piscivorous (eats fish) at smaller sizes than Sacramento pikeminnow, and ate more fish species during summer and fall regardless of size. No Delta smelt were reported in any of the stomachs of the three predators, and Chinook salmon were reported found in only one of the largemouth bass stomachs (.004% of 245), and 2 of the striped bass stomachs (.01% of 217). Additional non-identifiable fish remains were also found in the stomachs.
Based on the results of these and other studies, we can conclude that both striped and largemouth bass prey upon Chinook salmon and occasionally Delta smelt. The total amount is unknown but most likely predation occurs at times and locations where salmon and smelt are most abundant or most vulnerable to predation. Our conclusion: although salmon and smelt are not major prey species, they are occasionally eaten, which is probably not a big revelation to most Delta bass anglers. Nevertheless, the question remains - Do sport fishing regulations result in more nonnative fish predation on listed species, and would the elimination of angling regulations result in less predation? The assumption is based on the notion that without regulations, anglers would catch more bass and there would be fewer predators in the population.
Fisheryscientists and biologists have long understoodthatitisverydifficult, if not impossibleto eliminateafishpopulation byangling,especiallyinlarge lakes andreservoirs, ora system like the Delta. However, the structureofthepopulation can be altered through anglingregulationsand isa basisfor much fishery management. Generally,regulationsare designedto protectaparticularpopulation and allowan acceptable harvestofacertaingroup orsize offish. Thisistypically done throughsize,bag,season,or gear limits.
Most angling regulation studies conclude that protective bag and minimum size regulations protect the smaller sized fish while allowing limited harvest of larger individuals. This rationale is actually the basis for farm pond management throughout the nation: California’s 12-inch minimum size, the 5-fish bag limit on largemouth bass fisheries in the Delta and most reservoirs, and size and bag limits on Delta striped bass. The effectiveness of a size limit regulation on black bass was studied many years ago at Merle Collins Reservoir. Under the pre-size limit regulation, the population was dominated with smaller, slower growing fish, while larger, faster growing fish were harvested by anglers. Without any regulations, the population was dominated by small, undesirably sized bass that were not harvested by anglers. With a minimum size and reduced bag limit, smaller fish were
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protected and when they exceeded the minimum size, an allowable percentage of the population was harvested by anglers. Many of the same conclusions relate to striped bass fishery management. Years ago, overharvest was considered a major management problem. Today, the issue has largely disappeared because of the popularity of catch-and-release fishing and health warnings dealing with fish consumption.
Several years ago, the issue of de-regulation was the topic of a conference held in Oregon. I attended and spoke at the conference. Like the Delta, at issue were size and bag limits on smallmouth bass and walleye in the Columbia River, and predation by nonnative fish on native species, especially Chinook salmon. Information from Columbia River fish food habit studies was similar to that reported for the Delta; some juvenile Chinook salmon were eaten by the nonnative species but they were not a major food item. More importantly, ecologists and fishery scientists in attendance agreed that eliminating regulations on nonnative sport species would alter the population structure and result in larger numbers of smaller sized fish that were the most effective predators. Based on this information and conclusions, the issue of de-regulation was dropped by the regulating agencies.
Finally, will de-regulation affect my fishing success? I suspect it may over the long term but the effect will not be noticed immediately. The number of fish harvested from the Delta has most likely dropped in recent years because of a greater catch- and-release philosophy among anglers. Although numbers of striped bass are not reported as great as years ago, the largemouth bass fishery continues to thrive. In addition, the current health warnings on the consumption of fish from the Delta do not add to most anglers’ desire to keep and eat Delta fish. Some anglers do still keep and eat fish from the Delta, but I suspect they are a minority. Illegal take of under sized fish and certain species, such as sturgeon, continues to be a problem and will persist in spite of regulations or de-regulation.
Nonetheless, in spite of an abundance of good science, the topic of predator- prey relationships still comes up as special interest groups attempt to find ways to circumvent and divert attention from the real issues. How we as a society move and use water will continue to be an important and much-discussed topic. A little research on the subject can help every angler and interested individual become more familiar with the issues and the science, which will lead to better and more informed decisions.