FISHERY BULLETIN; VOL. 73, NO. 4 



Cove in June 1965 and in April, May, and June 1966 

 when salmon fry were present. The lowest abun- 

 dance in the inner bay, an average of 9 organisms 

 per liter, occurred in April 1966, when the abun- 

 dance was comparatively high in the outer bay, 51 

 per liter (Table 7). During the rest of the 1966 

 season, mean numbers ranged from 27 to 28 or- 

 ganisms per liter in the inner bay and 24 to 40 in 

 the outer bay. The highest numbers were observed 

 in the outer bay in June 1965 after most of the fry 

 had passed through the estuary. Zooplankters 

 tended to be more abundant at the mouth of the 

 bay, near the constriction, and at the head of the 

 bay than at intervening points along the shoreline. 



Fifty- two categories of zooplankters were iden- 

 tified from the Clarke-Bumpus samples, and 

 seasonal qualitative and quantitative changes 

 were evident in the composition of the zooplank- 

 ton (Table 8). The peak abundance for polychaete 

 larvae and cirrepede (barnacle) nauplii occurred in 

 April, whereas the peak for other invertebrate 

 larvae occurred in May. Rotifers, copepods 

 (including nauplii), and barnacle nauplii were also 

 very abundant in May. Cladocerans did not 

 become abundant until June. Variation between 

 years is indicated by the high abundance of ro- 

 tifers in June 1965 (~120,000/mO and the much 

 lower abundance of rotifers (-3,000/m') and possi- 

 bly higher abundance of other forms in June 1966. 



The predominant zooplankters during the 

 period of fry outmigration v/ere larvae of bar- 

 nacles, polychaetes, and molluscs and nauplii and 

 early copepodites of the copepods Acartia clausii, 

 A. longiremis, and Oithona helgolandica. Over 98% 

 of the zooplankters in the outer bay on 16 April 

 1966 were larvae, and as late as 7 June 1966 larvae 

 constituted more than 65% of the zooplankton. In 

 the inner bay on 18 April 1966 and 7 June 1966, the 

 proportions of larvae in the zooplankton were 72 

 and 58%, respectively. Late copepodites and adults 

 of calanoid and cyclopoid copepods were the next 

 most abundant groups of zooplankters and con- 

 tributed relatively more to the zooplankton as the 

 season progressed. An abundance of larval forms 

 was also characteristic of another southeastern 

 Alaska estuary, Auke Bay (Wing and Reid 1972). 

 Rotifers, although of minor importance in the diet 

 of salmon fry, were often the most abundant 

 zooplankters in the samples. Cladocerans and lar- 

 vaceans were rare in April and May but by June 

 constituted a significant portion of the zooplank- 

 ton. Adults and juveniles of benthic invertebrates 

 were rare in the plankton samples. Species com- 



Table 7. -Abundance of zooplankters determined from Clarke- 

 Bumpus sampler with no. 10 mesh net (158)U,m) at Traitors Cove. 



Inner bay 



Outer bay 



Number 

 of 



Organisms 

 per liter 



Number 

 of 



Organisms 

 per liter 



Date 



samples Mean Range samples Mean Range 



position of zooplankters differed between the 

 inner and outer bays of Traitors Cove (Table 8). 



The plankton samples contained zooplankton of 

 the kinds and sizes eaten in great numbers by pink 

 and chum salmon fry as well as smaller plankters, 

 which were not important in the diet of fry. As a 

 result, the average size of plankters in the net was 

 slightly smaller than the average size of items 

 eaten (Table 5). 



DISCUSSION 

 Initiation of Feeding 



Neither pink nor chum juvenile salmon ate very 

 much before leaving Traitors River, although 

 chum salmon fed more than pink salmon. Some fry 

 may have fed before they emerged from the redds. 

 The size (41 mm) of the largest fry collected in the 

 river suggests that at least a few individuals ac- 

 tually grew as a result of exogenous feeding 

 before they finally left the river. Mason (1974) 

 collected chum salmon fry up to 70 mm long from 

 Lymn Creek on Vancouver Island, British Colum- 

 bia, where they moved into and out of high- 

 salinity water and apparently fed in both media 

 over a period of 1 to 4 wk or more. 



Immature stages of chironomids were most 

 commonly eaten, but other bottom-dwelling 

 aquatic organisms also occurred in stomachs of 

 pink and chum salmon from Traitors River. Two 

 workers (Disler 1953; Sparrow 1968) reported that 

 zooplankton and bottom-dwelling aquatic or- 

 ganisms occurred in the diet of chum salmon in 

 freshwater. Although pink salmon apparently eat 

 little or nothing while migrating seaward in short 

 streams (Kazarnovskii 1962; Kobayashi 1968), as 

 at Traitors River, they are more likely to feed 

 while migrating long distances from large rivers 

 (Levanidov and Levanidova 1957; McDonald 1960). 



Once they had left the stream, pink and chum 

 salmon fry in Traitors Cove fed extensively on 

 such zooplankters as calanoid copepods, lar- 



854 



