TPWD 1961 F-6-R-8 #639: Basic Survey and Inventory of Fish Species present in Anzalduas Reservoir

Job Completion Report State of TEXAS Project No. F-6-R—8 Name: Fisheries Investigations and Surveys of the waters of Region B-B. JOb No. B—17 Title: Basic Survey and Inventory of Fish Species present in Anzalduas Reservoir. Period covered: January 1, 1960 - December 31, 1960 OBJECTIVES To determine the chemical and physical characteristics of the Anzalduas Reservoir and the relative numbers of the fish species present. PROCEDURE During February, a trip to Mission and McAllen was made to resurvey Bentsen State Park Lake. One day was spent in conferring with International Boundary and water Commission engineers about Anzalduas Reservoir and with the local state Game and Fish warden about finding boat landings on the reservoir. Only one netting trip covering three days was made by the project leader and two field assistants in October. Four gill net sets were made but neither water samples nor seining collections were made. The planned bi—monthly trips to the reservoir were not made because for the first six months of the period the project leader was unable to travel, recovering from surgery and almost continuous rains and floods during the second six months prevented access to the only available boat landing. FINDINGS No chemical analyses were made of the waters of the reservoir because reagents ‘were not taken along on the netting trip. Some physical data was obtained through confibrences with the engineers of the International Boundary and Water Commission of- fice at McAllen. Anzalduas Reservoir is formed by a dam across the Rio Grande about six miles southeast of Mission, Hidalgo County, Texas. The dam was closed in early summer of l960enm1its purpose was to raise the level of the river in order to provide gravity flow water to a large irrigation ditch serving the Mexican side of the lower Rio Grande Valley; A similar irrigation system is planned later for the American side. As yet, there are no available figures for the surface acreage or capacity of the reservoir. No map, except of the Rio Grande prior to flooding, is available. water is released from Falcon Dam, about 85 river miles above Anzalduas dam, on demand of irrigation needs. The water in Anzalduas reservoir is contained almost entirely within the natural levees lining the river and there is little overflow into adjacent flat farm lands. When water is being taken into the irrigation ditch, there age is an observable flow throughout the reservoir. At the only accessible and usable boat landing found, about eight miles above the dam, the water level seemed to fluctu- ate about three feet vertically. One netting trip was made in October, 1960, by the project leader and two field assistants. Four experimental gill nets were set approximately 2, 8, IA and 20 miles above the dam. Thirty fish of seven species were taken as shown in Tables 1 and 2. This catch was surprisingly low in numbers, variety and percentage of game fish. Both largemouth bass, Micropterus salmoides, and white bass, Roccus chrysogs, are known to produce very good seasonal fishing just below Falcon Dam, just about 5 river miles upstream from Anzalduas Dam. Several other species of fish were expected but probably missed due to netting error and the small number of nets set. Numerous signs of fishing with trotlines and throwlines were seen at several places along the lake where public access was available. Reports from several people contacted indicated that catfishing was very good at times. The local Mexican population apparently makes considerable use of both gars, Lepisosteus £23., and smallmouth buffalo, IctiObus bubalus. The only usable seining beaches seen while setting the nets were on the Mexican side of the reservoir, therefore no seining collections were made. CONCLUSIONS AND RECOMMENDATIONS On the basis of four netting collections, the fish population of the Anzalduas Reservoir seems to be very low in numbers and species. As the reservoir becomes better established, the population should increase. It is recommended that this job be con- tinued for another segment to obtain more information concerning both the fish and the physical and chemical characteristics of the reservoir. Prepared by Alvin G. Flury Approved by 2; ZW'foé' Project leader Director Inland Fisheries Division Date February 2M, 1961 Hdem H. wwmoHam om oodaeom ooHHeOdHoom.sHeSEwameHeooamH_meH beams boemHmomm memeseoHee Ooeoeme Hmmo. 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