The third area was a silt bank on the inside of a bend of 

 the river. The bed proper, consisting primarily of silt, muck, 

 and organic debris, measured 3h feet long with an average Tddth 

 of 2 1/2 feetj water depths ranged from 2 to 20 inches and the 

 bottom sloped at about a li^-degree angle. One collection was 

 made ivith the olectric shocker in the month of October, and 2^1 

 ammocoetes older than young-of -the -year were removed from this 

 area of 85 square feet. Concentrations of yo-ong-of-the-year 

 were estimated at about 8 per square foot. 



The silted bottoms of pools as deep as 7 l/2 feet were found 

 to contain fairly abundant populations as evidenced by Petersen 

 dredge samples. Tilhere cold, spring feeders (or spring seepages) 

 drain into the head of silted or muck bottom sloughs, larval popu- 

 lations are small or absent. Aquatic vegetation is sparse in the 

 lovrer two-thirds of the Ocqueoc River where amm-ocoetes occur. 

 Those plants which were present where collections were made were 

 predominantly Hajas flexilis, Po tamo ge ton epihydrus, and species 

 of Sagittaria . TOiere small patches of these grew in a given larval 

 bed the concentration of individuals was greatest. 



Bottom deposits of more nearly equal mixtures of fine sand 

 and silt, where they occur in quieter vra-ters, contain heavy sea- 

 sonal concentrations of young-of-the-year larvae but few if any 

 of the larger and older age groups. By the late autumn or early 

 spring of their first year of life, most of the young-of-the-year 

 have dispersed to other areas, generally those with more mucky 

 bottoms. Sandy sites, usually occurring at stream bends, below 

 islands, or even in midstream are shifting and unstable in char- 

 acter] this apparently discourages permanent occupancy. 



One sandy area in the Ocqueoc River was examined repeatedly 

 over several seasons. This bed was situated on the inside of a 

 bend in the river below a gravel spawning riffle. The current 

 passing over it was slow or sluggish; the bed was 8Ii feet long 

 and averaged 5 feet wide; maximum depth was 12 inches at mean 

 water levels. In August, 19U7, this bed "vvas found to have an 

 average content per square foot of 9 young-of-the-year (range: 

 3 to 12 individuals per square foot), and 1 larva of a larger 

 (and older) size group, usually a member of age group I {33-S9 

 millimeters in total length) . Twenty feet below this bed was the 

 quiet, muck-bottomed slough in a side channel of the river de- 

 scribed in a preceding paragraph. Nearly simultaneous collections 

 from this side channel displayed an equivalent concentration of 

 yo\ing-of-the-year but a far greater proportion of the larger size 

 groups. The distribution of sizes of larvae taken in both loca- 

 tions in August, 19hl, is illvis trated in Figure 53 (Figure 53 is 

 an inaccurate representation of the proportion of sizes present 

 because only a few of the young-of-the-year in the side channel. 

 Station 3, seen to be disturbed by the shocker, were collected 

 and measured on this date). 



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