9586

• UCREFRP Catalog Number: 9586
• Author: Desert Fishes Council.
• Title: Proceedings of the Desert Fishes Council Volume XXVI 1994 Annual Symposium.
• USFW Year: 1994.
• USFW - Doc Type: Furnace Creek, CA.
• Copyright Material: NO

DFC PROCEEDINGS - ABSTRACTS AND CONTRIBUTED PAPERS IN ORDER PRESENTED
*SJOBERG,J.C. (Nevada Division otwildlik, Region m, Las Vegas, NV)
Historic distribution and current status of the razorback sucker
in Lake Mead, Nevada-Arizona
Distribution histSrica y situaci6n actual del matalote jorobado
en el Lago Mead, Nevada-Arizona
KEYWORDS: razorback sucker; Lake Mead; Nevada; historic distribution; status; Colorado River
ABSTRACT
Although occupancy of Lake Mead by razorback suckers (Xyrauchen texanus) has been documented since
the reservoir's formation, the majority of management emphasis and research interest has focused on the larger
extant population in Lake Mohave immediately downstream. Most literature references to the Lake Mead razorback
population are anecdotal and historic observation records are scattered and poorly organized. A review of Nevada
Department of Wildlife (NDOW) and other agency field records documented observation or collection of 66 adult
razorback suckers in the period 1952 to 1980, with the largest number of collection sites in the Overton Arm and
Greg Basin/Grand Wash areas of the reservoir. No agency capture records have been located for the period 1980
to 1989. Intensive sampling efforts for razorback suckers by NDOW since 1990 have resulted in the capture of 49
razorback suckers at three locations, all in the February through April period. Gill net sampling lakewide in 1991
through April 1994 included 328 net nights at 62 locations, and trammel net sampling at 17 locations for 232 net
nights.
CLAVES: matalote jorobado; Lago Mead; Nevada; distribuci6n hist6rica; estatus; Rio Colorado
RESUMEN
No obstante de que la ocupaci6n del lago Mead por parte del matalote jorobado ha sido documentada desde
la formaci6n de los reservorios, la mayor parte del inter6s sobre manejo a investigaci6n se ha enfocado hacia la
poblaci6n mas extensa en el lago Mohave inmediatamente arroyo-abajo. La mayor parte de las referencias literarias
sobre el matalote del lago Mead son registros de tipo anecd6tico y los registros hist6ricos son dispersos y
pobremente organizados. Una revisi6n del Departamento de Vida Silvestre de Nevada (NDOW) y otros registros
de campo de las agencias observados y documentados o colecciones de 66 matalotes adultos en el periodo de 1952
a 1980, con el numero mas amplio de sitios de colectas en el Overton Arm y el area de Greg Basin / Grand Wash
en el reservorio. No se han localizado registros de captura por la agencia para este periodo de 1980 a 1989.
Esfuerzos de muestreo intensivo para los matalotes por NDOW desde 1990 han resultado en la captura de 49
matalotes jorobados en tres localidades, todos en los perfodos de Febrero a Abril. El muestreo con agalleras a to
amplio del lago en 1991 hasta abril de 1994 incluye 328 redes nocturnas en 62 localidades y el muestreo con
transmallos en 17 localidades por 232 redes nocturnas.
CONTRIBUTED PAPER
Because of a lack of recruitment and loss of adult
fish over time, mainstem reservoir populations of the
razorback sucker Xyrauchen texanus in the lower
Colorado River basin are considered to be generally
absent with the exception of Lake Mohave, which has
a large but rapidly declining adult population estimated
at not more than 25,000 individuals. The presence of
the large Lake Mohave population has logically
focused research and recovery efforts on that reservoir
and little recent effort has been placed on quantifying
the status of other relict reservoir populations. This
presentation summarizes current knowledge on the
status of razorback suckers in Lake Mead.
Jonez and Sumner (1954) reported razorback
suckers as widespread throughout Lake Mead during
their studies in the early 1950's, with particular
concentrations observed in, inflow areas and along
gravel shores during the spawning period. Field notes
from NDOW biologists in the 1950's mention
occasional observations of "hundreds" of suckers in
pelagic areas of the Boulder Basin, and near the mouth
of the Muddy River in the upper Overton Arm.
Although sightings of adult razorback suckers in Lake
Mead were reported as common through at least the
early 1970's (Allan and Roden, 1978), almost all
reports are anecdotal and few documented collections
or observations exist in published literature or agency
field records. A review of NDOW and Arizona Game
and Fish field records documented collections or
observations of 66 adult razorback suckers in the
period 1952 to 1980. These observations occurred at
25 locations in all four major areas of the lake, and
from a variety of methods.
Eight adult razorback suckers were reported as
killed in the Boulder Basin by deep water detonations
in June 1962 (Melander, 1962) and may indicate use of
deeper pelagic lake zones outside of the spawning
period. The detonations occurred at a 200-foot depth
one mile north of Saddle Island, and also killed
approximately 1,000,000 juvenile and adult game fish.
The majority of known collection sites (23 of 36)
for razorback sucker during the 1952-1980 period are
24