BAILEY: EARLY LIEE HISTORY OF PACIFIC HAKE 



ervation effects. Increase in weight also appears 

 to be slow for at least the first 30 d of posthatch- 

 ing life. 



Weight loss of fi rst- feeding larvae due to pres- 

 ervation in 80% ethanol was 57.8%, probably due 

 mostly to loss of lipids and soluble proteins; 

 weight loss in 3% Formalin was 24.1% (Table 2). 



Shrinkage in length of first-feeding larvae 

 preserved in Formalin was 8.9%; shrinkage of 

 larvae preserved in ethanol was 3.6% (Table 3). 

 Shrinkage due to delay in preservation was ex- 

 amined. Larvae in the 9-min delayed group de- 

 creased 17% in length, while those in the 29-min 

 group decreased 40% in length. Most larvae, and 

 especially larger larvae, probably do not die dur- 

 ing the tow, and I have observed that in Puget 

 Sound most larvae are alive after capture with a 

 jar-type cod end. However, after a typical 

 CalCOFI tow it probably takes an average of 

 5-10 min to remove and wash the cod end before 

 preserving the larvae. I estimate that in routine 

 sampling surveys small Pacific hake larvae 

 probably shrink 9-20% in length due to handling. 

 Shrinkage of large larvae was not tested and is 

 probably different. 



Table 2. — Weight loss due to preservation, determined by 

 comparing fresh-frozen larvae to preserved larvae. Dry 

 weights in milligrams. 



Live 



80% 

 ethanol 



3% 



Formalin 



Mean dry-weight (mg) 0.083 035 0.063 



Standard deviation 007 004 006 



No. of larvae 5 5 5 



% of live weight 100 42.2 75.9 



o 0.4 



IO M I2 I3 



TEMPERATURE (°C) 



Figure 6.— The effect of temperature on mean respiration 

 rates (/xl/animal per h) (if Pacific hake larvae of different 

 stages. Vertical bars are ±1 standard deviation. 



respiration rates for first-feeding larvae are 4.8- 

 6.8 ^1/mg-dry wt per h. These respiration rates 

 were determined in 30 ml bottles, which did 

 appear to slightly impair the swimming activity 

 of larvae. Consequently, these rates are consid- 

 ered to be within the range between routine and 

 active metabolism. The dry weights reported in 

 Table 4 are of Formalin-preserved larvae, un- 

 corrected for weight loss due to preservation. 

 With the correction, weight specific rates would 

 be 25% lower. 



Vertical Distribution 



Table 3.— Shrinkage in standard length of first-feeding lar- 

 vae due to preservative and related to delay in time of preser- 

 vation, determined by comparing standard lengths of live lar- 

 vae with preserved larvae. Three larvae per treatment; lengths 

 are in millimeters. 



Metabolic Rates 



Respiration rates for Pacific hake larvae in- 

 crease as a function of temperature and size (Fig. 

 6; Table 4). The experimental temperatures rep- 

 resent the range encountered by hake larvae 

 within the spawning region. At 12°C, the mean 

 temperature larvae experience off California, 



Ahlstrom (1959) noted that Pacific hake eggs 

 (and also most unsized hake larvae) were aggre- 

 gated near the base of the mixed layer. From my 

 analysis, most small larvae <8 mm were caught 

 in the 50-100 m depth interval (Fig. 7), which 

 corresponds to Ahlstrom's observations. Larger 

 larvae were caught deeper; however, large lar- 

 vae near the surface may be more able to avoid 

 capture. An analysis by Lenarz (1973) indicates 

 that larger larvae are probably able to avoid 

 plankton nets in daytime. Large larvae, >12 

 mm, appear to be close to the surface later in the 

 year (May-June), and have been caught at depths 

 of only 25-50 m in nighttime plankton tows (A. 

 Alvarino 3 ). From my own observation in June 



3 A. Alvarino. Southwest Fisheries Center La Jolla Labora- 

 tory, National Marine Fisheries Service, NOAA, P.O. Box 271, 

 La Jolla, CA 92038, pers. commun. June 1979. 



593 



