164 



Fishery Bulletin 94(1). 1996 



Figure 1 



Distal surface of a whole Atka mackerel otolith (25x mag- 

 nification) from a 180-mm-FL fish captured in May 1985. 

 A single translucent zone is apparent along the otolith mar- 

 gin. Bar = 500 /jm. 



margin and adjacent translucent zone is nearly one- 

 fourth the size of the previously deposited opaque 

 zone; stage 3 = area of opaque growth between the 

 otolith edge and adjacent translucent zone is nearly 

 one-half the size of the previously deposited opaque 

 zone; and stage 4 = area of opaque growth between 

 the otolith edge and adjacent translucent zone is 

 nearly equivalent in size to the previously deposited 

 opaque zone. 



Larval otoliths 



In April 1993, the AFSC's Fisheries-Oceanography 

 Coordinated Investigations (FOCI) scientists made 

 a special collection of 88 larval Atka mackerel from 

 one neuston-net trawl in the Akutan Pass region of 

 the Aleutian Islands. Larval standard lengths were 

 measured. Owing to the protocols of the different 

 surveys, lengths cited in this study for fish smaller 

 than 180 mm are standard length (SL) measure- 



ments and lengths cited for fish equal or greater than 

 180 mm are fork length (FL) measurements. 



Sagittal otoliths were extracted from 30 larvae and 

 otolith diameters were measured. Each otolith was 

 ground along one side of the sagittal plane until the 

 otolith core was clearly visible through a compound 

 light microscope at l,000x magnification. Un- 

 validated but presumed daily increments were 

 counted from the otolith core to the edge with a com- 

 pound light microscope at l,000x magnification. 



Adult otoliths 



To help distinguish between the larval and older fish 

 samples in our discussion, we will refer to Atka mack- 

 erel >180 mm FL as adult fish. Otoliths observed with 

 at least one translucent zone (250 mm FL— 390 mm 

 FL) were ground from both lateral sides until the 

 core was visible on the surface when examined 

 through a light microscope. Some otoliths were 

 ground along the transverse plane and others along 

 the sagittal plane. Unvalidated but presumed daily 

 increments were counted from the core to the first 

 translucent zone on 25 prepared otoliths with the 

 clearest incremental patterns. 



Five adult fish otoliths were prepared for viewing 

 with a scanning electron microscope (SEM). These 

 otoliths came from fish that were 250 mm FL to 280 

 mm FL and that had two translucent zones. Each 

 otolith was ground from both lateral sides along the 

 frontal plane until the core was visible on the sur- 

 face when viewed through a light microscope. The 

 samples were coated with platinum-palladium and 

 examined with a Hitachi S-2300 SEM. 



Seasonal length data 



FOCI larval data Most larvae from this collection 

 were captured in neuston nets ( some from bongo-net 

 tows) along coastal shelf zones around Kodiak Island 

 (a few specimens were collected from the eastern 

 Bering Sea). The survey years spanned from 1977 to 

 1986 and yielded larval length data from 1 ,545 speci- 

 mens (Table 1) from September to November and 

 from February to June. 



The average seasonal lengths for northeastern 

 Pacific larval Atka mackerel, calculated from FOCI 

 data, were compared with Gorbunova's (1962) re- 

 ported seasonal lengths for Atka mackerel larvae 

 captured near the Kamchatka Peninsula. Gorbunova 

 (1962) cited only monthly minimum and maximum 

 lengths (assumed to be standard lengths) from Sep- 

 tember to May; therefore, for comparative purposes, 

 we used the monthly midpoints. 



