Pi
II, 11
11.
The Composition of the Minch Herring Stocks
By I. G. B a x te r
Introduction 59 Herring fishing is in progress in the Minch almost continuously throughout the year. There are, however, two main periods of high activity and these occur between November and March and between June and September. A fairly reliable picture of the distribution of herring concentrations in the Minch can be gained from an examination of the fishing grounds (Figs. 1 and 2). The main fishing grounds throughout the year are basically the same, they lie along the east coast of the Outer Hebrides from the Butt of Lewis to Barra Head and generally within the 50 fathom contour. Between June and August, however, the grounds in the North Minch extend from the Lewis to the mainland coast and during that period of the year the catches are composed of maturing autumn spawners together with a mixture of immature adolescents of spring and autumn origin. Between September and May, the grounds along the east coast of the Hebrides are fished for spent and recovering spent autumn spawners but the catches also contain varying proportions of maturing spring spawners and adolescents of both groups. During February and March there is generally a fishery for spawning herring along the north-west mainland coast; and although this fishery is of short duration, very large catches of spring spawning fish are sometimes obtained. Other fishing grounds of less importance are located around the north-west coast of Skye and off the islands of Canna and Coll. These grounds are fished mainly between the autumn and early summer for recovering spents and adolescents of both races. In the Minch herring are caught by drift-net and ring-net. The landings from the North Minch, which Figure 1. Herring fishing grounds in the Minch between is more open and exposed, are obtained almost June and August. 6 82 -
LEWIS MAR.
SKYE
Figure 3. Minch herring landings by drift-net. January — December 1951—55. Figure 2. Herring fishing grounds in the Minch between ------= total landings (1,0 0 0 crans) September and May. ------= average landings per arrival (crans) entirely by drift-net, while in the South Minch where tions in the Minch and, secondly, to discuss the the coast provides more shelter fishing is carried out affinities of each group to neighbouring stocks of by ring-net as well as drift-net vessels. spring and autumn spawners. Since most of the fishing vessels are not based The material has been obtained to a large extent locally the exploitation of the Minch stocks is some from samples of commercial catches of both drift-net what erratic and depends to a large extent on the and ring-net vessels between 1951 and 1955. Some productivity of other herring fisheries nearer the of the data on spawning grounds have been collected home bases. From Figures 3 and 4 in which total during the cruises of the F.R.S. “Clupea” over the landings and landing per arrival for drift-net and same period. ring-net vessels are given, it will be seen that the late autumn and winter fisheries are generally more productive than the summer fishery. Problems affecting the study of a mixed Earlier work on the herring in the Minch has been population of a limited nature and has been concerned mainly The herring stocks in the Minch are composed of with the composition and characters of the spring spring and autumn spawners. Representatives of each spawning shoals along the north-west mainland coast. group occur in varying proportions in the majority References are found in the publications of J oha n sen of Minch catches throughout the year. It is essential, (1919), W ood (1923—37), B ow m an (1923), S torkow therefore, when studying the characters of each group (1923—40), Schnakenbeck (1927), L is sn e r (1934), to have some reliable method of separating them. and L e G all (1935). Although the degree of maturity may be used with The aims of this paper are, firstly, to describe the success to discriminate between the adults of the two characters of the spring and autumn herring popula- groups during the spawning periods, it is not a reliable - 83 — 11,11
method to use at other periods of the year and cer showed that the otoliths of the majority of Norwegian tainly never in the case of adolescent herring. spring spawners were characterized by having opaque Other biometric characters commonly used in de nuclei, while the otoliths of the Icelandic summer fining herring stocks such as vertebral numbers, spawners had clear or hyaline nuclei. The technique keeled scales, Zj material etc., have a limited value and validity of the otolith method for discriminating when dealing with a mixed population. These char between different groups of herring in Scottish waters acters can only be used to define the population as a is discussed in another paper contributed to this whole, and not in discriminating between individual symposium (P a r r ish and Sh arm an). The description groups within it. E in arsson (1951), faced with similar of the characters of each Minch group, which follows, problems while studying the herring populations in is based to a large extent on the initial analysis of Icelandic waters, found that herring otoliths could the material into spring and autumn spawners by be used in discriminating between the spring and otoliths. summer spawning groups in Icelandic waters. He
A. The Minch Spring Spawners
1. Spaw ning grounds The main centres of spring spawning in the Minch have been known for some time. B ow m an (1923) demonstrated that they were situated off the north mainland coast between Cape Wrath and the Island of Handa. W ood (1930) confirmed these observations by showing that most of the herring taken on the mainland grounds during the spring fishery were in a spawning condition. Spawning appears to take place along the mainland coast from Cape Wrath to Gairloch but particularly in the vicinity of the Islands of Handa and Bulgie (Fig. 5). The distribution of the fishing fleet suggests that spawning occurs almost entirely within the 40 fathom contour. Early records reveal that this fishery for spawning herring was a regular feature and that very dense shoals were usually encountered. More recently, however, it has been less successful and indeed the fishery failed completely in 1952 and 1955. During these two years the landings of spawning herring were almost entirely limited to small localized catches obtained by fishermen using anchored drift- nets close inshore. Table 1, in which the maturities of samples, from different areas in the Minch are given, shows that the composition of the herring shoals on the mainland grounds was quite different from those occurring on other fishing grounds in the Minch during February and March. The mainland grounds therefore must be considered as the spawning grounds during this period. I 2. Race characters of the Minch spring 4 0 \ spawners \ 30 • »I \ (a) Vertebral number. 20 ’ \ The Minch spring spawners appear to be similar to other spring spawning concentrations in Scottish waters. W ood (1936) found that the mean vertebral J FMAMJ J ASON D count (one sample) was 57-07, while for Shetland Figure 4. Minch herring landings by ring-net January— spring spawners he obtained values ranging between December 1951—55. 57-01 and 57-08. In the Clyde he found that there ------= total landings (1 ,0 0 0 crans) was some variation from year to year in the mean ------= average landings per arrival (crans)
6' Table 1 Percentage maturities of samples from the Minch in February and March 1951-55 February Stage Year -- No. of fish I II III IV V VI VIIVII-II Mainland Grounds 1954 0-7 1-2 17-1 17-6 18-0 44-8 0-2 0-5 433 Lewis Grounds 1952 15-6 16-4 2-4 2-7 5-5 0 7-8 49-6 255 1953 5-2 9-0 9-2 19-8 18-6 1-8 — 36-4 500 1954 28-9 8-1 0-8 0 1-2 15-5 7-3 38-2 250 1955 2-8 1-6 13-0 17-2 5-2 2-8 5-3 52-0 500 Harris N. & S. Uist 1952 20-0 8-9 0 0-4 0-7 0-4 22-2 47-4 270 Grounds 1953 3-6 11-7 9-7 4-0 0-4 0-4 0-8 69-4 250 1954 32-8 9-6 0-4 0-8 0-4 0 0-8 55-2 250 Barra Grounds 1951 2-9 6-6 0-8 0-4 0 0 0-5 88-8 214 1955 0 3-6 8-8 13-2 1-2 2-0 6-8 64-4 250
March Stage Year No. of fish I II III IV V VI VII VII-II Mainland Grounds 1951 0 0 1-0 7-7 8-7 70-8 6-7 5-2 496 1954 0 0 0 1-9 3-8 92-5 1-9 0 53 1955 0 0 0-82 —— 98-37 — 0-82 245 Lewis Grounds 1952 5-5 8-9 0-7 2-7 2-3 0-2 10-0 69-7 439 1953 5-0 28-1 0-4 0-8 0 1-0 7-8 56-9 498 1954 13-2 24-6 0-6 0-2 0 1-2 1-4 58-8 500 1955 3-7 3-7 2-9 7-7 2-0 3-1 3-1 73 7 350 Barra Grounds 1951 2-5 4-5 0-4 1-6 0-4 0 5-6 84-0 214 1952 3-6 14-9 0-6 0 0 0 7-7 734 222 1954 16-8 22-0 0 0-4 0 0-8 0 60-0 250 1955 11-2 5-6 0-4 0-4 0 0 12-4 70-0 250
Table 3 Percentage vertebral distribution of Minch spring spawners of individual year-classes on the spawning grounds (Feb.-March) 1951 1954 1955 Year-class...... 1948 1947 1946 1945 1951 1953 1952 1951 VS Age ...3 4 5 6 3 4 3 4 59 — 1-09 — 0-60 — — — — 5« ' 18-75 17-39 11-76 16-17 16-37 14-09 15-26 19-44 5 7 62-75 59-78 67-65 57-49 70-76 70-47 69-47 63-89 56 18-75 20-11 20-58 25-15 16-37 15-44 14-74 13-89 55 — i-63 —______o-6o —______—______0-53 -2-78 Number of fish...... 16 184 34 167 171 149 190 36 Mean...... 57-00 56-96 56-91 56-91 57-04 56-99 56-99 57-00 — 85 — 11,11
Table 2 Percentage vertebral distribution of Minch spring spawners on the spawning grounds All age-groups Wood 1951 1954 1955 VS (1936) (March) (Feb.-March) (March) 59...... 0-6 0-73 0-23 5 8 21-3 16-38 15-14 16-88 57 63-8 59-41 72-25 68-35 56 13-2 22-49 12-39 13-92 55...... 1-2 0-98 — 0-84 Number of fish...... 159 409 436 237 M ean...... 57-07 56-93 57-03 57-01
of vertebrae and means for individual year-classes are given. The vertebral means range from 56-91 for the 1945 year-class to 57-04 for the 1951 year-class. (b) Length at formation of first winter-ring (Ij). The values for the main age-groups on the spring spawning grounds between 1951—55 are given in Table 4. Although the range extended from 7—18 cm., the largest number of observations lay between 11 and 15 cm., the mode occurring at 13 cm. On the whole the Minch values are fairly uniform, suggesting that a single homogeneous stock is involved. They may be compared with the distribution of lengths of spring spawners in Shetland waters in 1953 and 1954 (Table 5, P a r r ish ) which shows a greater variation between year-groups and means. It must be remembered, however, that we are not dealing with a single spawning concentration off Shetland, as is confirmed by the analysis of the otolith material Figure 5. Spring and autumn spawning grounds in the from spring herring at Shetland. From the large Minch. number of growth calculations made by L ea (1910), //// = spring spawning grounds it is seen that the mean lx values of the Norwegian :::: = autumn spawning grounds spring spawning herring ranged from 7-0 cm. in northern Norway to 9-3 cm. in southern Norway, while he gives mean lx value of 11-9 cm. for spring vertebral number, the values given ranged between spawning herring at Shetland. Sto rro w (1923—40), 57-03 and 57-21. Other workers gave means of 56-78 working on the stocks of herring found in the winter (Schnakenbeck , 1927) and 57-13 (Le Ga ll, 1935) fisheries around the coast of Britain between 1923 and for the Minch spring spawners. S chnakenbeck ’s 1940, obtained mean values for Minch spring figure, however, was based on a single sample of 58 spawners ranging from 10-0 cm. in 1927 to 11-1 cm. fish. Prior to 1939 an important trawl fishery for in 1935. These values are 2—3 cm. lower than those herring was carried out between July and October obtained in the Minch during the period 1951—55, on the Klondyke grounds, which lie between Barra but are higher than the values obtained by L ea for Head and the nortli coast of Ireland, and L e G all Norwegian spring spawners. (1935) gives the mean vertebral count of these herring as 56-97. H e in c k e (1898) gives a mean of 56-97 for spring spawners off Barra Head, where a fishery for 3. Growth large fat recovering spring spents used to take place Perhaps one of the most remarkable features of the (prior to 1939) in the early summer months. Minch spring spawners is their fast growth-rate during The distribution and vertebral means obtained the first three years of their life. By the time the first between 1951 and 1955 on the spring spawning winter-ring has been laid down, the majority have grounds are shown in Table 2 ; they are in fairly close reached 13—14 cm. in length. These fish first begin agreement with earlier records from this area. The to appear in the commercial catches, as herring with amount of variation one can expect between year- one winter-ring on their scales, during the summer and classes is indicated in Table 3 where the distribution autumn, when some have attained a length between — 86 —
Table 4 ly distribution of Minch spring spawners on the spawning grounds 1951 Age cm.... 8 9 10 11 12 13 14 15 16 17 18 Total Mean 3 _ ____ 2 3 3 2 2 ____ —.— 12 12-92 4 — 1 4 16 30 33 27 21 10 —— 142 13-15 5 ...... ____ 1 2 6 4 5 4 1 1 1 — 25 12-48 6 ___ 1 4 13 22 38 34 14 5 4 1 136 13-25 7 2 2 1 2 7 13-43 1954 Age cm .... 8 9 10 11 12 13 14 15 16 17 18 Total Mean 3 __ 1 13 37 79 62 33 6 2 ____ 233 13-38 4 — 2 4 20 26 48 25 13 3 —— 141 12-82 1955 Age cm.. .. 8 9 10 11 12 13 14 15 16 17 Total Mean 3 _ 5 7 13 36 41 39 17 6 ___ 164 12-93 4 — 1 1 8 8 6 — 1 1 — 26 12-04
Table 5 /j distribution of Shetland spring spawners1) May-August 1953 Rings cm... 6 7 8 9 10 11 12 13 14 15 16 17 18 19 Total Mean 2 ___ 1 6 22 19 19 17 5 2 1 — — 92 12-48 3 ...... _ _ 3 5 32 37 4« 40 26 12 1 — 1 197 12-05 4 ...... _ i 2 4 5 8 17 22 37 6 2 1 — — 105 12-80 5 ...... 1 i 1 8 4 8 3 4 3 2 1 — 1 37 11-23 6 ...... _ 2 6 10 9 4 9 7 6 1 1 1 — 56 11-02 7 + ...... — 8 25 16 12 9 19 10 10 5 — — 114 11-46 May-August 1954 Rings cm.. . . 6 7 8 9 10 11 12 13 14 15 16 17 18 Total Mean 2 ...... _ ___ 4 5 7 10 4 — 2 — 32 13-41 3 ...... _ _ 1 5 12 37 53 50 33 12 2 1 — 206 12-41 4 ...... __ 1 9 22 35 41 32 16 5 1 —— 162 11-83 5 ...... _ _ _ 1 2 2 8 23 22 8 4 — 1 71 13-46 6 ...... 1 3 4 3 7 6 5 4 1 2 36 10-50
>) F ro m P a r r ish , personal communication.
Table 6 B Mean lengths of Minch spring spawners on the spawning grounds at point of age Table 6 A Mean lengths of adolescent spring spawners Age ...... 3 4 5 6 7 Number 1951 ...... 27-64 29-22 29-63 30-15 30-45 T,-rungs Mean lens-th cm. of fish (25) (195) (43) (2 2 0 ) (H) North Minch 1955 1954 ...... 28-29 29-61 30-00 ------— (October-December)...... 1 23-01 280 (257) (153) (15) South Minch 1955 1955 ...... 27-68 29-28 30-73 — — Coll Bank (December)... 1 23-94 155 (190) (36) (1 1 ) — 87 — 11,11
Table 7 Age composition (°/0) of Minch spring spawners on the spawning grounds (Feb.-March)
Year A ge... 3 4 5 6 7 8 9 1951 ...... 3-62 41-63 8-37 44-12 2-26 1954 ...... 50-43 43-02 4-27 0-57 0-57 0-57 0-57 1955 ...... 69-57 27-05 2-42 0-97 ———
Table 8 Age composition (°/0) of Minch spring spawners June-December Number Year Rings... 1 2 3 4 5 6 7 8 9 of fish 1953 ...... 12-55 38-38 33-95 2-95 3-32 3-32 3-32 1-11 M l 271 1954 ...... 3-59 70-70 19-12 4-76 0-67 0-33 0-08 0-17 0-50 1,198 1955 ...... 49-93 14-65 28-45 3-41 3-27 0-28 — — ■ — 703
Table 9 Maturities of spring spawners (°/0) June-August 1954 Rings Stage... I II III IV V VI VII VII-II 2 ...... 84-75 14-53 0 0-24 _ _ _ 0*48 3 ...... 29-6 47-2 6-4 0-8 2-4 — — 13-6 4 ...... 13-89 38-89 5-56 —— --- — 41*67
23 and 24 cm. The mean lengths of 1-ringed spring ber was very similar to that obtained on the spawning spawners taken in North and South Minch catches grounds during the following February and March in 1955 are given in Table 6 A and the mean lengths (Table 7). This suggests that the herring on the spawn of 3—7 years old spring spawning herring on the ing grounds are recruited in the main from the spawning grounds are shown in Table 6B. adolescent stock located in the Minch during the pre The main body of the fish which spawn as three- spawning period. W ood (1951) found similar condi year-olds have reached a mean length of between tions in the Clyde. 27 and 28 cm. Estimations of growth after the third The maturities of the Minch spring spawners be year are regarded as biased, since the majority of the tween June and August 1954 given in Table 9 show herring will have spawned as three-year-olds and that, although the majority of the Minch spring migrated out of the Minch. The four- and five-year- spawners appear to spawn for the first time as three- old groups will contain a percentage of slower growing year-olds, a percentage do not spawn until they are individuals which are spawning for the first time. 4 or 5 years old. It would appear, therefore, that after spawning for the first time the majority of spring spawners leave the Minch and do not return even to 4. Age composition spawn. The most striking feature revealed by the age- composition data from the spring spawning grounds given in Table 7 is that the stock during this period D iscussion was composed of relatively young fish. Herring older J o h a n sen considered that the spring spawning than 6 years formed less than 3°/0 of the total. In herring of Norway, Faroes, and Iceland could be 1951 six years old herring of the 1945 brood pre grouped into one race which he termed the “Atlanto- dominated. This year-class was also outstanding in Scandian” spring herring. Norwegian and Icelandic the Icelandic spring spawning stock but not in the tagging experiments have shown how closely related Norwegian spring herring at Iceland (F r ib r ik s s o n , these stocks of herring are. L issx e r (1934) thought 1953). During 1954 and 1955, however, over 90°/o of that the spring spawning herring of Scottish waters the stock on the spawning grounds were composed should also be included in J o h a n se n ’s Atlanto- of 3- and 4-year-old herring. Scandian group. L e G all (1935) proposed that all Table 8 shows that the age composition of spring the spring spawning herring of the North Atlantic spawning fish in the Minch between June and Decem should be grouped together under the title “Harengs Atlantiques”. The important characters of these The physical conditions under which the Atlanto- herring were as follows:— Scandian and Minch spring spawners spawn are quite different. The Atlanto-Scandian group, of which the 1. A mean vertebral number of 57 or more, Norwegian spring spawners are the main component, 2. A relatively fast growth-rate, and spawn in conditions of relatively low temperature 3. A spawning period during the early months of (5—6° C.) and salinity 33°/
B. The Minch Autumn Spawners 1. Spaw ning grounds herring larval surveys carried out on the west coast of The location of the main spawning centres of the Scotland (B a x t e r , 1954) indicate that autumn spawn Minch autumn spawning herring has presented some ing in the Minch is spread over a wide area extending difficulties. There is no fishery in the autumn for from the B utt of Lewis to the Island of Mull. spawning herring such as occurs along the mainland Centres of high density of newly hatched larvae coast in the spring. were obtained in the following regions (Fig. 5):— From Table 10, in which the maturities of Minch 1. On the south and west coasts of the Island of samples between June and September are given, the Mull. development of the gonads of the autumn spawners 2. On the north coast of Skye in the same region can be followed from stage II in June to stages IV as spawning herring were taken in 1955. and V in August, while in September spents and 3. Off the B utt of Lewis. recovering spents appear in the catches in large 4. On the mainland coast in the vicinity of the numbers. Herring in stage VI are conspicuously few Islands of Handa and Bulgie. in number throughout the Minch during this period. It would appear therefore that the majority of autumn Spawning appeared to take place earlier in the spawners leave the fishing ground for spawning be north than in the south and the period of spawning tween the stages IV and V. The results, however, of extended from August to the beginning of October. — 89 — 11,11
Table 10 Percentage maturities of samples from Minch Numbei 11 IV V VI VII VII-II Stage.. . I III fish Year June Lewis Grounds 1953 13-7 69-2 3-4 1-6 0 0 0-2 11-9 445 1954 32-5 46-5 1-0 0 0 0 0 0 200 1955 8-0 46-7 3-5 2-0 1-0 0 0 38-7 199 Mainland Grounds 1954 43-3 431 3-8 0-3 0-5 0 0 8-8 444 1955 8-7 49-3 2-0 1-0 1-0 0 0 38-7 150
July Lewis Grounds 1953 14-8 52-2 17-0 6-8 8-4 0 0 0-9 454 1954 36-5 43-7 8-7 3-9 6-3 0 0 0-9 460 1955 8-5 45-0 22-0 13-6 7-3 0-7 0 2-9 449 Mainland Grounds 1952 19-2 323 13-6 17-7 11-6 0 0 5-6 243 1955 0 24-0 20-0 20-0 320 2-0 0 2-0 50
August Lewis Grounds 1952 21-7 27-3 20-8 16-9 8-7 0 1-3 4-5 231 1953 28-7 12-0 16-2 27-6 14-1 0 0 1-6 192 1954 23-1 14-5 10-2 22-6 24-5 3-8 0-2 1-0 420 1955 8-7 17-3 24-9 25-1 11-5 10-0 0-4 2-2 550 Mainland Grounds 1953 10-4 19-8 11-4 11-9 19-8 1-0 11-4 14-4 202
September Lewis Grounds 1951 0-9 0 0-5 0-9 1-4 0 9tt-4 0 220 1952 17-0 11-2 24-5 10-7 2-0 0 14-2 200 736 1953 33-3 12-4 8-7 8-1 4-3 0-4 17-6 15-1 700 1954 21-9 17-3 5-4 3-4 1-4 0 20-5 301 498 1955 23-9 18-8 4-0 8-0 2-3 8-0 7-5 28-3 400 Barra Grounds 1954 22-0 12-4 7-2 4-0 1-6 0 42-4 10-4 250
2. Race characters of Minch autumn spawners distinguish the Minch autumn spawners from other (a) Vertebral numbers. neighbouring autumn spawning groups. In establishing the race characters of any stock the normal practice is to begin with the characters (b) Length of formation of first winter-ring (lj). of spawning herring and to use this standard as a The distributions of ix’s for different age-groups comparison for the groups in the pre-spawning and during 1954 and 1955, given in Table 12, show that post-spawning stages. Unfortunately in the Minch we the values obtained were spread over a considerable are limited to one sample of spawning herring which range from 7—19 cm., although the majority of was obtained by a ring-net vessel working off the observations lay between the 11 and 15 cm. groups. north coast of Skye on 30. August 1955. The mean The modes occurred mainly in the 13 and 14 cm. vertebral number of this sample was 56-45 which is groups. The 1952 brood appearing as 2-ringed fish very similar to the values given for neighbouring in 1955 had a mode of 15 cm. Greater variation in autumn spawning stocks. W ood (1936) found that the distribution of Z/s was noticeable in the older the mean vertebral count of Minch autumn spawning age-groups, suggesting that although the new recruits herring ranged from 56-42—56-48, while for Shetland to the stock might be derived from one nursery area, he gives 56-36—56-51 and for the Scottish north-east the older fish may have been derived from two or coast fishery 56-40—56-45. H sü e h (1939) working on more nursery areas. the race characters of the Manx autumn spawners A comparison of the lx material from the Minch and obtained means ranging from 56-38—56-54. The dis from the Scottish east coast autumn spawners given tribution of vertebrae and means of the main groups, in Table 13 shows that the Minch autumn spawning from samples of autumn spawners taken throughout herring have lower modes and means for the same the year, are given in Table 11. age-group and this is particularly noticeable in the It will be seen that the mean vertebral numbers younger age-groups where the modes differ by as ranged between 56-40 and 56-52. It is clear, therefore, much as 2 cm. that the distribution of vertebrae and the mean The distribution of l^s of the Kessock halfhn herring vertebral number cannot be used as a character to presented in Table 14 is more similar to the Minch lx — 90 —
Table 11 Distribution of vertebrae (°/0) of Minch autumn spawners 1953 Period...... April-June July-September October-December Year-class...... 1949 1950 1949 1950 1949 1950 1949 No. of rings...... 3 2 3 2 3 2 3 Vertebrae 59 ...... — 0-50 ———— 0-33 58 ...... 3-36 3-90 3-42 5-30 7-34 3-09 4-34 57 ...... 42-95 46-34 38-46 38-41 32-20 43-09 45-15 56 ...... 50-00 42-93 52-99 54-97 55-37 50-10 45-15 5 5 ...... 3-69 6-34 5-13 1-32 5-08 3-71 5-02 Total...... 298 205 117 151 177 485 299 Mean...... 56-46 56-49 56-40 56-48 56-42 56-46 56-50 1954 Period...... January-March April-June Julv-September October-December Year-class...... 1950 1949 1951 1950 1949 1951 1950 1949 1951 1950 1949 No. of rings...... 3 4 2 3 4 2 3 4 2 3 4 Vertebrae 59 ...... — — — — — 0-25 —— 0-20 —— 5 8 ...... 3-22 5-77 4-07 3-23 9-32 5-54 3-23 4-63 4-67 3-86 4-07 57 ...... 41-80 41-54 45-12 40-86 38-14 40-30 48-39 44-44 42-68 43-80 47-51 5 6 ...... 53-05 50-00 48-37 52-15 46-61 48-61 46-08 48-15 47-56 48-48 45-24 5 5 ...... 1-93 2-69 2-44 3-76 5-93 5-04 1-84 2-78 4-88 3-86 3-17 5 4 ...... — — — — 0-25 0-47 ——— — Total...... 311 260 246 186 118 397 217 108 492 363 221 Mean...... 56-46 56-50 56-51 56-44 56-50 56-47 56-52 56-51 56-48 56-48 56-52
Table 13 data than to the adult stock of autumn spawners of li distribution of Scottish east coast the Scottish north-east coast. H s ü e h (1939) found autumn spawners1) modes ranging between 10 and 13 cm. for different 1954 age-groups in the Manx herring. Year-class ...... 1951 1950 1949 cm. Rings. .. 2 3 4 3. Length composition In Table 15 the mean lengths are given for each 8 — 2 1 9 ...... 0 3 of the main age-groups of autumn spawners in the 1 0 — 2 11 Minch. The means obtained in the Scottish north 11 ...... 3 3 25 east coast fishery shown in Table 16 A (P a r r is h ) are 1 2...... 4 10 27 very similar. The data given by B o w er s (1955) for 1 3...... 16 19 35 the Manx autumn spawners (Table 16B), however, 1 4...... 21 27 32 show that the mean lengths at each group are con 1 5...... 23 27 36 sistently lower than both the Minch and Scottish east 16...... 16 23 25 17...... 19 14 11 coast autumn herring. 18...... 6 14 5 19...... 6 3 1 4. Age composition 2 0 1 1 In Figure 6 the age composition of the Minch T o tal...... 152 149 228 autumn spawners is given for the periods April to M ean...... 15-16 14-93 13-50 September and October to March. With the excep-
Table 14 li distribution of Kessock halflins1) Date Year-class cm. 7 8 9 10 11 12 13 14 15 16 17 18 Total Mean 20.11.51 . . 1949 _ 1 4 15 30 34 49 44 45 10 2 233 14-91 16.12.52 . . 1950 1 7 9 23 24 33 51 43 19 2 2 214 13-38 12.3.54 .... 1951 1 3 4 15 19 8 16 13 10 ——— 89 11-93 3.3.55 . .. 1952 —— 3 23 38 45 31 15 11 3 — 169 13-08 x) From P a r r i s h , personal communication. — 91 — 11,11
Table 12 h distribution of Minch autumn spawners 1954 Period...... April-June July-September October-December Year-class...... 1950 1949 1951 1950 1949 1951 1950 1949 1951 1950 1949 No. of rings...... 3 4 2 3 4 2 3 4 2 3 4 cm. 7 ...... — —— -- ————— 2 1 8 ...... — 1 1 4 1 — 1 — 1 6 _ 9 ...... 2 2 4 8 2 5 7 — 4 14 3 1 0 ...... 7 8 4 11 5 10 17 3 16 26 10 11 ...... 20 18 13 15 11 31 13 6 29 41 21 1 2 ...... 25 24 22 33 27 44 17 10 69 55 24 13 ...... 51 38 38 22 16 67 30 19 117 65 38 1 4 ...... 44 26 40 30 26 72 28 21 88 61 53 15 ...... 29 28 23 17 19 42 11 21 61 35 37 1 6 ...... 9 14 5 8 19 12 9 5 17 6 13 17 ...... 4 1 1 3 3 8 4 4 4 2 4 18 ...... 2 — 2 0 1 1 — 2 — — 19 ...... — —— 1 — — — —— — — Total...... 193 160 153 152 130 291 128 89 408 313 203 Mean...... 13-32 13-19 13-22 12-72 13-47 13-23 13-01 13-71 13-22 12-50 13-36
1955 Period...... January-March April-June July-September October-December Year-class...... 1951 1950 1949 1951 1950 1952 1951 1950 1952 1951 1950 No. of rings...... 3 4 5 3 4 2 3 4 2 3 4 cm. 7 ...... — 1 -—- — — — ————— 8 ...... 1 4 ——— 1 1 4 __ _ 2 9 ...... 3 21 3 3 1 3 13 8 1 4 6 1 0 ...... 5 36 16 7 3 9 29 11 4 10 12 11 ...... 16 31 13 21 8 16 49 12 9 10 11 12 ...... 35 27 26 28 9 27 82 13 9 41 12 1 3 ...... 56 43 33 38 10 29 86 11 18 43 15 1 4 ...... 47 45 43 33 9 41 79 11 23 34 13 15 ...... 19 36 33 20 14 51 40 12 24 27 7 16 ...... 9 6 15 3 8 26 13 3 17 6 4 17 ...... 2 7 2 1 5 10 2 2 8 3 4 18 ...... — — 1 — 2 7 1 0 4 3 2 19 ...... — ——— — 1 — 1 1 —— Total...... 193 257 185 155 69 221 395 88 118 181 88 Mean...... 13-11 12-45 13-30 12-92 12-77 13-90 12-71 11-90 14-16 13-09 12-56
tion of 1951 and the early part of 1952, the Minch autumn spawners of the Scottish north-east coast, but autumn spawners during 1951 to 1955 were composed was consistently higher at each age-group than the mainly of young fish with between 2 and 5 winter- values obtained by B o w er s (1954) for Manx autumn rings on their scales. A comparison of the age com spawners. The distribution of l^s and mean values positions in the two periods April to September and showed some differences from the Scottish north-east October to March shows that the age compositions of coast autumn spawners especially in the younger age- the summer and winter fisheries were fairly similar. groups, where modes and means were 1—2 cm. higher than those obtained in the Minch. The ix values for D iscussion the Kessock halflins, however, which are considered to provide some of the recruitment to the east coast The race characters of the Minch autumn spawners fishery, were more similar if somewhat lower than are similar to those obtained in neighbouring autumn those in the Minch. spawning stocks. The mean vertebral numbers range The results from tagging experiments in the Minch between 56-40 and 56-52 and therefore can’t be used during the period 1951— 55 have been disappointing as a character to distinguish the Minch autumn on account of the small number of returns. With the spawners from other stocks. The average length of exception of one herring which was tagged in the North each Minch age-group was similar to that of the Minch in August 1953 and recaptured on the Fladen — 92 —
APRIL-SEPTEMBER OCT O BER-MARCH Table 15 30 Mean lengths (cm.) of main age-groups of
20 Minch autumn spawners (Number of fish in brackets) January-March Year Rings.. . (2+)3 (3+)4 (4+)5 SO 1953 25-83 —— 4 0 1952 (310) 30 1954 25-29 26-82 — 20 (185) (199) 1955 25-26 26-72 27-85 10 (22 1 ) (304) (2 0 2 )
U April-June o 4 0 < 2 4 5 H Year Rings.. 3 z 3 0 I9S3 UJ 1953 24-23 26-07 —— \- U 20 (207) (1 2 0 ) ü. UJ IO 1954 24-11 25-84 27-37 — a (251) (194) (146) 1955 24-11 25-97 27-34 28-37 40 (46) (255) (96) (38) 3 0 1954 1954-1955 July-September 2 0 ’ Year Rings. 2 3 4 5 10’ 1953 25-27 26-87 —— (154) (183)
4 0 1954 24-81 26-68 28-15 — (419) (275) (124) 3 0 - 195 S 1955 OCT. DEC. 1955 25-00 26-79 27-96 28-87 20 (290) (479) (134) (61) October-December 2 J 4 5 6 7 a C l0*/0 .. 2 3 4 5 NO OF BINGS Year Rings. Figure 6 . Age composition of Minch autumn spawners. 1953 24-95 26-82 —— (504) (312) 1954 25-08 26-61 27-82 — (500) (381) (217) Ground in August 1954, all the other returns have 1955 25-36 27-23 28-02 28-80 been from the Minch itself. Such results as have been (134) (217) (102 ) (82) obtained suggest that there is a free interchange between the North and South Minch. A recapture in the Minch which is of special interest, was of a herring tagged off Peterhead in August 1954 and recaptured In early spring there appears to be a movement of in the North Minch in November of the same year. adult herring out of the Minch, since the concentra It would appear, therefore, that some interchange tions of herring are small during April and May. This may take place between the autumn spawners of the is probably a feeding migration and it is of importance Minch and the North Sea. to note that particularly high concentrations of Cala- The fishery for autumn spawners in the Minch is nus are found west of Orkney and also between unique for Scottish waters since it is in progress almost Barra Head and the north coast of Ireland during continuously throughout the year. The fishery, how this period (G ib b o n s , 1936). This spring emigration ever, is most productive between November and is followed in the summer by an immigration of some March when the total landings and catch per landing adult autumn spawners into the Minch. These herring are higher than in other months. The summer fishery appear to spawn in the Minch during the autumn. is dependent to a large extent on the size of the new The further increased productivity of the fishery, recruit brood coming into the stock. This fact was which takes place during the late autumn and winter demonstrated between 1951 and 1955 when in the months, suggests that the autumn spawning units three years of good recruitment, between 1952 and which are already in the Minch have been augmented 1954, the summer fishery was most productive, while by representatives of another autumn spawning group in 1951 and 1955 the recruitment was poor and also or groups which may not spawn in the Minch but the summer fishery. spend the winter there as recovering spents. - 93 - II, 11
Table 16 A Table 16 B Mean lengths (cm.) of main age-groups of Mean lengths (cm.) of main age-groups of Scottish east coast autumn spawners1) M anx autumn spawners (Number of fish in bra Year Rings... 2 3 4 5 May-September 1954 June...... 23-24 24-46 26-08 _ Year Rings... 2 3 4 5 (71) (6 8 ) (18) 1953 ...... 24-54 26-37 27-00 28-09 Ju ly ...... 34-33 25-48 26-38 27-35 (2,974) (2,167) (609) (515) (104) (123) (55) (33) 1954...... 24-69 26-92 28-12 28-71 August...... 24-39 25-81 27-02 27-68 (3,700) (1,438) (1,013) (325) (104) (162) (66 ) (35) 1955 ...... 24-18 26-81 28-68 29-34 September.... 24-14 25-87 26-96 27-89 (2,842) (863) (332) (305) (113) (83) (47) (2 1 ) 1) From P a r r i s h , personal communication. characters of each group are described and compared Conclusions with those of neighbouring stocks of spring and The data presented in this paper indicate that the autumn spawners. Minch spring spawning herring have certain meristic It was found that the mean vertebral number of and behaviour characteristics which distinguish them the Atlanto-Scandian group was consistently higher from the Atlanto-Scandian spring spawners. It is, than that of the Minch spring spawners and that the therefore, considered that Le G a l l ’s subdivision of Atlanto-Scandian group spawn in conditions of lower the spring spawning herring of the North Atlantic temperature and salinity. into Atlanto-Scandian and Hiberno-Calédoniens Le G a l l ’s subdivision of the spring spawning her groups is sound. ring of the North Atlantic into Atlanto-Scandian and It is suggested that the autumn spawners fished Hiberno-Calédoniens groups is considered sound. in the Minch are members of more than one group The racial characters of the Minch autumn spawners and these groups are broadly defined as follows:— are similar to those of neighbouring autumn spawning stocks. It appears that in early spring there is a (a) A local group which is present in the Minch movement of adult autumn spawners out of the during all or most of the year and which spawns Minch and that during the summer some of these there. return and spawn there. In November this stock is (b) A group (or groups) which does (do) not spawn augmented by representatives of another group or in the Minch but which spends the winter there groups of autumn spawners which probably do not as recovering spents. spawn in the Minch but spend the winter there as recovering spents. Tagging results indicate that there is some interchange of autumn spawners between the S um m ary Minch and the North Sea. Herring fishing in the Minch is in progress almost It is suggested therefore that the autumn spawners continuously throughout the year but there are two fished in the Minch are members of more than one main periods of high activity; November to March group and these groups are broadly defined as follows :•— and June to September. The late autumn and winter (a) A local group which is present in the Minch during fisheries are generally more productive than the all or most of the year and which spawns there. summer fishery. (b) A group (or groups) which does (do) not spawn The Minch herring population is composed of a in the Minch but which spends the winter there mixture of spring and autumn spawners. The racial as recovering spents.
R eferences
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L ea , E., 1910. “On the methods used in herring investiga Schnakenbeck , W., 1927. “ Rassenuntersuchungen am tions”. Publ. Circ. Cons. Explor. Mer, 53. Hering”. Ber. Dtsch. Komm. Meeresforsch., 3 (2): 95— Le Ga ll, J., 1935. “Le hareng Clupea harengus L in n é . 205. 1. Les populations de l’Atlantique Nord-Est”. Ann. Sto r r o w , B., 1923—40. “ Herring investigations”. Rep. Inst. Océanogr., 15, 215 pp. Dove Mar. Lab., 1923—40. L iss n e r , H., 1934. “On the races of herring”. J. Cons. W o o d, H., 1923. “Observations on the Scottish summer Int. Explor. Mer, 9 (3): 346—64. herring fishing of 1922”. Sei. Invest. Fish. Scot., 1923, P a r r ish , B. B., & S har m a n , D. P., 1956. “Some remarks 2, 42 pp. on objects and methods used in herring “racial” investi — 1930. “Scottish herring shoals: pre-spawning and gations with special reference to otolith studies”. This spawning movements”. Ibid., 1930, 1, 71 pp. volume, p. 66. 1936. “ Race investigations of the herring population R u n n str ö m , S., 1941a. “ Racial analysis of herring in of Scottish waters”. Ibid., 1936, 3, 52 pp. Norwegian waters”. Fiskeridir. Skr., 6 (7) 110 pp. 1937. “Movements of herring in the northern North 1941b. “Quantitative investigations on herring spawn Sea”. Ibid., 1937, 3, 49 pp. ing and its yearly fluctuations at west coast of Norway”. — 1951. “Observations on the value of in herring in Ibid., 6 (8 ) 71 pp. vestigations”. Rapp, et Proc.-Verb., 128 (1): 39—46.