Distribution and abundance of the fished population ... - Science Direct

E LS EV 1ER

Fisheries Research 21 (1994) 193-216

Distribution and abundance of the fished population of Loligoforbesi in UK waters: analysis of fishery data Graham J. Pierce a'*, Peter R. Boyle a, Lee C. Hastie b, Aileen M. Shanks b aDepartment of Zoology, Universityof Aberdeen, TillydroneAvenue, Aberdeen AB9 2TN, UK bScottish OfficeAgriculture and Fisheries Department, PO Box 101, VictoriaRoad, Aberdeen AB9 8DB, UK

Abstract

UK fisheries for the squid Loligoforbesi are described, based mainly on analysis offishcry statistical data (1980-1990) held in the Scottish Office Agriculture and Fisheries Department (SOAFD) and Ministry of Agriculture, Fisheries and Food (MAFF) databases, and synthesis of published and unpublished information from various sources including interviews with Scottish fishermen. The weight and value of squid landings in the UK have increased substantially during the last decade, particularly in Scotland. While squid landed in Scotland are thought to consist almost exclusively of Loligoforbesi, landings in England and Wales may contain a significant proportion of Loligo vulgaris. Squid are landed primarily as a bycatch of trawling and seining finfish fisheries although some directed fishing takes place, particularly at Rockall. There is limited use of jigs, although most reported trials of jigging gear have been unsuccessful. Squid are caught throughout UK waters, although the most important fishing areas vary from year to year. Scottish landings come from all around the coast of Scotland, particularly the Moray Firth, as well as from Rockall and (historically) Faroe Bank. Landings from Rockall are apparently unpredictable, with large amounts of squid being caught in 1986, 1987 and 1989 but almost none during the rest of the decade. Squid landed in England and Wales are also taken from a wide area, including the English Channel, Celtic Sea, Rockall, and (historically) the Bay of Biscay. Records of Scottish landings from 1904 suggest the existence of a 15 year cycle of abundance. The seasonal pattern of landings in Scotland shows a predictable seasonal pattern, with most landings from coastal waters occurring in October and November and most landings from Rockall in June and August. Results of correlation analyses of landings, fishing effort and CPUE data are generally consistent with a by-catch fishery on a patchily distributed resource, suggesting that CPUE is a reasonable index of abundance except for areas! such as Rockall where there is a significant proportion of directed fishing. UK squid * Corresponding author. 0165-7836/94/$07.00 © 1994 Elsevier Science B.V. All fights reserved SSDI 0165-7836 (94)02013-Y

194

G..I. Pierce et al. / Fisheries Research 21 (1994) 193-216

stocks are currently neither assessed nor managed, and the status of squid as primarily a by-catch precludes most management options. However, given the relatively high quality of data routinely collected, and assuming implementation of checks on species identification and compilation of data at least weekly, stock assessment should be possible. Keywords: Atlantic; Loligoforbesi; Population structure

1. Introduction

The veined squid Loligoforbesi (Cephalopoda: Loliginidae ) is a neritic species occurring in coastal waters throughout the northeast Atlantic (Voss, 1973). It is fished commercially by most western European countries and forms the basis of a significant by-catch fishery in the UK (Howard, 1979). Forty-seven cephalopod species were recorded from Scottish waters by Stephen (1944). Of the other squid species, Loligo vulgaris has a more southerly distribution, indeed the subspecies Loligo trulgaris reynaudii extends to the South African coast (Augustyn, 1991 ), and it is extremely rare in Scottish commercial catches (Pierce et al., 1994a). However, it is prominent in French, Spanish and Portuguese squid landings and is caught by UK vessels fishing in the English Channel (Neve, 1976), although its relative abundance in these catches is unknown. The other main loliginid species Alloteuthis subulata is very small (body length usually less than 15 era) and is presently of no commercial importance in UK waters, although it has in the past been landed and admixed with small Loligo sp. The ommastrephid squid Todaropsis eblanae is generally thought of as rare in Scottish waters (Stephen, 1944; Rae, 1961; Rae and Lamont, 1963) and effectively unmarketable (Davidson, 1963), but occasionally appears in very large numbers in certain localities, where it briefly replaces Loligoforbesi as the most abundant cephalopod caught by fishermen (Stephen, 1944; Rae, 1961; Rae and Lamont, 1963; Joy, 1989). A second ommastrephid, Todarodes sagittatus, is also sometimes landed in Shetland (Joy, 1990) and in the early 1980s formed the basis of an important Norwegian fishery (Sundet, 1985 ). Of other cephalopods, the cuttlefish Sepia officinalis and, to a lesser extent, the octopus Eledone cirrhosa are also landed commercially in the UK. Data on squid fisheries in Scotland have been previously summarised by Thomas ( 1969, 1973), Thomas and Davidson (1972), Stroud (1978), Howard (1979) and Howard et al. ( 1987 ). The present paper concentrates primarily on UK fisheries from 1980 to 1990, including data from England, Wales and Northern Ireland as well as Scotland. The broad aims of this analysis are to describe the current status of the UK squid fishery and to examine evidence for seasonal and regional changes in squid distribution and abundance.

G.J. Pierce et al. / Fisheries Research 21 (1994) 193-216

195

2. Sources of data

2. I. The Scottish fishery Data on landings of squid at Scottish ports and data on fishing effort by UKregistered vessels from 1974 onwards were extracted from a database at the Scottish Office Agriculture and Fisheries Department (SOAFD) Marine Laboratory in Aberdeen. Prior to 1974 these data are not available. Each record consists of monthly totals for landings (units of 100 kg) and hours fishing for a single International Council for the Exploration of the Sea (ICES) statistical rectangle (1 ° longitude × 0.5 ° latitude). It should be noted that 'hours fishing' refer to the total fishing activity of the fleet, very little of which is directed at squid. As such, derived figures for catch per unit effort (CPUE) may provide an indicator of squid abundance but cannot be used to in any way indicate the profitability of squid fishing. Four demersal gear-types contribute the bulk of squid landings over the period 1974-1990 and data were also extracted for each of these gears separately. The gears were motor (heavy otter) trawl, light otter trawl, demersal pair trawl, and seine net (see Strange, 1981 ). No separate extraction of data was made for the next most important gear-type (nephrop trawls). Heavy and light trawls are distinguished on the basis of boat size. Otherwise, however, fishing effort has not been adjusted to take account of fishing power: no corrections for boat size or gear-type have been made. Squid landings in Scotland are normally classified as Loligo spp. (Food and Agriculture Organization (FAO), 1992 ) and analysis of recent catches shows that almost all are L.forbesi (Pierce et al., 1994a).

2.2, England and Wales, Northern Ireland Databases for England and Wales and for Northern Ireland are held by the Ministry of Agriculture, Fisheries and Food (MAFF). Landings (units of 1 kg) and effort (hours fishing) data were extracted for the years 1980-1990. The data refer to UK-registered vessels landing in England or Wales and in Northern Ireland. The classification of gear-types is similar but not identical to that used in Scotland. While the same three categories of trawl are identified, a large proportion of trawler landings of squid are classified as otter trawl (unspecified). Seine net landings are subdivided into several categories, the most important of which is Scottish fly seine. Separate extractions were made for the three types of trawl and for Scottish fly seine. In FAO statistics, English plus Welsh squid landings are classified as Loligo spp~ or 'Squid Not Elsewhere Included (Loliginidae or Ommastrephidae)'. While the latter category is probably also mainly Loligo, the geographic distribution of catches (see below) is such that both Loligoforbesi and Loligo vulgaris may be caught. For the years 1980-1983 there are unexplained discrepancies between

196


published totals for landings in England and Wales (MAFF, 1989) and totals derived from the MAFF database, with the latter being lower. 2.3. Analysis

All data were transferred to a single PC-based database, written using DataEase (DataEase International, Sapphire International PLC). Analysis and graphical presentation were carried out using BMDP (Dixon et al., 1990), Minitab (Ryan et al., 1985 ), CricketGraph (Computer Associates International Inc., San Diego, CA) and SURFER (Golden Software Inc., Denver, CO) software. Landings data for all ICES rectangles in which there was some fishing effort were contoured using SURFER. A minimum convex polygon was drawn around rectangles with effort greater than 0 and contours were blanked from locations more than 1° of longitude and 0.5 ° of latitude outside the polygon. 2.4. Additional data

Other fishery statistical and trade information presented derives from published sources as cited, principally MAFF and FAO statistics and Business Monitor (Anonymous, 1988, 1989, 1990, 1991 ). A small number (n = 12) of interviews with fishing boat skippers was carried out at Kinlochbervie and Lochinver, Sutherland, to obtain information on methods currently used for catching squid. These two ports are currently the most important in Scotland in terms of weight and value of squid landed. 3.Thefishery 3.1. Current status

Annual landings of squid in the UK in the past decade rose from less than 500 t in 1980 to approximately 3100 t in 1989 before falling again in 1990 (Fig. 1; data from MAFF, 1989, 1992). The increase was largely due to increased landings in Scotland which consequently formed a much higher proportion of UK landings at the end of the decade. Landings by vessels registered outside the UK made up less than 5% of annual landings. The total value of squid landings in the UK also increased throughout the 1980s, reaching a peak of £4.3 million at first sale in 1989, although falling back to approximately £3 million in 1990 (MAFF, 1989, 1992). Whilst this represents a small percentage of the values of finfish landings (£425 million) or total shellfish landings (£97.7 million) in 1989, the relative importance of squid is increasing. During the last decade the value of UK finfish landings increased two-fold, shellfish landings three-fold, and squid landings ten-fold (MAFF, 1989). An alternative, in some respects more complete, picture of annual landings of squid may be derived from FAO statistics (Fig. 2; data from FAO, 1992). These refer to landings by UK-registered vessels and include landings by UK-registered vessels in other countries. The MAFF (1989, 1992) figures correspond broadly to FAO figures on squid landings from the northeast Atlantic (FAO area 27).

197


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Year Fig. 2. Annual landings of squid from the northeast Atlantic (FAO area 27) by UK-registered vessels, by country of registration, 1981-1990, from FAO statistics. These totals include squid landed in other countries by UK-registered vessels. Inset: total landings from area 27 contrasted with total landings from area 41.

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G.J. Pierce et al. / Fisheries Research 21 (I 994) 193-216

Table 1 UK trade in cephalopods 1988-1991 Category

Amount (t)

Value (£1000)

1988

1989

1990

1991

1988

1989

1990

1991

28 73

12 12

106 171

96 97

29 62

29 30

91 132

188 190

672 1958

701 1027 1980

242 503 1487

569 1709

866 2439

615 1268 2346

163 724 1658

824 1979

2031

1992

1658

1806

2501

2376

1790

2169

278 614 618

547 285 1166 2040 2087

1139 344 1416 2998 3013

594 986 996

698 478 2601 3808 3873

1071 405 2581 4238 4277

746 1585 1640

472 512

384 528 580 1683 1745

175 560 675 1555 1785

335 1108 1240

936 1034

503 992 992 2781 2885

194 857 876 2193 2522

643 1650 1899

1130

3832

4798

2617

2030

6758

6799

3539

Fresh imports EC

Total Preserved imports Netherlands EC

Total Totalimpons Fresh expo~s France Italy Spain EC

Total Preserved exports France Italy Spain EC

Total Totalexports

507 1303 1377

Although the picture is incomplete ( 1983 data for landings abroad are missing in the FAO statistics), the maximum recorded annual total weight of squid landed abroad by UK-registered vessels was in 1984 ( 383 t). Interestingly, much of this was landed in Norway and may therefore have been Todarodes sagittatus, which formed the basis of an important Norwegian fishery during much of the 1980s (Sunder, 1985; FAO, 1992 ). Otherwise, it is probably reasonable to assume that most landings are of Loligoforbesi or, for southern fishing areas, a mixture of L. forbesi and L. vulgaris. UK-registered vessels land squid in several EC countries, including France, Ireland and Spain, and little has been landed in Norway since 1984. Neve (1976) records the presence of Loligo vulgaris in catches by a small English trawler in the English channel and comments that the species is believed to spawn offthe Dutch coast during the summer and to occur at the western end of the Channel only during autumn and winter. From 1987 onwards there have been significant landings by UK-registered vessels of squid caught in the southwest Atlantic (FAO area 41 ), including Illex argentinus (Fig. 2, inset). Also, in 1989, 8 t ofMartiala hyadesi from FAO area 48


199

were recorded as having been landed by UK-registered vessels. All subsequent discussion of squid fishing will be restricted to data on Loligo spp. FAO statistics indicate that squid make up over half of the annual weight of cephalopod landings in the UK. Landings of octopus are relatively small, the highest UK total reported up to 1989 being about 150 t in 1989, while 3500 t of cuttlefish were landed in England and Wales in 1989, more than twice the amount reCorded in any previous year. Small amounts of squid are landed in the Isle of Man, with a peak in landings of 21 t for 1989 (FAO, 1992). Published figures on UK trade in cephalopods (Anonymous, 1988, 1989, 1990, 1991 ) do not distinguish between squid, cuttlefish and octopus (Table 1 ). Frozen material is classified as 'Preserved'. Imports of fresh cephalopods are minimal but around 2000 t of preserved cephalopods are imported annually. The value of cephalopod exports peaked at approx. £6.8 million in 1990, almost two-thirds of which was fresh cephalopods. It is likely that a significant proportion of fresh sqt~id landed is exported, indeed exports of fresh cephalopods in 1990 exceeded landings of Loligo in the UK in that year. Arnold (1979) commented that squid was not a traditional species for consumption in the UK but that assured export markets existed in Europe. The figures in Table 1 confirm that most exports of cephalopods from the UK go to other EC countries, where demand greatly exceeds landings (Shaw, 1994).

3.2, Fishing methods The contributions of the most important types of (demersal) gear to annual squid landings in Scotland are illustrated in Fig. 3. Heavy (motor) and light demersal single otter trawls, demersal pair trawls, seine nets and nephrop trawls currently account for nearly all squid landings. Other gears with which squid are caught are listed in Table 2. Data from England and Wales indicate that the same gear types are most important for catching squid, although again squid are caught using a variety of gears. Regardless of gear-type, squid is usually landed as a by-catch of more important species such as cod Gadus morhua, haddock Melanogrammus aeglefinus, whiting Merlangius merlangus or Norway lobster Nephrops norvegicus, although a directed fishery operated at Rockall in the early 1970s (Thomas, 1973; Howard, 1979) and squid may be specifically targeted by Scottish fishermen when particularly abundant at Rockall or in the Moray Firth (F.G. Howard, personal communication, 1993). There is also some directed squid fishing on the south coast of England (Shaw, 1994). Jigging is most commonly used commercially for ommastrephid squid, but the Japanese employ jigging methods very successfully for a range of species of Loliginidae (Hamabe et al., 1982). Also, directed artisanal fisheries for Loligo spp. in Spanish and Portuguese coastal waters and in the Azores are mostly based on jigging, using handlines rather than larger mechanised jigging equipment (Guerra et aL, 1994; Porteiro, 1994). Jigs have been used in Scotland to a very limited


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o

1000" w C

, R

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500"

O' 1974

1976

1978

1980

1982

1984

1986

1988

1990

Year Fig. 3. Annual landings of squid in Scotland by UK-registered vessels, 1974-1990, by gear-type. The category 'others' usually makes up less than 1% of catches. Table 2 Relative importance of different gears in Scotland, 1990 Gear name

Weight of squid (t)

Percent of landings

All gears Motor trawl Light trawl Demersal pair trawl Seine net Single nephrop trawl Beam trawl Industrial trawl Mechanical dredging Queen scallop trawl Demersal gill nets

1451.5 61.4 712.7 265.7 321.5 85.9 2.2 1.2 0.4 0.4 0.1

4.2 49.1 18.3 22.1 5.9 0.2 0.1 + + +

extent, in directed fishing by small vessels in the Moray Firth and some west coast areas, and also on the south coast of England (Shaw, 1994). There have been a number of trials of mechanised jigging machines for Loligo spp. in UK waters, carded out under the auspices of the former White Fish Authority (McDiarmid, 1975; Neve, 1976) and the Sea Fish Industry Authority (Neve, 1983a,b; Anonymous, 1984; Tumilty, 1987). Anonymous (1984) re-


201

ported reasonable success in jig trials in the Moray Firth but other trials generally met with very little success. Scrutiny of the reports of these trials, however, raise doubts as to whether gear was always properly deployed and whether it was used in areas and at times when sufficient concentrations of squid would have been present to make the method worthwhile. Aspects such as the types of jigs used, the depths at which they were fished, the use or otherwise of drogues, the use of lights, time of day, the likely squid concentration and the possibility of the use of acoustic marks, all require further evaluation. In Japan, specific types of jig are used for each squid species (Hamabe et al., 1982 ) and it is of note that the few squid taken in trials described by Neve (1983a) were all Todarodes sagittatus. No information is currently available on the amounts of squid discarded. The high value of squid should ensure that it is normally landed when caught in appreciable amounts and very small catches of squid are known to be landed by inshore fishing boats, particularly at ports such as Eyemouth, Pittenweem, Oban and those in the Clyde (F.G. Howard, personal communication, 1993). However, while Stroud ( 1978 ) states that squid on ice keep in saleable condition for up to 8 days and become inedible only after 13-14 days, our experience is that squid start to deteriorate significantly after only 1-2 days on ice. Thus squid may be discarded if caught early during long fishing trips. The majority of boats operating out of Kinlochbervie and Lochinver direct their effort at the demersal whitefish fishery, the principal gears used being demersal trawls (single and paired) and Danish seine. When fishing specifically for squid, a 'squid bag' (over 16 mm mesh, normally 30-40 mm mesh size) is used, attached to and covering the cod end. This was the most common alteration made to demersal trawl gear to enhance squid catches but other important changes include raising the headrope and enlarging the mouth of the net. Over the period analysed, the legal minimum mesh size for whitefish was 90 mm. However, fishermen targeting squid with a small mesh bag were allowed a whitefish by-catch of 10%. Many Scottish fishermen have fished specifically for squid, but very few of those interviewed had done so on a regular basis (1-3 weeks annually). Most skippers had tried it once or twice over an extended period ( 10-20 years). Despite the high market value of squid, there is a reluctance to reset gear accordingly, mainly due to the perceived unpredictability of squid fishing in Scottish waters. However, most fishermen interviewed expressed an interest in catching squid and a willingness to fish specifically for squid if squid were plentiful. The occasional large catches of squid landed, and the good prices normally paid, have influenced many fishermen to try fishing for squid at least once. 4. Distribution and abundance

4.1. Spatial distribution of catches ICES fishery subdivisions of the northeast Atlantic are illustrated in Fig. 4. Considering landings into the UK as a whole, the relative importance of different fishing areas can be seen to change between years (Fig. 5 ) with the Rockall fishery (VIb) being prominent in 1986, 1987 and 1989.


202

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Longitude°E Fig. 4. Map of the northeast Atlantic showing ICES fishery subdivisions.

Squid landed in Scotland (Fig. 6) are caught mainly in three ICES fishery divisions: IVa (northern North Sea), Via (West coast of Scotland) and VIb (Rockall). Smaller amounts are taken from IVb (North Sea), VIIa (Irish Sea) and, in the early 1980s, Vb (Faroes). Of catches in the northern North Sea, approximately 93% are from the Moray Firth (IVavi). Fishermen interviewed identified several inshore localities as good squid fishing areas (Whiten Head, Nun and Solan Banks) and reported that squid were taken equally at day and night, generally over hard/shingle substrates. Squid landed in England are taken from a wider range of areas (Fig. 7 ), with VIIg, h, j, k (south coast of Ireland) and VIIe (western English Channel) being of particular importance. In the first half of the 1980s, squid were taken from area VIII (Bay of Biscay) and, to a lesser extent, the Straits of Gibraltar and Mediterranean Sea, but there has been no fishing in these areas by UK-registered (and based) boats since 1985. Small amounts of squid are also taken from offshore banks at the eastern edge of areas X and XII (mid-Atlantic), including Hatton Bank, Fangorn Bank, Lorien Bank and Isengard Ridge.

203

G.Z Pierce et al. / Fisheries Research 21 (1994) 193-216

[] IVa

A

111 o

0 v

¢h

1500.

am

"0 c ,-I

1000 ¸

500

0 1980

1901

1962

1963

1964

1965

1906

1987

1988

1969

1990

Year Fig. 5. Annual landings of squid in the UK by UK-registered vessels, 1980-1990, by fishing area.

Squid landed in Northern Ireland (Fig. 8) are taken mainly from areas VIIa, VIIb, c (west of Ireland and Porcupine Bank), VIIf (Bristol Channel) and VIIg, h, j, k. Again there have been shifts in the relative importance of different fishing areas with areas VIIa and VIIg, h, j, k being most important before 1983, while VIIb, c and VIIf were the most important areas at the end of the decade. It is not clear to what extent reported fishing areas accurately reflect squid distribution. Firstly, the reliability of any conclusions depends on the reliability of the data. Apart from the possibility of errors at various stages of data compilation, misreporting of catch areas may occur. Since squid is normally a by-catch, and the stock is unregulated, deliberate misreporting is unlikely except as a consequence of misreporting for other species caught. Some of the marked shifts in location of catches undoubtedly reflect changes in the pattern of fishing on the target species. However, squid are not caught throughout fished UK coastal waters in every year and to this extent the distribution of catches may be indicative of squid distribution. Squid distribution offshore is poorly known, but squid clearly occur on those offshore banks which are regularly fished. Interannual changes in distribution would not be unexpected, since causal relationships between distribution and oceanographic factors are likely and have been documented for other squid species (Coelho, 1985; Kubodera, 1989; Augustyn, 1991; Andriguetto and Haimovici, 1991 ).

204

G.J. Pierceet aL / FisheriesResearch 21 (1994) 193-216

4.2. Temporal trends in Scottish landings 4.2.1. Interannual trends

An extended historical dataset is available for Scotland (Thomas, 1973; Arnold, 1979; Howard, 1979). Annual landings of squid in Scotland by UK-registered boats from 1904 to the present show an apparently cyclical pattern (Fig. 9). However, the first two troughs in the cycle correspond to the two world wars. Subsequently, landings peaked in 1960 ( 1120 t), 1971 ( 1367 t), and 1989 ( 1935 t), suggesting a cycle of availability with a periodicity of approximately 15 years. 4.2.2. Seasonal patterns

Scottish landings data from 1974 to the present show a strong seasonal pattern (Fig. 10), normally peaking in October or November. However, in 1974, 1986 and 1987 there was a strong summer peak (June or August) and in 1989 both summer and autumn peaks were prominent. The summer peaks consist almost (a)

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Fig. 6. Contour maps of squid catchesby UK-registeredvesselslanding in Scotland,data summed for: (a) 1980-1985; (b) 1986-1990. The contour maps use a grid with 0.5 ° intervals. Contour lines passing over land and those without a minimum convex polygondelineatingthe fishingarea are blanked. The superimposed outline maps show land masses and also Rockall Bank. The minimum contour is at 100 kg and the contours intervals are: (a) 200 kg; (b) 500 kg. entirely of squid landings from Rockall, as demonstrated by plotting landings for Roekall separately (Fig. 11 ). The winter peaks are typical of the Scottish inshore fishery, e.g. in the Moray Firth (Fig. 12 ). To examine the consistency of trends in monthly landings in Scotland statistically, a Box-Jenkins Autoregressive-Integrated Moving Average (ARIMA) model was fitted (Dixon et al., 1990). The best fit was obtained using an autoregressive term (predicting the series from previous values) with a time-lag of 1 m o n t h and a moving average term (predicting the series from previous r a n d o m errors or 'shocks') with a time-lag of 12 months. The form of the model is then


206

Zt -- C - t - ~ I Z t _ 1 "l'at --O12dt_12

where Zt is landings at time t, ~ is the autoregressive term (qh = 0.6023 ), O12 is the moving average term (O~2=0.7126), C is a constant (the average level of monthly landings) and at is the value, at time t, of random variable with zero mean and constant variance. The significant moving average term with a time lag of 12 months confirms the consistency from year to year of seasonal fluctuations in landings over the period considered while the autoregressive term indicates serial autocorrelation between landings in successive months. The difference in timing of the Rockall and coastal squid fisheries was noted by Thomas (1973) and the observed seasonal pattern has thus been consistent over many years. To the extent that seasonal patterns in landings are indicative of changing abundance they may be interpreted in terms of the life-cycle biology. Thus young squid recruit to the fished population largely in the summer (July-20 6S

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G.J. Pierce et al. /Fisheries Research 21 (1994) 193-216

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Fig. 7. Contour maps of squid catches by UK-registered vessels landing in England and Wales, data summed for: (a) 1980-1985; (b) 1986-1990. The contour maps use a grid with 0.5 ° intervals. Contour lines passing over land and those without a minimum convex polygon delineating the fishing area are blanked. The superimposed outline maps show land masses and also Rockall Bank. The minimum contour is at 100 kg and the contours interval is 500 kg. September) and the rising catches in the latter half o f the year are of maturing, pre-breeding squid. Breeding in inshore waters begins in December, reaching a peak in February or March but continuing into May (Pierce et al., 1994a). ThrOughout this period old animals will disappear from the population although it is unclear to what extent the rapid decline in catches from December onwards is a consequence o f fishing mortality and to what extent it is due to natural mortality and changes in distribution. Reduced catchability might occur due to horizontal or vertical movements into unfished waters. Spawning areas for Loligo forbesi are not well known although egg masses are recovered from creel lines (Lum-Kong et al., 1992 ) and breeding squid are caught in inshore waters.

208

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Fig. 8. Contour maps of squid catches by UK-registered vessels landing in Northern Ireland, data summed for 1980-1990. The contour maps use a grid with 0.5 ° intervals. Contour lines passing over land and those without a minimum convex polygon delineating the fishing area are blanked. The superimposed outline maps show land masses and also Rockall Bank. The minimum contour is at 100 kg and the contours interval is 100 kg.

T h o m a s ( 1 9 7 3 ) suggested that the differing patterns of squid availability in different areas, particularly the difference between coastal waters and RockaU, were consistent with the existence o f at least two stocks with different migratory patterns. While no consistent differences have been found in studies on morphometrics (Boyle and Ngoile, 1993; Pierce et al., 1994b,c) and allozymes (Brierley et al., 1994), there are limited data suggesting that squid caught at Rockall reach spawning condition 2 - 3 m o n t h s earlier than those in coastal waters (Pierce et al., 1994a).

209

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Fig. 10. Contour diagram of monthlylandingsshowingwith year (1974-1990) on the x axis month (January-December) on the y axis.

and

4. 3. Catch, effort a n d C P U E

Correlations between catch (weight of squid landed), effort (hours fished) and CPUE (overall catch per unit effort) were calculated for: (a) the entire set of monthly by square data; (b) for monthly totals summed across all squares; (c)

210


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Fig. 11. Areagraph of monthlylandingsin Scotland,by UK-registeredvessels,of squid from Rockall (ICES area VIb) and elsewhere (1974-1990). In months when squid were caught at RockaUvery little s q u i d was caught elsewhere.

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Fig. 12. Monthlylandings,in Scotlandby UK-registeredvessels,of squidfromthe MorayFirth (ICES area IVa6), 1974-1990. for yearly totals summed across all squares and months. In each case, data from Scotland, England and Wales, and Northern Ireland were treated separately. Scottish data were also subdivided on an area basis, with separate analyses for the Rockall (VIb) and Moray Firth (IVavi) fishery areas. Finally, since there are obvious statistical problems with summing effort across gear-types, the analyses were repeated for seining only, seines arguably being the gear-type least likely to

G.£ Pierce et aL / Fisheries Research 21 (1994) 193-216

211

be used in directed squid fishing since no modifications to enhance squid catches are possible. All correlations are tabulated in Table 3. Considering firstly the analysis of raw catch by square data, the most clear and consistent result across all subsets of data was that landings and CPUE are positively correlated. In the absence of correlations between landings and effort or CPUE and effort this is consistent with an undirected fishery for a patchily distributed resource, and suggests that CPUE can be used as an index of abundance. In the Moray Firth and at Rockall, landings were correlated with both effort and CPUE, implying that effort was concentrated at areas and times of high abundance. This does not necessarily imply targeting of squid per se, since fishing may be directed at species whose local abundance is correlated with that of squid. For Table 3 Correlations between total landings (L), total effort (E) and overall CPUE. There is almost no seine netting by UK-registered vessels landing in Northern Ireland Data set

N

L vs. E

(a) Monthly by square data 1980-1990 England & Wales 18629 E&W, seines Northern Ireland

Scotland Scotland, seines Rockall (VIb) Rockall, seines Moray Firth (IVa6)

Moray Firth, seines

E vs. CPUE

L vs. CPUE

- 0.022 -0.026 -0.023 - 0.025 - 0.044 0.201" - 0.025 0.046 - 0.057

0.334*** 0.586*** 0.099 0.524"** 0.547*** 0.556*** 0.726*** 0.749*** 0.538"**

3145 1046 17468 12315 440 153 1595 1486

0.126 0.101 0.256** 0.054 0.053 0.563*** 0.078 0.293** 0.123

132 132 132 132 132 132 107 132 132

- 0.061 - 0.163 - 0.092 0.302"* - 0.334*** 0.467*** - 0.064 0.265** - 0.330***

- 0.399.** - 0.346*** - 0.192 0.141 - 0.426*** 0.271"* - 0.099 0.176 - 0.410.**

0.801"** 0.888"* 0.936*** 0,959"** 0.954*** 0.832"* 0.995"** 0.968*** 0.968***

11 11 11 11 11 11 8 11 11

0.360 0.243 - 0.081 0.699* - 0.557 0.392 0.112 0.031 -0.936***

-0.662* -0.412 - 0.413 0.650* - 0.636* 0.054 -0.130 0.109 -0.927***

0.342 0.761"* 0.917*** 0.994*** 0.983*** 0.949*** 0.953*** 0.990*** 0.987***

(b) Monthly data 1980-1990 England & Wales E&W, seines Northern Ireland

Scotland Scotland, seines Rockall (VIb) Rockall, seines Moray Firth (IVa6) Moray Firth, seines

(c) Yearly data 1980-1990 Englgnd & Wales E&Wi seines Northern Ireland

Scotland Scotland, seines Rockall (Vlb) Rockall, seines Moray Firth (IVa6) Moray Firth, seines i

*P< 0.05; **P< 0.01; ***P< 0.001.

212


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Fig. 13. Monthly fishing effort and overall squid CPUE for UK-registered vessels deploying seine nets in the Moray Firth and landing in Scotland, 1980-1990. 120

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Fig. 14. Monthly fishing effort and overall squid CPUE for UK-registered vessels fishing at Rockall and landing in Scotland, 1980-1990.

seine net catches in these areas however, landings and effort are uncorrelated, suggesting that the overall correlation was due to targeting of squid. For landings in Northern Ireland, landings and effort were positively correlated, but landings and CPUE were uncorrela~ted, suggesting that squid were more evenly distributed in areas fished by these vessels. The correlation analyses of monthly summaries across all areas reveals some

213


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Fig. i 5. Annual squid landings, fishing effort and squid CPUE for UK-registered vessels landing in Scotland, 1980-1990.

additional points. Firstly, effort and CPUE were generally negatively correlated for seine net catches (e.g. Fig. 13) and for all catches landed in England and Wales, suggesting that most fishing effort took place at times of low squid abundance. The opposite is true for Rockall (all gears combined; Fig. 14), consistent with fishing being concentrated during periods of high squid abundance. Secondly, effort and landings were positively correlated for vessels landing in Scotland i implying some targeting of periods of high squid abundance, but negatively correlated when seine net catches are considered alone. The correlation analyses of yearly summaries broadly support results from the analyses of monthly data. Positive correlations in Scottish data indicate underlying trends of increasing fishing effort and increasing squid abundance (Fig. 15 ). Thus, in general, and certainly for seine net fisheries, results are consistent with an undirected fishery for which CPUE is a reasonable indicator of squid abundance. In particular fishing areas, notably Rockall, most fishing occurs during periods of squid abundance and at least some of this fishing is targeted at squid.

5. Conclusion

UK squid fisheries are not assessed and are unmanaged. Most squid are landed as a by-catch, which has the beneficial consequence that information on distribution and abundance may be inferred from landings and CPUE, revealing predictable seasonal patterns but marked year-to-year fluctuations in total landings coupled with shifts in distribution.

214


It is difficult to be certain of species identification although, at least in Scotland, the importance of species other than Loligoforbesi is thought to be negligible. The incidence ofLoligo vulgaris in landings from more southerly fishing areas, e.g. the English Channel, is unknown and needs to be monitored, e.g. following methods currently used for French landings from the English Channel fishery (Robin and Boucaud, 1993 ). In contrast to all other EC countries except France, squid landings in the UK are recorded on a catch-by-square basis. Even in France, this detailed recording does not extend to the entire fishery. The absence of detailed catch and effort data for countries with significant squid fishing activity in the northeast Atlantic, particularly Spain and Portugal, prevents any detailed assessment of stocks of Loligo species in this area. Nevertheless, in the UK context, using (say) weekly catch and effort data rather than the monthly summaries stored in the Lowestoft (MAFF) and Aberdeen (SOAFD) databases, application of assessment methodologies, e.g. DeLury depletion estimates of stock size (Rosenberg et al., 1990), may become possible for certain fishing areas. As long as landings arise primarily as a by-catch of finfish fisheries, management of squid catches is unlikely to be feasible (Pierce and Guerra, 1994).

Acknowledgements This work was funded by the Commission of the European Communities within the frame of the EEC research programme in the fisheries sector (FAR, Contract No. MA 1.146). Landings and fishing effort data were supplied by SOAFD and MAFF. We th~mk Colin Chapman (SOAFD), Mark Ellis and Chris Gooch (MAFF) for their assistance with extraction of fishery statistical data from source databases, Mike Heath (SOAFD) who supplied digitised coastline data for the contour maps, and the various fishermen who agreed to be interviewed.

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