CHANGES DURING EXPLOITATION 



It was desired tn li.ne the ])opulations as stable 

 as ])ossible before the start of e.\])loitatioii. Deoree 

 of stability was examined by studying the dis- 

 tribution of the iiidi\i(huil ])opulations with re- 

 sjiect to the caleirories "fry," "immature," and 

 "adult." For the 'A weeks immediately before the 

 start of exploitation al cacli diet level, comixisi- 

 (ious aecordino; to tliese categories revealed fairly 

 consistent patterns for the 0.5 and 1.0 levels 

 (figs. 'A and 4). Imih IxMwccn weeks and between 



Populotion 8 



Population A 



100 



50 







100 



cr 50 



UJ 



m 



§ 



z 



100 



50 







WEEK 28 



t?^ f^^ 



m 



WEEK 29 



PZ^ ITTTT, 



WEEK 30 



t^TTi F777\ 



m. 



m 



V///\ Ty^T^ 



^m 



< 



zzm u > ' >i 



VTTA 



Fry Im Ad Fry Im Ad Fry Im Ad 

 SIZE CATEGORY 



l'"i(aitE 3. — Composition acrordinp; lo catogoi-it'.s "fry," 

 "iiiunuturc," and "adult" (defined in section "Experi- 

 nu^ntal diet and proeednres") of popidations at the ().."> 

 diet level, immediately before cxjiloittLtion. 



poj)ulations. (Weeks of removal were staggered 

 to facilitate the hdxiratory routine. Thus, exploi- 

 tation at the 0.5 level began a week after thai 

 at the 1.0 level.) The comjxisitions are charac- 

 t(uistic of matiue popidations at or near the 

 a.symptotic level- mostly adults that are rather 

 stable in number aiul nuich smaller and somewhat 

 nu)re lluctiuiling nuinbei's of juveniles. 



Characteristics of the compositions were similar 

 al the 1.5 level (fig. 5) except for the lack of con- 

 sistency between populations. (Exploitation was 

 delayed 4 weeks in the ho|)e that this incon.sistency 

 migiii disapjicar.) Here the differences are marked 



100 



50 







100 



UJ 50 

 m 



s. 



2 



100 



50 



WEEK 27 



VTTA 



WEEK 28 



w 



y777\ 



WEEK 29 



r777i 



_^3_ 



^777\ 



^ V77A m 



VTTA UTTTi 



Fry Im Ad. Fry Im Ad. Fry Im 

 SIZE CATEGORY 



Ad 



"icCHE 4. — Compo.sition according to categories "fry," 1 

 "immatiu'e," and "adult" (defined in .section "Experi- 

 inental diet and procedures") of populations at the 1.(1 

 diet le\-el, immediately before exploitation. 



both in total number (as between C and E in week 

 :U) and in percentage com]iosition (as between 

 C and I in week 32). 'J'he.se differences are siir- 

 ]Dri.sing among populations held for more than 30 

 weeks imder conditions of food supjily, tem])era- 

 ture, light, and sjjace as nearly itlentical as j)os- 

 sible. No ready explanation could be found among 

 other conditions of the environment or among 

 j)rocedures of handling the fish. Prol)ably genetic 

 differences were iu)t averaged out iimong the 

 rather small numbers of adidts (15) in the initial 

 poj)nlations, in spite of the method of selection 

 (section, "Initial growlli of popidations"). The 

 differences may also have resulted from \ariations 

 in gravidity among the eight adult fenuiles in 

 each iniiial jmpulation. Siipjiort for some expla- 

 mition relatctl to the initial p<iptLliilions is found 

 in the fact that C exceeded E and I in ninuhcr 

 and weight almost finni the start of the ex])eri- 

 inent (weeks 2 to 2S. I able :-; : weeks 5 in 20 and 

 22 to 2N, table 4). 



The differences among popidations at llic 1.5 

 diet level persisted, e\'en though the start of ex- 

 ploitation was delayed 4 weeks beyond that for 



432 



U.S. FISH AND WILDLIFE SERVICE 



