NOTE Carlson. Yearly appearance of Theragra chalcogramma off southeastern Alaska 



387 



POINT 

 RETREAT 



Figure 1 



Location of the study site, in Auke Bay, near Juneau, Alaska, where young-of-the-year 

 walleye pollock, Theragra chalcogramma, were observed, 1973-94 (map from Bruce et 

 al., 1977). 



fiable fish and invertebrate species, and documented 

 life stage and relative abundance of commercially 

 valuable species. For age-0 walleye pollock, I visu- 

 ally estimated total length (TL) of individuals to the 

 nearest cm. These size-composition estimates were 

 corroborated by Salveson (1984), who collected and 

 measured hundreds of young pollock concurrently 

 with my diving observations in 1978 and 1979, dur- 

 ing growth and distribution studies in northern 

 Stephens Passage, including my site in Auke Bay. 

 These samples included 511 age-0 pollock collected 

 (by using explosives) during August and September 

 1979 from the same shoals that I observed. 



Results 



The first sightings of demersal age-0 walleye pollock 

 (Table 2) occurred most often in July ( 14 years) and 

 sometimes in August ( 5 years ); the first sighting was 

 later than August in only 3 of 22 years. 



General appearance and behavior of the young 

 pollock at the Auke Bay study site was similar 

 throughout summer and fall and from year to year. 

 Over the course of the study, size estimates of indi- 

 vidual fish were consistently 3-6 cm TL in July and 

 8-10 cm TL by October (Table 2). No size differences 



or environmental anomalies (sea temperature, sa- 

 linity profiles) were apparent in the three years of 

 later first sightings. The young fish formed shoals 

 composed of hundreds to a few thousand loosely ag- 

 gregated individuals within 1 m above the bottom or 

 off rocky ledges at 20-30 m. Currents were normally 

 slight, and these shoals moved and milled slowly, 

 apparently feeding on zooplankton. 



Each year, just before the shoals of demersal young 

 pollock appeared, I observed great sculpins, Myoxo- 

 cephalus polyacanthocephalus, distributed over the 

 slope and rocky ledges where the young pollock later 

 appeared. These large (many >60 cm) predators were 

 unusually abundant, often numbering as many 

 as 20-30 sculpins along a 15-20 m length of rocky 

 ledge. They lay in wait on the bottom and after the 

 young pollock appeared, were often seen pursuing 

 and capturing them. Some sculpins appeared so 

 gorged with young pollock that their gut was greatly 

 distended. 



As the juvenile pollock grew, they moved down the 

 slope into deeper waters. After reaching approxi- 

 mately 10 cm TL by October or November, they were 

 seen less frequently. By then the pollock were inhab- 

 iting waters 30 m or deeper, approaching the limits 

 of normal scuba operations. By December and into 

 winter, the juvenile pollock were seen infrequently 



