Abstract.- We determined the 

 patterns of disti'ibutit)n for eggs and 

 larvae of walleye pollock by analyz- 

 ing 1,929 ichthyoplankton samples 

 collected on 32 cniises in the western 

 Gulf of Alaska between 1972 and 

 1986. The combined effects of addi- 

 tions of recently spawned eggs, mor- 

 tality, dispersion, and advection deter- 

 mine the location and concentrations 

 of eggs and larvae. The vast major- 

 ity of the eggs were found in spring 

 samples, primarily in April. Larvae 

 were found mainly in late April and 

 May. Eggs occurred mostly in a 

 small area near Cape Kekurnoi in 

 Shelikof Strait, and larvae were 

 centered progressively to the south- 

 west of this area as they grew and 

 were moved by advection. By the 

 end of May, they were usually found 

 near the Semidi Islands. However, 

 comparisions of larval distributions 

 in late May showed significant inter- 

 annual variations in the area of con- 

 centration and larval size. 



Egg and Larval Distributions 



of Walleye Pollock 



Theragra chalcogramma 



\n Shelikof Strait Gulf of Alaska 



Arthur W. Kendall, Jr. 

 Susan J. Picquelle 



Alaska Fisheries Science Center, National Marine Fisheries Service, NOAA 

 7600 Sand Point Way N E , Seattle. Washington 981 15-0070 



Manuscript accepted 18 September 1989. 

 Fishery Bulletin, U.S. 88:133-1,54. 



Walleye pollock Theragra chalcogram- 

 ma is the dominant gadid in the sub- 

 arctic Pacific Ocean and in the Ber- 

 ing Sea. It is a moderate-sized (to 

 about 70 cm standard length) pelagic 

 or semidemersal fish that frequently 

 occurs in large aggi'egations. It feeds 

 primarily on copepods and euphau- 

 sids, although fish, including its own 

 young, enter its diet (see Lynde 

 1984). 



Intensive multinational midwater 

 trawl fisheries are conducted for 

 walleye pollock in the Gulf of Alaska, 

 the Bering Sea, and the northwest 

 Pacific Ocean. In recent yeai's, cat<?hes 

 of walleye pollock have been larger 

 by weight than those of any other 

 single species worldwide (Sharp 1987). 



Although pollock spawn intermit- 

 tently year-round, most spawning oc- 

 curs in spring. Walleye pollock spawn 

 planktonic eggs that require about 

 2-3 weeks to hatch, depending on 

 temperature. The planktonic larval 

 period lasts several weeks and the 

 transition to the juvenile stage seems 

 to be gradual. Considerable literatm-e 

 is available on the early life history 

 of walleye pollock, most of it concern- 

 ing the populations in the eastern 

 Bering Sea (Dunn and Matarese 1987). 



From 1972 tlii-ough 1986, the North- 

 west and Alaska Fisheries Center 

 (NWAFC, recently renamed the Alas- 

 ka Fisheries Science Center) con- 

 ducted plankton sampling in the Gulf 

 of Alaska, primarily in the Shelikof 

 Strait. Based on results of the sur- 

 veys before 1980, Kendall and Dunn 



(1985) found that walleye pollock 

 eggs, larvae, and spawning adults 

 were in low abundances throughout 

 the continental shelf and upper slope 

 of the Gulf of Alaska. In spring 1980, 

 however, a large spawning concen- 

 tration was discovered in Shelikof 

 Strait, and subsequent sampling in- 

 dicated that spawning occurred there 

 in spring every year through 1988. 

 No concentrations of similar magni- 

 tude have been found elsewhere in 

 the Gulf of Alaska, although other 

 areas have not been surveyed as in- 

 tensively (E.P. Nunnallee, Alaska 

 Fish. Sci. Cent., Natl. Mar. Fish. 

 Serv., NOAA, 7600 Sand Point Way 

 NE, Seattle, WA 98115-0070, pers. 

 commun.. June 1988). 



The migration of spawning adults 

 into Shelikof Strait has been moni- 

 tored in most years since 1980, and 

 has proven to be quite consistent 

 from year to year (Nelson and Nun- 

 nallee 1987). Most spawning in the 

 Shelikof Strait occurs in a localized 

 area in April, as demonstrated by the 

 occurrence of eggs in NWAFC plank- 

 ton samples. The vertical distribution 

 of walleye pollock eggs in Shelikof 

 Strait shows that a complex pattern 

 of interaction between stage of devel- 

 opment and local water density 

 determines their depth of occurrence 

 with a substantial portion occurring 

 below 200 m (Kendall and Kim 1989). 

 After hatching, larvae drift in the up- 

 per water column to the southwest 

 during a developmental period of 6-8 

 weeks (Kendall et al. 1987). This 



133 



