FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 281 



MARKING OF KARLUK RIVER RED SALMON 



The Karluk River is relatively shallow, and as the seaward migrant fingerlings 

 tend to congregate above the counting weir, they can easily be captured. A pen 

 about 5 feet square of K-inch bar wire netting, having a gate for the fish to enter, was 

 constructed in the river. A seine was passed around a school of fish, and an end of the 

 seine brought to each side of the gate. By gradually drawing in the ends of the seine, 

 the fish were induced to enter the pen, and the gate was closed. Several thousand 

 migrants can be held in the pen at one time without injury. Two or three hundred 

 migrants were caught and transferred to a wash tub partially filled with water. 

 The tub of fish was then carried from the pen to the marking shed below the weir. 

 The fish were removed from the tub one at a time, the adipose and one or two other 

 fins removed by means of a nail clipper, and the fish dropped into the river free to 

 proceed downstream. During the entire operation the fish are out of water for less 

 than 10 seconds. Samples of marked fish have been held in tanks for several days 

 after marking, and the fish have shown no ill effects from the operation, though some 

 of the fish marked by the removal of either of the pectoral fins appeared to have a 

 slight list. 



The age group composition of the marked migrants was determined by multi- 

 plying the number of migrants marked each day by the percentage of the various age 

 groups in the migration for that day as determined by the analysis of data obtained 

 from scale samples of the fish. 



RECOVERY OF MARKED FISH 



Owing to the magnitude of the run of Karluk red salmon, it was impossible to 

 examine every fish to search for marked individuals. The method employed to 

 determine the total number of marked fish was as follows: 



As large a portion as possible of each day's catch of red salmon, taken by moans 

 of beach seines near the mouth of the Karluk River, was examined for the presence 

 of marked fish by an employee of the Fish and Wildlife Service who, during the exami- 

 nation, was stationed in the cannery. Each red salmon was examined and counted 

 as it passed along the. chute. All fish with missing or mutilated fins were put aside 

 and re-examined later to determine whether they were marked fish. Scale samples 

 were taken from all marked fish found, and scale samples were taken at random 

 from the catch to determine the age composition. The number of marked fish of 

 each age found and the number of fish of that same age examined were determined 

 at weekly intervals throughout the season. The total number of marked fish of 

 each age found was divided by the total number of fish of the same age group ex- 

 amined to determine the percentage occurrence of marked fish in that age group. 

 Data were collected on the number of Karluk red salmon in the commercial catch and 

 also the number in the escapement, hence, the total number of fish of each age croup 

 in the run can be determined for the season. Multiplying the number of fish of a 

 given age in the run by the percentage occurrence of marked fish in that age group 

 gave the calculated number of marked fish of that age group returning. 



Since it is considered that there are two runs of red salmon to the Karluk River, 

 it would be preferable to divide each marking experiment into two parts, i. e., spring 

 run and fall run. Unfortunately, there is no way of determining which are spring 



