HERRING IN OTHER AREAS
35. Review of Japanese Herring Investigations By
SlGERU MOTODA Faculty of Fisheries, Hokkaido University, Hakodate, Hokkaido, Japan and
Y o s h im i H ir a n o Hokkaido Fisheries Experimental Station, Yoichi, Hokkaido, Japan
Introduction History of the herring fisheries in Japan The Pacific herring, Clupea pallasii Cuvier et Valen The main basis of the fishery in the period of pros ciennes, is distributed in the northern cold region of perity in the Japanese herring fisheries was the so- the North Pacific, and supports, or has supported, called Hokkaido “spring herring”, which appeared the great fisheries of northern Japan, Sakhalin, Korea near the shore to spawn, along the west and north and the Siberian coast in the north-western Pacific, east coasts of Hokkaido, from late March to late May. and those of Alaska and British Columbia in the north Historical records indicate that there were great eastern Pacific. In Japanese waters, tremendously large fluctuations in landings both between years and loca numbers of schools of herring appeared, in the past, lities. Since the towns and villages on the coast largely to spawn along the west coast of Hokkaido and smaller depended on the herring fisheries, their prosperity numbers (usually about 10% of the total catch) on and decline occurred in close correspondence with the the north-east coast, in the spring season, but they rise and fall of the herring catch (H i r a n o , 1947). have now almost disappeared (Figure 1). Since its According to written history, the herring fisheries establishment in 1902 herring investigations have been of Japan have been carried on since 1447, but stati one of the major undertakings of the Hokkaido Fish stical catch data were not recorded until 1870. In eries Experimental Station. They were initiated by the early days the herring were probably fished by very late Mr. M. Yamaguchi, and continued by the late primitive methods such as shore dip nets, and fishing Mr. M. Kuragami, then by Mr. Y. Kajita, followed was restricted to the northern part of the west coast by one of the present writers (Y. Hirano). Valuable, of Honshu, and around Tsugaru Straits, which se and voluminous papers on the fisheries and biology parate Honshu and Hokkaido. There is information of the Hokkaido herrings were published by earlier that set nets have been used since 1810, and further investigators (Araki, 1926; Yamaguchi, 1926 a, 1926 b; improvements in gear appeared in about 1856. The Fujita and Kokxjbo, 1927), and since those days in fishing area gradually extended northward on the numerable papers have appeared until the present west coast of Hokkaido in the Japan Sea, expanding time. Knowledge on the Japanese herring, thus accu farther into the north-east coast in the Okhotsk Sea mulated, was summarized by Ishida (1952), and the and even to the northern part of the east coast in present writers’ opinion on the Japanese herring are about 1810. It is said that the total landings gradually now being published (Hirano, 1961 a, 196lb, 1961c, increased during the period from 1447 to 1870, along 1961 d, 1961 e, 196If, 1961g). There are bibliographi with the expansion of the fishing area. cal compilations of herring studies published by Records of the total landings of Hokkaido spring Motoda and Takeuchi (1950), M acy (1955) and herring are available since 1871. These are given in SCATTERGOOD (1957). Figure 2. In the expression “fishing effort” in Figure 2, 250
U 6 UO U1 U 3 U 5 /SOUTH1 l SAKHALIN
ANIWA
BAY
OKHOTSK SEA Kutsugata @ JAPAN S EA v“gisof"ri
Mashike Ishi ka ri O ^ HOKKAIDO If I
<< ' 0 / ° / ‘\ 0 Sapporo
m b e &
Ina ho
Esashi
PACIFIC OCEAN
HONSHU
Figure 1. Map of Hokkaido and adjacent areas. 251
2 en -i< O2
f- O LO O lo LO o LO oLO o LO LO o LO o LO C" CD CD cn o O CM CM CO LO LO Figure 2. Fluctuations in annual landings of spring herring and in fishing effort on the western and north-eastern coasts of Hokkaido. ten drift net boats are equated to one ordinary set net; HIYAMA two small-sized set nets are considered equivalent to one ordinary set net. The number of nets in 1886- 1905 is estimated from the num ber of fishing licenses issued whereas before 1885 they are estimated merely on the assumption that the nets increased every year SHIRIBESHI at the same rate (Kawana, 1948). Since 1947 the numbers are based on the statistics recorded by the Division of Fisheries of the Hokkaido Provincial Government. The records show that the catch in creased until 1897 as a result of the increase in fishing effort, which was increased greatly by the invention of a special rectangular trap net, in about 1891. This net was very effective for catching fish moving towards ISHIKARI the shore. The period from 1894 to 1904 was the most prosperous in the history of the Japanese herring fisheries. In 1897 more than 5,000 set nets were in operation along the west and north-east coasts of Hokkaido, and the landings reached 975,000 tons, RUMOI which corresponded to approximately 4,000 million fish. After this period, total landing decreased year by year though there was a recovery during the period from 1913 to 1927. It is noticed that this decline of total landing occurred along with a very regular SOYA disappearance of the spawning runs, beginning in the south and extending northward along the west coast of Hokkaido (Fig. 3). No spawning run appeared in the south of Shakotan Peninsula after 1925, and no fish visited Ishikari Bay and to the south of it after ABASHIRI 1935. A decrease in landings, together with a northerly restriction of fishing area (spawning area) occurred for several years before the catch finally reached the (O CO (0(0(0 (O (O O minim um (12,800 tons) in 1938. Thereafter the catch coO o>o »— c n m sf in to improved somewhat to 1944-1945, but it has again cn cn o o> o cn declined drastically to the present day. In 1960 it was no more than 300 tons. During the period of the recovery after 1938, the fishing extended back to the Figure 3. Fluctuations in annual catches of spring herring at six south as far as Shakotan Peninsula. divisions on the western and north-eastern coasts of Hokkaido, averaged for 10-year periods to indicate the northerly restriction In addition to the Hokkaido fishery, spawning her- of the fishing area. 252 15 — Figure 4. Fluctuations in landings of South Sakhalin spring herring (R u m y a n t z e v , 1958; H ir a n o , 1959). Cfi £10 ring near the shore of South Sakhalin from April to May were also exploited by Japanese fisheries before the war. These spawning runs appeared on both the o west and east coast as well as in Aniwa Bay on the south coast of South Sakhalin. The landings in this fishery are shown in Figure 4. It is noticed that the fluctuati ons in landings in this fishery before 1934 seem to have alternated somewhat with those in the Hokkaido spring fishery, giving a reasonable steady catch for the two combined. This alternation disappeared after about 1935, when both fisheries declined greatly. The similar CM Lf> r- co ity of their racial characters and age compositions, as in in in in well as the inverse relation in landings (at least before 1934) suggests that the Hokkaido and South Sakhalin Figure 5. Annual landings of spawning herring in Akkeshi Bay- spring herring belong to the same population. Herring schools also appear off Aniwa Bay in the Okhotsk Sea in winter and through spring to early considerably in number in recent years. The Hokkaido summer and are fished commercially. The winter Fisheries Experimental Station has recently made ob schools have been fished by trawling since 1950, and servations in the behaviour of larval herring resulting the spring-summer school by offshore gill net fishing from the increased spawning in Akkeshi Bay (M ik a m i since 1957 ( K o n d a et al., 1958). The winter trawl fish et al., 1961). ery has further developed with the catch amounting to as m uch as about 4,000 tons in 1960, while the Life history and migration of Hokkaido spring herring spring-summer gill net fishery has yielded an annual Comprehensive studies of the habits of Hokkaido catch of about 15,000 tons ( K i t a h a m a and N a k a y a m a , spring herring were first published by Yamaguchi 1958). (1926a; 1926 b) ; many later works have supplemented Fishing of small herring, mostly 1—2 year-olds, also them. In early spring (February and March), herring takes place on the Pacific coast of Hokkaido, normally appear in the north of Hokkaido in the Japan Sea from May to July. Annual catches were less than and migrate to the south feeding voraciously on plank 50,000 tons up to 1950. Adult herring also appeared, ton animals, such as Euphausia pacifica, Thysanoessa iner- though in small numbers, on the Pacific coast to spawn mis, Calanus cristatus, Calanus plumchrus, Metridia lucens, mainly from winter to spring. The spawning area etc. (Motoda and Sakai, 1946; M otoda and T akeu- covered the east and south-east coasts of Hokkaido. chi, 1949; 1960). During this southward migration, The racial characteristics of this population resemble they mature and enter coastal waters, where the fe those of the spring herring, of the west coast ( F u j i t a males spawn on sea weeds or, abnormally, on gravel and K o k u b o , 1927; S a t o and Kobayashi, 1951). or rocks on the shallow bottom. The eggs are about There are local herring populations inhabiting the l -5 mm in diameter and adhere to each other and to brackish lakes, and adjacent, inshore waters on the the substratum. Their fecundity is calculated as about Pacific coasts, not only of Hokkaido but also of Honshu 40,000 in a 4 year-old female and about 50,000 in a 5 (e.g. Lake Akkeshi and Akkeshi Bay in Hokkaido, year-old. The density of eggs spawned on the sea weeds Lake Obuchi in Aomori Prefecture, and Lake Hinuma is calculated as 1,500,000-5,800,000 (Tamura et al., in Ibaragi Prefecture ( F u j i t a and K o k u b o , 1927; 1954) or 1,940,000-4,290,000 (Tamura et al., 1955) K o k u b o and T e z u k a , 1938; S a t o , 1944; K i t a h a m a in one square metre of the bottom in the most densely and F u j i m o t o , 1956; 1958). These populations still spawned area. Male fish then spread their milt in the persist in spite of depletion of the west coast spring her vicinity of the eggs, giving the spawning area a milky ring. As shown in Figure 5 the herring appearing to appearance. The spawning runs are normally composed spawn in the Lake and Bay of Akkeshi have increased of fish, 3-11 or more years old, the majority usually 253 being 4 and 5 year-olds. However, 2 year-old fish have They (mostly 2 year-olds) appear in abundance in come to join the spawning runs in recent years, to Aniwa Bay, and, before the war, were fished there. gether with fish older than 11. The ratio of females These so-called “small herring” also appear all the year to males in the spawning runs is reported as about round on the Pacific east coast of Hokkaido to as far 890:1000. The optimum temperature for the inshore north as Volcano Bay. They occur most abundantly spawning migration is about 4°-6°C. There is a ten in early summer and are fished commercially. In 1951, dency that older fish arrive at the spawning grounds the catch of these young herring off the Pacific coast earlier and come farther south than do the younger of Hokkaido amounted to over 22,800 tons, and over spawners. When dense populations of a diatom, Cos- 1,500 tons off the Okhotsk Sea coast, but only about cinodiscus asteromphalus, appears in the inshore water, 15 tons were caught off the Japan Sea coast (K o n d o the herring does not come to spawn there. This often and K it a h a m a , 1953). happens in early spring, when temperatures are above Recruit spawners first appear at 3 years old in the normal (I iz u k a and T a m u r a , 1953). spawning area on the west or north-east coast of The incubation period varies with temperature, Hokkaido, although in recent years, 2 year-old fish ranging from 16 days at 7-8°C to 22'9 days at 3-l°C have also appeared on the spawning grounds. After (Y a m a g u c h i, 1926a; F u j i t a and K o k u b o , 1927; T a first spawning, the fish again appear in the spawning m u r a and O k u b o , 1953 a). The fertilization rate is area every spring until they become old and die. 72-98 °/0 of total eggs in a mass, and the successful As mentioned above, large numbers of mature her hatch is 95-98 % of the fertilized eggs (T a m u r a et al., ring appear to spawn on the west coast of Hokkaido, 1954). Herring eggs deposited on sea weeds or gravel while the spawning concentrations on the east coast are favourite food for Atka-mackerel, Pleurogrammus are very small, although the spawning runs on the azonus (K o n d o and K in o s h it a , 1952; T a m u r a and Pacific coast have recently somewhat increased. These O k u b o , 1952). The eggs are often thrown up on the two facts led Y a m a g u c h i ( 1926 b) to imagine that larvae beach by wave action caused by strong winds forming of spring herring, born in the Japan Sea, in spring, long piles of eggs more than half a metre high (T a m u r a are transported to the Okhotsk Sea and then migrate et al., 1951; T a m u r a and O k u b o , 1953b). into the Pacific by autumn. After passing two years The adult herring migrate back to the north after in the Pacific they return to the Okhotsk Sea in autumn spawning, and seem to disperse into the open sea. and a part of these 2 year-old fish appear as 3 year-olds However, a concentration usually forms in the area on the west coast in the Japan Sea to spawn, in spring, off north-west Hokkaido, in early summer. These fish of the following year. The older fish, after spawning have fed heavily on plankton and are very fat, which in the Japan Sea, do not migrate into the Okhotsk gives them the name “oil herring” (also called “sum Sea or the Pacific, but spend the winter season in the mer herring”). They are fished by gill net in the off northern part of the Japan Sea until the next spawning shore areas. The main concentrations probably spend season. On the other hand, F u j i t a and K o k u b o (1927) the summer, feeding season in the northern part of the noted morphological similarities between Hokkaido, Japan Sea or the south-western region of the Okhotsk west coast, spring herring and east coast “small” her Sea. In the late autumn the schools in the Okhotsk Sea ring, and concluded that the Pacific coast “small” become concentrated in the region off Aniwa Bay, on herring originate from the west coast and are trans account of the movement of cold water from the north ported by abnormal currents to the Pacific. They may west. These concentrations are fished by the winter grow up to 3-4 years old, but they never join the spring trawl fishery. The cold water gradually extends further herring on the west coast; instead, they die in the and in December to January the herring migrate from Pacific Ocean, without maturing. These two hypothe the Okhotsk Sea to the Japan Sea. Then in early spring ses need further biological evidence to be supported. they begin their spawning migration towards the west Tagging experiments have been carried out since 1949 or north-east coasts of Hokkaido or the west coast of by the Hokkaido Fisheries Experimental Station on South Sakhalin, and Aniwa Bay (K o n d a et al., 1958). the 2 and 3 year-old “small” herring on the Pacific The newly hatched larvae are about 7 mm long, coast (K o n d o and K it a h a m a , 1953; K o n d o and N a - drifting with the currents; they then metamorphose k a y a m a , 1954; 1956; 1958). By 1957, 77,188 fish had into more active, feeding juveniles. On the west coast been tagged off the Pacific coast, of which, 3,093 had of Hokkaido they are transported by the Tsushima been recovered, mostly on the Pacific coast. It is very Current to the north, along the coast, and thence interesting that, (1) of 565 fish tagged off Hiroo (Paci supposedly by a branch of that current through Soya fic coast) on 6. July 1951, one fish was recovered at Straits into the Okhotsk Sea. The habitat of the young Mashike (Japan Sea) on 23. April 1953 (K o n d o and spring herring, up to three years old, is at least in K it a h a m a , 1953); (2) of 906 fish tagged off Taiki recent years in the southern part of the Okhotsk Sea. (Pacific coast) on 1. October 1953, one fish was recover- 254 YEAR-CLASS YEAR-CLASS 2 4 6 8 10 12 14 16 18 YEAR-CLASS YEAR-CLASS 2 4 6 1936 1949 80 1910 1923 40 „ f l n r L 1937 1950 80 1911 1924 40 n n r i r f i 1938 80 1912 1925 40 P r \ R r~»rv~v~1r- i i^r v - v n l flrir-i 1939 1952 80 1913 1926 40 -Pi—r^i 80 80 "I 1914 1927 40 _ n 1954 5 80 1915 1928 ~ 40 r nn'yvTV-’Pn-- a o : J i n r u 1955 S 80 1916 1929 1 “ Pr-n H -> 0 n , n , n , , , x 80 1917 1930 £ * » lrv—rWfl W~V" „ f i n LU 1957 o 80 1918 1931 CD ce 40 UJ Z 80 1945 1958 Z 80 1919 1932 : " i 40 , 80 1959 1920 1933 40 r -PFH n/T nnl ¥>»r»i T—I—I 1—I—I 1960 80 1921 1934 1947 40 ' n r r t L “ t t — i— i— i— i— i— i— r ~ 80 1922 1935 1948 1961 40 0 ' n f i T l n n Figure 6 a. Year-classes of spring herring caught on the western Figure 6 b. Year-classes of spring herring caught on the western and north-eastern coasts of Hokkaido. and north-eastern coasts of Hokkaido. ed off Churui (Nokke Passage) on 25. April 1954; ings have been made from the scales (W a t a n a b e , (3) of 404 fish tagged off Taiki on 4. October 1953, 1913 ; K u r a g a m i, 1914 ; K u r a g a m i and O s h im a , 1925). one fish was recovered off Hamaonishibetsu (Okhotsk Figure 6 indicates that most of the catch has been Sea) on 28. M ay 1954; (4) of 1,359 fish tagged off composed each year of one or two dominant year- Oshamambe (Volcano Bay) on 5. October 1953, one classes, except when catches were poor. Before 1945 fish fish was recovered off Ochiishi (northern Pacific coast) between three and eight years old, with 4-5 year-olds on 3. June 1954 (K o n d o and N a k a y a m a , 1954). Al predominating, made up the bulk of the catch. Since though these data are limited they suggest that there then, however, the proportion of older fish has in may be some mixing of herring populations between creased. This is not due entirely to the dominant, 1939 the Japan Sea and the Pacific Ocean. year-class; other, minor 'year-classes (e.g. 1942 year- class) also survived until they became very old. Such Age composition, growth rate and survival rate of a long duration of life has never been observed before. Hokkaido spring herring At the same time 2 year-olds (1954 year-class) have Observations on the age compositions of spring her appeared in spawning runs since 1956. ring landed on the west and north-east coasts of Hok Growth data for Hokkaido spring herring (K it a kaido have been made by the staff of the Hokkaido h a m a , 1955; MS) are given in Table 1. Fisheries Experimental Station for 51 years since 1910. It is shown, that, except during the period 1935— The age compositions are given in Figure 6; age read 1939 the lengths at age have increased over the period. 255 Table 1. (b) Spawning runs appearing in the northern Average body length (total length in cm) part of west coast (Japan Sea) and north-east of Hokkaido spring herring in different periods coast (Okhotsk Sea) were mainly 3-4 year- olds. Year of birth ASe 23456789 (c) Spawning season usually lasted about 60 days. 1907-1934...... - 25-6 28-3 30-0 31-5 32-7 33-6 34-4 II. Characteristics of population appearing in 1939— 1935-1939...... - 26-1 27-9 29-6 30-9 31-8 32-4 33-1 1945 : - 1940-1947...... - 26-6 29-4 31-1 32-7 34-0 34-9 35-9 1948-1955...... 25-3 27-3 32-4 33-6 35-1 36 0 - (a) Spawning area was restricted to the region north of the middle part of the west coast Year of birth 10 11 12 13 14 15 16 (Japan Sea) and north-east coast (Okhotsk Sea). 1907-1934...... 35-2 35-3 36 1 - 1935-1939...... 34-1 34-8 35-3 35-9 - (b) Catches of South Sakhalin spring herring did 1940-1947...... 35-9 36-6 37-3 37-5 37-7 37-8 38-1 not rise when those of Hokkaido spring her 1948-1955...... ______ring declined. (c) Percentages of higher year-class increased. Table 2. (d) Old and young herring appeared to spawn Survival rate of Hokkaido spring herring, in similar proportions throughout the west 1910-1950 and north-east coasts. (Ishida, 1952) (e) Spawning season started and ended earlier °/o 3—4 year-olds...... 3-33 than before; it was shortened to about 40 days 4—5 year-olds...... 1-26 (H i r a n o , 1953). 5-6 year-olds...... 0-53 (f) Growth rate increased (after 1940 year-class). 6-7 year-olds...... 0-46 It is also reported that the fatness of the her ring decreased. The average apparent survival rates of Hokkaido (g) Unusual characters of eggs observed in some spring herring between successive pairs of ages, cal females after 1950 (after 1946 year-class) ; in culated from data for the years 1910-1950 (I sh id a , particular a loss of adhesive properties (Hi 1952) are given in Table 2. r a n o , 1961c). For predicting the size of future spawning runs (fishery forecasting) the average survival rates for the I I I . Characteristics of population after 1955 : — preceding three years are used. This is because the (a) Total catches negligible, but herring appear long-term average may not be appropriate due to long in various seasons. term trends in survival rate with changes in the envi (b) Growth rate much higher than before. ronment. For the years 1946-1955 the prediction of (c) Fish survive to 18 or more years of age (1939 catch was generally successful, except for 1948 and and 1942 year-classes). 1949 (Hokkaido Fish. Exp. Sta., 1961). There is, how ever, as yet no way of predicting the 3 year-old recruits (d) 2 year-olds appear on spawning grounds (after (2 year-olds after 1957) which have not appeared pre 1954 year-class). viously in the spawning groups. In addition, the rates (e) In some young herring, scale rings are un of maturation of 3 and 4 year-olds seem to vary greatly clear (after 1954 year-class). In recent years year by year, and so the percentage of 4 and 5 year-old such scale features have been occasionally recruits is difficult to estimate. found in the herring caught before normal spawning runs occurred ( K i t a h a m a and N a- k a y a m a , 1957). They were thought to be Changes in biology of Hokkaido spring herring those fish which had stayed in local waters It is noticed that there are differences between the during the previous winter. biological characteristics of the herring populations (f) Unusual eggs frequently observed. along the Hokkaido coast between the periods before 1934, after 1939, and after 1955 (H ir a n o , 1961a). Long-term trends of marine environment These may be summarized as follows: - in northern Japan I. Characteristics of population before 1934: — The air temperature records from Suttsu, Sapporo, (a) Spawning runs were composed of 3-8 year- Obihiro and Nemuro, in Hokkaido indicate that the olds, most of them being 4-5 year-olds, norm “summer” climate (April-October), has been remark ally not including fish older than 8 years. ably warm since about 1915, and has become still 256 TAKASHIMA o UJ 3er < _ KUTSUGATA er UJ UJ Figure 7. Secular trends in annual mean sea temperature and the 5-year sliding means at Takashima and Kutsugata (Y a m a z a k i, 1960a-d). warmer since 1945. The winter air temperatures (November-March) have also increased, but to a smaller extent (Morita, 1956). It is also the experience of old fishermen that in the past (at least before 1925) strong north-westerly or north-easterly gales were fre quent on the west coast of Hokkaido, during the win- SPRING (APR.-JUNE) ter-spring season. They appear to have become less so in later years (H irano, 1961 d). Records of daily sea temperature at the following nine stations on the west coast of Hokkaido are avail able (Y a m a z a k i, 1960 a; 1960 b; 1960 c; 1960d):- Locality N E Since when Kutsugata.... 45° 11' 141°08' 1928 Y agishiri...... 44°26' 141 °01' 1947 Takashima . . . 43°13' 141 °01 ' 1899 Y o ich i...... 43° 12' 140°47' 1943 SUMMER (JULY-SEPT.) K am o i...... 43°20' 140°21' 1911 S u tts u ...... 42°48' 140° 13' 1915 In ah o ...... 42° 15' 139°33' 1911 £ 12 E sa sh i...... 41°52' 140°07' 1929 n A ï 11 'A h . A « Matsumae. . . . 41°25' 140°06' 1911 ui io In Figure 7 are shown the annual mean sea tempe AUTUMN (OCT.-DEC.) ratures recorded at Takashima and Kutsugata. An apparent rise in a five year sliding mean at Takashima is noticed after about 1910. This tendency was gener ally seen in all localities off the west coast of Hokkaido. The northerly shift of the spawning area of spring her ring, which was evident from about 1903, was much accelerated after 1910, though there still remained large extensions of the spawning grounds on the west coast, sufficient to yield a large catch as a whole. The total sum of the catches in Hokkaido and South Sakha WINTER (JAN.-MAR.) lin greatly declined after 1935. The records of sea I i I I I L_ L temperature at Takashima do not reveal any notice o in o ifl o in ° able increase in this period, but sea temperature at rn n ^ Lf> in 17 258 the west coast of Hokkaido and in South Sakhalin separated areas, at almost the same time. Such a occurred too suddenly to be explained in terms of phenomenon was not the result of depletion of the man-made effects. Generally for fish which spawn a population, but the cause of it. Lake herring, on the large number of small-sized eggs, there is no correla east coast of Hokkaido and northern Honshu, which tion between the abundance of eggs produced and the habitually stay in coastal waters and are well adapted size of population of adult fish which are derived from to low salinity of water have survived well; in fact those eggs. During the years 1939 to 1949 the larvae they have increased in number in recent years. These from a total of 2 X 1011 artificially fertilized herring local populations would not be strongly affected by eggs were released along the west coast of Hokkaido, changes in the oceanic environment. What, then, was but there was no resultant increase in the size of the the nature of the cause, which forced the herring to herring population. adapt different migration pattern and which must For species which spawn a large number of small have occurred in some years before 1938, and again sized eggs the size of the adult population will be in some years before 1955? governed largely by mortality during the juvenile sta As mentioned above the warming of the sea off the ges. Mortality in these stages is generally very high, west coast of Hokkaido during the years from 1932 and varies greatly with variation in physical and to 1938, and again more strongly after 1955, is indi chemical (temperature, etc.) or biological (amount of cated, not only by the temperature records, but also food, predation, etc.) environments. The majority of by various biological phenomena. Recent warming has Hokkaido spring herring pass through their juvenile occurred too in other regions of the sea. Evidence has stages in the Japan Sea, off the west coast of Hokkaido been reported of a long-term warming of the Arctic during the period from spring to summer. Therefore, and subarctic zones in the North Atlantic, during the the environmental conditions of this area over this last two or three decades ( T å n i n g , 1949; etc., from period will have the greatest effect upon their survival K e t c h e n , 1956). Similar warming of air and water rate. Ocean currents and wind as a promoting factor temperatures was reported by K e t c h e n (1956) on the of the surface current, may vary with years. Those British Columbian coast in the North Pacific. There factors transport the herring juveniles to favourable was an irregular increase in water temperature at or unfavourable areas, which affect their survival rate Departure Bay, British Columbia, from 1917 to 1940, (Nadiozhin, 1958; R a n n a k , 1958; H o u r s t o n , 1959; followed by a rapid decline between 1940 and 1945 P a r r i s h et al., 1959). Sometimes, mortality of larval ( T u l l y , 1950), and then a progressive increase of the herring depends upon the abundance of predators such area of warm water was observed from 1955 to 1958 as combjellies (Stevenson, 1947). Sunny days will ( T u l l y et al., 1959). Sea temperatures off the Califor encourage the growth of the phytoplankton which are nian coast in the eastern North Pacific were above the food of small zooplankton, and, in turn, supply average in 1926, 1931, 1939 and 1941 but below it in abundant food for herring juveniles, or promote their 1924 and 1933 ( R e id , 1960). The ecology of the herring survival in other ways. K u r a g a m i and K a j i t a (1926) is of course governed by a complex combination of many found a high correlation between the total sum of kinds of environmental factors, but the temperature bright sunny hours in May and June on the west coast increase would have been one of the most important of Hokkaido in a year and the population size of adult changes affecting it. herring born in that year. The number of adults de An increase in the body length of herring for each rived from the eggs spawned in each year computed age has been recognized since the recruitment of the by totaling the catch of each year-class, in successive 1940 year-class, and more remarkably in later year- years, until it disappeared. Such a correlation appar classes. The herring born after 1939, which spent their ently existed for the period 1906-1916, but not after young stages in the cooling period, and their older life wards. in the warm one survived to be as old as 18 years. The writers are of the opinion that the depletion of Long survival would be related to the retardation of Hokkaido and South Sakhalin spring herring may maturity of gonads under the influence of warming probably be due to a change of migration route of of the winter habitat. The female herring belonging the spawning runs, as a result of some drastic, widely to the 1947 and later year-classes often had unusual occurring change of environmental conditions in the eggs, indicating abnormal inhibition of maturation. northern Japan and Okhotsk Seas, or even over wider Similar observations were made by F r i d l y a n d (1949) spaces. An unfavourable spring-summer environment on the west coast of South Sakhalin in 1948. He con for juvenile herring off the west coast of Hokkaido sidered that they were probably caused by the high would not appear to be the major cause. As already temperature of the habitat before maturing. Further noted the restriction of the spawning area was a very increase in sea temperature along with the decrease remarkable phenomenon, which occurred, in widely in the range of seasonal variation since 1955 may have 259 forced some of the herring born after 1954 to stay in (6) The length of each age-group of spring herring local waters, instead of making extensive migration as increased after the entry of the 1940 year-class and, they have done before. As a result, their scale rings more remarkably, in later year-classes (Table 1). The have become unclear, and they have come to maturity 1939 and 1942 year-classes survived until they were at 2 years of age, as in the local population of herring 18 years old or more. Such long survival was never on the Maritime Province coast. Recent, spring her observed before. The female herring of 1947 and ring in Hokkaido, seem to be a local population, later year-classes often possessed non-sticky eggs. appearing on the west coast in all seasons. It is inter (7) Some of the herring born after 1954 have m atured esting that P a r r i s h and C r a ig (1957) mentioned that the age of first maturity has advanced, and the length at 2 years of age; some of these have shown unclear for age has increased in the North Sea herring in recent scale rings. In addition, herring have appeared along years. These changes have coincided with some marked the coast at all times of the year. These facts suggest changes in features of the environment in the North that in recent years the herring have stayed in local Sea, as represented by strong oceanic influence since waters without making extensive seasonal migration. 1951. (8) The climate in Hokkaido has been warm since 1915, and became even warmer after about 1954 Sum m ary (M o r it a , 1956). ( 1 ) The major basis of catches of the Japanese herring (9) Long-term trends of sea temperature, recorded fisheries was the spawning schools appearing off the on the west coast of Hokkaido (Figures 7 and 8) west coast (Japan Sea), and to a lesser extent off the indicate that there was a rise in temperature after north-east coast (Okhotsk Sea) of Hokkaido in spring 1910, which corresponded with the time of retraction (Figure 1). The catch in this fishery has become negli of the west coast spawning area from south to north. gible in recent years. Thelandings of spring herring have The sea has been warmed during the season from fluctuated greatly since it was first recorded in stati winter to spring since about 1930. Big runs of spawning stics in 1871, there having been a great decline in fish appeared on the South Sakhalin coast, instead of 1938 and again after 1956 (Figure 2). the Hokkaido coast, in about 1928-1932. The decline (2) The fishing area, which had covered the whole of sea temperature in 1940-1945 corresponded with of the west and north-east coasts, during the prosperous the recovery of the herring fishery in Hokkaido and fishing period, gradually became retracted from the South Sakhalin. A remarkable decline of catch after south. 1945 occurred in association with a new rise in sea temperature. (3) Herring eggs spawned on the sea weeds on the shallow bottom on the west coast of Hokkaido, hatch (10) Lessened annual variation of sea tem perature out after about a fortnight, and then develop into as indicated by the rise in winter-spring temperature juveniles. A large number of juveniles are transported and fall in summer temperature, after 1955, suggests by a current to the Okhotsk Sea by summer. Juveniles that the sea was becoming less turbulent. grow up to adults in the Okhotsk Sea or in the northern (11) W arming of the water in the above-mentioned Japan Sea, and appear on the Japan Sea and Okhotsk years was also indicated by various biological pheno Sea coasts of Hokkaido to spawn in spring. mena, such as difference in the yield of a warm-water (4) There are found abundant 1—3 year-old herring alga, Undaria, (Table 3), and the fluctuations in sar concentrations on the Pacific coast of Hokkaido. dine catch (Figure 9) on the west coast of Hokkaido. Although results of tagging experiments suggest that some of those small herring on the Pacific coast move (12) There must have occurred great changes in to the Okhotsk Sea, insufficient proof is available to the marine environment in about 1932-1938, which show that they are derived from eggs which had been would have some important bearing on herring life. spawned on the Japan Sea coast. Changes in environment as represented by warming of the sea would have caused the different pattern (5) Age compositions of spring herring fished on of migration of Hokkaido spring herring, which re the west and north-east coasts of Hokkaido (Figure 6) sulted in the restriction of the spawning area, and, in indicate that before about 1945 the spawning runs turn, the decrease in the size of the stock. Drastic were composed mostly of 3-8 year-olds, in which changes in marine environment which occurred in certain numbers of new 3-4 year-old recruits were about 1955 would have accelerated the decrease in included, while since 1946 fish older than 9 years have stock size and at the same time caused the changes appeared and, since 1956, 2 year-olds as well. in biology of the herring. 17 260 References A r a k i, U.. 1926. “History of the herring fishery and an investiga Lake Obuchi a brackish lake in the Aomori Prefecture, Japan”. tion of the causes for the decrease in herring”. Rep. Fish. Invest. Sei. Rep. Tohuko Imp. Univ., Ser. 4 Biol., 12 (4) : 639-70. Hokkaido Fish. sei. Inst., 75: 1-142. K o n d o , M ., T a k a h a s h i, T., & N a k a y a m a , N ., 1958. “ O n the F r id l y a n d , I. G., 1949. “ Razmnozhenie selidi u zapadnovo offshore spring herring fishery: on the movement of herrings poberezhiya Yuzhnovo Sakhalina”. Rybn. 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