FISHERY BULLETIN: VOL. 84, NO. 2 



4000 r 



3500 



3000 - 



2500 



2000 - 



1600 - 



1000 - 



600 - 



Figure 2.— Total numbers offish immigrating 

 as of week i by the weir count and total num- 

 bers of fish estimated by method three to have 

 died as of week i + 2. 



ability and/or survival with conditon among 

 "marked" (and thus decayed) animals (Fig. 3). For 

 each week, smaller and more decayed carcasses ap- 

 pear to have lower recapture rates. (Note that since 

 this figure represents catchability at and after the 

 earliest time of recapture, these data do not reflect 

 catchabilities of fresh fish. Also, recapture rates for 

 week 3 are higher than those for week 4 because 

 there is one more opportunity for recapture.) These 

 low recapture rates can be the result of either lower 

 survival or lower catchability of smaller and more 

 decayed carcasses. The effects of these differences 

 in catchability on absolute numbers of recaptures 

 would be small because of the small number of car- 

 casses in the lower capture probability categories. 

 Note also in Figure 3 that recapture rates of fresh 

 carcasses vary less with size than decayed carcasses. 



The expected and actual values for the tests for 

 differential catchability and mortality, the contribu- 

 tion of each difference to the x 2 value, and the nor- 

 mal and pooled x 2 values are presented in Tables 3 

 (Seber 1982) and 4 (Jolly 1982), respectively. Al- 

 though the fit between expected and observed 

 values appears to be quite good, the total differences 

 are statistically significant, hence catchability is not 

 strictly homogeneous. 



The comparison of estimated and actual param- 

 eters as suggested by Leslie et al. (1953, cited by 



08 



6 _ 



I 

 u 



0) 



tr 



2 - 



00 



Small 

 Medium - 

 Medium 

 Medium* 

 Large 



fresh decayed 

 (AL.F.D-I (D) 



very decayed 

 ID'.SK) 



fresh decayed 

 (AL.F.D-) (D) 



very decayed 

 (D*.SK) 



Week 3 



Week 4 



Figure 3.— Fraction of marked fish recaptured by size, condition, 

 and week of release. Circled data points have sample sizes of 

 numbers of fish recaptured <10. Where <5 fish were released, that 

 point was not plotted. Note that all fish are decayed upon recap- 

 ture. The "fresh" category here includes alive, fresh and decayed 

 minus; the "decayed" category includes decayed and the "very 

 decayed" category includes decayed plus and skeleton. 



Seber 1982) is presented in Table 5. The close agree- 

 ment between both sets of estimates indicates any 



266 



