Peter B. Bayley

PROJECTING THE BIOLOGICAL CONDITION OF STREAMS UNDER ALTERNATIVE SCENARIOS OF HUMAN LAND USE

We present regression models for estimating the status of fish and aquatic invertebrate communities in all second to fourth-order streams (1:100 000 scale; total stream length 5 6476 km) throughout the Willamette River Basin, Oregon (USA). The models project fish and invertebrate status as a function of physiographic, land-use/land-cover, and stream flow variables, with the latter two sets of variables subject to change under historical and alternative future scenarios of human development. Models are developed using sample data collected between 1993 and 1997 from 149 wadeable streams in the basin. Model uncertainties are propagated through model projections and into aggregated estimates of regional status. The projections show no significant change in basin-wide status in year 2050, relative to Circa 1990, for scenarios either of increased human development or continuation of current development trends, because landscape change under these scenarios is dominated by conversion of agricultural land to rural residential and urban uses, and because these changes affect only a small percentage of the basin. However, under a scenario of increased conservation, regional medians of biotic status indicators are projected to improve by 9-24% by year 2050. None of the changes projected between Circa 1990 and year 2050 is as large in magnitude as the decline in status projected to have occurred between the time of pre-European settlement and Circa 1990.

An Approach to Estimate Probability of Presence and Richness of Fish Species

Abstract Absence of a species when it is not observed from a given area is ensured only when the probability of observation, when present, is 1. This condition is rarely satisfied in surveys of animals in natural environments, particularly with elusive targets such as fish. Detectability (probability of species encounter) is a function of probability of individual capture, which varies widely with sampling method, fish size, physical habitat, and number of individuals present in a given area. An empirical Bayesian approach was developed for estimating probability of presence for zero-catch samples, in which the number of individuals present for a species is predicted from independent samples and used as an empirical prior. The model was illustrated for 16 species of fish sampled in 121 blocked-off stream reaches in which samples were collected using one of five primary gear methods; treatment with an ichthyocide followed. All species present were caught by the primary gear in only 17 (14%) of the samples....

Capture Efficiency of a Boat Electrofisher

Abstract Models for fish capture efficiency (catchability) using a boat-mounted AC electrofishing sampling protocol were estimated for warmwater fishes in Illinois lakes through a calibration process. Catchabilities were determined for 37 inshore zones in blocked enclosures or ponds and 5 large water bodies during fall or spring. The abundances of vulnerable fish populations were determined by census following draining or by treatment using rotenone or primacord of known catchability. Inshore catchabilities, based on a zone 0-13 m from shore, were strongly dependent on fish length (as a unimodal function), fish taxa, mean depth, and surface macrophyte cover. Under average environmental conditions, maximum catchabilities by taxon ranged from 0.0018 to 0.14 and ranked (highest to lowest) as follows: largemouth bass ? Micropterus salmoides, common carp Cyprinus carpio, crappies Pomoxis spp. in spring, shad Dorosoma spp., bluegill Lepomis macrochirus, green sunfish L. cyanellus, crappies in fall, freshwater d...

Freshwater fishes of the Amazon River basin: their biodiversity, fisheries, and habitats

Stretching more than seven million square kilometers, the Amazon River basin is the largest river basin in the world and discharges about one-sixth of all freshwater from the continents to the oceans of the world. The age of this ecosystem, its position near the equator and the enormous diversity of its aquatic habitats, have produced the most diverse fish fauna on the planet. About 2,500 fish species have already been described and it is estimated that more than 1,000 new species remain to be discovered. Knowledge concerning this multitude of fish species is still insufficient, which makes their management and protection difficult. About 50% of the species are thought to occur in the large rivers and connected floodplains and another 50% in headwater streams. Inland fisheries give rise to 450,000 t of fish each year and thus contribute substantially to the protein supply of local populations. However, despite their economic importance, these fisheries receive little attention from the respective governments. The fisheries are highly selective and several stocks of large species with high market value have been over fished. Fish culture is still in its infancy but its development is expected to provide high-quality species during periods of low supply. Over large areas, aquatic habitats are still in near-natural conditions because of the low densities of resident human populations. Nonetheless, over the last few decades, the pressure on aquatic ecosystems and habitats has steadily increased, mainly due to large-scale destruction of natural vegetation cover by agro-industries in the savanna belt (cerrado), small-scale agriculture in the Andean hill slopes, and logging in rain forests. These activities have placed aquatic biodiversity, including fishes, at serious risk. Many headwater species have restricted distributions and are therefore particularly vulnerable to large-scale environmental degradation. Moreover, the construction of large reservoirs for hydroelectric power generation has serious consequences for fish fauna. Currently, about 16.4% of the Amazon River basin is protected, and another 15.2% is under partial protection in indigenous reserves in Brazil. Another 9.1% will be implemented as reserves in the next 10 years in the Brazilian part of the basin. The formulation by the Amazonian countries of a coherent policy that integrates long-term management of the river basin with sustainable management of aquatic and wetland habitats, including their fauna and flora, is urgently needed.

The Efficiency of a Seine Net

Abstract We present a method to predict the capture efficiency of a 25-m, 5-mm mesh seine net as a function of fish size and taxon from a diverse fish community. This allows true abundance and size distribution to be estimated from observed catches. Predicted capture efficiency from an empirical model of field calibrations from the Amazon River floodplain was a positively skewed, unimodal function of fish length, whose magnitude depended on method of seine operation and fish taxonomic group. Capture efficiency is the product of efficiency of encirclement as the net is laid (which decreases with increasing fish size) and efficiency of retention as the net is hauled (which increases with increasing fish size). Retention was determined by modeling mark–recapture data. Dividing observed capture efficiency by this retention yielded empirical encirclement efficiency, which was then compared with encirclement efficiency determined from a simulation model of fishes evasive behavior. The simulation accounts for t...

Stream Fish Responses to Grazing Exclosures

Abstract Eight paired reaches of northeastern Oregon streams were selected such that one reach was an established livestock exclosure and a neighboring, geomorphologically similar reach was open to grazing. Exclosures varied in length from 123 to 436 m. Teams of snorkelers recorded fish species and size-groups in the exclosure and grazed reaches simultaneously so that diurnal changes in fish behavior did not confound results. Observed densities of age-0 redband trout Oncorhynchus mykiss in pools, corrected for snorkeler range of vision, were significantly different (P < 10−9), increasing by an average of 2.5-fold in exclosed reaches. Conversely, warmwater fishes (dominated by speckled dace Rhinichthys osculus) were negatively related to exclosures (P < 0.001). Densities of age-0 warmwater fish and age-0 O. mykiss were uncorrelated (P = 0.18). No first-order interactions existed among exclosure–control treatment, stream, and pool temperature variables in either age-0 analysis. Combined juvenile and adult O...

The Influence of Release Strategy and Migration History on Capture Rate of Oncorhynchus mykiss in a Rotary Screw Trap

Abstract Rotary screw traps are used in rivers throughout the west coast of North America to capture emigrating juvenile salmonids. Calibrating the capture efficiency of each trap is essential for valid estimates of fish passage. We released PIT-tagged Oncorhynchus mykiss upstream of a rotary screw trap in the South Fork John Day River, Oregon, to estimate capture efficiency. We used three strategies for release of fish recently captured in the trap. We recaptured 28% of medium-sized fish (86–145xa0mm FL) and 14% of large-sized fish (146–230xa0mm FL) released during daylight 1.6xa0km upstream from the trap. We recaptured 33% of medium-sized fish and 17% of large-sized fish released during daylight 4.8xa0km upstream from the trap. We recaptured 42% of medium-sized fish and 23% of large-sized fish released at twilight 1.8xa0km upstream from the trap. A PIT tag antenna detected summer-tagged parr (which were PIT-tagged upstream 1–5 months before migration) as they approached the trap to evaluate potential bias from re...

Response of Prochilodus nigricans to flood pulse variation in the central Amazon

The influence of the flood pulse on fish populations has been posited, but infrequently tested or quantified. Here, we tested the effect of habitat on population size, using Prochilodus nigricans as a case study species. Floodplain habitat was based on the littoral zone area occupied by P. nigricans to feed. The magnitude of this habitat in each hydrological year, the moving littoral (ML), was expressed as the sum of daily littoral areas during the advancing flood pulse, using satellite-based passive microwave data. Annual population size was estimated by age class, using a dynamic age-structured model (MULTIFAN-CL) based on catches, effort and fish length frequencies from the Manaus-based fishery over 12.75 years. The principal null hypothesis was that the ML, using three lag times, had no effect on population size of a single age class of P. nigricans. The population size at 29 months of age was positively related (pu2009=u20090.00030) to floodplain habitat (ML) earlier in the same year, when the fish were 21–27 months old. The result implies a density-dependent relationship for the population with respect to its feeding habitat. Potential mechanisms governed by flood pulse variation and habitat quality for this and other species using floodplain habitats are discussed.