Christopher P. Tatara

Copper-induced olfactory toxicity in salmon and steelhead: extrapolation across species and rearing environments.

Recent research has shown that hatchery coho salmon (Oncorhynchus kisutch) are vulnerable to the olfactory neurotoxicity caused by copper from urban runoff, pesticide use, and mining activities. To explore the broader application of this data to salmonids living in the wild, we exposed naturally-reared steelhead (O. mykiss) to copper (5 and 20 μg/L; 3h) and measured losses in olfactory function via electro-olfactogram (EOG) recordings. Copper exposure disrupted the olfactory responsiveness of steelhead to an amino acid (L-serine) in a dose-dependent manner that was equivalent to previously published data for hatchery coho. Our findings support extrapolation of copper toxicity data across species and from fish raised in hatcheries to fish in the wild.

Mechanisms influencing competition between hatchery and wild juvenile anadromous Pacific salmonids in fresh water and their relative competitive abilities

Avoiding negative effects of competition from released hatchery salmonids on wild fish is a primary concern for recovery efforts and fisheries management. Several factors affect competition among juvenile salmonids including: (1) whether competition is intra- or interspecific, (2) duration of freshwater cohabitation of hatchery and wild fish, (3) relative body size, (4) prior residence, (5) environmentally induced developmental differences, and (6) fish density. Intraspecific competition is expected to be greater than interspecific because of greater niche overlap between conspecific hatchery and wild fish. Competition is expected to increase with prolonged freshwater cohabitation. Hatchery smolts are often larger than wild, and larger fish are usually superior competitors. However, wild fish have the advantage of prior residence when defending territories and resources in natural streams. Hatchery-induced developmental differences are variable and can favor both hatchery and wild fish. Although all these factors influence competitive interactions, fish density of the composite population (wild + hatchery fish) in relation to habitat carrying capacity likely exerts the greatest influence. The extent of competition and relative competitive ability of wild and hatchery fish can be determined by additive and substitutive experimental designs, respectively, and the limited body of substitutive experiments suggests that the relative competitive ability of hatchery and wild fish is approximately equal when measured as growth. Conducting substitutive experiments becomes difficult as the spatial and temporal scales increase. Large-scale experiments comparing supplemented and control reaches or streams hold some promise for quantifying the effects of released hatchery fish on wild fish behavior, growth and survival.

Development of natural growth regimes for hatchery-reared steelhead to reduce residualism, fitness loss, and negative ecological interactions

Wild steelhead (Oncorhynchus mykiss) typically spend two or more years in freshwater before migrating to sea, but hatchery steelhead are almost ubiquitously released as yearlings. Their large size at release coupled with life history pathways that include both male and female maturation in freshwater present ecological risks different from those posed by hatchery populations of Pacific salmon. Yearling hatchery reared steelhead that fail to attain minimum thresholds for smoltification or exceed thresholds for male maturation tend to ‘residualize’ (i.e., remain in freshwater). Residuals pose ecological risks including size-biased interference competition and predation on juvenile salmon and trout. Three hatchery populations of steelhead in Hood Canal, WA were reared under growth regimes designed to produce a more natural age at smoltification (age-2) to aid in rebuilding their respective natural populations. Mean smolt sizes and size variability at age-2 were within the range of wild smolts for two of the three populations. The third population reared at a different facility under similar temperatures exhibited high growth rate variability and high male maturation rates (20% of all released fish). Experimentally comparing age-1 and age-2 smolt programs will help identify optimal rearing strategies to reduce the genetic risk of domestication selection and reduce residualism rates and associated negative ecological effects on natural populations. Investigations of Winthrop National Fish Hatchery summer-run steelhead will measure a) selection on correlated behavioral traits (‘behavioral syndromes’), b) degree of smoltification, c) changes in hormones that regulate gonad growth at key developmental stages, and d) conduct extensive post-release monitoring of fish reared under each growth regime.

Evaluation of a New Coded Electromyogram Transmitter for Studying Swimming Behavior and Energetics in Fish

Abstract A new coded electromyogram (CEMG) transmitter was recently introduced to the market to allow broader application and greater flexibility of configurations than the conventional noncoded version. CEMG transmitters were implanted into 20 steelhead Oncorhynchus mykiss and calibrated to swimming speed in a respirometer to determine the relationship between swimming speed and the output of the transmitters and also to determine how the output of a single transmitter varied when implanted in multiple fish. Linear regression models showed a strong positive relationship between the output from CEMG transmitters and swimming speed. However, grouping signals from multiple transmitters produced a less accurate relationship between CEMG output and swimming speed than using signals from individual transmitters. The results, therefore, do not suggest that the CEMG transmitters acted similarly in all fish. Calibration data from one transmitter were not readily transferable among multiple fish implanted with the...

Spawning by Female Chinook Salmon Can Be Detected by Electromyogram Telemetry

Abstract New methods to detect spawning of anadromous salmonids in their natural environment are needed to improve understanding of breeding behavior patterns, natural selection on reproductive traits (e.g., spawn timing), and interactions between artificially propagated and wild fish. We implanted maturing female Chinook salmon Oncorhynchus tshawytscha with coded electromyogram (CEMG) transmitters and continuously recorded spawning activity to develop an algorithm capable of accurately detecting spawning events from CEMG data. Marked increases in female digging frequencies immediately after spawning (cover digging) strongly correlated with CEMG values. The algorithm detected averages of 65% and 86% of the actual spawning events in 2003 and 2004, respectively. The algorithm accurately detected zero spawning events for the two female salmon that did not spawn. The presence of CEMG transmitters did not affect the digging frequency, number of nests constructed, or the reproductive life span of implanted fish...

Effects of Hatchery Fish Density on Emigration, Growth, Survival, and Predation Risk of Natural Steelhead Parr in an Experimental Stream Channel

Abstract Hatchery supplementation of steelhead Oncorhynchus mykiss raises concerns about the impacts on natural populations, including reduced growth and survival, displacement, and increased predation. The potential risks may be density dependent. We examined how hatchery stocking density and the opportunity to emigrate affect the responses of natural steelhead parr in an experimental stream channel and after 15 d found no density-dependent effects on growth, emigration, or survival at densities ranging from 1–6 hatchery parr/m2. The opportunity for steelhead parr to emigrate reduced predation by coastal cutthroat trout O. clarkii clarkii on both hatchery and natural steelhead parr. The cutthroat trout exhibited a type-I functional response (constant predation rate with increased prey density) for the hatchery and composite populations. In contrast, the predation rate on natural parr decreased as hatchery stocking density increased. Supplementation with hatchery parr at any experimental stocking density ...