.. International Council for the C M. 1964 , Exploration of the Sea Herring Committee att. Plankton Cornmittee No. 59
Herring-zooplankton relationships in the northern North Sea 1961-64 By James A. Adams
Introduction
In September 1960 the Marine Laboratory at Aberdeen started to collect data on the standing crop of zooplankton (dry weight) in the northern North Sea, to supplement the Laboratory's general plankton surveys (Fraser 1948-63), and the Plankton Recorder and Plankton Indicator surveys of the Oceanographic Laboratory at Edinburgh (Glover 1962, Glover et al. 1956, Glover 1957, Glover et al. 1961, Williamson 1961). The Laboratory has also obtained zooplankton standing crop data in continuation of the Laboratory's study of the environment of the herring fishery in the north eantern North Sea (Steele 1961). These latter surveys will be e referred to as the "Norwegian Deeps" surveys. This paper presents a preliminary review of some of the data with special e reference to herring-zooplankton relationships during the months of March to June for the period 1961-64. Zooplankton standing crop data from the Norwegian Deeps surveys in March and April 1961 have been incorporated with the data from the general surveys of the northern Iforth Sea. The data from the 1962, 1963 and 1964 Norwegian Deeps surveys are treated separately.
The author winhes to thank Dr. J. H. Steele and Mr. G. McPherson for thoir help in the preparation of this paper.
Methods
All zooplankton namplcs have been obtained with the Gulf 111 high speed sampIer fitted with a net of mean mesh nize 0.23 mm (60 meshes to the linear inch) and to~~d obliquely from near bottom to surface. The dates of the zooplankton surveys considered here are:-
Northern North Sea and Norwegian Deeps 2-17 March 1961 •e Northern North Sea and Norwegian Deeps 30 March - 20 April 1961 Northern North Sea 14-25 June 1961
Norwegian Deeps 2-15 May 1962
Northern North Sea 7-23 June 1962
Norwcgian Doepn 26 April - 7 May 1963
Northern North Sea 24 May - 10 Junc 1963
Norwegian Deops 23 April - 7 1~y 1964 The northern North Sea survey of May-JunG 1963 has been considcred representative of JunG an the general pattern of distribution and dry wcight changes but little during the months of May and June - see for example Figures 4 and 6. Further details are given by Adams (1963). Charts cf the distribution of herring have been based on three sources i) monthly charts cf the average catch in crans per 100 nets per shot per 10 mile square far the Scottish drift-net fishery, ii) ICES Statistical News Letters Nos 14 and 17 for other European herring fisheries and iii) echo-surveys by l".R S. "Scotia". - <:: -
RGsults und Discussion
Aseries of charts of zooplankton and herring distributions are shown in Figures 1-7. Chart A in each figure shows the zooplankton standing crop in g dry weight/100m3 Chart B in Figures 2-5 shows the distribution of catches by the Scottish drift-net fisher,y and in Figures 1, 6 and 7 the distribution of echo-traces. Chart C in Figures 1-4 shows the distribution of catches by se1ected continental herring fisheries, those fisheries selected being the ones best represented in the area in the months considered. Further details are given in the figure legends.
Figure 1 shows conditions similar to those found by Steele (1961) during the period before the west'ward diffusion of the "Baltic" type water. The relatively high zooplankton standing crop was large1y within the area of the Baltic outflow (western edge shov.n by the 6°C isotherm) and Figure 1B shows the importance of the euphausiid Meganyctiphunes norvegica (M. Sars) in determining this distribution. The echo-survoy \~s confined to the area east of 3°E, but both the distribution of traces and the yield of the Dutch trawl fishery, suggest that the herring wcrc concentrated along the edge of the Baltic outf1ow. Steele (1961) has postulated' that these features are duo to the herring sceking the area of high zJoplankton but also avoiding the water of the Baltic outf1ow.
By April (Fig. 2) the zooplankton standing crop had incrcased over a large area and the herring were largely concentrated within the area of zooplankton groater than 3 g dr,y wcight/100m.5.
e Figures 3-5 show, firstly the further westward movement of the herring, and secondly, that the marked variations in the main centres of the summer herring fisher,y of 1961, 1962 and 1963 were closely related to changes in the distribution • of the zooplankton in the three years. Exact correlations are ho~~ver limited by the intensity of the zooplankton sampling. Parrish et al (1963) have sho~ that the dominant yoar class north of 59°N in June 1961 ~ns that spa~ed in autumn 1956 (5-year old) while south of 59°N 3-, 4-, and 5- year fish were almost equally represented. Figure 3 B-C shows that the fishery south of 59°N was divided into two parts. Unpublished data at the Marine Laboratory show that the three year old autumn spawned fish (1958 year class) were present in greatest numbers in the southern part (57, 671 fish per 100 nets per shot) While in the northern part their abundanco ranged from 544 to 1,776 fish per 100 nets per shot, 4- and 5- yoar old fish being more abundant in this area.
Saville et al. (in press) havo shovm that in the north western North Sea in Juno 1962, 6-year old fish (1956-57 yaar class) formcd 46% of tho catches north of 59°N while south of 59°N 3-yoar old fish (195~/60year class) formcd 3~ und 5-year old fish 28%. In the north aastom North Soa 4-ycar old fish formed 27% and 6-year old fish 31%. Unpublished data show that cast of leE and south of 59°30'N 3-ycar old autumn spawnod fieh were present at an abundanco of 509 to 5127 fish per 100 nots • \~st per shot, whilo of leE and north of 58°30'N they variod from zero to 5140 fish. Thus both in 1961 and 1962 thc rccruit component to the herring stocks werc scarcc • in the Buchan area but wero more abundant on thc southern, castern and northern boundaries of the Buchan grounds. 1962 was also characterised by a productive fishary in the north eastorn North Sca during thc summer and autUFn in which Scottish drifters participatcd (Savillc et al. in press). It appears that the herring did not leavc their overwintcring grounds, at least in thc southern part of thoir range, a suggestion which is supported by tho close agreement betwccn the southern hcrring conccntrations shown in Figure 6B and the southcrn arca of above average catchcs in Figure 4B. 1963 (Fig. 5) offers a markod contrast. Saville et al. (in press) have sho~n that in tho area north of 59°N during Juno 3- yenr old fish (1960-61 yoar class) formcd 61.3% of thc catch, while south of 59°N they formcd 96.a.1o of the catch. The Scottish fishcr,y showod two main centres (Fig. 5B) v.hich can be regarded as that based on Shetland and that based on the Buchan ports. Howcver the gap does correspond with an nrea of low zooplankton, but until tho continental data are available it is difficu1t to assess this relationship. From an examinntion of thc zooplankton and herring data it seems that thc poor Buchan fishery in 1961 and 1962 was associntcd both with a low level of recruitrr.ent (Parrish et al. 1962, Parrish and Saville 1963) und low zooplankton standing crop off the north cast coast of Scotland which kept thc emaIl stock of recruits off the Buchan grounds. In contrast 1963, with strang rccruitmcnt (Parrish and Savillo 1964) and good plankton conditions over thc Buchan grounds rosultcd in a succcssful drift-net fishcry. - 3 -
The Norwegian Deeps Surveys 1962-64
Thü result of the surveys in 1962 und 1963 are shown in Figures 6 and 7. The greater intensity of sampling (151 Gulf 111 samples in 1962, 73 in 1963) allows more detailed charts to be prepared.
It is obvious that the main herring concentrations (as suggested by echo-traces) do not correspond with the centres of high standing crop () 3 g dry weight/100m3) but are either found in areas of low zooplankton o~ on the edge of the areas of high zJoplankton. This is in contrast with conditions in the Norwegian Doeps in April 1961 when the herring concentrations were largely within the areas of high zooplankton (Fig. 2 and unpublished echo-truces). Prelioinary results of the 1964 survey (23 April 7 1fuy) show that the zooplankton standing crop was similar to that in 2-15 r~ay 1962, and aS in 1962 and 1963 the echo-survey showed the herring concentrations to be outside or on the edges of the areas of high zooplankton.
Steele (1961) found that in 1959 there was a southerly flow of water of recent "Atlantic" origin across the area surveyed end that there was a "suggestion that the fish generally remained at either the surface or subsurface boundaries of the inflow of wanD. saline Atlantic water".
In April-1fuy 1963 a tongue of ~nter of temperatures greater than 7°C (Fig. 7) ald, at its oentre, of salinities greater than 35.3.%0 was observed. The herring traces e suggest that, as in 1959, the herring were concentrated along its boundaries. (Although the water tomperature was lowcr than that usod by Steel0 (1961) to donote the Atlantic wator - SoC - tho Indigonous North Sea water also showed lowor tomperatures • in 1963 - 5-6°c compared with 6-7°C. Tho salinities wore however normal). No indications of Atlantic ~TItor were found during 2-15 May 1962. During 23 April 7 1~, 1964 thoro itaS ovidonce of a narro~ tongue of Atlantic water centred on 3°E, but so narrow to have no markod offect on the distribution of tho horring truces.
Summary
Zooplankton standing crop data (dry weight) collected during the poriod 1961-1964 in the northern North Sea is roviewod with special referonce to herring-zooplankton relationships.
In March 1961 the areas of relatively high zooplankton standing crop (~l g dry weight/lOOm3) were inside the Baltic outflo~~ the herring were concontrated along its western edge. The survey in April 1961 showed an incrcase of the zooP3ankton, and to the west of the Baltic outflow values greater than 3 g dry weight/100m were recordcd• • The herring ~uro concentrated within the area of high zooplankton. An examination of the zooplankton and herring data for June in 1961, 1962, and • 1963 shows that the poor s~~er fishery on tho Buchan grounds during 1961 and 1962 ~ns due to low recruitmont of 3-yoar old fish ~hich was associated vdth a low zooplankton standing crop. In 1963 good recruitmont, associated with high zooplankton standing crop on the Buchan grounds gave a successful fiShery. There are strong indications that in 1962 the herring remained in the overwintering aroas, at least in the southern part of their range.
Detailed surveys of the "Norwogian Deeps" area in April-May 1962, 1963 and 1964 showed that the main horring concentrations were outside or on the margins of tho areas of high zooplankton. In 1963 the herring were located on the boundary of an inflow of Atlantic water. - 4 -
Referenees
Adams, J. A. 1963 "The standing crop of zooplankton". Ann. biol., Copenh., 18 (1961), 69 pp.
FraGer, J. H. 1948-63 "(Scottish plankton investigations from Aberdeon)" Ann. biol., Coponh., 2.. - 18 (1946-61)
Glover, R. S. 1957 "An üeological survey of the drift-net herring fishery off the North-East eoast of Scotland • Part II.The Planktonie environment of tho herring"• Bull. mar. Ecol., ,2: 1-43.
Glover, R. S. 1962 'The eontinuous Plankton Recorder" Rapp. Cons Explor, Mer, 153: 8-15.
Glover, R.S. 1956 "An oeologieal survey of the drift-net Cooper, G. A. & herring fisher,y off the North-East eoast of Brown, VI. W. Seotland. Part 1. On sampling by the e eommereial fishing fleet". Bull. mar• Eeol., A.: 141-78. • Glover, R. S. 1961 '~n eeologieal survey of a Seottish herring Cooper, G.A. & fishery. Part 111. Geographieal and Forsyth, D. C. T. eeologieal groups in tho plankton". BuH mare Eeol., ,2: 195-229.
Parrish, 13.13. & Savillo, A. 1963 "Foroeast for Seottish North Soa and ''("est Coast horring fisheries in 1963". Seot. Fish. Bull., No. 19: 3-5.
Parrish, B. B. & "Forecast for SeottiGh North Soa and 'Wost Saville, A. Coast horring fisheries in 1964". Seot. Fish. Bull. \ No. 21: 3-5.
Parrish, 13.13 . 1962 "ReGults of Scottish herring fishories in Savillü, A. & 1961 and prospeets for 1962". Seot. Fish. • Baxter, 1. G• Bull , No. 17: 3-12. Parrish, B. B. "Seottish FiGheries, 1961". Ann. biol., • Saville, A. Copenh., 18 (1961): 158-69. Baxter, 1. G. & Mcphürson, G.
Saville, .b.. In press "Scottish Fisheries, 1962". Ann. biol., McPherson, G. & Copenh., 1.2. (1962 ). Parrish, 13.13.
Saville, A. In prass "Seottish Fisheries, 1963". Ann. bio!., MePherson, G. & Copenh., 20 (1963). Parrish, B. B.
Steel0, J. H. 1961 "The environment of a horring fishery". Mar. Res. Seot. 1961 No. 6, 19 pp. Williamson, M. H. 1961 "An eeological survey of a Seottish herring fishery. Part rv. Changes in tho plankton during the poriod 1949 to 1959". Bull. mare Eeol., ,2: 207-29 - 5 -
Figure Legends
. CHART A. Figures 1-7 Zocpl~nktcn S~nding Crcp.
3 > 5 g dry woight/100 m ~~=l 1-3 11 11 11 11 ....-.- ...... -.' .. , .' CHART B. Figure 1 I!ß > 30 Me~anyctipho.nes ncrvegico./10o m3 + lIp1ume ll trace on echo-s cunder reccrd I lItick" tr~ces cn echo-scundcr reccrd Figures 2-5. Scottish drift-net fishery e Above avoro.ge yie1d • Be10w o.verago·yio1d Zero yie1d Figures 6-7 Norwegio.n Doop Surveys IItickll tro.cos cn echo-sounder rocord lI p1umo" tro.cGs cn echc-scunder record CHART C. Figure 1 Abcvo o.vero.ge yie1d Dutch herring tr~w1 Figure 2,• • Above ~verage yie1d Germo.n Lugger tr~w1 • 11 " 11 Po1ish Sto~m tro.w1 Figures 3-4 Above average yie1d Gormo.n Luggor tr~w1 11 " 11 Germo.n Lugger drift-nets Figures 1-4 ~. Other ~ro~s fished. - 6 - Chart B •e ~~? Coort C a 0 0 e Q 58 - ~ " C Cl " :j ~""'A » MI\R~H lq~l H"; 1_ "Pi po11r8 2, APRTT. 1 ~61 2° I A •• B •• o o o 8 o c o o c c o o \\ JUNE 1961 Figura (~cr exnlanntion cf fie:uros SOO DCU!O 5) \ ee 4 '. CD I 9° B 5 o Fi~uro 6. 2-15 MAY 1962 Figure 7. 26 APRIL - 7 lJAY 1963 B Fi~ure 5. (for explanation cf Figuros sec page 5)