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ICES Journal of Marine Science: Journal du Conseil Advance Access originally published online on June 19, 2008
ICES Journal of Marine Science: Journal du Conseil 2008 65(7):1346-1349; doi:10.1093/icesjms/fsn100
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© 2008 International Council for the Exploration of the Sea. Published by Oxford Journals. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org

The Lophius budegassa component of monkfish catches in Scottish waters

Chevonne H. Laurenson1, Helen Dobby2 and H. Anne McLay2

1 NAFC Marine Centre, Port Arthur, Scalloway, Shetland ZE1 0UN, UK
2 Fisheries Research Services, Marine Laboratory, PO Box 101, 75 Victoria Road, Torry, Aberdeen AB11 9DB, UK

Correspondence to C. H. Laurenson: tel: +44 1595 772306; fax: +44 1595 772001; e-mail: chevonne.laurenson{at}nafc.uhi.ac.uk

Laurenson, C. H., Dobby, H., and McLay, H. A. 2008. The Lophius budegassa component of monkfish catches in Scottish waters. – ICES Journal of Marine Science, 65: 1346–1349.

To date, research efforts on Lophius species in waters around Scotland (ICES Divisions IVa, VIa, and VIb) have focused almost exclusively on Lophius piscatorius. Here, the characteristics and distribution of the Lophius budegassa component of the catch are described using data collected by observers during commercial fishing trips and scientific surveys on chartered commercial fishing vessels between 1998 and 2006. At Rockall Bank (VIb), L. budegassa were rare, just 0.1% of the catch of Lophius spp., whereas west of Scotland (VIa) and around the Shetland Islands (IVa), they made up 18 and 2% of catches, respectively, with greatest prevalence towards the shelf edge. Fish length ranged from 16 to 89 cm with a modal length at 40 cm. Greater proportions of large individuals were recorded around the Shetland Islands than in other parts of the study area. Overall, the sex ratio was 1:1, and lengths at 50% maturity were estimated to be 70.4 cm for females and 49.4 cm for males.

Keywords: anglerfish, L. budegassa, monkfish, Rockall, Scotland, Shetland

Received 23 December 2007; accepted 23 May 2008; advance access publication 19 June 2008.


   Introduction
Top
 Introduction
Material and methods
 Results and discussion
 References
 
In the Northeast Atlantic, monkfish (Lophius spp.) have a broad distribution, are commercially important, and are represented by two species, which coexist over much of their range. Lophius piscatorius, often referred to as white-bellied monkfish or anglerfish, dominates north of 55°N (Kunzlik et al., 1995), whereas south of this, Lophius budegassa, the black-bellied monkfish or anglerfish, increases gradually (ICES, 2007).

In waters around Scotland [i.e. ICES Division IVa (northern North Sea) and Subarea VI (west of Scotland and Rockall Bank); Figure 1], a fishery for Lophius spp. developed rapidly during the late 1980s, peaking in reported landings in the mid-1990s. Although both L. piscatorius and L. budegassa are found in the area, they are not separated for sale or processing, and L. budegassa generally accounts for ≤5% of the catch (Kunzlik et al., 1995).


Figure 1
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  		Figure 1. Percentage of Lophius budegassa in the catch of Lophius spp. (shaded) by depth strata (0–200, 201–500, and 501–1000 m) in ICES statistical rectangles at Rockall Bank (Division VIb), west of Scotland (Division VIa), and the Shetland Islands (Division IVa). The areas and depths not sampled are unshaded.

 
The scientific understanding of L. piscatorius in areas IV and VI has improved in recent years, but there is still a lack of basic information on L. budegassa, only Anon. (2001) presenting some information on catch rates west of Scotland. Here, we provide an overview of the distribution and biological characteristics of L. budegassa based on a compilation of data collected during several studies in these areas.


   Material and methods
Top
 Introduction
 Material and methods
Results and discussion
 References
 
The dataset covers waters around the Shetland Islands (IVa), west of Scotland (VIa), and Rockall Bank (VIb), spans the periods 1998–2002 and 2005–2006, and was obtained during chartered surveys on commercial fishing vessels and by observers on commercial fishing trips, all of which covered the main areas of the fishery for Lophius spp. Data collected west of Scotland and on Rockall Bank were from vessels deploying twin-rig demersal trawls and nets with 110-mm codends and 90-mm square-mesh panels from 1998 to 2002, and 120-mm codends in 2005 and 2006. Data collected around the Shetland Islands were collected from vessels operating either single or twin-rig demersal trawls with 100-, 110-, or 120-mm codends. In 2000, Scottish legislation requiring Scottish whitefish vessels to use square-mesh panels came into force, and this became mandatory in European legislation in 2002 in the North Sea whitefish fisheries (in nets with a mesh size <120 mm). During 2005 and 2006, the codends on all commercial trips with observers had 120-mm mesh. A summary of the collections is given in Table 1.


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  		Table 1. Numbers of observer trips and chartered surveys in each area and quarter that constitute the dataset.

 
The total length of each L. budegassa sampled was recorded to the nearest centimetre. Other biological data, including sex and maturity, were recorded during some commercial trips and during each of the scientific surveys. Maturity was determined according to the staging scheme of Afonso-Dias and Hislop (1996).

Following Fmax tests for homogeneity of variance, we applied an ANOVA and post hoc Tukey test on data from west of Scotland, and a non-parametric Kruskal–Wallis test on data from the Shetland Islands, to determine if the prevalence of L. budegassa, as proportion per haul, was stratified by depth. Chi-squared tests were used to determine whether the sex ratios differed by area or by depth stratum. Lengths at 50% maturity (L50%) of males and females were determined by fitting a logistic curve to the proportion mature-at-length (King, 1995).


   Results and discussion
Top
 Introduction
 Material and methods
 Results and discussion
References
 
Lophius budegassa was widespread over the area sampled, taken in 45% of hauls and accounting for 6.4% of the catch of Lophius spp. by number, but its prevalence varied by area and depth (Table 2, Figure 1). Its abundance was greatest west of Scotland, where it was in 59% of hauls and constituted 15% of the catch of Lophius spp., whereas around Shetland and on Rockall Bank, it was recorded in 46 and 7% of hauls, and made up just 2.0 and 0.12% by number of Lophius spp., respectively.


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  		Table 2. Number and proportion of Lophius budegassa and total Lophius spp. in hauls in each area and depth stratum.

 
The scarcity of L. budegassa on Rockall Bank suggests that the area may be the western limit of its range. Its northerly decrease in prevalence (Figure 1) appears to continue north of our study area. Along the Norwegian coast (around 62°N), the species is thought to account for <1% of the catch of Lophius spp., and north of 68°N, its occurrence drops further and the species is considered rare (O. Bjelland, IMR, Bergen, pers. comm.). In Faroese waters, L. budegassa are also considered rare, with presence well below 1% (L. H. Ofstad, FFL, Tórshavn, pers. comm.). It should be noted, however, that the selectivity of the gillnets used in those areas may influence estimates of L. budegassa in catches as a result of its smaller size relative to L. piscatorius. South of our study area, L. budegassa reaches 60% presence in the Catabrian Sea (ICES Division VII; Olaso and Pereda, 1983) and >95% of the catch of Lophius spp. by weight in Greek waters (Maravelias and Papaconstantinou, 2003).

In the depth range 45–951 m sampled in our study, L. budegassa was caught from 82 to 880 m; a similar range to the 50–800 m reported by Duarte et al. (2001) off the Atlantic Iberian coast and the 15–757 m range found by García-Rodríguez et al. (2005) in the Spanish Mediterranean.

In this study, we found a significant depth effect on the prevalence of L. budegassa west of Scotland (ANOVA: F2, 146 = 11.16, p < 0.0001), with a post hoc Tukey test indicating lesser prevalence in the 501–1000-m stratum than in either the 0–200- or 201–500-m strata (p < 0.01). North of 59°N, no L. budegassa were recorded at depths ≥500 m (Figure 1). The greatest prevalence of L. budegassa in any haul was 46.9%, in the 201–500-m depth stratum west of Scotland. Off the Shetland Islands, the prevalence of L. budegassa was significantly different among the 51–100, 101–150, and 151–200-m depth strata (Kruskal–Wallis: {chi}2 = 34.44, d.f. = 2, p < 0.0001), and increased from 0.4 to 1.8% and 3.3%, respectively. Our observations of depth stratification and of greatest prevalence towards the shelf edge mirror observations from other areas. For example, off the Portuguese coast, over a range of 700 m, L. budegassa were most common at depths of 200–300 m (Vasconcelos et al., 1986), and in the Spanish Mediterranean, the species was scarce in depths <50 and >500 m (García-Rodríguez et al., 2005). Depth stratification is not, however, universal. For example, Azevedo (1995) found no stratification off the Alentejo region of Portugal.

The total length of L. budegassa in our study area ranged from 16 to 89 cm, with a modal length of 40 cm (Figure 2). Although the modal lengths from the Shetland Islands and west of Scotland were similar (37 and 40 cm, respectively), the length distribution from Shetland was skewed towards larger fish, and this difference was consistent over time. In each area, length distributions varied with both depth and time, but data were insufficient for a statistically robust analysis. The length range in our study area is similar to the range 10–90 cm presented by the WGHMM (Working Group on the Assessment of Southern Shelf Stocks of Hake, Monk and Megrim; ICES, 2007) for commercial landings between 1992 and 2006 in ICES Divisions VIIb–k and VIIIa,b, and the mean lengths of 36–45 cm compare well with the modal lengths from this study.


Figure 2
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  		Figure 2. Length frequency distributions of Lophius budegassa sampled at Rockall Bank, Shetland Islands, and west of Scotland.

 
We found no significant difference in the sex ratio of L. budegassa between Shetland (1:1.22; 134 males and 163 females) and west of Scotland (1:0.97; 784 males and 762 females; {chi}2 = 2.90, d.f. = 1, p > 0.05). Sex ratios close to unity have been reported for the Spanish and Portuguese Atlantic coasts (Duarte et al., 1997, 2001) and for the Spanish Mediterranean (García-Rodríguez et al., 2005), suggesting that similar patterns exist over much of the species’ range.

Depth apparently does not affect sex ratio ({chi}2 = 2.29, d.f. = 1, p > 0.05) with 1:1.11 at 0–200 m (370 males and 409 females) and 1:0.95 at 201–500 m (542 males and 517 females), but more extensive data would be required to determine whether there is a seasonal effect on the sex ratio in different depth strata. The sex ratio of L. piscatorius varies with both depth and season in our study area (Laurenson et al., 2008). Moreover, the proportion of female L. budegassa in the Spanish Mediterranean decreases with increasing depth, which may reflect a seasonal segregation (García-Rodríguez et al., 2005).

In our study area, the proportion of the catch of L. budegassa that were female increased from 40% <40 cm to 100% >67 cm (Figure 3). The maximum lengths of 67 cm for males and 89 cm for females are identical to those given by Duarte et al. (2001) and are similar to those presented by García-Rodríguez et al. (2005) for the Spanish Mediterranean, suggesting similar size maxima currently over much of the species’ range.


Figure 3
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  		Figure 3. Proportion of female Lophius budegassa by 2-cm total length interval.

 
Only 14 of the 443 females staged were maturing (Stage 3), and no ripe (Stage 4) or spent (Stage 5) fish were found. In comparison, all stages of maturity were observed in the 445 staged males. Taking stages 3–5 to be mature, L50% maturities were estimated at 70.4 cm for females and 49.4 cm for males (Figure 4). Several other studies on both L. budegassa (Quincoces et al., 1998a; Duarte et al., 2001) and L. piscatorius (Quincoces et al., 1998b; Duarte et al., 2001; Laurenson et al., 2001) have highlighted a scarcity of ripe females in catches, and the effects of factors such as migration, duration of the spawning phase, and changes in catchability have previously been considered as potentially responsible. The maturity index used in this study is similar to that used by both Quincoces et al. (1998a) and Duarte et al. (2001). They reported lower L50% values of 36.0 cm for males and 65.4 cm for females, and 38.6 cm for males and 53.6 cm for females, respectively. These lower values in the more southerly areas may reflect a latitudinal difference in length at maturity over the species’ range, although because of the small number of mature females we collected, a larger dataset does need to be used to confirm this hypothesis.


Figure 4
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  		Figure 4. Maturity ogives for female (upper panel) and male (lower panel) Lophius budegassa.

 
In summary, we have confirmed that L. budegassa is widely distributed throughout Divisions IVa, VIa, and VIb, that it exhibits a northerly decrease in presence over our study area, and that it is rare on the Rockall Bank. Although it is generally much less prevalent than in the more southern areas of its distribution, it can constitute a much more significant proportion of the catch of Lophius spp. towards the shelf edge west of Scotland than previously recognized. The depth range, depth stratification, length range, modal lengths, sex ratios, and the proportions female at length recorded here are similar to those reported for more southerly areas of the species’ distribution. However, we found larger lengths at maturity than other studies.

Although we have provided a brief overview of L. budegassa in Divisions IVa, VIa, and VIb, there are many aspects of the biology of the species that have not been investigated in these areas (e.g. growth rate, the timing and location of spawning activity, seasonal changes in sex ratio, and temporal changes in abundance). Given the prevalence of L. budegassa in areas west of Scotland, and the economic importance of the monkfish fishery in the region, we believe further research to be justified.


   Acknowledgements
 
We thank staff (past and present) at the NAFC Marine Centre and Fisheries Research Services (FRS) who were involved in data collection, Kevin Peach for extracting FRS datasets, and Otte Bjelland and Lise Helen Ofstad for information on L. budegassa in Norway and the Faroe Islands, respectively.


   References
Top
 Introduction
 Material and methods
 Results and discussion
 References
 

    Afonso-Dias I., Hislop J. R. G. The reproduction of anglerfish Lophius piscatorius Linnaeus from the north-west coast of Scotland. Journal of Fish Biology (1996) 49:18–39.[CrossRef][Web of Science]

    Anon. Distribution and biology of anglerfish and megrim in waters to the west of Scotland. In: Final Report European Commission – DGXIV Study Contract 98/096 (2001) Oban, Scotland: Scottish Association for Marine Science. 88. Coordinator J. D. M. Gordon.

    Azevedo M. A statistical analysis of black monkfish catch rates in ICES Division IXa. Fisheries Research (1995) 24:281–289.[CrossRef][Web of Science]

    Duarte R., Azavedo M., Landa J., Pereda P. Reproduction of anglerfish (Lophius budegassa Spinola and Lophius piscatorius Linnaeus) from the Atlantic Iberian coast. Fisheries Research (2001) 51:349–361.[CrossRef][Web of Science]

    Duarte R., Azevedo M., Pereda P. Study of the growth of southern black and white monkfish stocks. ICES Journal of Marine Science (1997) 54:866–874.[Abstract/Free Full Text]

    García-Rodríguez M., Pereda P., Landa J., Esteban A. On the biology and growth of the anglerfish Lophius budegassa Spinola, 1807 in the Spanish Mediterranean: a preliminary approach. Fisheries Research (2005) 71:197–208.[CrossRef][Web of Science]

    ICES. Report of the Working Group on the Assessment of Southern Shelf Stocks of Hake, Monk and Megrim (WGHMM), 8–17 May 2007, Vigo, Spain. ICES Document CM 2007/ACFM: 21 (2007) 700.

    King M. Fisheries Biology, Assessment and Management. (1995) Oxford, England: Fishing News Books. 341.

    Kunzlik P. A., Newton A. W., Jermyn A. W. Exploitation of monks (Lophius spp.) and megrims (Lepidorhombus spp.) by Scottish fishermen in ICES Division VIa (west of Scotland). Final report EU FAR contract MA–2–520 (1995) 125.

    Laurenson C. H., Dobby H., McLay H. A., Leslie B. Biological features of the Lophius piscatorius catch in Scottish waters. ICES Journal of Marine Science (2008) 65:1281–1290.[Abstract/Free Full Text]

    Laurenson C. H., Priede I. G., Bullough L. W., Napier I. R. Where are the mature anglerfish? The population biology of Lophius piscatorius in Northern European waters. ICES Document CM 2001/J: 27 (2001) 15.

    Maravelias C., Papaconstantinou C. Size-related habitat use, aggregation patterns and abundance of anglerfish (Lophius budegassa) in the Mediterranean Sea determined by generalized additive modelling. Journal of the Marine Biological Association of the UK (2003) 83:1171–1178.[CrossRef]

    Olaso I., Pereda P. The angler-fish Lophius piscatorius L. and L. budegassa Spinola in the European North Atlantic coast. ICES Document CM 1983/G: 51 (1983) 6.

    Quincoces I., Lucio P., Santurtun M. Biology of black anglerfish (Lophius budegassa) in the Bay of Biscay, during 1996–97. ICES Document CM 1998/O: 47 (1998) a:28.

    Quincoces I., Santurtun M., Lucio P. Biological aspects of white anglerfish (Lophius piscatorius) in the Bay of Biscay (ICES Division VIIIa,b,d), in 1996–1997. ICES Document CM 1998/O: 48 (1998) b:29.

    Vasconcelos M. E., Figueiredo M. J., Ribeiro-Cascalho A. Distribution and catch composition of monkfish Lophius piscatorius L. and Lophius budegassa Spinola, captured by trawl off the Portuguese coast. ICES Document CM 1986/G: 17 (1986) 8.


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