International Council for the Exploration of the Sea
C.M. 1996/S:30
Theme session:
Thc Shelf Edge Current and its Effect on Fish Stocks
(including results from EC-SEFOS)
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OCCURENCE OF BLUE WHITING IN TRAWL CATCHES DURING
SURVEYS FROM PORTUGAL TO FAROE ISLANDS, 1979-1995.
by
Terje Monstad and Jaime Alvarez
IMR, Bergen, Norway and
Jacques Rivoirard
CG, Fontainebleau, France
ABSTRACT
Historical data on blue whiting (Micromesistius poutassou) from survey trawl stations of 7 countries, have been congregated and prepared into special files, together with corresponding temperature and salinity observations. Tbe majority of the data originate from bottom trawl stations and hence represent the on-shelf part of the stock, Le. mainly younger age groups. The pelagic stations, mainly worked off the shelf over deeper water west of the British Isles, represent the more oceanic part of the stock, which are both young and older age groups. These biological data are presented on maps by quarter of year and age groups.
Special attention is paid to the data from the Norwegian surveys whose main target is blue whiting when this is congregated along the slope west of the British Isles to spawn. These data clearly show a south-bound tendency of the abundance with year in the 1980's. Age 1 is more frequent in the south and north than in the central area, Le. around lat. 55° N, while older fish are more uniformly distributed.
The increase in temperature and salinity southwards from lat. 59° N off North Scotland, is roughly linear, while the values North of Scotland show a much greater dispersion.

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INTRODUCTION
One of the coiruriercially important fish species distrlbuted alorig the shelf edge from
Portugal to the Norwegian Sea, is the blue whiting
It is fourid in most parts of the. warmer side ofthe.riortheast Atlantic. The distribution ranges from the
Mediterranean Sea in the south to the Bm-erits Sea and Spitzbergen iri the north, betweeri
SoutheaSt Greenland and the Kola peninsula (Monstad, 1990).
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The spawning period" is from JanuarylFebruarY to May/June, starting in the south and ending iri the Faroe/Shetland area. The peak spawning of the main oceanic stock, however, will be in March and April, along the continental slope at 300-500m depth, west of Ireland and Scotland respectively.
In the 197()'s the iriterest in commercial exploitation had a rapid increase, and an international fishery developed in the feeding areas in the
No~egiari
Sea during summer arid auturiiri as weIl as in the main spawrung area west of the British Isles during spnrig.
Iri addition, blue whitirig was caught th!oughout the year as by~atch in the. mixed iridustrial fishery in the NoIth Sea änd on the shelf off Portugal rind North-Spain. A total number of around 13 nations have used to exploit the bhie whiting stock.
Every spring since the beginning of the 1970's the
stock west of the British Isles has beeri monitored acoustically by vessels from one or more coimtfies, e.g. NOrWay, .
Russia, Scotland arid The Faroes, but duririg the last 10 years by Norway arid Russia only
"(Anon.; 1996). However, during the 1980's and -90's, other countrles have in addition carrled out bottom trawl surveys on the sheIf, and hence blue whiting has all in all been recorded over a rather wide area.
Blue wWting feeding iri the Norwegian Sea migrate every spring southwards to the spawrung groimds west of the British !sles, arid likewise blue whiting from the south migrate nortbwards to the. same area. Iri this context, the Porcupine bank area west of
Irelarid is considered an area where blue whiting from the riorth arid south mix during the spawning penod. However, the proportions originating from the riorth and south .
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respectively are unkriown, as weIl as how much of the spawning products drift north and south. Iri addition to oceanic parts of the stock, there is also a number of Iocal stocks in inshore waters.
Preliiniriaiy results of genetical invesiigatioris in 1991-1993 indicate that sevefaI populations of blue whiting could appear in the spawning area. However, therewere no, indications of genetical substructure among the blue whiting from west of the British Isles to Gibraltar (Mork and Girever, 1993) "
Blue whiting, its structure and composition within ceftain areas and seaSons, are fariUliar to various institutes. The total picture is iricomplete, for the distribution as weIl as for the inigrations of the various parts of the stock. This paper presents results of the trawl catch data collected from 7 countries, combined to describe distributiori for vanous age groups .
of biue whiting, on arid off the shdf from Portugal to Shetlarid and off the shelf west of the British isles.
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MATERIAL AND METHODS
Within the EU-project SEFOS (AIR-programme), survey data from 7 countries, Le. Frunce,
Spain, Tbe Netherlunds, Portugal, Scotlarid, Norway und Gerrnuny, have been coIlected.
und prepared into special standard formatted files. The data consist of survey trawl catches of blue whiting, trunsformed into numbers of specimens of each age groups 0-5+ years caught per hour trawling, together with corresponding temperature und salinity for the catch. The text tabIe beIow shows the various items for euch single trawl station in the datafile:
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Country, species, cruise, date, hauI no., ICES-rectangIe, position, hour, depth, temperature, salinity, 0 year, 1 year, 2 yeai', 3 year, 4 year, 5+year, total numbers as given in the foIlowing exampIe:
Sp,blw,N92, 120992,01,13E1,4214,0859W, 1215,98,13.1,3584, 60,579,226,24,0,0,889
OnIy Spain arid Norway supplied the bioIogical data as age distributioris for each station.
The other countries gave Iength distributions wheri avallabIe, or just "empty" stations.
Appropriate age-Iength keys were created for various quarters of the years und areas, und used to convert the Iength data irito age groups from 0-5+ years. For this, Spunish data were used feir the length distributions from southern areas und Norwegiun data for distributions from northern areas, Le. south arid north of approximately 50° N.
From this material a database for bIue whiting witb around 6000 sui-vey trawl stations collected from 7 countries, with corresponding temperature arid salinity observations, has been created in ASCII format. The data are also recorded in EXCEL format and as sAs dataset. Using a SURFER graphic prograrillne the data are plotted on maps for vririous aspects und combinations, such as distributions for each year group eir total, for separate surveys, seasons, quarter of year or·total. These Ure stored in a picture library for all distiibutiorial maps on bIue whiting.
The data are plotted on maps for each half year, as numbers of bIue whiting caught per hour separateIy of the age groups 0, 1, 2 und 3+ years. However, due to the Iong time series und consequentIy a large data base, only the years from 1989 to 1995 are presented on maps in the present paper. The distributions from earlier years, 1979-1986 are described in the text only.
Tbe Norwegiun surveys to the west of the British IsIes were alI acoustic assessment surveys with bIue whiting as the main target. The spawning stock size was assessed, with mapping of the stock distribution und investigatioris on its age, length, sex arid maturity composition. These arimial results are giveri iri e.g. Moristad und Midttun (1980), Monstad
(1990), Monstad und Belikov (1991), Monstad et al. (1992, 1994, 1995). Trawl stations were performed to identify the echo recordings as weIl as to collect biological sainpIes. A pelagic blue whiting trawl with vertieal opening of 20-25 m arid ari innemet in the eod end of I1mm mesh size, were used, und in some eases also a bottom trawl (Roekhopper), when sampling on the sheIf, i.e. in the Porcupine bank area.
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The hydrographie observations were made by a eID-sonde, both along standard sections arid 3t a web of stations mostly in con~ection with the trawl stations.
RESULTS
Table 1 shows the various countries', laboratories' or institutes' contributlons of blue whiting trawl survey datä to the special SEFOS-database, by year and quarters of the Year.
Most of the data originate from bottom trawl stations on the continental shelf, and only
Norway had data also from pelagie trawl stations off the shelf in the riorthern pari. These surveys were, however, all conducted during the spawning season only~ and hence the data afe from the oceanie part of the stock when it congregated along the shelf edge to spawn.
Theother data were obtained during various seasons, and they rather represent the "shelfpart" of the stock, which might be young fish and fish from Iocal stocks. The two types of sampIes to a large extent fill in for each other when describing the pattern of distribution.
Due tri a more or Iess constant inovement of the stock while migrating to arid from the spawnirig grounds, the picture of distribution varies from year to year clepending on the time period and the actual area surVeyed. However, it is not possible io obtairi complete pictures of the distribution, out the jointed sui-vey datä from the various countries, give valuable iriformation of the stock in a more complete way than before.
The O-group blue whiting, however, wem gerierally not caught during the first half year, and are hence present here for the second half year. Hut for 2 years, Le. 1986 in the southem ärea and 1995 iri the northem area, O-group blue whitirig appeared in the trawl catches, both years in June.
Distribution
For 1979 arid 1980. only Norway contributed with dat~ Le. data from 2nd. quarter of the year when surveying the spawning stock. In 1979 the area of investigation was limited to west of
Hebrides, but in 1980 it was extended sOlithwards to the Porcupine bank west of IreIand. For either of these two years the yoüng fish, Le. the l-group blue whiting, were present ina scattered way throughout th6 area surveyed~ best recordedwest of the
Hebrides. The 2-,and3.f.groups; however. were fairly weIl represented at St. Kilda west of the Hebrides, and in 1980 also at the Porcupine bank and nortb of Shetlarid.
In 1981 also Scotland contributed with data, starting aseries of 1st quarter data every year up to 1994, arid 4th quarter data from 1985 to 1995. l-gr. blue whiting were also preserit in 1981, but in ä rather scattered manner among the trawl stations. They appeared, h?wever. in some, riumbers
the Rockall brink. at the slope north of Faroe Isles, arid in the area between Faroe Isles and Shetland. The 2- and 3+ groups were found from North-
Ireland to southem part of the Norwegiari Sea.
In 1982 Scotland and Portugal eontributed with bottom tra,wl survey clata from 1st arid 4th quarter respectively. No informatiori of the stock beyond the shelf were available. In the
1st qmirter only low numbers of blue whiting rippeared in the catches from North-ireland .
. to north of the Hebrides; of which 1 and 2 year olds were found nortb of Irelarid, and 3+

6 year olds west of the Hebrides.
In the 4th quarter of 1982 rather good numbers of both O-group and l-group blue whiting were caught on the western and the southern Portuguese shelf. The 2 year and the 3+ year olds were found in slightly lower numbers. but also throughout the area surveyed.
In 1983 Scotland and Norway perfonned surveys in the northern area in 1 and 2 quarter respectiveIy. and Spain off its western and northern coasts in 3rd and 4th quarters.
In the.
1st half of the year a few l-group blue whiting were fourid on the shelf north of Irelarid and along the shelf edge west of the Hebrides. and in higher numbers between The Faroes and Shetland. Blue whiting, 1 group as weIl as 2 and 3+ groups. were also caught far offshore this year. Le. west and southwest of the Rockall bank. The oldest blue whiting, the 3+ group. were numerous on the shelf from west of the Hebrides to north of Shetland.
During the 2nd half of the year in the south. both O. 1.2. and 3+ years old blue whiting were found in rather significant numbers on the shelf off the Spanish coast.
For 1984 data were avaiIabie from Scotland. Norway and Spain in the 1st. 2nd and 3rd quarters respectiveIy.
Iri the north all the three groups of blue whitiog, i.e. 1. 2 and 3+ year oIds, were fouod off the shelf from south of the Porcupine bank to the Faroe-Shetland area. the 2-group. Le. the 1982 yearclass. being the most numerous one in the trawl catches.
In the south the picture was very much the same as in the 3rd quarter of 1983.
with 0-. 1-. 2- and 3+ year olds found in the catches along the entire western and northerri coasts of Spain.
In 1985 Scotland contributed with data from the 1st quarter from the northern area. Le. the shelf from North-Ireland to the Orkneys. and the 4th quarter from the shelf from South-
Ireland to the Orkneys. Portugal and Spain contributed with data in the 3rd and 4th quarters from the shelf off their northern. western and southern shelves. No data were available from the stock beyond the shelf area.
In the north during the 1st quarter only modest numbers of blue whiting were found in the catches in 1985, with l-group faund in highest number west af the Hebrides. During the
4th quarter some O-group of blue whiting were found both west of the Hebrides and in the
Minch. The other yearclasses were onIy poody represented in the catches.
In the south during the 3rd and 4th quarter rather good numbers of all the age groups were represented. found on the entire shelf area surveyed.
In 1986 data from 1st. 2nd and 4th quartes were available in the north and from 2nd. 3rd and 4th in the south. l-group blue whiting were caught in the 1st and 2nd quarters from the Porcupine bank area to Shetland. the highest numbers found in the trawl catches between The Faroes and Shetland. The 3+ group were, however. more frequent in the catchest found in almast all the off-shelf trawl stations. In the south during the 2nd quarter
(in June) O-group. as weIl as 1. 2 and 3+ group. were caught on most of the Portuguese shelf.
During the 4th quarter only very small numbers of blue whiting were found in the northern shelf area, while in the south during the 3rd and 4th quarters O-group as weIl as the other e ,.

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7 groups were found on the nortbern anei western Spanish shelves.
. In 1987 five countrles contrlbuted with trawl data to the daiä base. During 1st and2rid quarters, Scothind arid Norway in the riofth with data "from the shelf arid off the shelf respectively, .as marked on Figure 1a. Dunng the 4th quarter, Scotland iri the north arid
France, The Netherlands arid PortUgal in the south as marked ori Figure 2a.
riuiirig 1st and 2nd quarter l-:-group blue. whiting w~re found onthe southem part of tbe
POrCupine bank arid off the Hebiides and NW of Shetland, mostly off the shelf, arid also at orie station off the western Norwegian coast (Figure 1b). During the 4th quarter O-group bltie whitirig as weIl as l-group were found in the north, from the English Channel to
\Vest of Shetlririd~ mostly in the western part of the Channel, but also off the Hebridees. .
The highest numbers, however, were caught in the southern area in the 4th quarter, in Bäy of Biscay off the French cOaSt and on the Portuguese shelf (Figure 2a-b). Older fish were more.abundant in north during the 1st half of the year, arid more abundant in the south during the 2nd half of the year.
In 1988 six coritrles conducted surveys;
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j sUrVeys in the 1st half of,the year arid 5 surveys iri the 2nd half; Scotland arid France conduciirig surveys in both periods (Figures
3a and 4a).
.In the 1st half of the year in the northern area, the 2- and 3+ groups were found more 01less evenly distribuied from the Porciipine blink to The Faroes, white 1
~group were more scattered,
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west of South-Irelarid and off the shelf from west of the Hebrides to the .
Faroe-Shetlarid area~ arid at 2 statioris near Rockall. All of the age groups 0-3+ were caught on the shelf off the French coast in bay of Biscay, with the youngest ones, the land 2-groups mostly at the outermost stations at the edge, while 3+ group were caught both at the outer statioris arid at the inner stations near the coast (Figure 3).
During the 2nd half of the year O-group blue whlting were caught both in riorth arid south.
It was fourid iri the CeÜic Seä, near the coäSt west of Ireland, off the Hebndes aitd off
Shetland.
In the south, the O-group was still fOlmd in Bay of Biscay off the French coast, coniinuirig further along the sheives of the Spanish and the Portuguese coaSts. The I-group had a very much similar distribution, out iri a lesser degree in the riorth thari the O-group. ;
Older age groups were found scattered on the shelf in the northern area, with only small catches on 3 stations west of the Hebrides and 1 west of Shetland. In the south, the occurence of olde!" age groups were better, being caught on the shelf from the Chanriel to
South-Porttigal (Figure 4).
From
989 to 1992 alI the severi countries contributed with blue whitirig trawl data, either for the 1st half of the years, the 2nd halfor for both (Table 1).
Duririg the 1st half of the years iri this period, the coverage öf the entire shelf .edge area from Shetlärid to South-
Portugal, was not complete for any year (Figures 5,7,9 arid 11). Dunng the 2nd half of these years there_ were complete coverages of the shelf, excepi or 1991 (Figures 6,8,10 and
12).
In addition Norway exterided the areä from 1989 onwards, by contribtitirig with data from North Sea sUrVeys in the 2nd half of these years. These were, however, from bottom trawl surVeys. In 1989 the shelf area off the NOrWegiari coast riofthwards to 71°N was .

8 also surveyed, both with bottom and pelagic trawls. (Figures 13-16).
Durlng the 2nd half of the years, O-group was caugth every year over rather Iarge areas in the south, Le. mainly from southwest of Ireland to South-Portugal. In the area north of the
Porcupine bank, O-group was most of these years caught only at a few stations (Figures 6a,
8a, IOa and 12a).
In 1989, however, rather Iarge numbers were also caugth in the north during the seeond half of the year, Le. in notable numbers off the Hebrides in November (Figure 6a), and further also in Norwegian waters, both in the North Sea and northwards along the shelf up to Lofoten at 69°N (Figure 13). For the years 1990-1992; O-group blue whitiIlg were also caught in the North Sea surveys during Oetober, but at Iower riumbers (Figures 14-16).
Unfortunately no blue whiting surveys were conducted northwards along the Norwegian shelf these years.
During the 1st half of 1989 the 1- and 2-groups were found in notable numbers off the shelf west of the Briiish Isies northwards to the Hebrides, arid to a Iesserdegree at some stations in the Bay of Biscay (Figures 5b and c). During the 2nd half of 1989 these 2 age groups, however, were found to be more abundant in the south, being found in the Celtic
Sea and in the western part of the ChanneI, and further southwards on the shelf to the southern coast of Portugal (Figures 6b andc). The oidest age groups, 3+ year, were most abundant off the shelf from the Porcupine bank to the Hebrides in the 1st half of the year, and with Iower numbers but more frequently at stations in the Bay of Biscay and further southwards to the Portuguese shelf (Figures 5d and 6d).
The 1- and 2-groups during the 1st half of the years 1990-1992; were mostly found off the southwestern coast of Ireland, arid in 1991 when a lot more stations were worked, also in the Celtic Sea and further southwards along the French coast. (Figures 9b and c). The oider blue whiting in 1st half of these years were found mueh in the same pattern as in
1989, but also north of Scotland. In 1991 they were also caught in the Celtic Sea and in the Bay of Biscay, as the younger age groups were, but in 1992 they were not obtained off the shelf, as would be usual, because no stations were worked there.
During the second half of the years 1990-1992, most blue whiting were found in the southern area. Except for 1991 the entire shelf area from North of Scotlarid to south of
Portugal was surveyed (Figures 8-12).
In 1993 six eountries eontributed with blue whiting survey data, in 1994 all the seven countries and in 1995 five of the countries. Only modest numbers of l-group were caught in the fIrst half of these years, both in the north and in the south. (Figures 17b,19b and
21b). The 2- and the 3+ groups were caught rather in Iow numbers in 1994, and in high numbers in 1993 and 1995, especially the 3+ group for both of these years (Figures 17cd,
19cd and 21cd).
O-group blue whiting, however, was in 1995 for the fIrst time ever recorded, caught by trawl iri the northern area during the first half of the year.
It was caught with pelagic trawl along the continental siope in June, at one station south of Irelarid, arid in signifIcant numbers at stations from NW of Ireland to NW of the Hebrides (Figure 21a). This was the
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9 irrst indlcatlon of the 1995 yearclass as a very ilUmerous one.
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During the 2nd half of tbe yearS, the O-group was rather numerous in the sOlithem area from Ireland to South-Portugal in 1994 arid 1995, arid along the Spanish and Portuguese coasts in 1993.
In the northem area it was found from south of IreIand to north of the
Hebndes in 1993 and 1995, in the Iatter in significant numbei"s.
In the noith the other age groups were onIy found in reIative,modest IlUmbers all tbe th.fee years, while in the soutb they were as l:lsual caught in notable numbers aIong the sheIves of France, Spahi arid
Portugal in 1994 and 1995, the Iatter year having the highest numbers, arid off the Spanish' and Portuguese coasts in 1993 (Figures 18,20 and 22).
BIue whiting were also tbese Years.
c~lUght, with bottom trawl, in the North Sea dtirlng the 2nd half of
In 1993 O-group was caught in the Norwegian Trench at a few stations only
(Figure 23a), in 1994 in modest numbers at more stations (Figure 24a) and in 1995 in significant numbers at many stations from south of Bergen (at 60 0
25~).
N) to Katiegat (Figure
Also the l-graup was best represented in this area in 1995. Except for 1993 the land 2-grOl,ips were notably abundant in the Norwegian Trerich these yem-s. Blue whiting as a whoIe were, however, caught in significant mimbers (Figures 23,24 and 25).
The general impression of the preserited data is that most years ihe abtiridance of bIue whiiing is apparentiy higher in the southerri area than in the northerri; The number of stations workecl is highest in the south, and hence blue whiting seem to be more frequent there. However, when blue whiting are caught in the north, espechiIly in the 1st half of each year, the numbers are in most cases significantIy higher than in the south.
The migratory behaviour causes the appearence of bIue whitirig in the northem area, Le.
west of the British IsIes, during spring when the mature part congregates there to spawn.
In the 2nd haIf of e'ach year the stock has rettirned to the feeding grounds, either northwards or southwards, and the majority of the Iaivae and Iater the O-groups have
Iikewise drifted northwards or southwards.
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The southem area; Le. the shelf area from the Channel to Gibealtar, is to a Iarger exterit a mirsery
where the majority of nie southwards drifting IrirVae ends up, whiIe the shelf area in the noith remains an area with specimens mostly beIonging to Iocal populations.
The riorthwards drifting Iarvae end up in aCeas where the survey frequency is much Iower,
Le. inainly in Friroese waters, in the Norwegian Trench and further north along the
Norwegiari :coast, and hence the catch frequency of blue whitirig is mtich Iower tban in the south.
Iri addition there are also local stocks on the sheIves, both in the north and the south.
As mentioned earller
is ilOt possibIe to geta compIete plcture from the trawl station resuits alone, as, the number of stations arid ,their distribution are mostly in disaccordarice with the bIue whiting's abundance and availability.
fhe,bIue whiting data of the yeärs 1989-95 were set up as riumbers by age of fish caught per houe for each year in relation to the total mimber of stations warked (Figure 26), but no dear relation with the yearclass abundarice, level kriown from ather sourees, i.e. VPAruns arid catch statisiics
(ADon.~
1996), could be established. For most of these years the

10 values of the O-groups were higher thrin for other age groups, something which could be explained by the high number of trawl stations in the south where O-group were frequent.
Furthermore, the weIl known very abundant 1989 yearclass obtained lower values as 0group than the much poorer 1991 and 1992 yearclasses did, and the very rich 1995 yearclass lower value than the 1994 yearclass.
The maps merely show the geographical distribution of blue whiting within the shelf edge area from Gibraltar to the Norwegian Sea, and its level of ocurrence in the survey trawl catches, but to a certain degree could also reflect the yearclass strength.
Norwegian blue whiting surveys
As mentioned above, the NOrWegian surveys to the west of the British Isles, were all acoustic assessment surveys with blue whiting as the main target. Trawling is performed for identification and sampling of blue whiting and actually much more often on high concentrations than on weak ones. The trawl stations therefore to a certwn degree may represent an indication of abundance in the concentrations recorded, but will never give the precise picture. They rather supplement the picture obtained by acoustic recordings.
As an example of the acoustic blue whiting surveys the cruise track arid stations in spring
1995 are shown on Figures 27, and the distribution with relative abundance on Figure 28.
An example of blue whiting echo recordings is shown on Figure 29.
The majority of the trawl stations were worked in deep sea areas off the shelf, and hence represent the oceanic part of the blue whiting stock.
In spring the mature part of it, migrating from south arid from north, congregates along the coritinental slope to spawri, and then returns northwards to its feeding areas in the Norwegian Sea, and partly also southwards from the Porcupine bank area. This more or less constant inovement of the spawning stock to and from the spawning area, where also younger and immature age groups partly follow, causes difficulties in timing the surveys to the optimal period for the spawning stock within the area to be surveyed. The vaiiability in survey estimates therefore may be caused by this, in addition to weather conditions and progress of the gonad maturation and spawning, which again may be influenced by the hydrographie situation.
The Norwegian spring surveys, from 1979-1995 except for 1982 and 1985, were conducted in March to May. Due to short cruise time and very rough weather, only few stations were worked in 1979. The earliest survey wasconducted 1981 and the latest one in 1979
(Figure 30).
A scatterplot of the stations' latitudinal positions versus year is shown on Figure 31. A south-bound tendency can be observed in the 1980's, with the location being more or less stabilized after 1988.
Plots for age groups 1,2 and 3+ through years are presented in absolute numbers on
Figures 34 and in proportion of the total on Figure 35. Age 1 is obviously more present
(in absolute numbers as weIl as in proportion) in the northern arid in the southern parts of the survey areas; and less present in the middle. This tendency also exists, but to a lesser extent for age 2. The adults, Le. age 3 years and alder, are more evenly distributed over
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11 the whole area. There iso however. a shift to the South from the mid-80's onwards. as can be observed on Figure 34c, where the concentrations' center of gravity is marked.
The three years old and older are rather uniformly distributed. but with a decreasing tendency northwards. The rich 1989 yearclass is significantly visible, especially as 2 year olds in 1991. Also to be noted are the large numoers of 1 year olds in 1987 and 1995.
indicating the strength of the yearclasses 1986 and 1995. The 3 year olds arid older were also nlmierous in 1983. 1989 and 1992.
The represeniative temperatures and salinities for each trawl station at 200. 300, 400,
500m and at catch depth. were analysed for the years 1979-1985. except for 1982 and
1985 when data were not available. Scatter plots of the temperature and salinity at the catch depth versus year are shown on Figures 32 ~d 33 respectively.
For illustration of the blue whiting concentrations in relation to the hydrographical conditions; the echo recordings of blue whiting along a vertical section over the Porcupine bank (latitude 53°30'N) and the temperatures and salinities in spring 1995. are shown on
Figures 36a and b.
The temperature generally increases with salinity. and increases to the south, arid is Iower and more variable north of 59°N (off northern Scotland). where the pattern changes: The teniperature at catch depth
increasing from 8° to 11°C southwards and decreasirig from
8° to 2° C northwards; the salinity at catch depth, being generally between 35.20 arid
35.60°/
00
, decreases to 34.80°/
00 north of 59°N.
Plots of T-S values at catch depth for the whole period 1980-95 are shown on Figure 37, .
indicating the type of water where the bulk of blue whiting appears. T-S diagrams for each year are shown on Figure 38. A fitted line for the points
drawn for the average of all th6 yeai-s.
The main features of this figure are the following: The T/S diagrrims for 1980. -81 and -83 are. quite unusual.
In 1983 and 1980 the salinities are low while the temperatures are riot so low; in 1981. when the survey period was early. the temperatures are low. but not the salinities. In additiori; the year 1990 show parucularly high salinities with relatively high temperatures. something which is in agreement with the maximal salinity in Atlantic water in the Faroe-Shetland Channel, as the aririual mean at twostandardsections between The
Faroes and Shetland (With courtesy of the Marine Lab. Aberdeen. Bill
Turrel~ pers.
comm.). and also with conclusions drawn by Hariseri arid Jakupsstovu (1992) that a strong influx of Atlaritic water took place in 1990. However. no relation appears which could explairi the good recruitment for the years 1983. -89 and -95.

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REFERENCES
Anon. 1996. Report of the Northem Pelagie and Blue Whiting Fisheries Working Group,
Bergen 23-29 April 1996. ICES Ooe. C.M.
1996/Assess:14.
Hansen, B. and Jakupsstovu i, S. H. 1992. Availability of blue whiting (Micromesistius poutassou) in Faroese waters in relation to hydrography. ICES mar. Sei.
Symp., 195:349-360.
Monstad, T., 1990. Oistribution and growth of Blue Whiting in the Northeast Atiantie.
ICES, Ooe. C.M.
19901M:14.
47 pp.
Monstad, T. and Belikov, S.V., 1991. Report of a joint Norwegian-Russian aeoustie survey on blue whiting, spring 1991. ICES, Ooe. C.M.
19911H:4,14 pp.
Monstad, T. and Midttun, L. 1980. Norwegian blue whiting investigation in AprilfMay
1980. ICES, Ooe. C.M.
19801H:61, 23 pp.
Monstad, T., Belikov, S.V. and Coombs, S.M. 1994. Investigations on Blue Whiting in the area west of the British Isles, spring 1994. ICES, Ooe. C.M.
19941H:12.
Monstad, T., Borkin, I.
and Ermolchev, V., 1992. Report of the joint Norwegian-Russian
Aeoustie Survey on Blue Whiting, spring 1992. ICES, Ooe. C.M.
19921H:6.
Monstad, T., Belikov, S.V., Shamrai, E.U. and MeFadzen, I.R.ß.
1995. Investigations on blue whiting in the area west of the British Isles, spring 1995. ICES. Ooe. C.M.
19951H:7.
Mork, J. and Girever, M. 1993. Genetieal population strueture of Blue Whiting. ICES,
Doe. C.M.
19931H:4.
ACKNOWLEOGEMENT
The authors want to express thanks to the institutes and laboratories named in Table 1 for their contribution of blue whiting data under the EC-SEFOS projeet. A special thank to
Jostein Eide, IMR, Bergen, for computer handling of the data and to OIe Gullaksen, also
IMR, for proof reading and linguistie advice.
• e.-
•

..
-; .
Table 1. Survey trawl data ofblue whiting; 1979-95 by country and quarter ofyear.
I .
1
IFREMER· IEO RIVO, IJmuiden IPIMAR SOAFD, Aberdeen .
IMR IFS·SFF·
Year Nantes, France' IViao . Soain Netherlands Lisboa Portuoal Scotland Semen Norwa
J
Hamburo. Germanv
Fish/h St.N·· Q Fishlh St.N'
Fish/h St.N:
Fish/h St.N
Q Fish/h St.N
Q Fish/h' St.N
Fish/h, St.N:.
1979 2 52573 8
1980
1981
1982
1983
1984
1985
1986
"
3,4" 408056 111
3 499889
3 I' 479503
95
97
3,4 387567 92
1987 4 1110262 " 131 n.a.
1988
1989
1990
1991
2,4
3,4
3,4
2
4
799859 270 '3,4· 1026803 I' 102 4
288545 142 3,4· 368331 92 4'
390980 193 3,4 432813 122
I
4'
119981 .
199 /3,4 .852462 .
108 4
1992 3,4 347961 171 3,4 254731 118 4
1993 n.a.
1994
1995
3,4
4
1431049 • 156
513308 114
96901 110 • 4
364311 120 4
345373 122
1
4: 1183172 189 1
4
2,3
318574
104889
150
118
1
1
1,4
1,4
73204 ' 41 . 4·
15299 .
40 I' 4·
56061 .
55 3,4
3386
33680
532456
453152
82 1,4
98 1,4
565355 252 1,4
51 3,4' 737580 221 1,4
42 I· 3,4 559450 203 1,4
80206
13729 .
76064
36 ' 3,4
44 ' 1·4
48 . 4
3,4
361835 228 1,4
158763 207 1,4
338211 .
88 1,4
438411 169 4·
1242
2
38 1,2
236626
36436
49
28
3424
7375
20
30 n.a.
47 2· 1203692
12 1,2 147479
3434 103 n.a.
191 55 1,2
474 86 1,2
50540
29
31
13
375682 ' 23
29366
82340
5166
93 1,2 189485 49
96 1,2,4 747721 .
208 .'. 2
90 1,2,4 105359 132 1
55123 '
61278
39109 105 1,2,4 248352 146 1 135474
46 '
211"
34 '.
902 80 1,2,4 375879 138 2 201795
20545 85 1,2,4 137988 167 1
17015 .
79 1,2 49771 125 1
9974
6
210309 105 1,2 2397302 191 n.a.
60
24
2
"
Total
I',
5001945
13761c=J
5516740~I'
35162911· 3571c=J1 575184811.,· 20051ClI 42091211 11041c=J1 635488511 13371CJI 4636501CJ]Z] .
.'
St.N: Number of stations
I-'
W

14
44'
42'
40'
52'
50'
48'
46'
38'
36'
·25'
64'
62'
O-group
60'
58'
56'
Numbers/hour
... no catch
01·100
$100·1000
() 1000·10000
.>10000
54'
·20' -15-
"
·10' a
-'f
64'
62'
60'
58'
56'
1-group
50'
48'
44'
40'
38'
36'
·20' ·15' b
56'
54'
52'
50'
64'
62'
60'
58'
2-group
C
..,..
0
()
64'
62'
60'
58'
56'
54'
3+ group d
48'
46'
44'
42'
52'
50'
48'
46'
44'
42'
40'
~1
36'i
·25'
40'
38'
36'
·20' ·15' ·20' ·15' ·10'
Figure 1.
Survey trawl stations and catch of blue whiting (N/hour) in 1st half of 1987.
a) O-group, survey nation and date, b) l-group, c) 2-group, d) 3+ group.
0
$
()
't
<;Je,
.,
5'
_-
•

15 a
58'
56'
54'
52'
50'
64'
62'
60'
1-group
-20' ·15' b
..
.'.
46'
42'
48'
40'
50'
38'
36'
·25'
64'
62'
O-group
60'
Numbefs/hour
58'
0 ~~ ~~~h e
100·1 000
CI 1000·10000
56' • > 10 000
54'
52'
Netherlands: 10.11-2.12
·20' n .
58'
56'
•
~.4'
52'
50'
64'
62'
60'
2-group
48'
46' c 64'
62
3+ group d
44'
42'
42'
40'
40'
38' 38'1
36,jL
.25' -20'
- -
·15'
--..",.--_...l-.;?::=-=--,.,,.--_ _ -:l.
36'1:-:-_ _--:':":--_ _-.,-,-
·20' ·15'
---l.~=~e:-_----1
Figure 2. Survey trawl stations and catch of blue whiting (NJhour) in 2nd half of 1987.
a) O-group, survey nation and date, b) l-group, c) 2-group, d) 3+ group.
5'

r-----------~----
- - - - - - - - - -
16
4S'
46'
44'
42'
40'
38'
36"
-25'
64'
62'
O-group
60'
58'
56'
Numbers!hQur
• no catch
01·100 e
100·1 000
() 1000·10000
• >10000
54'
52'
50'
I
Fronce: 10.5-6.6
'20' ·15'
.
.
f-a
-'f
.
.-
'
..
.~#
44'
42'
40'
3S'
36"
52'
50'
48'
46'
58'
56'
54'
64'
62"
60'
1-group
-20' ·15'
..
.
~
.
~ b
-'f
0
.
64'
62'
2-group
52'
50'
48'
46'
44'
42'
60'
58'
56'
54'
C
""'f
64'
62
60'
58'
56'
3+ group d
54'
52'
50'
48'
46"
44'
42'
40'
38'
40'
38'
36'
-25'
36"
·20' ·15' -20' ·15'
Figure 3. Survey trawl stations and catch of blue whiting (N/hour) in 1st half of 1988.
a) O-group, survey nation and date, b) l-group, c) 2-group, d) 3+ group.
•

17
..
•
4Z'
44'
40'
46'
48'
SO'
38'
36'
·25'
64'
6Z'
O-group
60'
Numbersmour
58'
0 ~~~~~h e
100·1000
C» 1 000 ·10 000
56' • > 10 000
54'
SZ'
PO"" 01: 13.10-19.11
·20' ·15'
64'
62'
60'
58'
56' c a
60'
58'
56'
54'
52'
SO'
·ZO·
64'
62'
3+ group
·15' b d
."1"
52'
SO'
48'
46'
44'
42'
40'
38'
38'
36'
36'
·25' -ZO'
-20' ·15'
·15'
Figure 4. Survey trawl stations and catch ofblue whiting (N/hour) in 2nd haUof 1988, a) O-group, survey nation and date, b) l-group, c) 2-group, d) 3+ group,

18

tI
52'
50'
48'
46'
64'
62'
O-group
60'
Numbers/hour
58'
0 ~~~~~h e
100·1000
() 1 000 ·10 000
56' • > 10 000
54'
Nethe~ands: 14.11-4.12
a
~
19
52'
50'
48'
46'
44'
64'
62'
60'
58'
56'
54'
1-group b
40'
38'
36'
·25'
Portugal: 14.7-8.8
10.10·6.11
·20'
64'
62'
60'
58'
2-group
56'
·15' c
·20'
64'
62'
60
3+ group
·15' d
52'
50'
48'
46'
44'
42'
40'
38' •
38'
36'
·25'
36'
·20' '15' ·20' ·15'
Figure 6, Survey trawl stations and catch of blue whiting (N Ihour) in 2nd half of 1989, a) O-group, survey nation and date, b) l-group, c) 2-group, d) 3+ group,

20
40'
38'
36'
-25'
52'
50'
48'
46'
44'
42'
64'
62'
O-group
60'
58'
56'
NumbBcsthour
• no catch
01·100
EEll00·l000
() 1 000·10000 e>10000
54'
-20' -15'
'.
.
-10' a
-'(.
-5'
. .
' ..#
0'
48'
46'
44'
42'
~
<;7<:> 40'
38'
36'
S· ·25-
54'
52'
50'
64'
62'
60'
58'
56'
1-group
·20· ..15·10' b
-"f()
,5'
.
EEl
e
()
56'
54'
52'
50'
48'
46'
64'
62'
60'
58'
44'
42'
2-group
C
-"fe
.
EEl
•.:1
.'
64'
62'
60'
3+ group d
"1"EEl
40'
38'
36'
·25' ·20' ·15' ·10' -5' 0' 5' ·25' ·20' ·15'
Figure 7. Survey trawl stations and catch ofblue whiting (N/hour) in Isthalfof 1990.
a) O-group, survey nation and date, b) l-group, c) 2-group, d) 3+ group.
.
()
0'
0'
0
5'
--
•
•

. - - - - - - - - - - - - -
- -
21
52'
.;.
50'
..
48' e
44
'
42'
46'
40'
64'
62'
O-group
60'
58'
56'
Numbers!bour
• no catch
01·100
E9 100·1000
Cl 1 000 • 10 000
->10000
54'
Netherlands: 27.11-14.12
France: 25.9-10.11
Portugal: 6.7'30.7
27.10-6.12
38'
36'
·25' ,20' ·15' -10· a
--r
-5' O'
42'
40'
38'
50'
48'
46'
64'
62'
60'
58
56'
1-group
54'
5' ·25' _20' -15' ·10' b
"1"
64'
62'
60'
2-group
C
..,..
64'
62
60
3+ group d
..,..
58'
58 t
56'
"~4'
52'
50'
56'
54'
52'
50'
48'
48'
4S'
4S'
44'
44'
42'
42'
40'
40'
38'
38'
3S'
·25' ·20' ·15' ·10' -5', O'
3S'
5' ·25' ,20' ·15'
Figure 8. Survey trawl stations and catch ofblue whiting (N/hour) in 2nd halfof 1990.
a) O-group, survey nation and date, b) l-group, c) 2-group, d) 3+ group,
-5' 0' 5'

22
44'
42'
40'
38'
36'
·25'
52'
50'
48'
46'
64'
62'
O-group
60'
58'
56'
Numberslhour
' no catch
01-100 e
100·1 000
() 1000-10000
.>10000
54'
-20' ·15' ·10' a
..:r
·5' 0'
64'
62'
1-group
56'
54'
52'
50'
48'
46'
44'
42'
40'
38'
36'
5' ·25' ·20' -15' ·10' b
..:r
·5'
64'
62'
60'
SS'
56'
54'
52'
2-group
C
64'
62'
60'
SS'
56'
54'
52'
3+ group d
50' 50'
48' 48'
46' 46'
44'
42,j
44'
42'
40'1
38'
40'
38'
36'
·25'
36'
-20' ·15' ·20' -15·
Figure 9, Survey trawl stations and catch ofblue whiting (N/hour) in 1st half of 1991.
a) O-group, survey nation and date, b) l-group, c) 2-group, d) 3+ group,
·5'
0'
0'
5'
5'
--
-

23
52'
50'
• 48'
46'
64'
62'
Q-group
60'
Numbers/hQur
58'
0 ~o. ~~~h
EIl 100·1000
() 1 000·10000
56' • > 10000
54'
Netherlands: 13.11-3.12
40'
38'
36'
-25'
Portugal: 6.7-5.8
12.10-14.11
·15' a
..:1
52'
50'
48'
58'
56'
54'
46'
44'
42'
40'
38'
36'
64'
62'
60'
1-group
·20' -15' b
-20'
64'
62'
2-group c 64'
62'
3+ group d
60
60'
58' 58'
56'
•
56'
54'
52'
52'
50'
48'
50'
48'
++ ....
+
+ + + + + + + +•
.....
..
+
..
.. "
.. CD..
.. +
0.+-
+
+
.. .+ ........
.
~
...
46'
44'
46'
42'
40'
I
38'
44'
42'
<:;'"
40'
'Z •
38'
36'
-25' -20' ·15' ·10'
36'
5' -25' ·15'
Figure 10. Survey trawl stations and catch ofblue whiting (N/hour) in 2nd halfof 1991.
a) O-group, survey nation and date, b) l-group, c) 2-group, d) 3+ group,
.:1

24
44'
42'
40'
38'
36'
-25'
52'
50'
48'
46
64'
62'
O-group
60'
58'
56'
NumberslhQur
+ no calch
01.100
e
100·1 000
() 1 000 • 10 000
• > 10 000
54'
,20'
Portugal: 14.2·20.3
·15' ·10' a
+ ++.+ ....
"""f
+
+
+
++
+
.
.
#
"
64'
62'
60'
'l
<;J""
40'
38'
36'
S· ~25·
50'
48'
46'
44'
42'
58'
56'
54'
52'
1-group
·20' b
+
0
+ +
~~!t
-15·10'
64'
54'
52'
50'
48'
46'
44'
62'
60'
58'
56'
2-group
C
64'
62'
60'
58'
56'
54'
52'
50'
3+ group d
44'
42'
42·1
40,j
I
38'
40'
38'
36"
·25'
36'
-20' ·15' ·20' -15'
Figure 11. Survey trawl stations and catch of blue whiting (N/hour) in 1st half of 1992.
a) O-group, survey nation and date, b) l-group, c) 2-group, d) 3+ group, q
<;J""
5' e~
..
"

•
.4' 46'
42'
48'
40'
50'
38'
64'
62'
O-group
60'
Numbers/bQur
58'
0 ~~~~~h
$100·1000
() 1 000 • 10 000
56' • > 10 000
54'
52'
36'
-25'
Netherlands: 17.11·1.12
Portugal: 7.7-30.7
15.10·5.11
-20' -15'
64'
62'
60'
58'
2-group
56'
·10' c a
·5'
-.#
..#
0'
25
64'
62'
60'
58'
56'
54'
1-group
42'
40'
38'
50'
48'
46'
64
62'
60'
3+ group
·15' b d
•
52'
50'
48'
46'
44'
42'
40'
40'
38'j
36'
-25' ·20' ·15'
38'
36'
·20' ·15'
Figure 12. Survey trawl stations and catch of blue whiting (N/hour) in 2nd half of 1992.
a) O-group, survey nation and date, b) l-group, c) 2-group, d) 3+ group.

71
69'
O-group
Numberslhour
• no catch
01-100 e 100-1 000
() 1 000 -10 000 e>10000
67'
65'
61 a
~ e oe
• *
26
71
1-group
65'
63'
..
..
..
..
0 b
0
·0
.0
.
.
b
0 ee
0
0
59'
61'
63'
67'
65'
69'
71'
..
' -2' 0' 2' 4' 6' 8' 10' 12' 14' 16'
..
' -2' 0' 2' 4' 6' 8' 10' 12' 14' 16' 18' c
2-group 3+ group d
·0
,0
• Q b
0 eo
0
65'
'0
.0
• Q b
EIl 0
0
0
0'
0
0 0
"~ "~
.:: .
"
"
, ,
57' e~
"
..' ·2' 0' 2' 4' 6' 8' 10' 12' 14' 16' ..' ·2' 0' 2' 4' 6' 8' 10' 12' 14' 16' 18'
Figure 13, Survey trawl stations and catch of blue whiting (N/hour) in 2nd half of 1989, a) O-group, survey nation and date, b) l-group, c) 2-group, d) 3+ group,

27
57'
59'
61' a
O-group
'.f
·2' e
61'
55'
·4'
2-group c
~:
..
,.f
59'
0' 8'
59'
61' b l-group
'.f
1990
2nd hall
12'
Numberslhour
• no calch
01·100
9100-1000
() 1 000 - 10 000
.>10000
14' 16'
57'
18'
55'
·4' -2' 0'
2"
4' 6'
61' d
3+ group
59'
10' 12' 14' 16' 18'
I
Figure 14. Survey trawl stations and catch of blue whiting (N/hour) in 2nd half of 1990.
a) O-group, survey nation and date, b) l-group, c) 2-group, d) 3+ group.

28
51'
61'
59'
, a
O-group
:"
.q
55'
61'
59'
C 2-group
.
'
'.f
.'.
-2' 0' 2' 4' 6' a"
10"
I
59'
61' b
I-group
'.f
0
1991
2nd half
Numberslhour
• "0 catch
01·100 e
100·1000
() 1 000· 10 000
• > 10000
1." 16"
57'
18"
55'
·4" -2' 0' 2' 4" 6'
59"
61' d
3+ group
'.#
.
10' 14' 16' 18' e
&
·4"
0" 2" . ' 6' 8' 10'
Figure 15, Survey trawl stations and catch of blue whiting (NJhour) in 2nd half of 1991.
a) O-group, survey nation and date, b) I-group, c) 2-group, d) 3+ group,
16' 18'

29
SI'
59' a
O-group f.i::
:.
..
,.f
57'1
55
J
-4' -2' 0' 2' e
2-group
- S I '
59'
, rf:
..
'.f
6' 8'
59'
61' b l-group
·.f
1992
2nd hall
Numberslhour
• no ca Ich
01·100 e
100·1000
(J 1000·10000
.,10000
14' 16'
57'
18'
55'
·4' ·2' O· 2' 4' S' 8' 10'
59'
61' d
3+ group
..#
16' 18'
.~
,
Figure 16. Survey trawl stations and catch of blue whiting (N/hour) in 2nd half of 1992, a) O-group, survey nation and date, b) l-group, c) 2-group, d) 3+ group,

30
42·
40·
38·
36·
·25·
52·
50·
48·
46·
44·
64·
62·
O-group
60·
Numbers/hour
58
0
~O. ~~cih
E9 100·1000
() 1 000·10000
56· • > 10 000
54·
Gennany: 15.2-2,3
-20· ·15· a
..
"~
64·
62·
60·
~...L;'----_.....Jr58·
56·
1-group
-20· -15· b
58·
56·
54·
52·
50·
64·
62·
60·
2-group c
58·
56·
54·
52·
64
62·
60
3+ group d
48·
46·
44·
42·
40·1
38·
48·
44·
36·
·25· -20· -15· ·20· ·15·
Figure 17. Survey trawl stations and catch of blue whiting (N/hour) in 1st half of 1993.
a) O-group, survey nation and date, b) l-group, c) 2-group, d) 3+ group.
•
..

• e 44"
42"
46"
48"
50"
40"
38"
36"
·25"
64"
62"
O-group
60"
NumbBfS/hour
58"
0 ~~~~~h
E9
100·1000
() 1 000 • 10 000
56" • > 10 000
54"
52"
·20"
Netherlands: 2.11-17 .11
-15" a c
64"
62"
2-group
60"
58"
56"
'.~
31
64"
62"
60"
58"
56"
54"
52"
50"
48"
46"
44"
1-group
,,~
<j'"
40"
'i: •
38"
36"
-20"
64"
62"
3+ group
60
·15"
56" b
..
Q
0: o
Q: : .: ...
...
..
.
~
•
~~.
...
.+_'"
d
.)
52"
50"
48"
46"
44"
42"
40"
50"
48"
46"
38"
36"
·25" -20" ·15"
-20" ·15"
Figure 18. Survey trawl stations and catch of blue whiting (N/hour) in 2nd half of 1993.
a) O-group, survey nation and date, b) }-group, c) 2-group, d) 3+ group.
0" 5"

32

, - - - - - - - - - - - - - - - - -
- -
33
.44'
42'
46'
40'
38'
36'
·25'
52'
50'
48'
64'
62'
O-group
60'
Numbers"'our
58' (;
~~~~~h e
100·1000
() 1 000·10000
56' • > 10000
Scotland: 23.11-4.12
54'
Portugal: 16.10·22.11
·15' ·20'
64'
62'
2-group
60'
58'
56'
·10' c a
·5'
'.#
0'
46'
44'
42'
<:; q
40'
'l .
38'
58'
56'
54'
64'
62'
60'
1-group
50'
5' ·25' ·20'
64'
62'
60'
3+ group
·15' b d
44'
42'
40'
38'
52'
50'
48'
46'
36'
·25' ·20' ·15' ·20' ·15'
Figure 20, Survey trawl stations and catch of blue whiting (N/hour) in 2nd half of 1994.
a) O-group, survey nation and date, b) l-group, c) 2-group, d) 3+ group,
'.#

34
46'
44'
42'
40'
38'
36'
-25'
64'
62'
O-group
60'
Numbe[$/hour
58'
0 ~~~~~h e
100·1 000
() 1000·10000
56' • > 10000
54'
Norwa :27.3-16.4
52'
50'
48'
-20'
64'
54'
52'
50'
44'
1-group
-20' ·15' b
50'
48'
46'
56'
54'
52'
64'
62'
60'
58'
2-group
44'1
42,j c 64'
3+ group d
44'
42'
:::1
36'j
-25' ·20' -15'
< <7'
::1
~~36'
-10'
~, .25::-'---'-:'20::-'---'~15::-'---'~10::-'-----'
Figure 21. Survey trawl stations and catch of blue whiting (N/hour) in 1st half of 1995.
a) O-group, survey nation and date, b) l-group,. c) 2-group, d) 3+ group.
•

35
·10' a
-5'
0'
48'
46'
44'
42'
40'
38'
36'
64'
62'
1-group
60'
·20' ·15' b
·44'
42'
40'
38'
36'
-25'
52'
50'
48'
46'
64'
62'
O-group
60'
Numberslhoyr
58'
0 ~~ ~~~h
EIl 100·1000
() 1 000·10000
56' • > 10 000
Scotland: 31.10·17.11
54'
Portugal: 14.7-8.8
12.10-9.11
-20' ·15' c 64
62 d 64'
62'
2-group
60'
.,
.
56'
52'
60'
58'
50'
48'
46'
44'
44'
42'
42'
40'
40'
38'
38'
36'
·25'
36'
·20' ·15'
·20' ·15'
Figure 22. Survey trawl stations and catch of blue whiting (N/hour) in 2nd half of 1995.
a) O-group, survey nation and date, b) l-group, c) 2-group, d) 3+ group.
"~

61·
59·
57·
36
59·
57·
55·
61·' a
O-group
·.f
I
59·
"
...
..
1993
2nd half
Numberslhour 57·
• "0 eatch
01,100 e
100·1000
() 1 000 ' 10 000
• >
14-
10000
...
O· 4· 6· s· 12· 15·
1S-
55·
61·
...
b l-group
·.f
·2· O·
.
"
++• •
2· 4·
.'.
5· e
2·group gjr
..
'.f
• +. . .
51·
59· d
3+ group
·.f
.
" ...
..
I
14· 15· lS·
55··L ...,......-.,....l--,-------,---,.--..!L...-'-f...JL..::J..t---r..u.....,..--+
Figure 23. Survey trawl stations and catch of blue whiting (N/hour) in 2nd half of 1993.
a) O-group, survey nation and date, b) l-group, c) 2-group, d) 3+ group.
57·
59·
61· a
O·group
'.#
.
'
'.
, ,
55·
·4· ·2· O· 2· 4· 6· S· 10·
61·
I
59·
12·
1994
2nd half
Numberslhour
, no catch
01·100 e
100,1000
() 1 000·10000
• > 10000
14·
16-
57· lS·
55·
-4· b l'group
·.f
..
'.
..
-2· o· 2· 4·
57·
61·
59· e
2-group
~f
.
·.f
"
,
59·
51· d
3+ group
~r
..
..#
,
'.
.
S· 14· 16·
0 lS·
I
.~
.
..,
•
,
•
Figure 24. Survey trawl stations and catch of blue whiting (N/hour) in 2nd half of 1994.
a) O-group, survey nation and date, b) l-group, c) 2-group, d) 3+ group.

61' a
O-group
37
61'
,
59'
: b l-group
',#
-I' ·2' 0' 2' C' 6' S' 10'
1995
2nd hall
12'
Numborslhour
• no catch
57'
01·100
EIl 100 ·1 000
01000·10000
• > 10000
14' 16' IS'
55'
,C' ·2' 0' 2' C'
,
6' 8' 10' 12' 14'
, " ' \
16'
~
IS'
~
•
•
61'
C 2·g r ouP
"~
•
59'
61' d
3, group
'.#
Figure 25, Survey trawl stations and catch of blue whiting (N/hour) in 2nd half of 1995, a) O-group, survey nation and date, b) l-group, c) 2-group, d) 3+ group,
4500
4000 t
..
·
-
;
Cf) c
0 cu
::s
0
.r=
I
C ...
Cf)
-
3500
3000
2500
2000
Q)
-
Cf)
...
-
.0
E 1500
Z
::s
1000
500
0
857
1989 o O-year 0 1-year .2-year .3-year +
812
833
829
1990 1991
,
,",
,
1992
Year
636
1993
618
,".
....
1994
700
1995
Figure 26, Total blue whiting survey data 1989-95, Number of fish by age caught per hour trawling in relation to the total number of stations in a year.

65° j
.
~,'
!
t f
!
r - - - - - - - - . .
Ä Pe1agic Trawl
• Bottom Trawl
60°
!
r
50° ,
~
Figure 27. Criuse traek and stations of R.V. "lohan Hjort", Mareh/April1995.
a) Trawl stations, b) hydrographie stations .
., 4'• w co

1 o
58.
.
•
50
1 0 s..::0 ="'"'
1 50 . .
I • I .
I •
10° 5°
Figure 28. Distribution and relative density of blue whiting, March/April1995. Echo intensity (Sa-values) in m 2 /n.mile
2 x 11100.
<>
0° r
I

~~;~~
Figure 29. An example of blue whiting echo recordings from west of the British Isles.
Simrad EK-500 echo sounder, 38 kHz.
..
e e
_~
; .l:
,j::.
o

41
;
•
0
C")
~ I
I
+
>.0
ro~
"'O~ e: ro
::J
" - 0 cn
0
CO
1
1 fl
!
t,.;
I !+ tlij
It
!
t
,
+ th
t·1
'fot:!
I
'
"'"I' t
~
0 r"-
80 85 90 95
Figure 30. Julian days for the trawl stations of Norwegian surveys west of the
British Isles 1979-95. Dots: catch of blue whiting, cross: no catch.
g o
Ln
....
•
~f
I
.li
·t :
• • I
+.
+.
•
•
•
....
+.
• •
• I
•
•
.f.
•
•
::f +** ...
i
• • 1
• •
• I I
•
•
•
• • •
I · · · ·
I :
I
••
+:
I .
•
• i ; :
• •
•
I
+
:'lt1Illl:f
It.
ilt.-,-
I · ••, ~.,..
+
I
80 85 90 95
Figure 31. Latitudinal position of the trawl stations on Figure 30.
, ~
..
-e
0
~
IDCO
~
::J ro
~
ID(.O
c-
E
ID
--.:::I'"
C\I
.i
•
• t
•
•
+.
•
I
•
•
• •
I
•
•
....
i
.;.
+ •
•
• •
•
II
•
H
•
•
:f;
•
•
•
• i!HhH!I
• I I •
+
+
• •
....
+
•
•
...
·:t
'+
•
I
•
0
Ln
C")
I t •
I t -.:::I'" •J
, I
• ++ +
•
.
•
•
•
•
•
-
>.
0
(.0
Ln
C")
"e: 0
:= C\I roLn
C1JC")
0
0
Ln
C")
!
i.
~
. .....
I
I
~
.+
•
•
.
I
•
•
..
. ' -
~~
I
I
•
...
•
•
.
: :jl
·,t lt .
....
+
+.
.+
I • •
....
•
I
I
+
.
• • •
'+*
+
Ii-
• • •
• •
• • l
•
•
I
• t
80 85 90 95
Figure 32.
Temperature, t O C, at catch depth for the trawl stations on Figure 30.
-80·_·" 85 90 95
Figure 33.
Salinity, S%o, at catch depth for the trawl stations on Figure 30.

42
0
<D
Ol
"0
::l
~ lO lO lO
'" a)
9
0 lO
80 b)
~
0
9
" blw1 (max = 195919 )
~
0
Q
0
0
• t
I t
0
, t e
.
i i
.
0
Q
85 year blw2 (max = 57408)
90
0 e
Q
Ö
•
~
95 o
'" o
•
~
~ t
•
• i
6 i t o
LO c)
80 95 85 year blw3plus (max = 599067)
90 o
'"
Ol
"0 .a
"~
- l O
LO
8 :
I
•
H--
8·
~
6 o •
; ! ; t
: ' i .-----.
• o i~~ o
6
• t
"
•
o
1 :
•
~Q~~
•
1 ;
@ : ,
• a .
t t
0
I
.
.
i o
LO
80 85 90 95 year
Figure 34. Catch ofblue whiting by age group (in absolute numbers) and latitude, from the
Norwegian surveyswest of the British Isles 1979-95. a) I-group, b) 2-group, c) 3+ group.
,
·
•
..
fI

43 a) proportion for 1-group
III
CD
•
•
•
0
CD
Cl
"0 ..e
C;;lll
-lll
0
III
.;.
-
=
.
-
T
I
.
~
-
-
.
--
-
I
.
....
.
-
-
I
-
?
:§
-:-
.
-
-t-
-
!
l
:
.......
-
-'-
.:.
-
-
"="
":
.
I
!
--
·
T
-
-
--
-=-
•
80 85 year
90 95 b) proportion for 2-group
•
•
~e
0
CD
Cl
"0
"
.!l!lll
0
III c)
=
...
-
.
-:-
-
80
z=
.
.
.:.
-::;-
.-
-
.....
-
:
-
-
-
-
~
T
...
•
--
.
!
;
! .
~
--
~
.
·
.;.
-
-
-
l' -
.:.
.:.
-
-
:
!
95 85 year proportion f~r 3+ -group
90
III
CD
0
<D
Cl
"0
3
~
III
III
0
III
-
~
...
-
-
=
-
-
-
-
=
-
...
.
=
-
...
=0
-
-
-
-
-
.....
!!!!
~-
-
- .:x:..
-
-
~-
~
~.
.~
-
-
-
-
-
'='
-
-
-
-
~
......
-=-
-
~ ii:iii
-
-
-
-
--
-
~
.
80 85 90 95 year
Figure 35. Catch of blue whiting by age group (in proportion of the total) and latitude, from the Norwegian surveys-west of the British Isles 1979-95.
a) l-group, b) 2-group, c) 3+ group.

53
0
30'N
15°24.5'\'1
44 a
...
---::,-
,,'\\.
~-.
" \ \ \ \ \ "
\\,
Porcupine Bank
SEFOS Section DO.
14
12 n--5
53
0
30'N
15
0
24.5'W
4
10
12
14 c.
35 • 3
____ 35.2
b
Porcupine Bank
SEFOS Section
DO.
14
Figure 36. Echo recordings of blue whiting (red markings) and plankton and mesopelagic fish
(blue markings) along a hydrographie seetion at the Poreupine Bank, down to 1500m depth, spring 1995. a) with temperature, tO C, b) with salinity, S%o.
Depths in
1DOm 's seale.
53
0
30'N
12
0
26'VJ
•
•
•
•
•
,
•

45
,
I
•
/ j
-
IDCO
~
::J
CO
~
0><0
C-
E
0>
-~
0
C\I
•
•
• •
••
•
•
•
•
•
•
•
••
•
•
•
•
•
I
•
•
••
•
••
•
•
• •
•
•
•
• •
•
•
• •
•
..
' •
.....
••• •
•
-
U
111··.· .:
••1:'I!i.11
I·
,'11 1
•
••
• ••
I ·
•
••
• :
•
3500 3520
3540 3560
Figure 37. T-S plot of values from catch depth of all the Norwegian trawl stations west of the British Isles 1980-95 .

46
:;
~
~'"
E
CD
-~
3480 3500 3520 3540 3560 salinity
~eo
:J iü
~<D
E
CD
- - t
-
0
N year 81
3480 3500 3520 3540 3560 salinity
~eo
:J
~
~'"
CD
- - t
-
0
N year83
0
~eo
:J
~
~'"
E
CD
- - t
N
3480 3500 3520 3540 3560 salinity
3480 3500 3520 3540 3560 salinity
•
•
3480 3500 3520 3540 3560 salinity
3480 3500 3520 3540 3560 salinity
3480 3500 3520 3540 3560 salinity
3480 3500 3520 3540 3560 salinity
~eo
:J
~
~'"
E
CD
-~
0
-
N year90
3480 3500 3520 3540 3560 salinity
~eo
:J
~
~'"
-
0
CD
-~
N
3480 3500 3520 3540 3560 salinity
·348035003520 3540 3560 salinity
3480 3500 3520 3540 3560 salinity
Figure 38.
Separate T-S plots for each year
1980-95, of values from catch depth of the Norwegian trawl stations west of the British Isles. in relation to a fitted line for the average of points of all the years.
, •
3480 3500 3520 3540 3560 salinity
3480 3500 3520 3540 3560 salinity