Spatiotemporal dynamics of larvae and juveniles of two species of interest for fisheries in Itaipu: A big neotropical reservoir

Larval fish abundance and physical forcing in the Gulf of Alaska, 1981–2003

Patterns of distribution and abundance of larval fish in a southern temperate region.

Larvae feeding selectivity of Iheringichthys labrosus, Hypophthalmus edentatus and Plagioscion squamosissimus was assessed, examining the role of mouth gape in prey selection. Fish larvae were sampled in the Itaipu Reservoir (Brazil–Paraguay). Iheringichthys labrosus and H. edentatus larvae, with small and similar gape sizes, exhibited slightly different diets; I. labrosus preferred cladocerans (Bosmina hagmanni, Bosmina huauriensis and Bosminopsis deitersi) and the rotifer Brachionus calyciflorus. Hypophthalmus edentatus, however, primarily ingested the cladocerans B. hagmanni, Ceriodaphnia cornuta, Daphnia gessneri and Diaphanosoma spinulosum. Plagioscion squamosissimus, with a greater gape size, preferred Calanoida. The mechanistic processes that determine food selectivity of fish larvae in temperate aquatic systems were similar in the Neotropical system. The trophic spectrum of these species is characterized by small‐ to intermediate‐sized prey. Plagioscion squamosissimus larvae, which have larger mouths, exploit primarily larger prey differing from the most abundant species or size classes; consequently, their diet is quite different from I. labrosus larvae and modestly similar to H. edentatus larvae, opportunistic feeders that they eat more abundant prey.

The European hake (Merluccius merluccius) is represented as one of the most valuable fisheries in the Galician shelf. We analyzed the distribution, abundance, and environmental conditions of the southern-stock European hake larvae from the Galician shelf during the two main spawning peaks, winter-spring and summer, based on the data from three ichthyoplankton surveys (March 2012, March 2017, and June 2017). A total of 395 larvae in March 2012, 121 in March 2017, and 69 in June 2017 were captured. The northeast section of the study area, close to Estaca de Bares, primarily between 100 and 200 m isobaths, had the highest presence of the European hake larvae in all surveys. Generalized additive models (GAMs) indicated that the occurrence of larvae was significantly different between the surveys and was associated negatively with the temperature, while the abundance of larvae was significantly different between sampling years and was the highest at a temperature around 13.36°C and at sea surface heights of about −0.48 m. Studies of the distribution of early life stages and their relation to external conditions are essential to the understanding of the complex process of recruitment, especially in the exploited species and in highly dynamic environments like the Galician shelf.

The reproductive activity of the fish assemblage in a large Neotropical reservoir was evaluated by surveying the occurrence of ichthyoplankton in response to spatial and temporal variation in environmental factors. Fish reproduction was investigated by capturing larvae along representative spatial gradients in the main body (longitudinal) and arms (lateral) of the reservoir. After identification, the captured larvae were classified into different groups according to the functional traits of their parental stock. Sampling occurred monthly at night from October to March over five reproductive periods between 2009 and 2016, using conical‐cylindrical plankton nets with flowmeter. Water samples were taken simultaneously allowing the measurement of environmental factors related to reproductive activity. The relationship between the environmental factors and the functional traits was assessed using RLQ and fourth‐corner analyses. An evaluation of 51,995 larvae revealed there was greater larval abundance in the lacustrine and transition zones of both longitudinal and lateral gradients. Occurrences often correlated with temporal instead of spatial gradients. Higher rainfall correlated with abundances of detritivorous and migratory species. Higher water levels correlated with higher abundances of non‐native species, species without parental care, with external fecundation, and partial spawning. Dry periods, with lower water and higher dissolved oxygen, correlated with higher abundances of insectivores and sedentary species. Although the presence of a dam‐free stretch of river upstream of the reservoir had a positive influence on fish larvae in the fluvial zone, the results did not show differentiation along either gradient. Thus, the composition of the functional groups of fish species that reproduce in the Itaipu Reservoir appears to be predominantly influenced by the temporal variation in environmental factors rather than the formation of spatial gradients.

The purpose of this study was to evaluate the role of abiotic factors on fish larvae occurrence. Samplings were carried out monthly at 12 stations (grouped in four areas) in the Amambaí, Ivaí and Paraná rivers and in the Itaipu Reservoir (upper Paraná River basin), from October 1994 to January 1995 (spawning season). Simultaneously, we obtained water temperature, pH, electrical conductivity, dissolved oxygen, water level, water velocity, and rainfall. Principal Component Analyses (PCA) and Detrended Correspondence Analyses (DCA) were applied to summarize abiotic and larvae density data, respectively. Amambaí River differed significantly from the other areas in relation to abiotic factors. Itaipu Reservoir differed significantly from the other areas considering species composition, and the Ivaí River also differed from the Paraná River. The relationship among PCA and DCA axes were significant, indicating that abiotic factors do influence larva. For example: Leporinus elongatus prefered the Amambaí River, Hypophthalmus edentatus, Plagioscion squamosissimus, and Hoplias aff. malabaricus the Itaipu Reservoir, and Pimelodus maculatus, Auchenipterus osteomystax and Iheringichthys labrosus the Ivaí River. We suggest that species selected some abiotic factors characteristic to a given environment as spawning grounds.

BackgroundBehavior and activity patterns largely determine animal’s fitness and their ecological roles. Those patterns depend on many factors, being body mass, sex and age the most relevant in mammals. Particularly, those factors altogether with environmental conditions could influence movement behavior of mammals that hibernate, such as the Monito del monte (Dromiciops gliroides).MethodsTo evaluate its movement behavior and activity we radio-tracked D. gliroides 12 individuals (8 females and 4 males, corresponding to 5 adults and 7 sub-adults) during the austral summer. With the estimated locations we estimated home ranges, core areas and their relationship with body mass. We also assessed movement speed during early (19:00 to 01:00 h), peak (01:00 to 03:00 h) and late (03:00 to 07:00 h) activity periods. This study was conducted at the San Martín experimental forest (Valdivia, southern Chile).ResultsEstimated home range areas were 1.04 ± 0.20 ha, and core areas were 0.27 ± 0.06 ha; we found no significant differences between males and females, nor between adults and sub-adults. Home range and core areas were independent of body mass in females but showed positive relationships in males. Core area overlap was larger between sub-adult and adult individuals (35%) than between adult males and females (13%). Average movement D. gliroides speed was 1.45 m/min, reaching its lowest value during the peak activity period (01:00 to 03:00 h), but being faster during early and late activity periods. Those speed differences may be related to travelling and foraging activities.ConclusionHome range and core areas estimated here showed a large variability, which can be related to environmental factors. Home range size was positively correlated with body mass on males but not on females. Also, lower movement speeds at the peak activity period suggest that D. gliroides concentrates feeding activities at this time. As D. gliroides disperses the seeds of at least 16 native plant species, its movement behavior also has important consequences at the community level.

BackgroundAnopheles arabiensis (Diptera: Culicidae) is a potential malaria vector commonly present at low altitudes in remote areas in Reunion Island. Little attention has been paid to the environmental conditions driving larval development and abundance patterns in potential habitats. Two field surveys were designed to determine whether factors that discriminate between aquatic habitats with and without An. arabiensis larvae also drive larval abundance, comparatively in man-made and naturally occurring habitats.MethodsIn an initial preliminary survey, a representative sample of aquatic habitats that would be amenable to an intensive long-term study were selected and divided into positive and negative sites based on the presence or absence of Anopheles arabiensis larvae. Subsequently, a second survey was prompted to gain a better understanding of biotic and abiotic drivers of larval abundance, comparatively in man-made and naturally occurring habitats in the two studied locations. In both surveys, weekly sampling was performed to record mosquito species composition and larval density within individual habitats, as well as in situ biological characteristics and physico-chemical properties.ResultsWhilst virtually any stagnant water body could be a potential breeding ground for An. arabiensis, habitats occupied by their immatures had different structural and biological characteristics when compared to those where larvae were absent. Larval occurrence seemed to be influenced by flow velocity, macrofauna diversity and predation pressure. Interestingly, the relative abundance of larvae in man-made habitats (average: 0.55 larvae per dip, 95%CI [0.3–0.7]) was significantly lower than that recorded in naturally occurring ones (0.74, 95%CI [0.5–0.8]). Such differences may be accounted for in part by varying pressures that could be linked to a specific habitat.ConclusionsIf the larval ecology of An. arabiensis is in general very complex and factors affecting breeding site productivity sometimes not easy to highlight, our results, however, highlight lower populations of An. arabiensis immatures compared to those reported in comparable studies conducted in the African continent. Overall, this low larval abundance, resulting from both abiotic and biotic factors, suggests that vector control measures targeting larval habitats are likely to be successful in Reunion, but these could be better implemented by taking environmental variability into account.

Abstract– We determined the habitat use of age‐0 yellow perch (Perca flavescens) in two South Dakota (USA) lakes. Larval perch abundance was based on trawl catches and related to environmental variables on two late spring dates. Juvenile perch abundance was based on late July shoreline seine and bottom trawl catches. Day and night juvenile abundance relations to environmental variables were examined. Larval abundance appeared to be related to biological environmental variables, and no significant (P≥0.05) correlations with physical habitat variables were found. Juvenile yellow perch abundance was related to physical variables, particularly substrate, water temperature and water depth. The only biological variable that could be related to juvenile abundance was chironomid abundance. Finally, juvenile perch abundance was positively associated with abundance of other juvenile fishes and minnows, but these associations varied by lake, time of day and habitat type. Understanding age 0 perch habitat use will allow fishery biologists to better assess sampling designs and recruitment processes.

European hake represent one of the most valuable fisheries in the Galician Shelf. We analysed the distribution,abundance and environmental conditions of southern-stock European hake larvae onfrom the Galician shelf are analysed during the two main spawning peaks – winter-spring and summer – based on data from three ichthyoplankton surveys (March 2012, March 2017 and June 2017). A total of 395 larvae in March 2012, 121 in March 2017 and 69 in June 2017 were captured. The northeast section of the study area had the highest presence of European hake larvae in all surveys, close to Estaca de Bares, primarily between the 100 and 200 m isobaths. Generalized additive models indicated that the occurrence of larvae was significantly different between surveys and associated negatively with the temperature, while abundances of larvae were significantly different between sampling years and highest at temperatures around 13.36 ºC and sea surface heights around -0.48 meters. Studies of the distribution of early life stages and its relation with the external conditions are essential to understanding the complex process of recruitment, especially in exploited species and in highly dynamic environments like the Galician Shelf.

European hake represent one of the most valuable fisheries in the Galician Shelf. We analysed the distribution,abundance and environmental conditions of southern-stock European hake larvae onfrom the Galician shelf are analysed during the two main spawning peaks – winter-spring and summer – based on data from three ichthyoplankton surveys (March 2012, March 2017 and June 2017). A total of 395 larvae in March 2012, 121 in March 2017 and 69 in June 2017 were captured. The northeast section of the study area had the highest presence of European hake larvae in all surveys, close to Estaca de Bares, primarily between the 100 and 200 m isobaths. Generalized additive models indicated that the occurrence of larvae was significantly different between surveys and associated negatively with the temperature, while abundances of larvae were significantly different between sampling years and highest at temperatures around 13.36 ºC and sea surface heights around -0.48 meters. Studies of the distribution of early life stages and its relation with the external conditions are essential to understanding the complex process of recruitment, especially in exploited species and in highly dynamic environments like the Galician Shelf.

<p>The European hake (Merluccius merluccius) is represented as one of the most valuable fisheries in the Galician shelf. We analyzed the distribution, abundance, and environmental conditions of the southern-stock European hake larvae from the Galician shelf during the two main spawning peaks, winter-spring and summer, based on the data from three ichthyoplankton surveys (March 2012, March 2017, and June 2017). A total of 395 larvae in March 2012, 121 in March 2017, and 69 in June 2017 were captured. The northeast section of the study area, close to Estaca de Bares, primarily between 100 and 200 m isobaths, had the highest presence of the European hake larvae in all surveys. Generalized additive models (GAMs) indicated that the occurrence of larvae was significantly different between the surveys and was associated negatively with the temperature, while the abundance of larvae was significantly different between sampling years and was the highest at a temperature around 13.36°C and at sea surface heights of about −0.48 m. Studies of the distribution of early life stages and their relation to external conditions are essential to the understanding of the complex process of recruitment, especially in the exploited species and in highly dynamic environments like the Galician shelf.</p>

European hake represent one of the most valuable fisheries in the Galician Shelf. We analysed the distribution,abundance and environmental conditions of southern-stock European hake larvae onfrom the Galician shelf are analysed during the two main spawning peaks – winter-spring and summer – based on data from three ichthyoplankton surveys (March 2012, March 2017 and June 2017). A total of 395 larvae in March 2012, 121 in March 2017 and 69 in June 2017 were captured. The northeast section of the study area had the highest presence of European hake larvae in all surveys, close to Estaca de Bares, primarily between the 100 and 200 m isobaths. Generalized additive models indicated that the occurrence of larvae was significantly different between surveys and associated negatively with the temperature, while abundances of larvae were significantly different between sampling years and highest at temperatures around 13.36 ºC and sea surface heights around -0.48 meters. Studies of the distribution of early life stages and its relation with the external conditions are essential to understanding the complex process of recruitment, especially in exploited species and in highly dynamic environments like the Galician Shelf.

<p>The European hake (Merluccius merluccius) is represented as one of the most valuable fisheries in the Galician shelf. We analyzed the distribution, abundance, and environmental conditions of the southern-stock European hake larvae from the Galician shelf during the two main spawning peaks, winter-spring and summer, based on the data from three ichthyoplankton surveys (March 2012, March 2017, and June 2017). A total of 395 larvae in March 2012, 121 in March 2017, and 69 in June 2017 were captured. The northeast section of the study area, close to Estaca de Bares, primarily between 100 and 200 m isobaths, had the highest presence of the European hake larvae in all surveys. Generalized additive models (GAMs) indicated that the occurrence of larvae was significantly different between the surveys and was associated negatively with the temperature, while the abundance of larvae was significantly different between sampling years and was the highest at a temperature around 13.36°C and at sea surface heights of about −0.48 m. Studies of the distribution of early life stages and their relation to external conditions are essential to the understanding of the complex process of recruitment, especially in the exploited species and in highly dynamic environments like the Galician shelf.</p>

European hake represent one of the most valuable fisheries in the Galician Shelf. We analysed the distribution,abundance and environmental conditions of southern-stock European hake larvae onfrom the Galician shelf are analysed during the two main spawning peaks – winter-spring and summer – based on data from three ichthyoplankton surveys (March 2012, March 2017 and June 2017). A total of 395 larvae in March 2012, 121 in March 2017 and 69 in June 2017 were captured. The northeast section of the study area had the highest presence of European hake larvae in all surveys, close to Estaca de Bares, primarily between the 100 and 200 m isobaths. Generalized additive models indicated that the occurrence of larvae was significantly different between surveys and associated negatively with the temperature, while abundances of larvae were significantly different between sampling years and highest at temperatures around 13.36 ºC and sea surface heights around -0.48 meters. Studies of the distribution of early life stages and its relation with the external conditions are essential to understanding the complex process of recruitment, especially in exploited species and in highly dynamic environments like the Galician Shelf.