Stream and Lake Management 



Sport fishing has long been a means of recreation 

 and, in recent years, has achieved the status of big 

 business. In addition to the large investments for the 

 manufacture and sale of fishing gear, there is enor- 

 mous expenditure for hatchery production and stocking 

 of fish. More recently attention has been directed to 

 the improvement of natural waters in an attempt to 

 provide more fish at less cost than has been possible 

 with hatchery methods. This is a complicated subject 

 with ramifications that have no place in a book on 

 aquatic insects; therefore the present discussion 

 will be limited to the entomological aspects of stream 

 and lake management. 



Analysis of food grades and preferences. — Hatchery- 

 bred fish have been stocked in California waters for 

 more than half a century. Much of this was done with- 

 out regard to the natural food supply and hence with 

 no knowledge of the carrying capacity of the stream 

 or lake, but in recent years this situation has changed. 

 Pioneer studies by Embody (1927) provided the basis 

 for a stocking policy, and more recently investigations 

 have been made of the fish-food organisms of many 

 of our lakes and streams; stocking recommendations 

 have been based on them. 



Unfortunately, most surveys of stream-bottom organ- 

 isms have been made with a Surber Square Foot 

 Sampler. Although this is undoubtedly the most 

 practical sampler thus far devised for shallow riffles, 

 Needham and Usinger (1955) showed that it does not 

 give statistically significant data for total weights 

 and numbers of organisms, even in a single relatively 

 uniform riffle. It was found that 194 and 73 samples, 

 respectively, would be required to give reliable figures 

 at the 95 per cent level of significance. Hence all 

 existing data on stream-bottom organisms is statisti- 

 cally inadequate, but it is the best we have and may 

 be the best that can be obtained because of the 

 extreme variability of stream habitats. Examples of 

 this type of data are found in the unpublished reports 

 of Needham and Hanson (1935), Smith and Needham 

 (1935), and Taft and Shapovalov (1935) for the 

 Klamath, Shasta, Sierra, Mono, and Inyo national 

 forests. Some idea of average and extreme numbers 

 of bottom food organisms for various streams (Surber 

 samples) and lakes (Ekman samples) in California 

 are given in table 3. 



TABLE 3 (Introduction) 



Average numbers of bottom food organisms taken 



by square foot surber samplers in streams and by 



1/4 square foot ekman samplers in 



lakes of California in 1934 



National forests 



No. of 

 stream organisms 



No. of 

 lake organisms 



Klamath and Shasta 

 Mono and Inyo 

 Sierra 



380 

 370 

 143 



150 

 66 



26 



39 



Usinger: Introduction 



dwelling organisms. Therefore (he total volume or 

 "wet weight" may be more satisfactory. Wei wei 

 are commonly taken after drying the Bamplec for one 

 minute on blotting paper. In it quantitative teal u 



100 samples taken from a single riffle m I'm 



Creek near Truckee, California, Needham and I 

 (1954) found a minimum of i and a maximum of 198 



organisms per square fool with wet weights from 



0.15 grams to 2.31 grams. For comparative purpt 

 wet weights are sometimes calculated in pound- per 

 acre. Table 1 shows such figures lor Waddell Crook 

 near Santa Cruz, the Merced River m Yosemite 

 National Park, and Convict Creek at the head of the 

 Owens River (Needham, 1938, 193!); Maciolek and 

 Needham, 1952). 



TABLE 4 (Introduction) 



Standing crops of bottom organisms in pounds per 



acre at various seasons in Waddell Creek. 



Convict Creek, and the Merced River. 



Location 



Month 



Standing crop 

 lbs. per acre 



Waddell Creek 



February, 1933 

 May, 1933 



70 



472 



Convict Creek 



Low 



Mav to Sept., 1938 



High 



May to Sept., 1942 



68 

 197 



Merced River 



February 

 August 



103 



s5 



Attempts have been made to improve the techniques 

 for sampling fish-food organisms in order to obtain 

 more meaningful results. Such efforts are of greatest 

 importance to the aquatic entomologist who has found 

 himself too often in the past expending great effort 

 in the field to obtain data which are virtually mean- 

 ingless. 



One attempt at increasing precision is the "forage 

 ratio" (Hess and Swartz, 1941) proposed to aid in 

 interpreting the results of stomach contents investi- 

 gations. It was pointed out that the organisms found 

 in the stomach of a fish reveal nothing as to food 

 preferences unless it is also known what organisms 

 occurred in the immediate environment of the fish at 

 the rime it was feeding. The forage ratio (FR) is 

 obtained by dividing the percentage of a given kind 

 of organism in the stomachs by its percentage in the 

 environment. The formula may be expressed as follows: 



FR = 



n 



N_ 



N' 



Numbers of organisms can be quite misleading 

 because of the great disparity in size of bottom- 



where n = the number of any organism in the stomachs, 

 N = the total number of organisms in the stomachs, 

 n' = the number of the same organism in the environ- 

 ment inhabited by the fish, and N' = the total number 

 of food organisms in the environment. Weight or volume 

 may be substituted for number if desired. 



A forage ratio of 1 indicates that an organism is 

 being taken at random according to its relative abun- 

 dance in the environment; a forage ratio of more than 



