Dana L. Winkelman

Temporal and Spatial Variability in Otolith Trace-Element Signatures of Juvenile Striped Bass from Spawning Locations in Lake Texoma, Oklahoma-Texas

Abstract We assessed the potential of trace-element analysis for identifying spawning locations of striped bass Morone saxatilis in the two tributaries of Lake Texoma, Oklahoma-Texas, during 2002-2004. We also assessed the temporal stability of elemental signatures over 3 years. Elemental composition of juvenile striped bass otoliths varied considerably between the two tributary arms of Lake Texoma both within and among years. Overall reclassification rates within each collection year ranged between 81% and 93%. However, because of high interannual variability, classification functions could not reliably predict natal areas for individuals from other year-classes (19-62%). Although the mechanisms generating spatial and temporal differences in otolith chemistry are not well understood, spatial differences in otolith chemistry indicate that elemental fingerprints of striped bass from the two natal rivers in the Lake Texoma system provide natural tags of juvenile habitat. The temporal variability we observed...

An environmental oestrogen disrupts fish population dynamics through direct and transgenerational effects on survival and fecundity

Summary 1. Increased need for water and projected declines in precipitation due to climate change could leave waterways increasingly dominated by wastewater effluent. Understanding how components of wastewater influence fish populations is necessary for effective conservation and management. Despite research demonstrating effects of oestrogens, such as 17a-ethynylestradiol (EE2), on fish physiology and population failure, the generality of population responses is uncertain and the underlying mechanisms affecting population declines are unknown. EE2 is the steroid oestrogen in human contraceptive pills and has been measured up to 11 ng L 1 in the environment. 2. We identify disrupted population dynamics due to direct and transgenerational effects on survival and fecundity. We conducted a year-long study on three generations of fathead minnows Pimephales promelas Rafinesque in aquatic mesocosms and laboratory aquaria. We added environmentally relevant concentrations of EE2 daily using a static renewal, which approximates a pulsed exposure that fish experience in natural systems. 3. EE2 (3 2n g L 1 ) reduced F0 male survival to 17% (48% lower than controls) and juvenile production by 40% compared to controls. F1 fish continuously exposed to EE2 failed to reproduce, and reproduction of the F1 transferred to clean water was 70–99% less than controls. 4. F2 larval survival, exposed only as germ cells in their parents, was reduced by 51–97% compared to controls. The indirect effect on F2 survival suggests the possibility of transgenerational effects of EE2. 5. Synthesis and applications. Our results suggest that fish populations exposed to environmentally relevant 17a-ethynylestradiol (EE2) concentrations may not recover from exposure. Management of short-lived highly fecund fishes should be prioritized to protect fish from the embryo through gonadal differentiation. Reducing effluent will not be possible in many situations; hence, conservation of breeding and rearing habitat in unpolluted tributaries or reaches is needed. Additionally, resource managers could enhance habitat connectivity in rivers to facilitate immigration. Finally, investment in advanced wastewater processing technology should improve removal of bioactive chemicals such as EE2. Our results provide a baseline for regulatory agencies to consider when assessing the ecological effects of environmental oestrogens, and our approach to evaluating population-level effects could be widely applied to other contaminants.

Survival and Reproduction of Myxobolus cerebralis- Resistant Rainbow Trout Introduced to the Colorado River and Increased Resistance of Age-0 Progeny

Myxobolus cerebralis caused severe declines in rainbow trout populations across Colorado following its introduction in the 1980s. One promising approach for the recovery of Colorado’s rainbow trout populations has been the production of rainbow trout that are genetically resistant to the parasite. We introduced one of these resistant crosses, known as the GR×CRR (cross between the German Rainbow [GR] and Colorado River Rainbow [CRR] trout strains), to the upper Colorado River. The abundance, survival, and growth of the stocked GR×CRR population was examined to determine if GR×CRRs had contributed offspring to the age-0 population, and determine whether these offspring displayed increased resistance and survival characteristics compared to their wild CRR counterparts. Apparent survival of the introduced GR×CRR over the entire study period was estimated to be 0.007 (±0.001). Despite low survival of the GR×CRRs, age-0 progeny of the GR×CRR were encountered in years 2008 through 2011. Genetic assignments revealed a shift in the genetic composition of the rainbow trout fry population over time, with CRR fish comprising the entirety of the fry population in 2007, and GR-cross fish comprising nearly 80% of the fry population in 2011. A decrease in average infection severity (myxospores fish−1) was observed concurrent with the shift in the genetic composition of the rainbow trout fry population, decreasing from an average of 47,708 (±8,950) myxospores fish−1 in 2009 to 2,672 (±4,379) myxospores fish−1 in 2011. Results from this experiment suggest that the GR×CRR can survive and reproduce in rivers with a high prevalence of M. cerebralis. In addition, reduced myxospore burdens in age-0 fish indicated that stocking this cross may ultimately lead to an overall reduction in infection prevalence and severity in the salmonid populations of the upper Colorado River.

Reduced Myxobolus cerebralis Actinospore Production in a Colorado Reservoir May Be Linked to Changes in Tubifex tubifex Population Structure

Elucidating the dynamics of a parasitic infection requiring two hosts in a natural ecosystem can be a daunting task. Myxobolus cerebralis (Mc), the myxozoan parasite that causes whirling disease in some salmonids, was detected in the Colorado River upstream of Windy Gap Reservoir (WGR) in 1988. Subsequently, whirling disease was implicated in the decline of wild Rainbow Trout Oncorhynchus mykiss in the river when WGR was identified as a point source of Mc triactinomyxons (TAMs). Between 1997 and 2004, numerous investigations began to elucidate the etiology of Mc in WGR. During this period, Mc TAM production in WGR declined more than 90%. Explanations for the decline have included differences in stream discharge between years, changes in the thermal regime of the lake, severe drought, changes in the fish population structure in WGR, and reductions in the prevalence and severity of Mc infection in salmonids in the Colorado and Fraser rivers upstream of WGR. All of these have been discredited as explanations for the reduced TAM production. In 2005, a new study was conducted to replicate the studies completed in 1998. In this paper, the results of a new real-time polymerase chain reaction assay utilized to quantify the mitochondrial 16S rDNA specific to each of four lineages of Tubifex tubifex in pooled samples of 50 oligochaetes are presented. These results suggest that compared with 1998, the densities of aquatic oligochaetes and T. tubifex have increased, TAM production has been greatly reduced, and the decline is congruent with the dominance of lineages I, V, and VI of T. tubifex-three lineages that are refractory or highly resistant to Mc infection-in the oligochaete population. While it is possible that the resistant lineages function as biofilters that deactivate Mc myxospores, the reason for the decline in TAM production in WGR remains an enigma.

Reproductive failure of the red shiner (Cyprinella lutrensis) after exposure to an exogenous estrogen

Endocrine disrupting chemicals (EDCs) have been detected in surface waters worldwide and can lead to devel- opmental and reproductive disruption in exposed fishes. In the US Great Plains, EDCs are impacting streams and rivers and may be causing adverse reproductive effects. To examine how estrogenic EDCs might affect reproductive success of plains fishes, we experimentally exposed male red shiners (Cyprinella lutrensis) to exogenous 17b-estradiol. We character- ized the effects of estradiol on male gonadal histology and secondary sexual characteristics, determined whether exposure reduced reproductive success, and examined the effects of depuration. Adults were exposed to a mean concentration of 70 ngL -1 estradiol, a solvent control, or a water control for at least 83 days. Male exposure to estradiol resulted in ele- vated plasma vitellogenin concentrations, changes in spermatogenesis, reduced mating coloration and tubercles, altered mating behaviors, and reduced reproductive success with no viable progeny produced. Reproductive endpoints improved upon depuration (28 days). Exposure to estradiol had significant adverse effects on red shiners, indicating that wild popula- tions may face developmental and reproductive difficulties if they are chronically exposed to estradiol.

Brown Trout Removal Effects on Short-Term Survival and Movement of Myxobolus cerebralis-Resistant Rainbow Trout

AbstractFollowing establishment of Myxobolus cerebralis (the parasite responsible for salmonid whirling disease) in Colorado, populations of Rainbow Trout Oncorhynchus mykiss experienced significant declines, whereas Brown Trout Salmo trutta densities increased in many locations across the state, potentially influencing the success of M. cerebralis-resistant Rainbow Trout reintroductions. We examined the effects of Brown Trout removal on the short-term (3-month) survival and movement of two crosses of reintroduced, M. cerebralis-resistant Rainbow Trout in the Cache la Poudre River, Colorado. Radio frequency identification passive integrated transponder tags and antennas were used to track movements of wild Brown Trout and stocked Rainbow Trout in reaches where Brown Trout had or had not been removed. Multistate mark–recapture models were used to estimate tagged fish apparent survival and movement in these sections 3 months following Brown Trout removal. A cross between the German Rainbow Trout and Colorad...