SDAFS Reservoir Committee

SDAFS Reservoir Committee

Spring 2006 Project Summaries

Texas

Lake Fork Reservoir is an established trophy largemouth bass Micropterus salmoides fishery and has been managed under a protective slot limit since 1989. Largemouth bass 16 to 24 inches in length must be released, and only one fish over 24 inches may be kept. The fact that Lake Fork has produced 34 of the 50 biggest largemouth bass in Texas draws anglers from a broad geographic area and the trophy fishery provides a significant source of revenue for the local economy. Despite intensive sampling using standard procedures, fisheries managers in Texas have very little information on catches of trophy bass. We sought to characterize the Lake Fork trophy bass fishery using voluntary reporting of trophy fish catches. Initiated in March 2003, this ongoing survey targets bass weighing ≥ 7 lbs and/or measuring ≥ 24 inches.

Initially developed to provide recreational anglers with information on trophy bass catches, and to promote the bass fishery on Lake Fork, the trophy bass survey contains valuable information for managers. As of February 2006, we obtained information on over 5,200 trophy largemouth bass. Of the anglers reporting trophy catches, 61.7% were Texas residents. Residents of other states reporting trophy catches on Lake Fork include Oklahoma (6.0%), Missouri (5.9%), Louisiana (5.3%), and Arkansas (4.4%). Most trophy catches were reported during spring (March-May; 57.2%), followed by summer (June-August; 20.4%), winter (December-February; 12.6%), and fall (September-November; 9.8%).

We examined whether mean weight and body condition (Wr) varied as a function of year, season, moon phase, or time of day when the fish was caught. Preliminary analyses suggest mean weight and body condition of trophy bass caught during winter (December – February) were significantly higher than during all other seasons, while trophy bass mean weight and body condition during summer (June – August) were significantly lower than during all other seasons. Additionally, more trophy bass were caught per day during full moon periods than other moon phases, but this was only significant during fall months.

The number of trophy bass reported during a sampling quarter was positively correlated with directed angler effort as estimated by access creel surveys; however, the number of trophy bass caught per hour of effort was higher during the winter than during other seasons. Using trophy bass survey data in conjunction with angler access creel surveys, we conclude that the slot limit on Lake Fork is effectively sustaining the trophy bass fishery.

We are monitoring native plant introductions on Lake LBJ in Central Texas.  Eight species of native plants were introduced in 2000 at 6 sites on the reservoir to improve habitat for cover seeking species.  The reservoir shoreline is highly developed and about 80% is bulkheaded.   Introduced plants were protected by wire mesh cages and shoreline fences.  In 2002 two species of plants already present on the reservoir (water willow and spatterdock) prior to the introductions were transplanted into a new site and in-between cages at several old sites.  Minimal spread for all species outside the cages has been observed in five years, although the indigenous transplants (water willow and spatterdock) have increased significantly inside a large shoreline fence area.  Transplants used outside cages have survived, but have not increased as greatly as those put inside the shoreline fence.    

Three hundred and seventy eight fish attractors made of plastic piping were introduced at 15 sites in Canyon Reservoir in Central Texas in January 2005.  The purpose of the introductions was to improve angler catch rates.  The attractors resemble large bushes and the plastic is reported to have a life of 20 years.  Cedar trees were used at three additional sites.  All attractors were placed in 20-25 feet of water and site locations were marked with GPS and distributed to the public as requested.  In summer 2005 sites with water clarity adequate for observing fish were scuba dived.  No fish were observed on the plastic attractors, while many largemouth bass and sunfish were observed in the cedar tree attractors.  In January 2006 cedar trees were added to some sites which previously had plastic attractors only.  Sites (cedar only, plastic only and combination) will be compared again in summer 2006.

A volunteer trophy bass reporting project has been in place at Fayette County Reservoir in Central Texas since October 2004.  The purpose of the project is to supplement electrofishing data on largemouth bass greater than 21 inches in length.  This reservoir has a 14-24 inch slot length limit and electrofishing catches of bass greater than 21 inches have historically been low since the upper end of the slot limit increased from 21 to 24 inches in 1995.    Approximately 200 angler catches of bass greater than 21 inches have been voluntarily reported.  A concurrent traditional creel survey will be used to compare size distributions of the catch. 

Quarterly aquatic vegetation monitoring has been occurring on Lake Austin in Central Texas since May of 2003 to document the effects of grass carp introductions and a reservoir drawdown.  These control efforts were made in response to concerns about hydrilla coverage.  In May 2002 hydrilla covered 320 acres of this 1,599 acre highly developed urban reservoir.  Since February 2003 8,125 grass carp have been introduced and drawdowns have occurred each winter except  2005/06.   Hydrilla coverage has been reduced to less than 10 acres.  Other aquatic plants, dominated by eurasion water milfoil, still cover approximately 10 percent of the reservoir surface.  Aquatic plant coverage is highest in the upper end of the reservoir where cold water temperatures from hypolimnetic releases may be decreasing grass carp feeding rates.  Annual electrofishing surveys are being conducted to document changes in the reservoirs largemouth bass population.

Completed crappie telemetry project designed to determine if learning more about crappie locations could improve our ability to select trap netting sites.  We learned that knowing crappie locations did not improve trap net catch rates primarily because crappie often selected habitat variables (water depth, distance from shore, bank slope) where trap nets did not fish effectively.  We are beginning a new project to investigate alternative net designs and deployment strategies to better sample these fish.