ARCHIVES. , FISHERIES RESEARCH BOARD OF CANADA Translation Series No< 226 AN ECOLOGICAL STUDY ON THE SALIVï0N FRY, ONCORHYNCHUS KETA, IN THE COASTAL WATERS OF HOKKAIDO >Z. By Tateo Mihara (Hokkaido Fish Hatchery, Sapporo, Japan) Original Title: Hokkaido eng^an ni shutsugen suru sake chigyo no seitai ni tsuite From: Scientific Report of the Hokkaido Fish Hatchery (Suisan-Huka,jo Kenkyo Hokoku), No. 13, ppo 1-14, 195$ Translated by: Hiroshi Kasahara, International North Pacific Fisheries Commission (May, 1959) Distributed by the Fisheries Research Board of Canada, Biological Station, Nanaimo, B.C. 1959 -2- 2> Length and weight of fry at the time of release According to the data collected by the Salmon Hatchery of the Fisheries Agency, the length and weight of fry at the time of their release are as shown in Table 2. 3, Fry in coastal waters, their length and weight and coastal water temperatures After spending one to one and a half months in streams, fry enter brackish waters in the vicinity of river mouthso This entrance to brackish waters takes place in late April at the earliest and is completed in mid-Juneo The downstream migration of fry sharply increases as stream temperature rises`.• The 'followin:^ observations have been made regarding their seaward migration: According to the summary report by the Society of Aquiculture Studies for Utilization of Fresh Waters for the year 1924, it is stated (regarding Ishikari River fry) as follows: "rAccording to our study of fry from natural spawninthe fry emerged from the eggs deposited during the early winter of the previous year begin to swim out into streams for feeding in early May in the Chitose and Ishikari Riverso The length of fry at that time is 3,5 cmo, being approximately the same as that of artificially hatched fry. In early June, fry are found about 72 kilometers downstream, with a size of about 4.5 cm., and in late June or early July they are found about 120 kilo- meters downstream (in the vicinity of the Ishakari River mouth), showing an average length of about 5.2 cmo In other words, they travel a distance of about 120 kilometers in two months and attain a length increment of about 1,5 cmo during this period. Once they enter the seà, the growth become•s_vEry rapid and young chum salmon of about 9 cmo in body len^th are found in late July or early August in the vicinity of Otaru, but they soon disappear from the coasto" Also, Chiba (2] reports the results of his investigation in the vicinity of Mitsuishi, Hidaka, and Sano and Kobayashi [3] report on further studies of the Ishikari River chum salmon fry. Chiba, pa-rtisularly, points out that fry go downstream quickly when the stream temnerature rises to about 15°Co and his observations in this respect completely coincide with the results of investigations by the present writer, which covered most of the important streams in all districts of Hokkaido. Also, in coastal waters juvenile chum salmon quiçklS disappear when temperature becomes 17°Co or above, indicating that this wqter temperature may constitute the upper limit of the temperature range for the distribution of juvenile chum salmono After entering coastal waters, fry feed vigourously and gro^,^r very rapidly; the rate of increase in weight is, in general, faster than the rate of increase in length•à -`:L'he relationship It is important, for the protection of chum salmon fry, to know such things as the length of time required for downstream migration after they are released from hatcheries, timing of their entry to the sea and timing of their departure from the coast, The Fish Hatchery of the Province of. Hokkaido has been taking measures to protect chum salmon fry since 1952, with the assistance -• of the "Keison Hogo Kyoryoku Kai Rengo Kai'r9 an association estab- lished for assisting in the protection of salmon, This report contains certain findings on the ecology of chum salmon fry obtained by the Hokkaido Fish Hatchery in conducting its work for the protection of fry. The author wishes to express his thanks for the assistance given by Mr. Eguchi 9 Chief of the Research Section, and Messrs. Ito and Terao in compiling data. Also, data were made available by Messrs, Kobayashi, Terai and Homma of the Salmon Sectiono The author i s also grateful to Mr a Mat subara , Manager of the above association, for the assistance given by the Associationo 1. Release of chum salmon fry and length of stream residence In Hokkaido, chum salmon fry are released from hatcheries during the period of March to June, after they have started swim- ming, The actual time of release varies from hatchery to hatchery, depending on the temperature of water used for incubation (the length of time required for incubation depends mostly upon the temperature of water used^),o However, the release takes place, in general, during the above period. Fry start swimming in upper water layers of hatchery ponds when the yolk sac has been absorbed and they gradually enter streamso The period of the release of fry to natural streams in 1957 is shown in Table 1 for each river system. According to Yabe [5], Chiba [27 and Sano and Kobayashi C3.79 fry are active mostly at night during their downstream migrationo They form small schools, aviod strong currents and go downstream along the shore always facing upstreamo Few fish actively swim downstreamo The number of days required for their downstream migration to the sea differs depending upon the distance to the river mouth, obstacles in the stream, etc. However, in general, they reach the sea in 20-45 days< Regarding the downstream migration of fry in the Ishikari River, Handa C101 states as, follows: ''The salmon fry which have left the spawning beds of the Chitose 1 Rive'r in early May appear in the vicinity of Ebetsu in early June and are found in the vicinity of the Ishikari River mouth in early July. The body length at that time is about 5o2cmo" According to this statement, fry travelled a di-st,--M-,e of 90 kilo.- meters in two months; however, H anda4s observati„ns were made before the project of Ishikari River stream improvement started; therefore fry travelled following the old winding waterwayso The ebove project has almost been completed and therefore the number of days required for fry migration is probably somewhat less than it was before. -3- between length and weight is shown in Figure 1. Tables 4 and 5 show temperatures in various areas of the Hokkaido coast during the period of the coastal residence of young chum salmon and the length frequencies of the juvenile chum salmon found there. Although these length frequencies should not be considered characteristic of the young salmon found in the respective districts, because the periods of sampling are not the same, they give some idea of the size of young chums during their coastal residence. According to Oya C4], fry stày in the waters under the influence of stream water for a short while after entering the sea, and thereafter move with tidal currents in their feeding migration. 4. Scale pattern of fry (a) Body length and scale pattern It is reported by Kochi C$], Sano and Kobayashi 13], and Nakamura L9], etc., that scales begin to develop on chum salmon fry when their total length is about 4 cm. Observations by the writer usin',P, 40 fry with an average length of 4.5 cm, from natural spawning in the Tokachi River and fry with an average length of 3.5 cm. from a hatchery in the same district showed that elliptical scales of about 0.3 mm. in diameter with no circuli or one or two circuli had been developed on the fry from natural spawning, while nothing more than elliptical plates, which were seemingly initial scales, were found on the artificially hatched fry of about 3.5 cm. in total length. Accordingly, it was confirmed that scales began to develop when fry measured approximately 4 cm., as reported by the previous authors. The len^;th of fry caught in coastal waters ranges from 5 to 15 cm. in most districts and highest frequencies are seen between 6 and 13 cm. The scales from the smallest coastal fry, 5 or 6 cm., already show three to six circuli, the actual number of circuli varying from area to area, probably depending on prevailing water temperature and the distance of stream migration. It is not known when these fry have entered the sea; however, it is assumed that they have just entered the sea, judging from their total length. Supposing this is true and considering the abovementioned formation of initial scales on stream fry, it is assûmed that one to three circuli are formed during their downstream imigration. This coincides with the observations in the abovementioned reports. (b) Scale pattern during the çoastal residence Chum salmon leave coastal areas for offshore waters when coastal water temperature there becomes 17°C, or higher. In general, this takes place during late June and, therefore, it may be said that the coastal residence of juvenile chû.m salmon from Hokkaido streams lasts from April to late Juneo Figures 3 to 6 show changes in the number of circuli on their scales during this periodo Juvenile chum salmon of about 15 cma, which are almost the largest found in coastal waters,have 13 or 14 circuli on their scales and there are some widely spaced circuli near the edge of the scaleso This indicates that about 10 to 12 circuli",are formed during their coastal residence corresponding to an increment in length of about 10 cmo This coincides with the fact that chum salmon scales usually have a distinguishable central portion, which is called the stream-coastal zone and in which 12 to 13 circuli are spaced more narrowly t.ha-n those in the outer nortiono The growth of juvenile chum salnnon after t`h"ey have left for offshore waters is not known, but it is assumed tha't' their growth .'oecomes'" verÿ rapid and correspondingly widely sps.cëd circuli' are forfned.'ôzi,their scâles.