400 



Abstract.— Nursery areas of Pacific 

 herring, Clupea pallasi, and walleye 

 pollock, Theragra chalcogramma, were 

 identified by using acoustic surveys in 

 October 1995, and in March and July 

 1996 in Prince William Sound, Alaska. 

 Pacific herring and walleye pollock were 

 aggregated in the east-northeast and 

 west-southwest areas. Juvenile Pacific 

 herring spent the first two years of their 

 lives isolated within bays. Water tem- 

 peratures within bays were cooler in 

 the summer and warmer in the winter 

 compared with temperatures measured 

 along coastal passages and the open 

 coast. Although these temperature 

 differences were small and based on 

 point observations their accumulative 

 effect over the season may be consider- 

 able. The school structure of juvenile 

 Pacific herring varied seasonally. Newly 

 recruited age-0 Pacific herring were 

 tightly aggregated, forming a few, dense 

 schools within a single-size cohort, in 

 shallow water at the heads of bays 

 in July. Age-0 Pacific herring were 

 still aggregated within bays in shallow- 

 water in October, but the school struc- 

 ture was less cohesive and size cohorts 

 began to mix. School structure and dis- 

 tribution completely changed in March 

 as age-0 Pacific herring moved away 

 from the shores into deeper water and 

 spread out forming sparse shoals of 

 mixed-size cohorts. Juvenile Pacific her- 

 ring joined the adult schools after their 

 second winter, leaving as new recruits 

 entered the bays. Juvenile walleye pol- 

 lock also aggregated within bays and 

 were spatially segregated from adults. 

 However, there appeared to be little 

 overlap between Pacific herring and 

 walleye pollock juveniles because they 

 occupied different portions of the water 

 column within these bays. 



Spatial distributions of Pacific herring, 

 Clupea pallasi, and walleye pollock, 

 Theragra chalcogramma, 

 in Prince William Sound, Alaska 



Kevin D. E. Stokesbury 



Institute ol Marine Science 



University of Alaska-Fairbanks 



Fairbanks, Alaska 99775-7220 



Present address Center lor Marine Science and Technology 

 University ol Massachusetts Dartmouth 

 706 South Rodney French Boulevard 

 New Bedford, Massachusetts 02744-1221 



E-mail address kstokesbury aumassd edu 



Jay Kirsch 



Prince William Sound Science Center 

 PO Box 705 

 Cordova. Alaska 99574 



Evelyn D. Brovwn 



Institute ol Marine Science 

 University of Alaska-Fairbanks 

 Fairbanks, Alaska 99775-7220 



Gary L. Thomas 



Prince William Sound Science Center 

 PO Box 705 

 Cordova, Alaska 99574 



Brenda L. Norcross 



Institute of Marine Science 

 University of Alaska-Fairbanks 

 Fairbanks, Alaska 99775-7220 



Manu.script accepted 29 November 1999. 

 Fish. Bull. 98:400-409 (20001. 



In Prince William Sound, Alaska, 

 Pacific herring ( Clupea pallasi ) and 

 walleye pollock {Theragra chalco- 

 gramma) support major commer- 

 cial fisheries and are primary forage 

 for marine birds, mammals and 

 other fishes (Clausen, 1983; Hatch 

 and Sanger. 1992; Livingston, 1993; 

 Brown et al., 1996). Recently the 

 abundance of both these species 

 in Prince William Sound has fluc- 

 tuated, particularly that of Pacific 

 herring, which suffered a popu- 

 lation crash in 1993 resulting in 

 the closure of the commercial fish- 

 eries (bait, sac-roe, and roe on kelp) 



(Meyers et al., 1994; Paine et al., 

 1996). Little is known of the spa- 

 tial distributions and the physical 

 and biological variables influenc- 

 ing Pacific herring and walleye pol- 

 lock life histories in this biologically 

 rich, high latitude ecosystem ( Paine 

 etal., 1996). 



We identified Pacific herring and 

 walleye pollock nursery areas by 

 examining their small-scale (km) 

 spatial distributions in Prince Wil- 

 liam Sound, Alaska. We hypothe- 

 sized that juvenile Pacific herring 

 and juvenile walleye pollock were 

 contagiously distributed and that 



