FORTY-THIRD BIENNIAL REPORT 



41 



assume a fish diet and there are not enough fish of the 

 right size available in most California lakes. 



jMost native minnows, because of low productivity 

 or natural and man-made environmental changes, have 

 not been able to support the heavy predation required 

 of a good forage fish, and attention has been directed 

 to exotic species. The principal experimental intro- 

 ductions during the biennium have already been de- 

 scribed under "Management." 



Lack of success of forage minnows in some water 

 supply reservoirs is being investigated. The role of 

 copper sulfate, a widely used algicide, as a limiting 

 factor is being studied with promising result. 



Work also was begun to determine harvest rates of 

 black bass. This knowledge is needed to increase 

 understanding of black bass populations under Cali- 

 fornia conditions, and for formulating sensible regula- 

 tions. Tagging studies were begun at Clear Lake, Lake 

 Count\', and on several Southern California reservoirs 

 to discover how many of the bass are being caught 

 each year. 



Control of rough fish such as carp is the most 

 important management technique now in use. A pro- 

 gram to develop new methods of control was begun. 

 Promising preliminary results were obtained with the 

 use of poisoned bait for partial control of this species. 



Catfish Study 



Federal Aid project F-2-R was initiated in January, 

 1952, when there were indications that the Sacra- 

 mento-San Joaquin Delta white catfish fishery was 

 being depleted. Primary goal of the investigation was 

 to determine the rate of exploitation of the Delta 

 catfish population and the factors affecting its appar- 

 ent depletion. A detailed study of the life history of 

 the catfish was also planned. Knowledge about age 

 and growth, food habits, size and age at maturity, 

 reproductive characteristics, and migrations was 

 sought, since this information is fundamental to wise 

 management of the fishery. 



Activities of the project were focused on the study 

 of the Delta fishery for the first year. A thorough 

 study of the commercial catfish fishery was com- 

 pleted and was compared with the sport fishery. 



Results indicated that the catfish population was 

 under heavy fishing pressure and that the commercial 

 fishery, although a minor one in terms of average 

 annual gross income, was taking a disproportionate 

 share of the annual catch. It also was learned that a 

 number of commercial fishermen were wasting catfish 

 and, in addition, were illegally selling undersized fish. 



In brief, the small commercial fishery was producing 

 conflict out of all proportion to its value. 



By the end of 1952, the project had sufficient infor- 

 mation to justify a recommendation that commercial 

 fishing for catfish be banned in California. It was 

 predicted that elimination of this undesirable fishery 



n 





Catfish food studies being carried out at Carmichael Laboratory. Con- 

 tents of stomacfi are being examined. 



would result in improved angling and an increase in 

 size of the individual catfish in the Delta. This recom- 

 mendation was accepted by the 1953 Legislature with 

 passage of Senate Bills Nos. 44 and 45. 



Investigation of the valuable Delta fishery has con- 

 tinued to be one of the most important activities 

 of the project. Two tagging experiments have been 

 conducted to ( 1 ) develop a suitable tag for catfish, 

 (2) determine fishing mortality, and (3) obtain in- 

 formation about the movements or migrations of cat- 

 fish. 



Tagging Study 



From these experiments, a dependable catfish tag, 

 the disk-dangler, has been developed and adequate 

 information about the movements of the Delta white 

 catfish has been obtained. A third tagging study is 

 now in operation to determine angling mortality. This 

 additional study was deemed necessary because calcu- 

 lation of mortality rates from previous studies was 

 complicated by the presence of the commercial fishery 

 and lack of confidence in one type of tag that was 

 employed. 



A total of 6,966 white catfish has been tagged in the 

 Delta since inception of the project. Anglers who 

 captured tagged catfish have responded well to re- 

 quests for information pertaining to the catch of such 

 fish with 620 tags returned by July, 1954. 



The Foothill Sportsmen's Club of Oakland con- 

 tributed generously to the tagging publicity cam- 



