A synthesis of the early life history of the anglerfish, Lophius ...

ICES Journal of Marine Science, 58: 70–86. 2001
doi:10.1006/jmsc.2000.0991, available online at http://www.idealibrary.com on
A synthesis of the early life history of the anglerfish, Lophius
piscatorius (Linnaeus, 1758) in northern British waters
John R. G. Hislop, Alejandro Gallego,
Michael R. Heath, Fiona M. Kennedy,
Stuart A. Reeves, and Peter J. Wright
Hislop, J. R. G., Gallego, A., Heath, M. R., Kennedy, F. M., Reeves, S. A., and
Wright, P. J. 2001. A synthesis of the early life history of the anglerfish, Lophius
piscatorius (Linnaeus 1758) in northern British waters. – ICES Journal of Marine
Science, 58: 70–86.
Although the anglerfish Lophius piscatorius is now a species of major commercial
importance, our understanding of its basic biology is far from complete. Here, the
early life history of L. piscatorius is investigated by otolith daily increment analysis, the
application of a particle tracking model and an examination of the geographical
distribution of pelagic and demersal anglerfish. Otolith incremental analysis indicates
that the pelagic phase is relatively long (ca. 120 days) and growth during the first year
of life is rapid. A particle tracking model predicts that pelagic post larvae of known age
caught west of the Outer Hebrides could originate from the shelf edge west of Ireland,
the Rockall Plateau and the northern perimeter of the North Sea, whereas those
caught in the northern North Sea are likely to originate from the western edge of the
Norwegian Deep and the shelf edge west and north of Scotland. The model also
predicts that a large proportion of the young anglerfish originating from a spawning
area located west of the Outer Hebrides will enter the North Sea and that although
most of the spawning products originating at Rockall will recruit to the Rockall
Plateau some may be transported northwest and some to the northern perimeter of the
North Sea. The distribution of the demersal stages suggests that L. piscatorius spawns
in deep water, the transition from the pelagic to the demersal phase takes place in
relatively shallow water and most recruits enter the North Sea from the north and
west. The finding that some juveniles may settle on the seabed hundreds of kilometres
from the spawning grounds has major implications for the effective management of the
fishery.
Key words: anglerfish, Lophius piscatorius, particle tracking model, daily otolith
increments, recruitment, distribution, pelagic, demersal, juveniles, spawning.
Received 18 December 1999; accepted 24 June 2000.
John Hislop, Alejandro Gallego, Michael Heath, Fiona Kennedy, Stuart Reeves, Peter
Wright: FRS Marine Laboratory, PO Box 101, Victoria Road, Aberdeen, AB11 9DB,
Scotland, UK. Alejandro Gallego: Department of Zoology, University of Aberdeen,
Tillydrone Avenue, Aberdeen, AB24 2TZ, Scotland, UK. John Hislop: Present address:
100 Hammerfield Avenue, Aberdeen, AB10 7FE, Scotland, UK. Stuart Reeves: Present
address: Department of Marine Fisheries, Danish Institute for Fisheries Research,
Charlottenlund Slot, DK-2920 Charlottenlund, Denmark. Correspondence to Peter
Wright: Tel.: +44 1224 876544; Fax: +44 1224 295511; e-mail: P.J.Wright@
marlab.ac.uk
Introduction
Two species of lophiid anglerfishes occur in the northeast
Atlantic, Lophius piscatorius (Linnaeus, 1758),
sometimes referred to as the white anglerfish, and L.
budegassa (Spinola, 1807), the black or black-bellied
anglerfish. They are morphologically similar and usually
marketed together. Thus in the UK the trade names
‘‘monks’’ and ‘‘monkfish’’ are applied to both species.
Although the two species coexist over the greater part of
their ranges (Caruso, 1986), L. piscatorius predominates
north of latitude 55N, where it represents more than
98%, by weight, of the landings of anglerfishes from the
North Sea and west of Scotland (Kunzlik et al., 1995).
Anglerfishes have been exploited in northern European
waters for at least a century. For most of this period
they were a small but valuable by-catch but during
the last two decades they have become an extremely
1054–3139/01/010070+17 $35.00/0

A synthesis of the early life history of the anglerfish
71
62°N
61
Division Vb
1000 m
200 m
60
Shetland
Norwegian Deeps
59
Sub-area VI
(West of Scotland and Rockall)
Orkney
Latitude
58
57
Rockall Plateau
Outer Hebrides
Sub-area IV
(North Sea)
Division
IIIa
(Skagerrak)
56
55
54
Sub-area VII
53
–16
–14 –12 –10 –8 –6 –4 –2 0 2 4 6 8
Longitude
Figure 1. Main study area, showing relevant ICES areas and locations mentioned in the text.
10°E
important target species. In Scotland, for example,
anglerfishes were the second most important finfish
landed in 1996 and 1997, in terms of total quayside
value, whereas they were in sixth place in 1986 (source:
The Scottish Office Agriculture, Environment and Fisheries
Department). This change reflects both the high
price commanded by anglerfishes and the reduced
opportunities to exploit the depleted stocks of traditional
demersal targets (e.g. cod, Gadus morhua;
haddock, Melanogrammus aeglefinus; and whiting,
Merlangius merlangus).
Estimates of total international landings since 1950
from the area considered in this paper (Figure 1) are
given in Figure 2. There has been a sharp increase in
landings since the mid 1980s, corresponding to an
increase in Scottish landings from the northern North
Sea and west of Scotland. Landings from other areas
and by other nations over this period have remained
relatively small, with the percentage taken by Scottish
vessels increasing from close to 50% in 1985 to a peak of
75% in 1996. There are no indications that this increase
in landings reflects a corresponding change in the abundance
of anglerfishes. Rather, it is more likely that this
increase in landings has only been sustained by factors
such as reduced discarding, technical improvements
of gear and the expansion of the fishery into deeper
waters to the north and west of Scotland (ICES, 2000).
However, such developments cannot sustain a fishery
indefinitely and decreased landings in 1997 and 1998
may be a warning sign.
Preliminary management measures have been applied
to anglerfishes; precautionary Total Allowable Catches
(TACs) have been set for ICES Sub-areas VI (since
1986) and IV (since 1998). However, the development
and implementation of an effective stock management
Landings (tonnes)
40 000
30 000
20 000
10 000
0
1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000
IIIa IV VI Total
Figure 2. Estimated total international landings of anglerfishes
(L. picatorius and L. budegassa) from the Skagerrak and
Kattegat [ICES Division IIIa (........)], the North Sea [ICES
Sub-area IV ( )] and West of Scotland and Rockall [ICES
Sub-area VI ( )], 1950–1998. Figures for 1950–1972 are
figures as officially reported to ICES; figures for 1973 to 1998
are taken from ICES (2000). ( =Total).

72 J. R. G. Hislop et al.
strategy has been hindered by a lack of knowledge of
the basic biology of anglerfishes. For example, little is
known about when and where anglerfishes spawn in
northern European waters and there is uncertainty
about several key events during the first year of life. This
ignorance can be attributed to the unusual spawning
habits of Lophius. The eggs and larvae are pelagic.
However, whereas most marine fish produce individual
free-floating eggs that disperse over a wide range, anglerfish
eggs are extruded in a buoyant, gelatinous ribbon
that may measure more than 10 m25 cm (Prince,
1891; Fulton, 1898) and contain more than 1 000 000
eggs (Fulton, 1891). The highly clumped distributions of
the eggs and newly emerged larvae – up to 95 000 larvae
per 10 m 2 (O’Brien, 1986) – explains why conventional
egg and larval surveys have provided very little information
on the timing of spawning and the location of
the spawning grounds.
The early life history of L. piscatorius was the subject
of three major reviews in the first part of the 20th
century (Fulton, 1903; Bowman, 1920; Tåning, 1923).
Fulton and Bowman dealt mainly with the North Sea,
whereas Tåning also presented data from ichthyoplankton
surveys of the oceanic waters of the northeast
Atlantic, including the western seaboard of the British
Isles. It was evidently unusual to catch female anglerfish
on the point of spawning, although small numbers of
females in an advanced stage of maturity were taken in
the North Sea in February, May and July (Fulton,
1903). The few egg ribbons and isolated anglerfish eggs
caught in the Northeast Atlantic were taken between
February and early August. Bowman (1920) noted that
Lophius eggs and larvae were taken only in the northern,
i.e. deeper, parts of the North Sea and many of the
post-larvae caught west of the British Isles were taken
over or close to deep water (1000 m) (Tåning, 1923).
Larval and post-larval stages (20 mm) were taken west of the
British Isles in May, June and August (Tåning, 1923).
Taken together, these pelagic records suggest that
Lophius has a long spawning season. Although demersal
anglerfishes >200 mm were widely distributed over the
northern North Sea and were not uncommon on inshore
grounds, very few small (

A synthesis of the early life history of the anglerfish
73
Additional information on the size and distribution of
post-larvae and pelagic juveniles (hereafter referred to as
pelagic stages) was obtained from the International
0-group Gadoid Survey in the North Sea (IOGS). The
IOGS took place in June/early July in the years 1974–
1983. The sampling gear, the International Young
Gadoid Pelagic Trawl, has a mouth opening 10 m
10 m and a 10-mm (stretched) hexagonal mesh
codend. Stratified hauls (20 min near the sea bed, 20 min
at the thermocline and 20 min within 5–10 m of the
surface) were made at or near the centre of each ICES
statistical rectangle. The total lengths of all specimens
caught in the years 1977–1983 were measured to the
0.5 cm below. (For details of catches in the IOGS see
ICES Annales Biologiques, Copenhagen, Vols 34–40.)
Although we are confident that all the pelagic
specimens 30 mm were L. piscatorius the possibility
cannot be ruled out that some of the smallest individuals
were L. budegassa.
Daily otolith increment analysis
Initial preparation and examination of two otolith
pairs (sagittae and lapilli) indicated that the latter were
generally easier to interpret because of their more clearly
defined increments and, for fish >35 mm TL, their ease
of preparation. Preparation of a readable increment
sequence in sagittae from large fish was made dificult by
multiple planes of growth, associated with the presence
of accessory primordia. Further, it was necessary to
grind both sides of sagittae from fish >35 mm TL. For
these reasons, primary increments in the lapilli were used
to estimate age, assuming that these structures were
formed daily. Lapilli were removed by means of a dorsal
incision through to the otic capsule. They were mounted
on glass slides with a methacrylate adhesive (Loctite
glass bond) which was cured using ultraviolet light.
Otoliths from fish >36 mm TL were ground with a 2500
grit metallographic grinding paper disc lubricated with
1 μm alumina slurry, using a lapping wheel. Otoliths
from larvae 600 m). Seabed
topography, initial temperature and salinity data, air
temperature, humidity, precipitation and river run-off
data were used to configure and force the models.
Hainbucher and Backhaus (1999) described results of
simulations forced by a range of wind scenarios. We
have used data from a run in which the models were
forced with March–May seasonally averaged but
spatially varying wind stress derived from the Hellerman
dataset (Hellerman and Rosenstein, 1983). The models
were run to quasi-steady state with this wind forcing
pattern, and the results from the fine scale model
were taken to represent the climatological average
hydrographic and circulation conditions for the spring
period.
Particle tracking model
The stationary hydrodynamic data from the HAMSOM
were used to drive a particle tracking model (Bryant

74 J. R. G. Hislop et al.
et al., 1998; Gallego et al., 1999) configured to simulate
the dispersal of anglerfish eggs and larvae. It was
assumed that Lophius egg ribbons are spawned close to
the seabed, and rise slowly towards the surface. To
represent this pattern of vertical distribution in the
model, particles were released at nodes of a regular
15 km spaced horizontal grid covering an area simulating
the environmental spawning range of L. piscatorius
(see below). There are no data on the vertical distribution
of anglerfish eggs and larvae from which to gain
an indication of the likely ascent rate or precise depth in
the surface waters, and we therefore made a best guess at
these parameters, and conducted a sensitivity analysis of
the results (see below), with particular respect to the
ascent rate. The default configuration was that each
particle was initialised at a depth of 1 m above the
seabed, and was programmed to ascend at a fixed rate of
15 m d 1 until attaining a depth of 35 m, at which they
remained for the rest of the model run. Horizontal
positions of particles were updated at 1 h intervals
assuming passive transport, based on the magnitudes of
east–west (u) and north–south (v) velocity components
at surrounding nodes in the hydrodynamic model data,
and a Eulerian integration scheme to estimate velocities
at particle locations. The position of each particle was
saved at one day intervals for post-simulation analysis.
To test the sensitivity of the results to the assumed rate
of ascent, a separate model run was performed with a
rate of 150 m d 1 and the outcome compared with the
default results.
The daily resolution particle tracking model results
were investigated using a system based on ‘‘source’’ and
‘‘target’’ boxes. A source box was a geographical region
delineated by a polygonal shape defined by a series of
latitude and longitude locations, which was used to
subset the particle tracking results according to the start
location of individual particles. A target box was a
region, also delineated by a polygon, used to subset the
particle tracks according to their locations within a
prescribed age interval, age being the number of days
since release.
Modelling the environmental spawning range of
anglerfish
The potential geographical distribution of L. piscatorius
spawning was defined on the basis of two environmental
criteria; depth range and minimum temperature of
spawning. Unpublished data provided by scientific
observers from the Marine Laboratory Aberdeen (L.
Bullough, T. Blasdale) working on Scottish and French
commercial vessels fishing in deep water north and west
of Scotland indicated that mature L. piscatorius are
seldom caught deeper than 1100 m or at temperatures

A synthesis of the early life history of the anglerfish
75
additional trips could not be compared with the SWCS
and IBTS, because different trawls and larger codend
meshes (100 mm) were used, but information was
obtained on the vertical and horizontal distribution of
mature female L. piscatorius.
Inspection of the summed annual length frequency
distributions of both the SWCS and the IBTS identified a
pronounced trough at a length of approximately 30 cm.
Daily otolith increment counts (see Results) indicated
that fish in the length range 2–23 cm were approximately
9 months old and it was therefore assumed that all fish
measuring

76 J. R. G. Hislop et al.
(a)
(b)
Figure 3. Fine structure of the lapillus of L. piscatorius, showing checks presumed to be associated with hatching (HC), yolk sac
absorbtion (YSC) and settlement (SC). (a) Pelagic specimen, total length 80 mm, age: 90 days. Scale bar: 10 μm. (b) Demersal
specimen, total length 160 mm, age: 182 days. Scale bar: 100 μm. Inset: detail of settlement check (scale bar: 10 μm).

A synthesis of the early life history of the anglerfish
77
5
4
1994
14–24 May
250
200
Frequency
3
2
1
Total length (mm)
150
100
50
Frequency
0
20
6
5
4
3
2
40 60 80 100
Hatch date (Julian day)
1996
4 June–7 July
120
0
0
20 40 60 80 100 120 140 160 180 240 240 240
Age (days)
Figure 5. Estimated post hatching age (days) at total
length (mm) of pelagic () and demersal () juvenile
L. piscatorius. Fitted Gompertz curve: L=252 exp
{exp[0.0157*(age111.5)]}.
64°N
63
1
62
Frequency
0
20
18
16
14
12
10
8
6
4
2
0
20
40 60 80 100
Hatch date (Julian day)
1997
29 May–16 June
40 60 80 100
Hatch date (Julian day)
120
120
Figure 4. Estimated hatch date distributions of pelagic L.
piscatorius caught in 1994, 1996 and 1997.
distribution of the juveniles in this area is unknown
because sampling was restricted to a narrow band of
stations following the contour of the continental shelf.
The area north of 6000N was, however, more extensively
sampled and here the distribution of the juveniles
was also more or less restricted to the shelf edge. The
entire northern North Sea was surveyed systematically
for seven consecutive years during the IOGS. Although
few young anglerfishes were caught, virtually all were
61
60
59
58
57
56
55
–12 –10 –8
–6 –4 –2 0 2 4
taken north of 5900N, i.e. relatively close to the deep
water bordering the North Sea.
Estimates of the age stratified distribution of the
pelagic stages of Lophius were obtained by re-arranging
the Gompertz growth equation to determine age from
length. The distribution in space and time of all pelagic
specimens, stratified by 20 day age ranges, is presented
in Figure 7. This information provided the final
locations and pelagic durations used as input to the
larval transport model.
Potential spawning range of anglerfish
6°E
Figure 6. Presence () and absence () of pelagic juvenile
L. piscatorius in Norwegian surveys, 1995–1997 and the
International 0-group Gadoid Survey, 1974–1983.
The simulation of the potential spawning distribution of
anglerfish in the eastern Atlantic, based on temperature

78 J. R. G. Hislop et al.
62°N
19–39 day old larvae. Hatched March–April.
62°N
40–59 day old larvae. Hatched March–April.
61
61
60
60
59
59
58
58
57
57
56
56
55
–14
–12 –10 –8
–6 –4 –2 0 2 4
6°E
55
–14
–12 –10 –8
–6 –4 –2 0 2 4
6°E
62°N
60–79 day old larvae. Hatched April–July.
62°N
80–99 day old larvae. Hatched February–April.
61
61
60
60
59
59
58
58
57
57
56
56
55
–14
–12 –10 –8
–6 –4 –2 0 2 4
6°E
55
–14
–12 –10 –8
–6 –4 –2 0 2 4
6 °E
62°N
61
100–119 day old larvae. Hatched February–March.
60
59
58
57
56
55
–14
–12 –10 –8
–6 –4 –2 0 2 4
6°E
Figure 7. Distribution and month of capture [May (), June (), July ()] of individual pelagic larval and juvenile L. piscatorius,
stratified by 20 day age bands, taken in Norwegian surveys 1995–1997 and the International 0-group Gadoid Survey, 1974–1983.
The ages of the fish were either determined directly or estimated from their total lengths using the relationships shown in
Figure 4.

A synthesis of the early life history of the anglerfish
79
(a)
(a)
65°N
65°N
60
60
55
55
–20 –15 –10 –5 0 5 10
15°E
–20
(b)
–10 0 10 °E
65°N
(b)
65°N
60
60
55
55
–20
–10 0 10 °E
Figure 8. (a) Depth (100–1100 m), and seabed temperature
(5C, red) criteria applied to calibrated output from the
HAMSOM simulation of climatological spring (March–May)
conditions in the northeast Atlantic. Blue indicates

80 J. R. G. Hislop et al.
The simulated origins of particles occurring in the
Hebrides and northern North Sea target boxes were
robust with respect to the assumed ascent rate in the
model. With the default rate (15 m d 1 ), 16.7% of
particles from the entire potential spawning area were
encountered in the Hebrides target box within the
60–120 d age range, compared to 13.6% with the
higher ascent rate (150 m d 1 ). For the northern
North Sea target box, 11.1% were encountered in the
80–120 d age range with the default parameter, and
12.5% with the higher rate of ascent. The mean age at
entry to the target boxes was slightly decreased with
the more rapid ascent rate (Hebrides box: 81 d with
default ascent, 76 d with more rapid ascent; North
Sea box: 97 d with default ascent, 86 d with more
rapid ascent). These differences were relatively small in
themselves but, in addition, the spatial origins of the
particles encountered in the target boxes were relatively
unaffected by the ascent rate parameter. For the
Hebrides target box, 56.4% of the encountered
particles originated from the Rockall Bank source
region with the default parameter, and 50.4% with the
more rapid ascent. For the northern North Sea target
area, 22.9% of encountered particles originated from
the slope region west of 5W, compared to 33.7% with
the more rapid ascent rate. Overall, we conclude that
uncertainty in the vertical distribution of eggs and
larvae did not significantly undermine the conclusions
from the particle tracking model.
Dispersal of larvae from different spawning
regions
Two source boxes were configured to represent the
spawning regions identified from the trawl catches in
1999 (along the continental slope west of the Outer
Hebrides, and the Rockall Plateau) and the locations of
particles originating from those parts of the source
boxes which met the depth range and minimum temperature
of spawning criteria were plotted at 30 d age
intervals. The results (Figures 10 and 11) indicated that
larvae from the spawning area west of the Hebrides
should mainly contribute to juvenile populations in the
North Sea, with some dispersal to Iceland. In contrast, a
high proportion of the larvae produced at Rockall
should be retained in the vicinity of Rockall Plateau,
with some being dispersed to the north and northwest.
Distribution of demersal stages
The distributions of small (200mbyFRV‘‘Scotia’’ and MFV ‘‘Endeavour III’’ in
March–June 1999 measured less than 30 cm. Fish of
intermediate size were more evenly distributed over the
survey area, although overall distribution was similar to
that of the small fish. The highest catch rates of intermediate
sized fish were obtained at a few locations west
of the Outer Hebrides and the Orkney Islands. Large
fish, including potential spawning females, were caught
in very small numbers in the SWCS and IBTS. The catch
rates were, however, highest in the northern part of the
survey area. Figure 13 shows where the 18 pre-spawning
mature females (maturity stages 3 and 4, Afonso-Dias
and Hislop, 1996) were caught by FRV ‘‘Scotia’’ and
MFV ‘‘Endeavour III’’ in 1999. Seventeen of these fish
were taken in deep water (220–900 m) west of the Outer
Hebrides and at Rockall and one in shallower water
(160 m) west of the Shetland Islands.
Discussion
Early life-history
Estimates of yolk sac duration from this study (20 days)
are long relative to the eight and 15 days reported by
Lebour (1925) and Bowman (1920), respectively. However,
because Lebour’s yolk sac larvae were raised
under much warmer conditions (>18C) than those
prevailing over the continental slope west of Scotland
in March (8–9C; pers. obs. M.R.H.), the estimate
obtained from otolith microstructure may be realistic.
Assuming that otolith increments are formed daily,
the present study confirms the hypothesis proposed by
Fulton (1903) and Tåning (1923) that L. piscatorius
grows rapidly in its first year and specimens of 6–18 cm
total length caught on the bottom in summer and
autumn are 0-group. However, whereas Fulton (1903)
believed that the pelagic phase is short, our results
indicate that it lasts for three to four months after
hatching.
The daily increment counts for the lapilli of the
demersal specimens indicate that L. piscatorius in the
length range 10–30 cm caught in March/April are predominantly
1-group, i.e. they were spawned in the
previous calendar year. This is in agreement with
estimates of length at age of L. piscatorius in Greek
waters (Tsimenidis and Ondrias, 1980) and the Irish Sea
(Crozier, 1989), based on counts of presumed annual
growth zones in the sagittal otoliths. Slower growth
rates, based on the enumeration of annual zones in
sectioned illicia, have been reported for the Bay of
Biscay/Celtic Sea (Dupuoy et al., 1986) and Iberian
waters (Duarte et al., 1997).
The sizes of the pelagic and demersal juvenile stages
of L. piscatorius overlap. Specimens measuring up to
12 cm can be caught near the surface (this paper) and

A synthesis of the early life history of the anglerfish
81
(a)
(b)
65°N
65°N
60
60
55
55
–20 –10 0
10°E
–20 –10 0
10°E
65°N
(c)
65°N
(d)
60
60
55
55
–20 –10 0
10°E
–20 –10 0
10°E
65°N
(e)
60
55
–20 –10 0
10°E
Figure 10. Dispersal of particles originating in the West of Hebrides source box. (a) Age 0; (b) age 30 days; (c) age 60 days; (d) age
90 days; (e) age 120 days.
fish of 6–7 cm have been caught on the sea bed
(Bowman, 1920; Duarte et al., 1997; Marine Laboratory
Aberdeen, unpublished data). Evidently, factors
other than the attainment of a threshold length determine
when settlement takes place. The availability of a
suitable substrate may play a part. Depth may also be
important. In 1999, no small (200 m). This supports
Fulton’s hypothesis that settlement is in relatively
shallow water.

82 J. R. G. Hislop et al.
(a)
(b)
65°N
65°N
60
60
55
55
–20 –10 0
10°E
–20 –10 0
10°E
65°N
(c)
65°N
(d)
60
60
55
55
–20 –10 0
10°E
–20 –10 0
10°E
65°N
(e)
60
55
–20 –10 0
10°E
Figure 11. Dispersal of particles originating in the Rockall source box. (a) Age 0; (b) age 30 days; (c) age 60 days; (d) age 90 days;
(e) age 120 days.
Time of spawning
The numbers of daily increments in the lapilli of
the pelagic specimens imply that the majority had
hatched in the period February–April, consistent with
Afonso-Dias and Hislop’s (1996) conclusion that
spawning occurs between November and May. Most
of the specimens whose lapilli were examined were,
however, collected within a relatively short period
(May–early July). The archive data of Fulton,

A synthesis of the early life history of the anglerfish
83
62°N
(a)
62°N
(b)
60
60
Latitude
58
56
Latitude
58
56
54
54
52
52
–10 –5
0 5
Longitude
10 °E –10 –5 0 5
Longitude
10 °E
62°N
(c)
62°N
(d)
60
60
Latitude
58
56
Latitude
58
56
54
54
52
52
–10 –5
0 5
Longitude
10 °E –10 –5 0 5
Longitude
Figure 12. Catch rates, number h 1 , of three length classes of L. piscatorius in each statistical rectangle in the Scottish West Coast
Bottom Trawl Survey and the International Bottom Trawl Survey of the North Sea, 1985–1996. (a) =70 cm. The total fishing effort (hours) in each statistical rectangle is indicated in (d). Key: Catchrate 0.1 h1 , 1h 1 ,
5h 1 , 10 h 1 ; hours fishing, 1984–1996 1, 10, 50.
10 °E
Bowman and Tåning indicate that L. piscatorius has,
or at least had, a longer spawning season, because eggs
were caught over the period February–early August.
Furthermore, the numbers of daily increments in the
otoliths of demersal specimens imply hatch dates as
late as September.
Spawning locations
The spawning distribution of anglerfish cannot easily be
defined from trawl catches because of low catch rates of
mature fish. The impression gained from early records
was of spawning in deep water along the continental
slope west of the British Isles, and in deeper areas of the
northern North Sea. In this paper we have effectively
integrated the sparse survey data, using depth and
temperature as correlates of the distribution, in order to
produce a spatially detailed estimate of the potential
spawning distribution of the species from hydrodynamic
model results. The results cannot give any indication of
the relative abundance of fish in different regions, for
example Rockall compared to the northern North Sea;
merely an indication of potential presence and absence
of mature fish. Anecdotal information, for example
fisheries at Rockall, Faroe and Iceland – areas with few
scientific survey records of anglerfish catches, tend
to corroborate rather than contradict the simulated
distribution.
Dispersal of larvae
The particle tracking model gives indications of the
possible spawning origins of larvae caught in various
locations in the region. There are many uncertainties in

84 J. R. G. Hislop et al.
Latitude
62°N
61
60
59
58
57
56
–15 –10
–5
Longitude
1000 m
200 m
0°E
Figure 13. Locations where individual pre-spawning mature
female L. piscatorius in maturity stages 3 (triangle) and 4
(inverted triangle) were caught by FRV ‘‘Scotia’’ and MFV
‘‘Endeavour III’’ in March–June 1999. Small symbol: one fish;
large symbol: two fish.
the model, in particular, the depth of spawning, ascent
rate of egg ribbons, vertical migrations of larvae, and the
assumption that larvae are passively transported by
water currents up to 120 d of age.
Regarding the depth of spawning, we have assumed
that this happens close to the seabed, but there is no
firm evidence to support or refute this. Large anglerfish
have been caught near the surface, but their reproductive
status was not recorded (Hislop et al., 2000).
Given that spawning takes place near the bottom, the
egg ribbons must rise towards the surface because egg
ribbons have been seen at the surface (Bowman, 1920)
and most catches of egg and young larvae have been
within 100 m of the surface (Bowman, 1920; Tåning,
1923). Our model results were robust against an order
of magnitude variation in the assumed ascent rate, so
this aspect does not appear to be very important in
determining the results. Elsewhere, we have investigated
the consequences of diel vertical migrations in
the upper 100 m of flows simulated by HAMSOM, and
found that the tracking model produces results which
are very similar to those with particles held at a
constant depth of between 20 and 50 m (Gallego et al.,
1999).
The assumption of passive transport up to 120 d
of age is the most difficult assumption to defend.
Horizontal swimming ability certainly develops well
before 120 d age, but whilst this can be regarded as
essentially random it would be expected to act as an
additional diffusion term in the model, rather than a
systematic deviation from passive transport. In the
absence of any knowledge, we assume no directed
migration during the modelled period, but recognise that
this could be a potential source of error on the model
results.
There are two main areas where post-larvae have been
caught in recent years – west of the Hebrides, and in the
northern North Sea. The particle tracking model results
suggest that these may have originated from widely
dispersed areas, including the west of Ireland and the
Rockall Plateau, as well as the continental slope west
of Scotland which is a known area of abundance of
spawning fish.
In the absence of data, the particle model contains
no representation of the relative egg production in
different parts of the model region, and hence estimates
of the relative contribution of source regions
to the target areas assume a uniform distribution of
the spawning stock. Nevertheless, it is clear that any
spawning at Rockall has the potential to contribute to
the population of juvneiles on the shelf north and west
of the UK.
The existence or otherwise of a spawning population
of anglerfish at Rockall is perhaps the most intriguing
aspect of the spawning distribution and particle tracking
model results. The model indicates that a substantial
part of any larval production is retained over the Plateau
under average climatological conditions, suggesting that
the area has at least the potential to support a selfsustaining
population. There have not been any larval
fish surveys of the Rockall region in recent years, and
scientific trawl surveys have been restricted to depths

A synthesis of the early life history of the anglerfish
85
Conclusions
Our findings suggest that the spawning grounds of the
L. piscatorius exploited in north British waters are in
relatively deep water (150–900 m), although well within
the reach of fishermen employing modern technology.
We have also shown that post-larval anglerfish may be
transported over considerable distances before settling
on the seabed. Intensive exploitation of mature females
in one area may therefore influence recruitment to areas
that may be hundreds of kilometres distant. The particle
tracking model has raised the possibility that Rockall
may supply some recruits to the west of Scotland
shelf, and that some North Sea fish could have
originated from spawning grounds west of Ireland.
Understanding the evidently complex relationships
between L. piscatorius in different parts of the Northeast
Atlantic is vital if the fishery is to be effectively managed
and studies of the genetics of anglerfish and the elemental
composition of their otoliths are being conducted to
this end.
Acknowledgements
We are greatly indebted to Dankert Skagen (Institute of
Marine Research, Bergen) for bringing the Norwegian
catches of juvenile Lophius to the attention of J.R.G.H.
and making his specimens available. Martin Bailey
(Marine Laboratory Aberdeen) supplied the larval specimens.
Tom Blasdale, Luke Bullough, Finlay Burns and
Kevin Peach (Marine Laboratory Aberdeen) provided
data from commercial fishing trips. The cooperation of
skipper Peter Lovie, MFV ‘‘Endeavour III’’ is gratefully
acknowledged. Drs Henk Heessen (Netherlands Institute
for Fishery Investigations, IJmuiden) and Siegfried
Ehrich (Institut für Seefischerei, Hamburg) provided
IBTS data. The work on anglerfishes was supported by
EU Study Contract 98/096. The HAMSOM hydrodynamic
model data were produced by D. Hainbucher,
University of Hamburg, with support from the
EU-MAST ICOS project (MAS2-CT94-0085), which
also supported the development of the particle tracking
model code. Hydrographic data from the northeast
Atlantic were collected during the EU-TASC project
(MAS3-CT95-0039).
2001 Crown copyright
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