Young strIped Bass
Threadfin Shad Crustaceans American Shad
juvenIle strIped Bass
Threadfin Shad Delta Smelt Striped Bass Crustaceans American Shad
Prey items of Delta s the fish grows from a Other minor food ite
insects, Asiatic c
lamprey ammoco
Pacific herring, blu
three-spined stick blackfish and hitch,
sardine and (data from Turner, J.L Fish Bulletin 136. Eco
Sacramento-S
Part II: Fishes of th
Department of
mortality among migrating juvenile salmon.”
Is the plaintiffs’ contention correct – Do Delta striped bass sport fishing regulations result in more striped bass predation on listed species? Alternatively, will eliminating angling regulations result in less predation on salmon and smelt? Moreover, probably most important to anglers, will the changes affect my fishing success?
To answer these questions we must first examine the claim that striped bass eat juvenile winter run Chinook salmon and Delta smelt. Delta striped bass food habitats have been extensively studied and one early study is found in the Department of Fish and Game’s 1966 Fish Bulletin 136: Ecological Studies of The Sacramento-San Joaquin Delta , Part II: Fishes of The Delta, compiled by Jerry L. Turner and Don, W. Kelly. The bulletin included an article by Don E. Stevens, “Food habitats of striped bass, Roccus saxatilis , in the Sacramento-San Joaquin Delta”. This research was done at a time when neither Delta smelt or any runs of Chinook salmon were listed as protected species and we presume were more abundant than today.
Stevens reported that his study was based on an analysis of stomach contents of 8,628 striped bass from eight types of Delta environments. The stomachs were collected from September 1963 through August 1964. Stevens reported that the mysid shrimp, Neomysis awatschensis , and the amphipods, Corophium stimpsoni and Corophium spinicorne , were the most important foods of young bass. As bass grew their diet shifted to forage fishes, primarily small striped bass and threadfin shad,
32
Dorosoma petenens , another nonnative species. The composition of the diet varied by season and area and there was evidence that mysid shrimp were the preferred food of young bass.
Steven’s 1966 paper also reported that both king salmon Oncorhynchus tshawytscha and pond smelt (Delta smelt) Hypomesus transpacificus were found in the stomachs of all sizes of striped bass but the percentages were low. Stevens did not report which specific salmon run (spring, fall, late-fall, or winter) was eaten and the pond smelt were most likely Delta smelt. The taxonomy of the two smelt species is confusing and Pond smelt H. olidus , presently called Wakasagi H. nipponensis , are very difficult to distinguish from Delta smelt. Wakasagi were first introduced into California 1959 but were not reported from the Delta until after the species was introduced into several Central Valley reservoirs.
John Thomas, another DFG Fishery Biologist, reported that juvenile bass consumed quantities of small salmon in the spring and summer in the Sacramento River above the Delta in Fish and Game Quarterly (Vol. 53 No. (1) 1966) –“The diet of juvenile and adult striped bass, Roccus saxatilis , in the Sacramento- San Joaquin River”. It was suggested that the availability of salmon to striped bass might have been the result of greater clarity and smaller width of the river. Migrating juvenile salmon are also more concentrated in the relatively narrow river channel as compared to the Delta channels, and are most available to striped bass during the spring out migration period.
More recently, Matthew Nobriga and Fred