THEILACKER: MORTALITY OF SEA-CAUGHT JACK MACKEREL 



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Table 2.— Shrinkage of jack mackerel larvae. Parameters estimated from multi- 

 variate linear equations relating the ratio of the net-treated size of a mackerel body 

 part to its live size (y) with the net-treatment time (x). 



Net-treated size/ 

 live size 1 



(SE) 



(SE) 



pz 



Standard length (SL) 

 Head length (HL) 

 Eye diameter (ED) 

 Body depth (BD-2) 



1.0109 (0.0117) 



0.9281 (0.0157) 



0.9360 (0.0168) 



0.8980 (0.0177) 



-0.0105 (0.0008) 



-0.0038 (0.0011) 



-0.0027 (0.0012) 



-0.0014 (0.0013) 



<0.001 0.66 



0.001 0.12 



0.031 0.06 



0.280 0.02 



1 n = 89. 



Probability that slopes differ from zero. 



were calculated by 1) combining the shrinkage ratio 

 at 8 min (average elapsed time for field collections, 

 see Methods) with 2) the average shrinkage in 

 Bouin's preservative after the net treatment, and 3) 

 comparing the combined shrinkage with results from 

 shrinkage determined in the laboratory study 

 (Theilacker 1980a; Table 3). Also given in Table 3 are 

 average shrinkage ratios calculated for specified time 

 intervals. 



Adjustment factors for standard length, head 

 length, and eye diameter (Table 3) support the view 

 that shrinkage of field-collected fishes is greater than 

 shrinkage of fishes preserved in the laboratory. 

 Shrinkage of BD-2 was an exception to this pattern, 

 however, as less shrinkage occurred under simulated 

 field conditions (20-23%) than in the laboratory 

 (25%). I (Theilacker 1980a) reported a similar 

 paradox for northern anchovy where simulated-field 

 net treatments caused 8% shrinkage of BD-2 as com- 

 pared with 10% shrinkage for standard laboratory 

 preservation. Jack mackerel shrinkage was greater 

 in Bouin's solution than in Formalin, results which 



are consistent with studies on northern anchovy. 

 Also, as with northern anchovy, Formalin preserva- 

 tion caused a slight increase in the size of the jack 

 mackerel eye (Table 3). 



I adjusted the body measurements of the ocean- 

 caught jack mackerel with the shrinkage factors 

 (ratio R 8 , Table 3). Use of these adjustments should 

 equate the morphology of preserved, ocean-caught 

 jack mackerel (this study) with the morphology of 

 preserved, laboratory-raised jack mackerel that were 

 used to develop the morphological SWDA (see 

 Methods: Morphological Analysis). It was necessary 

 to reestimate the SWDA function for this study, 

 although nearly the same analysis was made 

 previously (Theilacker 1978). A new estimate was re- 

 quired because pectoral body depth was not included 

 in the shrinkage measurements in this study; hence, 

 an SWDA function that excluded this measurement 

 was needed. Elimination of pectoral body depth from 

 the analysis reduced the level of predictability from 

 85% to 78%. This new function was used here to 

 classify the condition of ocean-caught jack mackerel 



Table 3.— Shrinkage of jack mackerel larvae 1 . Treatment ratio (R) is treated size 

 divided by previous size (1.00 = no shrinkage). 



1 Range in standard length 3.35-4.10 mm. 



Calculated from regression (Table 2); ocean-caught fish preserved within 8 min; see text. 

 Shrinkage in fixative after net treatment. 

 "Data from Theilacker (1980a). 



Adjustment factor to equate measurements of field-collected mackerel (this study) with 

 measurements of laboratory-raised mackerel (Theilacker 1978). 



