26 

 24 

 22 



20 



U3 



g le 



a 



16 



14 



£ 12 



7.2 



9.4 



IL7 13,9 



TEMPERATURE (°C.) 



16.1 



18.3 



Appendix Figure 1. — Days required for fresh and frozen 

 Chinook salmon to float at water temperatures of 7.2° to 

 17.2° C. 



that floating time is unaffected by water tempera- 

 ture. 



To determine whether massive tissue damage 

 such as ruptured body cavities might aff'ect the 

 time required to float, we made another experi- 

 ment with 15 frozen carcasses. Slits of 2.5 to 7.5 

 cm. were made in the body wall of eight carcasses, 

 and full-length slits (from vent to isthmus) were 

 made in seven. 



Three fish, two with full length slits and one 

 with a 7.5-cm. slit, took only 4 or 5 days to float at 

 temperatures of 15.6° to 18.3° C. Of the remaining 

 12 fish, tested at water temperatures of 9.4° to 

 11.1° C, all but two floated — one of these had a 

 2.5-cm. slit and the other had a full-length slit. 

 Except for the two that did not float, the time 

 required for slit fish to float was about the same 

 as for intact fish: in the warm-water range, slit 

 fish required an average of 4.3 days to float com- 

 pared with 4.6 days for intact fish; in the cold- 

 water range, slit fish required an average of 12.8 

 days to float compared with 11.8 days for intact 

 fish. 



All the tagged experimental carcasses used for 

 the population estimates were intact. Some of the 

 natural population of killed fish had massive 

 wounds, and part of these could not float and be 

 recovered as floaters. Therefore, in the main body 

 of this report we have referred to such fish as 

 being unrecoverable, and in our basic model we 

 allow for the possibility that a fraction of the 

 fish that die are rendered unrecoverable. 



Pertinent results of the flotation experiment are 

 summarized as follows: 



1. All intact dead chinook salmon, fresh or 

 frozen, floated. 



2 The relation between water temperature and 

 time required to float was inverse, i.e., the colder 

 the water the greater the time required for the 

 carcass to float. 



3. No statistically significant or practical differ- 

 ences were found between floating times of fresh 

 and frozen fish over the range of temperatures 

 tested. 



4. A slit or puncture of the abdominal wall 

 usually did not greatly affect the floating qualities 

 of the fish. 



5. Fresh and frozen chinook salmon carcasses 

 have similar floating properties; therefore, frozen 

 carcasses can be used to simulate fresh carcasses. 



Disappearance of Floaters from Recovery Area 



We conducted another experiment to estimate 

 the rapidity of disappearance of floaters from the 

 surface of the Columbia River within the re- 

 covery area and to trace their dispersion from the 

 point of first appearance. From April 4 to July 22, 

 1955, all floaters in reasonably good condition 

 were tagged with Petersen disks and released 

 where they were found (appendix table 3). Of 

 289 chinook salmon floaters tagged, 11 percent 

 were recovered; 26 were recovered again after 

 the first release, and five after a second release. 

 The single recovery from the 17 chinook salmon 

 released above the dam at station 8 (The Dalles) 

 was by a fisherman about 4.8 km. downstream 

 from the release point. Nineteen percent of the 11 

 steelhead floaters were recovered. The greatest 

 distance traveled by any tagged floater before 

 recovery below the dam was 74 km. 



CHINOOK SALMON MORTALITY IN COLUMBIA RIVER NEAR BONNEVILLE DAM 



491 



