The Native Fish Lab's research is predominated by studies involving the razorback sucker and bonytail chub, two of the "big-river" fish endemic to the Colorado River basin.  These species, each critically endangered, warrant extensive reintroduction, recovery, and monitoring programs throughout their historic ranges.  The Native Fish Lab does not dedicate its efforts to the salvation of individual species, rather, we are concerned with the status of fish communities and ecosystems.  The projects listed below reflect only a few of the lab's activities.

Key terms are underlined below, indicating a link to further explanation.  Also see species of interest page.

Abstract:

Decline of Wild Razorback Sucker in Lake Mohave, AZ-NV and Population Augmentation by Repatriation

Status: Ongoing

Publication:  Karam et al. 2008

Report:  Kesner et al. 2008

During the few years of Lake Mohave's filling after the closure of Davis Dam in 1951, the razorback sucker experienced a local population boom within the new lake.  It is suspected that the big river fishes inundated the historical floodplains and the isolated lakes and ponds provided ample nursery habitat and a refuge from predation.  Once Lake Mohave was filled, the non-native fishes followed suit and established populations in the lake.  It is at this point that the razorback sucker ceased to recruit offspring.  Though the population of adults successfully spawns and produces many larvae in the lake, recruitment to adulthood has not been observed in decades.  The wild population that peaked to a hundred thousand or more in the 1950's has gradually declined to an estimated few hundred elderly fish.  A stocking program of hatchery-reared, PIT tagged fish was initiated in 1992 and continues today.  Nearly 150 thousand repatriates have been stocked into Lake Mohave, but we only estimate a population of about 1,500 fish by mark-recapture methods.  The Lake Mohave population is valued both intrinsically and politically in that federal policy requires the preservation of the genetic variation of the population in the lake.  To date, this variation has been successfully maintained.

Survival of Razorback Sucker Stocked into the lower Colorado River

Status: Completed

Final Report: Schooley et al. 2008

Razorback suckers have been repatriated to the lower Colorado River for nearly 30 years, but stocking has recently been qualitatively accelerated to meet requirements of a U.S. Fish and Wildlife Service Biological Opinion of lower river operations (USFWS 1997).  Moreover, monitoring of these fish has been largely sporadic and incidental to sport-fish related activities.  The purpose of this work is to assess survival of stocked fish by performing an intensive, opportunistic survey that targets razorback suckers in approximately 282 km of river from Parker Dam downstream to Yuma.  The intention is to collect multiple samples from the main channel and all watercraft-accessible backwaters and side channels to assess post-stocking survival, distribution, and abundance of the target species.  Population abundance of razorback sucker is to be estimated quantitatively using mark-recapture methods if adequate data are available.

To date (July 2006) sampling efforts have yielded 1,100 razorback sucker captures out of 60,000 fish collected.  Repatriates are consistently encountered near the stocking site and these stockings are supporting small populations in this reach.  Overall, survival remains low, yet long-term trends have yet to be revealed.

Dispersal of Razorback Sucker Stocked into the lower Colorado River

Status: Completed

Report:

In spring 2005, we added a dispersal aspect to the survival project described above.   The intent is to determine if an intermittently connected backwater would provide better acclimation of the fish and restrict dispersal.  Two batches of one dozen radio tagged fish were released into two backwaters on the lower Colorado River.  Phase One results show that fish stocked to a backwater with an open connection to the river dispersed immediately (presumably due to high daily fluctuations in river stage) whereas fish stocked to a backwater with an intermittent or restricted connection have held within the backwater though they have had opportunities to leave.  We speculate that a prolonged acclimation period post-stocking will result in increased survival.  Phase Two utilized surgically implanted sonic telemetry tags (see images here) with motion-sensitive mortality switches. 

A second aspect to this dispersal investigation involved the placement of a PIT tag scanner on the entrance/exit of the intermittently connected backwater.  This equipment passively monitors the exodus of PIT tagged fish from the backwater and provide additional information on post-stocking dispersal without the invasiveness of physical collections.  Data thus far have been minimal, but future stockings will likely increase the rate of exodus, as backwater carrying capacity is realized.

Temporal effect on larval detection following consumption by fishes

Status:  Completed

Publication:  Schooley et al. 2008

We have long been interested in predation as a mechanism of impact of nonnative fishes on native species.  Especially worrisome is that no published studies have reported fish larvae in digestive tract contents of potential predators, even though recruitment failure has been identified as a cause of decline of some native species.  We fed swim-up razorback sucker larvae to juveniles of five nonnative fishes (two minnows, two sunfish, and a bullhead catfish), documented consumption by direct observation, and sacrificed individual predators at fixed intervals after each consumption event.  Digestive tracts were excised and consumed larvae located and ranked according to extent of digestion from undamaged to unrecognizable.  Results within family were remarkably consistent.  Minnows masticated larvae and the process usually rendered them unrecognizable regardless of elapsed time post-consumption.  Sunfishes and bullheads swallowed larvae whole and chemical digestion proceeded rapidly; most larvae were unrecognizable within 30 minutes and essentially all within 60 minutes.  Standard techniques for assessing food habits are unlikely to detect larval fishes in predator guts, and thus impacts of predation may be overlooked or significantly underestimated.  Complete results are pending publication in the open literature.

Cibola High Levee Pond: a lower Colorado River refugia for razorback sucker and bonytail chub

See Cibola HLP page

Status: Completed

Cibola High Levee Pond, a man-made backwater in the historical Colorado River channel now isolated from the river by the placement of levees, was established as a native fish rearing facility in 1993.  All fishes were removed from the backwater and it was subsequently stocked with razorback sucker and bonytail chub.  Monitoring efforts have persisted to date and successful recruitment for both species has been observed in the absence of non-native predators.  The pond has provided a wealth of valuable information on growth rates, spawning behavior, feeding habits, and survival rates, just to name a few.

Razorback Sucker & Bonytail Chub Mark-Recapture Database

Status: Ongoing

M & A Native Fish Lab maintains extensive PIT tag mark-recapture databases for both the bonytail chub and razorback sucker, the latter of which is the largest such database for a freshwater species.  Much information is derived from this database, which represents decades of research by many dedicated groups and individuals, namely the Lake Mohave Native Fish Work Group.  This database is used to generate population estimates, document the predicted decline of a wild population and the development of a repatriated one. 

We have developed a web link to this database such that online PIT tag queries may be performed (i.e. enter a ten-digit PIT code and receive the entire release and capture history for that individual fish).  Please call the lab for permission to access this secure database.

Central Arizona Project (CAP) and Salt River Project (SRP) Canal Monitoring

Status: Ongoing

Stocking History for Razorback Sucker

Status: Completed

Publication: Schooley & Marsh 2007

The razorback sucker Xyrauchen texanus was historically widespread and abundant throughout the larger streams of the Colorado River basin, ranging from Sonora, Mexico to Wyoming.  The fish is federally listed as endangered (1991) and except for scattered individuals and small wild populations in Lake Mohave of the lower basin and the Green and lower Yampa rivers of the upper basin, the species is extirpated elsewhere.  The razorback sucker's decline is attributed to habitat loss and modification and predation by introduced, non-native fishes.  Despite substantial numbers, the early life stages of razorback sucker progeny are rapidly consumed by introduced predators which results in insufficient recruitment to adulthood.  The elderly, wild adults of this long-lived species are disappearing and recovery efforts now focus on replacement of these fish with repatriated (or reintroduced) adults.  Thirty years of federal and state efforts have resulted in the repatriation of millions of razorback suckers to the lower Colorado River Basin, but few have been captured as adults.  Stocking success and subsequent survival are highly dependent on size at release.  When estimates of size-based first-year survival rates were applied batches of repatriated fish, we observed, in total, less than 1% chance of first year survival and most fish stocked to date are expected to have been rapidly consumed soon after release.  Overall, stocking success has been nil, long-term survival is unknown, and no new populations have been established.

Abstract:

Bonytail Chub Foods and Feeding Habits, Cibola High Levee Pond, Lower Colorado River, Arizona and California, 2003-2004

Status: Completed

Report:

This report presents one aspect of ongoing studies of native bonytail Gila elegans and razorback sucker Xyrauchen texanus in the Cibola High Levee Pond (HLP).  The Cibola HLP is a small (ca. 5 acre) remnant of the lower Colorado River channel located between the river (lower) and inland (high) levees on the U.S. Fish and Wildlife Service Cibola National Wildlife Refuge in La Paz County, Arizona and Imperial County, California.  The pond was reclaimed to eliminate non-native fishes and first stocked with native species in 1993, and since that time the site has served both management and research roles (see LaBarbara 1999, Marsh 2000, Mueller et al. 2003).

The purposes of this investigation were to (1) document foods utilized by bonytail, (2) examine food utilization as a function of fish size, and (3) investigate temporal aspect of feeding habitats and food utilization by bonytail inhabiting the Cibola HLP.  These goals were to be accomplished by acquiring non-lethal stomach samples from evening and nighttime collections of bonytail representing relatively larger and relatively smaller fish across two years.