(d) The volume and weight methods. The volume or 

 weight of each food item, or of the total food of each 

 fish, is given, and is usually expressed as a per- 

 centage of the total weight of the fish. Some authors 

 calculate the weight of food eaten from the known 

 average weight of each individual of each food item. 

 Most workers use this method only to supplement some 

 other method, and it is often used to show seasonal 

 variation in food intake. Ricker, however, by count- 

 ing and "weighting" each type of food organism 



according to its known average weight, has evolved 

 a method similar to the points method (below). 



(e) The fullness method. Some workers wishing to 

 demonstrate seasonal variation in food intake have 

 used an arbitrary estimate of the fullness of the 

 stomachs. This is only a special extension of the 



|total volume method. 



(f) The points method. Swynnerton and Worthington 

 used a method in which the food items in each fish 

 were listed as common, frequent, etc., on the basis 

 of rough counts and judgment by eye, due regard being 

 taken of the size of the organisms as well as of their 

 abundance (i.e., one large organism counted as much 



COMBINATION WAVE-BREAKER WEED-BED 

 AND FISH SHELTERS 



43 

 Usinger: Introduction 



as a large number of Bmall one- ). Bach i 

 then allotted a number of points and all the points 

 gained i>\ each food item were summed and scaled 

 down to percentages, to give percenl ition 



of the food of all the fish examined. I'h 



tially a volumetric method, and ie similar in principle 

 to that of Ricker above. However, until dietetic values 



of food species are known, volume would appear to be 

 a satisfactory basis lor s ent, and this method 



has the advantage of being rapid. The point 

 of Swynnerton and Worthington has been modified 



slightly by taking into account also the degree of 

 fullness of the stomach. 



Consideration of the various methods indicates thai 

 the points method is the most satisfactory. Facts in 

 its favor are that it is rapid and easy, requires no 

 special apparatus for measurement, is not influenced 

 by frequent occurrence of a small organism in small 

 numbers, nor of heavy bodies, like snail shells and 

 caddis cases, and does not involve trying to count 

 large numbers of small and broken organisms. It also 

 does not give the spurious impression of accuracy 

 which is given by some other methods. 



SPAWNING AND FOOD PRODUCING DEVICES 

 SLAB TYPES 



3)4 'I 



1 & 



4^ lanjih io to loo ft 



le-qs to' to 24' illamcler 

 Wire* ve? yauyc 



WAVE- BREAKER SHELTER 



Oak or elm. 



WEED BED TYPE 



Square or rectanaular in. general shxipe, 



Mtn.im.um dimensions zoH * 20 ft 



Oa.tr or elm. 



short logs 



cample teat 



SLAB ft E T R EAT 



Ma.fcrt.als: siaos *A?/< inch** 

 m-tre ttf s> oauac* 

 stakes 4'diim sJ tona 



SLAB RAFT 



Materials 



toes 6 to to inches 

 s/aSs 4- to ,Z inches 



Water It 



ROCK TYPES 



D OMINO 



TILE BED 



LCG AND BRUSH 



Intro, fig. 59. Methods of improving shelter for aquotic orgonisms and fish 

 in lakes (Hubbs and Eschmeyer, 1938). 



