Diel Behavior Research Articles

Diving behaviour of the critically endangered tope shark Galeorhinus galeus in the Natural Reserve of Bahia San Blas, northern Patagonia

BackgroundTope sharks (Galeorhinus galeus) aggregate in large numbers during spring and summer in closed gulfs and bays in northern Patagonia; these locations are considered the main nursery areas for the species. However, little is known about the spatial ecology or diel behaviour of this critically endangered species. The aim was to evaluate the short-term diving behaviour and habitat preferences of tope sharks using electronic tagging.FindingsFive female tope sharks, four adult and one sub-adult, were tagged with pop-up satellite archival tags in the Natural Reserve of Bahía San Blas, northern Patagonia, during spring 2011 and 2012. High-resolution archived data were collected for 40 days, including 29 days for two recovered tags. Sharks travelled up to 51.2 km after release. Archived data indicated that female tope sharks preferred to remain within 24.5 m of the surface and that there were no diel changes in preference. Individuals spent most of the time within 10 m of the surface during the day (80%) and at night (83%), and were primarily in water between 17°C and 19°C (day, 75%; night, 70%). Moreover, tope sharks exhibited vertical oscillatory movement (‘yo-yo diving’). Maximum vertical speeds and dive depths were recorded at night. Ascents from depth had a greater speed than descents, overall.ConclusionsFemale tope sharks were found in shallow coastal areas during November at Bahía San Blas, near the surface at relatively restricted depths and temperatures. Longer tracking periods will be important for describing the species’ migratory movements across the south-west Atlantic.

Modeling temporal phenomena in variable environments with parametric models: An application to migrating salmon

Timing phenomena are integral to many ecological processes but are difficult to analyze due to the unique nature of timing data and because environmental conditions and behavior can vary during the observation period. We demonstrated methods, based on parametric hazard-rate modeling, to analyze “time-to-event” data under time-varying conditions. We developed routines in R to apply parametric models, based on the exponential, Weibull, and modified Weibull distributions, to time-to-event data. We applied the models to data on the time for migrating adult salmonids to successfully pass a hydroelectric dam. The model captured pronounced diel behavior and the effects of time-varying covariates river flow, spill, and water temperature on passage times. The methods we demonstrated have potential application to a broad range of ecological questions.

Cyclical patterns in long-term bioacoustic data

Cyclical patterns in biological systems occur from small to large temporal scales, and these cycles are also reflected in acoustic data. To interpret long-term patterns appropriately, knowledge about natural cycles is crucial. We will show examples of diel, lunar, and seasonal patterns for a variety of species from invertebrates to vertebrates. The observed patterns are likely driven by intra-specific communication, or prey behavior and availability, which in turn can be related to large scale and long-term environmental modulation. Absence of acoustic signals does not necessarily indicate absence of the caller but the calling behavior may be limited to a certain time of the cycle period. In addition, various acoustical sources can complicate results. Patterns from abiotic and anthropogenic sources may mask or alter natural biological acoustic cycles. Animals moving just outside of an acoustic recorder’s detection range may lead to misinterpretation of diel behavior. Effects of multi-annual or multi-decad...

Effects of ice cover on the diel behaviour and ventilation rate of juvenile brown trout

Summary Winter ice conditions in boreal streams are highly variable, and behavioural responses by fish to river ice may affect overwinter survival rates. One type of ice, surface ice, stabilises water temperatures, reduces instream light levels and may provide overhead cover. Because surface ice is believed to afford protection against endothermic predators, we predicted that metabolic costs associated with vigilance would be lower under surface ice than in areas lacking surface ice. This potentially favourable effect of ice cover was tested by observing ventilation rates of juvenile brown trout (Salmo trutta) in a laboratory stream at dawn, during the day and at night in the presence and absence of real, light‐permeable surface ice. Further, we offered trout drifting prey during daylight to test whether ice cover increased daytime foraging activity. Ice cover reduced ventilation rates during the day, but not at night or dawn. Moreover, fish made more daytime foraging attempts in the presence of ice cover than in its absence. We suggest that the most plausible explanation for these results is that fish experience a reduced perceived predation risk under surface ice.

Home range and diel behavior of the ballan wrasse, Labrus bergylta, determined by acoustic telemetry

Effective fisheries management needs to consider spatial behavior in addition to more traditional aspects of population dynamics. Acoustic telemetry has been extensively used to provide information on fish movements over different temporal and spatial scales. Here, we used a fixed-receiver array to examine the movement patterns of Labrus bergylta Ascanius 1767, a species highly targeted by the artisanal fleet of Galicia, NW Spain. Data from 25 individuals was assessed for a period of 71days between September and November 2011 in the Galician Atlantic Islands Maritime-Terrestrial National Park. Fish were present within the monitored area more than 92% of the monitored time. The estimated size of individual home ranges, i.e. the area where fish spent most of their time, was small. The total minimum convex polygons area based on all the estimated positions was 0.133±0.072km2, whereas the home range size estimated using a 95% kernel distribution of the estimated positions was 0.091±0.031km2. The core area (50% kernel) was 0.019±0.006km2. L. bergylta exhibited different patterns of movement in the day versus the night, with 92% of the fish detected more frequently and traveling longer distances during the daytime. In addition, 76% of the fish displayed a larger home range during the day versus during the night. The linearity index was less than 0.005 for all fish suggesting random movements but within a relatively small area, and the volume of intersection index between consecutive daily home ranges was 0.75±0.13, suggesting high site fidelity. The small home range and the sedentary behavior of L. bergylta highlight the potential use of small MPAs as a management tool to ensure a sustainable fishery for this important species.

Fine scale diel movement of the east Pacific green turtle, Chelonia mydas, in a highly urbanized foraging environment

Protection of endangered species requires an understanding of their spatial ecology in relation to human activities. Recent improvements in monitoring technologies, such as automated acoustic telemetry, have enabled the collection of these data for mobile marine organisms such as sea turtles. The east Pacific green sea turtle Chelonia mydas uses San Diego Bay, CA, a heavily developed ecosystem, as a year-round foraging ground. We used a combination of manual and automated acoustic telemetry from 2009 to 2011 to elucidate the distribution of green turtles throughout South San Diego Bay and to understand their diel behavior. Tracked turtles (n=20) ranged in size from 54.9 to 102.5cm straight carapace length and had fidelity to two sites: the warm-water effluent channel of a waterfront power plant and an eelgrass meadow. Turtles tracked manually during the night were more sedentary (mean swimming speed±SE: 0.38±0.03kmh−1) and generally restricted their activity to waters near the power plant. During the day, turtles swam at higher speeds (0.67±0.07kmh−1) and were mainly found in eelgrass meadows where they are known to forage. Turtles were occasionally found near a shipping terminal, which occurred almost exclusively during the daytime. Turtles in areas of increased boat traffic are at risk of vessel strikes, and future monitoring should investigate the potential for turtle–human interactions in other heavily-used areas of San Diego Bay. Future monitoring should also characterize how turtle behavior may change following the decommissioning of the power plant, which occurred six months before the end of this study.

Diel behaviour and habitat utilisation by the pearly razorfish during the spawning season

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 460:207-220 (2012) - DOI: https://doi.org/10.3354/meps09755 Diel behaviour and habitat utilisation by the pearly razorfish during the spawning season J. Alós1,*, M. Cabanellas-Reboredo1, S. Lowerre-Barbieri2 1Instituto Mediterráneo de Estudios Avanzados (IMEDEA; CSIC-UIB), Miquel Marqués, 21, Esporles, Illes Balears 07008, Spain 2Florida Fish and Wildlife Conservation Commission, Fish and Wildlife Research Institute, St. Petersburg, Florida 33701, USA *Email: pep.alos@uib.es ABSTRACT: Despite its small size, the pearly razorfish Xyrichtys novacula (Linnaeus, 1758) supports important targeted recreational and commercial fisheries. Here, we present the first data on the movements of this species obtained using acoustic telemetry in a temperate marine protected area (MPA). The results demonstrate that acoustic telemetry is well suited for behavioural studies, even in species of small size. The results confirmed previous speculations regarding the behaviour of this species, demonstrating a clear diel pattern with maximum rates of activity during the day and fewer detections at night, when the fish bury themselves in the soft bottom. X. novacula exhibited a sedentary lifestyle with limited movement. The fish occurred in an accumulated averaged area of 0.32 ± 0.13 km2 95% of the time (95% kernel utilisation distribution [KUD]) and in a core area (50% KUD) of 0.07 ± 0.02 km2. These small areas of habitat utilisation existed independent of sex and diel behaviour. No daily migration pattern or specific resting locations were detected. The linearity index (as a proxy of site fidelity) demonstrated that the movement of X. novacula was random within a specific home range area (sedentary behaviour) rather than directional (nomadic behaviour). The observed diel pattern of behaviour confirms that this species is not vulnerable to nighttime fishing, and the small spatial scale of habitat utilisation suggests that small MPAs can be an effective management tool. KEY WORDS: Acoustic telemetry · Continuous wavelet transform · Control tag · Home range · MPA · Protogynous hermaphrodite · Xyrichtys novacula Full text in pdf format PreviousNextCite this article as: Alós J, Cabanellas-Reboredo M, Lowerre-Barbieri S (2012) Diel behaviour and habitat utilisation by the pearly razorfish during the spawning season. Mar Ecol Prog Ser 460:207-220. https://doi.org/10.3354/meps09755 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 460. Online publication date: July 24, 2012 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2012 Inter-Research.

Context-dependent diel behavior of upstream-migrating anadromous fishes

Variability is a hallmark of animal behavior and the degree of variability may fluctuate in response to environmental or biological gradients. For example, diel activity patterns during reproductive migrations often differ from those in non-breeding habitats, reflecting trade-offs among efficient route selection, reproductive phenology, and risk avoidance. In this study, we tested the hypothesis that diel movements of anadromous fishes differ among freshwater migration habitats. We analyzed diel movement data from ~13 000 radio-, PIT-, and acoustic-tagged adult fishes from five Columbia River species: Chinook salmon, Oncorhynchus tshawytscha; sockeye salmon, O. nerka; steelhead, O. mykiss; Pacific lamprey, Entosphenus tridentatus; and American shad, Alosa sapidissima. All five species were active during most of the diel cycle in low-gradient, less hydraulically complex reservoir and riverine habitats. Movement shifted to predominantly diurnal (salmonids and American shad) or nocturnal (Pacific lamprey) at hydroelectric dam fishways where hydraulic complexity and predator density were high. Results suggest that context-dependent behaviors are common during fish migrations, and that diel activity patterns vary with the degree of effort or predation risk required for movement.

Sprat feeding behaviour, selective predation, and impact on plaice egg mortality

Abstract Plirú, A., van der Kooij, J., Engelhard, G. H., Fox, C. J., Milligan, S. P., and Hunter, E. 2012. Sprat feeding behaviour, selective predation, and impact on plaice egg mortality. – ICES Journal of Marine Science, 69: 1019–1029. Although the causes of fish egg and larval mortality are poorly understood, predation is thought to be a major contributing factor. The feeding behaviour of sprat at a plaice spawning ground in the Irish Sea during February 2009 is described and their contribution to plaice egg mortality investigated. Acoustic observations and analysis of stomach contents revealed diel behaviour, with dense schools associated with feeding formed during daylight dispersing into thinly spread aggregations at dusk. Of 338 stomachs analysed, 95% contained identifiable prey items. Feeding activity peaked between 10:00 and 18:00, for all food groups. Numerically, gadoid eggs were the most frequently consumed prey (64%), followed by copepods (25%) and plaice eggs (7%). Plaice eggs were present in 91% of the stomachs analysed. Converting stomach content data to daily consumption suggested that sprat may consume 73% of all plaice eggs spawned in the area. Predation by sprat appears to account for a large proportion of plaice egg mortality, so the abundance and distribution of this pelagic predator may have important consequences for the recruitment dynamics of other fish species. Moreover, fish eggs may be an important energy source for sprat during late winter, when alternative prey is scarce.

Diel vertical migration and feeding of three species of chaetognaths (Flaccisagitta enflata, Aidanosagitta delicata and Aidanosagitta neglecta) in two shallow, subtropical bays in Hong Kong

The diel behavior and feeding ecology of three coexisting species of chaetognaths in two shallow subtropical bays in the northeastern part of Hong Kong were studied in summer 2005 and winter 2005–2006. Average densities of adult Flaccisagitta enflata, Aidanosagitta delicata and Aidanosagitta neglecta ranged from 21 to 48 ind. m in the semi-enclosed Tolo Harbour, but densities of the two Aidanosagitta species were low in Mirs Bay, which is deeper and opens into the South China Sea. Adult F. enflata, the largest of the three species, exhibited the most pronounced diel vertical migration (DVM) and diel feeding rhythm. The smaller juvenile F. enflata and adult A. delicata did not exhibit DVM. Although copepods were the most abundant component of the mesozooplankton, they were not preferred prey of chaetognaths. Predation impacts on copepods were generally ,0.3% of the standing stock. Larvaceans, on the other hand, were highly preferred, with predation impact as high as .30%. As prey abundances in Tolo Harbour could be .9 10 ind. m, there was no evidence of resource partitioning behavior by the coexisting chaetognaths.

Spatial and temporal patterns in the movement of adult two-banded sea bream Diplodus vulgaris (Saint-Hilaire, 1817)

The patterns of spatial and temporal activity during the spawning season for an important recreational and commercial target species from the Mediterranean Sea and mid-east Atlantic, Diplodus vulgaris, were investigated using acoustic telemetry. No diel behavior was found in the detection pattern and the probability of detecting any tagged fish was independent of time. Individual fish spent 95% of their time in an area smaller than 1 km 2. The asymptotic value of home range (HR) was observed a few days after fish were tagged and released. There was high overlap in the areas used during the day and night, and individuals exhibited high site fidelity. The movements of D. vulgaris during the spawning season resembled random movement within a specific HR area (sedentary behavior) rather than directional movement (nomadic behavior) and daily migrations were discarded. The results provided here are useful for management and suggest that small protected areas can offer a promising approach to the sustainable development of this fishery.

Beyond the average: Diverse individual migration patterns in a population of mesopelagic jellyfish

We examined the diel behavior among the jellyfish Periphylla periphylla in Lurefjorden, Norway in a sampling campaign and by a > 3‐month continuous acoustic study. Jellyfish distribution and behavior were recorded by an upward‐facing, bottom‐mounted echo sounder at 280‐m depth. The population was typically divided into four groups, each with different behavior. Individuals of behavioral Mode 1 undertook synchronous diel vertical migrations (DVM) within the upper 100 m. Individuals of behavioral Mode 2, stayed at ~ 160‐200‐m depth during the day, and also exhibited synchronized DVM, ascending at dusk and descending at dawn. The smaller individuals of behavioral Mode 3 swam continuously up and down throughout both day and night, yet occurred below Mode 2 individuals in daytime (~ 200 m‐bottom), while their vertical range encompassed the entire water column during night. Mode 4 behavior was displayed by large jellyfish located between ~ 130 m and the bottom. These animals shifted between remaining motionless and relocating in rapid steps during both day and night. These four main behavioral patterns persisted throughout the registration period, although the synchronously migrating Mode 2 behavior became weaker in spring. This acoustic study has unveiled more diverse migration behaviors than previously derived from net sampling and remote‐operated vehicles methods and emphasizes the importance of studying individuals. DVM is complex because individuals in a plankton population may simultaneously engage in a range of various contrasting behaviors.

Fine-scale differences in diel activity among nocturnal freshwater planarias (Platyhelminthes: Tricladida)

BackgroundAlthough most freshwater planarias are well known photonegative organisms, their diel rhythms have never been quantified. Differences in daily activity rhythms may be particularly important for temperate-climate, freshwater planarias, which tend to overlap considerably in spatial distribution and trophic requirements.MethodsActivity of stress-free, individually tested young adults of three common planarian species was recorded at 3-h intervals in a 10-d experiment under natural sunlight and photoperiod during autumnal equinox (D:L ~12:12). Individual activity status was averaged over the 10-d experiment, each tested individual thus serving as a true replicate. Twelve individuals per species were tested. Food was provided every 36 h, resulting in alternating day- and nighttime feeding events. Activity during the first post-feeding h was recorded and analyzed separately. Statistical procedures included ANOVAs, correlations, and second-order analyses of angles.ResultsDugesia (= Girardia) tigrina Girard 1850 exhibited clear nocturnal behavior, Dugesia (= Schmidtea) polychroa Schmidt 1861 was predominantly but not exclusively nocturnal, and Polycelis tenuis Ijima 1884 was relatively more active from midnight through noon. Species-specific activity peaks were statistically similar, with peaks at dawn for P. tenuis and just before midnight for the two dugesiids; however, D. tigrina was comparatively more active in the early night hours, while D. polychroa was more active than D. tigrina during daytime. D. tigrina also responded less readily to daytime food addition. P. tenuis remained poorly active and unresponsive throughout the experiment. Individual variability in diel behavior was highest for D. polychroa and lowest for D. tigrina. P. tenuis's general low degree of activity and late activity peak in the experiment may be related to a strong reliance on external stimuli.ConclusionsThe tested species are mainly nocturnal, consistent with their photonegative characteristics. The fine-scale differences in diel behavior among these three triclad species may not be sufficient to allow coexistence in the wild, with the nonnative D. tigrina eventually displacing D. polychroa and P. tenuis in many European waters. The link between planarian diel rhythms and ecological characteristics are worth of further, detailed investigation.

Diel Behavior of Rearing Fall Chinook Salmon

In fisheries science, habitat use is often inferred when fish are sampled or observed in a particular location. Physical habitat is typically measured where fish are found, and thus deemed important to habitat use. Although less common, a more informative approach is to measure or observe fish behavior within given habitats to more thoroughly assess their use of those locations. While this approach better reflects how fish use habitat, fish behavior can be difficult to quantify, particularly at night. For example, Tiffan and others (2002, 2006) were able to quantify habitat availability and characteristics that were important for rearing juvenile fall Chinook Salmon (Oncorhynchus tshawytscha) in the Hanford Reach of the Columbia River.

Characteristics of Marine Recreational Fishing in the anakkale Strait (Turkey)

The economic and harvest impacts of Marine Recreational Fishing (MRF) in Çanakkale Strait were analysed along with fishing policy, sociology and habits of fishers. Data sources included field survey data carried out along the entire length of the Çanakkale strait and policy information gathered from published sources. MRF policy is commendable, even in the fishing tourism sector, and is better developed than that in many other European countries. In Çanakkale, 9.9% of the population is recreational fishers. Recreational fishers are typically men (90%), primarily those between the ages of 25 and 49 yrs. The occupation of the recreational fishers ranged from self-employed (28%), students (28%), retired persons (22%) and public employees (15%), to currently-unemployed persons (7%). An analysis of diel behaviour showed that most recreational fishers preferred fishing during the day (56.1%), while the evening was the next most preferred time for fishing (18%), followed by the night-time (9.8%), while a substantial number of recreational fishers (16.1%) reported that they fished at any time of day. The most popular type of fishing was shore-based (68%), followed by boat-based (21%), and underwater fishing (11%). The mean daily fishing times were 6.07 h d-1, 6.18 h d-1 4.75 d-1 for boat-based, underwater and shore-based fishing, respectively. Summer and autumn were the preferred seasons for shore-based and underwater fishing, while autumn and winter were preferred for boat-based fishing. The highest Catch per Unit Effort (CPUE) was observed for boat-based fishing (2.77 kg h-1), followed by underwater (0.97 kg h-1) and shore-based fishing (0.81 kg h-1). The catch composition included 51 species, though the catch composition of each fishing type was mostly comprised of only 3 or 4 species. The impact of the MRF harvest was high (30% of commercial fishing), particularly for bluefish (Pomatomus saltatrix) and picarel (Spicara smaris) species. The economic impact of MRF was highly negative. Several indicators including the following revealed a high percentage of trading catch (47%) being conducted under the guise of a recreational label: annual fishing intensity, total costs, target species, and sales. At present, it is evident that the highly developed recreational fishing policy in Turkey is not sufficient to ensure that recreational fishing is sustainable or to prevent fishing conflicts in Turkey. This study revealed the need for establishing monitoring, control and surveillance programs to ensure the sustainability of fish resources and fisheries including MRF.

Evaluating migratory fish behaviour and fishway performance: testing a combined assessment methodology

To provide passage for migratory native fish, a series of 14 vertical-slot and lock fishways are being constructed on the Murray River in south-eastern Australia. Three of these vertical-slot fishways, at Locks 7, 9 and 10, have a conservative slope (1V : 32H) and are designed with internal hydraulics suitable for the passage of a broad size range of fish (30–1000 mm long). An assessment of these fishways was performed using a combined trapping survey and passive integrated transponder (PIT) approach to determine fishway effectiveness at passing an entire fish community. Fish were trapped within the three fishways between 2004 and 2006, where a total of 13 626 individuals comprising 13 species were collected from 48 sample days (24 h each). Trapping data revealed that the three fishways successfully passed fish within the target size range, though significantly greater numbers of individuals smaller (10–29 mm long) than the target size range could not ascend. PIT tagging revealed important information on fishway ascent times, descent times, seasonality and diel behaviour of medium and large fish. Although each method alone had advantages and disadvantages, the dual assessment approach was useful as it permitted an assessment of fishway success and also provided insights into migratory fish behaviour.

Satellite tagging of blue sharks (Prionace glauca) and other pelagic sharks off eastern Australia: depth behaviour, temperature experience and movements

Satellite telemetry was used to study the movements and behaviour of ten blue sharks and one individual each of shortfin mako, thresher and bigeye thresher off eastern Australia. The tracks showed latitudinal movements of up to 1,900 km, but none of the sharks travelled away from the eastern Australian region. Tracking periods did not exceed 177 days. All species showed oscillatory dive behaviour between the surface layers to as deep as 560–1,000 m. Blue sharks spent 35–58% of their time in 300 m. Of these four species, the bigeye thresher spent the least time in the surface layers and the most time at >300 m depth. All four species showed clear diel behaviour generally occupying shallower depths at night than during the day. Blue sharks were mainly in 17.5–20.0°C water, while the thresher sharks showed a more bimodal temperature distribution.

Diel behavior of sardine and anchovy schools in the California Current System

Diel behavior of sardine and anchovy schools in the California Current System

Seasonal variation in diel behaviour and habitat use by age 1+ Steelhead (Oncorhynchus mykiss) in Coast and Cascade Range streams in Oregon, U.S.A.

The seasonal diel behaviour of age 1+ steelhead from Coast and Cascade Range streams in Oregon was examined in the field and in laboratory streams. During the summer, fish from both areas were active during the day in natural streams: they held position in the water column in moderate velocities and depths. At night, fish were in slower water, closer to the bottom above smaller substrates. In winter, diel behaviour differed between the two groups. Coastal fish exhibited behaviour similar to that observed in the summer. Cascade Range fish were not observed during the day, but were found at night, holding positions close to the bottom in slower water. In laboratory streams, fish from both regions were subjected to a decreasing temperature regime from 16°C to 2°C. Use of cover for concealment during the day was negatively correlated with water temperatures for both groups. However, the shelter-seeking response to declining water temperatures was significantly greater for Cascade fish than it was for coastal fish. Field and laboratory observations of diel behaviour support the hypothesis that steelhead from the two geographic regions have different adaptive strategies for winter conditions and that these differences, because they persisted even in laboratory conditions, are probably genetically based.

Diel behavior of stable isotopes of dissolved oxygen and dissolved inorganic carbon in rivers over a range of trophic conditions, and in a mesocosm experiment

Rates of diel (24-h) biogeochemical processes in rivers and their effect on daily changes in the concentration of metals and metalloids have been well documented in the literature over the last 20 years. Investigations into the effects of these processes on aquatic systems and the underlying mechanisms that control the processes can significantly improve our understanding of how natural aquatic environments function and will respond to changing environmental conditions and anthropogenic impacts. Daily changes in the rates of biogeochemical processes have, more recently, been shown to influence the stable isotope composition of dissolved oxygen and dissolved inorganic carbon in natural waters. Here we present a comprehensive picture of the persistence and reproducibility of diel cycles of the 18O composition of dissolved molecular oxygen ( δ 18O-DO) and the 13C composition of dissolved inorganic carbon ( δ 13C-DIC) across five Montana, USA rivers investigated over a 4-year period. A mesocosm experiment showed the same behavior in δ 18O-DO and δ 13C-DIC as seen in riverine settings across light and dark periods. A cross plot of δ 18O-DO and δ 13C-DIC from each stream exhibits a clockwise elliptical pattern which is attributed to the daily changes in the balance of metabolic rates as well as air–water gas exchange. The amplitude of the change in the isotope composition is shown to be directly related to the trophic state of the river and a relationship between net productivity and diel changes in δ 18O-DO and δ 13C-DIC is presented. This relationship between trophic status with δ 18O-DO, δ 13C-DIC and production emphasizes the significance of how rates of biogeochemical processes in natural systems can influence the daily changes in the composition of surface waters.