Direct Underwater Observation Research Articles

Habitat Suitability Criteria for Fishes of the South Fork of the Shenandoah River and an Investigation into Observer Effects Associated with Two Techniques of Direct Underwater Observation

Habitat Suitability Criteria for Fishes of the South Fork of the Shenandoah River and an Investigation into Observer Effects Associated with Two Techniques of Direct Underwater Observation

Mesohabitat use by brown trout (Salmo trutta) in a small groundwater‐dominated stream

ABSTRACTGroundwater‐dominated streams have particular flow regimes that commonly support populations of trout. Meso‐ and micro‐habitat surveys were carried out on a reach of the river Tern that drains a Triassic sandstone aquifer in the English West Midlands, to investigate brown trout (Salmo trutta) habitat use with varying flows. Mesohabitats were mapped over a range of summer and autumn flows and coupled with direct underwater observation (snorkelling) of fish locations together with point measurements of velocity and depth. The number of habitat types recorded was low and dominated by glides, runs, and backwaters. Brown trout showed a strong association with glides and runs with adults being more associated with runs and parr with glides. General habitat use curves showed brown trout to favour depths between 0.30 and 0.40 m and velocities below 0.40 m s−1. A clear preference was shown for sand and gravel bed materials. However, the differentiation of hydraulic habitats was weak and there was no trend in mesohabitats or change in trout use of mesohabitats with discharge. The study raises limitations of the mesohabitat survey approach when linking fish ecology, flow and physical habitat in small streams with low flow variability and low habitat diversity. In these situations, other factors (especially cover features) appear to strongly influence brown trout distribution. Copyright © 2010 John Wiley & Sons, Ltd.

First record of the silver porgy ( Diplodus argenteus) cleaning green turtles ( Chelonia mydas) in the south-west Atlantic

The silver porgy (Diplodus argenteus) of the Sparidae is an occasional cleaner of two species of fish in the south-west Atlantic (Sazima, 1986; Krajewski, 2007). In a recent overview of fish that clean sea turtles (Sazima et al., 2010), 18 reef fish species in seven families are recorded as cleaners/grazers of epibionts of three turtle species of the Cheloniidae. Nine of these fish species (50%) are recorded for the south-west Atlantic (Sazima et al., 2010). The only sparid recorded associated with sea turtles is the sheepshead bream (Diplodus puntazzo), cleaning the loggerhead turtle (Caretta caretta) in the Mediterranean Sea off Greece (Schofield et al., 2006). We record herein for the first time a sparid (Diplodus argenteus) associating with green turtles (Chelonia mydas) and cleaning their carapaces in the south-west Atlantic. Field work was conducted at the rocky shores of Arvoredo Island (about 27817′S 48818′W), off Santa Catarina, southern Brazil. From 2004 to 2008, 334 SCUBA and snorkelling dives (227 hours) at depths 0.5–17 m were conducted in bays of Arvoredo Island, totaling 23 hours of direct underwater observation of turtle behaviour. Ad libitum and ‘behaviour’ samplings (Martin & Bateson, 1986) of general behaviours of focal animals were recorded in sessions that lasted 1–30 minutes. When a cleaning behaviour was sighted, both the turtle and the fish had their sizes estimated (curved carapace length (CCL) and total length (TL), respectively). One cleaned turtle was caught after a cleaning session to collect a sample of epibionts from the spot where the fish were feeding. Only immature individuals of the green turtle were recorded at the shores of Arvoredo Island, which seem to present a degree of residency at this protected area (Reisser et al., 2008). Silver porgy (Diplodus argenteus) juveniles 3–4 cm TL were observed repeatedly biting at the carapaces of green turtles (Chelonia mydas) 30–60 cm CCL on five occasions. One to two juvenile fish individuals feeding on the same turtle were recorded (Figure 1). The cleaned turtle was either swimming slowly in the water column (N 1⁄4 2) or hovering while feeding on red algae (Pterocladiella capillacea) belts on rocky reefs (N 1⁄4 3). The epibionts scraped from the green turtle were mostly Cyanobacteria (blue green ‘algae’) of the Chroococalles, both colonial (63.1%) and unicellular (27.6%), and Oscillatoriales including Lyngbya sp. (4.6%). Chlorophyta (green algae) comprised 3.7%, and the remaining microorganisms found on the carapace were Bacillariophyta (diatoms, 0.7%), and Ciliophora, Vorticellidae (ciliates, 0.2%). Juvenile porgies are omnivores that feed on benthic invertebrates, seaweeds, and zooplankton (Sazima, 1986; Carvalho-Filho, 1999), and most likely benthic microorganisms and epibionts such as those listed above are part of the diet of the small juveniles we recorded cleaning green turtles. Our findings are consistent with a study of the diet of the silver porgy in the same general area we conducted our observations (Dubiaski-Silva & Masunari, 2004). Juvenile silver porgies are able to change their cleaning stations while servicing fish (Krajewski, 2007), which is consistent with our observations of sea turtle cleaning. Our records, although admittedly few (N 1⁄4 5) demonstrate that juvenile porgies are able to move along with slowly swimming turtles, and that they join green turtles at their feeding grounds. Reef fish cleaning sea turtles has been claimed to be a localized phenomenon, restricted to particular populations and/or individuals (Losey et al., 1994). However, data from literature and the present study indicate that reef fish that graze on, clean, or use sea turtles as feeding grounds otherwise, are more common than the available records would indicate (Sazima et al., 2010). Corresponding author: I. Sazima Email: isazima@gmail.com

Redd Site Microhabitat Utilization and Quantitative Models for Wild Large Brown Trout in Three Contrasting Boreal Rivers

AbstractRiverine spawning areas are important but restricted source habitats for large brown trout Salmo trutta (≥40 cm total length). In hydrophysically different reaches within three contrasting boreal rivers, redds larger than 100 cm in length were located by direct underwater observation in 1998 and 2001 (n = 157 redds; range = 10–60 redds per reach and year) and were characterized based on 29 habitat variables. The microhabitat of utilized redd sites (total redd length: mean ± SD = 206 ± 83 cm, range = 100–615 cm) was typified by a mean total water depth of 103 ± 39 cm with a wide optimum (range = 23–215 cm) and a mean water velocity of 47 ± 32 cm/s (range = 2–124 cm/s). Mean velocity measured at 5 cm above the substrate was 29 ± 20 cm/s (range = 0–82 cm/s). Mean substrate particle size was 7 ± 6 cm and demonstrated a narrower optimum (range = 2–37 cm) than the other variables. Substantial differences among the three rivers, particularly in water depth and velocity measures, largely reflected size and gradient differences and indicated some flexibility in spawning microhabitat utilization. The use of substrate particle size was less variable. Multivariable analysis indicated that water velocity (except velocity measured just above the substrate) and water depth explained most of the variation. Depths and substrates utilized were larger than previously reported, probably reflecting the in situ habitat availability in the relatively large study rivers.

Summer stream habitat partitioning by sympatric Arctic charr, Atlantic salmon and brown trout in two sub‐arctic rivers

Summer habitat use by sympatric Arctic charr Salvelinus alpinus, young Atlantic salmon Salmo salar and brown trout Salmo trutta was studied by two methods, direct underwater observation and electrofishing, across a range of habitats in two sub‐arctic rivers. More Arctic charr and fewer Atlantic salmon parr were observed by electrofishing in comparison to direct underwater observation, perhaps suggesting a more cryptic behaviour by Arctic charr. The three species segregated in habitat use. Arctic charr, as found by direct underwater observation, most frequently used slow (mean ±s.d. water velocity 7·2 ± 16·6 cm s−1) or often stillwater and deep habitats (mean ±s.d. depth 170·1 ± 72·1 cm). The most frequently used mesohabitat type was a pool. Young Atlantic salmon favoured the faster flowing areas (mean ±s.d. water velocity 44·0 ± 16·8 cm s−1 and depth 57·1 ± 19·0 cm), while brown trout occupied intermediate habitats (mean ±s.d. water velocity 33·1 ± 18·6 cm s−1 and depth 50·2 ± 18·0 cm). Niche overlap was considerable. The Arctic charr observed were on average larger (total length) than Atlantic salmon and brown trout (mean ±s.d. 21·9 ± 8·0, 10·2 ± 3·1 and 13·4 ± 4·5 cm). Similar habitat segregation between Atlantic salmon and brown trout was found by electrofishing, but more fishes were observed in shallower habitats. Electrofishing suggested that Arctic charr occupied habitats similar to brown trout. These results, however, are biased because electrofishing was inefficient in the slow‐deep habitat favoured by Arctic charr. Habitat use changed between day and night in a similar way for all three species. At night, fishes held positions closer to the bottom than in the day and were more often observed in shallower stream areas mostly with lower water velocities and finer substrata. The observed habitat segregation is probably the result of interference competition, but the influence of innate selective differences needs more study.

Diel Habitat Use by Fishes in a Blue Ridge Stream, Georgia

ABSTRACT We determined diel habitat use by fishes in a Blue Ridge stream in Georgia using direct underwater observation on two occasions in September 1999. During both day and night sampling periods, individuals in the family Centrarchidae were most commonly found in shallow (< 20 cm depth) and deep (>= 20 cm depth) areas with low water velocities (< 10 cm·s−1 average velocity). During the day, representatives of Cyprinidae were most common in deep areas with higher water velocities (> 10 cm·s−1 average velocity) but shifted to shallow areas with low water velocities during the night. Differences in diel habitat use by the two families are best explained by differences in predator avoidance strategies.

Effect of aquatic mosses on juvenile fish density and habitat use in the regulated River Suldalslågen, western Norway

AbstractTwo morphologically distinct moss communities were found in the River Suldalslågen. The liver moss community consists of species which form a dense mat on the bottom, while the river moss (Fontinalis) community forms long tufts. Moss growth has increased since hydropower regulations due to reduced floods and increased winter flows. Increased moss cover affects the bottom structure, as well as intra‐gravel and near‐bottom hydraulics. We studied densities of juvenile Atlantic salmon (Salmo salar) and brown trout (Salmo trutta) by electrofishing and habitat selection by direct underwater observation, in areas with natural moss cover compared with areas where mosses were experimentally removed. Areas with dense mats of liver mosses held lower densities of young of year (YoY) and older salmon parr than areas where liver moss had been removed. No differences in densities of YoY salmon were found between areas with and without Fontinalis. For older salmon, parr results were inconclusive. In some samples more and in others fewer fish were found in areas with Fontinalis moss removed. For trout, densities were higher in areas with Fontinalis, while results for liver moss were inconclusive. No major differences were found with regard to microhabitat selection between areas with and without river moss, suggesting that habitat quality in these areas was similar during summer, except with respect to substrate. Salmon held more exposed positions in areas without liver moss, but this is mainly attributed to different habitat availabilities. It is concluded that the relative increase in liver mosses in the River Suldalslågen has a negative impact on juvenile Atlantic salmon fish density. Copyright © 2002 John Wiley &amp; Sons, Ltd.

Static habitat partitioning and dynamic selection by sympatric young Atlantic salmon and brown trout in south-west England streams

Direct underwater observation of micro-habitat use by 1838 young Atlantic salmon Salmo salar [mean LT 7·9 ± 3.1(s.d.) cm, range 3·19] and 1227 brown trout Salmo trutta (LT 10·9 ± 5·0 cm, range 3·56) showed both species were selective in habitat use, with differences between species and fish size. Atlantic salmon and brown trout selected relatively narrow ranges for the two micro-habitat variables snout water velocity and height above bottom, but with differences between size-classes. The smaller fishes <7 cm held positions in slower water closer to the bottom. On a larger scale, the Atlantic salmon more often used shallower stream areas, compared with brown trout. The larger parr preferred the deeper stream areas. Atlantic salmon used higher and slightly more variable mean water velocities than brown trout. Substrata used by the two species were similar. Finer substrata, although variable, were selected at the snout position, and differences were pronounced between size-classes. On a meso-habitat scale, brown trout were more frequently observed in slow pool-glide habitats, while young Atlantic salmon favoured the faster high-gradient meso-habitats. Small juveniles <7 cm of both species were observed most frequently in riffle-chute habitats. Atlantic salmon and brown trout segregated with respect to use of habitat, but considerable niche overlap between species indicated competitive interactions. In particular, for small fishes <7 cm of the two species, there was almost complete niche overlap for use of water depth, while they segregated with respect to water velocity. Habitat suitability indices developed for both species for mean water velocity and water depth, tended to have their optimum at lower values compared with previous studies in larger streams, with Atlantic salmon parr in the small streams occupying the same habitat as favoured by brown trout in larger streams. The data indicate both species may be flexible in their habitat selection depending on habitat availability. Species-specific habitat overlap between streams may be complete. However, between-species habitat partitioning remains similar.

Static habitat partitioning and dynamic selection by sympatric young Atlantic salmon and brown trout in south‐west England streams

Direct underwater observation of micro‐habitat use by 1838 young Atlantic salmon Salmo salar [mean LT 7·9 ± 3.1(s.d.) cm, range 3·19] and 1227 brown trout Salmo trutta (LT 10·9 ± 5·0 cm, range 3·56) showed both species were selective in habitat use, with differences between species and fish size. Atlantic salmon and brown trout selected relatively narrow ranges for the two micro‐habitat variables snout water velocity and height above bottom, but with differences between size‐classes. The smaller fishes &lt;7 cm held positions in slower water closer to the bottom. On a larger scale, the Atlantic salmon more often used shallower stream areas, compared with brown trout. The larger parr preferred the deeper stream areas. Atlantic salmon used higher and slightly more variable mean water velocities than brown trout. Substrata used by the two species were similar. Finer substrata, although variable, were selected at the snout position, and differences were pronounced between size‐classes. On a meso‐habitat scale, brown trout were more frequently observed in slow pool‐glide habitats, while young Atlantic salmon favoured the faster high‐gradient meso‐habitats. Small juveniles &lt;7 cm of both species were observed most frequently in riffle‐chute habitats. Atlantic salmon and brown trout segregated with respect to use of habitat, but considerable niche overlap between species indicated competitive interactions. In particular, for small fishes &lt;7 cm of the two species, there was almost complete niche overlap for use of water depth, while they segregated with respect to water velocity. Habitat suitability indices developed for both species for mean water velocity and water depth, tended to have their optimum at lower values compared with previous studies in larger streams, with Atlantic salmon parr in the small streams occupying the same habitat as favoured by brown trout in larger streams. The data indicate both species may be flexible in their habitat selection depending on habitat availability. Species‐specific habitat overlap between streams may be complete. However, between‐species habitat partitioning remains similar.

Contrasting temperatures, waterflows, and light: seasonal habitat selection by young Atlantic salmon and brown trout in a boreonemoral river

AbstractHabitat use and habitat selection by young Atlantic salmon and brown trout were investigated by direct underwater observation. We sampled during winter and summer water temperatures (low: 3–7°C; high: 9–12°C) coinciding with low and high waterflows (12–20 and 60–80 m3s−1), and during day and night in winter, and on six selected stations in the river. Observations of 396 salmon and 120 trout indicated a distinct seasonal pattern in behaviours and habitat selection. Feeding was the dominant behaviour at high water temperatures during summer. In winter, there was a diurnal pattern in behaviour; both species sheltered in interstitial spaces in the substrate during daylight, but during night held positions on or close to the substrate in slower flowing stream areas. Coarse substrate providing cover was therefore an important habitat factor during daylight at low water temperatures, while slow‐flowing water was important during night. Although spatial niche overlap was considerable both in summer and winter, salmon and trout segregated with respect to meso‐ and microhabitat selection, and relatively more at low temperatures. Both species changed their use of mesohabitats towards more slow‐flowing glide/flat habitats in winter. Irrespective of season, trout preferred in general more slow‐flowing water than salmon did, but the difference was more pronounced in winter. Salmon used a wider range of water depths and in particular water velocities, than did trout. Both species were less tolerant of high water velocities at low water temperatures. The seasonal and diurnal pattern in habitat selection reported have important implications for habitat research and habitat‐hydraulic modelling. Copyright © 2001 John Wiley &amp; Sons, Ltd.

Evidence of Differential Detectability of Lotic Adult Rainbow and Brown Trout: Implications for Habitat Use Inference from Direct-Underwater Observation

ABSTRACT The number of observations of brown trout Salmo trutta was significantly lower than expected based on the ratio of estimated densities of brown trout and rainbow trout Oncorhynchus mykiss and the number of tagged rainbow trout and brown trout in a Sierra Nevada river. We believe that behavioral differences as well as abundant cover composed of large substrate in the study area were major factors contributing to the lack of brown trout observations relative to observations of rainbow trout. These results should be considered by managers and researchers who collect habitat use data for brown trout with direct-underwater observation because that data could be considerably biased.

Marine geophysical methods for archaeological investigation of volcanic and bradyseismic areas

The aim of this work was to test several geophysical methods for the identification and study of submerged prehistorical coastlines and archaeological sites. This research program was carried out in collaboration with the &lt;&lt;Osservatorio Vesuviano&gt;&gt; in the Gulf of Pozzuoli and dealt in particular with the bathymetric strips extending from - 5 m to - 50 m Within these strips we identified the coastline dating from the Rornan period. former beach boundaries associated with the vertical movements of the earth's surface caused by seismic-volcanic activity, and the variations in sea level following the climactic changes throughout the last 15000 years. The UNIBOOM system was used for this part of the programme, perinittiilg the identification of several coastlines and submerged beaches lying at different levels. The use of a modern Side Scan Sonar - for the morphological invesdgation of the sea bed - in a zone which had been the object of numerous archaeological surveys in the past, permitted previously unknown structures near the Lacuus Baianus to be identified. Other features worth pointing out include the operating speed of the system (15000 m'lfirst minute approx) and its observation capacity in cloudy waters compared to visible radiation, as well as its ability to penetrate thin layers of mud which generally impede direct underwater observation.

Homeostatic Behavioural Responses in a Changing Environment: Brown Trout (Salmo trutta) become Nocturnal during Winter

Behaviour and microhabitat selection by brown trout in two streams presenting severe winter conditions, were investigated in south-central Norway. Fish were studied by direct underwater observation in different habitat types, during day and night, and with simultaneous sampling for dietary analysis and invertebrate drift. During the day in winter, brown trout exhibited two different behavioural strategies, depending on fish size. Smaller fish (<25 cm) sheltered passively in the substrate or in submerged vegetation, and were almost never active during daylight hours. This behaviour was consistent throughout the winter until water temperatures rose in spring. Larger trout (25-60 cm) were actively aggregating in deep-slow stream areas during the day. During the night the trout exhibited a third behavioural strategy. The trout were active throughout the night from dusk to dawn, and this behaviour was consistent throughout the winter

Short-Term Seasonal Changes in Composition and Abundance of Fish in Sagehen Creek, California

Abstract Direct underwater observation was used to quantify numbers and locations of eight species of fish in 100-m sections along a 1,200-m reach of Sagehen Creek, California, at biweekly intervals between 5 July and 22 September 1983. Most of the eight species exhibited significant short-term changes in abundance and reached peak abundance at different times. Total fish abundance was highest in mid-July; the Margalefindex ofdiversity was highest in mid-August. Lahontan redside Richardsonius egregius, Tahoe sucker Catostomus tahoensis, and mountain sucker C. platyrhynchus appeared to migrate from a downstream reservoir into the stream during the spawning season. In addition, fish were not distributed evenly in the study reach. All species tended to prefer pool habitat and pools were not uniformly distributed. Relative fish composition determined at long-term permanent sections by electrofishing was not significantly associated with most underwater counts made at different times or stations. This study il...

Near-bottom copepod aggregations around the nursery ground of the juvenile red sea bream in Shijiki Bay.

Near-bottom copepod aggregations were investigated in Shijiki Bay by means of stomach content analysis of juvenile red sea bream, near-bottom towing of plankton nets and direct under-water observation with the aid of scuba-equipment. The stomach contents of 220 red sea bream juveniles, 12.7 to 43.7mm in FL, were examined. Nearly 80% of the total food items consisted of copepods, 97% of which were pelagic species. The overwhelming majority of them were Acartia omorii and A. steueri. The near-bottom towing of plankton nets revealed a landward increase in the abundance of pelagic copepods. Two types of near-bottom aggregations were recognized by scuba-diving; a flat carpet-like type with thickness of about 30cm, and a discrete ball-like swarming type with a long axis of about 50cm. The former appeared to be formed by A. omorii and the latter by A. steueri. The maximum density found was 326 per liter far A. omorii and 511 for A. steueri, these being 100 times greater than the background density. The three approaches used in the present study clearly demonstrated the existence of near-bottom aggregations of Acartia omorii and A. steueri; the former rather widely distributed, whereas the latter is restricted to the innermost area shallower than 15m. These two species each shows a distinct macro- and microdistribution pattern which results in a high degree of habitat segrega-tion.

Observations sur le comportement d'alevins de saumon (Salmo salar L.) après leur déversement en rivière

Over two summers we used direct underwater observation to determine the principal causes for the predation of newly planted Atlantic salmon f ries (Salmo salar) by brook trout (Salvelinus fontinalis). Bad conditions affecting the transportation of the salmon from the hatchery to the planting sites and an inadequate planting method could be considered responsible for most of the predation by the brook trout. This predation could be prevented by allowing the fries a recuperation period and by scattering them in habitats possessing suitable carrying capacity.

Changes in the Selection of Microhabitat by Juvenile Atlantic Salmon (Salmo salar) at the Summer–Autumn Transition in a Small River

Over three summers we used direct underwater observation to examine the summer to autumn differences in seven microhabitat properties of three age-classes of juvenile Atlantic salmon (Salmo salar) in the Little Sevogle River of northeastern New Brunswick. Salmon of all three age-classes occupied a wide range of water depths during summer, but were concentrated mainly in depths of 24–36 cm. In autumn, they occurred in this range almost exclusively. The streambed stones most closely associated with the individual positions of all ages were always &lt;20 cm in summer and mostly (84–92%) &lt;10 cm in diameter. In autumn, all ages were associated with home stones up to 40 cm in diameter, with 65–83% of the stones exceeding 20 cm; the size of home stones selected increased with fish age in autumn. There was no apparent relationship between the water depth and home stone size distributions occupied by all age-classes and available in the stream during either summer or autumn. Summer focal water velocity (velocity at the fish's snout) was predominantly 10–30 cm∙s−1 for 0+, 10–40 cm∙s−1 for 1+, and 30–50 cm∙s−1 for 2+ salmon, but during autumn it was almost always &lt;10 cm∙s−1 for all ages. The bottom and surface water velocities as well as the maximum water velocity within 1 m of fish stations increased with fish age during summer and autumn. At the summer–autumn transition, 0+ salmon selected higher bottom, surface, and maximum water velocities, 2+ salmon selected lower velocities, but selection by 1+ salmon remained unchanged. We view substrate size followed by water depth as the primary properties influencing stream suitability for juvenile Atlantic salmon in autumn.