CM_1999_M_03.pdf (690.3Kb)

International Council for the Exploration of the Sea

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Oceans at Micro- to Mesoscales

INFT~lTENCF

OF

SEA TFMPEKI\TURE ON HERPJNG DISTPJBUTION ANV MIGRAnON IN THE NORWEGIAN SEA IN A PRJL 1997

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... .1\fter spa\vning at the \vest coast of l'~or.;;ay, the }.J"orwegian spring spawuing herring migrates nort .. lnxlest\¹/ards into t..l:te Norwegi~"1 Sea to feed in earl y April. The herring enters area.s with

the warrn Atlantic water and t..he cold .Arctic \¹/ater. The .. A"'tla..Tl.tic \vater enters t.~e central Norwegian Sea by mea.ns of the outer br~nch of the No!'Negian ... L\.tlantic ~urrent which n:ms northeastwards and further north- and nort..hwestwards from t..l:te Faroe Islands as ., a.?J unstable frontal jet.

To investigate the influence of sea temoerature on the distribution and mhrration of ^{- ~ _ Q} _ _ _ _ _ _ _ _ - ----o• herrin<>

we performeå two synoptic transects with the research vessels RJV "G.O. Sars" and RJV

"Håkon Mosby" in Aprill997. The RIV ''G.O. Sars" recorded the herring distribution by echo integtation, tracked selected schools by sonar and took samples by pelagic trawl. while RJV

"Håkon Mosby" canied out continuous sea temperature and saiinity recordings of the transects by operating a SeaSoar vehicle, undulating from sea surface to 300 m depth.

The relations bet:w~een sea temperatwe, herring distribution and migratio~S horizontaUy and vertically are studied by combining U'le synoptic recordings from the iwo research vessels.

i

LeifNøttestadi, Ole _Misund, and Bente Hoddevik,· Institute of Marine Research, P, O Box 1870, N-5817 Bergen, Norway (tel: +47 55 23 85 OO,fax: +47 55 23 68 30, e-mail:

[email protected]). ²Kjell Arild Orvik: Geophysical Institute, University of Bergen,

Alli~gaten 70, N-5007 Bergen, Norway

Introduction

The polar front between warm Atlantic water and cold Arctic water is characterised by a sharp decline in temperature together with high concentrations of zooplankton (Blindheim 1989).

We presume the front offers profitable foraging on zooplankton for actively feeding herring that are highly motivated by hunger proceeding the non-feeding periods of overwintering and spawning (Nøttestad et al. i996, Femo et al. 1998, Slotte 1999). The relationship between herring distribution and temperature is likely to be indirect, possibly through effects on biological production. There is generally higher concentrations of phyto- and zooplankton in frontal areas ('vviborg 1955; Mann and Lazier 1991), and this will attract pelagic fish to such productive areas (Skjolda! et al., 1993; N1eHe ei al., 1994).

The rn.igration of the matu..-e heu~ng a.a.~er the spawT.ting season are generally downstream in the direction of the CU.L""Tent, and the stock appears to be contained wit..L..in the t-.lorwegian Sea gyral (Harden Jones, 1968). RunnstrOm (1936) and Fredt"'iksson (1944) suggested that the herring keep \Vit.h..in the cyclonic cu..."Tent system of the :Non.vegian Sea, thus lirr.Jting t.lte horizontal temperature ra11ge herring \Vill experience during L'le feeding 1rJgration. HeiT.~.~.~g in the Norwegian Sea are ~lso !"-nown to perform substa..'ltial seasonal va..riations in vertical disLribution (Devold 1963; Nøttest~d 1999), influencing the herring's vertical temperature range (Misund et ~l, 1997a)~

After spawning at the banks of the Norwegian coast in February- March, most of the spent herring in recent years migrate out in the Norwegian Sea through a corridor between 67°N and 68°N (Mjsund et al., 1998) ... .r\dult herring follo\v the plankton bloom north\vest\-vards in order to feed on th.e spawning concentrations of zoopla",kton (Pavshtiks, 1959; Østvedt, 1965;

~1elle et al., 1994). In .. .o\pril, herring S\vim \VeSt\vards into L~e polar front areas between the 'va..rm A •. tla.11tic 'vater and t..l)e cold i~Jctic \Vater (lv:!isund et al., 1997a). Smaller fish do not move so far to the nort~J, a.'ld \¹/est during t..l:te feeding season as compa..~d to larger fish (} ... 1a.."'ty and Wilson 1960, Nøttestad et al., in press). Recent investigations on herring distribution in relation to temperatnre have suggested that he-rring do not mo ve into co l der 'Hater than approximately 2°C (Misund et ::.l., 1997a; 1998), and herring has not been observed to cross the polar front du..ri~T'lg t.he feeding lT'igration after the stock collapse in the late 1960's (Røttingen 1989; 1992; Dragesund et al., !997; Misund et al., 1997b; Vilhjhlmsson et al., 1997). In the sixties7 on the other hand~ berting were found feeding along the cold front east of Iceland, but passed throug_h the front containing sea temperatnres below 2°C and entered the feeding ::.reas nort..h of Iceland in earl y June (Østvedt 1965). The present cruise was part of the ICES coordinated su_rvey activity on Norwegian spring spawning herring a.T'ld the

environment in the Norwegian Sea that have been established between EU, the Faroes, lceland, Norway and Russia (Anon 1997b).

The spring movements of the herring may be governed by the seasonal changes in the

production and distribution of their food (Femti et al., 1998). Biological spring spreads north and nonh-west across the Norwegian Sea aiong the line of the branches of the Atlantic

current. Pavshtiks (1959) suggested that the larger herring move from region to region feeding heaviily on ihe pre-spawning concentrations of Calanus ;1nmarchicus to reach the polar front at the time of bioiogicai spring when Ca! anus hyperboreus is abundant in the cold water.

3

Thus, temperatnre preferences con..11ected to food concentration a.11d dist..ribution are believed to gi ve useful information a...nd k_nowledge on herring rlistribution (see also Maravelias and Reed 1995). The problem is aJthough complex 11.nd a simple interpretation does not seem applicable, because the nature of the migratory mechanism is not fully understood (Harden Jones 1968; Femo et al., 1998).

The purpose of this cruise was primarilv to studv the relationshio between the ohvsical and

- - ~ - ~ ... . & . " "

bioiogical environment and the rnigration behaviour of herring schools in the Norwegian Sea This fieid work aimed to gi ve a synoptic view of herring distribution and rnigration in relation io temperature åistribution using a SeaSoar undulating sensor. Two research vessels were used, RIV "G.O.Sars" and RIV "Håkon Mosby", and the spatio-temporal temperature prot1les _{- - -} were linked to 3-D recordings of herring schools based on echosounder and sonar

observations. This is one of the frrst studies attempting to iink herring distribution to

temperatwe profiles on Ui.e sat-ne spatio-teu1poral scale (micro-to meso-scale) (Levin, 1992;

... Material and J~et!:ods

herring, we performed two synoptic t..ransects (Figure l) \Vit.~ t..l-te research vessels HIV "G.O.

Sars" and RN "Håkon Mosby" in April1997 (Figure 2). Contl11ous acoustic recordings of fish and plankton were m11de onboard RIV "G.O.Sars" from 6-22 April !997 by a calibrated echo integration unit consisting of a 38 kHz Sim....rad EK500 wor!dng at a range of 0-500 m.

The integration unit was connected to a Bergen Echo Integrator (BEI) for postprocessing of the recordings and allocation of area backscattering strengths (s,J to species. The sA-

recordings per nautical Ir...ile \Vere averaged over five nautical IP...iles. The echo sounder \Vas operated ':vith the follo\x;ing settings: ma"<. po\ver: 4000 W, time varied gain: 20 logR, pulse lengt ... IJ.: l n1s, bandwidth: wide, angle sensitivity: 21.9, 2-\vay bea.tn angle: -21.0 rrR, Sv

transducer g~l11: 25.0 iiR,TS tra..T'!.sducer g!:l;n: 24.9 dB, 3 dB bea..rnwidth: 7.0 eiR (A_non 1997a).

A 95 k...Hz Si!!l..rad SA950 sonar w~~ used to record schools near surface at ara.Tlge of 50-300 m to the side of the vessel, and to track selected schools in the smvey ørea for a period of up to one hour each. The sonar was operated with the following settings; TX power: ma_x, ra..nge:

300m, pulse: FM auto, gain: 9, display gain: 9, TVG: 30 log R, AGC: weak, Normalization:

weak, Ping-to ping filter: weak. The sonar is connected to a HP 9000 work station with software for detection and measurements of schools. This school detection system was operated with the following settings; minimum range; 50 m, maximum range: 300 m, colour detection threshoid. 15, detection radius: 30 ro, minimum gap: 5 m, minimum width: 5 m, minimum interval: 5 m, minimum detection pings: 4 (Anon l997a).

The aim of school tracking was to obiain information about the dynamic behaviour of herring dw.-=.lllg their feeding wig.tation in the l'~orwegian Sea. A differential geographicai posistioning system ( dGPS) was applied for precise positioning of the tracked schools. In addition to depth, direction and speed of rr..igration and the search path of schools in different areas, the school dynamics was studied by recording intra- and interschool events observed on U1.e sonar screen on sheets a..Yld video=tapes for later analyses (Pitcher et al., 1996; ~,.1ackinson et al., (in press)). The school detection progra..-rn calculated nun1ber, area and relative densit'=J of schools . Trawl stations by use of the P.J<Ja-trawl

.

\'ifit.lt a vertJcal ope:ning of about 30m \Vere taken to

identify the species. At each trawl station CTD a..Tld MOCNESS stations \x;ere also taken to enable us to relate herring behaviour to t.he !ocal physic!:~l a.Tld biologic::~l environ..T!lent.

5

SeaSoar survey

FJV "Håkon Mosby" conducted continous environmenta! recordings applying a SeaSoar CTD l ADC'P v"hide~ ADC'P w".< nmnin" continon<lv with 'i min "v"'"""" intP.rv"l ""d <om"

· - - - - ---· - - - - - - - - o - - - - - - - - J · · - - - o - - - - - - - - -

varvino- cmi<ino- sneed --.~---c---c-.c:---"_---_,---(4-5 knots)~ SeaSoar wa< n<erl hetwe"n the <nrf""" rlown to 100m - - - - · - - - -

denth with 500 m - - . c · · - - - -cahle~ Transects were nerformerl - - - . c - - - · - - - · - - - -M t'il'l⁰10' N h"twP.P.n 1 °"\?''iR F.

""rl

.ASCII-files witb. acoustic data from th.e echosounder (BEI) \Vas imported to S"'A~S system for Windows, Release 6.12 for fiJrt..her analyses. Grap}-lical output on acoustic herring

registrations w~~ given:::.~ contour plot in AutoCft n LT 98, i\utoC.AD Release 14.

Temperature data from the SeaSoar sensor w::~~ also imported to SAS and an~lysed in

comoarison to the acoustic data. Geoo-raohical mans were desio-nerl in M"nTnfo ProfP.ssion"l .L ...., .._ ---.c- - - - ----.._.---r---- - - ,

Version 5.0.1.

Herring survey

For mapping åistribution, recording abundance and tracking selected herring schools, an area between 66"- 67" 30' N and 2" E-4" W was surveyed by a regular grid with 30 nautical mile spacing north-south (Figure l). In nine cases a proper herring sample was caught by the peiagic trawi. The herring in the area averaged 31.3 cm and 0.203 k_g. The herring catches

- - - -

contained more than 50% femaies. The weather conditions were rather bad during the

surveys, and we had wind stronger than 25 ms·' (Baufort force 6) for i2 of the 15 days at sea.

In three occations when the wind was aboui 45 ms~' (storm) we had to turn the vessel up against the waves and reduce the speed.

Results

Temperature distribution

In April 1997 there were considerable horizontal and vertical gradients in the sea temperature

within the study area, while herringwere mainly distributed between 1-5°C (Figures 3 & 4).

The herring made diurnai verticai rnigrations from between 300-400 m depth during the day io above 50-100 m during ihe nighi. T'ne iemperai:Ure range beiween the surface area and 400 m depih was up io 4°C in some areas. Distribution ofherring aiong the horizontai (east-west) transects at 66°30' N and 67"00' N showed that herring did not cross the 2"C isotherm.

However. tracked herring schools were sometimes observed in deep water masses below 2"C for shorter oeriods (Firure .L ' ...., 5). ~ The temoerature in the area surveved was charactf>ri:z"d hv a .L - - - - - - - . " - - - - - - - . " -

distinct front from east to west which bad its direction north - south at about O"~ At 50 m depth the temperature w~~ about 4° C at ~hout 0°, decreasing westwards aTJ.d increasing eastwards .... .1\.t 300 m depth the temperature "vas abcut 2° C at about

oo,

and similarly decreasing "vest\vards and increasing eastwards.

Herring distribution and migration

A total of 32 herring schools between 8-18 P. ... prlJ 1997 were tracked from about 20 to 65 tr..i..."l

in different positions wit..h..in the study area (Fi~.l!e 6). The schools \Vere distri.buted all over the snrvey area, and occured at depLhs from about 20m to about 350m. Gener~ l! y, the

schools were swimmin~< ...., at deoths from 150-350 m durin" davtime ~ - - - - - - - ---~ ---."~---- roR,00-1 .. - - - - - - - - , T 7 R·OO)~ aocf>nrl"d tn ----~--- - -

the surface during the evening, and descended during the night. Number of schools recorded on the echosounder within a distance of 5 nm varied between O and 13 distinct schools along the predetermined transects. After dawn the schools generally spread out el ose to surface to form ioose shoais with iow relative density, while reorganized into tight schools in the

7

moming. Schools recorded west of 0° occu..rred at greatest depths (Figtrre 5). The horizontal IPigration speed va..ried from 0,07 to l, 75 m s·^1• Schools S\Va..Tll faster the higher the prevailing sea temperatu..re in the range 1,43°C -6,24°C (r

=

^0,54, p< 0,05). Herring schools S\.Va..""U faster in \.V3.J.?Jner 3.J."1d shallower water masses th&.• deeper down in the water colurnn, \Vhereas no significant differences were found ber...veen school area and temperatun~. Smaller schools

S\Va..lJl faster th.a...Tl larger schools, although no significant differences were found ( r = 0.34, p >

0,05). Most schools headed in a south\-vestern direction, especially those schools swiiThT.ing in sha!low \Vater (Figu.re 5). The average Ir...igration direction for t..'le schools tracked was 195°

and the average :rnigration speed in t.;.at direction was 0,33 m s·1. The analysis revealed that the S\Vi...T..rr...ing speed \-vas significantly faster (\Vilcoxon 2-Sfu11ple test, p < 0,05) for the schools tracked during t..~e night (average speed= 0,60 m s·¹, SD= 0.46 m s·¹, n = 21)

compared with the schoo!s tracked du.Iing the day (average speed= 0,33 m s·¹, SD= 0,09 m s

1

1 n = 11) (Figu.re 7). There w~~ no sigpificant difference (Wilcoxon 2-smn.ple test, p> 0,05) in swimming direction for schools tracked during the day or at night. Thus, the heading of the schools was indenendent of time of dav_ Herrin<r _{... - - - -- .. -}---c;;~ school size - - - -me~snrf>rl ~• s.-v~ln~> shnw~>rl -i"'lo • - - -~~-•• - -

significant positive correlation with depth along 6r N (r = 0,60, p< 0,05), wbile sA-va!ue showed a non-significant negative correlation with de-pth along 66°30' N (r

=

-0,45, p> 0,05).

Tne schools were relatively stable and the event rate was Jow ( e,.,rngo = 1,89 events

*

^{h ·').}

However, bothjoining (i.="= 0,50 ioins*h ·')and splitting (s,""""" = 0,66 splits*h ·')of schools were repeatediy observed, indicating adaptive adjustments of school size to the prevailing conditions. Intraschooi events such as clumping (c•=>< = 0,12 clumpings*h _,) and reorganization (r •=•,= 0,15 reorganizations*h -'j were aiso observed, as well as ring

fonnation (r* ... "."= 0,09 ring formations*h ·'). Number ofneighbouring schools observed

.l~---=--... __ ^-1-~ -- - - - - ~ ' . . • -.-. f r . . - 1 ro. ... , ... • - · • -

uwmg ua<.aung vaneo suosranuauy tV ro >!V, n ,_,,,= !,05 ). tnere were some mcl!catJons ot

antipredator behaviour pattems. However, no ma..T..mal predators were observed visually in the distribution area of the herring schools, nor were an y fish predators caught during the rather intensive trawling. Herring schools were observed to migrate vertically during the tracking period. When pa';sing over the school after trac!dng to estimate school size and vertical extent, some but not all schools dived rapidly downwards up to 100m. The r1;ving reaction reflects antioredator behaviour. and the resnonse variation mav he can•P.rl hv .... , - - . L - - - - - - - - - ----...~ - - - - - - -...~

ditierences in the state of the schools.

Inspections of stomach content showed - C. ~ finmarchicus. Euvhausiids and Chaetmmaths to be - ... <..;>

important food iterns. At one station apparent feeding on larger food items. Chaetormaths and

-- - -

^{- '-"}

C. hyperboreus at almost 400 m depth during da y time was observed.

Discussion

Herring n1igrations have been investigated over man y years (Harden Jones i968; Jacobsson &

Østvedt 1996). }v1ost studies are, howe-ver, descriptive and little is published about the factors

monitoring survey.

Atlantic herri_ng tolerate a wide range ofte-mperatu.res and saliP..ities (Blaxter, 1985), and our results support this finding. The temperatnre tolerance of the herring probably changes \Vith the season and other internal and extemal factors (Misund & ~l. 1997a). Marchal! and E!!iott (1998) showed that herrin2: distribution wa• correlaterl to tP.mnP.rMnr" _{- - ... --- ---} --- --- -- ----.r---,

-&-

~nrl th~t ^~-

.. .. -...

t.•mnProture r ... -

proved to be the best predictor of total abundance. Herring are sensitive to temperature change

9

(Murawski 1993)7 and most pelagic species are able to detect temperature va..riations as small as O.l°C (Sundet al_7 !98!) or less (Murray, 1971; Hoar andRa11dall, 1979), wPJch allows them to orientate to\x;ard areas '..vhere the prey are usually more abundant (Fem5 et aL, 1998).

Cushing ( 1968) stated that there is no simple relation bet\.veen herring and temperature because the fish are found in dense patches at all temperatures from 2°C to 9°C. Y et, L1.e distribution of sonar traces of herring in the ~~orwegian Sea bem-s some relation to the CUiTent stn.1cture and frontal a..reas (Tfu'...ing et aL, 1955). Another bounda..--f at vvt-Jch heu~ng gather has been described by Steele ( 1961) in th.e eastern 1'-Iort...h Sea in spring. Fonner studies suggest that herring during feeding wigration avoid vePJ lo\v temperatures by sv.rL.T.~..~.TJng fast out of such areas (Jakobsson 1969; Jakobsson and Østvedt 1996). Results from ?\1aravelias {1997) indicated that areas with higher probabillty of finding herring present were located in '''ell- mixed waters and transition zones between frontal and stratified waters. The !argest herring agll;re)!:ations were consistentlv observed in the same - - - 4 area~. - - - - - Herrin"- annear".-1 to avoi.-1 th" rnl.-1 ---~ --s::c - - - - -- - - -

bottom waters of the North Sea during the summer. orobablv due to the relativelv noor fno.-1 _{- -...} ~ --- --., s::--- - - - -

resources there (Maravelias 1997).

Mocness-samples of zoopiankton from stuåies in the cold front in the Norwegian Sea in April 1995 and 1996 showed ihat the prey organisms most important to herring peaked in

abundance at 200-400 m depih (Dalpadado & al. 1996). By swimming at great depth, the

heu~ng th.ereby also increase the probabiiity of encountering prey paiches (Misund & al 1997a). The schools were relatively stable and the event raie was iow compareå to what has been obsenred in oL,er situations (Pitcher et al., 1996; :tv1ack.inson et ai., (in press)). Low temperatu.res measUt~d in frontal areas wit.~ tracked schools u1ay have reduced the swirnming activity level of herring. The wJgration behaviour of the he11ing schools seen1ed to be

influenced by the ter11.perature distribution in the front.

Temperature may have both direct a..'ld indirect impact and implications for herring distribution a..Tld !!lJgration. Direct influence cou!d appear L'l very cold \Vater masses, \Vhere temperature drop below 1-2 °C. LT! our study, the wigration or S\ViTP ... Ting speed \Vas sigr1ificantly lo\ver 1n cold and deep \Vater compared to the \.Va..'TI'ler water higher up 1n the water colurnn. Lo,·v tempera~.Jres may put liir..itations on s\vim.T...ing capacity and speed (He 1993; Videler a..r1d Warille 1991; Videler !993), general metabolism (Videler 1993), as \Vell as reduce the energy absorption capacity and physiological processes (7!lcha..riassen, 1992).

Woodhead (1959) have found that cod talcen from water colder tha.11 2 °C have more chloride in their blood than those taken from water warmer th~n 2 °C. Tn the co!der water, then, the chloride-secreting cells in the gills were not functioning properly, in spite of the fact Lh"t these cells proliferate in fish in cold water (Cushin!!. ~ ~ ... 1968). , With decreasing- temnerature enzvmatic = -- ---... --- ---J---~---

processes slow down and thereby also the chloride-secretion over the gills for marine fish, and if the bodyfluids ionic concentrations becornes altered, it rnay bee lethal to the fish (Zachariassen, 1992). Since investigations on herring distribution in relation to ternperature indicate that herring do not rnove into colder water than approxirnately 2" C over longer periods (tv1isund et al., 1997a; 1998), the effect that ternperature has on rnernbrane transport may therefore be a lhuiting factor for the outer distribution of these marine fish species.

Additionally, various temperatllie regi1nes rnay 1ndirectly infiuence the concentration and dist..-ibution of prey species in mixed water masses in cold front areas.

Ul . h "h • . . ~

TY aters \VlL. speChlC temperat-..:rre properues are attractlve to hemng due to the process 01 frontal TPjxing \Vhich e~l)ances prima.···"'; and seconda.. .. ·y production. Results indicate that herring appear to prefer t..qe \Vell-Irixed \vaters and trunsition zones and avoid !.L1.e stratified a..11d frontal a.reas (Maravelias and Reid, 1997). The older year~classes of herring showed a

i l

.,

westerly movement along the tra11sect from i\pril to June-, a.11d were found"fa..rthest to the west (Misund et aL, 1997b). The herring did not cross the cold front although feening conrlitions, judged from zooplankton biomass distributions, seemed far hetter than in Atlantic water

(Melle et al., 1994). Similarly, Misund et al., (1997a) found in another experiment that herring did not seem to cross the oolar front when reachin!! the cold-water front. at ahout O de!!'rees . .L ... ' - - - o - - - - ,

and the herrin!! turned southward alon!! the front. Herrin!! seem to concentrate at. or near such

-

^... ... ^__ , - - - -

boundary areas, which are associated with high productivity (Maraveliasand Reid, 1995).

Since there is a preference towards these areas one mil!:ht SU!!l!:est that herrin!!. to fora!!e _- -

--

^{... . ...}

optimally, stay in the warmer waters because of the benefits from higher ·swimming capabiiities with higher water temperatures. Swimming and foraging in areas with too low temperature may cost more than its benefits, even though food concentration may be highest in the coldest area (see MeHe et al., 1994). Clearly, extreme temperatures may have a direct effect on he.uing behaviour, distribution and migration.

Acknowledgements

We are grateful to the captain and crew ofR.N G.O.Sars for good cooperation during the cruise.

A.Iton. 1997a. L"lteme Notat l'-1r. 7 ~Cruise Report Cntise :t'.J"o. 199705 R7V "G.O. Sars".

Norwegian Sea (PGSPEN), !CES C.M. 1997/H:3, pp. 1=14.

Bla_xter, J.H.S. 1985. The herring: a successful species? Can. l. Fish. A.quat. Sei. 42 (SuppL 1):21-30.

Blindheim, J. 1989. Ecological features of the Norwegian Sea. Pp. 366-401 in: Rey, L. _A_TJd V. Alexander (eds). Proceedings of the sixth conference of the Cornitte A.rctique Internationall3-15 May 1985. E.J. Brill, Leiden.

Dragesund, 0., A. Johannessen and Ø. Ulltang 1997. Variation in mi!!ration and abundance of

-

- -

Norwegian spring spawning herring (Clupea harengus L.). -Sarsia 82:97-106.

Cushing, D.H., 1968. Fish Bioiogy. The University of Wisconsin Press, London. 200 pp.

D31padado~ P.~ Melle, W., Ellertsen, B., and Donunasnes, .A .... 1996. Fcod and feeding conditions ofherring Clupea h:uengus in the Norwegiafl Sea. ICES CM1996/L:20, 1- 25.

Devold, F. 1963. The life history of the Atlanto-Scandian herring. Rapp. Cons. !nt l'E.xplor.

Mer. 154:98-108.

Ferno, A., T.J. Piicher, L. Nøtiestad, W. Melle, S. Mackinson, C. Hoilingworth. 1998. The challenge of the herring in the Norwegian Sea: making optimal collective spatia!

decisions. Sarsia 83:149-167.

Fredt_;..ksson, A. 1944. t{ordurlands-Slldin. Atvinnudeleild Hask61ans -Rii Fiskideiiåar l. 390 pp.

Harden Jones, F.R. 1968 . .~.J:?ish Afigration. -Edva..-d A.tu.old Ltd., London, 325 pp.

13

Symposia: Actes du Symposium, 196:183-189.

Hoar, W.S. and Randall, D.J. 1979. Fish Physiology, voL V. Academic Press, New York.

Jacobsson, J. 1969. On herring migrations in relation to changes in sea temnerature . ... ._.. ...., J..---r-.Tøkull - - , - - - · 1 Q·l 14- 145.

Jacobsson; J. and Østvedt O.J. 1996. A preliminary review of the joint investigations on the

distribution of herring in the Norwegian and Icelandic seas 1950-1970. ICES Council Meetin!!.

-

-

1996iH:i4, 44 p.

Levin, S.A. 1992. The problem ofpattem and scale in ecology. Ecology 73 (6): 1943-1967.

S. ~ilackinson, L. ~~øttestad, S. Guilette, O.A. tvfisund, T. Pitcher and A. FemO 1999.

n;"trihnt~ ... ." ... ^...:~ 'h""'h ... ~ ... l ^...:~ ... ^~ ... + 1'\.T ... -··--= ... - -.:.r,-,,·-,,Q ;;;.n"·-w--llll'-lg- , .. J~m---~n·· g· ^u·'·un· 'ng

~~~L..L. VU.UVJ.J. "-L.IU V'-'J..lQV.lVUJ.Q.l UJ.l..la.l.ll..l'-';:) V~ J."'V.l W~Cld.J.J "'r O ~r ""

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migration and abundance of Norwegian spri..ng-spawning herring in relation to t..IJ.e temperature

15

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17

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- -

^{"-'' ...}

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13(8):29-47.

Figure legends:

Firure l. Man over the !!emrranhical nositions of the two investi "atecl east-we.st clir""t"cl trans""ts ^{' - ' .._ ..., _Q' ___} .L _______ c _________ --- ---o~---·----~---

along 66°30' ( - . -) and 67°00' N (- - )during the synoptic surveys 14-16 April ! 997 onboard RJV

"G.O.Sars" a..11d FJV "Håkon Mosby" in the Nonvegian Sea.

Fhmre 2. A svnontic survev desiPn which _{... - J -.L---- - - - - ...} - - - - l ; ' - - - -illns.tr::~tes RN "(1_0 · - · - · - - -S::.r.~" nP.rfnnnlncr r---~-e ~rnndl(" m~nn1na - - -.... - - -.... -rr ... o

with sonar and echosonnder as well as pelagic trawling, Mocness and CID stations along predefined transects. while RIV "Håkon Mosbv" annlied the ondulatin!! SeaSoar CTD sensor to continonslv _{- - ... .._ '-'} ---J

monitor the temperature profile from the surface down to 300 m depth along the same transects.

Figure 3. Horizontal and vertical distribution and consentration (sA-values) of herring in relation to iemperaiure profiles down to 300m along 66°30' N (002° E to 004° W). Note day/night marking and density differences in acoustic observations, and results from stationary CTD stations included down to 500 m along the transect. A total distance of 165 nm were analysed.

Figure 4. Horizont::~l and vertica! distri.bution and consentration (sA=values) ofherring in relation to temperature prof!les down to 300 m ::.long 67°00' N (002° E to 004° W). Note day/night marking a"1'}d

to 500 m along the transect. A. total distance of 165 nm \vere analysed.

Figure 5. ~"1igration speed, direction and depth for 32 tracked heuing schools in relation to sea temperatu.re and geograpt.Jcal position along an east-west axis (3°00' \V - 2°00' E).

L,creasing lengd1 of t.,.e ai-rows indicate increasing rrtlg.rations speed, whiie a colour scaie is included to distingu.ish the sea temperature related to each school.

19

Figure 6. Map inclurling roigration speed a..11d direction of 32 tracked herring schools in relation to geographicollocation of the schools and sea temperature in those spe-cific areas.

Figure 7. Relation between herri..ng migration speed (ms-¹⁾ a11d temperature (°C) at recorded roigration depth for 32 tracked herriÆg schools.

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