GRISWOLD and SMITH: LIFE HISTORY OF NINESPINE STICKLEBACK 



were obtained by bathythermograph at each 

 station. 



Trout index trawling aboard SLscowet was 

 done for two 2-wk periods annually, one spring 

 and one fall. A total of 286 tows, each 1 mile 

 long, were conducted during the stickleback 

 study from April 1967 through May 1970. 

 Additional records from 322 index tows taken 

 in all ice-free months dating back to April 1965 

 were also included in the study of distribution. 

 A total of 46 V4-mile tows were made from 

 June through September, 1968 and 1969, with 

 the small outboard trawl, and 18 tows were 

 made with the sled at various times of the year 

 at the index stations in 1968 and 1969. Trawl 

 samples were separated by species, and the fish 

 were counted. After lake trout were measured, 

 fish samples were put in jars of appropriate 

 size and preserved in 10% Formalin.'^ Samples 

 from the plankton sled were flushed directly 

 into jars and preserved in Formalin. 



The main limitation of this sampling scheme 

 was that the index trawl series was conducted 

 at a limited number of stations representing 

 t trout nursery areas. It is possible that the bio- 

 logical communities and the resultant ecological 

 -interrelationships in these areas may not be 

 representative of the entire Apostle Islands 

 area. Also, since areas of sampling were lim- 

 ited and the efficiency of the index trawl was 

 unknown, it was impossible to estimate absolute 

 biomass of the stickleback population. Alter- 

 nate methods of population estimation were 

 unfeasible because of the immensity of the pop- 

 ulation and the area. 



Additional methods are discussed in appro- 

 priate sections throughout the paper. 



DESCRIPTION OF GROWTH 



Sticklebacks used for age and growth studies 

 were stratified by length, subsampled if catches 

 were large, and frozen. Otoliths (sagittae) were 

 removed, cleaned, dried in alcohol, cleared in 

 creosote, and mounted on microscope slides in 

 Canada balsam as described by Jones and 

 Hynes (1950). The otoliths contained a series 



^ Reference to trade names does not imply endorsement 

 by the National Marine Fisheries Service, NOAA. 



of transparent and opaque rings, and it was 

 evident that the transparent zone was laid down 

 at the beginning of the growing season in late 

 June and early July. Therefore, the annulus was 

 considered the outer edge of the opaque zone. 

 Nomographs, based on the male and female 

 body length-otolith length curves, respectively, 

 were used to calculate body length at each an- 

 nulus (Carlander and Smith, 1944). 



Validation of the Otolith Method 



Determination of age from otolith rings was 

 made with little difficulty. In older fish the an- 

 nulus on the outer margin was not as distinct 

 as in young fish, but usually could be identified 

 at the posterior portion of the otolith. After two 

 independent age determinations of 808 pairs of 

 otoliths, 37 pairs required reexamination be- 

 cause the first two were not in agreement. 



Otoliths were analyzed from sticklebacks 

 taken with experimental trawls in 1967 and 

 1968. The samples represented six year classes 

 and five age-groups. The otoliths were from 372 

 fish taken at station 2 and 436 taken from 

 station 3. Length-frequency distributions were 

 estimated from 18,175 fish measured from 80 

 trawl samples. 



The following evidence indicates that annuli 

 on otoliths provide an accurate measure of 

 stickleback age and growth : 



1. Length distribution by age-group based 

 on otolith readings and modes in length- 

 frequency distribution of all measured 

 fish were in close agreement; however, 

 most distributions exhibited some degree 

 of overlap (Figure 2 and 3). In the June 

 sample (Figure 2), the distribution of age- 

 group fish truncated on the left-hand 

 side because it had been discovered that 

 all of these smaller fish were of 0-group. 



2. Calculated lengths at the end of each year 

 of life corresponded well between the 

 various year classes (Tables 1 and 2). 



3. There was a general increase in average 

 body length with assigned age of the fish 

 (Tables 3 and 4). 



4. The average empirical length of aged fish 

 collected in spring prior to annulus for- 



1041 



