The Pelagic Fish Stocks, Pilot Whales and Squid in Faroese Waters - Migration Pattern, Availability to Fisheries and Possible Links to Oceanographic Events

ICES CM 2002/N:07

The pelagic fish stocks, pilot whales and squid in Faroese waters - migration pattern, availability to fisheries and possible links to oceanographic events.

Stein Hjalti í Jákupsstovu

Abstract

Around the Faroe Plateau a complicated system of ocean currents at various depths is created by the advection of warm Atlantic water from south and west, and cold east Icelandic water north of the Faroes running to the south and east and the very cold deep Norwegian Sea water running south and west trough the Faroe Channels. Time series of salinity and temperature data indicate the strength of each of these currents to vary both inter annually and between years. The availability to fishery of several pelagic fish stocks, pilot whales and squids migrating regularly or occasionally to and trough the Faroe area has also varied. In the paper biological and fisheries time series are presented and the possible links between the variations in the fisheries data and the variations in the hydrography are explored. In addition, special oceanographic events are described and their effect on the fish stocks and the production in the area discussed.

Keywords: Faroe Islands, blue whiting, mackerel, herring, capelin, pilot whale, squid, migration, oceanographic variations, oceanographic events.

Stein Hjalti í Jákupsstovu. Faroese Fisheries Laboratory, Nóatún 1, P.O. Box 3051, FO 110 Tórshavn, Faroe Islands, e-mail: [email protected]

1 Introduction The East Greenland-Scotland ridge divides the Nordic Seas from the Atlantic Ocean. Across the Ridge flows warm and saline waters to the North in the upper layers and in the deeper layers cold and less saline waters flows to the South (Hansen and Østerhus, 2000). The inflow of warm water ensures a mild climate much further north in the Northeast Atlantic then otherwise possible in addition to enhancing a large marine biological production (Figure 1). Time series monitoring of various oceanographic parameters have shown the northward flow of warm water and southward flow of cold water vary both inter annually and seasonally. For the Faroe Islands, situated on the ridge midway between Iceland and Scotland, the influence of the warm and cold currents have major impacts as their relative strength affect the productivity of the area.

Figure 1. Main features of the near surface circulation in the Eastern North Atlantic of significance for the species dealt with in this paper. (Redrawn from Hansen and Østerhus (2000)).

A number of pelagic fish stocks as well as stocks of marine mammals migrate annually to and through Faroese waters on their feeding and spawning migrations. And in addition other pelagic stocks may occasionally invade the area for a short period. Pilot whales are mainly found in Faroese waters during the months of July-September, probably arriving from South in search for their main food item squid. They can, however, be observed in the area throughout the year (Joensen and Zachariassen, 1982). Blue whiting after spawning west of the British Isles during March-April migrates through the Faroese area on way to the feeding areas in the Norwegian Sea. In late autumn and winter the migration route towards the spawning area also goes through Faroese waters (NEAFC, 1999).

2 Atlantic mackerel from the spawning areas south and west of England and Ireland migrates in May north into the Norwegian Sea to feed and back again in the winter and spring. Although the main routes appear to be along the shelf edge West of the British Isles a part of the northbound route also goes through the western part of the Faroe Shetland Channel (ICES, 2002 b). A significant proportion of the European stocks of Atlantic salmon feeds in the Norwegian Sea north of the Faroes (Jacobsen, 2000). In the last five years a pelagic longline fishery for Atlantic tuna has been developing in Faroese waters in late summer and autumn. The distribution of the fishery, conducted mainly by Japanese fishing vessels indicate a northward feeding migration in late summer and autumn from the central mid Atlantic to the Northeast (Faroese Fisheries Laboratory, unpublished data). With several years apart, large concentrations of squid (Todarodes sagittatus) during summer invade the Faroe Plateau (Hoydal and Lastein, 1993, FFL, unpublished data) During the 1950'ies and 1960'ies the large stock of spring spawning Atlanto Scandian herring, both on its feeding distribution in the Norwegian Sea and the spawning migration back to the major spawning areas along the west coast of Norway's distributed in and migrated trough Faroes waters north of the Faroes. In addition a part of the stock also spawned in Faroese waters (Anon, 1995 a). In 1990 and 1991 large concentrations of autumn spawning herring were found and fished on the eastern part Faroe Plateau. A small local stock of autumn spawning herring exists inshore at Faroese, however, the catches of 5000 and 16000 tonnes in the respective years by far exceeded the capacity of this stock. Based on vertebra count and age distribution the most likely suggestion was, that the herring in question belonged to the West of Scotland Northern North Sea autumn spawning stock complex (Jacobsen, 1990; 1991). 0-group capelin is in some years found in low abundance on the Faroe Shelf during summer. However, in 1991 it was very abundant and even outnumbered the 0-group cod on the shelf (Jákupsstovu and Reinert, 2002).

From the whaling statistics in Faroese waters a pattern of seasonal migration to Faroese waters by many of the larger whale species is apparent (Bloch et al, 2000). And finally tagging of hooded seals with satellite tags in the area west of Jan Mayen has shown a significant migration to the Faroese area of these seals. The timing and depth distribution of the dives by area indicate this to be a feeding migration targeting blue whiting (Folkow and Blix, 1999)

During the period from which we have information on the distribution of the individual stocks, significant changes appear to have taken place. And a natural question is to what extent these changes have been caused by changes in the oceanographic regime or by changes in stock size caused by natural changes in recruitment and fishing pressure. As most of the information on the distribution and migration routes arrives from the fisheries it is not possible in any quantitative term to depict the temporal and spatial distribution of any of the stocks. And the information on the variation in the hydrographic regime available is not collected and processed with this question in focus.

3 Nevertheless, during the post war period some striking hydrographic events have been reported, and in the wake of these also biological events have been seen and reported to. In this paper an attempt is made to map the oceanographic events related to Faroese waters and to explore to what extent biological signals by the various stocks might be coupled to these.

Hydrography

The Faroe Islands emerging out of the Iceland Scotland submarine ridge system and border the Nordic Seas to the North and the Atlantic Ocean to the South. Across this ridge flows trough a complicated system Atlantic water to the north and cold water to the south. These currents trough annual, long term and sporadic variations in direction and strength have great impact on the marine ecosystem on the Faroe plateau as well as on the large pelagic fish stocks seasonal migration in and out of the Faroese area. The relative strength of the various currents has formerly been estimated from temperature and salinity measurements using geostrophic models. Since 1995, however, time series of current measurements have been obtained using ADCP profilers (Hansen et al., 1999), and from these a far better understanding of the flow around the Faroes has been obtained. In general two sources of Atlantic waters feed the Northern areas as seen in Figure 1. Modified Atlantic Water (MNAW) flows from the Midatlantic Ridge in two main directions. One northwards as the Irminger Current (IC) flows into the Irminger Sea and the other slightly more to the east into the Island Basin as the North Atlantic Current (NAC). The other source is the slightly more saline North Atlantic Water (NAW), which flows from the Bay of Biscay to the north along the continental shelf edge as Continental Slope Current (CSC). Most of the Atlantic water entering the Faroese area arrives from the NAC, which south and west of the Faroes breaches into several branches. One goes to the east into the Faroe Shetland Channel south of the Faroes, the other flows to the north on the west side of the Faroes, one to the west towards Iceland and then to the nast north of the Iceland Faroe Ridge. This branch admixed with the other branches of MNAW flowing north to the west of the Islands and colder and fresher East Icelandic Water flows further to the East and is now renamed the Faroe Current (FC). The greater part of this water mass continues to the north into the Norwegian Sea forming a gyre. In addition a part of the EIC flows to the south into the Faroe Shetland Channel soon submerged under the north flowing NAC. Further south a submarine front is established between this water and the north flowing NAC. On the Eastern side of the Faroe Shetland Channel, the more saline CSC dominates the water masses. This current continues to the north with branches into the North Sea and further into two branches along the Norwegian shelf now renamed the Norwegian Atlantic Current (NWAC). In a preliminary balance estimation of Atlantic water into the Nordic Seas Hansen and Østerhus (2000) arrive at 1 Sv flowing trough the Denmark Strait, 3.3 Sv trough the Faroe Iceland gap and 3.7 Sv through the Faroe Shetland Channel. They suggest a branch of the MNAW into the Rockall Trough, but they put a question mark on it and they do not divide the poleward flow trough the Faroe Shetland Channel into water of NAW origin and MNAW origin. Holliday et al (2000) using a period of 23 years of multi annual surveys in the Rockall Trough arrived trough geostrophic calculations at the same

4 total flux trough the FS-Channel as Hansen and Østerhus (2000) namely 3.7 Sv. But they found high-level interannual variability ranging from 0 to 8 Sv. They name the MNAW entering the Rockall Trough to Eastern North Atlantic Water and estimate the flow of this water on average to be 0.7 Sv and the Continental Shelf current to carry on average 3.0 Sv. over the 23 year period.

The hydrographic section Noslø-Flugga has been run for more then 100 years, and yields a good overview of the annual variation of the temperature and salinity in the Faroe- Shetland Channel. For the purpose of this paper data from this section has been made available by the Marine Laboratory in Aberdeen. And used by me is the water with the greatest salinity at the four innermost stations on the Faroe side averaged. In Figure 2 is shown the annual average temperature and salinity on the Faroese side of the channel for the period 1947-2001.

One interesting feature in Figure 2 is the great fluctuations in the salinity. In the period up to 1970 a variation in general between 35.18 and 35.34, then followed by very low salinity's in the seventies. Since 1980 the salinity's have in general been lower then in the fifties and sixties. However with one exception in 1990, when a record high average salinity of 35.37 was recorded. An other interesting feature is the pulsating variation in the salinity, as is seen when a three year running mean is plotted.

35.4 10 9 35.35 Temperature 8

35.3 re u y 7 t

35.25 era lin 6 p

a m S

5 e

35.2 T Salinity 4 3 years running mean 35.15 3 35.1 2

1947 1951 1955 1959 1963 1967 1971 1975 1979 1983 1987 1991 1995 1999

Figure 2. Annual average salinity and temperature on the Faroese side of the Faroe Shetland from the Nolsø- Flugga section 1947-2000. The running mean (3 years) is also plotted.

Hansen and Østerhus (2000) give the salinity range of MNAW to be between 35.1‰ and 35.3‰ and NAW to be between 35.35‰ and 35.45 ‰. In the period since 1947 pure NAW has, according to the Nolsøe Flugga section dataonly been encountered once (in 1990), but water more saline then MNAW were observed on 22 occasions (Table 1) but only two times since 1970.

Table 1. Months in any year where the average salinity was found higher then 35.3‰ on the Faroe side of the Faroe Shetland Channel.

Year Month Salinity Temp. 1947 6 35.306 7.48 1947 7 35.301 8.23 1950 5 35.344 7.1 1950 7 35.303 10.73 1952 2 35.306 6.09 1953 6 35.343 8.08 1955 5 35.454 7.3 1955 9 35.316 8.26 1956 11 35.334 8.71 1957 6 35.304 10.04 1959 7 35.305 8.53 1960 1 35.331 7.13 1960 7 35.305 8.54 1960 9 35.33 9.1 1960 10 35.315 9.34 1961 6 35.326 9.49 1961 7 35.314 9.16 1961 8 35.32 8.64 1961 10 35.319 9.07 1961 12 35.36 8.3 1963 5 35.323 7.3 1968 6 35.342 7.84 1968 7 35.3 9.06 1969 6 35.333 8.86 1990 9 35.368 8.02 1999 6 35.305 9.37

Pilot whale (Globicephalus meleana)-Grind (in Faroese).

The pilot whale has for centuries been of paramount importance for the livelihood of the people of the Faroe Islands. Pods of pilot whales sighted within a comfortable herding distance of the shore are driven by small boats into a suitable bay, forced to strand on the beach, and slaughtered. The meat and blubber is then by a strict and complicated system divided between the man participating in the hunt and the people in the community. The sharing system has been altered during the centuries. However the basic principle that everyone in the community is entitled to a share has always been in force. A proper sharing requires a census of the catch, and this has always been the responsibility of the local authorities. Each whale killed is numbered and with a length ruler assessed to weights in skinn (1 skinn= appr.75 kg of meat and blubber). Based on this the total catch in skinn the catch is then divided between those entitled to a share. The basic records have the been archived. Müller (1884) from the archives was able to present data on

6 number of grinds (pods), by year, number of whales by pods and the number of skinn by pods for the periods 1584-1641 and 1709-1884. Later Joensen (1962) revised these data and extended the period to 1962. Since then a strict census has been kept of every grind killed. This series of pilot whale catch data is the longest catch statistic on record. In Figure 3 is shown the number of pods killed and the total number of whales by year for the period 1713-2001. However, there might be some missing data, especially for the more ancient part of the period, and great variation in number of grind and total number of whales killed by individual years, a long term variation in the availability of grind is apparent in the dataset. This is becomes even more apparent, when the data are presented as nine years running mean (Figure 4). This indicates a top in the early 18 century, a low availability in the middle and latter half of the same century. This is followed by a gradual increase in the first half of the next century culminating in a top in the middle of the nineteen century and then a gradual decline to the end of that century and a continuous low up to the nineteen thirties. From then on the availability of grind is on a higher level then previously found, however, with significant variations.

5000 30 Number of pods 4500 4000 Number of whales 25

3500 20 s 3000 2500 15 2000

10 No's of pod

No's of whales 1500 1000 5 500 0 0 1709 1725 1743 1796 1812 1828 1844 1860 1876 1894 1911 1929 1945 1961 1977 1993

Figure 3. No's of pods of grind caught by year, and the corresponding total number of whales killed. 1709-2001.

2500 20 Number of pods 18 2000 Number of whales 16

e 14 ds

h 1500 12 po

w f 10 o s of ' s ' 1000 8 o o N

N 6 500 4 2 0 0

1713 1729 1748 1800 1816 1832 1848 1864 1880 1898 1915 1933 1949 1965 1981 1997

Figure 4. No's of pods of grind caught by year, and the corresponding total number of whales killed. 1709-2001, presented as 9 years running mean

The long time variation in numbers of pod and whales caught might indicate a significant variation in availability of pilot whales in Faroese near shore waters. But the absolute levels is most likely also influenced by factors as increase in the population at the Faroes with time and the significant increase since the nineteen thirties onwards, most probably are due to this, and the motorization of the inshore fishing fleet. Pilot whales are found distributed over a wide area in the North Atlantic as shown in the distribution map compiled by Abend and Smith (1996) (Figure 5).

Figure 5.Distribution of long-finned pilot whales in the North Atlantic and Mediterranean Sea based on sighting data from 1952 to 1992 (Form a working paper by Abend and Smith (1996) presented to the ICES Study Group on long finned Pilot Whale, Cambridge 1996.).

Number of whales killed per month (%)

35 30 25 20 % 15 10 5 0 123456789101112 Month 8

Figure 6. The total number of whales killed since 1709 divided into percent per month.

Very little is known about any annual or seasonal migration pattern. But, although pilot whales can be found throughout the year at Faroes there is a significant peak season in the months July-September as shown in Figure 6. this indicates higher concentrations during these months as compared to the rest of the year, and is most likely due to increased abundance of squids around the Faroes in late summer.

Several attempts have been made to relate the long-term variations in the catches of grind at the Faroes to long term changes in the overall climate, however, without any obvious success. Since 1893 the standard hydrographic section Nolsoe-Flugga has been worked, and when possible up to several times per year by the Marine Laboratory in Aberdeen. For the period since 1947 up to present in Figure 7 is plotted the number whales killed by year against the average salinity on the Faroese side of the Faroe Shetland Channel.

3500 35.4

Salinity 35.35 3000

d 35.3 2500 ille k 35.25 s y

e 2000 l it a h

35.2 lin

a w S f 1500

o Pilot whales 35.15 's o 1000 N 35.1

500 35.05 0 35

1947 1951 1955 1959 1963 1967 1971 1975 1979 1983 1987 1991 1995 1999

Figure 7. The number of whales killed by year since 1947 and annual average salinity on the Faroese side of the Faroe Shetland Channel

The period 1946-1969 was characterised by high salinity, followed by the very low salinity's during the mid seventies and then increased salinity's in the following years. The number of whales killed each year to a certain extent images the salinity figures, with fewer whales killed when the salinity was low compared to when it was high. Especially when the increased boat and motorsizes in the last thirty years is taken into account. It should, however be noted, that the decrease in whale availability starts before the salinity decreases.

In order to explore this further the number of pods killed by year is plotted against the salinity for the entire period of the Nolsoe-Flugga dataset (Figure 8).

Although not significant, there seems to be a slight tendency, that the chances of higher availability are increased by higher salinity's. But years with few pods can happen whatever the salinity is in the Faroe Shetland Channel. An alternative interpretation is that there is a salinity window, which favours pilot whale availability (Figure 8)

30 25

20 ds

. po f 15 o

o N 10

0 -0.1 -0.05 0 0.05 0.1 0.15 0.2 Salinity anomaly

Figure 8. No's of pods of pilot whales killed against average salinity on the Faroese side of the Faroe Shetland Channel.

Blue whiting (Micromesistius poutassou)

Blue whiting is distributed and fished over a wide area in the Northeast Atlantic. In Figure 9 is shown the distribution of the total international caches by area for the period 1977-to 1997 as compiled by NEAFC (1999). Since then due to high recruitment in a number of years, changed national zonal jurisdiction, improved technology, higher prizes and a general increased international interest in the fisheries for blue whiting, the fisheries have been extended into wider areas, as in the Icelandic zone and into areas outside national jurisdiction to the west of the British Isles. This can be seen in the distribution of the catches in 2001 (Figure 10)

Total 1977-1997

Blue whiting catch (t) 100,000 to 9,999,999 (29) 10,000 to 100,000 (179) 1,000 to 10,000 (272) 0 to 1,000 (494)

Figure 9. Blue whiting total catch by statistical rectangle 1977-1997 (NEAFC, 1999).

Figure 10. Total catches of blue whiting in 2001 by ICES rectangle. Grading of the symbols: small dots 10-100 t, white squares 100-1 000 t, gray squares 1 000-10 000 t, and black squares > 10 000 t. (ICES, 2002 a)

The main spawning areas for blue whiting are off the shelf edge west of the British Isles from south of Porcupine Bank to the Hebrides, with peak spawning in March-April. The eggs and larvae drift with the prevailing currents, which from these areas are mostly to the north, however, some eggs and larvae may also drift to the south to the Bay of Biscay (svendsen, et al., 1996). The nursery areas are along the shelf edges over a wide area. In the Bay of Biscay in the south, off the West coast of Scotland, off the Northern North Sea and Norway (The Norwegian Deep), along the Norwegian coast further north, around the Faroe Plateau, South and East coast of Iceland. Occasionally, with very good year classes nursery areas are also found off East Greenland. After 1- 1½ year the juvenile blue whiting leave the nursery areas for the feeding areas, which in the north are mainly found in the Norwegian Sea. The adult post spawning blue whiting migrate to north to the Norwegian Sea to feed. On route they pass the Faroe Plateau partly through the Faroe Bank Channel and partly trough the Faroe Shetland Channel. In some years, when more blue whiting migrate trough the Faroe Bank Channel as compared to other years, the availability to the fisheries is greater then in the years, where the main migration is trough the Faroe Shetland Channel. Hansen and Jákupsstovu (1992) attribute this difference in availability to variations in the hydrographic regime in the area.

The extensive migration between the feeding areas in the Norwegian Sea to the spawning area and back is clearly demonstrated by the distribution of the international fishery in for blue whiting in the Northeast Atlantic (Figure 11).

12 March June 1977-1997 1977-1997

April July 1977-1997 1977-1997

May August 1977-1997 1977-1997

Figure 11. Distribution of blue whiting monthly catches 1977-1997 (NEAFC, 1999).

13 September December 1977-1997 1977-1997

October January 1977-1997 1977-1997

November February 1977-1997 1977-1997

Figure 11. Continued

14 The annual catches of blue whiting in the Northeast Atlantic (Figure 12) varied in the period 1981-1997 between 400 and 800 thousand tonnes with an average of 600 thousands tonnes. Since then the annual landings have increased every year and were in 2001 almost 1.8 mill tonnes. Very good recruitment to the blue whiting stock in recent years (Figure 13) combined with increased international effort is the main reasons for the increased catches.

2000 1800

s 1600 1400 1200 1000 800 600 Thousand tonne 400 200 0 1981 1983 1985 1987 1989 1991 1993 1995 1997 1999 2001

Figure 12. Landings of blue whiting 1981-2001 (ICES 2002a).

60 50

s n 30 illio B 20 10

1981 1983 1985 1987 1989 1991 1993 1995 1997 1999

Figure 13. Recruitment (O-years billions) to the blue whiting stock (ICES, 2002a)

Mackerel (Scombrus scombrus).

Mackerel in the Northeast Atlantic have for the last few years been assessed as a single stock, composed of three components. The Southern Mackerel component, spawning in

15 the Bay of Biscay, the Western component, spawning to the West and South of the British Isles and the North Sea Mackerel. One of the main reasons for combining the three stock components into one units were tag returns from mackerel tagged in the Bay of Biscay just of the Iberian peninsula from very wide areas to the north including the Norwegian Sea an the North Sea (Uriarto and Lucio, 2001). The recapture sites and time of recapture clearly indicated a systematic migration pattern. Mackerel is, due to the absence of swim bladder, difficult to detect acoustically, and a picture of the migration path has to be depicted from egg surveys, tag returns and the distribution of the fishery. However, this may be improved in forthcoming years due to more sophisticated equipment, including aerial surveys (ICES, 2002 c) The spawning areas for the western and southern mackerel components extends from the Bay of Biscay to the West of the Hebrides with peak spawning from mid April to Mid June between 50oN to 56oN. The spawning takes place on or just off the shelfedge. The eggs and larvae drift with the currents and the prevailing nursery areas are on the shelfedge west of the British Isle, in the North Sea and along the Norwegian Shelf. Juvenile mackerel are only very rarely found over deeper water off the shelf, and very rarely at the Faroes. The adult mackerel migrates to the Norwegian Sea for feeding. In early summer over a wide area, but later more in Norwegian waters in the Eastern Norwegian Sea and in the North Sea. The migration south to the spawning areas begins in late autumn early winter, and is mainly along the shelf edge west of the British Isles.

The catches of adult mackerel by quarter during the period 1977-2000 (Figure 14 (ICES, 2002 c)) have been distributed over a wide area. Due to varying management regimes the distribution of the catches, however, do not fully represent the availability by national zones. Russian vessel (formerly USSR vessels) have through bilateral fisheries agreements with the Faroe Islands fished mackerel in Faroese waters since 1989, and have in addition also fished mackerel in areas outside national jurisdiction in the Norwegian Sea. The distribution of these catches (Figure 15) by month each year during the period 1989-1997 indicates the mackerel catches is mostly to be distributed in the eastern part of the area along the border of the EEZ's of EU and Norway. However, in some years also in the central and western parts of the Faroes and International waters Belikov et.al, 1998).

The total landings of the Western mackerel stock (Figure 16) have for a number of years fluctuated between 400 and 800 thousand tonnes, and in the most recent years been stable around appr. 600 thousand tonnes. The recruitment (Figure 7) has fluctuated between 2 and 8 billions at age 0.

16 70°N 70°N

65°N 65°N

60°N 60°N

55°N 55°N

50°N 50°N

45°N 45°N

40°N 40°N 30°W 20°W 10°W 0°E 10°E 20°E 30°W 20°W 10°W 0°E 10°E 20°E

Quarter 1 Quarter 3

70°N 70°N

65°N 65°N

60°N 60°N

55°N 55°N

50°N 50°N

45°N 45°N

40°N 40°N 30°W 20°W 10°W 0°E 10°E 20°E 30°W 20°W 10°W 0°E 10°E 20°E

Quarter 2 Quarter 4

Figure 14. Distribution of the total mackerel catches by rectangle and by quarter from 1977-2000 (ICES, 2000).

17 June 1989 July 1989 August 1989

June 1990 July 1990 August 1990

June 1991 July 1991 August 1991

Figure 15 a. Catches of mackerel by the Russian trawler fleet by statistical area in June-August 1989-1991. The symbol size is graduated by the catch in tonnes.

18 June 1992 July 1992 August 1992

June 1993 July 1993 August 1993

June 1994 July 1994 August 1994

Figure 15 b. Catches of mackerel by the Russian trawlerf leet by statistical area in June-August 1992-1994. The symbol size is graduated by the catch in tonnes.

19 June 1995 July 1995 August 1995

June 1996 July 1996 August 1996

June 1997 July 1997 August 1997

Figure 15 c. Catches of mackerel by the Russian trawler fleet by statistical area in June-August 1995-1997. The symbol size is graduated by the catch in tonnes.

900 800 700 600 500 400 300

Thousend tonnes 200 100 0 1972 1974 1976 1978 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000

Figure 16. Landings of Western Mackerel 1972-2000 (ICES, 2002 b).

6 Billions 4

0 1972 1974 1976 1978 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000

Figure 17. Recruitment age 0-Western Mackerel (ICES, 2002 b)

Herring (Clupea harengus)

Three stocks of herring are found in Faroese waters. The spring spawning Atlanto Scandian herring stock is historically the largest. The stock later renamed Norwegian spring spawning herring has been sampled for almost a century, and in ICES (2002 a) a VPA run for the period 1907-2000 is presented. This shows that the stock has undergone great fluctuations in stock size and catches during

21 the entire period (Figure 18) and that the recruitment is characterized by in general low year classes interspersed with very large year classes several years apart (figure 19)

2500

' 2000 s

e nn 1500 to

nd a

s 1000

u o h T 500

1907 1913 1919 1925 1931 1937 1943 1949 1955 1961 1967 1973 1979 1985 1991 1997

Figure 18. Landings of Norwegian spring spawning herring 1907-2001 (ICES, 2002a).

800 700 600

s 500 n 400

Billio 300 200 100 0

1907 1913 1919 1925 1931 1937 1943 1949 1955 1961 1967 1973 1979 1985 1991 1997

Figure 19. Recruitment (0 year) of the Norwegian spring spawning herring 1907-1999 (ICES, 2002a)

This stock, which was depleted in the late 1960ies and recovered in the 1990ies has the last fifty years shown great variations in distribution and migration which has been described by a number of authors e.g. Dragesund, et al, 1980; Hamre, 1990; Anon, 1995, Dragesund et al., 1997. The main spawning areas are along the Norwegian West Coast from Karmøy in the south to Lofoten in North. The larvae drift with the prevailing current to the north, In most years the main nursery areas are in the coastal and fjords of Western Norway, however, in years with good recruitment the main nursery areas are in

22 the Barents Sea (Figure 20). The relative importance of the various spawning grounds has varied. After spawning in March-April the adult herring in the fifties and sixties migrated out into the Norwegian Sea to feed and the most important feeding areas were in the western parts of the Norwegian Sea between north of the Faroes, North of Iceland and Jan Mayen (Figure 21 a.) In this period the main wintering area was in the frontal region between Faroes and Iceland. The spawning migration route was mainly due north of the Faroes. In addition to the spawning areas of Norway, the stock also spawned on the banks east of the Faroes. In the sixties in addition to the feeding areas in the Western part of the Norwegian Sea herring also fed in the Northern Norwegian Sea, and an additional wintering area off Northern Norway was occupied (Figure 21 b). In the last years before the stock collapsed (1966-1967) The feeding area was in the Northern Norwegian Sea to the west of Bear Islands, from there they migrated to the wintering area between Faroes and Iceland (Figure 21 c).

Following the stock collapse in the late sixties the stock changed its feeding, nursery and wintering areas from oceanic to coastal migration, and the stock spent the entire life cycles in near shore waters (Dragesund et al., 1980; Røttingen, 1990; Hamre 1990). With the recruitment of the strong 1983-year class to the spawning stock 1987 onwards, the stock commenced wintering in the Vestfjorden area and in other fjords in that area and the feeding areas were extended to the West. With the increasing spawning stock the spawning areas were gradually extended southwards (Slotte, 1998). With the recruitment of the very big 1991 and 1992-year classes the spawning stock was rebuilt to historic levels, and the feeding area was extended further to the west into the Norwegian Sea. (Slotte and Dommasnes, 1998). However the wintering areas remained the same coastal fjords. Since 1995 the distribution of the feeding herring in the Norwegian Sea has been monitored annually by national (especially Norwegian and Russian) and coordinated international multi ship surveys (Anon,1995;Vilhjálmsson et al, 1997; Holst et al., 1997; Holst et al., 2001). During these surveys, the greatest distribution was observed when the stock peaked in 1995 and 1996 (Fig 22 a) when the feeding area was extended to the South almost to the Faroese Shelf in May. Later the stock moved to the North into the International and Jan Mayen area in June and later even further to the North and west into Norwegian waters in July and August. With the gradual reduction of the stock due to the fishery and natural mortality outweighing the recruitment to the stock, the southern extension of the feeding area has gradually been reduced as seen in Figures 22 b, c and d.

The smallest herring stock at the Faroes is a local stock of summer/autumn spawning herring, which spawns within the bays and sounds of the Islands. Both nursery and feeding areas are inshore. There is only a minor fishery on this stock. Occasionally, shoals of autumn spawning herring are found on the banks and shelf of the Faroe Islands. These occurrences are infrequent, and practically no fishery takes place on this stock concentrations. However, in 1990, and especially 1991, the concentrations were large and widely distributed, and a fishery by purse seine took place (Jacobsen, 1990, 1991). Based on biological characters such as age composition, growth rate and

23 vertebrae counts Jacobsen (1991) concluded that the concentrations most likely originated from the North Sea autumn spawning stock complex. The total catches of autumn spawning herring on the Faroe Plateau in 1990 amounted to 4-5 000 t and in 1991 to 16 000 t. Occasionally, catches of this herring have taken place since, but the catch in any subsequent year has never exceeded a few hundred tonnes.

Figure 20. Distribution of young herring and direction of post larval drift (Redrawn from Anon, 1995)

Figure 21 a. General presentation of the migration patter 1950-1962 (Redrawn from Anon, 1995).

Figure 21 b. General presentation of the migration pattern in the period 1963-1966 (Redrawn from Anon, 1995).

Figure 21 c. General presentation of the migration pattern in the period 1967-1968 (Redrawn from Anon, 1995).

Figure 22 a. Inferred migration pattern of the Norwegian spring spawning herring in 1995 (Anon, 1995)

Figure 22 b. Inferred migration pattern of th Norwegian Spring spawning herring in May 1997 (Vilhjálmsson, et al, 1997).

Figure 22 c. Inferred migration pattern of the Norwegian spring spawning herring in March-April (blue arrows, near cost) and May-June (red arrows, NW. Distribution by isolines is as measured during the international survey in May 1997 (Vilhjálmsson, et al., 1997).

Figure 22 d. Inferred migration pattern of the Norwegian spring spawning herring in July (red arrows) and August-September (blue arrows), 1999 (Holst et al., 1999).

Figure 22 e. Inferred migration patter of the Norwegian spring spawning herring in April (blue arrows, pointing into isolines), May (isolines and June (red arrows, pointing out of isolines), 2001 (Holst et al., 2001)

Tuna (Thunnus thynnus)

In later years (since 1997) blue fin tuna has been observed and fished in Faroese waters. The fishery has almost exclusively been by Japanese tuna long lining vessels with permission to fish in Faroese waters. The fishery normally starts in the South western parts of the Faroese EEZ in September and then moves gradually to the North East. The vessels are obliged to carry onboard Faroes observers, which sample the catches. From these it is apparent that the tuna in Faroese waters feed almost exclusively on squid, however, also blue whiting, silver smelts and other pelagic fish species are found in the stomach content. It is not known to what extent this migration of tuna to the Northeast is a new phenomenon, but there are no or at any rate very few records of accidental catches of tuna in Faroese waters previously.

Squid (Todarodes sagittatus, Lamarck,1798).

The squid (Todarodes sagittatus) may in some years enter Faroese waters during summer, especially in July-September. In some years they are quite numerous and in these years a special fishery for squid develops. The catches of squid at Faroes were only recorded from 1973 onwards, and since then significant catches have only been recorded in the years 1980-1984 (Table 2). When squids are found in inshore waters a fishery for them takes place. This is a very special fishery, where everyone is able to participate, and this is an event, which in most cases is noted by the newspapers. By going through the local newspapers it has been established, that significant fisheries for squids at least took

28 place in the years 1952, 1954, 1957, 1961 1967, although no official catch records are available.

Table 1. Faroese catches of squid in Faroese waters in the period 1980-1986 by month (in tonnes). (From Gaard, 1988)

Year July August September Total 1980 236 191 77 504 1981 1224 756 151 2131 1982 5 228 15 248 1983 - - - 200 1984 0 951 197 1147 1985 <1 <1 2 2 1986 0 0 0 0

Periods with and without squid seem to co-occur in the Faroes, Iceland and Norway. However, during the 1980'ies, when squid occurred in all three areas as high squid concentrations appeared the same years in Iceland and at the Faroes, while the highest concentrations were found in Norway in other years (Gaard, 1988) (Figure 23)..

Figure 23. Annual catches of squid (Todarodes sagittatus) at Faroes, Iceland and Norway 1974- 1986 (Redrawn from Gaard, 1988).

However, no strict recordings are of any spawning area for the squid, it has been suggested by Sennikov et al. (1986) and Shimko (1989) from distribution of small juveniles to be in the area of the Midatlantic Ridge. From the spawning area the larvae and juveniles are assumed to drift more or less passively with the North Atlantic current to the North. The age distribution of the young squid caught at the Faroes multiplied with the average speed of the Atlantic drift compares well with the distance from the Faroes to

29 the Midatlantic Ridge. (Gaard, 1988). And similar figures are also found by other authors (Gaard, 1988).

The fishery for squid at the Faroes always starts in the sounds between the northernmost islands, and then moves gradually further south to the central sounds and fjords of the Faroes. That and the fact, that the squid fishery at Faroes and Iceland occurs in the same years would indicate that the squids coming to the Faroes mostly drifts/migrates in the western part of the FC, which also reaches Iceland. And that, in years where squids are fished in Norway and not as much at the Faroes and Iceland, they are drifting/migrating in the eastern part of the FC.

In Figure 24 are shown the annual number of whales killed 1946-2000, the annual average salinity on the Faroe side of the Faroe-Shetland Channel. Years where significant catches of squid have been have been taken in Faroese waters are indicated by arrows.

Number of pilot whales and average salinity by year

3500 35.4 3000 Salinity 35.35

2500 35.3 35.25 2000 35.2 1500 Pilot whales 35.15 1000 35.1 500 Squid years 35.05 0 35 1947 1951 1955 1959 1963 1967 1971 1975 1979 1983 1987 1991 1995 1999

Figure 24. Salinity on the Faroe side of the Faroe Shetland Channel (yellow-individual years, green-3 years running mean), Number of pilot whales caught by year (blue-individual years, red- three years running mean) and years with significant catches of squid.

The figures for number of whales and average salinity are also plotted as three years running mean. Squids were caught in the years indicated by arrows.

Discussion

Great variations have been observed in the salinity on the Faroe side in the Faroe Shetland Channel (Table 3) since 1947. This most probably indicates great variation in the strength of the various water masses entering the area: the East Icelandic Current (EIC), the North Atlantic Current (NAC) and the Continental Shelf Current (CSC). Inter annual variations in strength of the various currents has also been reported by several authors: Holliday et al. (2000) from a 23 year long dataset describe large inter annual variations in the pole ward transport trough the Rockall Trough. Holliday and Reid (2001) link high transport of water trough the Rockall Trough to ecological changes in the North Sea. Hansen and Østerhus (2000) describe from a number of authors long term variations in the Atlantic inflows to the Nordic Seas. Off north Iceland, long term hydrographic investigations have demonstrated large variations in the amount of Atlantic water present on the shelf with both inter annual and decadal time scales (Malmberg et al., 1994). Hansen and Kristiansen (1994) describe reduced inflow of NAW to the Faroese waters in the late 1980'is. Similarly in the Norwegian Sea during the PGSPFN surveys in the Norwegian Sea since 1994 (Anon, 1995; Vilhjálmsson et al., (1997); Holst et al., (1999, 2001)) great variations have been observed in the area occupation of East Icelandic Water. And finally Hansen et al., (2000) have described decreasing overflow from the Nordic seas into the Atlantic Ocean trough the Faroe Bank since 1950.

Table 3. Average annual salinity's on the Faroe side of the Faroe Shetland Channel in three periods since 1947.

Period Salinity 1947-1969 35.275 1970-1979 35.199 1980-2001 35.236

From Figure 2 and Table 3 three regime shifts in salinity appears to have taken place in the period 1947-2001.

From the description of the migration of the various fish species it appears that quite a significant amount of pelagic fish biomass migrates to and trough Faroese waters on their seasonal cycle. And in addition so do pilot whales, other cetaceans (Bloch et al, 2001) and hooded seals (Folkov and Blix, 1995). By these migrations the various areas, often discussed in isolation are inter linked in a number of ways. Mackerel ties together the Bay of Biscay, the areas west of the British Islands with the Norwegian Sea and the North Sea. So does blue whiting, however adding to the areas at east and south Iceland and East Greenland. The Norwegian Spring Spawning herring links the Barents Sea to the Norwegian Sea, and formerly also the areas North of Iceland. Icelandic capelin links together the area north of Iceland to the Norwegian Sea and the areas south of Iceland. By feeding in one area and spawning in another, assimilated energy is transported between the areas in a not easily quantifiable way. Predators as pilot whales, other cetacean and seals also migrate in a seasonal pattern and tax the pelagic biomass in an unknown way, as they forage across area boundaries.

31 The hooded seals alone may consume approximately 100 000 tonnes of blue whiting in Faroese waters (Folkov and Blix, 1995).

From the fisheries of the various pelagic species, great inter annual variations in areas have been observed, which is linked to the variations in the distribution and strength of flow of the various water masses. But there are no comprehensive investigations to fully substantiate this suggestion. From the distribution of the fisheries of blue whiting influences on the migration route past the Faroe Islands from the prevailing currents has been shown by Hansen and Jákupsstovu (1992). The changes observed in the distribution of the fisheries for blue whiting since 1996 may to a large extent be due to changes in effort, new technology and changed coastal states regime, but increased spawning in the Rockall area can not be precluded.

The distribution by month of the fisheries by Russian vessel for mackerel in the Faroes EEZ and the area outside national jurisdiction north of this ( Belikov et al.,1998) shows great variations. Although overall most of the catches were taken in the eastern parts of the area, there were significant deviations. The vessels were not limited by any area restrictions other than to be within the two zones, and assuming some sort of co-operation between the vessels, this would indicate real variations in distribution of the mackerel possibly caused by differential distribution of water masses.

Up to the nineties the catches of pilot whales to a large extent images the average salinity in the Faroe side of the Faroe Shetland Channel, and the fisheries for squids appears to have taken place only when the salinity's were high. The preferred food for pilot whales is squid (Desportes and Mouritsen, 1993). As the main season for both species at Faroes is in July-September it seems likely that the pilot whale migration to the Faroese waters is a feeding migration. Similarly tuna migration into Faroese waters appears to be a pursuit of squid (Faroese Fisheries Laboratory unpublished material). Three pre requisites have to be met for squids to reach the Faroe Islands in any significant numbers. A strong yearclass is needed, it must drift in the western part of the NAC and the flow of the NAC must be sufficiently strong to reach the Faroes in the required time available. Squids have not been observed in any significant number inshore of the Faroe Islands since 1984. It is not possible with the present knowledge to relay this to a reduced inflow of NAW.

The quite distinct difference in feeding areas and migration pattern of the Norwegian spring spawning herring since the recovery of the stock in the mid nineties as compared to the patterns in the fifties and sixties is quite a puzzle, which creates great attention. Apart from learning factors as the younger fish follows the older a hydrographic explanation can not be excluded. It is also a puzzle why the North Sea Mackerel component does not recover after so many years.

The best success criteria for a spawning area, is the survival of the progeny. This is also the basis for the long distance spawning migration by many fishspecies. The eggs and larvae drift with the prevailing current to a suitable nursery area and from there to a

32 suitable feeding area. From the feeding area they migrate to the spawning area and after spawning back again to the feeding area. All the species we are dealing with in this paper show long range seasonal migrations. Mackerel and blue whiting, respectively, spawn at and off the shelf edge to west of the British Isles. The eggs and larvae drift to the north in the water mass where they have been spawned. And as these are slightly different the nursery areas are different. In both cases the main feeding areas are in the Norwegian Sea, and although, there are overlap the adults are mainly distributed differently both horizontally and vertically. The Norwegian spring spawning herring spawns along the Norwegian coast and the eggs and larvae drifting with the prevailing currents grow up in nearshore Norwegian waters, the Norwegian fjords and in the Barents Sea. Before the collapse of the stock in the late sixties they also spawned on the banks to the east of the Faroe Islands (Jakobson, 1970), and the Icelandic spring spawning herring stock became extinct. There is a growing interest in the role Taylor columns and the anticyclonic circulation created by them play in retaining fish eggs and larvae over a restricted area and by this in the recruitment process. Taylor columns, are observed in several areas encountered by the different branches of the Atlantic drift. On the Faroe Plateau, the key to a distinct and separate marine ecosystem is the retention of the inner water masses within the tidal front (Hansen, 1992; Larsen et al., 2002) which keeps the holo and meroplankton, as well as fish eggs and larvae in place over the Plateau. Jákupsstovu and Reinert (2002) suggest that the front and the anticyclone circulation in addition to the tidal forces also is affected by the strength of the flow of the various oceanic currents outside the Plateau. Mohn et al. (2002) describes anticyclonic circulation over the Porcupine Bank and suggest that a persistent Taylor column circulation around the Porcupine Bank provide an important mechanism for retention of pelagic eggs and larvae of the marine species spawning in the area. Similarly Sætre et al. (2002) correlate the spawning success of Norwegian spring spawning herring off the Norwegian coast to the formation of Taylor columns over the most important spawning grounds on the shelf off western Norway, especially the Halten and Sklinna Bank and other banks on the Norwegian Shelf. In later years a much larger proportion of the catches of spawning blue whiting than previously have been caught to the west and south of the Rockall bank, which might suggest an increased spawning in these areas. An increased effort in these areas as compared to previous years and consequently increased catches have been caused by changes in regulation of this area, from EU zone to an area outside national regulation as well as new and more efficient vessels and pelagic trawl. Since 1995, however, the recruitment to the blue whiting stock has by far exceeded the recruitment in the period 1981-1995. A possible explanation might be that due to Taylor column formation in the Rockall area survival of the blue whiting larvae has been enhanced. The three-year running mean of the average annual salinity on the Faroese side of the Faroe Shetland Channel suggest a pulsating nature of the characteristics of the water mass. Given the complicated current system in the area this indicates an inter annual variation in the relative strength of the various branches, which again affect both the migration and spawning success of any species adapted or favoured by individual branches.

33 In the period late 1980s - early 1990s, the recruitment to the major ground fish stocks and the fish growth rates in Faroese waters were very low and in the same period the fishing mortality was continuously high. Together this resulted in a collapse of the fisheries and subsequently the Faroese economy. In retrospect evidence has emerged, which indicates that unusual oceanographic conditions occurred in 1991 inducing a major disturbance of the marine life around the Faroes. One of the events was great influx of capelin in 1991 (Jákupsstovu and Reinert, 2002); others were immigration of autumn spawning herring (Jacobsen, 1990; 1991) and a very low primary production on the Faroe shelf affecting the whole ecosystem on the Faroe Plateau. (Gaard et al, 2002).

Jákupsstovu and Reinert (1994) showed that the mean weights at age of cod on the Faroe Plateau had decreased over time. They suggested that one possible explanation for this could be genetic changes due to selective cropping, but pointed also on great fluctuations in the food availability to the cod stock on the Plateau. Brander (1995), however, suggested that long term changes in temperature better explained the changes in mean weight at age of Faroe Plateau cod. A tentative plot of the mean weights at age against the NAO index indicate this also to be an explanatory candidate (Figure 25).

6 5 4 3 2 y = -0.3221x + 3.554 2 Mean weight (kg) 1 R = 0.3473 0 -2 -1 0 1 2 3 NAO index

avg3-7 Linear (avg3-7)

Figure 25. Mean weight at age of the Faroe Plateau co stock (average 3-7 years) against the NAO index 1961-2000.

Jákupsstovu and Reinert (1994) demonstrate that the variations in mean weight at age are not caused by density dependent growth limitations, but rather to variations in food availability. This has later been verified by Gaard et al 2002) and Steingrund et al. (2002). Jákupsstovu and Reinert (2002) suggest that the variations in primary production on the Faroe Plateau is partly caused by variations in the Atlantic flow past the Plateau. If correct the variations in the Atlantic flow not only affects the pelagic stocks migrating trough Faroese waters off the shelf, but also the ecosystem on the Plateau.

34 Acknowledgement

For the purpose of this paper data from the Nolsø Flugga section has been made available by the Marine Laboratory in Aberdeen. This and the help from William R. Turrell in particular is greatly acknowledged. Furthermore the help from and discussion with my collegues Eilif Gaard, Hjálmar Hátún and Jan Arge Jacobsen in preparation of this paper is also acknowledged.

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