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An Historical Review of the
Fish and Wildlife Resources of the
San Francisco Bay Area

by John E. Skinner
June, 1962

Part 6 of 6

Striped Bass  Pages 71 - 83

Striped Bass Life History Notes (Continued)

From the available data, it may be concluded that the very young fish at first depend on the microcrustacea, diatoms and other minute invertebrates. From one to four inches they depend heavily on larger crustaceans, Neomysis mercedis, Crago sp., aquatic isopods, amphipods, and marine worms. During succeeding years their diet becomes largely piscivorous, although crustaceans continue to be important.

Growth. The growth rate and relationship between age, length and weight was first worked out by Scofield (1931) for California striped bass. Robinson (1960) recently completed another study of the subject to determine if any appreciable change had occurred over the intervening 30 years. Both studies show a rapid gain in length for the first 4 years of life after which the rate becomes progressively less. Robinson, however, found that growth both in length and weight was more rapid than shown by Scofield, the difference being about 10 percent greater length and 25 percent greater weight by the end of the 7th or 8th years of life. Difficulty in aging specimens after their 7th year of life precluded accurate interpretations beyond this age without a great deal of careful study. Stripers reach a length of about 32 inches and a weight of 14 pounds by their 9th year of life. The maximum length attained in California may exceed 50 inches while the maximum weight may exceed 60 pounds (a 63 pound striped bass has been recorded). Fish attaining the above dimensions are most likely 20 years of age or over. Stripers gain weight at a relatively constant rate after their fifth year of life; the gain may be in excess of 2 pounds per year.

Age to Maturity. Scofield (op. cit.) made a careful study of maturing bass and came to the conclusion that 35 percent of the females mature by their fourth year, 87 percent by the fifth year, 98 percent spawn in their sixth year and 100 percent thereafter. Males mature earlier, many spawning while only 2 years old and most by the time they are three. Morgan and Gerlach (1950) reported mature male fish at one year of age. Males may be scarcely more than 10 inches in length by the time they mature. Females, on the other hand, are generally more than 18 inches long.

Artificial Propagation. In California, between 1907 and 1910, a brief attempt was made to propagate this species artificially. A small hatchery was built on Bouldin Island and operations were carried on for several seasons but the difficulties encountered, particularly the inability to collect ripe spawn, resulted in the abandonment of operations.

On the Atlantic Coast there still exists a hatchery at Weldon, North Carolina for this purpose.

Striped bass are extremely prolific and attempts to propagate them artificially are unwarranted. So many fry are produced through natural propagation that almost any contribution from artificial sources would be superfluous. Once established in an area any decline in the population is most likely the result of environmental factors rather than insufficient natural propagation.

Sources of Mortality. This phase of the life history of striped bass requires more investigation. Information simply is not available concerning the ages at which various types of mortality occur. Several earlier attempts to obtain data on angler haryest were attempted, but these met with difficulties.

An unknown proportion of the eggs deposited by the female are not fertilized. Losses occur while the eggs and larvae develop in their hazardous position of drifting in the river or tidal currents. Predation, sudden changes in temperature, pollution, and a number of other factors must also take a tremendous toll of eggs and larvae. As the yolk material is used up the larval fish must begin to fend for themselves, and it is at this stage that perhaps the greatest losses occur. Those which survive are continually subjected to predation, diversions and pollution, each of which could account for significant losses. Predation is everywhere apparent, but losses to pollution and water diversions occur at specific locations.

Losses at diversions are similar to those previously described for king salmon and need not be repeated here, except to say that the magnitude of striped bass losses at diversions far exceeds those of any other species in the Bay and Delta area. Some idea of the numbers involved can be obtained from recent tests at two major water diversions in the Delta.

The Contra Costa Steam Plant of the Pacific Gas and Electric Company located near Antioch requires 868 cubic feet of water per second for cooling purposes at peak capacity. Screening small fish from this amount of water presented a formidable problem but one which was eventually overcome by research and cooperation between the Pacific Gas and Electric Company and the Department of Fish and Game. This plant alone, it was estimated, could conceivably affect 10 percent of the annual striped bass fry population which, it will be recalled, was estimated at 35 million fish in 1951. Fortunately, salvage operations have greatly reduced the numbers of small fish destroyed at the installation.

Similarly, but on a more gigantic scale, the Tracy Pumping Plant of the Central Valley Project draws water from Old River and pumps it into the Delta- Mendota Canal for irrigation purposes in the San Joaquin Valley. A very conservative estimate of fry under the influence of this large diversion (designed to draw 4,600 cfs at peak periods) would be 10 to 15 percent of the population each year. Research by the Bureau of Reclamation and the Fish and Wildlife Service in cooperation with the Department, resulted in a revolutionary new type of salvage facility termed the "louver facility". Up to 98 percent of fish one inch or more in length have been successfully deflected from the diversion by it. From March through August of 1957, the completed structure bypassed over 1,750,- 000 striped bass, 217,800 salmon and steelhead, 1,187,- 000 catfish, and 261,800 miscellaneous fish.

Pollution affects fish in several ways: the most obvious, of course, is the direct lethal action of toxic substances which results in mass kills but which is seldom detected. Small fish under the influence of tidal currents are carried in the vicinity of toxic discharges which they might otherwise avoid. Even the adults are sometimes caught in particularly toxic discharges as in the case of the Stauffer Chemical Company fish kill in San Francisco Bay in May of 1957 and the Napa River die-off of several years ago.

Usually, however, polluting substances destroy the bottom fauna or food organisms upon which fish depend, or set up a barrier in the form of odors, acidity, temperature or some other condition which is detected by the fish and which they avoid. The latter two are not sources of mortality but they restrict the habitat and result in loss to the fishery.

Predation undoubtedly causes large losses among striped bass under 12 inches in length. After this, however, they themselves are predators and are pretty well removed from the forage class.

Old age, diseases, and parasites also take their toll of fish. Little work has been done concerning the former two. The author has observed striped bass completely riddled with the larval form of a cestode of the order Trypanorhynca. It is thought to be of the genus Gymnorhynchus. Striped bass are the intermediate host of this parasite which has as its definitive host certain sharks, skates and rays. Another common parasite observed was the nematode Contracaecum, of undetermined species.

Scofield (1929) reported injuries to striped bass from lampreys, presumably the Pacific lamprey (Entosphenus tridentatus). The author has observed a large number of striped bass with lamprey scars, and in a few instances with fairly fresh wounds. The effects of predation by lampreys cannot be assessed at this time without considerable conjecture; nevertheless, it is thought that lampreys are not a particularly important source of mortality.

Commercial exploitation was prohibited by law in 1935 largely eliminating this source of mortality. However, studies by the writer (Skinner, 1957) from 1954 to 1957 showed that a considerable number of striped bass were destroyed incidental to commercial shad and salmon netting operations. At a minimal estimate, 22,000 fish weighing about 250,000 pounds were destroyed in netting operations during the fall of 1955 and the spring of 1956. The total poundage destroyed each year by this method could easily have amounted to 500,000 pounds. By law, fish taken by the netters had to be returned to the water upon removal from the nets whether dead or alive. Legislation in 1957 prohibited all gill and trammel netting within the Golden Gate, thus eliminating such losses in the future.

Prior to 1935 striped bass were taken commercially. The amount taken each year is described in an earlier section of this report.

The next and probably the greatest single source of mortality among legal size fish is incurred from angling. Tagging studies aimed at measuring the exploitation from this source have not been wholly successful. Clark's tagging study (1934 and 1936) was not intended for this purpose primarily and certain deficiencies in it do not permit application of the results to the fishery in general. He recovered about 10 percent of the fish he tagged within one year of the date of release.

A very intensive tagging program conducted by Alex Calhoun of the Department of Fish and Game was specifically designed to measure the proportion of the population caught by anglers. It soon became apparent, however, that the commercial gill net fishery in the Delta and Suisun Bay region was seriously interfering with the study. The gill netters removed the tagged fish before the anglers had the opportunity to catch them and furthermore, the placement of tags on the fish was found to increase the chances of a fish being captured by the gill nets. Other adverse factors included the reluctance of sport and commercial fishermen to return tags from captured fish. Because of these conditions only the roughest sort of estimate was possible regarding the proportion taken by anglers. The writer made a brief study of tag returns from the above program and concluded that the proportion exploited by both sources, anglers and gill nets, was in excess of 25 percent of the legal population annually. Chadwick, (unpublished data) in a later review estimated a minimal annual rate of exploitation of 10 percent. Anglers, of course, were presumed to catch the greater share by quite a large margin.

Chadwick (unpublished data) initiated another tagging program in the spring of 1958 after removal of the gill net fishery. Preliminary analysis of the first three years of tag returns indicate angling mortality on the order of 20 to 30 percent annually on the population over 16 inches in length.

In spite of all the factors acting against it, the natural survival of this species is obviously high. The frequency with which individuals in excess of 30 or 40 pounds (over 15 years of age) are encountered lead to the conclusion that natural mortality is low.


Striped Bass - Page 169

Generally speaking, this fishery has remained relatively stable. The species was completely removed from the commercial category in 1935 and since then has been subjected to hook-and-line fishing only, except for fish which were taken incidentally with shad and salmon by the gill net fishery. The sport fishery is so intense it is believed that up to 25 percent of all legal-sized fish are removed from the fishery each year.

A review of the catch records and other pertinent data revealed a decline in the fishery from 1944 through 1955. As a consequence, further restrictions in size and bag limits were put into effect to bring the fishery into balance. This appears to have been accomplished.

Under present conditions, it appears that the sport fishery is now exerting sufficient pressure to have a definite influence on striped bass stocks. The governing factor, however, lies in the change in environmental conditions. These have been modified so greatly over the past fifty years that there has been an appreciable loss in the total habitat available to striped bass.

At least three adverse factors, excluding angling, are affecting the striped bass population: reclamation, water development projects, and pollution. It would be next to impossible to evaluate the relative importance of each. Reclamation, many years ago, resulted in extensive habitat changes which removed rich nursery grounds. Water development projects have modified temperature, flow, and salinity patterns in the Delta and in spawning areas, and numerous diversions take a heavy toll of fish. Pollution has resulted in an extensive loss of habitat, destruction of forage organisms, and, frequently, in the outright killing of the fish themselves.

The absence of striped bass in many areas of the Bay may be taken as rather clear evidence of pollution. South San Francisco Bay in particular can be cited, and there are other once-favorable localities which are now similarly devoid of striped bass. End

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Calhoun, A. J.
1949 California Striped Bass Catch Records From the Party Boat Fishery; 1938-1948. California Fish and Game, Vol. 35, No. 4, pp. 211-253.
1950 California Angling Catch Records from Postal Card Surveys: 1936-1948 With an Evaluation of Postal Card Non-response. California Fish and Game, Vol. 36, No. 3, pp. 177-233.
1951 California State-Wide Angling Catch Estimates for 1949. California Fish and Game, Vol. 37, No. 1, pp. 69-75.
1952 Annual Migrations of California Striped Bass. California Fish and Game, Vol. 38, No. 3, pp. 391-403.
1953a. State-Wide California Angling Estimates for 1951. California Fish and Game, Vol. 39, No. 1, pp. 103-113.
1953b. Distribution of Striped Bass Fry in Relation to Major Water Diversions. California Fish and Game, Vol. 39, No. 3, pp. 279-299.
1957 Striped Bass Fishing Map (Revised by John E. Skinner). California Department of Fish and Game.

Calhoun, A. J., and John E. Skinner
1954 Field Tests of Stainless Steel and Tentalum Wire with Disk Tags on Striped Bass. California Fish and Game, Vol. 40, No. 3, pp. 323-328.

Calhoun, A. J., and C. A. Woodhull
1948 Progress Report on Studies of Striped Bass Reproduction in Relation to the Central Valley Project. California Fish and Game, Vol. 34, No. 4, pp. 171-187.
1950 Striped Bass Reproduction in the Sacramento River System in 1948. California Fish and Game, Vol. 36, No. 2, pp. 135-145.

Clark, G. H.
1929 Sacramento-San Joaquin Salmon (Oncorhynchus tshawytscha) Fishery of California. California Fish and Game, Fish Bulletin No. 17.
1932 The Striped Bass Supply of California, Past and Present California Fish and Game, Vol. 18, No. 4, pp. 297-298.
1933 Fluctuations in the Abundance of Striped Bass (Roccus lineatus) in California. California Department of Fish and Game, Fish Bulletin No. 39.
1934 Tagging of Striped Bass. California Fish and Game, Vol. 20, No. 1, pp. 14-19.
1936 A Second Report on Striped Bass Tagging. California Fish and Game, Vol. 22, No. 4, pp. 272-283.
1938 Weight and Age Determination of Striped Bass. California Fish and Game, Vol. 24, No. 2, pp. 176-177.

Cole, Charles E.
1930 Angling for Striped Bass. California Fish and Game, Vol. 16, No. 4, pp. 286-290.

Craig, J. A.
1928 The Striped Bass Supply of California. California Fish and Game, Vol. 14, No. 4, pp. 265-272. 1930 An Analysis of the Catch Statistics of the Striped Bass (Roccus lineatus) Fishery of California. California Department of Fish and Game, Fish Bulletin No. 24.

Hatton, S. Ross
1940. Progress Report on the Central Valley Fisheries Investigations, 1939. California Fish and Game, Vol. 26, No. 4, pp. 334-373.

Jackson, H. W. and R. E. Tiller
1952 Preliminary observations on spawning potential in striped bass (Roccus saxatilis). Maryland Dept. Res. and Ed., Pub. 93, pp. 1-6.

Johnson, W. C, and A. J. Calhoun
1952 Food Habits of California Striped Bass. California Fish and Game, Vol. 38, No. 4, pp. 531-533.

Morgan, Alfred R. and Arthur R. Gerlach
1950 Striped Bass Studies on Coos Bay, Oregon in 1949 and 1950. Oregon Fish Commission, Contribution No. 14.

Pearson, John C.
1938 The Life History of the Striped Bass or Rockfish, (Roccus saxatilis) (Walbaum). U. S. Department of Commerce Bureau of Fisheries, Vol. XLIX, Bulletin No. 28.

Raney, Edward C, Ernest F. Tresselt, Edgar H. Hollis, V. D. Vladykov and D. H. Wallace
1952 The Striped Bass (Roccus saxatilis). Bulletin of the Bingham Oceanographic Collection, Vol. 14, Article 1.

Scofield, N. B.
1910 Notes on striped bass in California. Biennial Report, Calif. Board of Fish and Game Commissioners for 1909-1910, pp. 104-109.

Shapovalov, Leo
1936 Food of the Striped Bass. California Fish and Game, Vol. 22, No. 4, pp. 261-270.

Skinner, John E.
1955a. California State-Wide Angling Estimates for 1953. California Fish and Game, Vol. 41, No. 1, pp. 19-32.
1955b. Observations on the Shad Gill Net Fishery in 1954. California Department of Fish and Game, Inland Fisheries Branch, Administrative Report 55-3.
1957a. Incidental losses of Striped Bass in the Sacramento River Gill Net Fisheries for Shad and Salmon. California Department of Fish and Game, Inland Fisheries Branch, Administrative Report 57-2.
1957b. Status of the Striped Bass—Sturgeon Study and Suggestions for its Future. California Department of Fish Fish and Game, Inland Fisheries Branch, Administrative Report No. 57-11.

Smith, Hugh M.
1895 The Striped Bass History and Results of Introduction. U. S. Fish Commission Bulletin, Vol. 15, pp. 449-458.

Woodhull, Chester
1947 Spawning Habits of the Striped Bass (Roccus saxatilis) in California Waters. California Fish and Game, Vol. 33, No. 2, pp. 97-101

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