Abstract. — Condition of field- 

 caught walleye pollock, Theragra 

 ehalcogramma, larvae was assessed 

 by using a measurement of midgut 

 cell height that reliably diagnosed 

 the nutritional status of laboratory- 

 reared walleye pollock. The midgut 

 cell height was simple to measure 

 on histological sections. Several 

 correction factors were developed 

 for applying the midgut measure- 

 ment to a field study. These in- 

 cluded regressions to characterize 

 change in larval length associated 

 with net collections of various 

 elapsed times and with fixation in 

 several types of preservatives. The 

 response of midgut cell height to 

 field collection procedures also was 

 tested. The field study indicated 

 larval walleye pollock were starv- 

 ing in the Shelikof Strait, Gulf of 

 Alaska, in 1991. At some stations 

 up to 40% of the larvae were in poor 

 condition. Larvae were most vul- 

 nerable to starvation for 2 weeks 

 following the day of first-feeding. 



Condition of larval walleye pollock, 

 Theragra ehalcogramma, 

 in the western Gulf of Alaska 

 assessed with histological and 

 shrinkage indices* 



Gail H. Theilacker 

 Steven M. Porter 



Alaska Fisheries Science Center 

 National Marine Fisheries Service, NOAA 

 7600 Sand Point Way NE, Seattle. WA 98 1 ! 5 



Manuscript accepted 12 September 1994. 

 Fishery Bulletin 93:333-344 ( 1995). 



In 1986 the Fisheries-Oceanogra- 

 phy Coordinated Investigations 

 (FOCI) program of the Alaska Fish- 

 eries Science Center and the Pacific 

 Marine Environmental Laboratory 

 began studying the biological and 

 physical processes controlling vari- 

 ability in recruitment of walleye 

 pollock, Theragra ehalcogramma, in 

 Shelikof Strait, Gulf of Alaska. Each 

 year, large concentrations of adult 

 walleye pollock aggregate in the 

 Strait and spawn in late March and 

 early April, producing dense patches 

 of eggs at a depth of about 200 m; 

 there is little variation in the tim- 

 ing or location of the spawning ( Kim 

 and Kendall, 1989; Kendall and 

 Picquelle, 1990; Schumacher and 

 Kendall, 1991). After hatching, lar- 

 vae rise to the upper waters where 

 they may be transported along the 

 Alaska Peninsula, off the shelf to 

 the southeast, or be retained in ed- 

 dies (Vastano et al., 1992). It is be- 

 lieved that the area young pollock 

 occupy during the larval stage is 

 important for their survival (Schu- 

 macher and Kendall, 1991 ). Assess- 

 ing the nutritional condition of lar- 

 val pollock collected from different 

 areas in Shelikof Strait should aid 

 in determining whether food avail- 

 ability is one of the factors influenc- 

 ing survival and recruitment. 



A variety of indices have been ap- 

 plied to examine the nutritional 

 condition of larval fish. However, for 

 most of the indices, the response 

 rate of the variable to changes in 

 feeding is unknown. Thus, it is dif- 

 ficult to apply the index to estimate 

 mortality rates in the field and sub- 

 sequent recruitment variability. 

 Histological analyses have yielded 

 valuable information on larval nu- 

 tritional condition (O'Connell, 1976; 

 Theilacker, 1978; O'Connell and 

 Paloma, 1981; Sieg, 1992). Further- 

 more, starvation-induced mortality 

 rates for histological studies have 

 been estimated by combining the re- 

 sults from histological condition as- 

 sessments with information on 

 growth and starvation rates (Theil- 

 acker, 1986; Theilacker and Wata- 

 nabe, 1989). Using the estimate of 

 starvation-induced mortality rates, 

 attempts have been made to calcu- 

 late the proportion of natural mortal- 

 ity due to starvation mortality (Hewitt 

 et al., 1985; Owen et al., 1989). 



Preliminary studies on larval wall- 

 eye pollock have revealed that the 

 height of the midgut mucosal cells 

 are sensitive to starvation, decreas- 

 ing in height measurably over time 



* Contribution FOCI-0191 to NOAA's Fish- 

 eries-Oceanography Coordinated Investi- 

 gations, Seattle, WA 98115. 



333 



