Cobble Substrate Research Articles

Habitat characteristics of crayfish (Paranephrops planifrons) in New Zealand streams using generalised additive models (GAMs)

Quantitative data on the habitat characteristics of stream crayfish have been generally lacking and competing demands on water resources has created a need to address this knowledge gap. We investigated day-time habitat relationships of stream crayfish (Paranephrops planifrons White) from 793 quadrats at 30 rivers and streams in the North Island, New Zealand to develop models of koura presence–absence and abundance. The model (stepwise GAM) included width, cover, median substrate size, edge location, velocity and depth, and correctly predicted presence–absence of crayfish (8–39 mm OCL) at 73.4% of quadrats and of young-of-the-year (YOY) ≤8 mm OCL at 83.4% of quadrats. Streams ranged from 1.6 to 11.5 m in width and the probability of finding both crayfish size classes reduced sharply as streams became wider than 6 m and as the substrate became large (i.e., boulder > 256 mm). Crayfish, particularly YOY, were most likely to be found in association with cover and at the stream edge. YOY were associated with shallow depths and fine substrates, whereas larger crayfish showed a preference for cobble substrate. Undercut banks, leaf litter, tree roots, and woody debris were strongly related to the presence–absence of crayfish. The model for crayfish abundance (log-linear Poisson GAM) explained 50% of the variation between quadrats with cover, velocity, edge location, depth, and the overall crayfish abundance at each particular stream being significant variables. Highest crayfish numbers were recorded in still or slow flowing water, with the majority occurring where velocities were below 0.4 m/s. Water depths up to 0.7 m were sampled, but highest numbers were found in depths of 0.2–0.3 m. Our presence–absence model determined variables that were significant over all streams, whereas our abundance model determined variables that were significant within streams. Use of the GAMs models enabled us to untangle the multiple factors contributing to habitat selection. Cover, velocity, and locations at the stream edge were important determinants of both presence–absence and abundance. Generally, substrate was important when comparing between streams, but not within streams, whereas depth was a significant determinant of abundance within streams, but not presence–absence between streams.

Intertidal sand body migration along a megatidal coast, Kachemak Bay, Alaska

Using a digital video‐based Argus Beach Monitoring System (ABMS) on the north shore of Kachemak Bay in south central Alaska, we document the timing and magnitude of alongshore migration of intertidal sand bed forms over a cobble substrate during a 22‐month observation period. Two separate sediment packages (sand bodies) of 1–2 m amplitude and ∼200 m wavelength, consisting of well‐sorted sand, were observed to travel along shore at annually averaged rates of 278 m/yr (0.76 m/d) and 250 m/yr (0.68 m/d), respectively. Strong seasonality in migration rates was shown by the contrast of rapid winter and slow summer transport. Though set in a megatidal environment, data indicate that sand body migration is driven by eastward propagating wind waves as opposed to net westward directed tidal currents. Greatest weekly averaged rates of movement, exceeding 6 m/d, coincided with wave heights exceeding 2 m suggesting a correlation of wave height and sand body migration. Because Kachemak Bay is partially enclosed, waves responsible for sediment entrainment and transport are locally generated by winds that blow across lower Cook Inlet from the southwest, the direction of greatest fetch. Our estimates of sand body migration translate to a littoral transport rate between 4,400–6,300 m3/yr. Assuming an enclosed littoral cell, minimal riverine sediment contributions, and a sea cliff sedimentary fraction of 0.05, we estimate long‐term local sea cliff retreat rates of 9–14 cm/yr. Applying a numerical model of wave energy dissipation to the temporally variable beach morphology suggests that sand bodies are responsible for enhancing wave energy dissipation by ∼13% offering protection from sea cliff retreat.

Refuge‐use strategies of stream fishes in response to extreme low flows

Low flows were simulated in an artificial stream to determine the refuge‐use strategies of two benthic New Zealand fish species, Canterbury galaxias Galaxias vulgaris and upland bullies Gobiomorphus breviceps, and to investigate how refuge availability and the rate of flow recession affect the type and incidence of refuge use. When riffles dewatered, upland bullies tended to move to runs, whereas Canterbury galaxias showed a stronger propensity to burrow into the substratum. Both species showed a strong and consistent tendency to move upstream when emigrating from riffles. Burrowing was more frequent on coarse substrata and during rapid flow recessions. The incidence of surface stranding increased with the rate of flow recession, but only when interstitial refugia were unavailable, and was higher on gravel than on cobble substrata. The effect of rate of flow recession and substratum size on the probability of stranding depended upon the type of refuge‐use strategy adopted by the fishes. Rate of flow recession affected upland bullies more than Canterbury galaxias, whereas substratum size affected Canterbury galaxias more than upland bullies. These results suggest that the impact of disturbance is contingent upon species‐specific refuge‐use strategies, which result from interplay between refuge availability, the nature of the disturbance and species’ behaviours and morphologies. When component species adopt contrasting refuge‐use strategies, disturbance events may not consistently favour one species over another but rather inflict species‐specific mortality that varies both temporally and spatially.

Effects of beach erosion on abundance and distribution of toheroa (Paphies ventricosa) at Bluecliffs Beach, Southland, New Zealand

Data on abundance, distribution, and size structure of toheroa (Paphies ventricosa) on Bluecliffs Beach, Southland, New Zealand from 42 surveys (1966 to 2005) are presented. Toheroa abundance declined from over 2 million adults in the mid 1960s to c. 80000 by 1990 and since then has remained low but relatively stable. The decline mirrors that of other toheroa populations throughout New Zealand. Recent recruitment was highly variable but low compared with historical levels in the 1960s. Length frequency distributions are characteristically bimodal with a strong adult mode and a juvenile mode of variable strength, with relatively few toheroa of intermediate size. The distribution is related to mortality and growth characteristics of Bluecliffs Beach toheroa. Spatial distribution of adult toheroa has progressively changed over the last 40 years—historical distribution included the entire beach and toheroa were most dense just east of the Rowallan Burn. Since 1997, they have been aggregated into one large bed just west of the Rowallan Burn. Toheroa showed intertidal size zonation with small juveniles near high water and larger toheroa near mid to low water. Beach profile surveys were carried out in 1997, 2001, and 2005 to assess the dynamics of beach geomorphology and erosion. The surveys indicated a net loss of sand from the beach between 1997 and 2005, exposing underlying gravel and cobble substrates, and a general erosion of the vegetated dunes. Aerial photos from 1947 reveal that Bluecliffs Beach was homogeneous sand substrate—significant erosion and loss of sand began in the mid 1980s and only c. 54% of the beach surface is now fine/coarse sand. Our results indicate that distribution and abundance of toheroa on Bluecliffs Beach is related to the amount and distribution of sand on the beach. If the erosion continues with loss of sand habitat, the toheroa population may be at risk of collapsing.

Priority habitats for the conservation of large river fish in the Ganges river basin

Abstract Three classes of habitat used by groups of fish species classified as conservation and management priorities were developed for the Gerua River (also known as the Girwa River, Karnali River) in the Ganges river basin. This river is large (mean annual discharge ca 1500 m3 s−1, up to 900 m wide), surrounded by protected lands of India and Nepal, and upstream of major diversions and river alterations. Fish and habitat sampling was conducted at 45 sites from 2000 to 2003. Data were analysed for 2172 fish of 14 species. Species and life stages found occupying a statistically distinct subset of the river habitats were grouped to identify classes of river habitat for conservation. Most species and life‐stage groups specialized on specific habitat conditions revealed by multivariate analyses of variance and a principal component analysis. The most numerous and diverse group (six species, 15 life stages) was associated with deep depositional habitats with sandy substrate. Two species covering three life stages were primarily oriented to erosional habitat marked by fast current velocity with pebble and cobble substrate. A third group of three species of adults and juveniles were intermediate in habitat use. River conservation for fish faunas should maintain both erosional and depositional channel habitats with depths, substrates, and current velocity inclusive of the ranges reported. The erosional and depositional nature of the key habitats requires that rivers be maintained with flows capable of channel‐forming functions. Copyright © 2006 John Wiley & Sons, Ltd.

Variables Influencing the Presence of Subyearling Fall Chinook Salmon in Shoreline Habitats of the Hanford Reach, Columbia River

AbstractLittle information currently exists on habitat use by subyearling fall Chinook salmon Oncorhynchus tshawytscha rearing in large, main‐stem habitats. We collected habitat use information on subyearlings in the Hanford Reach of the Columbia River during May 1994 and April–May 1995 using point abundance electrofishing. We analyzed measures of physical habitat using logistic regression to predict fish presence and absence in shoreline habitats. The difference between water temperature at the point of sampling and in the main river channel was the most important variable for predicting the presence and absence of subyearlings. Mean water velocities of 45 cm/s or less and habitats with low lateral bank slopes were also associated with a greater likelihood of subyearling presence. Intermediate‐sized gravel and cobble substrates were significant predictors of fish presence, but small (<32‐mm) and boulder‐sized (>256‐mm) substrates were not. Our rearing model was accurate at predicting fish presence and absence using jackknifing (80% correct) and classification of observations from an independent data set (76% correct). The habitat requirements of fall Chinook salmon in the Hanford Reach are similar to those reported for juvenile Chinook salmon in smaller systems but are met in functionally different ways in a large river.

Benthic Metabolism as an Indicator of Stream Ecosystem Health

We tested direct and indirect measures of benthic metabolism as indicators of stream ecosystem health across a known agricultural land-use disturbance gradient in southeast Queensland, Australia. Gross primary production (GPP) and respiration (R-24) in benthic chambers in cobble and sediment habitats, algal biomass (as chlorophyll a) from cobbles and sediment cores, algal biomass accrual on artificial substrates and stable carbon isotope ratios of aquatic plants and benthic sediments were measured at 53 stream sites, ranging from undisturbed subtropical rainforest to catchments where improved pasture and intensive cropping are major land-uses. Rates of benthic GPP and R-24 varied by more than two orders of magnitude across the study gradient. Generalised linear regression modelling explained 80% or more of the variation in these two indicators when sediment and cobble substrate dominated sites were considered separately, and both catchment and reach scale descriptors of the disturbance gradient were important in explaining this variation. Model fits were poor for net daily benthic metabolism (NDM) and production to respiration ratio (P/R). Algal biomass accrual on artificial substrate and stable carbon isotope ratios of aquatic plants and benthic sediment were the best of the indirect indicators, with regression model R-2 values of 50% or greater. Model fits were poor for algal biomass on natural substrates for cobble sites and all sites. None of these indirect measures of benthic metabolism was a good surrogate for measured GPP. Direct measures of benthic metabolism, GPP and R-24, and several indirect measures were good indicators of stream ecosystem health and are recommended in assessing process-related responses to riparian and catchment land use change and the success of ecosystem rehabilitation actions.

Secondary production and trophic basis of sinopotamon teritisum in Heizhuchong Stream, Hanjiang Catchment

Macrozoobenthos community plays an important role in material cycle and energy flow in riverine ecosystem. During the period of June, 2003 to June 2004, an investigation on the life cycle and production of the dominant species of macrozoobenthos community in a second-order river of Hanjiang River Basin was carried out. From the upper to the lower reach of Heizhuchong stream, we chose six types of habitats to collect quantitative samples. Station 1 (S1) lied in the middle of the stream with big round rocks in the upper reach, station 2 (S2) was in the inner part of a weir with cobble substratum, station 3 (S3) in the middle of a peacefully flowing section with gravel-sand bottom, station 4 (S4) at the side of the riparian with aquatic macrophytes and snags, station 5 (S5) in the middle of the riffle, station 6 (S6) at the lower reach with a sewage outlet ca 100 meters uppstream. At each station, four quantitative samples were taken with a 167μm D-frame kick net or a Surber net, and the samples were sieved with a 167μm net, sorted in a porcelain dish with naked eye. The specimens were kept in 10% formalin for later processing. The life cycle of the S. teritisum Dai et al. population was analysed by the monthly size-class frequency distribution, the cohort and annual production were estimated by size frequency method. The results showed that S. teritisum completed one generation for nearly 4 years, the reproduction mainly occurred in from middle August to middle October, and most of the senescent individuals died in February. The abundance of the population varied greatly during the year, probably due to the relatively smaller sampling area compared with the strong activity of motion of S. teritisum. Whereas, the variation of the biomass followed the same pattern of the abundance. The a-bundance attained its peak in September with 35 ind/m2, and biomass reached its highest level in June at 41. 7 g/ m2. The estimated cohort production and cohort P/B ratio by size-frequency method were 605.2g/(m2·a) (wet wt) and 5. 5, respectively; the annual production and P/B ratio were 151. 3g/(m2·a) ( wet wt) and 1.4. The reason why the annual production of the animal in Heizhuchong Stream was the relatively higher was because of its high density. By analyzing its stomach content, the proportions of amorphous detritus, caridina, aquatic insect larvae, gastropods and vascular tissues were 45.4% , 10.9% , 35.6% , 5.7% , 8. 1% . Therefore, the contribution rates of the above types of food to production were 10.84% , 18.21% , 59.49% , 9.52% , and 1.94% , respectively.

Ecology of the Jollyville Plateau Salamander (Eurycea tonkawae: Plethodontidae) with an Assessment of the Potential Effects of Urbanization

The Jollyville Plateau salamander, Eurycea tonkawae Chippindale, Price, Wiens, and Hillis, inhabits springs and wet caves of the Jollyville segment of the Edwards Plateau, Texas. The known range of this species is limited to six stream drainages, and most known localities are at risk of impairment from urban development. Our purpose was to gather needed autecological information on E. tonkawae and evaluate factors that may affect the distribution and abundance of the species. We conducted visual salamander surveys at nine stream sites across the Jollyville Plateau between December 1996 and December 1998. The survey sites were classified as undeveloped or developed based on watershed impervious cover estimates. We characterized the habitat for each site, including substrate type, discharge, and water quality. Salamander counts varied seasonally, but generally were higher during spring and summer. Salamander densities across sites were positively correlated with rubble and cobble substrate density as preferred cover, and negatively correlated with the standard deviation of water temperature, as expected for a spring-adapted species. In addition, we found that mean salamander densities at sites occurring in undeveloped watersheds were significantly higher than at developed sites, where specific conductance of the water was higher. The results of this study suggest that while habitat and seasonal factors influence surface salamander densities, E. tonkawae populations may be most vulnerable to effects associated with urbanization.

Seasonal Movement and Habitat Use by Subadult Bull Trout in the Upper Flathead River System, Montana

AbstractDespite the importance of large‐scale habitat connectivity to the threatened bull trout Salvelinus confluentus, little is known about the life history characteristics and processes influencing natural dispersal of migratory populations. We used radiotelemetry to investigate the seasonal movements and habitat use by subadult bull trout (i.e., fish that emigrated from natal streams to the river system) tracked for varying durations from 1999 to 2002 in the upper Flathead River system in northwestern Montana. Telemetry data revealed migratory (N = 32 fish) and nonmigratory (N = 35 fish) behavior, indicating variable movement patterns in the subadult phase of bull trout life history. Most migrating subadults (84%) made rapid or incremental downriver movements (mean distance, 33 km; range, 6–129 km) to lower portions of the river system and to Flathead Lake during high spring flows and as temperatures declined in the fall and winter. Bull trout subadults used complex daytime habitat throughout the upper river system, including deep runs that contained unembedded boulder and cobble substrates, pools with large woody debris, and deep lake‐influenced areas of the lower river system. Our results elucidate the importance of maintaining natural connections and a diversity of complex habitats over a large spatial scale to conserve the full expression of life history traits and processes influencing the natural dispersal of bull trout populations. Managers should seek to restore and enhance critical river corridor habitat and remove migration barriers, where possible, for recovery and management programs.

Size‐dependent microhabitat use and intraspecific competition in Cottus gobio

An electrofishing survey of daytime shelter microhabitat use of bullhead Cottus gobio in a southern English chalk stream revealed positive selection for moderate water velocity, vegetation cover and coarse substrata. Water depth, other forms of cover, shade and substratum embeddedness had no significant influence on the distribution of fish. Microhabitat use was size‐dependent, with patches occupied by adult fish containing coarser substrata and less blanket weed (Cladophora algae) than those occupied by smaller juvenile conspecifics. Differences in substratum use between size‐classes were less pronounced in parts of the stream shaded by the tree canopy. In laboratory tanks stocked at low fish density, both juveniles and adults favoured use of cobbles over pebbles. The response of fish to increased conspecific density was size‐dependent; juveniles reduced use of the coarse substratum whereas adults maintained their predominance in this habitat. An apparently greater shift by juveniles when in the presence of adults was significant at α = 0·10 only, as was an apparent reduction in interactions between size‐classes under low light intensity. The displacement of small juvenile fish from the preferred cobble substratum is consistent with the hypothesis that intraspecific competition contributes to the size‐related microhabitat shift observed in the field. Although there was a tendency for the strength of competition to be reduced at low light levels, the mechanism by which tree canopy cover affects microhabitat use remains uncertain.

Spawning ecology of the American brook lamprey, Lampetra appendix

We observed spawning American brook lamprey, Lampetra appendix, in coldwater streams in Minnesota to assess various aspects of their spawning behavior and spawning habitat requirements. Spawning occurred during April and May, at water temperatures ranging from 8.7 to 15.5°C. Average adult lamprey length and mass differed significantly among streams, but there were no significant differences in length or mass between males and females. Overall sex ratio was 1:1, although one stream had significantly more males than females and one stream held significantly more females. Lampreys spawned in groups of 2–14 individuals, averaging 4.2 adults per nest across all streams. Nests were constructed in gravel and cobble substrate just upstream of riffles, spaced at an average density of three nests m−2. The typical nest was 16 cm in diameter in water 31 cm deep with a bottom current velocity of 14 cm s−1, and was excavated to a depth of 4 cm below the stream bottom; however, some nest characteristics varied significantly in a few streams. Nests were larger in streams with larger spawning groups, deeper water, and slower current velocities. American brook lamprey exhibited spawning behaviors and spawning habitat requirements similar to those of other species of lamprey in North America.

Assessing the effectiveness of enhancement activities in urban streams: I. Habitat responses

AbstractEffects of stream enhancement on habitat conditions in five spring‐fed urban streams in Christchurch, New Zealand, were investigated. Stream enhancement consisted of riparian planting at three sites, and riparian planting and channel modifications at two sites, where a concrete dish channel and a timber‐lined channel were removed, and natural banks reinstated. Sites were surveyed prior to enhancement activities and 5 years after, and changes in riparian conditions (composition, horizontal and vertical cover), instream conditions (bank modifications, inorganic and organic material on the streambed), and hydraulic conditions (wetted perimeter, cross‐sectional area, depths and velocities) quantified. Enhanced sites generally had higher marginal vegetation cover, as well as increased overhanging riparian vegetation, reflecting planting of Carex sedges close to the water. Bed sediments changed at some sites, with the greatest change being replacement of a concrete channel with gravel and cobble substrate. Bryophyte cover declined at this site, reflecting loss of stable habitat where these plants grew. Bed sediments changed less at other sites, and cover of fine sediments increased in some enhanced sites, presumably from sediment runoff from nearby residential development. Filamentous algal cover decreased at one stream where shade increased, but increased in another stream where the removal of timber‐lined banks and creation of a large pond decreased shade. Stream enhancement increased variability in velocity at three of the five sites, but overall changes to stream hydraulics were small. Although enhancement activities altered the physical conditions of the streams, major changes occurred only to riparian vegetation and bank conditions. Lack of other major changes to instream physical conditions most likely reflected the limited range of channel morphology alterations undertaken. Moreover, the flat topography of Christchurch and naturally low stream discharge further constrained changes to instream physical conditions from enhancement activities. Sediment inputs from continuing urban development also negated the effects of adding coarse substrates. These over‐arching factors may constrain the success of future stream enhancement projects within Christchurch. Copyright © 2005 John Wiley & Sons, Ltd.

Habitat Associations of the San Bernardino Springsnail, Pyrgulopsis bernardina (Hydrobiidae)

ABSTRACT We studied a critically-endangered hydrobiid snail, Pyrgulopsis bernardina, in Snail Spring, Cochise County, Arizona. We determined the relationships between its abundance and a suite of habitat variables and document formerly-occupied sites. Using Akaike's Information Criterion for model selection and averaging, 14 models were defined a priori using eight habitat variables to explain its abundance. All biologically supported predictors, in the first order, provided the most parsimonious explanation of P. bernardina densities. Structural variables received stronger support than physicochemical variables. P. bernardina densities were positively associated with sand and cobble substrates, vegetation density, water velocity, and dissolved oxygen, as well as water temperatures of 14–22°C and pH values between 7.6 and 8.0. Snail densities were negatively associated with silt and organic substrates, deep water, and high conductance. The current and all former localities for P. bernardina are associated with a shallow aquifer that is distinct from an adjacent deep aquifer.

The influence of juvenile brown trout (Salmo trutta) on habitat use of inanga (Galaxias maculatus) in a stream simulator

Introduced salmonid fishes may have affected native galaxiid fishes in New Zealand by forcing alterations in their use of spatial resources. A stream simulator was used to test the effects of juvenile brown trout (Salmo trutta) (fork length range 66–115 mm) on habitat use of inanga (Galaxias maculatus) (fork length range 51–100 mm) during autumn. The stream simulator consisted of a single run‐riffle‐pool sequence lined with gravel and cobble substrates, and c. 8 m3 of untreated artesian water was recirculated through the stream simulator at a rate of 3 litres s‐1. Stream invertebrates were introduced into the stream simulator to provide food for the fish. Four experiments were run, each consisting of three 1‐day trials using either 10 inanga, 20 inanga, or 10 inanga and brown trout. Counts of inanga visible in each of 12 designated habitat zones were made throughout the day, and proportions of visible inanga were used in repeated measure ANOVAs to test whether the proportion of fish visible varied according to the time of day, the density of inanga, or the presence of trout. Our experiments showed that neither the presence of juvenile brown trout nor the density of inanga had significant influence on inanga habitat use in the stream simulator. We conclude that in New Zealand streams any influence of brown trout on inanga is more likely to result from predation and/or competition for food by larger brown trout.

Ecological and genetic evidence for impaired sexual reproduction and induced clonality in the hydroid Sertularia cupressina (Cnidaria: Hydrozoa) on commercial scallop grounds in Atlantic Canada

Colonial epifauna are vulnerable to the effects of bottom fishing, but impacts on the life histories of these non-target animals have not been examined extensively. Dredging potentially impairs sexual reproduction by invoking regeneration and induces clonality by severing colonies or through the abortion of damaged modules. This study investigated the potential for commercial-scale scallop dredging to alter sexual and asexual (“clonal”) reproduction in the hydroid Sertularia cupressina. In total, 1,071 colonies from 104 epizoic microhabitats (upper valves of live scallops relatively undisturbed by fishing) and 75 epilithic microhabitats (cobbles more severely disturbed by fishing) were collected from 53 to 94-m depths in the Bay of Fundy (Atlantic Canada). Colony abundance, injury frequency (proportion of colonies with sealed, snapped off stems), percentage of fertile colonies and sexual fecundity (number of gonophores and gonophore dimensions) were measured on all substrata. Ten randomly amplified polymorphic DNA (RAPD) primers were used to estimate clonal diversity. Field experiments found no significant effect of microhabitat differences between scallop and cobble substrata on fecundity and clonality in S. cupressina, while experimentally-induced injuries suppressed the percent of fertile colonies. On the fishing grounds, colonies on scallop valves were more abundant and sexually fertile than their counterparts on cobble, and all were sexually derived. In contrast, colonies on cobbles had a greater percentage of injury, were less fertile and were frequently clonally-derived. Impacts of fishing-related injuries on reproduction in colonial epifauna have been overlooked, yet the long-term consequences of such impacts could result in reduced adaptability, recruitment and recovery potential of these and dependent organisms.

An Evaluation of Multipass Electrofishing for Estimating the Abundance of Stream-Dwelling Salmonids

Failure to estimate capture efficiency, defined as the probability of capturing individual fish, can introduce a systematic error or bias into estimates of fish abundance. We evaluated the efficacy of multipass electrofishing removal methods for estimating fish abundance by comparing estimates of capture efficiency from multipass removal estimates to capture efficiencies measured by the recapture of known numbers of marked individuals for bull trout Salvelinus confluentus and westslope cutthroat trout Oncorhynchus clarki lewisi. Electrofishing capture efficiency measured by the recapture of marked fish was greatest for westslope cutthroat trout and for the largest size-classes of both species. Capture efficiency measured by the recapture of marked fish also was low for the first electrofishing pass (mean, 28%) and decreased considerably (mean, 1.71 times lower) with successive passes, which suggested that fish were responding to the electrofishing procedures. On average, the removal methods overestimated three-pass capture efficiency by 39% and underestimated fish abundance by 88%, across both species and all size-classes. The overestimates of efficiency were positively related to the cross-sectional area of the stream and the amount of undercut banks and negatively related to the number of removal passes for bull trout, whereas for westslope cutthroat trout, the overestimates were positively related to the amount of cobble substrate. Three-pass capture efficiency measured by the recapture of marked fish was related to the same stream habitat characteristics that influenced (biased) the removal estimates and did not appear to be influenced by our sampling procedures, including fish marking. Simulation modeling confirmed our field observations and indicated that underestimates of fish abundance by the removal method were negatively related to first-pass sampling efficiency and the magnitude of the decrease in capture efficiency with successive passes. Our results, and those of other researchers, suggest that most electrofishing-removal-based estimates of fish abundance are likely to be biased and that these biases are related to stream characteristics, fish species, and size. We suggest that biologists regard electrofishing-removal-based estimates as biased indices and encourage them to measure and model the efficiency of their sampling methods to avoid introducing systematic errors into their data.

Spawning Habitat Selection by Rainbow Trout in the Pere Marquette River, Michigan

We evaluated habitat features (i.e., substrate particle size, water depth, water velocity) at spawning redds and randomly selected reference locations (where spawning activity was not apparent) to determine importance of these features to rainbow trout (Oncorhynchus mykiss) spawning habitat use in the Pere Marquette River, Michigan, 1997 to 1999. Rainbow trout selected areas with small gravel, large gravel, and small cobble substrates for redd construction over areas with clay, silt, sand, and large cobble. Rainbow trout redds were located in areas where the stream velocity was significantly higher (F = 97.77, df = 630, p < 0.0001) than velocities that were recorded at reference sites, and redds were located in water that was significantly shallower than what was typically found in the study reaches (F = 113.84, df = 629, p < 0.0001). Water temperature did not affect selection of redd locations. Because rainbow trout spawn during spring in Michigan when water temperatures are cool, within-reach variation in water temperature may have minimal influence on choice of locations for redd construction. These microhabitat data provide an indication of rainbow trout spawning habitat utilization, and can be used to identify critical habitats that may serve as rainbow trout spawning sites, and provide guidance on targets for habitat improvement projects in the Pere Marquette River and elsewhere.

Fin Erosion in Aquaculture and Natural Environments

Fin erosion occurs when the fins of afflicted fish become degraded from a variety of sources, which can include abrasion with rough surfaces, fin damage from aggressive encounters between fish, nutritional deficiencies, and bacterial infection. Fin erosion has become a concern in fisheries management because of aesthetic and fish survival issues. Preven-tative measures for controlling fin erosion in hatcheries include: (i) feeding fish to satiation, (ii) increasing water velocities such that the energetic costs of fighting outweigh the gains, (iii) duoculture to reduce intraspecific aggression, (iv) use of a sand or cobble substrate on the bottom of rearing raceways and tanks to reduce abrasion, and (v) tank design. Various effective chemical treatments of fin necrosis have been developed which will be discussed. Fish diet supplementation, particularly with amino acids such as lysine, is a promising area of research to reduce fin erosion. Additionally, fish diets devoid of micronutrients such as copper have been found to lead to substantial fraying of dorsal and caudal fins in salmonids. Fin necrosis is related to fin erosion and is reviewed as well, especially bacteriology and stress-related aspects. For instance, stress is a factor that has been found to exacerbate both conditions. This review examines all the potential causes and effects of this serious condition, which occurs in propagated and wild fish populations.

Faunal Description of an Irish Cobble Site Using Airlift Suction Sampling

SHORT COMMUNICATION FAUNAL DESCRIPTION OF AN IRISH COBBLE SITE USING AIRLIFT SUCTION SAMPLING A. Linnane, B. Ball, B. Munday, R. Browne and J.P. Mercer INTRODUCTION One of the pnrmary goals in marine ecology is to understand themechanisms that control population dynamics in benthic habitats. One such habitat type is cobble (32-256mm particle diameter, Phi scale range = - 5 to - 8, (Wentworth 1922)), a substratum that is particularly common at the base of many subtidal reefs off the west coast of Ireland. Due to the interstitial nature of cobble, such sites have long been considered an important nursery area formany organisms (Hudon 1987; Able et al. 1988). Quantitative descriptions are sparse, however, as conventional sampling methods such as cores and grabs are unsuitable for gravel and cobble substrata. This problem was addressed with the development of the airlift suction sampler, which was first used in the 1960s (Brett 1964; Barnett and Hardy 1967) and later developed specifically for cobble areas in the United States as a means of identifying benthic recruitment habitats and nursery grounds of juvenile American lobsters Homarus americanus (Incze and Wahle 1991; Wahle and Steneck 1991). The advantages of suction dredging over manual sampling are that divers are not constrained by low visibility and replicate samples are easily achieved. Furthermore, tests indicate that sampling efficiency ranges from 70 -80% (R.Wahle, pers. comm.). As a result, suction samplers have had considerable success quantifying recruitment densities of juvenile lobsters and other benthic crustaceans within cobble substrata (Wahle and Incze 1997; Palma et al. 1998; Robinson and Tully 2000a,b). The aim of this study was to obtain both qualitative and quantitative data on the fauna of an Irish subtidal cobble site. This was achieved by standardised airlift suction sampling over a five-day period at four sites in Galway Bay. MATERIALS AND METHODS Field sampling was carried out on the west coast of Ireland in September 1997 at an area known as Aughinish Shoal in inner Galway Bay. The experimental ground was discovered through a series of reconnaissance dives from the MRV Connemara. Visual observations by two divers confirmed that an apparently homogenous cobble habitat existed. The cobble area was situated along the base of a reefwhere thewater depth ranged from 9m to 14m. The underlying substratum consisted of sand and bedrock. Benthic sampling of cobble habitat was conducted using a diver-operated airlift suction sampler (Incze andWahle 1991; Wahle and Steneck 1991). The airlift consisted of a 170cm length of 7cm diameter black PVC tube, with a scuba cylinder supplying air, fitted 10cm above the mouth of the tube. The other end of the tube was affixed to a 1mm mesh nylon bag that could be removed, closed and replaced underwater. The suction sampler was operated by two divers and was used in conjunction with a 0.5m2 quadrat constructed from buoyant PVC piping, a30cm high sheet of lnmmmesh curtain and a heavy chain base. This design prevented the escape ofmobile decapods from the quadrat. The cobble area was sampled at four sites; ten quadrats were sampled in each of two sites, while nine quadrats were sampled in the remaining two, giving a total sample area of 19m2.On sampling, the quadrat was placed randomly on a suitable cobble patch. One diver then removed the cobble stones by hand, while the second diver operated the airlift, ensuring that themouth of the tube reached into the interstitial spaces of the substratum. The divers worked slowly until all of the interstitial spaceswere exposed and sampled. Periodically, sample bagswere returned to the surface where they were analysed immediately or preserved for future examination. Prior to identification, samples were preserved by freezing or storage in 70% alcohol. All animals were identified at least to class level. RESULTS In total, 74 families of animals were sampled across the four sites (Table 1). The molluscan gastropods were the numerically dominant group (Fig. 1)with A. Linnane (corresponding author; email: adrian.linnane@ nuigalway.ie); B. Ball, B. Munday and J.P. Mercer, Martin Ryan MarineScience Institute, National University of Ireland, Galway R. Browne, National University of Ireland, Galway, Martin Ryan Institute Laboratories, Carna, Co Galway. Received 30 April2002. Read7October2002. Published 31 July 2003. BIOLOGY...