Term Paper: Marine Mammal Impact on Fisheries

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Sacramento Basin

The project is designed to examine the link between marine mammals and fisheries in the area of the Sacramento Delta, looking particularly to the impact pinnipeds have on the anadramous fish populations and recreational fishery in this region.

The goal of this research project is to assess the distribution and abundance of pinnipeds in the Sacramento and San Joaquin Rivers during the migration of fall and winter runs of anadramous fish populations. The intent is to see what effect an increase or decrease in the number of pinnipeds in the region has on the size and vigor of the fish populations in the same area, measured in terms of the impact on recreational fishing. Any effect would also mean an impact on the economic viability of the marine region and on the ecology of the delta.

Significance

This project will provide information on the variation in population size of both the pinniped population and the fish population in the Sacramento Delta and show how the two figures are linked. The ecological impact of an increase in the pinniped population could be devastating if it means a diminution in the fish population in the same region. The fishing industry in the delta area is an important economic element for the local population and keeps people coming back to the area year after year for recreation and for commercial fishing. Knowing the cause of an increase or a diminution in the fish population is the first step toward doing something about it. Assuming that the pinniped population is indeed increasing, it is presumed that this is because of wider ecological changes and problems, such as a loss of prey affecting the abundance, availability, or quality of prey so that the foraging range of sea lions and harbor seals would increase, causing an adverse impact on the fish population in the delta. This project can help clarify the issue with observations of the population now, compared to observations recorded in the past to see the degree and direction of change. A comparison of the pinniped population and the fish population over time can show any relationship between the two, a correlational description that would be suggestive and that would indicate the need for more data to ascertain the reason for the correlation and what effects it might have on the ecology of the region.

Background

For decades, there has been competition between marine mammals and commercial fisheries worldwide.1,2 Anadramous fishes found in the Sacramento Delta are part of commercial and recreational fisheries from the coastal regions to the breeding habitats far inland.

The California Sea Lion (Zalophus californianus) and Pacific Harbor Seal (Phoco vitulina) are known to prey on salmonids in the ocean and bays.3 the population of California Sea Lions in the U.S. was estimated at 237,000 for 2006 and is increasing at an annual rate of 5.4

6.1% per year.4

With the population of these opportunist feeding marine mammals growing at such a rapid rate, competition with fisheries has increased.

The anadramous fish populations which migrate inland throughout the Sacramento Delta have declined dramatically in the past 50 years, due to a combination of factors including habitat destruction and overfishing.5,6 These populations include the Winter Run Chinook Salmon (Oncorhynchus tshawytscha) listed as Federal and State

Endangered Species, Spring Run Chinook Salmon (Oncorhynchus tshawytscha), listed as Federal and State Threatened,7,8 Steelhead (Oncorhynchus mykiss),

Federal Threatened,8 Striped Bass, White Sturgeon (Acipenser transmontanus) and Green Sturgeon (Acipenser medirostris). California Sea Lions and Pacific Harbor

Seals have been protected by the federal Marine Mammal Protection Act since

1972.9 Although some marine mammals, such as the Hawaiian Monk Seal and the Stellar Sea Lion, remain endangered,10 the California Sea Lion and Harbor Seal have experienced a population explosion resulting in increased competition for foraging. Consequently, these pinnipeds need to increase foraging ranges as a means of survival. As foraging ranges increase, energy demands increase. The end result is increased consumption of available resources.

As Sea Lions and Harbor Seals move up into the river system where their natural predators, the killer whales and great white sharks11, are not present, they find themselves at the top of the food web. Therefore, their main competition for resources is humans, particularly recreational fishermen.

Recreational fishermen, some fisheries biologists, lawmakers, and other interest groups have proposed solutions included culling sea lions, hazing them,12 and most recently, in the states of Oregon and Washington, killing some individual rogue" sea lions.13 Yet no study or model exists that establishes what impact California Sea Lions and Pacific Harbor Seals have on the declining anadramous fish populations and the recreational sport-fishery in the rivers and sloughs of the Sacramento Delta.

A study of San Francisco Bay suggests some of the dynamics involved. This system is located at the mouth of the Sacramento-San Joaquin River system, which carries runoff from 40% of the surface area of California. The San Francisco estuary consists of five distinct subareas: Suisun Bay, Carquinez Strait, San Pablo Bay, Central Bay, and South Bay, each with its own characteristic biological assemblage. Reduction in freshwater inflows from the Sacramento and San Joaquin Rivers has profoundly altered the aquatic environment of the estuary, standing today at less than 50% of historic levels because of diversion of water from the Sacramento-San Joaquin River system away from San Francisco Bay, producing profound effects on the marine resources of the Bay, most noticeably on the anadromous fishes such as striped bass and salmon. The biological resources of the San Francisco Estuary also have been greatly affected by the introduction of non-indigenous species. 5

The system as a whole is today governed by the Marine Life Protection Act (MLPA), which was signed into law in 1999 and which calls on the state to redesign the system of marine protected areas to be more coherent and effective in protecting marine life and habitats, marine ecosystems, and marine natural heritage, as well as to improve recreational, educational, and study opportunities provided by marine ecosystems. 6 Data open this area and linkages between different marine and river systems is available 7, as is data on the species common to the region in question. 8

Various sources for the diminution in anadramous fish populations in the ara have been examined, among them climate change (including global warming and so the actions of humans I altering the climate) 9 and the blockage of the river in certain areas. 10,14

The issue is also raised in the Integrated Regional Water Management Plan in which it is noted how water policy can affect the fish population and how finding a balance between the water needs of the region and the protection of the fish population must be found. 15 Some of the technologies designed to produce more potable water affect the anadramous fish populations in the region as well. 16 Studies have been conducted of the effect on the fish population of an increase in mammals in various river regions. 17,18 in the Sacramento region, fall and winter runs of anadramous fishes occur after the breeding season of pinnipeds, and it has been primarily male seal lions and harbor seals found preying on fish in the Delta river system.

Outline of Proposal

Proposed Methods:

The method for this proposal is that of an observational study combined with a fisherman survey. An observational study is necessarily prone to more researcher bias and other errors but is necessary when a controlled experiment is not feasible, as it would not be given the different populations involved in this area and the numerous factors that can affect the outcome. Such a study is largely preliminary, helping to develop more cogent hypotheses about what is happening in a given situation and eliminating some of the variables for future studies. The fishermen survey gathers data from a less formal type of observation study, asking what fishermen in the area have seen and how they interpret what they observe.

Following the survey observation methods in 17,18, detailed observations of the mammal population in the area will be made, associated with the season. The observations of fishermen relate more to the size of the fish population over time, as indicated by the size of the catch over time.

The fishermen survey methods are to be modeled after the survey methods used in 19.

The area to be covered is limited to the Sacramento River from Rio Vista, California to Colusa, California and the San Joaquin River. The Sacramento Delta region is formed by the mouths of two major rivers, the Sacramento River and the San Joaquin River. The mouths of these rivers serve as important agricultural, wildlife, and recreation centers. The Sacramento Delta is located northeast of the San Francisco Bay and contains an archipelago of fertile islands; below sea level, and protected by levees. The Delta also serves as a major stopping point for migratory birds such as double-crested cormorants and northern shovelers. The Delta is augmented by runoff from over 40% of the State's land area, and this… [END OF PREVIEW]

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