Kendall and Nakatani: Early life history of Theragra cha/cogramma in Shelikof Strait and Funka Bay 



133 



Incubation temperature C 



Figure 3 



Incubation period of walleye pollock eggs from Funka Bay, 

 Japan (based on Nakatani 1988); Resurrection Bay (based on 

 A.J. Paul, Univ. Alaska, Seward, pers. commun.) and Auke 

 Bay, Alaska (based on Haynes and Ignell 1983). 



all stages was 350,000 eggs/m^ in the area of max- 

 imum concentration; about 15 times the maximum 

 abundance observed in Funka Bay. By late April, egg 

 abundance is reduced as eggs are spread more evenly 

 throughout the southern two-thirds of the strait and 

 the area immediately to the southwest of the strait. By 

 late May, egg abundance is further reduced, but the 

 area of occurrence is still similar to that seen in late 

 April. As opposed to Funka Bay, there is little evidence 

 of drift of eggs in Shelikof Strait. It appears that the 

 adults spawn some eggs in the southwestern part of 

 the strait as they move toward the main spawning area 

 off Cape Kekurnoi. Later spawning in late April and 

 May seems to be dispersed throughout the strait and 

 occurs at a much reduced level. Measurements of cur- 

 rents in Shelikof Strait also indicate that little drift 

 would be expected in the deep waters (>150m) where 

 most eggs occur (Kendall and Kim 1989). 



of eggs from Shelikof Strait varied from 1.0243 to 

 1.031g/cm3, whereas the water density varied from 

 1.0256 to 1.0259g/cm3 (in 1985). Less than 20% of 

 eggs of all ages occurred above 162 m in Shelikof Strait. 

 Over 80% of early- (fertilization to morula) and late- 

 stage eggs (embryo more than one-half circumference 

 of yolk to hatching) occurred between 216 and 277 m 

 (near bottom), while over 60% of middle-stage eggs 

 (gastrula) occurred between 162 and 216 m (Kendall 

 and Kim 1989). Thus eggs in Shelikof Strait are heavier 

 and occur deeper than those in Funka Bay. 



Horizontal distribution The horizontal distribution 

 pattern of eggs in Funka Bay was fairly consistent 

 among the 3 years (1977, 1978, and 1987) for which 

 data are presented (Nakatani 1988, Nakatani and 

 Maeda 1981 and 1989). Younger eggs are mainly found 

 just outside the entrance to the bay and older eggs are 

 found inside the bay, indicating that spawning occurs 

 outside the bay and the eggs drift into the bay as they 

 develop. During the period 24 January to 11 February 

 1978, egg abundance reached 13,424 Stage-4 eggs/m^ 

 at a station just south of the entrance to the bay where 

 large numbers of Stage 2-5 eggs were also present, 

 producing a total of 23,817 eggs/m^. 



The egg distribution pattern in Shelikof Strait was 

 most intensively examined in 1981; however, sampling 

 in other years (1978-86) indicates similar patterns. The 

 first appearance of low numbers of eggs occurs in 

 March and early April, mainly in the southern part of 

 the strait (Kendall and Picquelle 1990). The highest con- 

 centrations of eggs occur off Cape Kekurnoi in early 

 April, where abundances of Stage-2 and -3 eggs ex- 

 ceeded lOOO/m^ in 1981. The combined abundance for 



Larvae* 



Vertical distribution The ecology of walleye pollock 

 larvae has been investigated in both Funka Bay and 

 Shelikof Strait. In both areas most larvae occur above 

 50 m in the water column and exhibit limited diel ver- 

 tical migration (Kamba 1977, Kendall et al. 1987). Few 

 larvae are collected at the surface, but some larvae 

 move up to 1 0-20 m depth in the evening. At night they 

 are fairly evenly distributed throughout the upper 50 m, 

 and in the early morning they are again concentrated 

 above 20 m. During midday they are most abundant at 

 20 m and deeper to 50 m. The larvae sampled by Ken- 

 dall et al. (1987) in Shelikof Strait averaged 11.0mm 

 (SD 1.7mm), while those in Funka Bay sampled by 

 Kamba (1977) had a wide range of lengths from 4.6 to 

 26.4mm, although most were 4. 6-12. 8mm. Kamba 

 (1977) indicated that larger larvae (> 13.7 mm) were 

 more often collected in shallow tows at night and in 

 deep tows during the day, suggesting that either the 

 larger larvae migrated more than the smaller ones or 

 that the larger larvae were more successful at avoiding 

 the shallow nets during the day. No large larvae were 

 collected by Kendall et al. (1987). Kamba (1977) con- 

 cluded that the diel vertical movements of pollock 

 larvae in Funka Bay corresponded to those of their 

 zooplankton prey. Both Kamba (1977) and Kendall 

 et al. (1987) found a diel pattern in gut fullness, with 

 little food found in guts at night and most food found 

 in guts during the day. 



* Lengths of larvae and juveniles are reported here as standard length 

 (SL, from the tip of the snout to the end of the notochord or base 

 of the hypural plate), although in the Japanese literature they were 

 given as total length (TL). Conversion from TL to SL is based on 

 our paired measurements of 1048 fish (4.2-103 mm SL) which 

 resulted in the relationship: SL(mm) = 0.108 + 0.907 TL(mm). 



