The Delta is also a habitat for many species of fish, birds, mammals, and plants, and it supports agricultural and recreational activities while also being the focal point for water distribution throughout the State.
The development of the Delta as it exists today started in late 1850 when the Swamp and Overflow Land Act transferred ownership of all swamp and overflow land, including Delta marshes, from the federal government to the State of California. In 1861, the State Legislature created the Board of Swamp and Overflowed Land Commissioners to manage reclamation projects, and in 1866, the authority of the Board was transferred to county boards of supervisors. The Delta now covers 738,000 acres interlaced with hundreds of miles of waterways, with much of the land below sea level, relying on more than 1,000 miles of levees for protection against flooding. 20
White sturgeon is one of the most spectacular native species in California, and the population has been depleted at times by unrestricted commercial fishing in both the Columbia and the Sacramento-San Joaquin systems. Sturgeon populations vary through time and are also affected by drought conditions, long-term exposure to chemical contaminants, collisions with boat and ship propellers, and other causes.
The methodology for this study is first to conduct observational studies in areas of known sea lion predation and areas where reported haul-outs have occurred within the Sacramento Delta.
Also, researchers will conduct dockside interviews with recreational fishermen at public launch areas on the Sacramento and San Joaquin Rivers. Researchrs will further distribute preaddressed and stamped voluntary interview forms to Sacramento
Delta marinas for Harbormasters to hand out to fishermen so they can report encounters or observations of sea lions.
The proposed dates for data collection are September 2007-January 2008.
This study clearly has limitations, first based on the use of observational methods subject to bias and to various forces that can alter what is observed at a given time. Such observations also may not show the sort of data needed to gauge the scope of the problem or to ascertain specific causes for changes that might be noted.
Certain questions cannot be answered by this sort of study, though some of the data that could be useful in finding answers to these questions might be clarified for further study. Among the questions of interest that cannot be answered directly here are the following:
Have fishery catches changed the composition of the fish community causing increased competition for prey with sea lions and harbor seals resulting in increased foraging ranges?
Have removals of prey by fisheries reduced ecosystem-wide prey abundance or availability, resulting in increased foraging ranges of sea lions and harbor seals?
Have environmental changes altered the composition of the fish community, reducing the abundance, availability, or quality of prey resulting in increased foraging ranges of sea lions and harbor seals?
Have rapidly growing populations of pinnipeds altered the composition of the sea lion community, reducing the abundance, availability, or quality of prey for sea lions resulting in increased foraging ranges?
Answering these questions might provide more specific information on the causes of the depletion of the fishing stock over time and could be valuable in determining the precise relationship between mammals in the area and the population of fish. The present study is intended to ascertain whether these two populations are growing or diminishing and whether they are doing either at the same time or is one growing while the other diminishes. Even in the latter case, a diminution in one population while there is a rise in the other does not necessarily indicate causation, but the nature of the change has to be ascertained before the reason for that change can be investigated. Indeed, there are so many reasons cited for any curtailment of the fish population that it becomes important to differentiate the various causes and how much they contribute to the change seen. This research is a beginning to an analysis of the different causes to see which is more cogent in the present situation.
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