3 .ct SURVIVAL AND SPAWNING OF GILL-NET-MARKED RED

RESEARCH REPORT 40 FISH AND WILDLIFE SERVICE UNITED STATES DEPARTMENT OF THE INTERIOR ABSTRACT

On Kodiak Island in Karla Lagoon, 6,253 salmon were tagged in 1953 to determine the effect of gill-net marks on survival and spawning. Approximately half of these fish were gill-net marked and the remainder unmarked (control) fish. Numbered tags of several color combinations were used so that observations could be made on each group of fish both enroute to and on the spawning grounds. The results of the study show that the greatest mortality of net- marked fish occurred shortly after the fish were tagged and released. It is estimated that between 10 and 20 percent of the gill-net-marked fish escaping from gill nets die from webbing injuries. No dif- ference was noted in the travel time of tagged control and tagged gill-net-marked fish from the lagoon to the spawning grounds. No significant difference was found between the spawning conditions of gill-net-marked fish and the control fish. There was a general tendency for gill-net marks to heal, and no relation was found between the seriousness of the gill-net marks and the survival of the fish. SURVIVAL AND SPAWNING OF GILL-NET-MARKED RED SALMON

By PHILIP R. NELSON and

CARL E. ABEGGLEN, Research Biologists

RESEARCH REPORT 40

Fish and Wildlife Service, John L. Farley, Director

United States Department of the Interior, Douglas McKay, Secretary

UNITED STATES GOVERNMENT PRINTING OFFICE : 1955

For sale by the Superintendent of Documents, United States Government Printing Office Washington 25, D. C. - Price 20 cents CONTENTS Page Description of the experiment ...... 2 Location of the site ...... 2 Design and operation of the fishing gear ...... 2 Tagging operation ...... 5 Experimental limitations ...... 6 Analysis of results ...... 7 Recoveries of tagged fish in the Karluk Lagoon ...... 7 Observations and recoveries of tagged salmon at the Karluk weir and on ihe spawning grounds ...... 7 Effect of tagging and gill-net marks on the sexes ...... 10 Migration rate of gill-net-marked and control fish ...... 11 Spawning condition of gill-net-marked and control fish ...... 11 Healing of gill-net marks and the effect of the net mark on survival of salmon ...... 13 Discussion ...... 1 8 Summary and conclusions ...... 18 Literature cited ...... 19 SURVIVAL AND SPAWNING OF GILL-NET- MARKED RED SALMON

Salmon are captured commer- hatchery 1 mile below Bonneville cially in Alaska by the use of Dam, and the Big White Salmon a variety of fishing devices. In hatchery 30 miles above the dam. recent years, the standardized meth- Schaefer (1951) reported the fol- ods most used are, in decreasing lowing in connection with tagging order of importance: traps, purse done on the Harrison River trap seines, gill nets, and lines. The during 1939 through 1941: "There salmon that escape from the fishing is nothing in these data to indicate gear are often marked or injured that injury by gill nets reduces the in some manner. The evidence is chances of recovery of the tagged readily observed in the many gear- fish. . . . The possibility of injury marked fish seen at weirs, on the by gill nets is not disproven, but if spawning grounds, and in the such exists the data on hand are fishery. insufficient to demonstrate it." Gill-net marks are the most The above work indicates that no prevalent fishing-gear marks ob- differential mortality of net-marked served. In Bristol Bay, Alaska, and unmarked fish was evident gill nets are the only fishing gear between observations of fish some used for the capture of red salmon. distance from where the fish were During the past 9 years, counts of net-marked and subsequent ob- gill-net-marked salmon through the servations of fish on or near the Brooks River weir, Bristol Bay spawning grounds. However, it district, show that 6.3 percent of does not estimate mortality which the annual escapement of salmon is may occur from the point of in- gill-net marked. At Karluk River ception of the net mark to the on Kodiak Island, the proportion spawning grounds. Because the is less than 2 percent. Fraser Alaska gill-net fishery is so im- River escapements contain large portant (of the Alaska salmon numbers of marked fish (Talbot catch, years 1943 through 1952, 1950). On the , gill nets took an average of 24 Hansen and others (1950) reported percent or 15 million fish annually), about 5 percent of the salmon the Service proposed an experiment marked by gill nets. to measure the mortality of gill- Some evidence of the fate of net-marked fish from the point of gill-net-marked fish has been pub- inception of the net mark to the lished. For example, Hansen and spawning grounds. Such an ex- others found no difference in the periment was conducted at the percentage of gill-net-marked fish Karluk Lagoon, Kodiak Island, in in samples taken at the Bonneville the summer of 1953. The authors wish to acknowledge Donald Bevan and Charles Walker the assistance of John Finucane, of the Research Institute who did most of the tagging. The for assistance in the recovery of kind cooperation given by the tagged fish on the spawning grounds Alaska Packers Association, es- and to Elizabeth Vaughan and pecially Axel Carlson, is greatly Reynold A. Fredin for their help appreciated. We are grateful to in the statistical analysis.

DESCRIPTION OF THE EXPERIMENT

Location of the fishing site the design was such that fish would The differential mortality between lead into compartment 1 of the unmarked salmon and salmon trap where some could be removed marked by gill nets was measured and tagged as control fish and by tagging operations at a gill-net others could be net-marked in the site. In selecting the site (fig. 1) it gill net suspended between the was necessary to find a location two compartments, and sub- where sufficient numbers of fish sequently tagged. The trap was could be caught. The watershed located approximately 100 feet from had to be small so that it would be shore on the edge of a channel used possible to obtain enough recoveries by the migrating salmon. The to measure any differential in loss flow of water through the gear at between net-marked and unmarked this point ranged from 1 to 2 feet fish. The Karluk Lagoon was the per second. This current, together most suitable location available, with algae and debris collecting on and tagging at that point had cer- the webbing of the lead made it tain advantages: a large number of difficult, in fact impossible, later fish were available; a weir operated on in the season to keep the leads about 23 miles upstream enabled in contact with the bottom. Part measurements to be made of the of the time it was necessary to differential in survival of tagged obtain fish for tagging by seining control and tagged gill-net-marked in the channel above the trap. The fish reaching that point; the streams seine-caught fish were placed in entering the lake above the weir large screen live-boxes. Fish were were small and shallow and offered dipped from the boxes, some tagged good opportunities for recovery of for control fish, and others placed dead fish. From recoveries on the in the trap (compartment 1). streams, the difference in survival Within a short time, fish in the trap of the net-marked and control were struggling in the gill net groups could be measured between stretched diagonally between the the weir and the spawning grounds. two sections. Some fish succeeded in escaping from the net by either Design and operation of the working through into compartment Fishing gear 2, or backing out. By raising the In mid-June a trap was assembled walls of the trap these fish were at the lagoon (fig. 2). In principle, captured by dip nets for tagging.

2 KARLUK LAKE WATERSHED KODIAK ISLAND ALASKA

SC ALE 0 MILES KILOMETERS

Figure 1.—The Karluk Lake watershed. Each end of the gill net was and fastened by rings to the pipe fastened by rings to a vertical half- and to the webbing on the floor of inch pipe whereby the net could be the trap; thus, as the gill net was lifted for removing fish from the raised the seine closed off the two webbing. A strip of 3-inch compartments. A lead line was stretched mesh seine webbing was attached to the bottom of the gill attached to the base of the gill net net so that, once the fish had been

3 TAGGING BOX

TAGGING PLATFORM

HOLDING BOX

GILL NET WEB 5 1/2" STRETCH

COMPARTMENTS

POT WEB 3" STRETCH

HEART WEB 3" STRETCH

LEAD WEB 3 V2 " STRETCH

Figure 2.—The red-salmon trap. removed, the net could be dropped Fish escaping the net, by either back into position (fig. 3). going through or backing out, to- It was necessary to prevent fish gether with those removed from the from passing from one side of the net, were tagged with variously gill net to the other except through colored tags in order to measure the net. Otherwise, it would be survivals in each group. difficult to distinguish which fish The gill net was of 534-inch had been net-marked by going stretched mesh, the type used through or backing out of the net. commercially in the area. Linen

4 GILL NET RINGS ATTACHING GILL NET TO PIPE SLIDE

LEAD LINE BARRIER, SEINE WEB

Figure 3.—The gill net attached to the trap webbing. nets were used except during the group B fish. Red-and-blue tags last week of tagging, when a nylon were used to identify fish marked net was substituted. Nylon dem- in the net and escaping by backing onstrated one advantage in this out of the net. Control fish were work; fish were more easily removed correspondingly tagged with blue- from this webbing than from linen. and-red tags. These tagged fish will be known as group C fish. Tagging operation During the period July 8 to August During the early part of the 15, green tags were used in place of season, June 16 to July 7, 1953, blue tags in all categories. Petersen disk tags of various color Fish removed from the gill net combinations were applied to net- were usually placed immediately marked and control fish. The tags in a tagging box mounted on a plat- were affixed beneath the dorsal fin form beside the trap, tagged, and by the conventional stainless-wire then released. Occasionally, in- pin. White-and-blue tags were used clement weather or a small crew on fish removed alive from the gill necessitated the fish being placed in net. The numbered white tag was holding boxes, mounted beside the placed on the left side of the , for a short time before being and the blue on the right side. tagged. Table 1 gives color com- Numbered tags of similar colors binations used and number of tags were applied to the control fish for applied, by groups. Equal numbers this group, with the position of the of control and net-marked fish were colors reversed. For convenience, tagged daily when possible. Daily this category will be called group differences in numbers of control A, net-marked and control fish. and net-marked fish tagged in any Fish marked by passing through group were not considered great the gill net into compartment 2 enough to influence measurement of were tagged with yellow-and-blue survival. Plans had been made to tags. Blue-and-yellow tags were tag considerably more netmarked applied to the control fish in this and control fish in the early period; group. These control and net- the objective was not realized be- marked fish will be referred to as cause of difficulties encountered in 5 Table 1.—Schedule of combinations of colored tags used and number of tags applied in each group, 1953

June 12-July 7 July 8-Aug. 15

Group Num- Num- Color code ber Color code ber applied applied

Group A: Net-marked fish White-blue 176 White-green 2, 134 Control fish Blue-white 174 Green-white 2, 136 Group B: Net-marked fish Yellow-blue 18 Yellow-green 589 Control fish Blue-yellow 18 Green-yellow 623 Group C: Net-marked fish Red-blue 4 Red-green 193 Control fish Blue-red 4 Green-red 184 All groups: Net-marked fish 198 2,916 Control fish 196 2, 943 getting the gear in operation. Be- the webbing 1 to 15 minutes. cause of the small number of fish Gilled fish subject to suffocation in tagged in the early period, for pur- a short time were removed first poses of analysis both periods have because facilities were indequate been combined. for disposal of large numbers of dead fish. The few experimental Experimental limitations losses were sold to the Alaska Packers Association for account of There are certain differences be- the Government. It is quite pos- tween our method of fishing and sible that some of the fish removed commercial gill netting. Most im- from the net might have escaped portant is that between the tagged later and would have been more gill-net-marked fish and the net- severely marked. Mortalities of marked fish escaping a commercial net-marked fish in excess of those net. Nets in the fishery are often of the control fish in this group not tended for hours at a time. might be caused by excessive han- Hence, some fish tangled in the dling in removing fish from the net, webbing may escape after a short plus injury from the gill-net mark. time; others may escape after an This excessive handling of net- extended period and be so weakened marked group A fish might com- that they die shortly after. In pensate for losses of fish dropping other cases, it has been reported, a from commercial nets and for com- small number of fish die in the net mercial net-marked fish being more and drop free, to be carried away severely net-marked. by the ocean currents. In the Group B fish, net-marked upon experiment it was not possible to passing through the gill net, and measure losses of dead fish dropping group C fish, marked in the gill from the net. net and escaping by backing out Net-marked fish in group A of the net, were handled in much were removed from the net by hand the same mailer as the control fish. usually after they had struggled in Since some fish removed from the

6 net and tagged as A group fish the web of commercial nets. How- might have escaped the net later, ever, with net-marked fish in all groups B and C probably contained groups, it is possible that the a smaller precentage of severely handling during tagging, and the net-marked fish than would be tagging itself, is more injurious found in a group of fish escaping to them than to the control fish.

ANALYSIS OF RESULTS

Recoveries of tagged fish in the severely net-marked than were the Karluk Lagoon net-marked fish in other groups would probably account for this The effects of gill-net-marks on group having the highest differential fish might be best demonstrated mortality. As the number of at points progressively upstream recoveries in the lagoon was small from the spot of tagging. The the high differential mortality of closest point of recapture was the net-marked and control fish as upper section of the Karluk Lagoon, indicated is not representative of an area in close proximity to the the actual condition. However, tagging site. as shown in the following section, During the season 110 tagged it is indicative of the fact that a fish were recovered dead in the differential mortality exists. lagoon. Seventy-nine (72%) were tagged gill-net-marked; the remain- Observations and recoveries of ing 31 (28%) were controls. The tagged salmon at the Karluk recovered fish were all unspawned weir and on the spawning and they probably represent the weaker fish which in the case of the grounds control fish died from the tagging The weir located approximately process, or with net-marked fish 200 yards from the outlet of Karluk as a result of the tagging process, Lake is about 23 miles from the the net marks, or a combination point of tagging. As the water is of these factors. Since very few clear and shallow throughout the untagged dead fish were picked up watershed, tags can readily be seen in this area, death from natural on fish passing over the white causes can be dismissed as a factor. counting boards at the weir and on It was found that the highest fish in the spawning streams. Table percentage of dead fish recovered 2 shows the number of net-marked occurred in the net-marked A and control fish in each group group. In some instances with net- tagged, counted through the weir, marked fish in this group, the web and recovered on the spawning was cut to free the fish, but in the grounds. The percentages of tagged majority of occurrences the fish fish passing through the weir differs were slipped from the webbing by considerably among the control hand. The additional handling groups. Theoretically, the per- together with the fish being more centages would be the same if

342065 0 - 55 - 2 7 comparable percentages of fish in mortality of net-marked fish. As each group were tagged from the in the A group no significant dif- same stock of fish each day. Actu- ferential mortality occurred between ally among the groups there was a the weir and the spawning grounds. wide range at the time the fish were Observations at the weir ac- tagged. It is possible that the counted for 94 (50.0%) control fish percentage of fish destined to spawn and 100 (50.8%) net-marked fish in below the weir or the percentage of C group. The difference in the fish that moved out of the lagoon percentages indicates no significant into the fishery varied during the difference in the survival of the tagging period. This could account net-marked and control fish. As for differences in the percentages with the other groups no differential of control fish through the weir in the survival of the net-marked from the three groups. Although and control fish occurred between a few tags were recovered below the weir and the spawning grounds. the weir and in the fishery, re- Thus in groups A, B, and C coveries are inadequate to deter- differential mortalities ,of 19.5, 13.1, mine during which periods of tag- and 0 percent, respectively, were ging, fish were destined to these measured between the lagoon and locations, or if there was a time the weir. From the weir to the element involved. spawning grounds no significant Table 2 shows that 1,473 (63.8%) differential mortality was obtained. of the control fish, and 1,024 This result is in conformity with (44.3%) of the net-marked fish of the observations of Hansen and group A were observed passing others (1950), and suggested by through the weir. The difference Schaefer (1951). The variance in in the percentages indicates a dif- the differential mortalities of the ferential mortality of 19.5 percent groups is probably due to the fact of net-marked fish. From the weir that fish in the A group were to the spawning grounds no sig- handled in removing them from the nificant difference in the percentage net, and the cuts and abrasions recovery of dead net-marked and appeared to be deeper than those control fish was found. Thus, in in the other groups. Similarly as this group the mortality of net- will be shown later B fish were marked fish occurred shortly after more seriously injured than those tagging, enroute between the lagoon in group C. Although we do not and the weir. From the weir to know the percentage of fish escap- the spawning grounds the marks ing commercial nets which go seemed to have no effect on survival. through or back out of the nets, In the B group of 641 control and observations at the experimental 607 net-marked fish tagged a total net show that most fish endeavor to of 448 (69.9%) control and 345 work through the net. In fact it (56.8%) net-marked tagged fish was difficult to obtain for tagging a were counted through the weir. sufficient number of fish that had The difference in the percentages backed out of the net. Hence it is indicates a 13.1 percent differential believed that most fish escaping a

8 Table 2.—Tagged fish counted through the Karluk weir and tagged fish recovered dead on the spawning grounds with the percentage recovery and differential mortality for the fish in each group

Tagged Percentage Differential Tagged Tag recov- Differential Total fish ty fish re- ery percent- mortality Group number counted tagged fish mortali covered on age (weir to (weir to tagged through through (lagoon spawning spawning spawning weir weir to weir) ground grounds) grounds)

prouarc Ai:ed 2, 310 1, 024 44. 3 1 19. 5 265 25. 9 1 Control 2, 310 1, 473 63.8 J 387 26, 3 J I 0. 4 aroup B: Marked 607 345 56.8 1 73 21. 2 t Control 641 448 69.9 J 13. 1 114 25. 4 J I 4 2 Grottliar%d 197 100 60.8 1 33 33.0 1 Control 188 94 50.0 I —O. 8 a3 35. 1 J I 2. 1

I A chi-square test of the number of recoveries showed no significant difference in the mortality between test and control. commercial net were net-marked to 20 percent (1,575 salmon) of the while passing through the webbing. total number originally marked in It was previously pointed out that the fishery would have perished. in a commercial net a small per- This would represent a loss of from centage of fish die in the net and 0.7 to 1.6 percent of the seasonal subsequently fall free, also that the escapement. Such a loss is low, fish are probably more seriously however, the loss during the height net-marked than are the net-marked of the fishing season would be con- fish in the experiment. On the siderably greater percentagewise. other hand, net-marked fish prob- Talbot (1950) shows the percentage ably are harmed more from hand- of net-marked red salmon in the ling during tagging than are the daily catch below Hell's Gate dur- control fish. Thus, the differential ing 1943-1947 to range from 0 to mortality of net-marked fish over 75 percent. The maximum per- unmarked fish in commercial nets centage net-marked during a weekly may range from 10 to 20 percent. period was 45 percent. At the The importance of the differen- Karluk River and Brooks River tial mortality between net-marked weirs, the percentage of net-marked and unmarked fish may be illus- fish was less, but infrequently it trated by a hypothetical example. has exceeded 20 percent for indi- As previously mentioned the great- vidual weeks. Thus certain seg- est measured annual percentage of ments of the escapement may suffer gill-net-marked fish occurs at the appreciably from the differential Brooks River weir, where a yearly mortality between net-marked and average of 6.3 percent of the escape- unmarked fish. Before a total as- ment is gill-net-marked. Thus sessment of the damage to the fish with an annual escapement of by net marks can be made, the 100,000 salmon 6.3 percent or effect of net marks on the sexes, 6,300 salmon would bear gill-net travel time, and spawning condition marks, and 10 percent (700 salmon) of the fish must be considered.

9 Effect of tagging and gill net unspawned, it appears females were marks on the sexes not able to withstand the tagging and gill-net marks so well as the A record was kept of the sex of males. each fish at tagging and recovery. As to the spawning ground re- It was then possible to determine coveries, it will be subsequently whether a differential mortality, shown that a high percentage of caused by net marks or tagging, the fish recovered had spawned existed between the sexes. Table 3 and that no significant difference shows by sex the number of fish was found between the percentage tagged and recovered; also the per- of spawned males and females. centage of recovery at the lagoon Since a considerably larger num- and on the spawning grounds in the ber of fish was recovered on the control and net-marked groups. spawning grounds than from the As only 15 fish from groups B and lagoon, recoveries from the former were recovered in the lagoon, give a more valid measurement of they were omitted from the table. a change in the sex ratio. Unlike As noted inthe table of recoveries the recoveries in the lagoon, which made in Karluk Lagoon, the per- were made up of the more seriously centage recovery of females was net-marked or weaker fish that died almost twice that of males in both before spawning, the spawning net-marked and control categories ground recoveries represent fish in the A group. To determine that survived the tagging and net whether this change in the sex marks, to die after spawning. ratio is significant, the chi-square It was thought the females might test was applied to the numbers of be more available than the males fish in each sex at tagging and on the spawning grounds as they recovery. Results of the test show tend to remain in the vicinity of a significant change in the sex their nests after spawning, and die ratio of net-marked fish, while no nearby. However, upon compar- significant change in the sex ratio ing recoveries of dead spawned-fish of the control fish occurred between above the Karluk weir, where the the two locations. Since all of the sexes are equally available, with fish recovered in the lagoon were recoveries of fish on the other

Table 3.—Male and female red salmon tagged and recovered in the net-marked and control groups

Number tagged Number recovered Percentage Location of recovered Group tagged fish recovered Fe- Fe- Males Total Males Total Males males males males

Group A: Control ------Lagoon ------1, 085 1, 225 2, 310 8 14 22 0. 74 I. 14 Marked ------do ------1, 118 1,192 2,310 24 49 73 2. 15 4.11 Control ------Spawning grounds_ 1,085 1, 225 2,310 189 198 387 17.42 16.16 Marked ------do ------1, 118 1,192 2,310 146 119 265 13.06 9.98 Groups B and C: Control ------do ------319 510 829 48 99 147 15.05 19.41 Marked ------do ------364 440 804 49 57 106 13. 46 12. 95

10 spawning grounds no significant thus arrive at their destined spawn- difference was found in availability. ing grounds at an unfavorable en- Thus a change in the sex ratio vironmental time. To test this, between the point of tagging and curves were made showing the the spawning grounds would indi- daily accumulated percentage of cate the sex which suffered the fish tagged during the season of highest mortality during the period. both net-marked and control fish. Chi-square tests (run on the num- Similarly, curves were made of the ber of fish in each sex at the time accumulated daily percentage of of tagging and recovery for the tagged control and net-marked fish spawning ground A control and counted through the weir and re- net-marked and B and C control covered on the spawning grounds. and net-marked categories) show Figure 4 shows the curves to be the sex ratio to have changed closely superimposed indicating no significantly in the A net-marked differential in travel time between group only. The percentage re- test and control from the lagoon to covery of females was significantly the weir and from the lagoon to the less than the percentage recovery spawning grounds. The mean time of the males. This substantiates lapse in days from tagging to the results from the salmon ex- recovery was 43.8 days for the con- periment in the lagoon. Fish in trol fish and 42.2 days for the net- this group were subjected to in- marked fish. This time interval juries resulting from being removed represents the period of travel to from the gill net, the tagging the lake, the sexual maturity period process, and from gill-net marks. in the lake, and the spawning period This combination of factors was on the streams. more detrimental to the females than the males. On the other hand, Spawning condition of gill-net- recoveries from the tagged control marked and control fish fish and net-marked fish of the B In order to determine whether gill plus C groups show that tagging net marks hampered the spawning itself or the tagging of gill-net- activity of salmon, all dead tagged marked fish in these groups is no fish were examined on the spawning more harmful to females than males. grounds to determine whether they Thus it would appear that of fish had spawned. In each case, the body escaping commercial gill nets a cavity was opened for examina- differential mortality of the sexes tion. In table 4 the spawning con- would probably only occur in the dition of the control and net-marked segment of the most severely net- fish is given for each group tagged. marked fish. Female salmon were considered spawned-out when less than half Migration rate of gill-net-marked of their eggs remained in the body and control fish cavity at death. The spawning It was suggested that net-marked condition of the males was based fish might be delayed in their migra- on the size of the gonad together tion as a result of being injured and with the external appearance of the 11 100

5

40

2

Figure 4.—Curves showing the accumulated percentage of net-marked and control fish tagged at the lagoon, observed passing through the Karluk weir, and recovered on the spawning grounds. fish. When doubt existed concern- ed-out. A large number of male ing spawned or unspawned, the fish salmon are grouped under unknown was classified as unknown. Of the spawning condition. Unlike the reCoveries made, the sexes have females, the bulk of these fish were been kept separate, because of intact, yet by examination it was possible errors involved in deter- not evident whether or not they had mining the spawning condition of spawned. It was thought, how- the males. In a few instances, ever, that most of these fish were female salmon were so badly decom- unspawned. posed or mutilated, their spawning Under males spawned out, two condition could not be determined. values are given. The first value These were grouped under unknown shows the percentage spawned when and have been omitted in calculat- the unknown are all considered to ing the percentages of those spawn- be unspawned fish; the second value

1 2 Table 4.—Spawning condition of the tagged fish recovered on the spawning grounds

Females Males

With With Group un- un- Spawn- Un- Un- Spawn- Spawn- Un- Un. known; known ed spawn- known' Total ed ed spawn- know& Total un- omit- ed ed spawn- ted ed

Group A: Number Number Number Number Percent Number Number Number Number Percent Percent Marked 101 15 3 119 87. 1 127 3 16 146 87.0 97.7 Control 166 31 1 198 84.3 158 13 18 189 83.6 92.4 Group B: Marked 45 1 47 97. 8 21 4 26 80. 8 95. 5 Control—_ _ 69 9 2 80 88. 5 31 2 34 91. 2 96. 9 Group C: Marked 9 0 1 10 100. 0 22 1 23 95.7 100. 0 Control 17 2 0 19 89. 5 9 5 14 64.3 100. 0 Total marked_ _ _ 155 16 5 176 90.6 170 4 21 195 87.2 97. 7 Total control__ 252 42 3 297 85.7 198 14 25 237 83.5 93.4

I Doubt exists whether these fish have spawned. shows the percentage with the un- fish. A first-degree net-mark was known omitted from the analysis. noted when the webbing had broken The latter percentage would be the skin of the fish, a second-degree almost the same if all the unknown mark was a series of prominent web were considered to be spawned. marks on the fish, the third-degree As shown in table 4 there appears mark was usually fewer than four to be a closer relationship between web marks and these less prominent sexes in the percentage of spawned than the second-degree mark. At fish when the unknown males are the time of recovery the fish were considered to be all unspawned. again examined to determine the The numbers of spawned fish in condition of the mark. Examples the net-marked and control groups of the net-marked categories at the were tested by the chi-square meth- time of tagging and at the time of od. No significant difference was recovery on the spawning grounds present in the spawning condition are shown in figures 5 to 10. of net-marked and control fish in The distribution of marks among any of the tagged groups in either the three degrees within the three sex. Hence, it appears gill-net tagged groups is presented in table marks do not influence the spawning 5. Numbered tags were used. It is activity of the salmon. therefore possible to give for each group the number and percentage Healing of gill-net marks and the of fish in each degree of mark at the effect of the net mark on time of tagging, also the number of survival of salmon recoveries from each degree of mark for fish taken on the spawning At the time each fish was tagged grounds. The composition of net a record was kept of the color com- marks on the recovered fish is also bination and number of the affixed presented, as determined from a re- tags, the sex of the fish, and the examination of the dead fish. In degree of seriousness of the net all groups no significant difference marks on the tagged gill-net-marked was found between the percentage

13 Figure 5.—A first-degree-marked salmon at the point of tagging. The arrow indicates where the webbing has broken through the skin.

Figure 6.—A second-degree-marked salmon at the point of tagging. Note the many web marks.

14 Figure 7.—A third-degree-marked salmon at the point of tagging. Note the two web marks.

Figure 8.—A spawned male salmon recaptured on the spawning grounds. This fish bears a First-degree mark.

15 Figure 9.—A spawned female salmon recovered on the spawning grounds. Arrows indicate a few of the many net marks that appeared healed. The fish is judged to bear second- degree marks.

Figure 10.—A spawned female salmon recaptured on the spawning grounds. Arrows indicate the two marks at the isthmus. This fish is judged to have third-degree marks. 16 of fish in the net-marked categories were grouped as "degree of mark at the time of tagging and the per- unknown." A considerable change centage at the time of recovery on in the degree of net mark occurred the spawning grounds. It would on tagged net-marked fish at the seem that a lower percentage of point of tagging and on the spawn- recoveries might be expected from ing grounds. For example in group fish more severely net-marked; how- A, 37 first degree net-marked fish ever, there is little evidence in our were tagged, of which 5 were re- data to indicate this. Perhaps if a covered on the spawning grounds. more precise method of judging the However, of the net-marked fish in seriousness of net marks were em- group A reexamined on the spawn- ployed the results would indicate a ing grounds, 59 had first degree net differential mortality. marks. In this instance, it appears In reexamining the net-marked second and third degree net marks fish on the spawning grounds, the later developed into first degree net same degrees of net-marks were mark. As a rule, however, the used as previously mentioned, with net marks showed a high degree of two additions. Net marks which had healed to the point no longer healing; for example, of the net- distinguishable, were classified as marked fish in group B reexamined "mark not visible." Fish which on the spawning grounds 68.5 per- were badly decomposed or mu- cent had net marks that had either tilated, the absence or presence of a disappeared or could scarcely be net mark being thus obliterated, distinguished.

Table 5.-Composition of gill net marks at the time of tagging, recoveries of fish from each degree of mark, and composition of marks based on the reexamination of tagged marked fish on the spawning grounds

Degree of mark

not Degree of First Second Third Mark mark Group visi ble unknown Total num- ber Num- Per- Num- Per- Num- Per- Num- Per- Num- Per- ber cent ber cent ber cent ber cent her cent

Group A: Degree of mark at time of tagging 37 1.6 2, 012 87. 1 261 11. 3 2, 310 Recoveries of marks_ _ __ 5 1.9 228 86, 0 32 12. 1 265 Degree of mark at re- covery 59 22. 2 120 45. 3 22 8. 3 47 17. 7 17 6. 4 . 265 Group B: Degree of mark at tag- ging 6 1.0 171 28. 6 420 70. 4 597 Recoveries of marks_ ___ 1 1.4 16 21.9 56 76. 7 73 Degree of mark at re- covery 1 1.4 4 5.5 9 12. 3 50 68. 5 9 12.3 73 Group C: Degree of mark at tag- ging 5 2. 5 27 13. 7 165 83.8 197 Recoveries of marks_ ___ 0 0.0 6 18.2 27 81.8 33 Degree of mark at re- covery 1 3. 0 1 3. 0 7 21. 2 19 57. 6 5 15. 2 33

17 DISCUSSION

It would have been desirable to observations of the net marks in- conduct the tagging at a commercial flicted by our net appeared similar gill net site if possible. However, to those seen on commercial gill-net on examining records of the annual marked fish. catches from a number of gill net Just what effect the handling sites, it became apparent that in- during tagging and the actual tag- sufficient numbers of fish could be ging has on the control and net- obtained for tagging. Conditions marked fish is not known. It is were somewhat different between possible the injured net-marked fish the lagoon location and locations of may be harmed more than the con- commercial net sites. The latter trol fish during this procedure. are usually located in salt water and Thus there are a number of factors the nets are fished under varying to consider in the assessment of a tidal conditions. Whether the salt differential mortality between con- water offers a therapeutic treatment trol and net-marked fish, but we to the net marks is questionable, believe that the observed 10 to 20 but the possibility exists. On the percent mortality of gill-net-marked other hand, wave and tidal action fish is representative of the mortal- in some cases may cause more dead ity obtaining in the commercial fish to wash out of the net than are fishery. Important is the fact that accounted for in the text. Also, it the surviving net-marked fish are might be pointed out that although not delayed in their migration, and the gill net material used in the trap that net marks do not affect their and the mesh size are comparable spawning, or have an appreciable to commercial nets, the action of detrimental effect on one sex rather the net with salmon entangled in it than the other. Since in most in- would differ as commercial nets are stances a low percentage of gill-net- longer and deeper. What variance marked fish is found in the escape- in the action of the nets would have ment, the actual loss of fish by net on the degree of marks on fish es- marks from the commercial fishery caping is difficult to say. However, is probably of minor importance.

SUMMARY AND CONCLUSIONS

1. In fishing areas where gill nets were tagged. Three groups of net- are used, the annual escapement of marked fish were tagged, namely, salmon is found to contain as high fish removed from the gill net as 6.3 percent of gill-net-marked (group A) , fish passing through the fish. net (group B), and fish caught in 2. At the Karluk River lagoon on the net and backing out (group C). Kodiak Island, a combination trap For each category of net-marked and gill net was operated from which fish approximately an equal num- gill-net-marked and control fish ber of control fish were tagged.

18 3. Experimental limitations of 5. The mortality of gill-net- this work include the following: marked fish in groups A and B a. It was not possible to measure occurred shortly after tagging, i. e., the loss of gilled fish that die in the between the lagoon and the weir. webbing and drop free. From the weir to the spawning b. Net-marked fish in group A grounds there was no significant were removed from the webbing difference in the percentage re- usually after 1 to 15 minutes. covery of net-marked and control Fish escaping a commercial net fish. probably would be more severely 6. It is estimated that from 10 net-marked as they would have to 20 percent of the gill-net-marked spent more time struggling in the fish escaping commercial nets die webbing. The excess handling in because of injuries inflicted by the removing group A fish from the webbing. web might compensate for losses 7. The only significant difference of dead fish dropping from com- in the survival of the sexes occurred mercial nets plus differential mor- in the net-marked A group. Fe- talities which might ensue from the males were not able to withstand likelihood of commercial net-marked the handling during tagging and fish being more severely marked. net-mark injuries so well as the c. Groups B and C fish probably males. in general were less severely net- 8. No differential in the travel marked than fish escaping com- time was found between tagged mercial nets as some fish removed control and gill-net-marked fish from the net and tagged possibly from the lagoon to the weir or from would have escaped later with the lagoon to the spawning grounds. severe marks. 9. There was no significant dif- d. The tagging operation may be ference between the spawning con- more injurious to net-marked fish dition of the gill-net-marked and than control fish. control fish. 4. The increased mortality of 10. There is a general tendency gill-net-marked fish over control for gill-net marks to heal. No fish was 19.5 percent for group A, relationship was found between the 13.1 for group B, and 0 percent for seriousness of the gill-net marks, as group C. defined in the text, and the survival. LITERATURE CITED

HANSON, HARRY A., P. D. ZIMMER, and I. J. DONALDSON. 1950. Injured and dead fish in the vicinity of Bonneville Dam. U. S. Fish and Wildlife Service. Spec. Sci. Rept.—Fisheries No. 29. SCHAEFER, MILNER B. 1951. A study of the spawning populations of sockeye salmon in the Harrison River system, with special reference to the problem of enumeration by means of marked members. International Pacific Salmon Fisheries Commission, Bull. No. 4. TALBOT, G. B. 1950. A biological study of the effectiveness of the Hell's Gate fishways. Inter- national Pacific Salmon Fisheries Commission, Bull. No. 3, part 1. 19

U. S. GOVERNMENT PRINTING OFFICE: 1955 0 - 342065