136 Theories and Techniques of Management 



Anyone who has made an intensive study of a fish population inhabiting 

 a pond or lake will discover after a few years of sampling of young that 

 the total numbers and relative abundance of these young may vary greatly 

 from year to year. Also, the young of a given species may appear to be 

 very abundant in the early summer when the young are small, but later, 

 if the rate of survival was low, they may have become relatively scarce. 



Minnow-Seine Method of Pond Analysis. According to the minnow- 

 seine method of testing ponds containing largemouth bass and blue- 

 gills,^^- the condition of the fish population ("balance") may be judged 

 on the basis of the success of reproduction of bass and bluegills for the 

 current year and the past survival of bluegill spawn beyond the first year 

 (3-, 4-, and 5-inch length groups of bluegills). The method is based on 

 the hypothesis that with an overabundant stunted population of blue- 

 gills, the bass (and sometimes bluegills, too) will be unable to produce 

 enough to assure their appearance among fish caught in a reasonable 

 number of minnow-seine hauls. On the other hand, with an overabundant 

 stunted population of bass, there will be no intermediate-sized bluegills, 

 and a scarcity or absence of small bluegills and perhaps small bass. These 

 assumptions are valid if interference in spawning has not come from 

 water too cold, turbid, or saline, with a pH too high or low, and if there 

 is no great rise or drawdown of water levels at the wrong time.^^^ 



In 1950, an airing of conflicting ideas on minnow-seine sampling oc- 

 curred when Dr. Gustav A. Swanson, editor of the Journal of Wildlife 

 Management, published some pro and con opinions of it.^ Long-term 

 intensive studies of populations, in which minnow-seine collections were 

 interpreted by the minnow-seine hypothesis, often failed to accurately 

 define the type of population present. If these studies could not demon- 

 state the consistent validity of the method, one may doubt the value of 

 less intensive investigations, regardless of the number of ponds sampled 

 and catches subjected to the test formula. As stated in 1950,^ the author 

 has found no published information ( an adequate series of experiments in 

 which minnow-seine analyses were followed by draining or poisoning 

 censuses of the adult fish populations ) to prove the value of the minnow- 

 seine method. Tests of the method in lowa,-^ through use of a larger seine 

 and age analyses of fish, demonstrated errors in interpretation of results 

 from minnow-seine collections. 



However, shoreline seining with a fine-mesh seine to catch the smaller 

 fish in a body of water can furnish a great deal of information about a 

 fish population. Some acceptable values are as follows: 



(1) In previously unsampled waters it will give a partial, and in some in- 

 stances, a complete list of species inhabiting these waters. 



(2) The collection of the young of bass, walleyes, northern pike, or other 

 game fish not only indicates their presence in the water but also their 



