Role of different habitats for the functional response of Crytorrhinus lividipennis (Hemiptera: Miridae) on Nilaparvata lugens (Hemiptera: Delphacidae)

The functional response of a predator, Cyrtorrhinus lividipennis, on the brown planthopper, Nilaparvata lugens, was investigated in two different experimental habitats: a piece of tiller in a petri dish (5.5?cm in diameter) and a rice plant in a net cage (5.5?cm diameter?×?43?cm height) for 24?h at room temperature. In the petri dish experiment, 2nd–5th instar nymphs, adult male, and female C. lividipennis were introduced in separate experiments to eggs of N. lugens at densities of five, 10, 20, 30, and 40 eggs per piece of rice. In the rice plant experiment, each C. lividipennis was introduced to a cage with a rice plant containing N. lugens eggs. After 24?h, the number of dead eggs and remaining eggs were counted and data fitted to three functional response models. Among the three types of functional responses, Type II best described the predator response to host densities in N. lugens in both experimental habitats, according to the logistic regression analysis value. The results showed that C. lividipennis was a more effective predator in the rice plant experiment compared to the disc experiment. Additionally, the searching efficiency and handling time parameters were different in the two different experimental habitats. This may cause errors when applying the functional response to biological control and predator–prey models. Different habitats and other environmental conditions from the experiment and natural rice field have to be considered.     

Disturbance of freshwater habitats by anadromous salmon in Alaska

High densities of habitat modifiers can dramatically alter the structure of ecosystems. Whereas spawning sockeye salmon (Oncorhynchus nerka) dig nests that cover over 2 m² and are at least 20 cm deep, and can spawn at high densities, relatively little attention has been devoted to investigating the impacts of this disturbance. We hypothesized that this temporally and spatially predictable bioturbation has large impacts on the coastal aquatic habitats used by sockeye. We experimentally investigated the impacts of disturbance caused by spawning sockeye in two streams and two lakes in Alaska by excluding salmon from 2.25 m² plots where they traditionally spawn. We sampled exclusions and control plots before, during, and after spawning. During sockeye spawning, fine sediment accumulated in areas where sockeye were excluded from spawning. In addition, sockeye spawning significantly decreased algal biomass by 80% compared to exclusion plots. We found mixed effects of spawning on the invertebrate assemblage. Tricladida and Chironomidae densities increased by 3x in exclusion plots relative to control plots in one creek site. However, for most taxa and sites, invertebrate densities declined substantially as spawning progressed, regardless of experimental treatment. Habitat modification by spawning salmon alters both community organization and ecosystem processes.     

Assessing the effect of the Three Gorges reservoir impoundment on spawning habitat suitability of Chinese sturgeon (Acipenser sinensis) in Yangtze River,China

The Chinese sturgeon (Acipenser sinensis), a kind of maricolous anadromous migratory fish species, is endangered and protected in China. Historical spawning habitats were distributed in the lower reaches of Jinsha River and the upper reaches of Yangtze River. Since the establishment of the Gezhouba water conservancy pivot in 1981, the migratory route of Chinese sturgeon spawning was blocked. Therefore, the fish was forced to propagate in a new spawning ground which was mainly distributed in the 4-km-long mainstream from Gezhouba Dam to Miaozui in the middle Yangtze River. After water storage and power generation of the Three Gorges reservoir (TGR) in 2003, the propagation of Chinese sturgeon has been impacted gradually. According to field surveys, the fish used to spawn twice a year before TGR impoundment, but only once happened after that. Besides, the spawning scale is also declining with each passing year.In order to simulate and evaluate the effect of TGR impoundment on spawning habitats of Chinese sturgeon, with consideration of their reproductive characteristics, an eco-hydrodynamic model was established by coupling a two-dimensional hydrodynamic model and a fuzzy fish habitat module based on fuzzy logic inference. Flow fields at the studied site in an impoundment scenario and an assumed no impoundment scenario were simulated with the 2D hydrodynamic model. Afterwards, by linking hydrodynamic conditions to the expert knowledge base, the fuzzy habitat model used fuzzy logic inference to compute habitat suitability of the Chinese sturgeon. In addition, the approach was used to propose a suitable instream flow range during the propagation period for Chinese sturgeon. The results indicated that the suitable instream flow needed for Chinese sturgeon spawning in middle Yangtze River should be between 10,000 m³/s and 17,000 m³/s and it also showed that after TGR was put into pilot impoundment operation at the designed water level of 175 m, the habitat suitability has decreased significantly in October. Besides, the water temperature of spawning habitat increased to a higher level in propagation period due to the impoundment of the TGR. All these alterations have had imposed tremendous impacts on the propagation of Chinese sturgeon. Therefore, adjusting impoundment schedule of the TGR to recover the water flow over spawning habitat in October is a crucial way to improve the habitat suitability. Furthermore, the presented method also provides a theoretical basis for further research on the assessment of habitat suitability of aquatic species at a micro-habitat scale.     

Lake water level increase during spring affects the breeding success of bream Abramis brama (L.)

In Lake Constance, Eurasian bream Abramis brama (L.) spawn in very shallow littoral areas by the beginning of May. They attach their adhesive eggs to pebble and cobble substratum at <40 cm depth. Increasing water levels before spawning inundate bare substratum to which bream eggs may attach better than to deeper substratum covered by epilithon. Consequently, the water level increase prior to spawning should determine the amount of pristine spawning substratum available to bream and thus influence their breeding success. In order to test this hypothesis, the influence of hydrology and climate on the abundance of age-0 bream was combined with the results from field investigations on the egg survival and abundance of age-0 bream. A strong positive correlation between the mean water level increase during the spawning season of bream (April–May) and the abundance of juvenile bream was found. In contrast, the absolute water level during spawning and during the nursery stage in summer, the cumulative temperature during the egg, larval and juvenile stages and two North Atlantic Oscillation (NAO) indices did not affect the abundance of juvenile bream. The field investigations confirmed that bream eggs attach better to and have higher survival rates on bare substratum than on substratum with epilithon cover. Accordingly, eggs within a spawning habitat of bream were most abundant between 10 and 20 cm depth, where the epilithon cover was lower than at depths exceeding 30 cm. The results of this study confirm an adverse influence of epilithon cover on the attachment and subsequent survival of bream eggs and emphasize the importance of spring inundations for the successful breeding of the bream. Handling editor: J. A. Cambray     

Artificial Spawning Habitats Improve Egg Production of a Declining Diadromous Fish,Galaxias maculatus (Jenyns, 1842)

Anthropogenic impacts from urbanization, deforestation, and agriculture have degraded the riparian margins of waterways worldwide. In New Zealand, such impacts have caused changes in native vegetation, enhanced invasion by exotic grasses, and altered river bank morphology. One consequence has been a great reduction in obligate spawning habitat of a diadromous fish, Galaxias maculatus. Juvenile G. maculatus comprise a culturally important fishery that has been considerably reduced over recent decades. Rehabilitation of riparian vegetation needed for spawning is relatively straightforward, but slow. We hypothesized that artificial spawning habitats could accelerate restoration of fish egg production by creating an environment that would support at least the same density and survival of eggs as non‐impacted vegetation. We tested three artificial devices (straw bales, straw tubes, and moss tubes) in degraded and intact sites. Eggs were laid in all of these with numbers and survival usually exceeding that in riparian grasses. Where habitat was degraded, artificial spawning habitats yielded up to 10,000 eggs compared to none in nearby natural spawning habitat. The ground‐level environment of artificial habitat was similar to that of intact vegetation in buffering ambient temperature and humidity fluctuations. Crucial properties of the artificial habitats were (1) shelter to provide shade and hold moisture; (2) accessibility to allow adult fish to deposit and fertilize eggs; and (3) robustness to provide reliable surfaces and protection for the eggs during their development. We show that artificial spawning habitats are a viable short‐term alternative to rehabilitating spawning habitat while legacy effects abate and riparian vegetation recovers.     

Reproductive biology of four large riverine fishes (Cyprinidae) in a man-made lake,Orange River,South Africa

The reproductive biology ofBarbus holubi, B. kimberleyensis, Labeo capensis andL. umbratus was examined in a large reservoir on the Orange River, South Africa. The findings are integrated into the existing knowledge on largeBarbus andLabeo species, which coexist in most river systems in Africa and Asia.LargeBarbus spawn on gravel beds within the river channel during floods in spring or summer. In continuously flowing regulated rivers, time of spawning is governed by water temperatures. They have moderate fecundity; large eggs, incubation time of several days and the larvae are initially immobile with large yolk sacs. In the impoundment, they spawn in the inflowing regulated river withB. kimberleyensis spawning four to six weeks later than the more cold-tolerantB. holubi, the dominant largeBarbus. Survival is generally good and the juveniles disperse throughout the lake, but unseasonal release of cold water from an upstream impoundment may cause poor reproductive success.In contrast,Labeo species generally spawn on newly flooded ground, usually leaving the main river channel. Spawning may or may not be preceded by a longitudinal migration. Labeos are relatively fecund with small (30%Barbus size) eggs which hatch quickly and the larvae swim in bursts up into the water column before sinking down again.L. capensis does not require a longitudinal spawning migration and breeds throughout the lake, depending on local conditions. Large temporal variation in gonadal development within the population can result in more than one spawning. Dispersal within the lake is poor.L. umbratus uses larger inflowing tributaries for spawning thanL. capensis and its juveniles have a much greater power of dispersal. Early dependence on external feeding and undependable occurrence of conditions for spawning and juvenile feeding makes for variable reproductive success.     

Editorial

Quantitative and qualitative analyses of filming studies reveal that fundamental differences exist between the gaits of the New Zealand fur seal (Arctocephalus forsteri) and the Hooker's sea lion (Phocarctos hookeri). Terrestrial locomotion of the latter species is similar to that of terrestrial vertebrates in which the limbs are moved in sequence, alternately and independently. In contrast, the gait of the New Zealand fur seal does not conform to this sequence, the hind limbs being moved in unison. The gaits of both species are defined and illustrated. The limbs of otariids are structurally adapted for a semi-aquatic lifestyle and consequently large oscillations of the centre of gravity are necessary to enable the limbs to be lifted and protracted during terrestrial locomotion. Phocarctos hookeri achieves this by transferring weight in the transverse plane while in A.forsteri it is in the sagittal plane. Hind limb movements are distinctly different; P. hookeri moves each hind limb individually by the combined action of limb protraction and rotation of the pelvis while A. forsteri moves its hind limbs together, predominantly by flexion of the posterior axial skeleton. While terrestrial locomotion in these species is achieved by fundamentally different gaits, post cranial elements of A. forsteri and P. hookeri are barely distinguishable; selection for the behavioural control of terrestrial locomotion has apparently preceded structural modifications. The gaits are considered to be ecological specializations which are adaptations to the mechanical problems imposed by different habitats. Gaits of these species appear typical or representative of members of their inferred subfamilies (Arctocephalinae and Otariinae). The gaits of A. forsteri and P. hookeri are however paradoxical in light of their inferred evolutionary history since the gait of the Hooker's sea lion resembles more closely that of the putative ancestors of otariids (arctoid fissiped carnivores) than does the gait of the supposedly more primitive New Zealand fur seal.     

Biological Studies of the Pearl Spot Etroplus suratensis (Pisces,Cichlidae) from three Different Habitats in Sri Lanka

The morphometry, feeding habits and reproductive biology of Etroplus suratensis, an indigenous cichlid food fish, were studied for a period of one year on specimens from three different habitats in Sri Lanka. The morphometric studies implied that the length weight relationships are curvilinear. Macrophytic fragments formed the most important component of food, although detritus, diatoms, and animal matter are also ingested. First sexual maturity is attained in the length ranges 8.0-9.0 cm in females from brackish water habitats. Fecundity ranged from 700-3900 eggs in mature specimens. The wide range of the gonadosomatic index suggests that spawning occurs several times during the year.     

Life-history effects of migratory costs in anadromous brown trout

Mean size of sexually mature anadromous brown trout (sea trout) Salmo trutta in south-east Norway increased significantly with migratory distance ( D ) between the feeding area at sea and the spawning area in fresh water, from 32 cm for those spawning close to the river mouth to 43 cm at the spawning grounds 40 km inland. This was largely due to an increased size of the smallest anadromous spawners with increasing D . The raised mean size of the long-distance migrants is paralleled by an increased age at sexual maturity. Body mass at the same length of sea trout decreased with D in fresh water, meaning that the fish moving far inland was slimmer than those spawning near the coast. Gonadal mass of first-time spawning anadromous males declined significantly with D , and the fecundity and the ratio of fecundity over mean mass of the individual eggs adjusted for variation in fish mass, increased with D . There was no clear relationship between the ratio of anadromous to resident fish and D , probably because more variables than D , influence this relationship in the study streams.     

Edge Effects on the Density of Cheirogaleus major

We investigated how greater dwarf lemur (Cheirogaleus major) densities, ambient air temperature, and dendrometrics (tree height and diameter) varied along forest edge-interior gradients in the Vohibola III Classified Forest in SE Madagascar. We also assessed if spatial variations in densities of Cheirogaleus major provide indirect evidence of increased predation pressure in the transition zone between edge and interior forest habitats, i.e., an ecological trap. We conducted diurnal temperature surveys (N = 394) and nocturnal surveys of Cheirogaleus major (N = 182) over 2 yr along 4 1250-m transects that ran perpendicular to the forest edge in Vohibola III. We did not see Cheirogaleus major from May to mid-September, and the highest sighting frequency occurred during October–November. Cheirogaleus major exhibited a negative edge response because densities ranged from low levels in edge habitats to higher levels in the forest interior. After we tested for spatial autocorrelation, edge-related variations in densities of Cheirogaleus major covaried most strongly with tree diameter. Edge responses of Cheirogaleus major may reflect spatial variations in fruit and liana abundance, though data are needed on the precise relationship between tree diameter and food production to confirm the relationship. Edge-related variations in densities of Cheirogaleus major may also provide indirect evidence of an ecological trap. Testing and controlling for spatial autocorrelation should be important components of future studies of primate conservation biology and ecology.     

Reproductive behavior of the Atlantic silverside,Menidia menidia (Pisces,Atherinidae)

Synopsis The spawning behavior of the Atlantic silverside,Menidia menidia, was studied at two sites on the North Edisto River estuary in South Carolina. Prespawning schools moved back and forth along the shoreline as the time of high tide approached. Spawning runs took place in the upper intertidal zone at high tide.Spawning fish deposited their eggs on three types of substrates: 1) the lower stems of cordgrass plants,Spartina alterniflora, 2) detrital mats, and 3) exposed cordgrass roots along erosional scraps. Spawning behavior during egg deposition and fertilization was similar for all three substrates. Females released eggs during a rapid fluttering motion of the posterior half of the body. A similar movement accompanied release of sperm by males. Behavior of fish just prior to spawning insured deposition of gametes at locations that provided protection from thermal and drying stress during development. Eggs were deposited at mean intertidal elevations of 1.8 and 1.5 meters above mean low water (MLW) at respective study sites. They were exposed to the atmosphere for approximately ten hours between successive high tides.During spawning runs in which eggs were deposited at the base of cordgrass plants, ambient dissolved oxygen concentrations of the water in the spawning area were sometimes reduced to < 1.0 mg. 1^–1. Spent fish, apparently incurring an oxygen debt while spawning, formed a nonschooling aggregation offshore from the spawning zone.The recurrent use of specific spawning substrates for egg deposition resulted in an uneven distribution of spawning runs along the shoreline at each study site.Contribution No. 409 to the Gulf Breeze Environmental Research Laboratory. Contribution No. 377 to the Belle W. Baruch Institute for Marine Biology and Coastal Research.     

Nonselective use of vegetation for spawning by the diadromous fish Galaxias maculatus

Terrestrial egg development is advantageous for the amphidromous fish Galaxias maculatus because it increases access to oxygen, increases incubation temperatures, and reduces aquatic predation. The characteristics of New Zealand's riparian vegetation have changed considerably since colonial times from native vegetation to exotic grasses, with potential effects on the spawning dynamics of fish. Here, we used a series of experiments to test preferences of G. maculatus for egg laying in combinations of a native sedge and rush, and two exotic grasses. In laboratory experiments, G. maculatus spawned in all available habitats with no preference for native over exotic vegetation. Egg survival did not differ between the vegetative habitats, but in a treatment where only river stones were available, eggs were laid but they dehydrated and died. In a field experiment, there was no evidence for a preference for spawning in native vegetation, and no association between a “key” feature of vegetation—tiller density—and the number of eggs laid. The microclimate beneath dense vegetation in experimental treatments was more constant than ambient conditions with few extreme temperatures and low humidities. Given the readiness of G. maculatus to spawn in exotic vegetation, there appears to be no benefit in restoring native vegetation to enhance egg laying or survival of these taxa.     

Lake sturgeon spawning on artificial habitat in the St Lawrence River

In 1996, lake sturgeon (Acipenser fulvescens) spawning was documented for the third consecutive year on an artificially placed gravel bed in the St Lawrence River. Two distinct spawning periods were observed in 1996. Spawning initially commenced on 17 June, when water temperature reached 15°C. A second spawning event was documented from 28 June to 1 July (16°C). Sturgeon egg densities were monitored in three transects on egg trays, on the gravel surface, and within interstitial spaces in the gravel. Counts of developing eggs in the gravel bed during both spawning periods were used to estimate a total of 275 000 eggs on the study area (0.075 ha). Average egg density was highest in the transect with the highest water velocities. Lake sturgeon fry were first observed in the gravel on 24 June (15.5°C), and first emergence from the gravel was documented on 28 June. Hatching following the second spawning event commenced on 3 July. Based on assessment of average embryo viability (61.6%) and egg‐to‐emergent fry survival (17.6%) an estimate of about 171 000 sturgeon eggs hatched, producing over 49 000 emergent fry. Current velocity, substrate particle size, depth of substrate, and maintenance of sediment‐free interstitial spaces are important considerations in planning future spawning habitat enhancement projects.     

条纹短攀鲈的交配习性和筑巢生境

条纹短攀鲈栖息于静止、植被茂密、靠近稻田和池塘边缘的浅水中。本文研究了它在泰国稻田和小池塘两种生境中的繁殖特征。与池塘相比,稻田筑巢地的pH值、溶解氧的含量和温度较高,而电导、溶解的固体物浓度较低,水也较浅。稻田中的种群密度低于池塘。雄性个体的体重和体长均大于雌性个体,且其体重与体长和体宽正相关,但雌性个体的体重仅与体长正相关;泡巢的面积与雄性个体的体长和重量均不相关。繁殖期间,条纹短攀鲈雌、雄个体交尾多次。每次交尾产卵3.74±1.02(Mean±SD)粒,每个繁殖季节交尾84±12.97次;在一个持续178±51.17min的产卵时段里,条纹短攀鲈平均产卵314±109.77粒。鱼苗孵化需30.75±0.55h,2日龄个体的大小平均为3.21±0.29mm。     

Deepwater broadcast spawning by Montastraea cavernosa, Montastraea franksi, and Diploria strigosa at the Flower Garden Banks, Gulf of Mexico

Broadcast spawning by corals is a tightly synchronized process characterized by co-ordinated gamete release within 30–60 min time windows once per year. In shallow water corals, annual water temperature cycles set the month, lunar periodicity the day, and sunset time the hour of spawning. This tight temporal regulation is critical for achieving high fertilization rates in a pelagic environment. Given the differences in light and temperature that occur with depth and the importance of these parameters in regulating spawn timing, it has been unclear whether deeper coral can respond to the same environmental cues that regulate spawning behaviour in shallower coral. In this report, a remotely operated vehicle was used to monitor coral spawning activity at the Flower Garden Banks at depths from 33 to 45 m. Three species Montastraea cavernosa, Montastraea franksi, and Diploria strigosa were documented spawning within this depth range. All recorded spawning events were within the same temporal windows as shallower conspecifics. These data indicate that deep corals at this location either sense the same environmental parameters, despite local attenuation, or communicate with shallower colonies that can sense such spawning cues.     

Characterization of Pallid Sturgeon (Scaphirhynchus albus) Spawning Habitat in the Lower Missouri River

Acipenseriformes (sturgeons and paddlefish) globally have declined throughout their range due to river fragmentation, habitat loss, overfishing, and degradation of water quality. In North America, pallid sturgeon (Scaphirhynchus albus) populations have experienced poor to no recruitment, or substantial levels of hybridization with the closely related shovelnose sturgeon (S. platorynchus). The Lower Missouri River is the only portion of the species’ range where successful reproduction and recruitment of genetically pure pallid sturgeon have been documented. This paper documents spawning habitat and behavior on the Lower Missouri River, which comprises over 1,300 km of unfragmented river habitat. The objective of this study was to determine spawning locations and describe habitat characteristics and environmental conditions (depth, water velocity, substrate, discharge, temperature, and turbidity) on the Lower Missouri River. We measured habitat characteristics for spawning events of ten telemetry-tagged female pallid sturgeon from 2008–2013 that occurred in discrete reaches distributed over hundreds of kilometers. These results show pallid sturgeon select deep and fast areas in or near the navigation channel along outside revetted banks for spawning. These habitats are deeper and faster than nearby river habitats within the surrounding river reach. Spawning patches have a mean depth of 6.6 m and a mean depth-averaged water-column velocity of 1.4 m per second. Substrates in spawning patches consist of coarse bank revetment, gravel, sand, and bedrock. Results indicate habitat used by pallid sturgeon for spawning is more common and widespread in the present-day channelized Lower Missouri River relative to the sparse and disperse coarse substrates available prior to channelization. Understanding the spawning habitats currently utilized on the Lower Missouri River and if they are functioning properly is important for improving habitat remediation measures aimed at increasing reproductive success. Recovery efforts for pallid sturgeon on the Missouri River, if successful, can provide guidance to sturgeon recovery on other river systems; particularly large, regulated, and channelized rivers.     

Comparative biology and management of Arctic and European grayling (Salmonidae,Thymallus)

Summary The biological and ecological features of Arctic grayling (Thymallus arcticus) relevant to its management and enhancement are reviewed over its range in North America as well as in Asia, and are compared with those for the European grayling (Thymallus thymallus). Populations of both species have declined in some areas where angling pressure has been severe and where major alterations of their habitats have occurred. But native populations of Arctic grayling have been extirpated in eastern parts of its North American range, and nearly so in south-western parts, whereas the range of European grayling has been extended, especially in the United Kingdom and in Finland, by introduction. Furthermore, in contrast to the Arctic grayling, the European grayling, in Scandinavia at least, seems to have been less severely affected by impoundment of rivers and lakes for hydroelectric generation, perhaps because it has been able to successfully reproduce in large rivers below dams, especially those where fluctuation in water level is small.The success of various grayling management and enhancement practices, including hatchery culture and stocking, angling restrictions, spawning and rearing facilities, competitor and predator control, stream habitat restoration, lake and stream fertilization, and invertebrate prey introduction, are evaluated and compared for both species.     

Reproductive strategies in female polar and deep-sea bobtail squid genera <Emphasis Type="Italic">Rossia</Emphasis> and <Emphasis Type="Italic">Neorossia</Emphasis> (Cephalopoda: Sepiolidae)

Female reproductive features have been investigated in five polar and deep-sea bobtail squid genera Rossia and Neorossia (R. macrosoma, R. moelleri, R. pacifica, N.c. caroli and N.c. jeannae). These species are characterized by asynchronous ovary maturation, very large eggs (>10% ML), fecundity of several hundred oocytes, very high reproductive output, and continuous spawning with low batch fecundity. This adaptive complex of reproductive traits evolved in these small animals as an optimum strategy for polar and deep-water habitats.     

Flood-induced interspecific interactions in spring-fed tributary as an ecosystem function of heterogeneous river networks

Understanding the migratory community dynamics of river networks is important for maintaining lotic system integrity. River animals migrate to their preferred habitats in spatiotemporally heterogeneous river environments. Spring-fed habitats are uniquely characterized by stable temperature and flow regimes, which create suitable spawning habitats for the chum salmon Oncorhynchus keta. O. keta exhibits “run up” to its birthplace for spawning, especially during floods. Because the eggs deposited by this anadromous fish are nutritious and actively consumed by freshwater animals, the location and timing of O. keta spawning events affect the spatiotemporal accumulation of mobile consumers. In this study, we examined changes in temporal population density in spawning O. keta and a mobile consumer (juvenile O. masou masou) in a lowland, spring-fed tributary in northern Japan during a 48.5-mm autumn rainfall event. In both species, population density increased, and then decreased, after the rainfall event. In O. keta, these changes were closely associated with rainfall intensity, whereas in O. masou masou the peak was delayed until 3 days after the rainfall event. A comparison of the gut contents of O. masou masou sampled from a spring-fed tributary and an adjacent non-spring-fed tributary indicated greater consumption of O. keta eggs in the spring-fed tributary. These results suggested that preferential migration of O. keta into spring-fed tributaries for spawning induces subsequent accumulation of juvenile O. masou masou, in turn increasing O. keta egg consumption. These findings improve our understanding of community dynamics during floods in a heterogeneous river network environment.

     

Isotope analysis reveals proportional change and site-selection variation of river- and lake-produced eggs of a landlocked migratory fish

Changes in the proportions of river- and lake-produced eggs of a landlocked amphidromous fish, ayu (Plecoglossus altivelis altivelis) in the Lake Biwa water system, Japan, were monitored by stable isotope analysis, based on different δ¹⁵N and δ¹³C values of prey organisms between the lake and its tributaries. During the 3 month reproduction season, the δ¹⁵N values of spawned eggs decreased with time. This result implies that there was a shift from lake-produced eggs to river-produced eggs within a reproductive season, based on the observation that adult fish in the lake had previously been shown to have eggs with distinctly higher δ¹⁵N values in their ovaries than those in the tributaries. This explanation was also supported by the change in δ¹³C values of the spawned eggs. Furthermore, eggs with lower δ¹⁵N and higher δ¹³C values tended to be spawned at less variable depths, suggesting that females spawning river-produced eggs selected the spawning sites from a narrower range. We conclude that stable isotope ratios of spawned eggs can be indicators of the relative contributions of different food chains and can enable comparisons of reproductive characteristics between types of egg.