Studies of Ecological Requirements and Role of Stocking Augmentation for Endangered Razorback Sucker and Bonytail in the Lower Colorado River Basin - Fish densities and population estimates

Data was collected in order to evaluate the status of endangered razorback sucker and bonytail in the lower Colorado River Basin and to assess the success of augmentation programs. Specifically this project looked at the survival of razorback suckers and bonytail chub stocked in Lake Havasu and into the Colorado River below Davis Dam as part of a multiagency effort to augment endangered fish populations. Field sampling focused on 1) maximizing contacts with razorbacks, 2) improving population estimates, and 3) identifying specific spawning sites of razorbacks. Survey techniques included trammel nets, larval light raps, and sonic and radio tag telemetry. Three trends have been observed during razorback sucker monitoring efforts over the past seven years (1999-2005): 1) A steadily decreasing catch per unit effort, 2) a change in sex ratio of razorbacks caught and 3) the majority of fish captured have come from more recent stockings. The current population estimate for this reach is 1652 fish (95% confidence limits 706 to 5164): 1532 stocked razorbacks and 120 Lake Mohave stocked or wild razorbacks. This represents an overall survival rate of about 5% for the 30,807 razorbacks stocked into Lake Havasu. Calculated survival rate in 2005 varied by agency stocking the fish. In 2005, survival of razorbacks stocked by Arizona Game and Fish Department (AZGF) was 5%, Fish and Wildlife Service/ Bureau of Land Management (FWS/BLM) was 2% and Bureau of Reclamation (BOR) was 18%. Similarly, in 2004 the calculated survival was 5% for fish stocked by AZGF, 2% for fish stocked by FWS/BLM, and 27% for fish stocked by BOR. One possible factor was stocking location. Fish stocked by BOR were released in Laughlin lagoon which is a large backwater furthest upstream. AZGF stocked fish were released at Windsor Beach. This is furthest downstream location which is relatively close to water outtake structures. Fish stocked by FWS/BLM were primarily released at Golden Shores which is a large backwater found between the two other locations.

Data and Resources

This dataset has no data

Field	Value
access_constraints	["Use Constraints: These data contain locations of a threatened and/or endangered species. Given the sensitive nature of the data, access and use will be limited. Please contact the distributor for more information.", "Access Constraints: These data contain locations of a threatened and/or endangered species. Given the sensitive nature of the data, access and use will be limited. Please contact the distributor for more information."]
bbox-east-long	-114.12
bbox-north-lat	35.22
bbox-south-lat	34.2
bbox-west-long	-114.67
coupled-resource	[]
dataset-reference-date	[{"type": "publication", "value": "2005-01-01"}]
frequency-of-update	notPlanned
licence	["Although this data and information has been processed successfully on a computer system at the USGS Fort Collins Science Center, no warranty expressed or implied is made regarding the accuracy or utility of the data and information on any other system or for general or scientific purposes, nor shall the act of distribution constitute any such warranty. This disclaimer applies both to individual use of the data and information, and aggregate use with other data and information. It is also strongly recommended that careful attention be paid to the contents of the metadata file associated with these data and information. The USGS shall not be held liable for improper or incorrect use of the data and information described and/or contained herein."]
metadata-date	2005-09-26
metadata-language	eng; USA
metadata_type	geospatial
progress	completed
resource-type	dataset
responsible-party	[{"name": "U.S. Geological Survey, Fort Collins Science Center, FORT", "roles": ["pointOfContact"]}]
spatial	{"type": "Polygon", "coordinates": [[[-114.67, 34.2], [-114.12, 34.2], [-114.12, 35.22], [-114.67, 35.22], [-114.67, 34.2]]]}
spatial_harvester	true
temporal-extent-begin	1999-01-01
temporal-extent-end	2005-01-01
Groups	AmeriGEOSS National Provider North America
Tags	amerigeo amerigeoss aquatic-biology arizona az california ckan co davis-dam ecology fish-stocking geo geoss lake-havasu lower-colorado-river national north-america populations stocking-survival united-states western-us
isopen	False
metadata_created	2025-11-19T19:23:38.073663
metadata_modified	2025-11-19T19:23:38.073669
notes	Data was collected in order to evaluate the status of endangered razorback sucker and bonytail in the lower Colorado River Basin and to assess the success of augmentation programs. Specifically this project looked at the survival of razorback suckers and bonytail chub stocked in Lake Havasu and into the Colorado River below Davis Dam as part of a multiagency effort to augment endangered fish populations. Field sampling focused on 1) maximizing contacts with razorbacks, 2) improving population estimates, and 3) identifying specific spawning sites of razorbacks. Survey techniques included trammel nets, larval light raps, and sonic and radio tag telemetry. Three trends have been observed during razorback sucker monitoring efforts over the past seven years (1999-2005): 1) A steadily decreasing catch per unit effort, 2) a change in sex ratio of razorbacks caught and 3) the majority of fish captured have come from more recent stockings. The current population estimate for this reach is 1652 fish (95% confidence limits 706 to 5164): 1532 stocked razorbacks and 120 Lake Mohave stocked or wild razorbacks. This represents an overall survival rate of about 5% for the 30,807 razorbacks stocked into Lake Havasu. Calculated survival rate in 2005 varied by agency stocking the fish. In 2005, survival of razorbacks stocked by Arizona Game and Fish Department (AZGF) was 5%, Fish and Wildlife Service/ Bureau of Land Management (FWS/BLM) was 2% and Bureau of Reclamation (BOR) was 18%. Similarly, in 2004 the calculated survival was 5% for fish stocked by AZGF, 2% for fish stocked by FWS/BLM, and 27% for fish stocked by BOR. One possible factor was stocking location. Fish stocked by BOR were released in Laughlin lagoon which is a large backwater furthest upstream. AZGF stocked fish were released at Windsor Beach. This is furthest downstream location which is relatively close to water outtake structures. Fish stocked by FWS/BLM were primarily released at Golden Shores which is a large backwater found between the two other locations.
num_resources	0
num_tags	21
title	Studies of Ecological Requirements and Role of Stocking Augmentation for Endangered Razorback Sucker and Bonytail in the Lower Colorado River Basin - Fish densities and population estimates