ill ,t^ Iii5l7&5 111', ' -'((V. ;^.;;j lilfl llllll fililil liilltii mm lii iilll mm Ill iill iii III liii lilif iili iliii! iili^i^l iii ■;;W,|lS,<;ii|ii; |si!|l|i|j|ijj| Class.. ^3JdJ-^i THE SALMON OF THE YUKON RIVER :::::: ::::::::::::::: By Charles H. Gilbert From BULLETIN OF THE BUREAU OF FISHERIES, Volume XXXVIII, 1921-22 Document No. gzS : : : : : : : : : : : : : Issued November 21, 1^22 nUCXi 20 CERTS Sold only br the Sapcrinteadent of Docnm«nt9, Government Printlnf Oflteei WuhinitOBi D. C< WASHINGTON GOVERNUENT PRINTING OPPICB THE SALMON OF THE YUKON RIVER :::::: ::::::::::::::: By Charles H. Gilbert From BULLETIN OF THE BUREAU OF FISHERIES, Volume XXXVIII, 1921-22 Document A'o. g2S : : ; ; ; ; ; ; ; ; .- Issued Xovember 21, 1^2:^ PRICE, 20 CENTS Sold only by the Sun? riuteadeut o( Documents. Government Priutjug Office, \^'a3hia£toa. D. C. WASHINGTON COVERNMKNT PRINTING OFKICK : -^^'S" ^'^ r LIBRARY OF CONQRE88 --CEIVED JAN 241 '-''S OOCUMtNTii i."»!Vii(ON THE SALMON OF THE YUKON RIVER. By CllARI.i:S H. GlI.HKKT, Professor of Zoolotiy, Stanford University. CONTENTS. Piige. Introdiictii)n 317 Tlic king salmon (Oiicorhynchiis tschmcylscha) 31S Rate of travel 318 Growth and age at maturity 320 The chum or dog salmon (Oncorhynchus kflo) 325 Rate of travel 326 Year classes 326 Proportions of sexes. . 327 Size at maturity - 328 Growth and scale readings 329 The sockcye salmon (Oncoihynchus nerka) 330 The coho salmon (Oncorhynchus kisutch) 331 The hum])back salmon (Oncorhynchns gorhuscha)- . 332 INTRODUCTION. Tlie summer of 1920 was spent by tlie writer, in company with Henry O'lMalley, at that lime field assistant of tlie United States liureau of I'isherics, in investigating the rims of salmon to the Yukon River. The primary object of the expedition was to ascertain the advisability of permitting the operation of one or more salmon canneries on the Yukon, in view of the possibility that they might so curtail the salmon supply that it would fail to provide natives, and white inhabitants as well, with the stores of fish that they find essential under the rigorous conditions f)f the far northern climate. It was to be deter- mined whether there existed an excess above the needs of the inhabitants that could safely be used for commercial purposes for export beyond tlie boundaries of Alaska. This phase of the situation has been dealt with in a report to the Commissioner of Fisheries and was published in 1921.' Some of the details that are given in that report concerning the movements of the salmon during their run and the rate of travel that they maintain in their ascent of the river are herein repeated, but the body of the present paper is concerned with the growth-history of the Yukon salmon and the ages at which they have reached matiuity. The Yukon River is near the northern limit of range for the Pacific salmon. The effect of the arctic cold on growth and age of maturing is an interesting problem. 'Investigation of the Salmon Fishcrit-s 2 June 21 Jime 22 June 23 June 24 June 27 June 28 June .'9 Rapids July i Circle ': tulv ii Paimiiit •17 Charlie Creek Kajile lie WoU's fii>h camp. Dawson July 12 July 1,1 J"iy 14 ,..do...- Halls Rapids, above Anvic. Camp SI miles below Kaltag . . . Kaltag 50 $1 The season of 1920 was notably late in Alaska ; tlie break-up occurred in the Yukon fully a week later than usual, and the salmon were equally delayed in entering. As shown by the above table, the first king salmon taken in the delta was captured June 13. 320 BULLETIN OF THE BUREAU OF FISHERIES. The run culminated quickly within a week after that date, then maintained itself at a fair level for about three weeks, and was practically over by the close of the first week in July. Stragglers appeared during subsequent weeks in July and August but became less and less numerous. GROWTH AND AGE AT MATURITY. We have no knowledge concerning the feeding grounds of the Yukon salmon and must leave the question open to what extent, if at all, the young traverse the passes in the Aleutian Chain and attain their growth in the North Pacific. It is entirelv possible that throughout their life in the ocean, they remain within the confines of the Bering Sea. None of them have been detected traversing the channels between the Aleutian Islands, nor have they been recognized elsewhere along lines of their migration routes in the sea. Conditions in Bering Sea, it would seem, must be less favorable for rapid growth than in districts farther south. The northern part of the sea and a strip around the coasts, in- cluding Bristol Bay, are covered with ice floe during the winter and early spring months. The temperatures to which the salmon are tlien exposed must be near the freezing point. At the time they seek the river nioutli in May or June the surface temperature in Bering Sea approaches 40° F. Under such adverse conditions growth during the winter season must be at or near a standstill and in the spring might well not be resumed before the beginning of the streamward migration. In that event tlie scales would exhibit no growth accomplished during the year in which the fish was captured. A salmon in its fifth year would indicate in its scale structure the completion of four full years' growth, and the margin of the scale would be formed by tlie wnter check of the fourth year. In other districts to the southward the salmon of the spawning run have already responded to spring conditions and have begun a period of rapid growth before entering the streams. The scales have participated in this renewed growth, and the margins exhibit a larger or smaller band of widely spaced rings, which lie out- side the winter check of the previous year. But in the case of the Yukon king salmon this is not present. The winter check of the previous year forms the margin, and usually no trace exists of any growth belonging to the cuixent year. A very few cases form doubtful exceptions to this genei-alization, with the outer one to three rings more widely separated at least in a portion of their course. This featiu-e is shown dis- tinctly in the accompanying series of photographs of tlie scales of Yukon king salmon, ranging from those in their third to those in their seventh year (Figs. 276 to 2S5). Another striking peculiarity of the Yukon king salmon is found in their early his- tory as fry and fingerlings. We did not secure any of the yoimg, although attempts were made to capture them with minnow seines on their downward migration, near the mouth of the river. But tlie central areas of the adult scales contain records of the early history and show conclusively in every instance that the young remained in fresh water for a full year's growth before descending to the sea. In the photographs that follow, the line "i" points to the outer margin of the stream growth, which presents a nucleus of finely crowded lines, beyond which are the \videly spaced lines indicating rapid growth after reaching the sea. This habit of the Yukon kings is in striking contrast to what is obser\^ed in streams farther south. In the Fraser River, the Columbia, the Klamath, the Sacramento, and SALMON OF THE YUKON RIVER. 32 1 all other streams thus far examined a eonsiderable proportion of the adult salmon are developed from fry that passed to sea during their first year and com[)leted only a small portion of their first year's growth in fresh water. This "sea tyi)e" dcvelojis at an earlier age than do those that tarry a year in fresh water, and it frequently constitutes half or more than half the entire run. The absence of the "sea type'' in the Yukon may well be related to the severity of the fall and winter, the lateness of the sjiring, and the shortness of the summer season. It would seem that tiie hatching of the eggs, the absorption of the _\i>lk, and the emergence of the fry from the gravels must be corresjjondingly retarded. A third ijeculiarity of the \'uk<)n king salmon consists in the retardation of the age at which they attain maturity. In the Columbia River, where, owing to the use of beach seines, wheels, and tra])s, the smaller salmon arc captured in due juoportion with those of larger size, the youngest chinooks of stream tyjie that are captured in the sjjawning run are in their second year. These arc all male fish, as are those of the ne.\t larger size, which arc in their third year. T'emale chinooks of stream tvpe do not inatiu'c in the Columbia until their fourth \'ear, when they arc not far inferior in muiilx-rs to males of equal age. The commercially valuable portion of the Columl^ia Ri\er run con- sists of 4 and 5 year fish. Com[)aratively few individuals reach their si.Ktli year, and none has to my knowledge been re])orted in its seventh year. The condition in the Yukon is far dilTerent. Ko 2-year fish were secured, and but one 3-year fish, which was a male, 16 inches king, the scale of which is represented in Figure 276. In spite of the fact that fishing was prosecuted exclusively bv gill nets, whicli during tlie king salmon run were of large mesh (8i or Sj inches), fish of diminutive size were frequently entangled in the web and captured. Special attention was paid to the.se, witli tlie object of ascertaining the earliest age at which maturity would be attained in the Yukon race. In addition to the 16-inch individual in its third year, above noted, we examined 44 specimens ranging from 17 to 27 inches, all of them males, in tlieir fourth year. I-'rom this it is aj)parent that no female king saluKin mature on the Yukon until after their fourth year. They are therefore retarded at least one year in reaching maturit\', as compared Avith king salmon in the more southern part of the range of the species. (See Figs. 277 and 278.) Continuing the examination of larger sizes we encountered tlie first 5-year male at 25 inches, the males of this age ranging from 25 to 40 inches. In the fifth year, for Uie first time, we encountered female salmon, but these were very few in luimber. Among the 131 individuals in their fiftli year that we have examined, selected wholly by size witliout reference to sex, there are iig males and only 12 females. This indi- cates a still furtlier retardation in age of maturing of females. \ot only arc there no 4-year mature females (so abundant in more temperate latitudes), but comparati\'ely few females develop maturity even at the age of 5. The 12 of which we have record lie in size within the range of the 5-year males, the smallest being 30 and the largest 37 indies long. (See Figs. 279 and 280.) The male 6-year fish are numerous, the 79 individuals represented in our series ranging widely from 29 to 48 inches. There is thus a wide overlap in size between the 5 and the 6 year fish, as is always the case, although, as will be noted, the 4 and the 5 year males show but little overlap. Among the 6-year fish, for the first time, females 322 BULLETIN OK THE BUREAU OF FISHERIES. are really abundant, exceeding in number the males of equal age. Of the 185 6- year individuals, selected without reference to sex, 79 are males and 106 females. (See Figs. 281 to 28.V) Another e\adence of retai'ded development is found in the class of 7-year fish. In streams thus far studied from, the vSacramento to the Fraser it is very rare for a king salmon lo attain the age of 7 years. Only two such specimens have been observed to my knowledge. In the Yukon, however, members of this class are not uncommon. Although not specially sought for, 42 are included in our series, 10 of these being males and 32 females. Here, again, the late development of females compared witli males is made evident. (See Figs. 284 and 285.) Table 2 gives the distribution by sex, age, and length of all the king salmon of our Yukon series of the run of 1920. For comparison similar data from a series taken from the run of 1919 by C. F. Townsend, fisheries inspector for the Bureau of Fisheries, are included in tliis table. It should be noted that the relative size of these various classes in our series does not represent their relative abimdance in the run. While no selec- tion was made by sex, frequent selection was made by size at critical points. Thus, special attention was paid to the smaller sizes, and these appear in our series in more than their normal proportions. The same is ti'uc of individuals approximating 30 inches in length. It was at this size that females first were found, and individuals of this length were specially selected for examination. T.\BLK 2. — King S.\lmon rnoM Moith Yiko.n- River, 1920 and 1919, Distributi;d by Age and bv Length. Nunibcr of specimens, 1920. Number of specimens, 1919. LpQglb. 4 vears — Malcs.i S years. 6 years. 7 years. 4 ^ears— Males.- S ycart. 6 years. 7 years. >'-'-' nS«. Males, Fe- males. >'■""■ miles. Males. Fe- males. Males. I'C- malcs. Males. Fe- males. I 3 4 3 3 6 10 S .1 4 , i .. . , 1 , ^ ( 1 3 2 inches I 5 5 II 10 6 2 24 inches I 27 inches s I " ;9 inches 20 1'^ ' II 3 5 3 JO 2 9 4 1 2 1 1 I 4I 2 1 H ?o inches I I j2 inches 5 s I ^4 inches 1 . . . . 5 3 9 10 3 10 9 .S 7 14 s 13 3 13 7 S 6 7 1 3! ' ■ I 1 T I ;s inches ... 3 ■■■■,0!;:::.:: 4 ' 5 1 57 inches 1 4 6 2 i ,... ^Q inches ;;;;;;; I , 40 inches 7 \' I 4.; inches I I 2 \ ■, I X I I 47 inches I t i 1 y-'-- ■■■■■■■ Total 44 119 12 79 I oft 10 -,2 j 40 16 ! 5 ! 20 1 35 1 7 1 S Average length in inches ;.!■ 4 31.3 ; 33-5 3S. 7 3S. 5 41. 8 1 ^0. I 1 26. ^i 31 1 SJ.l. 1 37- S 36 41.7 }•-,■ 7 ' One ,^-year-iiId i()-inch male was discovered in i(>;o. No 4-year-old females were oh-ervcd. ' No 4-year-old females were found. SALMON Ol' THE VVKOX KIVKR. The follnwiiij; laljle (.;) gives the average sizes attained by tlie dilTcreiil year classes in the two years kjiq and 1920, the males and females being stated separately. In comparing these with similar averages obtained in other districts, we must bear in mind that our Yukon material shows no growth belonging to the season in which the fish were captured. Our 4-year indi\-iduals had comi)leted three years of growth, but no more, and similarly v.-ith each of the other year groups. However, no strict comparison is possible between ^■ukon 4-year fish anfl the vycar fish from other localities, for although the latter had produced a certain amount of new growth in their third year, they had not eom]ilcted the growth of the tiiird year when they ceased feeduig and were caj)- fnrcd. In like manner no e.\act correspondence c;ui be expected between ,s-\ear \'ukon individuals p.nd 4-year material from the Columbia or the I'raser. In com- jxiring growth rates from these different U)calities, the most satisfactory basis will be found in com[)leted lengtiis of the different yeai' classes, computed from the .scales. Ijy length is meant the distance, measured over the curve of the body, from ti]) of snout to distal end of midtlle caudal rays. 'r.\m.i; ;. — .\vi;K.\r,i; I,i;.n(;ths i'dr Cicrt.mn \'v..\k C.Kori's nv N'ikijn' Ki\<; S.\i mox. nj-'o .\n'i> 1019. t>cx an -■9 ^9 1 7 8 9 s Average , awn her oi rings K. 5 9 I THE CHUM OR DOG SALMON (Oncorhynchus keta). The chum or dog salmon of the Yukon docs not differ from other races of chums that frequent streams in the more southern portion of its range either in external appearance or in any of the structural peculiarities that distinguish this s[)ecies. As is the case else- where, individuals captured in the sea or those that enter streams well in advance of the spawning period are symmetrical silvery fish, easily mistaken at a glance for the sockeye salmon. The discoloration of the skin and the elongation of the jaws, which are later provided with greatly enlarged teeth, are of universal occiuTcnce in this sjiccics (as, indeed, in all of the species of Pacific sahnon) when sexual maturity is ajiproachetl. In shorter streams that arc colonized by chum salmon, the fish delay entrance until nearly ripe and when first seen have already lost their silver}- livery. But in the Yukon, this species penetrates to spawning gravels in the far ui)per reaches of the river, and it pop- ulates as well practically all the tributaries in the middle and the lower course of the stream. We find, accordingly, among tlie chmns entering the mouth of the river a mixture of colonies, some of \vhich are bound for the headwaters, in reaching which thev ^vill spend six weeks or more, and otliers that have not far to go. It is undoubtedly for this reason that the etitering fish vary so widely in different portions of the nm in the extent of development of those sbiking characteristics that accompany maturity. During the season of 1920 all the early chums were of bright silvery color and had abundant oil and a pinkish flesh that turned a deeper red on drying. Hut in a short time changes appeared, even at the mouth of the river. At first occasional individuals, usually males, appeared in a more advanced stage, with brightly colored bars on the sides of the body and with long hoolced jaws. When these were first observed they stood out conspicuously from their fellows, which were still in the "silver" stage. By the last of June these seasonal changes had become ol:)\'ious in the great mass of chums then nmning. It was the rule for tlie males to exliibit elongated jaws, provided with canine teeth, and to show the beginnings of the bright cross-bars that characterize the spawning males of this species. It might be thought that this dc\'elopment would continue uu- 326 BULLETIN OF THE BUREAU OP FISHERIES. cliecked until the end of the season, but, strangely, during the second week in July a fresh run of chums that was no further advanced than were the chums of early June made its appearance. These also were of bright silvery color and had symmetrical jaws and abundant oil. Although entering relatively late, it seems safe to assume that this run was far from its spawning period and had far to go. Along all the lower and middle portions of the river fishermen who prepare dried salmon for winter use dis- tinguish between the silvery chums and the others. The " silvers'' have flesh of brighter color, rich in oil, and of more substance when dried. The others are known as "dog salmon," with intermediate stages called "half-breeds," and are far inferior in val-ue for human consumption or as dog feed. The Yukon chums in their prime are doubtless of far higher quality than chums from any other river. The differences between them and other races of chums are of similar nature to those that distinguish the Fraser River sockeyes from the same species known as red salmon in the average Alaska streams and to those that distinguish thechinook salmon of the Columbia from the same species ("king salmon") in the shorter streams of the north. The differences in all these cases are not only of similar nature, the}' are due to the same cause. The fine quality of Yukon chums, Fraser sockeyes, and Columbia chinooks is due to the great length of stream which they must traverse, while fasting, on the way to their spa^vning grounds and to the large store of oil that they must lay up for use at this time. In no other respects are the clumi salmon of the Yukon different from tlie same species found elsewhere. The Yukon king salmon, as we have previousl)' noted, are characterized by the same excessive provision of oil. They also exhibit in the different portions of the run equally striking differences between bright individuals, relatively green as to eggs and milt, and the sexually advanced forms, mth hooked jaws and discolored skin. It would be no less logical to recognize two or three kinds of king salmon than it is to distinguish, as is popularly done on the Yukon, two or three kinds of chums, according to the degi'ee of their advancement toward spawning. RATE OF TRAVEL. The chum salmon is generally known as a species that spawns e.Kclusively in the lower courses of streams, often scarcely above the reach of the tides and never far from salt water. It is a remarkable reversal of habit in the Yukon chums that colonies of them should penetrate more than 2,000 miles to the upper tributaries of that great river; and it testifies to the fle.\ibility of organization in salmon that a species that is in general not adapted to long journeys while fasting, can, under spur of necessity, make such journeys without food and exhibit great speed and endurance. From records of the first appear- ance of chums at a large number of stations during the season of 1920, it was apparent that their rate of travel was not far below tliat of the powerful king salmon. They entered the river about a week later than the kings, at Tanana they were not more than 10 days behind the latter, and at Dawson they were some 14 days behind the kings. The lower 800 miles of the river, as far as Tanana, were traversed at the rate of 50 miles per day, and the next 700 miles, between Tanana and Dawson, were covered at the rate of 35 miles per day. The lower 1,500 miles were ascended at the rate of 42 miles per day. YEAR CLASSES. We have already noted that the king salmon of the Yukon are retarded in their (le\-elopment and mature on the average more than one year later than the king salmon SALMON Ol' THE Vl'KON KIVEK. from southern waters. A similar retardation is observed in chum salmon, which aver- age distinctly older in the Yukon than in any other region of which we have record. The earliest report on the ages attained by this species and on the relative propor- tions of the year classes was based on a small collection taken at liellingham, Wash., early in August, 1910.'' The number investigated was too small (58 in all) to give reliable averages, but the percentages indicated do not differ materially from those obtained in 1916 by Dr. C. M. Fraser from collections of adequate size taken at Xanaimo and Qualicum, in the Gulf of Georgia. In both cases the majority of the chums were found maturing at the age of 3 and 4 years, with very few individuals at 5 j'ears and an occasional rare specimen in its second year. Table 7 gives the results derived from both sources and also, for comparison, includes a similar groui)ing of Yukon chums. Tah' - - Vi-:ar-Ci..\ss DiSTKimTio.v. .Soi tiihkn .\.\u Vlkox Ciu'M S.M..\t!ix. Origin of salmon. : years. J years. 4 years. 5 years. Total. Southern chums: Rclliiigliara Per cent. 0. I Per cent. 53- 5 .>4 5 Per cent. 44- ■< 64- 3 5-' 4 Prr cent. I- 7 1. 2 ■ 9 Kitmher. 1.300 Qualicum 0. I 44. s 3-3 5.S- 8 68 I 1. t .•S,6 44* The Yukon chums mature in their third, fourth, and fiftli years, as is the case in more southern waters, but the number of 5-ycar-olfls is diniinislied from nearh' half to one- thirtieth of the total number, and the 5-year iish show a corresponding increase from i to nearly 30 per cent. The retardation in the maturing of the northern race is thus cx'idcnt. PROPORTIONS OF SEXES. It has coninmnly been reported that dog-salmon males arc grcatlv in excess of (lie females, but no thoroughly satisfactory investigationof this subject has been made. To accomplish this, an examination would have to be made of the ratio of males to females at frequent intervals throughout an entire run. It might well be ex;)ccted that the proportions of the sexes would differ widely dining consecutive portions of the run, with the result that any deficiency in the number of females observed at the beginning of the run would be compensated for by an excess of females later on. Such an occur- rence lias been repeatedly observed in certain sockeye colonies. Four-year male sock- eyes entering Rivers Inlet, British Columbia, in 1917, varied from io''^'- mlLJ^'-''- Filth year. J 17 1 7 <;i 1 2^ ';^ 5" ' iS 47 2 23 6 Fe- males.. Weight. I? pounds, n pounds. 14 pounds., 17 poiuids., Number of individuals in- Third year. ToUl Averaj;e wcichi in pounds Fe- males. Fourth year. 164 Fifth year. Fe- males. 141 f.. 5 Fe- males. The length-weight relationship, indicated in Table 10, is given without reference to age. The average weight of all males and, separately, of all females that have the same lengtli is stated. According to this tal>le, females average shghtly lighter than males of equal length, those from 23 to 38 inches in lengtli averaging 97 per cent of the correspond- ing males. The reverse of this might have seemed reasonable because of the slightly lengthened jaws in tlic males. Tahi.e 10.- AvivKAGK Wkigiits, BY Ukits or Length, Yt kox Cmums, 1020. Length. 21 inches, 3i inches, 3i inihes. T-i inches, 2$ inches ,•6 inches. Males. Females. i Speci- mens. Nutnber. 19 =;6 A vcragc weight. Average weight. Speci- i mens. 1 Pounds. P^y^^ nds. A 5-1 5-7 6.1 7- J 7-9 NunibcT. 1 J: 5-7 6. 7 7- "1 8. -> Females. Length. ?7 inchc .'8 inchc 29 inchc ,10 iiulir ji inchc Speci- mens. Nu'nhrr. Average Average weight. weight. Pounds, 9.1 10.3 Spcci men-. Pounds. I Xufithcr. 9 j : 9-5 ■ GROWTH AND SCALE READINGS. In Figures 290 to 298 are presented photographs of a series of scales of Yukon chum salmon that include rei)resentatives of all the year classes found in our collection. All of these agree in belonging to the sea type — that is, the scales were wholly formed in the sea, the fry having passed out of the river at a very early age, before even the nuclear p'ate and the first scale ring had been formed. The Yukon chums agree in this respect with their souUicrn relatives. All lea\'e their native streams as soon as the yolk is absorbed and the)' are free swimming. In more southern districts this seaward migration is easily accomj^lished. The eggs are laid in gravels not far removed from the tides, and the young, when free, easily drop down with the current to the shore line. The case is less simple with the Yukon fish, many of which have 2,000 miles or more to cover at a period when they average only i j< inches long. No information is available concerning the dates on which this migration is effected. Observations farther south indicate a very early descent to the sea in the spring of the year. It is not known, however, to what extent hatching of the eggs and development of the young on the Yukon are retarded by the very low temperatures to 330 BULLETIN OF THE BURH.MT OF FISHERIES. which they are exposed. Growth during the seaward migration can not be considerable, for .none of the material that we have examined indicates the formation of the scale nucleus while still in the stream. Growth of this species in the sea seems to proceed wth remarkable regularity, with the result that the scales are diagrammatic in their simplicity and seldom afford any difficulty in determination of age. In the case of the Yukon race, such uncertainty as may be experienced is concerned with the interpretation of the peripheral region of the scale and is based on the fact that the scale margins differ widely in condition among individuals captured on the same date. It is generally recognized that individuals of a given race will vary materially in the date on which they begin the rapid growth of the spring after the winter pause. Among the fish captured in May or early June in more southerly waters an occasional individual may indicate no growth of the curretit season, while others will vary in the number of peripheral wide rings by which the amount of spring growth may be computed. In the Yukon dog salmon, however, this variation at the time they leave their feeding grotmds and enter on their spawning run is extreme. .\n occasional fish, as shown by Figure 2')(', had begun no new growth of the year, the margin of the scale being formed by the clo.se-rmged check of the previous winter. Others, as represented in Figure 294, had barely inaugurated the new growth, which is indicated bv two or three wide rings outside the winter check. There then follow fairly complete series with ever-increasing growth of the season, as shown in Figm-es 297, 290, 291, and 292, the last named having finislicd an average season's growth for the third year, with the exception of the winter check. WTien it is recalled that these dog salmon enter the Yukon in company with the king salmon and that the king salmon have not in any case made unmistakable growtli for the current season, the habit of the dog salmon in this regard seems most peculiar. In the early and middle parts of the run, to which alone we had access, none of the individuals examined had begun a winter check at tlie margin of the scales for tlie cur- rent )-car. Wliere a marginal winter checlc existed, it had been formed the previous winter and presented no real difficulty in determining age. If the latter part of the run should be found to contain a group of individuals in which a check was forming at tlie scale margin and also another group with scales like Figure 293, in which tlie marginal check belonged to the previous winter and no furtlier growth had been regis- tered, a real difficulty might arise in determining tlie age of such individuals. The two groups would show essentially similar scale structure, but one would be one year older than the other. It is not probable, however, that representatives of these two classes would be found together in any portion of the run. As the season advanced we should expect to find extremely few, if any, that had failed to produce some new growth of the year. THE SOCKEYE SALMON (Oncorhynchus nerka). A few scattering sockeyes (Alaska red salmon) enter the Yukon River during July and early August. In 1919 tlie Carlisle Packing Co. put up 22 cases of tails and 6 cases of flats of this species and handled a total of about 300 fish. The sockeyes appeared even less numerous in the following year, when only 5 cases, containing about 60 fish, were packed. If a permanent colony of red salmon exists in the Yukon, it must ascend to the lakes near the source of the river, but we have no knowledge that such spawning grounds for this species exist. That individuals ascend the river for long distances is certain, SALMON or Tun VUKOX RIVER. 331 for we learned of their occasional occurrence up the river from men who were acquainted with the different species of salmon, and we obser\-ed one, a male, decidedly pink in color, at Ruby on August i-j, 1920, some 650 miles above the mouth of the river. We examined 23 specimens in 1920 on July 5, 7, 8, 9, and 13. Thirteen of tliesc were in tlieir fifth year (see Figs. 299 and 300), having spent their llrst year (perhaps 15 montlis) in fresh water and having descended to the sea in their second year. The scales exhibit a vigorous fresh-water growth, followed by three complete year records at sea. A few (jf these scales, as in Figure 300, have a marginal check, which was formed during the preceding winter; but a majority have at the margin from one to four wide rings denoting new growth of the year. In addition to the individuals in their fifth year, one year of which was speut in fresh water, we have eight that had remained in fresh water an additional \car and were maturing in tlieir sixtli year. A scale of one of the latter class is represented in Figure 301, the division between first and second year's growth in fresh water being clearly indicated. Here, again, the growth of ihe new year is faintly but unmistakablv showTi along the anterior left-hand margin of the scale. A tliird class of individuals is represented by Figure 302, thcsj having descended to tlie sea soon after hatching and prior to the gi-owth of tlie scale. The two salmon we examined belonging to the sea type, one a male 2 7>.. inches long, the other a female 23J/2 inches long, had matured in tlieir fourth year, one year earlier th;in any of those that had lingered in fresh water. Whether the Yukon red salmon arc strays from some colony to tlie southward or form an unflourishing local race can not be determined at present. There is no reason to believe that more than one race is represented in our meager material. THE COHO SALMON lOncorhynchus kisutch). The colic or sOver salmon develops a regular run in the Yukon River, appearing sparingly at the mouth of the river in the latter part of July, but the run docs not show any real development until in August. The Carlisle Packijig Co., in 1919, packed 7 cases of cohos on July 14 and 3 on August 2. From August 3 to 9, 59 cases were put up and in the following week 9S5 cases. The total pack to August 30 was 3,181 cases. In 1920 this species was entering the mouth of the river in very limited numbers during the last week in July and does not appear in the cannery puck of that year, as canning operations were discontinued Ijefore the run had developed. During the cailv half of August, between the mouth of the ri\-er and Tanana, we found at all lishing camps that occasional individuals were being taken. But we were unable to learn of its occurrence in the main river above Tanana. It is well attested that the species enters the Tanana and spawns in one or more tributaries of the Kantishna. How generally it is distributed over the basin we were unable to ascertain. When the coho enters the river it is a perfectly symmetrical fish, with brilliant silvery color, but in traversing the lower portion of the river it takes on a red livery, iuid the males assume at the same time the characteristic snub-nosed appearance of the breediiig fish, the upper jaw becoming bluntly hooked over the lower in a manner characteristic of this species. Scales of Yukon cohos are represented in Figures 2S6 to 289. As in all other coho colonies that we have examined, those from the Yukon are always in their second year (14 17°— 22 2 332 BULLETIN OF THE BUREAU OF FISHERIES. of sea growth when captured,^ Outside the narrow-ringed central area, which records the life in fresh water, we invariably find in this species a vigorous summer growth, succeeded by a well-marked wijiter check, and this in turn followed by an extensive marginal growth of widely-spaced rings, which measure the growth of the current season of capture. In the southern part of its range, where the coho uniformly spends one season in fresh water before migrating seawards, the spawning run (aside from a few male grilse in their second year) consists exclusively of 3-year fish. As we proceed northward, how- ever, we encounter indi\'iduals that have tarried two years in the streams and are maturing in their fourth year. These are more abundant in the Yukon than in any other stream we have examined. Our small collection of 31 individuals comprises 12 that have spent one year in a stream and are 3 years old (see Figs. 286 and 287) and 18 that remained two years in fresh water and are in their fourth year (Fig. 288). If the customary proportions are shown in this collection, some 60 per cent of the young spend two years in fresh water. One individual of our collection (Fig. 289) had appar- ently spent three years in the river and was maturing in its fifth year. The number of individuals at our disposal is too small in the various classes to give reliable averages. Six 3-year males average 23.8 inches in length (middle caudal rays included, as in all our measurements) ; four 3-year females, 24.6 inches. Eleven 4-year males (two years in fresh water) average 24.5 inches; si.x 4-year females, 25.3 inches. As males are consistently larger than females among Pacific salmon, we have additional reason for distrusting the adequacy of the above figures. The 5-year male (three years in stream) is 23 inches long. THE HUMPBACK SALMON (Oncorhynchus gorbuscha). Scattering humpbacks enter the river in July and August and are then so near their spawning time that they would be unable to ascend the stream for any considerable distance. We observed one ripe male at Andreafski on August 3 and were unable to learn of the occurrence of the species beyond that point. The individuals observed were all small and without value, having often liquid milt and partly free eggs. Four specimens measured from 20 to 22 inches in length and weighed from 4 to 5 pounds. As in the case of all other humpbacks that have been examined for age, these were in their second year and had proceeded to sea as soon as free swimming, their scales registering none but .sea growth. The small size was doubtless due in part to the fact that they were maturing so early in the season, thus greatly limiting the growth of the second year. The scales all indicated this history, for the area representing growth of the second year was narrow and contained a partial check at the margin. * We do not here include the tew male grilse, which in more southern districts mature durina the first year at sea. o c C 1} J J S. Z c. OS i; O ^ o o O o I d D a c 3 rt ^ E W^"^^' I '3^ J D s 3 v^ e a I g .- I'.ri.i.. r. S. 11. ]'., I'jji-Jj. (Dor. qjS.) i^f ili;!i:l WFi-'i 'iiiiittii'' •VV , yi..sf^' I'u;. jS;.— Scale «if kiu'^ ;^.ilin..ii lakvii Imiii iikhUIi VuUini Ki\-i. r J ill-,' s. i->iv. M.iK-. .;;'-■ iiirhcs li'ii,;; 111 il^ ^fVi-iUli j'l-ar. S a d I s s I ^ o c I ri pq a % I 3 H S - P ^ ■I. - t ■ S- c. C ^, uu(b; in its third year. ]',ri.i.. V. S. r.. I'., u)2i-22. (Doc. 928.) I-'IG. .•.;!.— Sc.ik- ..i iliiiin ^almim t.ikcu (i.^n iimulh Vukmi Kivtr .liilv (I inniuiLi. Ill u- llurd ytur. o. l-Linalc. :4'.. imhcs Ion;;. nt'i':lit Bull. r. S. B. F., 1921-22. (Doc. >)2S.) Fig. 2yj.— Scale of chum s.ilniou taken frum iiioiil!! Yii!>oii River July 7, i^jo, M.ile, .3 inches long, weight 6 puunds; in its third yL-ar. ]'u;. 2jj. — ImjIc of cliinn bjliiion taktii (rum nioulh Yukdu River July 31, i'j:o. Mule, .^t'j iuclu-s luii.:;. wcii;lu y puuiuh; iu iu lourth year. Bull. U. S. IJ. I'., i')2i-22. (Due. n:S.) •W^*' Fig. :'m- — ^^calc of Lhuiu ^ahuun lakcii from niuuth Yukon Ki\ cr July 7, I'^.'o. Kcmalc, 23 iuchfb loup, ^vvi^;ht 5 pounds; in its fourth year. ll'LL- U. S. r>. 1'., lO-I---. { I^"C. 0^!^^ ) I'ir. :j5. — SluK- nf fhum salni.iii l,iki.n in. in niniih \'ukMii ki\.i luK ii. i^^i. Male, j;',- irRlR> !oii.;, wcj^li ') iiuuiiii^, ill its (((urlli scar BUI.L. U. vS. P>. I-., 1921-22. (Doc. 928.) Fig. .'96.— Scale o[ lIiuui -.alniuu Uiktii In m iiuiuili \ vikon Kivcr July 2. ig-'o. Female, ib mcUcb long, weight 7 pounds; in it^ fifih year. Hull. U. S. P.. I'., ic)2r-22. fDoc. 02.S.) Fig. 2<-)-. — Suit- of clunii ^.lllllnll uiLtii limii iii-inih \ukiiii |-;i\ir JiiK- 7. igjo. iVinak', .-.i', nu lu-. luu^. weii:lit 7 [»oiuid\; in its liiiU ytar. bt'tx- r. s. r>. F., 1921-22. (1)00.028.) Fir.. 29R.— Scale of (^linni ^.ilmmi lakcu inun ninnili Vukuii UiviT July 7. ' '-'o. Malt', 'S iiulK--> lon^. wcinlit 10 puimd^". in it? liflh >'car. ■■i;0 t '"fp«" ■3- CO CN lO *3- CO C-l f ^'SRARV OF CONGRESS 002 850 1 1^'y