7835 - Laserfiche WebLink

Home Browse Search

SYNOPSIS Introduction This volume binds together three separate reports on life history and population studies of the Colorado squawfish (Ptychocheilus lucius) in the upper Colorado River. Principal topics covered are, 1) growth and adult survival rates, 2) dispersal patterns of sub- and young adults, and 3) status and trends of the Colorado River population. One integrated study design and field effort was used to collect most of the data used in these investigations. At the beginning of each report an executive summary provides the highlights of that study. The following is a synopsis of the collective results along with recommendations for future studies and management activities. Growth rate, survival rate, and dispersal patterns are fundamental components of most demographic studies of long-lived species and are essential to understanding population dynamics. Determination of population status and trend and identification of factors limiting population increase are requisite to formulating recovery goals and management strategies for endangered species. Colorado squawfish, an endangered, long-lived, cyprinid endemic to the Colorado River system, has been the focus of much life-history research in recent years. However, many fundamental questions regarding its life history remain unanswered. Ptychocheilus lucius is well known for its potential to grow to large size and for its annual, potamodromous, spawning migrations. However, previous studies of age and growth of Colorado squawfish have relied on scale analysis. Because of the inherent problems in scale-based aging and growth estimation for long-lived species, there was a need to refine and validate existing growth estimates. Though spawning migrations and the long-distance drift of resulting larvae have been well documented, little is known about dispersal patterns of juveniles and young adults. In addition, no serious attempt has been made to estimate population size in any of the extant riverine populations. For the Colorado River population, no previous effort had been made to assess recruitment or adult survival rates. Much can be learned of long-lived fish from mark-recapture studies. Such studies require multi-year, intensive capture efforts that are systematic and river wide in scope. Most importantly, a large number of fish representing a significant portion of the population must be sampled and a safe, reliable method must be used to individually and permanently mark the fish. For this study, two relatively new methods greatly facilitated the investigators to meet these requirements: 1) an effective netting technique that trapped Colorado squawfish in backwaters where they are seasonally concentrated, and 2) passive integrated transponder (PIT) tags that are small, implanted internally, and read externally with an electronic scanner.