Foraging mode variation in three stream‐dwelling salmonid fishes

Despite long‐standing interest in foraging modes as an important element of animal space use, few studies document and compare individual foraging mode differences among species and ecological conditions in the wild. We observed and compared foraging modes of 61 wild Arctic charr, Salvelinus alpinus, 42 brown trout, Salmo trutta, and 50 Atlantic salmon, Salmo salar, in their first growing season over a range of habitats in 10 Icelandic streams. We found that although stream salmonids typically sit‐and‐wait to ambush prey from short distances, Arctic charr were more mobile during prey search and prior to prey attack than Atlantic salmon, whereas brown trout were intermediate. In all three species, individuals that were mobile during search were more likely to be moving when initiating attacks on prey, although the strength and the slope of this relationship differed among species. Arctic charr also differed from salmon and trout as more mobile individuals travelled longer distances during prey pursuits. Finally, coupled with published data from the literature, salmonid foraging mobility (both during search and prior to attack) clearly decreased from still water habitats (e.g., brook charr), to slow‐running waters (e.g., Arctic charr) to fast‐running waters (e.g., Atlantic salmon). Hence, our study suggests that foraging mode of young salmonids can vary distinctly among related species and furthers our understanding of the behavioural mechanisms shaping the geographical distribution of wild salmonids.     

Perceptual constraints on stream fish habitat selection: effects of food availability and water velocity

Abstract– Habitat selection theory assumes that individuals either know the quality of habitats a priori or can learn it through experience. This work tests the effects of total food supply and of water velocity on the ability of drift-feeding stream fish ( Rhinicthys atratulus ) to discriminate between two patches in a laboratory flow-tank that differ only in the amount of food in the patch. If the fish can discriminate between the patches, their distributions should be predicted by ideal free distribution models; otherwise, their distributions should be random. The results show that at high total food supply levels, fish distributions differ from random in general agreement with ideal free distribution models; total food supply decreases, fish distributions become random, indicating that total food supply levels affect the ability of fish to discriminate between habitats that differ only in food supply. Increased water velocity was expected to affect fish distributions similarly, but its effect was not significant. The results suggest that habitat selection theory should consider both differences between habitats and the ability of fish to perceive those differences.     

Assemblage structure and habitat use of fishes in a Central European submontane stream: a patch-based approach

Abstract –  We examined macrohabitat patch level assemblage composition and habitat use patterns of fishes over four seasons in a second-order submontane stream (Danube drainage, Hungary). Rainfall data indicated that our study included both high- and low-water periods, and hence our results may be applicable to broader time scales. Principal component analysis of physical habitat data from 13 macrohabitat patches indicated that these patches represented a riffle-pool continuum. Correspondence analysis of fish assemblage structure data from these patches identified a continuum in assemblage composition that was positively correlated with the habitat continuum. The riffle fauna was dominated by stone loach ( Barbatula barbatula ), whereas chub ( Leuciscus cephalus ) were most abundant in pool patches. We detected little evidence of seasonality in either fish assemblage structure or habitat use. Fish density did not differ significantly among macrohabitat patches in two (summer and autumn 1999) of three seasonal samples, although riffle patches displayed significantly higher fish abundance in late spring 2000. This difference primarily was due to higher abundance of juvenile stone loach in riffles. Two species, stone loach and minnow ( Phoxinus phoxinus ), displayed generalized habitat use patterns, whereas chub and rare species (i.e., gudgeon, Gobio gobio ; dace, Leuciscus leuciscus ; Barbus petenyi ; and burbot, Lota lota ) were significantly over-represented in pool habitats. We hypothesized that pool specialists (i.e., chub and rare species) were responding primarily to the increased depth of these habitats. Nevertheless, our data did not demonstrate the presence of separate pool and riffle habitat guilds. In conclusion, we believe that our understanding of stream fish ecology will be greatly facilitated by use of a 'patch-based approach'.     

Effects of within-patch habitat structure and variation on fish assemblage characteristics in the Bernecei stream, Hungary

Abstract –  Over a 3-year period we examined variability in physical habitat structure and species richness, abundance and assemblage composition of fishes in 13 habitat patches in the Bernecei stream, Hungary. Principal component analysis of habitat structure data from patches elucidated a riffle-run-pool habitat gradient across patches. Temporal habitat variability increased significantly from riffle to pool patches. Fish assemblage characteristics displayed relatively continuous change over the habitat gradient and were relatively stable within patches. Assemblage structure properties (e.g., species richness) displayed different responses to the habitat gradient and to within-patch habitat variability. In general, pool patches had more diverse assemblages and greater within-patch assemblage variability than riffle patches. However, within-patch dynamics were largely determined by the population dynamics of a habitat generalist (i.e., minnow). Broad scale environmental variability (i.e., a catastrophic 100-year flood) also appeared to affect within-patch fish assemblage characteristics. Our results demonstrate that fish assemblage structure is influenced by physical variability (i.e., both floods and spatio-temporal habitat variability) within the Bernecei stream.     

Effects of littoral habitat complexity and sunfish composition on fish production

Carey MP, Maloney KO, Chipps SR, Wahl DH. Effects of littoral habitat complexity and sunfish composition on fish production. Ecology of Freshwater Fish 2010: 19: 466–476. © 2010 John Wiley & Sons A/S Abstract – Habitat complexity is a key driver of food web dynamics because physical structure dictates resource availability to a community. Changes in fish diversity can also alter trophic interactions and energy pathways in food webs. Few studies have examined the direct, indirect, and interactive effects of biodiversity and habitat complexity on fish production. We explored the effects of habitat complexity (simulated vegetation), sunfish diversity (intra‐ vs. inter‐specific sunfish), and their interaction using a mesocosm experiment. Total fish production was examined across two levels of habitat complexity (low: 161 strands m^?2 and high: 714 strands m^?2) and two sunfish diversity treatments: bluegill only (Lepomis macrochirus) and bluegill, redear sunfish (Lepomis microlophus), and green sunfish (Lepomis cyanellus) combination. We also measured changes in total phosphorus, phytoplankton, periphyton, and invertebrates to explain patterns in fish production. Bluegill and total fish production were unaffected by the sunfish treatments. Habitat complexity had a large influence on food web structure by shifting primary productivity from pelagic to a more littoral pathway in the high habitat treatments. Periphyton was higher with dense vegetation, leading to reductions in total phosphorus, phytoplankton, cladoceran abundance and fish biomass. In tanks with low vegetation, bluegill exhibited increased growth. Habitat complexity can alter energy flow through food webs ultimately influencing higher trophic levels. The lack of an effect of sunfish diversity on fish production does not imply that conserving biodiversity is unimportant; rather, we suggest that understanding the context in which biodiversity is important to food web dynamics is critical to conservation planning.     

Growth and mortality of prairie stream fishes: relations with fish community and instream habitat characteristics

Abstract – Few studies have been conducted to describe the age structure, growth rates and mortality of fishes in small stream ecosystems. The purpose of this study was therefore to determine age structure, growth rates and mortality (i.e., total annual mortality and, age-specific mortality) of central stonerollers Campostoma anomalum , creek chubs Semotilus atromaculatus , red shiners Cyprinella lutrensis and green sunfish Lepomis cyanellus from 13 streams on Fort Riley Military Reservation, Kansas, using incremental growth analysis. Further, we were interested in determining the influence of fish community and instream habitat characteristics on growth rates. The age structure of central stonerollers, creek chubs, and red shiners was dominated by young individuals (i.e., less than age 2); however, over 60% of the green sunfish were age 2 to age 4. Mean total annual mortality was >60% for cyprinids and averaged approximately 44% for green sunfish. The age-specific mortality of central stonerollers and red shiners was generally less than 45% between age 0 and 1 and increased to over 85% for fishes greater than age 1. Fish community characteristics (e.g., catch per unit effort of trophic guilds) and chemical habitat (e.g., total phosphorous) were not related to growth rates ( P >0.05). Growth of central stonerollers was not significantly correlated with physical habitat ( P >0.05). However, the growth increments of creek chubs, red shiners, and green sunfish were related to the amount of woody debris (e.g., total woody debris, log complex habitat; r >0.60; P ≤0.05). The results of this study provide important information on the population dynamic rate functions of cyprinid and green sunfish populations in small prairie streams. Furthermore, these data suggest that woody debris is important habitat influencing growth of stream fishes. ^Note     

Effect of predation and habitat quality on growth and reproduction of a stream fish

Billman EJ, Tjarks BJ, Belk MC. Effect of predation and habitat quality on growth and reproduction of a stream fish.
Ecology of Freshwater Fish 2011: 20: 102–113. © 2010 John Wiley & Sons A/S Abstract – Anthropogenic disturbances are rarely independent, requiring native fishes to respond to multiple factors to persist in changing environments. We examined the interaction of predation environment (presence of introduced brown trout, Salmo trutta) and habitat quality on growth and reproduction of southern leatherside chub, Lepidomeda aliciae, a small‐bodied stream fish native to central Utah, USA. Southern leatherside chub were sampled from four streams representing a complete two‐factor cross of predation environment and habitat quality. Growth was estimated using increment analysis of annuli on otoliths, and reproductive traits were measured for both sexes. Southern leatherside chub growth was greater in high‐quality than in low‐quality habitats, and greater in predator than in nonpredator environments. However, fish exhibited a greater growth response to presence of brown trout in low‐quality habitats. Southern leatherside chub growth followed predictions of plastic responses to resource availability based on habitat quality and predation environment (lethal vs. nonlethal effects). Reproductive allocation (gonad wet mass) was significantly greater in low‐quality versus high‐quality habitats, but was unaffected by predation environment. Other female life‐history traits were affected either by both effects or their interaction. Reproductive responses to habitat quality and predation environment were consistent with predictions based on differential mortality. Southern leatherside chub growth and reproduction responded differently to the combination of habitat quality and predation environment, thus demonstrating the importance of assessing interacting effects of anthropogenic disturbances to more fully comprehend impacts on native species and to appropriately manage, recover and restore these species and their habitats.     

Cohort‐specific variation in juvenile coho salmon habitat use

In this study, we examined summer and fall freshwater rearing habitat use by juvenile coho salmon (Oncorhynchus kisutch) in the quickly urbanising Big Lake drainage in south‐central Alaska. Habitat use was assessed by regressing fish count data against habitat survey information across thirty study sites using generalised linear mixed models. Habitat associations were examined by age‐0 and age‐1+ cohorts separately, providing an opportunity to compare habitat use across different juvenile coho salmon life stages during freshwater rearing. Regression results indicated that the age‐0 cohorts were strongly associated with shallow, wide stream reaches with in‐stream vegetation, whereas age‐1+ cohorts were associated with deeper stream reaches. Furthermore, associations between fork length and habitat characteristics suggest cohort‐specific habitat use patterns are distinct from those attributable to fish size. Habitat use information generated from this study is being used to guide optimal fish passage restoration planning in the Big Lake drainage. Evidence for habitat use partitioning by age cohort during freshwater juvenile rearing indicates that pooling age cohorts into a single “juvenile” stage for the purposes of watershed management may mask important habitat use dynamics.     

Evaluating habitat associations of a fish assemblage at multiple spatial scales in a minimally disturbed stream using low‐cost remote sensing

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Effects of off‐bottom shellfish aquaculture on winter habitat use by molluscivorous sea ducks

• 1. Shellfish farming is an expanding segment of marine aquaculture, but environmental effects of this industry are only beginning to be considered.
• 2. The interaction between off‐bottom, suspended oyster farming and wintering sea ducks in coastal British Columbia was studied. Specifically, the habitat use of surf scoters (Melanitta perspicillata) and Barrow's goldeneyes (Bucephala islandica), the most abundant sea duck species in the study area, was evaluated in relation to natural environmental attributes and shellfish aquaculture.
• 3. The extent of shellfish farming was the best‐supported habitat variable explaining variation in surf scoter densities, and the only habitat attribute from the considered set that was a strong predictor of Barrow's goldeneye densities. In both cases, the findings indicated strong positive relationships between densities of sea ducks and shellfish aquaculture operations. These relationships are presumably the result of large numbers of wild mussels (Mytilus trossulus) that settle and grow on aquaculture structures and are preferred prey of these sea ducks.
• 4. Previous work has shown that aquaculture structures provide good conditions for recruiting and growing mussels, including refuge from invertebrate predators, which in turn provides higher densities of higher quality prey for sea ducks than available in intertidal areas. This offers a rare example in which introduction of an industry leads to positive effects on wildlife populations, which is particularly important given persistent declines in numbers of many sea ducks.

Copyright © 2008 John Wiley & Sons, Ltd.     

The effects of wood on stream habitat and native fish assemblages in New Zealand

Historic deforestation has deprived many river systems of their natural wood loadings. To study the effects of the loss of wood from waterways, a field trial was conducted in three small forested streams in New Zealand. The objectives were to (i) examine differences in fish assemblages among wooded pools (where wood provided cover), open pools and riffles and (ii) measure the effects of wood removal on channel morphology and fish assemblages. In the first part of the study, no significant differences were found in total fish density among the three habitats. However, total fish biomass was significantly higher in wooded pools (64% of total fish biomass) compared with open pools and riffles. Mean density and biomass of banded kokopu (Galaxias fasciatus) and mean biomass of longfin eel (Anguilla dieffenbachii) were highest in wooded pools, whereas the density and biomass of bluegill bully (Gobiomorphus hubbsi) and torrentfish (Cheimarrichthys fosteri) were highest in riffles. In the second part of the study, wood was removed from a 200‐m section (treatment) in each stream, significantly reducing pool area and increasing the proportion of channel area and length in riffles. At the habitat scale, banded kokopu and large longfin eel were the two species mostly affected by wood removal. At the reach scale, banded kokopu biomass was significantly lower in the treatment sections. Although wooded pools were a small portion of total habitat, they provided important habitat for two of New Zealand's larger native fish taxa.     

The complementary role of lentic and lotic habitats for Arctic grayling in a complex stream‐lake network in Arctic Alaska

Lakes can be important to stream dwelling fishes, yet how individuals exploit habitat heterogeneity across complex stream‐lake networks is poorly understood. Furthermore, despite growing awareness that intermittent streams are widely used by fish, studies documenting the use of seasonally accessible lakes remain scarce. We studied Arctic grayling (Thymallus arcticus) in a small seasonally flowing (June–October) stream‐lake network in Alaska using PIT telemetry. Overall, 70% of fish visited two lakes, 8% used a single lake, and 22% used only stream reaches. We identified five distinct behavioural patterns that differed in dominant macrohabitat used (deep lake, shallow lake or stream reaches), entry day into the network and mobility. Some juvenile fish spent the entire summer in a shallow seasonally frozen lake (average 71 days), whereas others demonstrated prospecting behaviour and only entered the stream channel briefly in September. Another group included adult and juvenile fish that were highly mobile, moving up to 27 km while in the 3‐km stream‐lake network, and used stream reaches extensively (average 59 days). Lentic and lotic habitats served differing roles for individuals, some fish occupied stream reaches as summer foraging habitat, and other individuals used them as migration corridors to access lakes. Our study emphasises the importance of considering stream‐lake connectivity in stream fish assessments, even to shallow seasonally frozen habitats not widely recognised as important. Furthermore, we demonstrate that individuals may use temporary aquatic habitats in complex and changing ways across ontogeny that are not captured by typical classifications of fish movement behaviour.     

Spatial arrangement and physical characteristics of structural woody habitat in a lowland river in south‐eastern Australia

• 1. The importance of structural woody habitat (SWH) as instream fish habitat in eastern Australia has been well documented. In response, many native fish restoration programmes are returning SWH to rivers where it had previously been removed. However, there is little information to direct the placement of this SWH within a river landscape.
• 2. Low‐level, high‐resolution aerial photographs were used to investigate the spatial pattern of SWH in the Murray River between Lake Mulwala and Tocumwal. It was found that SWH occurred in aggregations that were closely associated with eroding banks on meanders.
• 3. The physical characteristics of the SWH in these aggregations varied (basal diameter range 0.44–2.45 m, length range 1–44 m); however, small‐ to medium‐sized trees (basal diameter range 0.7–1.4 m, length range 5–20 m) were most common.
• 4. The association between eroding banks and SWH suggests that bank erosion may be an important determinant in the formation of SWH aggregations.

Copyright © 2004 John Wiley & Sons, Ltd.     

Seasonal variation in habitat use by salmon, Salmo salar, trout, Salmo trutta and grayling, Thymallus thymallus, in a chalk stream

Abstract A portable multi‐point decoder system deployed in a tributary of the River Itchen, a southern English chalk stream, recorded the habitats used by PIT‐tagged juvenile salmon, Salmo salar L., trout, Salmo trutta L. and grayling, Thymallus thymallus L., with a high degree of spatial and temporal resolution. The fishes’ use of habitat was monitored at 350 locations throughout the stream during September/October 2001 (feeding period) and January/February 2002 (over‐wintering period). Salmon parr tended to occupy water 25–55 cm deep with a velocity between 0.4 and 1.0 m s^?1. During both autumn and winter, first year salmon (0+ group) were associated with gravel substrate during the daytime and aquatic weed at night. In autumn, 1+ salmon were strongly associated with hard mud substrates during the day and with marginal tree roots at night. In winter, they were located on gravel substrate by day and gravel and mud at night. Trout were associated with a greater range of habitats than salmon, generally occupying deeper and faster water with increasing age. During the autumn, 0+ trout were located along shallow (5–10 cm) and slow (?0.1–0.4 m s^?1) margins of the stream, amongst tree roots by day and on silty substrates at night. During winter the 0+ trout occupied silty substrates at all times. As age increased, trout increasingly used coarse substrates; hard mud, gravel and chalk, and weed at night. All age groups of grayling (0+, 1+ and 2+) tended to occupy hard gravel substrate at all times and used deeper and faster water with increasing age. The 1+ and 2+ groups were generally found in water 40–70 cm deep with a velocity between 0.3 and 0.5 ms^?1, whilst the 0+ groups showed a preference for shallower water with reduced velocity at night, particularly in the winter. There were greater differences in the habitats used between species and age groups than between the autumn and winter periods, and the distribution of fish was more strongly influenced by substrate type than water depth or velocity. The results are discussed in relation to the habitat requirements of mixed salmonid populations and habitat management.     

Physical habitat utilization of fish in a Sonoran Desert stream, Arizona, southwestern United States

Abstract– The physical habitat utilization of 7 species of native fishes in a Sonoran Desert stream, Aravaipa Creek, Arizona is described. The species occupied significantly different depths and velocities of water. Longfin dace ( Agosia chrysogaster ), speckled dace ( Rhinichthys osculus ) and loach minnow ( Tiaroga cobitis ) used similar depths and velocities. Two of the three larger species (Sonora sucker [ Catostomus insignis ] and roundtail chub [ Gila robusta ]) used areas of greater depth and reduced velocity. Desert sucker ( Catostomus clarki ) grouped with loach minnow and speckled dace in the velocity of water occupied, but utilized deeper waters. The spikedace ( Meda fulgida ) aligned very closely with desert sucker in use of all 3 physical habitat variables.     

Potential impacts of climate change on growth and prey consumption of stream‐dwelling smallmouth bass in the central United States

Smallmouth bass (Micropterus dolomieu, SMB) is a broadly distributed, economically important species in the USA and Canada. Although previous research has suggested that projected climate warming may allow SMB to thrive beyond their current northern distribution, little research has been devoted to the population‐level effects of climate change on warm‐water fishes, including SMB. We modelled the impacts of projected climate change on growth of stream‐dwelling SMB along a north–south gradient in the central USA. Using downscaled regional projections from three global climate models, we generated scenarios for thermal habitat change for four populations (in Oklahoma, Missouri, Iowa and Minnesota) and used bioenergetics simulations to estimate prey consumption and growth under future projections. Bioenergetics simulations showed that prey consumption is expected to increase in all populations with moderate stream warming (2–3 °C). Growth potential is predicted to increase by 3–17% if not limited by food availability with stream warming by 2060 and was most pronounced for southern populations. For each 1 °C increase in stream temperature, SMB consumption would be expected to increase by about 27% and growth would increase by about 6%. Due to implications for species interactions, population performance and regulation of local fisheries, a better understanding of how SMB populations will respond to climate change is recommended for effective management and conservation.     

Habitat use by Thymallus thymallus in a chalk stream and implications for habitat management

Abstract Results of a number of studies on the interactions between grayling, Thymallus thymallus L., and its habitat in tributaries of the River Itchen, a chalk stream in Hampshire, southern England are reported. These include an investigation into the effect of riparian shading on T. thymallus growth and population density in relation to the development of in‐stream macrophyte cover, and the use of a multi‐point decoder system to record micro‐habitat use and preference of individual T. thymallus. In all stream sections, T. thymallus recruitment fluctuated greatly. Densities were generally low often restricting meaningful comparisons. However, where large differences occurred, wooded sections, with less aquatic macrophyte cover, generally had higher densities of T. thymallus. All age groups of T. thymallus (0+, 1+ and 2+) tended to occupy hard gravel substratum, both by day and by night in the autumn and winter, and used deeper and faster water with increasing age. The 1+ and 2+ groups were generally found in water 40–70‐cm deep with a velocity between 0.3 and 0.5 m s^?1, whilst the 0+ group showed a preference for shallower water with reduced velocity at night, particularly in the winter. The results are discussed in relation to habitat management where T. thymallus occur with other salmonids.     

Size influences the spatial distribution and fish‐aggregating device use of five Mediterranean fish species

Abstract Fish‐aggregating devices are floating objects used worldwide to improve pelagic fishery yield. Fish‐aggregating devices use the natural attraction exerted by floating objects on juveniles and adults of both pelagic and demersal fish. In this study, it was hypothesised that fish change their degree and type of interaction with moored floating objects depending on size. This is because fishes in early life stage remain close to floating objects, using them as a shelter, but as they grow they move further away from floating objects spending their time swimming to seek food. To test this hypothesis, the spatial distribution and habitat use of five Mediterranean fish species were quantified. The results enabled the hypothesis to be accepted for all species, except Balistes carolinensis Gmelin. For this species, a shelter from predator model was applicable, but for the other species, the generalised meeting point model was more adaptable.     

Fish use of ecohydraulic‐based mesohabitat units in a low‐gradient Illinois stream: implications for stream restoration

• 1. A classification scheme for ecohydraulic‐based mesohabitat units was developed for a summer low‐flow period. Mesohabitat unit designations were based on the integration of three‐dimensional channel hydraulics, geomorphic maintenance processes of bed morphology, and biological resource needs of fish. Ecological relevance of the units was evaluated by a study of fish mesohabitat use patterns, and species relationships to feeding guild. By portraying the stream as a mosaic of hydraulic habitat patches that provide specific biotic resource needs, this study's aim was to advance how ecological information may be incorporated into the stream restoration design process.
• 2. Nine mesohabitat units were designated, including pool‐front, ‐mid, and ‐rear units, scour pool, simple and complex riffles, glide, submerged point bar, and channel expansion marginal deadwater. Physical habitat structure differed among the nine mesohabitat units by length, water depth, and bed slope and complexity. Fish were collected in specific unit volumes by use of prepositioned areal electrofishing devices, in which distinct patterns of fish mesohabitat use were observed.
• 3. A key finding was the differences in fish assemblages among the pool units, in which fish densities were greatest in the pool‐front and scour pool units. Also, fish density in the pool‐front unit was positively correlated with pool entrance slope. Biomass was greatest in the pool‐front and ‐mid units, and it was correlated with maximum mid‐pool depth. Density and biomass were generally lowest in the pool‐rear unit. Other unique relationships were also observed among the mesohabitat units.
• 4. Based on feeding guild, patterns of fish mesohabitat use were observed for this summer low‐flow period; insectivores dominantly used pool‐front and scour pool units, herbivores dominantly used complex riffle units, and piscivores used pool‐front and ‐mid units.
• 5. Useful ecological information was derived from fish species‐habitat relationships observed in this study, linking mesohabitat units with species requirements for food resources. Such findings support advancements to ecological design strategies for stream restoration that promote hydraulic habitat diversity.

Copyright © 2008 John Wiley & Sons, Ltd.     

The potential of flat-bed passive integrated transponder antennae for studying habitat use by stream fishes

Abstract – Describing habitat use by stream fishes is important from both basic ecological and fisheries management points of view. The most widely used methods of measuring habitat use vary in degree of effort required, level of intrusiveness and in the level of spatial and temporal resolution. In this paper, we describe a remote monitoring technique that can provide detailed and continuous data on habitat use of individual fish in the field. The technique is based on the passive integrated transponder (PIT) system, in which a newly developed flat-bed antenna is placed on the stream bottom and simply requires a PIT-tagged fish to swim over it. We present data obtained from work using this new technology on brown trout ( Salmo trutta ) in stream enclosures, in which we describe habitat use and temporal patterns of movement by individuals and relate such data to growth rate and sex of the individual fish as well as to pool depth and time of day. In addition, we describe the range of applications of the flat-bed PIT-antenna as well as the advantages and disadvantages of using the system. ^NOTE