spatial scales. Consequently, attempts to conduct genetic mixed‐stock analyses of inland fisheries have often been unsuccessful. Advances in genomic sequencing offer the ability to discriminate among populations with weak population structure, providing the necessary resolution to conduct mixed‐stock assignment among previously indistinguishable stocks. We used genomic data to conduct a mixed‐stock analysis of eastern Lake Erie's commercial and recreational walleye (Sander vitreus) fisheries and estimate the relative harvest of weakly differentiated stocks (pairwise F ST < 0.01). Using RAD‐capture (Rapture), we sequenced and genotyped individuals from western and eastern basin local spawning stocks at 12,081 loci with 95% reassignment accuracy, which was not possible in the past using microsatellite markers. A baseline assessment of 395 walleye from 11 spawning stocks identified three reporting groups and refined previous assessments of gene flow among walleye stocks. Genetic assignment of 1,075 walleye harvested in eastern Lake Erie's recreational and commercial fisheries indicated that western basin stocks constituted the majority of harvest during the peak walleye fishing season (July–September), whereas eastern basin individuals comprised much of the early season harvest (May–June). Clear spatial structure in harvest composition existed; catches in more easterly sites contained more individuals of eastern basin origin than did more westerly sites. Our study provides important stock contribution estimates for Lake Erie fishery management and demonstrates the utility of genomic data to facilitate mixed‐stock analysis in exploited fish populations having weak population structure or limited existing genetic resources.

The life history and populations of chum salmon (Oncorhynchus keta) in China: An otolith isotopic investigation

Stable isotope ratios of otoliths (δ13C and δ18O) can be used as a habitat index in anadromous fish, because there are marked differences between freshwater and marine settings. Here we report the results of 84 otoliths of chum salmon (Oncorhynchus keta) collected from three locations (Site-A, Site-B, and Site-C) in China, where all the estuaries for chum salmon ocean entry are located in Russia or North Korea and no biological observation data being obtained. In this study we adopted a blind-test protocol and applied stable isotope analyses in chum salmon otoliths. Two aragonite powder samples were taken from each otolith: one from the nucleus of otoliths; the other from the 2nd summer growth zones. Overall the δ13C values of chum salmon otoliths ranged from −10.9 to −4.0‰, whereas δ18O values of the same samples ranged from −6.4 to +1.9‰. Based on δ18O values at about −3.5‰ (the boundary line), two different spawning populations or stocks have been identified (p-value = 0.008). The Site-A samples were collected from the Amur River, while the Site-B samples were collected from the Tumen River. The Suifen River (Site-C) samples had some mixing with the Amur River chum salmon, but they were essentially classified into the Tumen River population. Comparison between our data and the previously reported sockeye salmon and chinook salmon data in North America indicated that the chum salmon in China are anadromous, and have the same life history from freshwater to marine as other populations over the world.

Reduced recruitment of Chinook salmon in a leveed bar-built estuary

Estuaries are commonly touted as nurseries for salmonids, providing numerous advantages for smolts prior to ocean entry. In bar-built estuaries, sandbars form at the mouth of rivers during periods of low stream flow, closing access to the ocean and preventing outmigration. We evaluated how summer residency in a leveed bar-built estuary affects the growth, survival, and recruitment of a Chinook salmon (Oncorhynchus tshawytscha) population. We performed a mark–recapture study on outmigrants to determine juvenile estuary abundance, growth, and survival. We used returning adult scales and otoliths to determine the relative proportion of summer estuary residents in spawning adults. Juveniles in the estuary grew less after mouth closure, and ultimately summer estuary residents had lower smolt-to-adult survival and contributed disproportionately less to the spawning population than juveniles that reared in the ocean their first summer. Mouth closure may lower food availability and deteriorate estuary conditions by reducing marine prey influx and estuary circulation. This research demonstrates the complexity of estuary dynamics and function as salmonid nurseries, particularly when considering the extensive modification of estuaries.

Recolonization of lake whitefish river spawning ecotypes and estimates of riverine larval production in Green Bay, Lake Michigan

Lake whitefish (Coregonus clupeaformis) within the waters of Green Bay, Lake Michigan have recently shown a substantial increase in abundance. Furthermore, after over 100 years of extirpation, adult lake whitefish are found spawning within major Wisconsin tributaries to Green Bay. Many knowledge gaps still exist with respect to the chronology of adult river migrations, including the physical characteristics of upstream habitats selected for reproduction and the extent of larval production by these riverine ecotypes. Here, we use hydroacoustic imaging along with egg and larval surveys to evaluate this novel riverine spawning in 2017 and 2018. Highest abundance of adults was observed in the month of November as temperatures declined below 8 °C. Spawning areas consisted of cobble substrates, and site-specific fish densities were primarily correlated with river flows between 0.3 and 1.0 m/s, with specific values varying by tributary and year. Locations of egg deposition mirrored areas of high observed fish densities. Larval production was documented on each tributary using active trawl ichthyoplankton sampling, and larvae were observed outmigrating to open water environments. We estimated tributaries produced 452,000 larvae in 2017 and 721,000 larvae in 2018. To our knowledge, this represents the first documentation of successful lake whitefish larval production from Green Bay tributaries and suggests tributary spawning populations contribute to the greater abundance of lake whitefish observed in recent years.

Rainbow smelt spawning population and habitat characteristics in a Missouri River reservoir

Rainbow Smelt Osmerus mordax are the primary coldwater forage species in Lake Oahe, South Dakota, yet most aspects of their life history remain unknown. As Missouri River reservoirs present a novel habitat compared to elsewhere in the Rainbow Smelt’s range, we investigated their spawning site use relative to available physical and thermal habitat from spring 2016 − 2018 using a mobile horizontal-beaming hydroacoustic survey. We mapped spawning habitat using side-scanning sonar to establish relationships with site bathymetry and thermal spawning conditions. From our site mapping, we determined the depth, slope, bottom hardness, and ruggedness of individual sites. We used a PCA to condense our physical habitat metrics, with PC1 representing 77% of cumulative variance. Peak abundance was linked to a physical habitat gradient, representing [steep slope, deep, soft bottom] to [low slope, shallow, hard bottom]. Peak Rainbow Smelt spawning aggregations were observed at 6.8 ± 1.7 °C (Mean ± StDev). An information-theoretic regression analysis revealed an interactive effect of temperature and habitat, whereby shallower, warmer sites typically had a lower peak abundance. These results represent the first step toward understanding habitat use characteristics of spawning Rainbow Smelt in reservoir systems.

Diversity and sexual dimorphism in the head lateral line system in North Sea populations of threespine sticklebacks, Gasterosteus aculeatus (Teleostei: Gasterosteidae)

The mechanosensory lateral line of fishes is a flow sensing system and supports a number of behaviors, e.g. prey detection, schooling or position holding in water currents. Differences in the neuromast pattern of this sensory system reflect adaptation to divergent ecological constraints. The threespine stickleback, Gasterosteus aculeatus, is known for its ecological plasticity resulting in three major ecotypes, a marine type, a migrating anadromous type and a resident freshwater type. We provide the first comparative study of the pattern of the head lateral line system of North Sea populations representing these three ecotypes including a brackish spawning population. We found no distinct difference in the pattern of the head lateral line system between the three ecotypes but significant differences in neuromast numbers. The anadromous and the brackish populations had distinctly less neuromasts than their freshwater and marine conspecifics. This difference in neuromast number between marine and anadromous threespine stickleback points to differences in swimming behavior. We also found sexual dimorphism in neuromast number with males having more neuromasts than females in the anadromous, brackish and the freshwater populations. But no such dimorphism occurred in the marine population. Our results suggest that the head lateral line of the three ecotypes is under divergent hydrodynamic constraints. Additionally, sexual dimorphism points to divergent niche partitioning of males and females in the anadromous and freshwater but not in the marine populations. Our findings imply careful sampling as an important prerequisite to discern especially between anadromous and marine threespine sticklebacks.

Genetic Assessment of Inconnu (Stenodus leucichthys) in Great Slave Lake, Northwest Territories, Canada

Inconnu (Stenodus leucichthys) is a large freshwater migratory coregonid species that is commercially fished in some parts of its range. In Great Slave Lake, NT, Inconnu are one species that is caught in a mixed species gillnet fishery that is subject to restrictive management because four of the seven known stocks are declining or have been extirpated. The seven known Inconnu stocks have been identified based on the river systems that support or once supported a spawning population. To help identify key geographic areas for harvest control and other management approaches, we estimated the genetic diversity and population genetic structure of Inconnu in this area with 17 microsatellite loci. Temporal and spatial genetic structure was examined in four river systems, lower and upper Mackenzie River, Buffalo River, Slave River and Marian River/Lake and within Great Slave Lake. Analyses suggested that genetic diversity was greater in lower/upper Mackenzie River populations compared to populations in Great Slave Lake. Genetic structure was temporally stable at all locations except one, and spatial structure was found with significant isolation by distance detected among locations. Bayesian clustering analysis suggested five genetic groups of Inconnu, one in the lower and upper Mackenzie River and four within Great Slave Lake. The substructuring within Great Slave Lake included a genetic group representing fish collected in the lake itself. In addition, three genetic groups corresponded to river systems (Buffalo River, Marian River/Lake, Slave River), indicating that each river has genetically distinct Inconnu populations. These results suggest that the sustainability of Inconnu in and around Great Slave Lake depends upon maintaining stocks associated with river systems, especially those that are geographically disparate.

Genetic population structure of the monogenean parasite Gyrodactylus thymalli and its host European grayling (Thymallus thymallus) in a large Norwegian lake

Understanding how populations are structured in space and time is a central question in evolutionary biology. Parasites and their hosts are assumed to evolve together, however, detailed understanding of mechanisms leading to genetic structuring of parasites and their hosts are lacking. As a parasite depends on its host, studying the genetic structure of both parasite and host can reveal important insights into these mechanisms. Here, genetic structure of the monogenean parasite Gyrodactylus thymalli and its host the European grayling (Thymallus thymallus) was investigated in 10 tributaries draining into the large Lake Mjøsa in Norway. The population genetic structure of spawning grayling was studied using microsatellite genotyping, while G. thymalli was studied by sequencing a mitochondrial DNA gene (dehydrogenase subunit 5). Two main genetic clusters were revealed in grayling, one cluster comprising grayling from the largest spawning population, while the remaining tributaries formed the second cluster. For both taxa, some genetic differentiation was observed among tributaries, but there was no clear isolation-by-distance signature. The structuring was stronger for the host than for the parasite. These results imply that moderate to high levels of gene flow occur among the sub-populations of both taxa. The high parasite exchange among tributaries could result from a lack of strong homing behavior in grayling as well as interactions among individual fish outside of the spawning season, leading to frequent mixing of both host and parasite.

Inter-estuarine Variation in Otolith Chemistry in a Large Coastal Predator: a Viable Tool for Identifying Coastal Nurseries?

Coastal estuaries provide essential juvenile habitat for many commercially and recreationally important fish, which may move between estuarine and coastal environments throughout their life. Identifying the most important estuarine nurseries that contribute to the broader stock can support targeted management of juvenile and spawning populations. The objective of this study was to (1) compare chemical fingerprints within sagittal otoliths of juvenile Mulloway (Argyrosomus japonicus) sampled from putative south-eastern Australian nurseries, (2) assess their potential as natural tags to distinguish nursery grounds for the broader coastal Mulloway stock and (3) assess the viability of otolith chemistry as a fisheries management tool when limited to opportunistic, fisheries-dependant, otolith sample collection from by-catch. Otoliths from juvenile Mulloway (0 to 3 years, 4 to 44.8 cm total length) were obtained from 8 major estuaries and 2 inshore ocean locations along coastal south-eastern New South Wales, Australia, from April 2015 to July 2018. Concentrations of Sr, Ba, Mg, Mn and Li in the otolith region corresponding to the juvenile nursery stage were determined using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). The element to Ca ratios of fish from coastal estuaries differed significantly among collection areas, based upon multivariate elemental fingerprints, with some exceptions. When the otoliths of fish were analysed in a multinomial logistic regression (MLR) classifier, there was an overall mean allocation success of 59% to the estuary of capture. This study highlights the use of otolith ‘fingerprints’ as natural tags in Mulloway, and contributes to progressive research in environmental reconstruction applications of otolith chemistry.

The aquaculture of acipenseriformes. Part 5. Dunabe Basin and Middle East

The history and contemporary state of global aquaculture of sturgeons and paddlefish are reviewed. 5th part is devoted to sturgeon breeding in the basin of Black sea (without countries of former USSR reviewed earlier) аnd in the Middle East. Six species of sturgeon once migrated in the Danube River and Turkish rivers Yeşilırmak, Kızılirmak and Sakarya for spawning: anadromous beluga Huso huso, Russian sturgeon Acipenser gueldenstaedtii, stellate sturgeon A.stellatus, European sturgeon A. sturio and the river resident ship sturgeon A. nudiventris and sterlet A. ruthenus. Sturgeons had played an important role in the history Black sea fisheries, but due to overexploitation, followed by extensive river regulations and deterioration of water quality decrease in their populations has led most of them to the verge of extinction. During the 20th Century, world demand for sturgeon meat and caviar has inflated the economic value of sturgeons so Danube basin countries and Turkey develop commercial aquaculture and conservational programs. As result of protective measures the limited natural spawning of beluga, Russian and stellate sturgeons and sterlet is preserved in Danube. In Sakarya River last spawning population of stellate sturgeon exists. These species and Siberian sturgeon are important objects of commercial aquaculture in all countries of Black sea basin. The leaders of commercial sturgeon farming in this region are Bulgaria and Israel. The sturgeon aquaculture of Hungary and Turkey developed rapidly. Saudi Arabia and United Arab Emirates are important importers of caviar. Saudi Arabia is large consumer of caviar and UAE is one of main re-exporter of caviar. Both Arab countries develop own sturgeon aquaculture.

Egg size and fecundity of biannually spawning corals at Scott Reef

Egg size and fecundity are often used as proxies for coral reproductive success and health. The amount of energy a coral invests in reproduction reflects its environmental conditions during gametogenesis. Additionally, assuming resources for reproduction are limited, it is thought that an increase in egg size should result in a decrease in the number of eggs produced i.e. investing in many small eggs or fewer larger eggs. The biannually spawning populations of Scott Reef offer a unique opportunity to compare the egg size and polyp fecundity of corals exposed to different environmental conditions during gametogenesis, prior to spawning in autumn (March) and spring (October). In this study, we investigated the relationship between egg size and polyp fecundity within and between seven Acropora species from 2008 to 2010. We also quantified the fecundity and egg size of four Acropora species that spawn during both autumn and spring (2008–2010). We found no seasonal variability in egg size and fecundity in the species studied here, possibly as a result of a summer light regime being impacted by high cloud cover in cyclone season. There was high natural variability and no apparent trade-off between egg size and fecundity, both within and between each species. These findings challenge the assumption that egg size and fecundity are negatively correlated, or that a simple, energetically constrained trade-off exists between the two.

Analysis of the spawning population of common carp in the lower reaches of the Ural River within the borders of the West Kazakhstan Region

The article presents the results of a study of the hydrological regime of the Ural river in the territory of the West Kazakhstan region, the average annual flow of the river, as well as the average decadal water levels during the spring flood. According to the presented results, there is a noticeable decrease in annual runoff, which directly has a negative impact on the local ichthyofauna of the reservoir. The decrease in the water level in the Ural river affects the efficiency of natural reproduction of phytophilic fish. In 2019, due to a decrease in the water content of the Ural river, carp fish, namely common carp, did not have the opportunity to spawn in floodplains and flood meadows of the river. When catching producers for the purpose of artificial reproduction, the spawning herd of common carp was represented by individuals aged from 5 to 12 years.

Distribution and genetic variability of young-of-the-year greater amberjack (Seriola dumerili) in the East China Sea

We examined the distribution and genetic variability of the greater amberjack Seriola dumerili in the East China Sea (ECS) from the mitochondrial DNA (mtDNA) control region of young-of-the-year (YOY) individuals, which may reflect the genetic characteristics of the spawning population. In the years 2016 and 2017, a total of 165 YOY S. dumerili were collected from two different locations in the ECS: the southern part of the ECS, and western Japanese coast. The spawning period was estimated using otolith daily increments from a total of 67 larvae and juveniles collected in the ECS. Results from size and age distribution indicated that S. dumerili spawned near the shelf break region in the southern ECS from January to April. Phylogenetic analysis based on mtDNA sequence data showed no significant genetic differentiation among samples collected from different locations, implying S. dumerili in the ECS is mainly composed of one population. S. dumerili around the Japanese coast may be originated from the southern ECS.

Spatial and temporal distribution of larvae and juvenile Coilia nasus in the lower reaches of the Yangtze River

刀鲚（Coilia nasus）是长江下游重要的经济鱼类之一，具有溯河洄游型和淡水定居型两种生态类型.本研究于2016年5-8月在刀鲚繁殖高峰期内同时对长江下游湖口、安庆和靖江江段进行刀鲚早期资源调查，研究分析对比了长江下游江段刀鲚仔稚鱼的丰度情况、时空格局及其与主要环境因子的关系.结果表明：在调查期间，靖江江段刀鲚仔稚鱼平均密度最高；刀鲚仔稚鱼在调查各江段于6月下旬至7月上旬之间均出现一段较短时间的高峰期，这与刀鲚的产卵类型有关；湖口刀鲚仔稚鱼的爆发时间早于安庆和靖江江段，这种现象可能是由于湖口江段存在的定居型刀鲚产卵造成的；推测长江江水倒灌的特殊环境现象刺激了刀鲚性腺的发育，使得湖口江段8月产卵群体较多；各江段断面空间上的刀鲚仔稚鱼密度差异可能是沿岸地形和水体动力学差异所产生的现象；各江段刀鲚仔稚鱼密度最高峰时的水流量均处于较低水平，水温分别为25.87、25.27和21.67℃，均达到了刀鲚产卵所需条件.研究结果初步反映了长江下游刀鲚仔稚鱼的时空特征，为长江下游刀鲚资源的保护提供了参考依据.;Coilia nasus is one of the most important economic fishery species in the lower reach of the Yangtze River. It has two ecological types, one is anadromous and the other is freshwater resident. This study investigated the early resource of Coilia nasus in the lower reaches of the Yangtze River in Hukou, Anqing and Jingjiang during the peak breeding season from May to August 2016. The abundance, temporal and spatial distribution patterns of larval and juvenile C. nasus in the lower reaches of the Yangtze River and their variation and relationship with major environmental factors were analyzed. Results showed that the mean density of larvae and juveniles C. nasus in the Jingjiang section was highest during the investigation period. There was a short peak period between late June and early July in the surveyed river section, which may be related to the C. nasus spawning type. The occurrence of larval and juvenile C. nasus in Hukou section was earlier than in Anqing and Jingjiang section, which may result from resident C. nasus spawning in Hukou section. It is inferred that the special environment phenomenon of the back-flow of the Yangtze River stimulates the C. nasus gonad development, which resulted in more spawning populations in the Hukou section in August. The density difference of larval and juvenile C. nasus in the three sampling sites may be due to the difference between coastal topography and water dynamics. The water flow of larval and juvenile C. nasus at the highest density was lower in all river segments, and the water temperature was 25.87, 25.27 and 21.67℃, respectively. The hydrodynamic environment of the three sites meet the requirement for C. nasus spawning. Results in this study preliminarily reflect the spatial-temporal characteristics of larval and juvenile C. nasus in the lower reaches of the Yangtze River and provide information for C. nasus resource conservation.

The genetic composition of feeding aggregations of the Atlantic mackerel (Scomber scombrus) in the central north Atlantic: a microsatellite loci approach

AbstractThe impacts of climate change on marine ecosystems can be seen in the changing distribution, migration, and abundance of species in the oceans. For some species this changing environment may be beneficial and can support population expansions. In the northeast Atlantic (NEA), the Atlantic mackerel (Scomber scombrus) is undergoing an increase in stock size accompanied by changing summer migration patterns, which have resulted in an expansion further north and north west than previously recorded. This study uses microsatellite loci to confirm the differentiation among NEA and northwest Atlantic (NWA) mackerel spawning populations and to assess the level of structuring within these populations. In addition, to enable population-specific exploitation rates to be factored into fisheries management, we identified the origin of individuals composing the expanding feeding aggregations in the central north Atlantic (Greenland, Iceland, Faroes), with all aggregations tested originating from spawning populations in the NEA. This study showed that microsatellite loci were useful to assess the contribution of NEA and NWA populations to mixed feeding aggregations across the north Atlantic for large pelagic fish stocks but were not powerful enough to evaluate the specific contribution of known stocks within NEA and NWA.

RAD‐Seq Refines Previous Estimates of Genetic Structure in Lake Erie Walleye

AbstractDelineating population structure helps fishery managers to maintain a diverse “portfolio” of local spawning populations (stocks), as well as facilitate stock‐specific management. In Lake Erie, commercial and recreational fisheries for Walleye Sander vitreus exploit numerous local spawning populations, which cannot be easily differentiated using traditional genetic data (e.g., microsatellites). Here, we used genomic information (12,264 polymorphic loci) generated using restriction site‐associated DNA sequencing to investigate stock structure in Lake Erie Walleye. We found low genetic divergence (genetic differentiation index FST = 0.0006–0.0019) among the four Lake Erie western basin stocks examined, which resulted in low classification accuracies for individual samples (40–60%). However, more structure existed between western and eastern Lake Erie basin stocks (FST = 0.0042–0.0064), resulting in greater than 95% classification accuracy of samples to a lake basin. Thus, our success in using genomics to identify stock structure varied with spatial scale. Based on our results, we offer suggestions to improve the efficacy of this new genetic tool for refining stock structure and eventually determining relative stock contributions in Lake Erie Walleye and other Great Lakes populations.

Reproductive biology and behavior associated with a spawning aggregation of the yellowfin grouper Mycteroperca venenosa in the US Virgin Islands

The reproductive characteristics, movement patterns and courtship behaviors associated with a yellowfin grouper (Mycteroperca venenosa, Linnaeus, 1758) fish spawning aggregation (FSA) were assessed between 2004 and 2014. The FSA was located on the Grammanik Bank, a seasonally closed area on the edge of the Puerto Rico platform, south of St. Thomas, US Virgin Islands. Fish arrived at the FSA site around full moon and departed 10–12 days after full moon (dafm), during two or three consecutive months, from January to May each year. Males were significantly larger than females and preceded females at the spawning site. Courtship coloration and behaviors showed distinct patterns relative to lunar date and time of day. Spawning was observed for several days each month in 2008, 2009, 2011 and 2014, from 6 to 10 dafm. Female gonadosomatic index (GSI) values were highest from 4 to 7 dafm. Spawning, which began at sunset, consisted of 7 to 12 males following one female along the bottom before ascending 10–20 m, then "rushing" upward to release gametes. Histological analysis of ovaries indicated females spawned every 2–3 nights, although 11.6% were capable of spawning two consecutive nights. Total spawning population size of yellowfin grouper fluctuated from 600 to 1100 fish during the study period, but consistent annual population assessments using scuba were difficult to carry out due to ocean conditions. Based on size-frequency analysis and other metrics, the M. venenosa spawning population at the Grammanik bank appears to be stable at this time with existing regulations.

Genomic Characterization of Coho Salmon Spawning Populations from the Hood Canal

AbstractWe investigated the genetic structure among Coho Salmon Oncorhynchus kisutch spawning populations in the Hood Canal of western Washington State, USA. Freshwater tributaries that drain into this marine fjord support natural production of Coho Salmon. Furthermore, there is a hatchery that produces a stock of Coho Salmon genetically distinct from local natural‐origin populations. Both stocks support multiple fisheries in the Hood Canal, which would benefit from data regarding the extent of gene flow between the tributaries themselves and also with the hatchery stock. We used restriction‐site‐associated DNA sequencing to generate genomic data, which we aligned to the Coho Salmon reference genome to identify variants. Over 30,000 single‐nucleotide polymorphisms were identified among the 420 samples we sequenced. There was little genetic differentiation between Coho Salmon sampled from the tributaries, suggesting that they form a genetically homogeneous population. In contrast, the local hatchery stock was highly differentiated from the tributary spawning populations. Distinct genetic groups emerged from the hatchery samples that corresponded to broodlines on a 3‐year cycle, likely due to low levels of inclusion of 2‐year‐old jacks in hatchery propagation. Hybridization between the hatchery stock and natural populations appeared to be low, and few of the returning adults sampled in the local tributaries had high genetic assignment to this stock. Our results provide insights into the population dynamics of naturally spawning populations of Coho Salmon in the Hood Canal and the extent of gene flow with a highly differentiated hatchery stock. These data will inform fisheries management, including the potential impact of harvest on naturally produced Coho Salmon, and have implications for hatchery propagation in this region.