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Why do shrimps leave the water? Mechanisms and functions of parading behaviour in freshwater shrimps

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An understanding of the mechanisms and functions of animal migratory behaviour may provide insights into its evolution. Furthermore, knowledge about migration may be important for conservation of rare species and may help to manage species in a rapidly changing world. Upstream migration is common in riverine animals, but little is known about proximate cues and functions of the upstream migration in aquatic macroinvertebrates. In Ubon Ratchathani, Thailand, locals have observed a synchronous mass migration of freshwater shrimps on land. This so‐called ‘parading behaviour' occurs annually during the rainy season and has become a large ecotourism event. Yet, we know little about the natural history, proximate causation and function of this extraordinary behaviour. Here we describe the natural history of parading behaviour and report the results from a series of experiments and observations to address its mechanisms and functions. Parading behaviour is not associated with breeding and spawning; rather, shrimps leave the water to escape strong currents. Conditions promoting shrimps to leave the water include low light, high water velocity and low air temperature. In addition, there is variation explained the specific location. River topology that creates hydrological variability and turbulence plays a role in triggering the shrimps to move out of water. Furthermore, turbidity and water chemistry were associated with shrimp activity. Finally, our results support that parading behaviour in freshwater shrimps is a mass movement upstream due to hydrological displacement. This study highlights the mechanisms that stimulate parading behaviour; a common activity in Macrobrachium and other decapod crustaceans.
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... Downloaded from https://academic.oup.com/cz/advance-article/doi/10.1093/cz/zoab017/6151757 by guest on 28 February 2021 Parading shrimps Macrobrachium dienbienphuense, an Asian endemic species of freshwater shrimps, perform a unique type of group movement known as "Parading Behavior" (Figure 1 A, B; Video 1). This behavior is unique in that the freshwater shrimps, which have an obligate aquatic lifestyle, climb out of a river at night and walk en masse upstream on land along a river bank within a splash zone for 5-20 meters before heading back to the river before sunrise (Hongjamrassilp et al. 2020). This natural phenomenon occurs annually during the rainy season (mid-August to early October) at the Lamduan rapids, in Ubon Ratchathani province, Thailand. ...
... Previous research found that the shrimps, especially juveniles, collectively move on land to escape strong water currents that otherwise would wash them downstream. The main environmental factors associated with parading include high water velocity, low light, and low air temperature (Hongjamrassilp et al. 2020). These shrimps are strictly aquatic, and by leaving the water to move on land, they experience several costs such as desiccation and predation from terrestrial animals (W.H. unpublished observations). ...
... Previous studies revealed that water velocity and light are two main factors that play a vital role in triggering shrimp parading (Lee and Fielder 1979;Fièvet 1999;Torkkola and Hemsley 2019;Hongjamrassilp et al. 2020). To explore how shrimps integrate these two factors in their decision to climb out of the river, we conducted an experiment in an artificial stream which was adapted from Hamano et al. (1995) and Olivier et al. (2013). ...
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An increase in ecotourism adversely impacts many animals and contributes to biodiversity loss. To mitigate these impacts, we illustrate the application of a conservation behavior framework towards the development of a sustainable ecotourism management plan. In Ubon Ratchathani, Thailand, thousands of tourists annually come to see a unique mass migration of shrimps on land (referred to as “shrimp parading”). Preliminary work suggests that this tourism has negatively impacted the shrimps. To reduce tourism-related impacts we studied: (1) the decisions shrimps make when parading, and (2) how shrimps respond to different light intensities and colors. We created an artificial stream and tested the conditions that influence parading by experimentally varying the presence of light and systematically manipulating water velocity (10, 60, 100 cm/s). Additionally, we conducted an in situ experiment to study how shrimps respond to tourists’ lights under three intensities (50, 400, 9000 lux) and four colors (white, blue, green, orange, and red). We found most shrimps prefer to leave the river when it is dark and there is low water flow. Shrimps responded the least to red (λmax = 630 nm) and orange (λmax = 625 nm) light at 50 lux. These findings were used to develop a management plan by creating three different tourist zones, which maximize tourist needs and minimize the anthropogenic impacts on the shrimps. This work could be used as an example of the application of conservation behavior framework in developing management plan for sustainable ecotourism for other invertebrate taxa.
... This natural phenomenon occurs at night when millions of freshwater shrimp collectively climb out of the Lamduan rapids and start to parade on land toward the headwater in the Thailand-Cambodia border. Research from Hongjamrassilp et al. (2020) reveals that the shrimp leave the water to escape the strong water current in the rapids. They do not perform this unique migration for reproduction, as observed in other riverine animals, such as salmon. ...
... Following the first publication (in November 2020) that described the Thai parading shrimp, there were a number of high-profile international press reports such as The New York Times, National Geographic, and Smithsonian Magazine (Buehler, 2020;Fox, 2020;Preston, 2020). Hence, Macrobrachium shrimp might have potential to serve as a flagship species for freshwater conservation since they have relatives on every continent except Antarctica and Europe that engage in similar behavior (Holthuis and Ng, 2010;Hongjamrassilp et al., 2020). More investigation into this is warranted. ...
... These results are not surprising because when the government promoted this Shrimp Watching in 1998-1999, little was known about the fundamental biology of the shrimp and nothing was known about anthropogenic threats to the shrimp. The first study studying parading shrimp biology and their responses to the anthropogenic threats came out in 2020, two decades after this ecotourism event was created (Hongjamrassilp et al., 2020). This Shrimp Watching tourism in Thailand is a case study showing the importance of developing a formal understanding of the effect of anthropogenic impacts on animals to properly manage them. ...
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Interest in wildlife ecotourism is increasing but many studies have identified detrimental effects making it unsustainable in the long run. We discuss a relatively new wildlife ecotourism event where tourists visit Ubon Ratchathani, Thailand to witness a mass migration of freshwater shrimp that emerge from the water and move across land known as “shrimp parading.” As this has been developed into a tourist event, the number of migrating shrimp have declined, suggesting that it may be unsustainable as currently practiced. We used a questionnaire to ask how locals, tourists, and stakeholders value the shrimp and their willingness to change their behavior to mitigate anthropogenic impacts. We found that three groups of participants were not aware of potential negative impacts to the shrimp from tourism. Locals valued the tourism in terms of the economy, culture, and environment less than tourists and stakeholders. The local government applied a top-down approach to manage this tourism without a fundamental understanding of the shrimp's biology, impacts of tourists on the shrimp, or the various stakeholder perceptions. We discuss the problems and possible solutions that may be employed to help sustain this fascinating biological and cultural event and propose a framework to develop a sustainable wildlife ecotourism management plan. This case study serves as a model for others developing wildlife watching ecotourism, especially in developing countries.
... Many freshwater shrimps migrate to obtain resources necessary for growth and reproduction, as represented by amphidromous species Crustacean Research 50 (Shokita, 1985;Fièvet et al., 2001;Bauer & Delahoussaye, 2008;Bauer, 2013;Kounthongbang et al., 2015). Their migratory activities are often influenced by biological and physical factors in the streams (March et al., 1998;Hein & Crowl, 2010;Bauer, 2018;Hongjamrassilp et al., 2021). The presence of predators, in particular, has a great impact on their activities. ...
... sively migrate to the forest streams by walking along the riverbank at night before the rainy season begins Kounthongbang et al., 2015; Supplementary Fig. 1). This migratory behavior of the juveniles is gradually becoming common in freshwater shrimps (Bauer, 2018;Hongjamrassilp et al., 2021). Of course, nocturnal predators exist, however nighttime migration during the primary life cycle of this species helps to reduce predation risk, which is an adaptive behavior to avoid predators such as carnivorous and omnivorous fishes (Kikkert et al., 2009;Bauer, 2018). ...
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From 2008 to 2014, we monitored the abundance and daytime habitat use of the freshwater shrimp Macrobrachium yui at a fixed site on a tributary of the Xuang River in northern Laos. Throughout the monitoring period, the shrimp M. yui showed strong preference for cobble and small boulder substrates, as well as moderate preferences for 21–30 cm depth and the midstream (251–350 cm distance from the bank) as daytime habitat factors. The shrimp M. yui, on the other hand, exhibited intense avoidance for shallower water depths (less than 10 cm), stagnant (0 cm s⁻¹) and faster water velocity (greater than 60 cm s⁻¹), finer substrates (from silt to gravel), and stream margin (less than 50 cm from the bank). During the day, the habitat with the cobble and small boulder in the midstream is probably the best place for the shrimp M. yui to hide from predators. The abundance of the shrimp M. yui had positive and negative correlations with water depth and sand percentage in the bottom sediment, respectively. It suggests that a decrease in water depth caused by increased deposition of fine sediment from the catchment has a negative impact on the shrimp abundance.
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... Lima & Oshiro (2002) and Lima et al. (2006) reported a greater preference of P. brasiliana (as P. glabra) adults to environments with rocks, slopes, and points with greater hydrodynamism. This preference is also observed in some freshwater prawns (Macrobrachium spp.) that show upstream migration (Kikkert et al., 2009;Hongjamrassilp et al., 2021). According to Covich et al. (2009) andEbner et al. (2021) these shrimps crawl through very high and steep waterfalls seeking refuge environments from predators and most resource availability (Bauer, 2023). ...
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Aim: The aim of this study was to investigate the isotopic signature of P. brasiliana captured in three different points along the river flow toward the sea of the Prumirim River, northern coast of the state of São Paulo/Brazil in order to test the hypothesis of similarity between isotopic signature of individuals living in separated areas of the river. Methods: We used stable isotope analyses (δ13C and δ15N) at three points of the river and ANOVA and Bayesian Ellipses analyses were performed. Results: Our results showed that are a differential isotopic enrichment along the river course in 13C, providing important results on the environmental condition and anthropogenic impacts in the region. In addition, the food biology of P. brasiliana was characterized as a primary consumer corroborating with the detritivores feeding habit observed in previous studies of stomach content analysis. Conclusions: Our research, limited to a single area along the northern coast of the state of São Paulo, uncovers intriguing findings that merit replication in other areas within the region. This is particularly crucial given the rising number of anthropogenic influences resulting from urban development, underscoring the need for improved monitoring of these areas.
... In Thailand, thousands of freshwater shrimp crawl onto land at night in September to parade upstream. Having observed this strange behavior, Hongjamrassilp et al. (2021) tested a series of hypotheses and uncovered a likely function (it is a way to migrate upstream while avoiding rapids). This is the inverse Krogh approach. ...
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Since the first major hadal sampling efforts in the 1950s, crustaceans of the order Decapoda have been thought absent from the hadal zone (6000–11,000 m) with no representatives documented >5700 m. A baited video lander deployed at 6007, 6890 and 7966 m in the Kermadec Trench, 8798 and 9729 m in the Tonga Trench (SW Pacific), 6945 and 7703 m in the Japan Trench and 5469 m in the Marianas region (NW Pacific) has now revealed a conspicuous presence of the Benthesicymid prawn Benthesicymus crenatus Bate 1881. Decapods were observed at all sites except at 7966 m in the Kermadec Trench and the two Tonga Trench sites, making the deepest finding 7703 m in the Japan Trench, 2000 m deeper than previously thought. These natantian decapods were readily attracted to fish bait and, rather than feeding on the bait itself, were observed preying upon smaller scavenging amphipods. These are the first observations of predation in the hadal zone. In less than 10 h of bottom time, 12 observations of 10 individuals were documented at 6007 m and 5 observations of 3 individuals were documented at 6890 m in the Kermadec Trench. In the Japan Trench at 6945 m 29 observations of 20 individuals were documented whilst only one individual was seen at 7703 m. Two individuals were observed in the abyssal Marianas Region (5575 m). Also, in the Kermadec Trench, individual caridean prawns (Acanthephyra spp.) were observed at 6007 and 6890 m, proving categorically that the crustacean order of Decapoda is represented in the hadal zone.
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A guide to using S environments to perform statistical analyses providing both an introduction to the use of S and a course in modern statistical methods. The emphasis is on presenting practical problems and full analyses of real data sets.
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Caridean prawns of the genus Macrobrachium Bate, 1868 (Crustacea, Decapoda, Palaemonidae) collected from the Laotian river system were studied. Fourteen species are recognised in this study, including one unidentified species. Their taxonomy is discussed and illustrated, of which 11 species are new records to the Laotian fauna. The identity of species of the "M. dienbienphuense" group has been remained obscure, and this study, which incorporated the 16S rRNA mitochondrial gene analysis, demonstrated that M. amplimanus Cai & Dai, 1999, M. dienbienphuense Dang & Nguyen, 1972, and M. eriocheirum Dai, 1984 are valid species. The Macrobrachium fauna in Laos exhibited closer affinity to that of the tropical Indo-China and Sunda elements (southern Yunnan Province, south-western China, northern Vietnam as well as north and north-eastern Thailand), implying that the Mekong River system contributes substantially to the regional freshwater prawn biodiversity.
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The relative selectivity of two fast-flowing concrete channels acting as passage facilities for shrimps was investigated at two low-head dams by comparing shrimps migrating through the channels to shrimps captured by experimental (trapping) passes offering splash zones. Complementary visual observations of shrimp behaviour were also carried out. At both dams (150 and 320 m above sea level (a.s.l.)), the upstream migration was mainly undertaken by small (subjuvenile) individuals but some larger ones, notably Atya innocous adults, were also captured. Strong water currents (1.5 m s−1) in the concrete channels compelled most shrimps to climb over the vertical walls but only the smallest individuals were able to do this. Thus, lower proportions of larger individuals were captured in the passage facilities than in the experimental passes. In the same way, the lightly built Macrobrachium spp. was found in lower proportions in the passage facilities than in the experimental passes. Furthermore, because of submerged orifices and whirling currents, the continuous-flow tanks which supplied the channels with water trapped numerous climbing shrimps. Hence, because they do not take biological criteria into account, the passage facilities investigated here were not only selective but also inefficient for shrimps. Finally, the benefits of such installations for shrimps are doubtful and simple waterfalls flowing over spillways would be at least as efficient, if not more so. Copyright
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ABSTRACT Egg and clutch sizes of the fresh-water prawn Macrobrachium nipponense (de Haan) varied remarkably among local populations, corresponding to the hydrogeographic features of their habitats; spawning of many small eggs (approximately 0.05 mm3 in volume per egg) in a single clutch at river mouths, a few but large eggs (approximately 0.1 mm3) in inland fresh waters, and a moderate number of intermediate-sized eggs in brackish-water lagoons. The weight of egg mass deposited in one spawning also varied among populations from 15.6-24.3% in dry weight ratio to the female body weight. This change seemed to come largely from temporary environmental factors. Accordingly, the variation of clutch size among populations was partly due to temporary environmental factors, and partly due to the difference in egg size. This species is considered to be splitting into local populations with distinct reproductive traits through reproductive isolation in patchily distributed inland waters. Adaptive significance of varied egg and clutch sizes is discussed with emphasis on the role of larval dispersal.
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The shrimp Macrobrachium ohione (Decapoda, Caridea) was once numerous in the Mississippi River System (MRS) as far north as the Missouri and lower Ohio Rivers but is now abundant only within the lower Mississippi and Atchafalaya Rivers. Adult M. ohione live and breed in fresh water, but larval development occurs in brackish and marine waters, a life history pattern termed amphidromy. A downstream female “hatching” migration may ensure that the stage-1 larvae reach the required salinity in time for the critical molt to stage-2 (first feeding larval stage). This study tested the hypothesis that embryo-bearing females deliver larvae to the estuaries of the Mississippi and Atchafalaya Rivers in Louisiana. To test the prediction of a downstream migration, this investigation examined the reproductive condition and the spatial-temporal distribution of reproductive-sized females during 2008 and 2009. Shrimps were collected by trapping at downstream (Pass A Loutre, Atchafalaya Delta) and upstream (St. Francisville, Butte La Rose) locations within the Mississippi and Atchafalaya Rivers, respectively. During M. ohione's reproductive season, a significantly larger proportion of females incubating embryos at any stage of development were observed downstream in the Atchafalaya River (AR) but not in the Mississippi River (MR). However, in the MR, a positive association between the proportion of females incubating near-hatching embryos and the downstream sample site was found in both years. In the AR, a similar association was found in 2009 but not in 2008. Females with near-spawning ovaries were positively associated with the downstream sites in the MR in 2009 and the AR in 2008. During the reproductive season, females in both the AR and MR were observed with near-spawning ovaries while simultaneously incubating near-hatching embryos. Thus, females may produce multiple broods during the reproductive season. In general, relative abundance (Catch Per Unit Effort) of reproductive-sized females was higher at downstream sites during the reproductive season. However, the predicted seasonal increase into downstream sites was statistically significant only in the AR in 2008. Overall, results of this study support the hypothesis that reproductive females migrate downstream to deliver larvae to the sea in both the AR and MR. Nevertheless, the exact mechanics of the migrations may vary with river characteristics such as length and water velocity.
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Basic conditions of fishways for freshwater amphidromous shrimps, two atyids Caridina japonica and Paratya compressa and a palaemonid Macrobrachium japonicum, which migrate to upstream habitats by walking at night, were studied using an experimental apparatus comprised of ten distinct flooring materials. As a result, effective fishway conditions were defined as follows: three-dimensional mesh structure (0.5mm in mesh sizes), e.g., cellular concrete, in the flooring, ≤50° at the inclination, and ≤65cm/s at the surface current velocity in the fishway. A plan for modifying and improving existing fishways and a proposal for preserving populations of amphidromous shrimps above dams are discussed.
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The larval development of Paratya australiensis consisted of 8 stages and lasts between 28 and 45 days in the laboratory. Stages I-IV were regular, but stages V-VIII were irregular with "mark-time molts" and a "skipped stage" common. Metamorphosis occurred after 7-12 ecdyses. This development is intermediate between the abbreviated development of Caridina spp. and the extended development of other atyids. Eggs and early stage larvae were larger and brood sizes were smaller in P. australiensis collected from riverine locations than those collected from an estuarine location in the same river system. There were no differences in development between laboratory-reared larvae from the two habitat types. The apparent plasticity of development is discussed in relation to environmental conditions.
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Although many species that live in low-order rainforest streams obtain much of their energy in the form of terrestrial leaf detritus, marked regional differences in the quantity, quality, and seasonal timing of leaf fall occur at different latitudes. There are also major seasonal, elevational, and historical differences in the frequency of floods and droughts that influence patterns of leaf input, transport, and decomposition. These differences may provide a basis for comparing stream communities in terms of biotic diversity and modes of detrital processing. At present, regional patterns of community structure are apparent in temperate-zone streams, but no distinct general patterns of biotic diversity or functional feeding groups are clearly evident in stream communities across latitude. Diversity of stream-dwelling detritivorous fishes is apparently highest in the large, geomorphologically complex Amazon basin where environmental conditions have remained highly variable throughout the Pleistocene. Diversity of other neotropical fish communities is regionally influenced by proximity to marine coastal habitats. Some insect and decapod crustacean taxa show higher species richness in mainland montane streams; high levels of endemism characterize some insular streams. As field experimentation increases, the underlying bases for evolution of specific adaptations by benthic invertebrates in highly seasonal neotropical streams can be interpreted more reliably, and detritivory can be placed in a latitudinal perspective. Human-induced disturbances are rapidly increasing in frequency and intensity in tropical regions; the biotic richness of low-latitude streams is being altered and opportunities for research on community dynamics are being lost.
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Macrobrachium ohione is an amphidromous species (i.e. lives and breeds in fresh water with larval development in estuarine, brackish or coastal waters) that has experienced population declines in the Mississippi River ( MR ) System, possibly due to extensive human modification (e.g. wing dikes, levees, channelisation and dams). Old River Control ( ORC ) is a complex of locks and dams in Louisiana that separates and controls the volume of water that flows into the Atchafalaya River ( AR ) from the MR . In this study, we tested the hypothesis that ORC impedes or prevents movement of juvenile M. ohione from the AR into the MR . Juvenile migrants were sampled using unbaited traps placed in the channels leading into and out of the river control structures. Variables such as location (above or below structure), water temperature and channel discharge were documented to determine their effects on juvenile migration. Migrant densities were significantly affected by the interaction between trap location and channel discharge. The densities of juveniles in the channels leading into the structures (downstream) were greater than those leading out of the structures (upstream). In addition, the densities of juveniles were consistently greater in the channels where channel discharge was the greatest. These results suggest that upstream juvenile migration is impeded by the structures, reducing the recruitment of shrimps from the AR into the MR . As a possible solution to allow shrimps to bypass the river control structures, this study tested the hypothesis that M. ohione juveniles are able climb up structures, a behaviour observed in several amphidromous species. A laboratory experiment tested the climbing ability of juvenile migrants (i.e. number of individuals on the ramp) and climbing performance (i.e. number of individuals that completed the climb) when presenting the shrimps for 1 h with a 1.5 m ramp at various ramp angles (30°, 40°, 60°) and water velocities (0, 45, 65, 140 cm s ⁻¹ ). Most shrimps were observed climbing when water velocity was 65 and 140 cm s ⁻¹ . Climbing performance was also influenced by the angle of the ramp, with the greater number of shrimps climbing at inclinations of 30° and 40°. Our results suggest that the installation of shrimp ladders and migratory conduits at river control structures could contribute to the restoration of M . ohione populations in the upper MR .
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Two methods are suggested for generating R measures for a wide class of models. These measures are linked to the R of the standard linear regression model through Wald and likelihood ratio statistics for testing the joint significance of the explanatory variables. Some currently used R 's are shown to be special cases of these methods.
Article
The hypothesis of an amphidromous life history pattern, with a female hatching migration from the river to an estuary, larval development in saltwater, and a return upriver migration by postlarvae (juveniles) was tested in the river shrimp Macrobrachium ohione in the Atchafalaya River, Louisiana, U.S.A. in 2006. A possible female migration from the river to the Atchafalaya Delta estuary (AD) to hatch incubated embryos was tested by comparing reproductive status of females sampled monthly from stations 146 km (Butte La Rose = BLR), 42 km (Berwick = BR), and 0 km from AD. Females only occurred in traps at AD only during the reproductive season (March to August) but were present throughout the year at other stations. The highest percentages of prehatching females occurred at the AD and BR stations while prehatching females were relatively rare at the upriver BLR station. Salt water requirements for larval development were tested by incubating first stage larvae from individual hatches in freshwater and saltwater (15 ppt) treatments (n = 10). The first stage (nonfeeding) larvae did not molt to second stage (feeding) larvae in freshwater, with significant mortality beginning after day 5. In saltwater, survival was high and most hatching larvae molted to stage 2 after 4-5 days of hatching. An upstream migration of juveniles began in mid-July 2006 and continued until October. Juvenile migrators were observed swimming near the surface from approximately one hour after sunset until at least early morning in a band of hundreds to thousands of individuals 1-2 m wide along the shore. Body size of migrators increased from downstream to upstream, suggesting that juveniles are feeding and growing during the migration. Hypotheses about whether formerly abundant far northern populations migrated to and from the sea are discussed. The decline of the species in the northern part of its range might be partially explained by human impacts on the juvenile migration and subsequent upstream recruitment.
Article
[Im Labor bei konstant 25°C und einer Photoperiode (L/D) von 14/10 aufgezogene Juvenile von Macrobrachium australiense sowie aus Freilandfangen stammende Juvenile und Adulti einschlieslich eiertragender Weibchen, die an dieselbe Temperatur und Photoperiode wie die Laborzuchten gewohnt worden waren, schwammen bestandig gegen eine Wasserstromung von 10 cm s-1 an. Umgekehrt war die Reaktion bei Garnelen aus dem Freiland, die im Winter bei einer Temperatur von 15°C gefangen worden waren. Flusaufwarts gerichtete Wanderungen, wie sie von dieser Suswassergarnele fur die Zeit vor der Eiablage bekannt sind, werden wahrscheinlich durch die in entgegengesetzter Richtung verlaufende Wasserstromung ausgelost und haben vermutlich die Funktion dem Verlust der Planktonlarven entgegenzuwirken., Im Labor bei konstant 25°C und einer Photoperiode (L/D) von 14/10 aufgezogene Juvenile von Macrobrachium australiense sowie aus Freilandfangen stammende Juvenile und Adulti einschlieslich eiertragender Weibchen, die an dieselbe Temperatur und Photoperiode wie die Laborzuchten gewohnt worden waren, schwammen bestandig gegen eine Wasserstromung von 10 cm s-1 an. Umgekehrt war die Reaktion bei Garnelen aus dem Freiland, die im Winter bei einer Temperatur von 15°C gefangen worden waren. Flusaufwarts gerichtete Wanderungen, wie sie von dieser Suswassergarnele fur die Zeit vor der Eiablage bekannt sind, werden wahrscheinlich durch die in entgegengesetzter Richtung verlaufende Wasserstromung ausgelost und haben vermutlich die Funktion dem Verlust der Planktonlarven entgegenzuwirken.]
Article
Introduction. ? Macrobrachium australiense Holthuis is a very widely distrib uted species of freshwater prawn found in coastal and inland waters of eastern Australia (Riek, 1959). Apart from descriptions of its larval life history by Fielder (1970) and its mating behaviour by Ruello et al. (1973), little has been written of its biology. This paper records observations of a large scale upstream migration of a population living in the Dawson River, S.E. Queensland. Study site. ? The Dawson River originates on the eastern slopes of the Great Dividing Range, more than 300 km from the coast. It regularly dries up into a series of oxygen depleted waterholes along much of its length (Lake, 1971) and is subject to flash flooding during the summer rainy season. Approximately 180 km from its source the Dawson is dammed by the Glebe Weir, the point at which the migration of Ai. australiense was observed. The spillway of the weir is approximately 6 m above river level and has a steplike buttress to one side (pi. 1). The buttress rises vertically from the river to a flat platform which was 1 m above the river level during the observations. The spillway was just covered by overflow due to early September rains. The water was very turbid and light penetration was less than 4 cm. Spillway water temperatures measured at 0730 hrs on each day of the observational period (October 4-8, 1978) ranged between 199 and 20? C
Article
The relative selectivity of two fast-flowing concrete channels acting as passage facilities for shrimps was investigated at two low-head dams by comparing shrimps migrating through the channels to shrimps captured by experimental (trapping) passes offering splash zones. Complementary visual observations of shrimp behaviour were also carried out. At both dams (150 and 320 m above sea level (a.s.l.)), the upstream migration was mainly undertaken by small (subjuvenile) individuals but some larger ones, notably Atya innocous adults, were also captured. Strong water currents (1.5 m s−1) in the concrete channels compelled most shrimps to climb over the vertical walls but only the smallest individuals were able to do this. Thus, lower proportions of larger individuals were captured in the passage facilities than in the experimental passes. In the same way, the lightly built Macrobrachium spp. was found in lower proportions in the passage facilities than in the experimental passes. Furthermore, because of submerged orifices and whirling currents, the continuous-flow tanks which supplied the channels with water trapped numerous climbing shrimps. Hence, because they do not take biological criteria into account, the passage facilities investigated here were not only selective but also inefficient for shrimps. Finally, the benefits of such installations for shrimps are doubtful and simple waterfalls flowing over spillways would be at least as efficient, if not more so. Copyright © 2000 John Wiley & Sons, Ltd.
Article
The Thai freshwater prawns of the genus Macrobrachium are reviewed. A taxonomic synopsis is given here of the 25 species of Macrobrachium so far known from Thailand, including three new species, namely M. thai, M. tratense and M. dolatum. Nine species are recorded for the first time from Thailand, namely M. amplimanus Cai and Dai, 1999, M. assamense (Tiwari, 1955), M. dienbienphuense Dang and Nyuyen, 1972, M. eriocheirum Dai, 1984, M. forcipatum Ng, 1995, M. hendersoni (De Man, 1906), M. malayanum (Roux, 1934), M. mieni Dang, 1975 and M. trompii (De Man, 1898). A neotype is designated for M. hirsutimanus (Tiwari, 1952). Descriptions for new species, diagnosis for newly recorded species and taxonomic discussions for all species are provided. A key to all the known Thai Macrobrachium species is included.
Article
Migration of large-bodied ''macroconsumers'' (e.g., fishes, shrimps, and snails) is an important functional linkage between many tropical rivers and their estuaries. Increasingly, this linkage is being severed by dams and water abstraction. The ecological impacts of these activities are poorly understood and are largely being ignored by dam operators. We investigated the direct effects of a water intake and low-head dam on the migration of amphidromous freshwater shrimps between the headwater streams and estuary of the Rio Espiritu Santo, Puerto Rico, USA. Both downstream migratory drift of larvae and upstream migration of postlarvae had strong diel patterns, with most activity occurring at night. Unlike large dams on the island, this low-head dam did not act as a complete barrier to the upstream migration of metamorphosed postlarvae. However, the dam did cause large numbers of postlarval shrimps to accumulate directly downstream of the struc- ture. Mortality of drifting first-stage larvae by entrainment into the water intake during downstream migration averaged 42% during the 69-d study period. During low discharges, 100% of the drifting larvae were entrained by the intake. The rate of nocturnal entrainment- induced mortality averaged 233 larvae/s and peaked at 1167 larvae/s. We used our field data and a 30-yr discharge record to model the long-term impacts of different intake man- agement strategies on the entrainment mortality at this dam. The simulation model estimated long-term mean daily entrainment mortality at 34-62%, depending on the amount of water extracted from the river. Monthly differences in mean daily entrainment mortality (27-76% depending on estimates of abstraction) were caused by seasonal variation in discharge. Modeling of mitigation options suggested that daily entrainment mortality of larvae could be reduced to 11-20% if water abstraction was halted for 5 h during evening periods of peak drift. Impacts of the dam and operations can be significantly ameliorated by 3-5 h stoppages in water abstraction during peak nocturnal larval drift, upkeep of a functional fish ladder, and maintenance of minimum flow over the dam. Since the impacts of dams depend on the hydrology and design of specific water intake systems, mitigation strategies must be tailored to individual dams and intakes. However, our approach and results are likely to apply to low-head dams throughout the range of amphidromous species.
Article
1. Analysis of drainage networks provides a framework to evaluate the densities and distributions of prey species relative to locations of their predators. Upstream migration by diadromous shrimp (Atya lanipes and Xiphocaris elongata) during their life cycle provides access to headwater refugia from fish predation, which is intense in estuaries and coastal rivers. 2. We postulate that geomorphic barriers (such as large, steep waterfalls >3.5 m in height), can directly limit the distribution of predatory fishes and, indirectly, affect the densities of their prey (freshwater shrimps) in headwater streams. 3. We compared densities of shrimp in pools above and below waterfalls, in four headwater tributaries in two river basins of the Luquillo Mountains of northeastern Puerto Rico. We measured shrimp densities twice a year over 8 years (1998–2005) in Prieta, Toronja, Bisley 3 and Bisley 5 streams, which differ in drainage network positions relative to steep waterfalls in Río Espíritu Santo and Río Mameyes. 4. Predatory fishes are absent in the Prieta and Toronja pools and present in Bisely 3 and in lower Bisley 5 pools. Atya lanipes and X. elongata rarely occur in the Bisley streams where predatory fishes are present but these shrimps are abundant in Prieta and Toronja, streams lacking predatory fishes. 5. The mean carapace length of X. elongata is longer in pools where fish are present (Bisley 3 and lower Bisley 5) than in pools lacking fish (Prieta, Toronja, Upper Bisley 5). The increased body size is primarily due to significantly longer rostrums of individuals in stream reaches with fish (below waterfall barriers) than in those reaches lacking fish (above waterfall barriers). Rostrum length may be an adaptation to avoid predation by visually feeding fishes. 6. Atya lanipes and X. elongata distributions and densities were predicted primarily by drainage network position relative to the presence or absence of predatory fishes. High, steep waterfalls effectively impeded fish from moving upstream and created a spatial refuge. Xiphocaris elongata may rely on size refugia (longer rostrum) to minimize predation where spatial refugia are lacking.