|
|
EFAN Report 2-2000 |
3rd
International Ageing Workshop
on
European Anglerfish
IPIMAR, Lisbon, 8-12 March 1999
|
European Fish Ageing Network (EFAN) |
|
Phone: (47) 37 05 90 00;
Fax: (47) 37 05 90 01; Email: bente.lundin@imr.no Office address: Flψdevigvn.
49, Hisψy (Arendal), Norway. Coordinator: Erlend
Moksness, Phone (direct): (47) 37 05 90 41; E-mail: moksness@imr.no |
Contents
1.
Introduction
.
4
2.
Objectives of the workshop
.
. 5
3.
Participants
. 6
4.
Materials and Methods
. 6
4.1. Illicia
reading
..
.. 6
4.1.1. Samples
.. 6
4.1.2. Age reading
..
.. 7
4.1.3. Data analysis
..
9
4.2. Age reading criteria
..
. 11
5.
Results of the age readings
.
. 12
5.1. Lophius budegassa
...
12
5.1.1. First reading (exchange)
...
. 12
5.1.2. Second reading
..
. 14
5.2. Lophius
piscatorius
.
.. 14
5.2.1. First reading (exchange)
..
.. 14
5.2.2. Second reading
16
6.
Discussion of the age readings
..
.. 17
6.1. Lophius budegassa
.
.. 17
6.2. Lophius
piscatorius
.
.. 18
7.
Ageing criteria
..
19
8.
Conclusions
..
21
9.
Recommendations
..
21
10.
References
. 23
11.
Working documents presented to the workshop
. 24
Annexes
Annex 1 Participants address
Annex 2 Protocol for the Lophius budegassa illicia exchange
Annex 3 Protocol for the Lophius piscatorius illicia exchange
Annex 4 Images
Annex 5 Scanning electron microscopy
Annex 6 Guide to the anglerfish ageing
Annex 7 Image of illicia with tetracycline mark
1. INTRODUCTION
Black
(Lophius budegassa) and White (Lophius piscatorius) Anglerfish are two
important species of groundfish fisheries in the North East Atlantic. They are
evaluated annually at the ICES Working Group on the Assessment of the Southern
Shelf Demersal Stocks.
In
the last two decades several studies on age reading and growth of North Eastern
Atlantic and Mediterranean Anglerfish have been carried out (Anon, 1991; Anon.,
1998a; Azevedo, 1996; Crozier, 1989; Duarte et
al., 1997; Dupouy and Kergoat, 1985; Dupouy et al., 1986; Landa and Pereda, 1997; Landa et al., 1998; Pereda and Landa, 1998; Peronnet, et.al., 1992; Quincoces et al., 1998 (a, b); Tsimenidis, 1984 and
Tsimenidis and Ondrias, 1980).
The
Workshop on Sampling Strategies for Age and Maturity (ICES CM, 1994) indicated
that it is necessary to convene a specific workshop on age determination when
the results of the stock assessment research suggest inconsistencies in the
data or whenever new inexperienced staff becomes involved with those age
determinations. For these reasons, it was deemed
necessary to convene workshops on Anglerfish age determination.
The first
ageing Workshop for Anglerfish was carried out in 1991 (Anon., 1991) involving
readers from France and Spain. In 1997 (Anon., 1998) a second workshop was
conducted with additional participation by Portugal. These Workshops were
considered to be the first steps in trying to achieve a consensus in ageing
criteria on Anglerfish.
This
Workshop (3rd) is undertaken as part of the EU Study Contract
No.97/015 (New assessment and biology of the main commercial fish species:
Hake and Anglerfishes of the Southern shelf demersal stocks in South Western
Europe DEMASSESS). The workshop can also be considered within the main
objectives of the European Fish Ageing Network (EFAN), which aims to develop,
conduct and co-ordinate collaborative research and training, and thereby ensure
that age determination becomes a reliable element of the assessment underlying
the scientific management advice on fisheries and environmental
resources. Participants from various
institutes who were present at the previous workshop participated in this, the
3rd workshop. In addition
two personnel from the MIFRC, Dublin participated in an Angler fish Ageing
Workshop for the first time. Prior to this workshop
an illicia exchange was carried out
with participation of all institutes.
The workshop was structured in the following way for each species:
·
Analysis
and discussion of the exchange (1st reading) results
·
Discussion
on ageing criteria
·
2nd
readings performed on a sub-sample
·
Analysis
and discussion of the 2nd reading results
·
Final
discussion on ageing criteria
·
Preparation
of the report
2. OBJECTIVES OF THE
WORKSHOP
The
objectives of the 3rd International Ageing Workshop on European
Anglerfish (L. budegassa and L.
piscatorius) are to:
·
Analyse and
discuss the results of the age determination based on the illicia exchange, in order to clarify the main problems of
Anglerfish age reading
·
Continue the
work started in the Workshops held in 1991 and 1997 and improve agreement
between readers
·
Elaborate
ageing criteria based on agreement between readers
·
Introduce new
readers from countries involved in the assessment of Anglerfish, to age
determination of the species
3.
Participants
|
Manuela
Azevedo |
IPIMAR
- Lisbon |
Portugal |
|
Rafael
Duarte Chairman |
IPIMAR
- Lisbon |
Portugal |
|
Hervι
Dupouy |
IFREMER
- Lorient |
France |
|
Bernard
Kergoat |
IFREMER
- Lorient |
France |
|
Jorge
Landa |
IEO
- Santander |
Spain |
|
Paulino
Lucio |
AZTI
- Sukarrieta |
Spain |
|
Helen
McCormick |
MIFRC
- Dublin |
Ireland |
|
Cristina
Morgado |
IPIMAR
- Lisbon |
Portugal |
|
Iρaki
Quincoces |
AZTI
- Sukarrieta |
Spain |
|
Fiona
Woods |
MIFRC
- Dublin |
Ireland |
|
Asier
Zamakona |
AZTI
- Sukarrieta |
Spain |
Addresses
of participants are in Annex 1.
4. MATERIAL AND
METHODS
4.1. Illicia reading
4.1.1. Samples
First reading
(exchange)
Two
illicia collections from each of the
two species were prepared for the exchange. The ageing-structures included in
the sets were randomly sorted from different length classes.
The
L. budegassa collections totalling
138 illicia, consisted of 70 illicia from the Northern Stock (ICES
Div. VIIIa,b,d) prepared by AZTI from commercial sampling and 68 illicia from the Southern Stock (ICES
Div. VIIIc and IXa) prepared by IPIMAR from commercial sampling and demersal
surveys. The Southern collection also contained some corresponding second
dorsal fin rays. The illicia selected
for both collections covered a length range between 15 and 88 cm (Figure 1)
over a one-year sampling period.
The
L. piscatorius collections totalling
147 illicia, consisted of 73 illicia from the Northern Stock (ICES
Div. VIIIa,b,d) prepared by AZTI from commercial sampling and 74 illicia from the Southern Stock (ICES
Div. VIIIc and IXa) prepared by IEO from commercial sampling. The illicia selected for both collections
covered a length range between 19 and 140 cm (Figure 2).
Second reading
After
a discussion on ageing criteria a random subsample of 35 illicia from each species were chosen. The illicia were selected from the Northern collections and represented
the total length range (Figures 1a and 2a).
4.1.2. Age reading
Eight
readers participated in both the exchange and workshop but not all of the
readers read both Northern and Southern collections due to insufficient time
being available. The reader codes, names and expertise of the readers who
participated in the illicia exchange
are presented in the following table.
|
|
|
Lophius budegassa |
Lophius piscatorius |
||
|
Code |
Reader |
Northern
Collection |
Southern Collection |
Northern
Collection |
Southern Collection |
|
R1 |
Iρaki Quincoces |
*** |
*** |
*** |
*** |
|
R2 |
Asier Zamakona |
** |
** |
** |
** |
|
R3 |
HelenMcCormick |
* |
No participation |
* |
* |
|
R4 |
Fiona Woods |
* |
No participation |
* |
* |
|
R5 |
Jorge Landa |
*** |
*** |
*** |
*** |
|
R6 |
Hervι Dupouy |
No participation |
*** |
*** |
No participation |
|
R7 |
Bernard Kergoat |
No participation |
** |
** |
No participation |
|
R8 |
Rafael Duarte |
*** |
*** |
** |
** |
* Readers with no experience
**
Readers with experience
***
Expert readers
A protocol, by species (Annex 2, 3), was prepared in advance of the exchange and circulated amongst readers. This gave information on the collection preparation, ageing and measurement methodology and a time schedule for ageing amongst readers.
First reading
(exchange)
The
observation of the illicia was
carried out using an optical microscope under transmitted light with x100
magnification, for the most part. R3
and R4 did not have access to a microscope with x100 magnification and
therefore age reading was performed using the maximum magnification available
to them, which was x50. Information on the total length and the time of capture
of each specimen was given to the readers. Wherever possible each reader attributed
an age to each illicium and gave
information about the ageing credibility and the first ring measurements. The
age credibility was classified according to one of four levels of readability
(U unreadable; L - low; M - medium; H high). The ring diameter was measured in micrometres (mm) in two perpendicular directions. For the first ring
measurements some readers used a calibrated eyepiece whilst others used an
image analysis system. The latter system is more precise than the former and
this fact should be taken into account when interpreting the results. R3 and R4
extrapolated their first ring measurements to x100 magnification. When the
readers attributed more than one age to the same illicium, the first age was considered. For the Southern L. budegassa collection, reading was
also performed on the 2nd dorsal ray, when present.
Second reading
For
the second reading of the Illicia,
some microscopes were set at a higher magnification than the recommended x100
(due to the combined magnification of their component parts). This was thought
to be a possible source of error in the age interpretation of the illicia. It was generally thought that
this influence may have been stronger with respect to the second age readings
of the L. piscatorius samples, whereby the poorest microscopes were excluded and each reader used only
one microscope to read all samples. Those readers who read at a higher
magnification (x125 or higher) may have been susceptible to this source of
error. When the second reading of L. budegassa was performed, samples were located at specific
microscopes, thus all readers read the same samples with the x125 microscopes
and the influence, if any, of varying levels of magnification would at least
have been, homogeneously distributed between all the readers.
The
light sources for some microscopes were adjustable whilst others were not.
Those readers who used the microscopes with fixed light sources may have been
working at a disadvantage. As in the first reading, the total length and the
catch date for each illicium was
available to the readers. Wherever possible each reader attributed an age to
each illicium and gave information
regarding the ageing credibility using the same parameters as in the first
reading. It should be noted and taken into consideration when analysing the
results, that second readings of both species were performed under the pressure
of limited time.
4.1.3. Data analysis
Prior to the analysis of the data, all ageing results were
observed. From this, it was decided
that illicia from L. budegassa having three or more Low
or Unreadable credibility levels assigned to them, should be excluded from
the exchange results analysis. If the
inexperienced readers made up one or more of these, then the modal ages amongst
the remaining readers were observed and if there was high agreement, these illicia were not excluded. For the
exchange results of L. piscatorius
and for the second reading of both species, all illicia were considered in the analysis.
Several
methods have been used up to the present time to analyse the results of these
exchanges such as tests to examine between-reader bias: the paired t-test, the
Bowker΄s test of symmetry and the Wilcoxon rank sum test (ICES CM, 1994).
Nevertheless, these methods are considered inappropriate in performing multiple
paired comparisons when more than two readers are involved in ageing the same
collection, which is the case in this exchange (Azevedo, in prep.). To compare
levels of agreement between groups of readers (test the reproducibility of the
results fbom ageing structures, stocks or preparation methods), the average
percent error (APE) from Beamish and Fournier (1981), the index of precision
(D) from Chang (1982) and the chance-corrected measure from O΄Connell and
Dobson (1984) have been proposed. It should be stressed that the aforementioned
measures of agreement, although computed in this report, must be interpreted
with caution since they have been criticised as not providing an appropriate
measure of ageing agreement between readers.
It
was decided that an exploratory analysis should be the first step in analysing
the results, as recommended in the ICES CM (1994). Exploratory analysis was
performed by collection. The statistical analysis consisted of computing
agreement and variability measures.
Exploratory data
analysis:
The
modal age was determined based on the expert reader's results (see Table on
page 4). For each illicium the
difference between the readers age and the modal age was calculated. Following the methodology described by
Eltink (1994) the average age was plotted against the modal age for each reader
and for all readers combined. In the
case of the first readings of L.
piscatorius (Southern collection), there were only two expert readers
involved in calculating the modal age and so whenever they differed on the age
of an illicium, this piece of data
was totally excluded from the analysis, which resulted in a large reduction of
data. Therefore it was decided to use the modal age based on readers with
experience (all readers excluding R3 and R4) when producing the bias plots.
A box-whisker plot (mean, mean±std. dev., mean±1.96std. dev.) of all ages attributed by readers was produced. A cluster analysis was performed using euclidean distances and single linkage. Readers were linked according to the attributed ages.
Ageing credibility
percentages were calculated by reader for all collections.
For
the first ring diameter analysis, the average diameter for L. budegassa and the horizontal and vertical diameters for L. piscatorius were calculated by reader
and by age. This information was plotted by reader in box-whisker plots and by
reader and age in a line graph. The
nucleus and first ring of L. piscatorius
have a characteristic oblong shape which means the larger and smaller axis
diameters are very different, therefore it is not appropriate to calculate the
average between them, as with L.
budegassa. The analysis was based only on the largest axis because it is
the wider measurement and differences between readers are probably more
noticeable. In this report, the largest axis of the first ring of L. piscatorius is also called the horizontal diameter.
Statistical data
analysis:
The
following measures were determined:
The
average percent error (APE) (Beamish and Fournier, 1981):
where,
n
= number of illicia
r
= number of readers for each illicium
xij=
the j value of age estimation for the illicium
i
= average age calculated for the illicium i
where,
s.d.i
= standard deviation calculated for the illicium
i.
The index of precision (D)
(Chang, 1982):
Analyses
were performed using Statistica software (StatSoft, Inc., 5.1) and Excel (Microsoft
97) spreadsheets.
4.2. Age reading
criteria
For
the discussion of the age reading criteria a projector was used to project the
image magnified by the microscope, onto a screen. Any alteration in the image focus or lighting could be directly
observed on the screen. In this way, each reader could show their personal
reading method (focusing, lighting and ring counting) and discussion would
follow. For each image shown on the
screen each reader identified the annual rings according to the ageing criteria
they were using. When initial agreement was not reached between readers,
agreement was sought through communal discussion. ,/span>From numerous discussions, a list of the main peculiarities
associated with illicia reading was
produced and is presented in Chapter 7 of this report.
5. RESULTS OF THE AGE
READINGS
5.1. Lophius budegassa
5.1.1. First reading
(exchange)
The
ageing results obtained by reader and basic information about the illicia, for each collection, are
presented in Tables 1 and 2.
Northern collection
Considering
the bias plots for readers R1, R2, R5 and R8 together (Figure 3c), it can be
observed that the mean age is very close to the modal age and that deviations
do not increase with age.
The
statistical analysis shows that when readings from R3 and R4 are excluded,
better results are obtained and the APE, CV and D decrease (Table 5).
Ageing
credibility percentages calculated for each reader are given in Table 6.
Although results are different between readers, it can be observed that, in
general the Medium credibility level has the highest percentage.
The
box-whisker plot of the first ring diameter shows two main groups: one
consisting of the expert readers R1, R5 and R8 and another consisting of the
non expert readers R2, R3 and R4 (Figure 6). The average diameters of the
expert readers are similar and lower than 100 mm, whilst the
non expert readers attain average values higher than 150 mm (R2) and 200
mm (R3 and R4). The graphical representation of the average 1st
ring measurement by age for each reader (Figure 7) clearly illustrates that
expert readers present similar average diameters for all ages. On the other
hand, 1st ring measurements by R2 increase with age and the
measurements of R3 and R4 are twice that of other readers. According to the
expert readers, the 1st ring diameter should be approximately 100 mm for this
species.
Southern collection
For
this collection, the exploratory data analysis shows that the average ages are
close to the modal ages for all readers (Figure 8). From Tables 7 and 8 it can be seen that even in older age groups,
agreement between readers is high.
R2
seems to have some discrepancies relative to the other readers. In Figure 8a
this reader shows higher mean ages in the older age groups. The same is
observed in Figure 9 where the mean age and standard deviation of R2 are higher
compared to the other readers.
The
cluster analysis shows that R1, R5, R6, R7 and R8 are linked in a narrower
group and R2 is separated from this group (Figure 10).
From
the statistical analysis (Table 9) it can be seen that the APE, CV and D
indices, for all readers, are much lower than those of the Northern collection.
If only expert readers are considered in the present analysis, the value of the
indices decreased slightly.
The
credibility analysis (Table 6) shows that Medium and Low credibility levels
present higher percentages.
R2
gives larger measurements for the 1st ring diameter compared to
other readers (Figure 11) and seems to increase this parameter in older ages
(Figure 12). As with the Northern collection, the first ring diameter from
specimens in the Southern collection seems to be around 100 mm.
5.1.2. Second reading
The
results obtained for the second reading are presented in Table 10. An overall
improvement in ageing is observed, since readers R3 and R4 are close to the
other readers (Tables 11 and 12, Figures 13, 14 and 15). The values of the
indices computed, are lower than those for the first readings (Table 5). The
APE decreased from 36% in the first reading to 10% in the second, taking all
readers into consideration. By excluding R3 and R4, no improvement was observed
(10% in the first and second readings).
5.2. Lophius piscatorius
5.2.1. First reading
(exchange)
The
ageing results obtained by reader and basic information about the illicia, for each collection, are
presented in Tables 13 and 14.
Northern collection
Considering
the modal ages obtained from expert readers, the exploratory analysis shows
that the ages attributed by R3 and R4 are substantially different from those
attributed by other readers, presenting large differences to the modal age
(Tables 15 and 16, Figure 16). The bias plots for readers R1, R2, R5 and R6
(Figure 16a), show that the mean age is very close to the modal age and
deviations are small.
The
box-whisker plots of the mean ages by reader show two main groups: one which
consists of the expert (R1, R5, R6) and partially experienced readers (R2, R7,
R8) and another which consists of the non experienced readers (R3, R4) (Figure
17).
The
dendrogram obtained from cluster analysis point out the presence of two clear
groups: one group consisting of R3 and R4 and another, which includes all the
remaining readers (Figure 18). Euclidean distances indicate that R3 and R4 are
distinctly separated from the other readers.
The
statistical analysis shows that if R3 and R4 are excluded, significantly better
results are obtained, the APE, CV and D decreasing considerably (Table
17). No substantial differences
are observed when comparing results from all readers, for the 1st
and 2nd semester.
Ageing
credibility percentages by reader are given in Table 18. Differences are
observed between readers with the Medium credibility level appearing most
frequently.
Southern collection
Modal
ages were obtained from all readers excluding R3 and R4. As observed in the
Northern collection, the exploratory analysis shows that the ages attributed by
R3 and R4 differ substantially from other readers and present large differences
to the modal age (Figure 21a and Table 19 and 20). R8 presents some remarkable
differences to the modal age but only in the higher ages. Considering the bias
plots for readers R1, R2 and R5, it appears that the mean ages are very close
to the modal ages and deviations are low (Figure 21a). In Figure 21b the mean ages
for all readers combined are underestimated relative to the modal ages. Deviations are very high and increase with
age.
The
box-whisker plots of the ages clearly show two different groups: one composed
of the expert (R1 and R5) and experienced readers (R2 and R8) and another
composed of the non experienced readers (R3 and R4) (Figure 22).
The
dendrogram obtained from the cluster analysis points out the presence of two
clear groups (Figure 23). One group
consists of R3 and R4 and another consists of the remaining readers. These two groups are clearly separated.
A
box-whisker plot of the 1st horizontal ring diameter (Figure 24)
confirms the results of the Northern collection. R2 presents higher values
compared to all readers. R1 and R3 are
very similar and present higher values than R5 and R8 which are also very
similar to each other. The average "horizontal diameters for R1 and R3
are approximately 250 mm and approximately 180 - 200 mm for R8 and
R5. The extreme mean values are
presented by R2 at 400 mm.
From
Figure 25 it can be seen that in the present collection the measurements of
first ring diameters by R2 increase for older ages. Expert readers maintain
consistent average diameter measurements for older ages and present similar
values.
5.2.2 Second reading
The
results obtained for the second reading are presented in Table 22. With regard
to L. budegassa, an overall
improvement was obtained in the second reading (Figure 26a, 27 and 28), however
some discrepancies are still observed for older ages (Figure 26b). R3 and R4
are closer to the rest of the readers but still present some deviations (Table
23 and 24). The
group of readers with good results in the first reading also achieve very good
agreement between each other in the second reading. The values of the
statistical indices decreased from the first reading to the second reading
(Table 17).
6.
Discussion of the age readings
6.1. Lophius budegassa
From
the first reading it can be seen that a group of 5 readers (R1, R5, R6, R7 and
R8) seem to have similar age reading criteria. The exploratory analysis shows
consistent age reading amongst these readers and the statistical analysis
indicates high agreement. The first ring determination is also consistent for
this group of readers.
R2
seems to have similar ageing criteria to the group mentioned above, but for
older ages, this reader shows certain discrepancies. This was observed from the
results of the first reading, especially for the Southern collection, where
this reader overestimated the age in older individuals. This reader increases
the first ring diameter in older individuals and because of this, introduces a
bias in the age reading.
In
the first reading R3 and R4 used different ageing criteria to the other readers
and thus underestimated all ages. The lack of previous experience in Anglerfish
ageing and the low magnification used in the first reading were the most likely
reasons for the observed discrepancies.
From
the results of the second reading an overall improvement in ageing is observed.
The group of readers R1, R5, R6, R7 and R8 maintain consistent age reading and
R2 is closer to this group since the average age increment in older ages is not
as significant. Since the first ring diameter was not
measured in the second reading, the deviations in the first ring measurements
in older ages shown by R2 in the first readings, could not be verified. In the second reading R3 and R4 are much closer to
the rest of the readers. The higher
magnification used by these readers in the second reading (x100) was considered
to be the main reason for better results being obtained. It was concluded by the group that insufficient
detail of the illicium section is
shown under x50 magnification (that magnification used by R3 and R4 to carry
out the first reading).
6.2. Lophius piscatorius
From
the data analysis of the first reading it can be seen that R2 and R7 seem to
have similar ageing criteria to the group mentioned above although they tend to
underestimate the older ages. The 1st
horizontal ring measurements obtained by R2 seem to be consistently much
higher than the rest of the readers.
The
first reading shows that R8, whilst having similar ageing criteria to the main
group mentioned above, tends to overestimate older ages.
R3
and R4 show different ageing criteria to the other readers. This is probably
due to their lack of previous experience in Anglerfish age reading and the use of
significantly lower magnification during first reading.
A
general improvement was obtained from the second reading. The readers R1, R5
and R6 maintained high agreement.
The
fish sizes in the sample of L.
piscatorius were in general larger than those in the sample of L. budegassa. This may account for the higher variability in the older
ages.
The
1st ring measurements ("horizontal" diameter ) in illicia from L. piscatorius seem to be around 200 - 250 mm.
7. Ageing
criteria
Anglerfish
ageing using illicia consists of
counting translucent and opaque rings.
At times these rings are well defined and clearly visible, but most of
the time, rings appear doubled and are not well defined, which makes ring
counting very difficult. From the open discussion and communal interpretation
of illicia sections during the
workshop, some peculiarities inherent to illicia
ageing were defined (Annex 4 contains the images that are referred to in this
section):
·
The length of
the fish can be a useful piece of information in ageing illicia.
·
It may be
useful to read the second fin ray to confirm the age attributed based on the illicium (Image 1).
·
Confusion
after age 6 may be related to first maturation which causes changes in the
growth pattern.
·
At times the
outer ring(s) are not visible in the whole illicium,
this may be because the section has not been cut perpendicularly (Image 2).
·
The area of
the illicium that is chosen for
cutting has an influence on the size and shape of all rings (Image 3). A
standardised cut position at about 5 mm from the illicium basis is recommended.
·
Rings may not
be visible in all the axes of the section.
·
Defined rings,
which are clearly visible in one part of a section may be less defined or even
appear to double in another part of the section. The counting should be based upon the area where good contrast
between rings exists.
·
Bands in illicia differ in composition. As a result, the surface appears as
alternative high and low areas. The
difference in levels relates directly to dark and light bands. This
characteristic is very apparent from research carried out using scanning
electron microscopy (Annex 5).
·
Unlike
otoliths where band widths tend to decrease as you approach the edge, in illicia bands remain approximately the
same width throughout the section or bands close to the border may even be
larger than those closer to the nucleus (Image 4 and 5).
·
Readers may
find it helpful to alter the light and focus as they interpret the sections.
·
Light
diffraction may change the ring coloration, bright to dark or vice versa (Image
2 and 6) depending on the focus or the way the illicium was cut.
·
The first
well-marked ring is considered to be a consequence of a change in the life
cycle (changing from planktonic to benthic living), and is therefore designated
as the benthic ring. The next ring is considered to be the first annulus (Image
7 and 8).
·
When
identifying the first annulus the
diameter of the benthic ring can be of assistance. The distance of the first annulus from the benthic ring is usually
not greater than half the distance of the diameter of the benthic ring.
·
For L. budegassa the horizontal or vertical
distance of the first ring tends to be at 100 mm. The first ring is circular in shape
(Image 7).
·
In L.
piscatorius the first ring tends to be oblong in shape thus the largest
axis tends to be between 200 and 250 mm and the smallest axis tends to be between 80 and 160 mm (Image 8).
·
Two distinct
criteria for first ring identification of L.
piscatorius were identified from the discussion and measurements. R1, R6
and R7 identified a larger ring and R5 and R8 a smaller ring, as the first
annulus (Image 9). It was agreed by all readers that the larger ring should be
considered to be the first annulus, thus the criterion of R1, R6 and R7 was
adopted.
8. CONCLUSIONS
From
the present ageing workshop a group of readers with good agreement, was
identified for each species. The exploratory and statistical analyses showed
that ageing was very consistent and first ring identification very similar, for
these groups. The APE index had decreased substantially compared to previous
workshops.
Limiting
ages, above which, agreement between readers diminished considerably, were
established for both species. This age was 14 years for L. budegassa and 10 years for L.
piscatorius. These limits could be considered as the confidence limits for
ageing both species and could serve as the plus group for stock assessment.
9. RECOMMENDATIONS
·
Produce a
training guide to ageing illicia.
This should include elements from the protocol of illicia age determination, age reading
criteria and digitised images. These images will have been annotated by
the more experienced illicia readers
to illustrate the peculiarities of illicia
ageing. This document will be a live document and will be open to updating as
and when more research is carried out and advances are made on ageing criteria
(Annex 6).
·
It is
recommended that the Working Group on the Assessment of Southern Shelf Demersal
Stocks examines the + group for Anglerfish when constructing the age/length
keys. At present it is 10+ for both species, perhaps this could be
raised.
·
When the next
exchange occurs, both illicia
sections and their respective digitised images should be circulated. The
position of the rings can be annotated on the images and these can be compared
at the workshop.
·
In future
exchanges when asked to measure the first ring of each species, it is only
necessary to measure the horizontal diameter of L. budegassa as this ring is circular in shape. Both the horizontal and vertical axes of L. piscatorius must be measured because
of the oblong shape of the first ring.
·
Validation of
age reading is necessary and this should be carried out on more than one
structure. Methods of tagging and chemical marking (Annex 7) should be used in
addition to modal length distribution analysis.
·
It is
recommended that in future illicia
exchanges, older fish (>50 cm L. budegassa and >70 cm L. piscatorius) and younger fish (<20
cm for both species) should be included in the samples.
·
Digitising and
multimedia systems are recommended to aid communal readings and discussions.
·
More readers
should become involved in age determination of Anglerfish for stock assessment
purposes.
·
A regular illicia reading exchange is considered
necessary for the purpose of checking the precision of all readers involved in
age determination.
·
In order to
improve ageing agreement, it is recommended that workshops are held regularly
amongst the countries involved in stock assessment. The collection of Illicia should include samples from all
North Eastern Atlantic European Anglerfish Stocks.
·
More studies
based on life history events of Anglerfish are strongly recommended in order to
identify the occurrences of some characteristic rings (Image 6 and 7), which
are very prominent in the illicium.
10. REFERENCES
ANON.,
1991. International Ageing Workshop on European Monkfish. (Lorient 25-28 June
1991).
ANON.,
1998. International Ageing Workshop on European Monkfish. (Lorient 9-11 July
1997).
Azevedo, m., 1996. Contribution to the study of the biology of black monkfish,
Lophius budegassa, Spinola (ICES
Divisions VIIIc and IXa). Bol. Inst.
Invest. Marit., Lisboa,1996
Beamish, R. J. and Fournier, D. A. 1981. A method for
comparing the precision of a set of age determinations. Can. J. Fish. Aquat.
Sci., 38: 982-983.
Chang, W.Y.B.
1982. A statistical method for evaluating the reproducibility of age
determination, Can. J. Fish Aquat. Sci., 39: 1208-1210.
CROZIER,
W.W. 1989. Age and growth of angler-fish (Lophius
piscatorius L.) in the North Irish Sea. Fish.
Res., 7: 267-278.
DUARTE,
R., AZEVEDO, M. and PEREDA, P. 1997. Study on the growth of southern black
monkfish and white monkfish stocks.
ICES Journal of Marine Science, 54:866-874.
DUPOUY,
H. and KERGOAT, B. 1985. Donnιes sur la croissance de la Baudroie blanche (Lophius piscatorius) des cτtes franηaises
de l'Atlantique (Division CIEM VII et VIII). CIEM CM 1985/G: 36.
DUPOUY,
H., PAJOT, R. and KERGOAT, B. 1986. Etude de la croissance des baudroides, Lophius piscatorius et L. budegassa, de l'atlantique nord-est
obtenue partir de l'illicium.. Rev. Trav. Inst. Pκches marit., 48(3 et 4):
107-131.
Eltink, A.
1994. Comparision of otolith reading. Working document for the Workshop on
sampling strategies for age and maturity, 1994 at ICES Copenhagen.
ICES,
1994. Report of the workshop on sampling strategies for age and maturity, ICES,
C.M. 1994/D:1
LANDA,
J. and P. PEREDA, 1997. Growth of white monkfish (Lophius piscatorius, L.) in the Northern Spanish continental shelf
(ICES Divisions VIIIc and IXa). ICES C.M. 1997/CC:07.
LANDA,
J., PEREDA, P., DUARTE, R. and AZEVEDO, M. 1998. Growth study of white and
black anglerfish (Lophius piscatorius, L.
budegassa) based on annual sampling from ICES Divisions VIIIc and IXa. ICES
C.M. 1998/O:21, 39 pp.
PEREDA,
P. and LANDA, J. 1998. Recuperaciσn de dos ejemplares de rape blanco Lophius piscatorius Linnaeus, 1758 en el
stock norte (divisiones VIII a y b del CIEM) tras ser marcados en el stock sur
(divisiσn VIII c) Bol. Inst. Esp.
Oceanogr. 13 (1 y 2). 1997: 15-24
PERONNET,
Y., DUPOUY, H., RIVOALEN, J.J. and KERGOAT, B., 1992. Methods of ageing based
on caudal fin-rays for megrim (Lepidorhombus
wiffiagonis) and on sections of illicium for anglerfishes (Lophius piscatorius and L.budeg). Colloq. Natl. ORSTOM/INRA.
Boudy (France) 4-6 marzo 1991.
QUINCOCES
I., LUCIO P. and SANTURTΪN M. 1998. Biology of black anglerfish (Lophius budegassa) in the Bay of Biscay
waters during 1996-1997. ICES C.M. 1998/O:47, 28 pp.
QUINCOCES
I., SANTURTΪN M. and LUCIO P. 1998. Biological aspects of white anglerfish (Lophius piscatorius) in the Bay of
Biscay (ICES Division VIIIa,b,d) in 1996-1997. ICES C.M. 1998/O:48, 29 pp.
TSIMENIDIS,
N. 1984. The growth pattern of otoliths of Lophius
piscatorius L., 1758 and Lophius budegassa Spinola, 1807 in the
Aegean sea.. Cybium 1984, 8 (3):
35-42.
TSIMENIDIS,
N.CH. and ONDRIAS, J.CH. 1980. Growth studies on the anglerfishes Lophius Piscatorius L. 1758 and Lophius budegassa Spinola. 1807 in greek
waters.Thalassographica, vol. 3, 2.
11. WORKING DOCUMENTS
PRESENTED TO THE WORKSHOP
Duarte,
R.; Azevedo, M.; Morgado, C. 1999. Preliminary analysis of the Black Anglerfish
(Lophius budegassa) (Spinola, 1807) illicia exchange 1998 -1999. Working Document of the 3rd
International Ageing Workshop on European Anglerfish, IPIMAR, Lisbon, 8-12
March 1999.
Dupouy,
H. and Deloison, E., 1999. Amelioration de la lisibilite des sections
d΄Illicium de Baudroies par la coloration au Lugol. Working Document of the 3rd
International Ageing Workshop on European Anglerfish, IPIMAR, Lisbon, 8-12
March 1999.
Lucio,
P.; Santurtϊn, M.; Quincoces, I.; Zamakona, A. Notes for the preliminary
analysis of the White Anglerfish (Lophius
piscatorius) illicia exchange
1998 -1999. Working Document of the 3rd International Workshop on
European Anglerfish Age Reading, IPIMAR, Lisbon, 8-12 March 1999.