According to TPWD:

"Hybrid Striped Bass are returning to Lake Nasworthy. Last week we stocked ~ 100,000 fingerling hybrid striped bass for the purpose of improving the gizzard shad population.

Gizzard shad are the primary prey species in Lake Nasworthy. However, historical sampling data has shown that the gizzard shad population is composed mostly of large fish (10+ inches), which are to big to be eaten by most sportfish, such as crappie and largemouth bass. Additionally, when large adult shad are over-abundant, it suppresses their own natural reproduction, meaning fewer small shad as prey. As a result, crappie and bass populations have shown slow growth and have been under weight, due to the lack of small prey.

Research has shown that stocking hybrid striped bass, at a high enough rate, can reduce the abundance of large shad and lead to better natural reproduction. The goal of stocking hybrid striped bass in Lake Naswrothy is to reduce the over-abundance of large shad, which should lead to improved shad reproduction, resulting in more small shad for bass and crappie to feed on.

The expected benefits include (1.) improved condition and growth of crappie and bass, and (2.) creation of a hybrid striped bass fishery for those angler who enjoy fishing for hybrids. Keep in mind, this is a long term plan. It will take the hybrid striped bass about 3 years to grow about 18 inches long, and we expect to see the gizzard shad population restructure within 3-5 years. As always, we will continue to monitor these populations to determine if these stockings produce the desired results."

Texoma is an example of all species living together and thriving. Not a lot of lakes you can catch Trophy Black Bass, Trophy Smallmouth and Big stripers on the same day. I have spent the last 45 years in and around Texoma, my Granpa was a guide back in the 70's, my uncle was a striper guide until an accident a couple years ago. And another aunt and uncle owned two large marinas until they retired.

Nothing more fun than catching Bass on a point and a stiper smash a top-water or crank-bait.

I'd say Mother Nature has the most say in shad populations as well as it influences whether or the striper can spawn, which they don't in Tawakoni like Texoma or PK regardless of water level. Hybrids can't reproduce so I'd say they're easier to control the cycle of the fluctuating prey:predator ratio. I'm guessing Nasworthy doesn't have very big Bucketmouth Bass as they should handle gizzards as well as a smaller mouth hybrid, Fork and Ray Roberts don't have a problem lacking Stripers or Hybrids. I'd say both of those species do ultimately have an impact on the number of giant largemouthbass as I believe the lakes in California that Striper were introduced into don't produce the record size black bass they used. I've caught Striper at Texoma bouncing a jig off rocks fishing for smallmouth back when the shad kill happened, like any predator they'll eat whatever moves when they get hungry enough so shad isn't their only prey.