Chilliwack River Research Articles

Population variability in thermal performance of pre-spawning adult Chinook salmon.

Climate change is causing large declines in many Pacific salmon populations. In particular, warm rivers are associated with high levels of premature mortality in migrating adults. The Fraser River watershed in British Columbia, Canada, supports some of the largest Chinook salmon (Oncorhynchus tshawytscha) runs in the world. However, the Fraser River is warming at a rate that threatens these populations at critical freshwater life stages. A growing body of literature suggests salmonids are locally adapted to their thermal migratory experience, and thus, population-specific thermal performance information can aid in management decisions. We compared the thermal performance of pre-spawning adult Chinook salmon from two populations, a coastal fall-run from the Chilliwack River (125km cooler migration) and an interior summer-run from the Shuswap River (565km warmer migration). We acutely exposed fish to temperatures reflecting current (12°C, 18°C) and future projected temperatures (21°C, 24°C) in the Fraser River and assessed survival, aerobic capacity (resting and maximum metabolic rates, absolute aerobic scope (AAS), muscle and ventricle citrate synthase), anaerobic capacity (muscle and ventricle lactate dehydrogenase) and recovery capacity (post-exercise metabolism, blood physiology, tissue lactate). Chilliwack Chinook salmon performed worse at high temperatures, indicated by elevated mortality, reduced breadth in AAS, enhanced plasma lactate and potassium levels and elevated tissue lactate concentrations compared with Shuswap Chinook salmon. At water temperatures exceeding the upper pejus temperatures (Tpejus, defined here as 80% of maximum AAS) of Chilliwack (18.7°C) and Shuswap (20.2°C) Chinook salmon populations, physiological performance will decline and affect migration and survival to spawn. Our results reveal population differences in pre-spawning Chinook salmon performance across scales of biological organization at ecologically relevant temperatures. Given the rapid warming of rivers, we show that it is critical to consider the intra-specific variation in thermal physiology to assist in the conservation and management of Pacific salmon.

Chinook salmon (Oncorhynchus tshawytscha) genome and transcriptome.

When unifying genomic resources among studies and comparing data between species, there is often no better resource than a genome sequence. Having a reference genome for the Chinook salmon (Oncorhynchus tshawytscha) will enable the extensive genomic resources available for Pacific salmon, Atlantic salmon, and rainbow trout to be leveraged when asking questions related to the Chinook salmon. The Chinook salmon’s wide distribution, long cultural impact, evolutionary history, substantial hatchery production, and recent wild-population decline make it an important research species. In this study, we sequenced and assembled the genome of a Chilliwack River Hatchery female Chinook salmon (gynogenetic and homozygous at all loci). With a reference genome sequence, new questions can be asked about the nature of this species, and its role in a rapidly changing world.

Watershed-scale effectiveness of floodplain habitat restoration for juvenile coho salmon in the Chilliwack River, British Columbia

Although billions of dollars have been spent restoring degraded watersheds worldwide, watershed-scale studies evaluating their effectiveness are rare. To mitigate damage from past logging activities, the floodplain of the upper Chilliwack River watershed (∼600 km2) was extensively restored from 1996 to 2000 through off-channel habitat restoration. The contribution of restored habitat to watershed-scale production of wild coho (Oncorhynchus kisutch) smolts was estimated through an extensive mark–recapture program in 2002. 27%–34% of the production of the estimated 247 200 out-migrating coho smolts could be attributed to the 157 000 m2 of newly created habitat. Area-based habitat models from the literature performed reasonably well in predicting smolt production from restored habitat, providing an acceptable first-order approach for evaluating production benefits of restoration. The costs of smolt production integrated over 30 years ranged from US$0.69–US$10.05 per smolt, falling within the range of hatchery production costs reported elsewhere (typical cost of ∼US$1.00 per smolt) at the most cost-effective restoration sites. This study demonstrates that large-scale habitat restoration can effectively enhance fish production at a watershed scale, at a cost that may be comparable to hatchery smolt production.

Modelling changes in suspended sediment from forest road surfaces in a coastal watershed of British Columbia

Erosion from logging road surfaces, cut slopes, banks, and ditches represents a chronic source of sediment input to streams that can degrade aquatic habitats. Road surface erosion is of particular concern because the magnitude of sediment generation when traffic levels are high can be large. Current models for predicting sediment production from roads require information on area-specific sediment delivery, which is not often available. Here, we developed a model to quantify suspended sediment concentrations (SSC) generated by forest roads surfaces under different conditions of use and density. This model is designed for a typical medium-size coastal watershed of British Columbia or the American Pacific Northwest, and was applied to the Chilliwack River watershed as a case study. The results illustrate that intensive use of forest roads combined with high road density can increase the number of extreme sedimentation events over a predetermined threshold. A comparison of the effects of road density and the level of road use suggests that the level of road use is more important than the road density for the generation of fine sediment from road surfaces. However, the model omits the impact of roads on mass movements in a watershed, which represent a major source of sediment in steep watersheds, so the effect of road density is likely more substantial than the model predicts. The model is an attempt to overcome field data limitations by using an empirical relation between SSC and traffic variables, and presents a starting point for more intensive field studies that could be used to validate it. Copyright © 2013 John Wiley & Sons, Ltd.

Estimating suspended sediment concentrations in areas with limited hydrological data using a mixed‐effects model

AbstractSediment rating curves are commonly used to estimate the suspended sediment load in rivers and streams under the assumption of a constant relation between discharge (Q) and suspended sediment concentrations (SSC) over time. However, temporal variation in the sediment supply of a watershed results in shifts in this relation by increasing variability and by introducing nonlinearities in the form of hysteresis or a path‐dependent relation. In this study, we used a mixed‐effects linear model to estimate an average SSC–Q relation for different periods of time within the hydrologic cycle while accounting for seasonality and hysteresis. We tested the performance of the mixed‐effects model against the standard rating curve, represented by a generalized least squares regression, by comparing observed and predicted sediment loads for a test case on the Chilliwack River, British Columbia, Canada. In our analyses, the mixed‐effects model reflected more accurate patterns of interpolated SSC from Q data than the rating curve, especially for the low‐flow summer months when the SSC–Q relation is less clear. Akaike information criterion scores were lower for the mixed‐effects model than for the standard model, and the mixed‐effects model explained nearly twice as much variance as the standard model (52% vs 27%). The improved performance was achieved by accounting for variability in the SSC–Q relation within each month and across years for the same month using fixed and random effects, respectively, a characteristic disregarded in the sediment rating curve. Copyright © 2012 John Wiley & Sons, Ltd.

Low-flow hydraulic geometry of small, steep mountain streams in southwest British Columbia

This investigation explores the at-a-station hydraulic geometry (AHG) of small, steep mountain streams at low discharge. Thirteen reaches in five tributaries of Chilliwack River, British Columbia, ranging in size from 12 to 77 km 2 are examined. The resulting data set is composed of eight to twelve measurements of water-surface width, mean depth, and mean velocity at each of 61 cross sections or 625 unique combinations of the three variables. Mean velocity in a given cross section responds most rapidly to changing discharge, and 31 of the 61 cross sections have velocity exponents that are greater than the water-surface width and mean-depth exponents combined. The velocity exponent ( m) averages 0.51, while the mean water-surface width exponent ( b) and mean-depth exponent ( f) average 0.20 and 0.29, respectively. Somewhat surprisingly, the AHG of steep mountain streams can be reasonably predicted from just a few measurements of the primary flow variables and stream discharge. While conditions at the cross section appear predictable from a few measurements, extrapolating the results from one cross section to another in the same reach involves large errors. The section-to-section variability of the exponents and coefficients, even when they are located in similar channel units such as riffles, prevents accurate extrapolation to unmeasured cross sections.

Instability in eight sub-basins of the Chilliwack River Valley, British Columbia, Canada: A comparison of natural and logging-related landslides

Logging causes increased landslide frequency in British Columbia. In this study, the slope, type, initiation location, aspect, rate, bedrock geology, and size of mass movements located in eight logged tributary valleys of the Chilliwack River Valley are investigated. A landslide inventory was created by digitizing landslides identified on aerial photographs dating from 1941 to 2002. This database was analysed using qualitative observations and simple statistical tests, and a comparison between natural and logging-related landslides was made. Slope tests displayed a significant difference between natural and logging-related events, indicating that, on average, logging-related landslides require lower slope gradients to initiate than natural events. Although aspect, initiation location, and landslide type did not show a significant relationship between natural and logging-related landslides, they do suggest subtle differences. Landslide rate was calculated and compared for natural and logging-related landslides. It was significantly higher for logging-related events, attaining a maximum of 31 times the natural rate in 1978 and an overall average increase of nine times the natural rate. Logging-related landslides were on average smaller than natural landslides but this nevertheless resulted in a 3.1 times increase in area affected by logging-related landslides compared to natural landslides. Geology may influence landslide frequency as well; it appears to be higher over the less resistive sedimentary rocks of the Cultus Formation and Chilliwack Group and lower in granodioritic areas. Finally, roads affected slope stability more than clearcuts in the early decades of the study, but this effect decreased over time, suggesting a correlation with improved road construction.

Catchment‐scale effects of forestry practices on benthic invertebrate communities in Pacific coastal streams

Summary 1. Catchment‐scale effects of forestry practices alter stream physical structures and influence composition and abundance of benthic communities. Looking beyond the reach‐scale effects to disturbance impacts that come from upstream catchments is rare. Understanding of effects of large‐scale catchment disturbances on downstream habitats is crucial to better manage the impacts or mitigate the effects of forest management. 2. By comparing catchments with different forestry histories, we examined the impacts of past forestry practices on stream habitats and benthic invertebrate diversity in six reference streams in mature forests and five previously logged streams in young‐growth forests in the Chilliwack River basin, Canada. Principal components analysis separated the reference streams and the previously logged streams by their physical characteristics. Streams in mature forests had coarser substrates than in young‐growth forests. 3. Using partial least squares projection to latent structures (PLS) modelling, we assessed the relationship between multiple environmental variables and benthic communities. Predictive PLS models were developed based on environmental variables and community response variables at reference streams. The observed taxon richness and relative abundance of total benthos, scrapers and predators at previously logged sites were significantly lower than the model predicted. The biomasses of total benthos and shredders at previously logged sites were significantly lower than those at reference sites. 4. Synthesis and applications. This study demonstrates that a legacy of measurable logging impacts on habitats and invertebrate community metrics can be detected up to 40 years after logging on these streams and at a catchment‐scale. This predictive model approach combined with intensive field observations has potential for assessing the catchment‐scale effects of forestry on stream ecosystems. This method also can be used to estimate the time to recovery from harvesting and to assist the evaluation of improving management decisions to reduce the negative impacts of forest harvesting on stream ecosystems.

Wing Morphology Varies with Age but not Migratory Habit in American Dippers

We investigated variation in morphology of American Dippers (Cinclus mexicanus) in the Chilliwack River watershed, British Columbia in relation to gender, age and migratory habit. Male dippers had linear dimensions that were 2–9% longer and, on average, were 16% heavier than females. Adults (AHY) were the same structural size as yearlings (HY). Yearlings, however, had shorter and more rounded wings than adults providing support for the hypothesis that an increased vulnerability to predation may lead to selection for traits that improve take-off performance and maneuverability. Yearlings also had shorter tails suggesting other selective pressures shape tail morphology. Dippers in this population may be sedentary or migrate short distances to breed at higher elevations. We found no evidence that wing or tail morphology varied with migratory habit or that sedentary dippers, that have higher reproductive success, are larger or heavier than migrants.

Flow resistance in steep mountain streams

AbstractResistance to flow at low to moderate stream discharge was examined in five small (12–77 km2 drainage area) tributaries of Chilliwack River, British Columbia, more than half of which exhibit planar bed morphology. The resulting data set is composed of eight to 12 individual estimates of the total resistance to flow at 61 cross sections located in 13 separate reaches of five tributaries to the main river. This new data set includes 625 individual estimates of resistance to flow at low to moderate river stage. Resistance to flow in these conditions is high, highly variable and strongly dependent on stage. The Darcy–Weisbach resistance factor (ff) varies over six orders of magnitude (0·29–12 700) and Manning's n varies over three orders of magnitude (0·047–7·95). Despite this extreme range, both power equations at the individual cross sections and Keulegan equations for reach‐averaged values describe the hydraulic relations well. Roughness is divided into grain and form (considered as all non‐grain sources) components. Form roughness is the dominant component, accounting for about 90% of the total roughness of the system (i.e., form roughness is on average 8.6 times as great as grain roughness). Of the various quantitative and qualitative form‐roughness indicators observed, only the sorting coefficient (σ = D84/D50) correlates well with form roughness. Copyright © 2008 John Wiley & Sons, Ltd.

Breeding territory fidelity in a partial migrant, the American dipper Cinclus mexicanus

178.American dipper Cinclus mexicanus populations are frequently composed of residentindividuals that occupy permanent territories year round and migratory individualsthat overwinter with residents but migrate to breeding territories on higher elevationcreeks each spring. Between 1999 and 2004 we examined how migratory strategy(resident/migratory) and sex differences influence breeding territory fidelity ofAmerican dippers occupying the Chilliwack River watershed, British Columbia,Canada. Counter to expectation we found that the migratory strategy of Americandippers did not influence whether birds breeding in one year were found on theirformer breeding territory in the next. Migratory strategy also did not affect theprobability that known surviving dippers occupied the same breeding territory in thefollowing year. Males and females were equally likely to be found on their formerterritory in the following year (females 43%, males 41%) and known survivors hadsimilar levels of breeding territory fidelity (females 74%, males 68%). However,breeding territory fidelity of males and females varied in response to different factors.Surviving female dippers were more likely to be found on their former breedingterritory in the subsequent year following a successful breeding attempt than anunsuccessful breeding attempt. Prior reproductive performance did not influencewhether surviving male dippers were found on their former breeding territory. Maledippers were more likely to be found on their former territory and, if they survived,have higher breeding territory fidelity when their mate also returned to that sameterritory. Mate retention also influenced whether females were found on their formerterritory in the following year but had no effect on the breeding territory fidelity ofknown survivors. We argue that sex-specific dispersal decision rules in Americandippers are driven by sex differences in the predictability of breeding performancebetween years and sex differences in how mate retention influences subsequentreproductive success.H. A. Middleton and D. J. Green (correspondence), Centre for Wildlife Ecology,Department of Biological Sciences, Simon Fraser University, 8888 University Drive,Burnaby, BC V5A 1S6 CANADA. E-mail: djgreen@sfu.ca. C. A. Morrissey, CanadianWildlife Service, 5421 Robertson Road, Delta, BC V4K 3N2 Canada.

Identifying Sources and Biomagnification of Persistent Organic Contaminants in Biota from Mountain Streams of Southwestern British Columbia, Canada

We assessed whether biota occupying mountain streams accumulate and biomagnify remotely derived organic pollutants originating from atmospheric inputs to snowpack and glacial runoff and from marine sources introduced by migrating anadromous salmon. Several persistent organic pollutants including polychlorinated biphenyls (PCBs), p,p'-dichloro-diphenyl-dichloroethylene, hexachlorobenzene, and trans-nonachlor were commonly detected in benthic invertebrates, salmon fry (Oncorhynchus spp.), and eggs of an aquatic passerine, the American dipper (Cinclus mexicanus) from the Chilliwack River watershed, British Columbia, Canada. Total PCBs and several organochlorines (OCs) biomagnified from benthic invertebrate composites to salmon fry to dipper eggs. Invertebrate samples generally did not differ significantly in contaminant burdens between the river main stem where salmon are more abundant and higher-elevation tributaries where the salmon density is lower. Concentrations of total OCs and total PCBs in dipper eggs were positively related to drainage basin area and collection year but not to elevation. No differences in PCB congener patterns existed between dipper egg samples from the Chilliwack watershed and other watersheds in southwestern British Columbia. However, principal component analysis revealed significant spatial differences in egg PCB congener patterns between the main Chilliwack River and the higher-elevation tributaries. This difference was primarily due to a greater occurrence of lower chlorinated PCB congeners (66 and 105) in dipper eggs collected from the tributaries and higher loadings of the more stable and persistent congeners (153, 138, 130, and 128) in eggs from the river main stem. The results suggest that atmospheric sources are the main contributor of contaminants detected in biota from the region and that biomagnification is a common pathway for accumulation in lotic predators such as the American dipper.

Behavior and Survival of Wild and Hatchery‐Origin Winter Steelhead Spawners Caught and Released in a Recreational Fishery

AbstractMandatory catch and release of wild fish and supplementation with hatchery‐reared fish are commonly used to sustain sport fisheries on low‐abundance populations of wild steelhead. However, their effectiveness in limiting angling mortality on wild fish is uncertain. We radio‐tagged 226 (125 wild, 101 hatchery) angled adult steelhead Oncorhynchus mykiss near the mouth of the Vedder−Chilliwack River, British Columbia, in 1999 and 2000 and monitored their subsequent movements to determine survival to spawning and overlap in the distributions of inferred holding sites, spawning sites, and spawning times. The distributions of prespawning holding sites did not differ between wild and hatchery fish in either year, but spawning locations differed. Holding and spawning sites used by hatchery fish were restricted to the lower two‐thirds of the river, downstream of the hatchery where they were reared but well upstream of their smolt release site. Wild fish spawned throughout the watershed. Spawning times did not differ between wild and hatchery fish, but varied with run timing. The maximum mortality from the initial catch and release and radio‐tagging was 1.4% in 1999 and 5.8% in 2000; true mortality rates were lower because tag regurgitation was indistinguishable from death. The fishery subsequently killed 2.5% of tagged wild fish and harvested 20% (1999) and 43% (2000) of the hatchery fish. Seventy‐two tagged fish were recaptured and released in the sport fishery up to three times without any mortality before spawning. Hatchery fish were recaptured at twice the rate of wild fish. At least 92% of unharvested fish spawned, and 75% of successful spawners survived to emigrate from the watershed. The incidence of postspawning death did not vary with the frequency of capture and release. Catch‐and‐release angling imposed small costs in terms of survival; however, behavioral differences existed between adult wild fish and the adult F1 progeny of wild fish reared to smolt stage in a hatchery.

REACH SCALE HYDRAULIC ASSESSMENT OF INSTREAM SALMONID HABITAT RESTORATION1

ABSTRACT: This study investigates the use of a two‐dimensional hydrodynamic model (River2D) for an assessment of the effects of instream large woody debris and rock groyne habitat structures. The bathymetry of a study reach (a side channel of the Chilliwack River located in southwestern British Columbia) was surveyed after the installation of 11 instream restoration structures. A digital elevation model was developed and used with a hydrodynamic model to predict local velocity, depth, scour, and habitat characteristics. The channel was resurveyed after the fall high‐flow season during which a bankfull event occurred. Pre‐flood and post‐flood bathymetry pool distributions were compared. Measured scour was compared to predicted shear and pre‐flood and post‐flood fish habitat indices for coho salmon (Oncorhynchus kisutch) and steelhead trout (O. mykiss) were compared. Two‐dimensional flow model velocity and depth predictions compare favorably to measured field values with mean standard errors of 24 percent and 6 percent, respectively, while areas of predicted high shear coincide with the newly formed pool locations. At high flows, the fish habitat index used (weighted usable area) increased by 150 percent to 210 percent. The application of the hydrodynamic model indicated a net habitat benefit from the restoration activities and provides a means of assessing and optimizing planned works.

SEASONAL TRENDS IN POPULATION DENSITY, DISTRIBUTION, AND MOVEMENT OF AMERICAN DIPPERS WITHIN A WATERSHED OF SOUTHWESTERN BRITISH COLUMBIA, CANADA

Abstract American Dippers concentrate on low-elevation streams during fall and winter in many parts of their range; however the breeding origin relative to the wintering location is poorly understood. Our objectives were to identify seasonal changes in the density and distribution of American Dippers, to classify the migratory behavior of the local population, and to determine the origin of winter migrants within a coastal watershed of British Columbia, Canada. During 1999–2002, we color banded 522 dippers and radio-tagged 14 in the Chilliwack River watershed. Using mark-resighting techniques, we identified peak densities on the main river during early November (9.8 ± 1.4 [SE] birds per stream km), which was nearly 5 times higher than in early July (2.1 ± 0.3 birds per stream km). The watershed's total population size, estimated from November surveys, was 429 ± 64 [SE] dippers in 1999, 682 ± 79 in 2000, 697 ± 123 in 2001, and 550 ± 72 in 2002. The majority (79– 90%) of the dipper population seasonally mig...

Dispersion of gold in Slesse Creek, British Columbia

Because of the high costs and difficult logistics of geochemical surveys in remote regions, sediments collected from large streams must often suffice to determine the presence or absence of mineralization. Here we study this problem in Slesse Creek, a gold-rich river that drains north from the Mt. Baker District, Washington, USA, to enter the Chilliwack River, British Columbia, c . 90 km east of Vancouver. Anomalous Au values are derived from the abandoned Red Mountain Mine just south of the USA–Canada border. Sediments were collected from Slesse Creek and its tributaries, and from other large streams in the Chilliwack River basin. Concentrations of Au in tributaries from the Red Mountain Mine range from 250 to 2330 ppb and are much greater than in other tributaries. Sediments from Slesse Creek also have anomalous, but extremely erratic, Au values. This erratic distribution of Au is generally similar to that of magnetic grains and associated elements (e.g. V) but is negatively correlated with elements, such as Na, associated with light minerals. Results are interpreted as an evolution in sediment geochemistry from the tributaries to Slesse Creek: composition of the former appears to be controlled by source (i.e. geology) whereas geochemistry of sediments in Slesse Creek has been strongly modified by fluvial processes that concentrate Au and other heavy minerals. This shift from source- to process-related geochemistry invalidates the traditional geochemical dilution model and gives long anomalous dispersion trains for Au. These provide suitable targets for low-density regional surveys, but are difficult to interpret because of their erratic character. The contribution of fluvial processes to the concentration of Au can, however, be evaluated by comparison with elements such as V, that are associated with ubiquitous heavy minerals, or by plotting data on x – y – z source–process plots.

Clearcut logging restricts the movements of terrestrial Pacific giant salamanders (Dicamptodon tenebrosus Good)

Pacific giant salamanders (Dicamptodon tenebrosus Good) in the Chilliwack River valley of southwestern British Columbia are at the periphery of their range, and therefore of conservation concern. Although logging is a potential threat to the species, no studies have examined how clear-cutting affects its terrestrial stage. We used radio telemetry to compare the movements of 35 terrestrial Pacific giant salamanders at sites with three different logging histories: forested, clearcut to the stream margin, and clearcut with riparian buffer strips. The results demonstrate that logging affected movements of the salamanders. Salamanders in clearcuts remained significantly closer to the stream, spent more time in subterranean refuges, and had smaller home ranges than those at forested sites. During a dry year, salamanders in clearcuts were significantly more dependent on precipitation for their movement than salamanders in forested habitats. Salamander movement behavior in riparian buffer strips was not significantly different from that at forested sites but was significantly different from that at clearcut sites. Riparian buffer strips appear to mitigate some of the negative effects of clearcuts on salamander movement.

Bed‐material transport estimated from channel morphodynamics: Chilliwack River, British Columbia

Bed‐material transport estimated from channel morphodynamics: Chilliwack River, British Columbia

Bed-material transport estimated from channel morphodynamics: Chilliwack River, British Columbia

This study investigates the relation between channel changes, as mapped from aerial photography, and bed-material transport along Chilliwack River, British Columbia. Detailed mapping of channel features was completed for five dates between 1952 and 1991 using an analytical stereoplotter. Data were transferred to a geographic information system (GIS) to analyse changes during four consecutive periods. Erosion and deposition volumes along channel reaches were estimated by multiplying measured areal changes by the bed-material depth along each reach. Bed-material transport rates are related to morphologic changes using a sediment budget approach. The highest rate of transport for the four study periods is estimated as 55 000 ± 10 000 m3 a−1 between 1983 and 1991. These rates are compared with estimates from short-term (1–2 year) changes along the lower reach to investigate variations in sediment flux that may otherwise remain undetected. Significant morphologic change occurs roughly once every 5 years when flows are large enough to erode and entrain large volumes of bed material stored within the contemporary floodplain. In the absence of large floods, transport rates decline and vegetation begins to establish new floodplain. Copyright © 2000 John Wiley & Sons, Ltd.

Geographic Distribution of Chromosome and Microsatellite DNA Polymorphisms in Oncorhynchus mykiss Native to Western Washington

Chromosome studies of native populations of Oncorhynchus mykiss (steelhead and rainbow trout) in western Washington and southern British Columbia revealed the presence of two evolutionarily distinct chromosome lineages. Populations between, and including, the Elwha River, Washington, and Chilliwack River, British Columbia, contained 2n = 60 chromosomes. Populations on the central Washington coast contained 2n = 58 chromosomes. The north Washington coast and western Strait of Juan de Fuca contained individuals with 58, 59, or 60 chromosomes, suggesting this is a transition zone between 58 and 60 chromosome groups. The differences in chromosomal structure between 2n = 58 and 2n = 60 groups are presumably a Robertsonian rearrangement and an inversion. Alelic variation at three microsatellite loci (One ,u6, One u11 and Omy 77) also was examined, and no significant variation was detected among the 58 and 60 chromosome races. A hypothesis is presented concerning the origin of the 60 chromosome lineage.