Experiment 1 1 



Experiment 13 



Objective: To validate the mortality and tag- 

 shedding rates obtained with juvenile tags in 

 Experiment 7. 



Procedure: Thirty-five starved fish (mean 

 length 82 mm) from the same group used in 

 Experiment 7 were tagged with juvenile tags. 



Results: Two fish died and four shed their 

 tags. 



Discussion: These starved fish did not suffer 

 high tagging mortality rates when tagged with 

 juvenile tags. The rate of tag shedding prob- 

 ably decreased in this experiment as a result 

 of tagging gun modifications. 



Experiment 12 



Objective: To further substantiate the effects 

 of intestinal fullness on mortality of juvenile 

 fish tagged with adult and juvenile tags. 



Procedure: Fifty fish (mean length 83 mm) 

 from a group that had been fed a light diet for 

 the preceding 5 days were tagged with adult 

 tags, and 49 fish from the same group were 

 tagged with juvenile tags. Fifty-one fish were 

 used as controls. 



Results: The tag loss was 54% for adult tags 

 and 37% for juvenile tags (Table 7). Death ac- 

 counted for 48% and 6% , respectively. 



Discussion: Since only 48% and 6% of the 

 fish died, as opposed to 95% in Experiments 

 8-10, we concluded that fish similar in size to 

 those in Experiment 12 have a good chance of 

 surviving if tagged with juvenile tags and not 

 overfed. As in previous experiments, most of 

 the mortality occurred within 3 days and tag 

 shedding within 2 weeks. 



Table 7. — Experiment 12; effects of adult and juvenile tags 

 on the mortality and shedding in juvenile fish without 

 distended intestines. 







Number of 











Type tag 





fish 



in 











used 





expei 



iment 



Dead 



Shed 



Total 



loss 











Number 



Number 



Percent 



Adult tag 





50 





24 



3 



27 



54 



Juvenile tag 





49 





3 



15 



18 



37 



Control (not 



tagged) 



51 









- 











Objective: To gain a better understanding of 

 the tag-loss rate from juvenile fish under field 

 conditions. 



Procedures: We tagged 50 juvenile fish (mean 

 length 101 mm) with adult tags and 50 with 

 juvenile tags in an estuary and then transport- 

 ed them with control fish to the laboratory. 



Results: Eighty-six percent of the adult tags 

 were lost, mostly from mortality; 64% of the 

 juvenile tags were lost, mostly from shedding 

 (Table 8). 



Discussion: No handled controls died, indi- 

 cating that mortality, which occurred within 

 3 days, was caused by tagging. The fish in this 

 experiment contained more food material than 

 the well-fed fish used in Experiments 8-10. The 

 first fish to die had punctured intestines, sug- 

 gesting that mortality of field-tagged juveniles 

 may be directly related to the fullness of the 

 intestines. Since most previous tag losses had 

 resulted from juvenile tags being shed and from 

 mortality in fish with excess intestinal contents, 

 we devised experiments to test further tag shed- 

 ding and to determine further the effects of in- 

 testinal contents on tagging mortality. 



Table 8. — Experiment 13; effects of adult and juvenile tags on the 

 mortality and shedding in groups of 50 juvenile fish tagged in the 

 field and transported to a laboratory tank. 



Type 

 tag used 







Dead Shed 



Total loss 









Number 



Number 



Percent 



Adult 







41 2 



43 



86 



Juvenile 



tag 





11 21 



32 



64 



Control 



(not 



tagged) 















Experiment 14 



Objectives: (1) To determine if different 

 amounts of intestinal contents affect tagging 

 mortality of juvenile fish; (2) to determine if 

 inserting the tag at a different angle than pre- 

 viously affects the tag-shedding rate. 



Procedures: Fish (mean length 101 mm) were 

 kept in two tanks. Five times as much food 

 was given to fish in one tank as was given to 



