RESEARCH PAPER
The fishery for black scabbardfish (Aphanopus carbo Lowe,1839) in the Portuguese continental slope
Pedro Bordalo-Machado Æ Ivone Figueiredo
Received: 30 October 2007 / Accepted: 23 April 2008 / Published online: 24 May 2008
� Springer Science+Business Media B.V. 2008
Abstract The black scabbardfish is a deep-sea
teleost species with high commercial interest in the
NE Atlantic. While it is caught by large offshore
trawlers in the North of Europe, in the south it is
captured by artisanal longlines. On the Portuguese
continental slope, in the south of ICES Division IXa,
a longline fleet has been engaged in the capture of
black scabbardfish for more than 20 years. This paper
reviews and analyses the features of this fishery from
a temporal perspective based on information from
different data sources. The fishery is based on the port
of Sesimbra, where a family type fishing community
strives to keep catches profitable without altering the
artisanal features that characterizes the fleet.
Although the fleet has experienced some technical
improvements through time, the fishing operations
and strategy have changed very little. Fishing occurs
at particular areas on the slope, where individual
vessels have their own fishing grounds. Annual
landings surpassed 4,000 tonnes in the early 1990’s,
but decreased to nearly 3,000 tonnes and have
remained at this level since 2000. The length
structure of the landings was stable from 2000 to
2005, with a modal (total length) class of 1,090 mm.
Monthly landings per unit effort estimated by a
generalized linear model did not present any marked
trend for the period 2000–2004. The landings
reported in mainland Portugal were compared with
the ones from other regions of the ICES area and the
different characteristics of the fisheries operating in
the north and south of Europe were analysed.
Keywords Artisanal � Deep-sea �Landings � Longline � Length structure �Generalized linear model
Introduction
The black scabbardfish (Aphanopus carbo Lowe,
1839), family Trichiuridae, belongs to the bentho-
pelagic category of deep-sea fishes, in which the fish
are more proximate to the demersal fishes of the
continental shelf and live close to the bottom (Gordon
2001; Merret and Haedrich 1997). It occurs on NE
Atlantic slopes, around isolated island groups and
seamounts (Martins and Ferreira 1995) from 200 to
1,800 m. And it is mainly found in the west of British
Isles (Tucker 1956), in waters around Iceland (Mag-
nusson and Magnusson 1995), in the Portuguese
continental slope and in the south of Madeira Island
(Martins et al. 1987). There are also occurrences of
the species reported from the Indian and Pacific
Oceans (Fitch and Gotshall 1972; Whitehead et al.
P. Bordalo-Machado (&) � I. Figueiredo
Departamento de Recursos Marinhos, INRB – IPIMAR,
Av. de Brasılia, 1449-006 Lisboa, Portugal
e-mail: [email protected]
I. Figueiredo
e-mail: [email protected]
123
Rev Fish Biol Fisheries (2009) 19:49–67
DOI 10.1007/s11160-008-9089-7
1986). However, these findings are doubtful and may
come from identification problems. For instance,
Stefanni and Knutsen (2007) suggest that the two
species from the genus Aphanopus are very similar
morphologically.
It feeds mainly on fish, squid and crustaceans
(Nakamura and Parin 1993, Santos 2000), matures at
about 1,000 mm total length (Figueiredo et al. 2003),
and attains a maximum age of 12 years based on
whole otolith readings (Morales-Nin et al. 2002).
Early life stages are still unknown and juveniles are
rarely caught. The smallest specimens sampled, at
100–150 mm TL, were taken from the stomachs of a
midwater fish, Alepisaurus ferox, caught off Madeira
(Maul 1948), whereas the largest (also from Madeira
waters) had a total length above 1,400 mm (Santos
2000). Madeira waters are, so far, the only confirmed
spawning area of the species, where spawners
commonly occur from September to February. In
other areas of the NE Atlantic, off the northwest of
Scotland and on the Portuguese continental slope, the
specimens analyzed were immature or in an early
maturing stage (Figueiredo et al. 2003). Fully mature
specimens were also captured off Iceland and the
Azores islands (Magnusson and Magnusson 1995;
Santos 2000). However, it is not clear if the mature
individuals reported from this last area belong to
A. carbo or A. intermedius (Stefanni and Knutsen
2007). The length frequency range of black scab-
bardfish in market samples also varies between areas.
Specimens from northern European waters are typ-
ically smaller, usually below 110 cm total length
(Bordalo-Machado et al. 2001), than specimens cap-
tured in southern waters (Carvalho and Figueiredo
2001). Different biological characteristics of the
species observed in separate areas of the NE Atlan-
tic, led several authors to suggest the existence of
horizontal migrations to spawning and nursery
grounds (Santos 2000; Figueiredo et al. 2003;
Geistdoerfer 1982; Kelly et al. 1998).
The fishery for black scabbardfish is quite old.
Though the first scientific description of the species
by Richard Lowe was made in 1839, its first historical
records date back to the seventeenth century, from
Madeira Island. For several decades, this was the only
fishery targeting black scabbardfish in the northeast
Atlantic, using simple handlines at the beginning and
longlines later on (twentieth century). The quality and
flavour of the fish were crucial factors to the increase
market demand in that region (Noronha 1924). In the
early 1980’s, an artisanal longline fishery targeting
this species was initiated in Portuguese continental
waters. The fleet was composed of small vessels
(ca. 15 vessels with length over all below 12 m),
which fished grounds located on the slopes around the
centre of mainland Portugal and landed into Sesimbra
port (south of Lisbon—lat 38�200 N) (Martins et al.
1989). In the north of Europe, west of the British
Isles, the species has been mainly captured by French
trawlers since the early 1990’s, following the devel-
opment of a multi-species fishery in which target
species vary seasonally according with market
demand. Besides black scabbardfish, the different
species caught include roundnose grenadier (Cory-
phaenoides rupestris), deep-sea sharks (mainly
Portuguese dogfish Centroscymnus coelolepis and
Leaf-scale gulper shark Centrophorus squamosus),
blue ling, ling (Molva molva), saithe (Pollachius
virens) and monkfish (Lophius piscatorius, L. budeg-
assa) (Holley and Marchal 2004). In the early years
of these fisheries, black scabbardfish was mostly
rejected since no market had developed for the
species.
At present, the fleet targeting black scabbardfish in
Portuguese waters still displays artisanal features,
while more industrialized fleets such as the large
(49–55 m) and powerful (&2,000 Hp) French deep-
water freezer trawlers continue to operate in northern
European waters (ICES 2006b).
The appearance of black scabbardfish on the fish
market is also different between northern and south-
ern European regions. Specimens caught by longlines
are generally in better condition than those caught by
trawlers, where the skin is usually missing from most
of the body so that landed specimens appear white.
Fish landed from Spanish and French trawlers may be
frozen with the head and guts removed, while in
Portuguese ports they are landed fresh as a whole,
with only the guts removed (Bordalo-Machado and
Figueiredo 2002).
Black scabbardfish has been one of the main
commercial deep-water species landed in Europe
over the last 10 years, which makes it one of the most
important among the various deep-water species that
are covered by the ICES Working Group on the
Biology and Assessment of Deep-sea Fisheries
Resources (WGDEEP). In fact, the scientific advice
produced by ICES on the exploitation status of black
50 Rev Fish Biol Fisheries (2009) 19:49–67
123
scabbardfish has been used as the key source for
establishing member states’ biannual quota regimes
for this species in the last 4 years.
Knowledge of fleet characteristics and dynamics is
important for the evaluation of the exploitation
patterns of fisheries resources. Fishermen respond
dynamically to changes in stock size, and it is
possible to monitor their response by investigating
aspects such as investment, catching power and
profitability in temporal and spatial scales (Hilborn
and Walters 1992). Although the importance of this
research is recognized, there have been few papers in
the scientific literature since the thorough investiga-
tion of a particular commercial trawl fleet by Gulland
(1956). The majority are either considered as grey
literature (Kulka 2001) or are presented as part of
research project reports (Davidse and de Wilde
2001).
This paper attempts to analyze in more detail the
features of the fishery for black scabbardfish on the
Portuguese continental slope (ICES sub-area IXa)
since the early 1980’s until the present. Our purpose is
to describe the major developments of the commercial
fleet following the work of Martins et al. (1989) and
Martins et al. (1994) on the evolution of the fishery
using both historical and recent data.
Data
Data from different sources and time periods were
pooled and analysed. Landings data (period: 1988–
2004) at different temporal scales (day, month and
year) provided by the Portuguese General Directorate
of Fisheries and Aquaculture were used to evaluate
the general trends in the fishery. Market samples
collected from black scabbardfish landings in the
period 2000–2005 were used to estimate length
frequency distributions, which were then raised to
the total annual landings. Interviews with the skippers
of fishing vessels, held in 1999 and 2004, were
examined to get information on fishing activity, gears
and areas and also on target species, by-catch and
discards. Analysis of fleet technical characteristics
used information from the Sesimbra Port Adminis-
tration archives. Vessel Monitoring System (VMS)
data (period: 2000–2004) from the Portuguese sur-
veillance and monitoring system that records the
activity of fishing vessels (MONICAP) were analysed
to assess the distribution of the fishing grounds and
fishing time.
Methods
The black scabbardfish fishery of mainland Portugal
was analysed throughout five sections: 1—Fleet
(including crew characterization), 2—Fishing gear
and operation, 3—Fishing areas, 4—Landings
(including length frequencies composition) and 5—
Fishing effort.
In the fleet section, the temporal changes in vessel
characteristics and fleet size are described. Vessels
were considered to have their activity directed to
black scabbardfish if the species was landed from a
minimum of 6 trips per month for at least 6 months
per year. Crew number is also addressed. Vessels data
matrix included information on individual vessels’
attributes, namely, age (years), gross tonnage (T),
engine’s power (HP) and Length-Over-All (LOA, in
m), pooled by year from 1995 to 2004.
Average and standard deviation estimates of
tonnage (GT—Gross Tonnage), engine’s power
(Horse Power) and LOA (m) were calculated using
black scabbardfish monthly landings data by vessel.
The annual number of vessels participating was
estimated by considering only vessels which had
landings of black scabbardfish higher than 1 t per
month in at least 6 months.
In order to find groups of vessels with similar
characteristics, a hierarchical cluster analysis was
performed using three distinct agglomeration meth-
ods: Ward, Complete linkage and Centroids. The
distances between the different pairs of vessel per
year were calculated using four distance types:
Manhattan, Euclidean, Euclidean squared and Cheby-
chev. The evaluation of the results was based on the
Cophenetic correlation coefficient and the Hubert Cstatistic (Haldiki et al. 2002) values.
The cophenetic correlation gives a measure of the
linear correlation between the distances obtained
from the dendrogram tree, and the original distances
(or dissimilarities) used to construct the tree. Thus, it
is a measure of how faithfully the dendrogram
represents the dissimilarities among observations.
The Hubert’s Gamma statistic measures the correla-
tion between two square matrices (1 and 2) of the
same size. It considers as the matrix 1, the proximity
Rev Fish Biol Fisheries (2009) 19:49–67 51
123
matrix of all the points in the data set and as matrix 2,
the proximity matrix of the centers of the cluster to
which each point belongs. A high value of this
statistic (closer to 1) implies well-separated clusters.
The fishing gear and operation section describes
the gear used to catch black scabbardfish and the
normal operations schedule involved with the deploy-
ment and recovery of the gear at sea as well as its
preparation on land.
The fishing areas section shows the geographic
location of the main areas where the fishery occurs.
Fishing areas were inferred from the interviews held
with fishermen and from the analysis of a MONICAP
dataset for the period 2000–2004 (not discussed in
this paper). MONICAP data processing was con-
ducted in an ORACLE 9i database using a software
package developed in PL/SQL language. This pack-
age enabled individual fishing trips to be identified by
vessel, total fishing time and fishing ground areas.
The detection of fishing locations by the package
involves the assignment of a status attribute to each
dataset record, which characterizes the vessel’s
activity at the time of data generation by the VMS
equipment installed onboard, taking into account the
vessel’s geographic position and speed. According to
these two conditions, it is possible to define five
vessel status: 1—Motionless in the fishing harbour
area; 2—Moving in the fishing harbour area; 3—In
transit over the open sea (not fishing, vessel speed
above 6 knots); 4—Hauling the gear (vessel speed:
0–1 knot); 5—Setting the gear (vessel speed:
5–6 knot). Using this classification, it is possible to
trace the periods and locations of fishing operations.
Details on the software package and its performance
results are described in Bordalo-Machado et al.
(2007) and Bordalo-Machado and Figueiredo (2007).
The landings section presents an analysis of the
quantities of black scabbardfish and associated by-
catch species landed in mainland Portugal. The
income from the fleet is also presented. These
estimates as well as their variances were obtained
after conducting several processing steps based on
Cochran (1977) sampling techniques. Length fre-
quency distributions were constructed based on the
estimates of the number of landed specimens by Total
Length (TL) class and, separately, by specific market
landing commercial categories (1 for large size fish, 2
for small size fish). The estimator of the total number
of landed specimens by TL class for each category
was derived by a two-stage design, where simple
random sampling was used in both stages. It was
assumed that fish categories were independent of
each other. Under these assumptions, the estimator of
the total number of landed specimens (YLcatC) in the
lth length class (l = 1, 2, …, L) and in the Cth
category (C = 1,2), corresponds to the product of
two ratio estimators:
YLcatC ¼ N�PnS
i¼1 TCiPnS
i¼1 Ti
�XmC
j¼1
yLj �WCj
sWCj
; ð1Þ
where N is the total number of landings on the
species for a particular year, nS is the annual number
of samples collected, TCi is the weight of category C
in each sampled vessel i, Ti is the total weight landed
on black scabbardfish by each sampled vessel i, mC is
the total number of vessels with samples of length
class L in category C, yLj is the frequency of L in
category C for each vessel j, WCj is the total weight
of category C landed by each vessel j and sWCj is the
total weight of category C sampled in each vessel j.
The variance of YLcatC was estimated as:
Var YLcatCð Þ ¼ N2 � y22 � var y1ð Þ þ y2
1 � var y2ð Þ� �
;
ð2Þ
where,
y1 ¼PnS
i¼1 TCiPnS
i¼1 Ti
!
and y2 ¼XmC
j¼1
yLj �WCj
sWCj
!
Expression (2) is valid if both var(y1) and var(y2) are
small in relation to y12 and y2
2 (Cochran 1977).
The final section investigates the fleet’s fishing
effort (either defined as the number of trips or the
number of hooks used) directed to black scabbardfish
in the period 2000–2004 and how the vessels’
technical attributes contributed to catching power.
For this purpose, monthly effort standardized for
vessel characteristics were estimated through a
Generalized Linear Models (GLM) approach (Hilborn
and Walters 1992). In this approach, the log-trans-
formed LPUE (Landings-Per-Unit-Effort) was
regressed against a group of explanatory variables
that include the vessels’ attributes used in the cluster
analysis of section 1. LPUE was calculated by month
for each vessel as: (i) the ratio between species landed
weight (kg) and the total number of trips and (ii) the
ratio between species landed weight (kg) and the total
52 Rev Fish Biol Fisheries (2009) 19:49–67
123
number of hooks deployed. To estimate the total
number of hooks per month, the average number of
hooks by trip (value given by the skipper) was
multiplied by the total number of trips in each month.
The backward stepwise regression method was
applied to select the best set of explanatory variables
based on the A.I.C. criteria (Akaike 1974; Hastie and
Pregibon 1992). The purpose of this analysis was to
account for the contribution of vessel technical
characteristics in the landings per effort ratio, i.e.
how much can they explain from the LPUE variabil-
ity. Standardization of fishing effort did not
incorporate spatial or time effects, which will be
examined in a forthcoming study on the species’
abundance. The general expression of the GLMs
adjusted to LPUE data is presented below:
log(LPUEik) ¼ b0log(AGEik)þ b1log(POWik)
þ b2log(TONik)þ b3log(LOAik)
þ eik; eik� N(0, r2), ð3Þ
where LPUEik is the monthly rate of landed fish by
the i-th vessel relative to the k-th month-year pair
(e.g., 01-2001), AGEik, POWik, TONik and LOAik,
are the vessel’ age (in years), engine’s POWer,
TONnage and Length-Over-All of each vessel i in the
k-th month–year pair, and b0, …, b3 are parameters to
be estimated. The quality of model adjustment was
evaluated by quantile residuals analysis. These
residuals are well suited for situations such as log-
normal models by presenting exactly normal behav-
iour, apart from sampling variability, on the
parameter estimates (Dunn and Smyth 1996).
Statistical analyses were conducted in R-2.4.1 for
windows software. Cluster analysis used the func-
tions dist(), hclust(), cophenetic() from the Stats
package and cluster.stats() from the fpc package.
Generalized linear models were fit by the step() and
glm() functions of the Stats package.
Results
The fishery for black scabbardfish on the Portuguese
continental slope started in 1983 at grounds around
Sesimbra port (south of Lisbon—Latitude 38�200 N),
following a series of exploratory surveys conducted
by the Portuguese Fisheries Research Institute
(former IPIMAR) in close collaboration with the
fisheries sector. These surveys involved searching for
fishing grounds for the species, the environmental
characterization of the ocean layer where black
scabbardfish occurs, experimental longline fishing
and preliminary studies on the biology of the species.
For this venture, fishermen from Madeira with
extensive experience in deep-sea longline fishing
have greatly contributed. The number of vessels
involved in this fishery rapidly increased, and 15
longline vessels fished in 1984.
Fleet
Data on the black scabbardfish fleet technical char-
acteristics, including tonnage (GRT—Gross
Registered Tonnage), engine’s power and Length
Over All (LOA) was initially presented by Martins
et al. (1989, 1994), covering the period 1984–1992
(Table 1). It is not possible to compare vessel
tonnage between 1984–1992 and 1995–2004, since
GT was established on the basis of the total volume
of the vessel, whereas the GRT measurement
excludes certain spaces of the vessel which are
deemed to be non-productive (Anon. 1998).
At the beginning of the fishery, the fleet comprised
small artisanal vessels, having an average LOA
around 11 m and an average tonnage of ca. 16
GRT. In 1988, there was a slight increase in both size
and engine power. There was a further rise of about
30% in the average LOA and engine power registered
between 1992 and 1995. In 2000, the fleet again
experienced technological improvements, indicated
by the increase in average values for engine power,
tonnage and LOA. This was due to 4/15 vessels, as
shown by the increase in standard deviation values
(Table 1).
The number of vessels in the fleet reached a
maximum in 1986, and decreased from 1995 to 2004,
when the number of vessels was the same as in 1984
(Table 1). In the period 1995–2004, the number of
new vessels that entered the fleet attained its max-
imum in 1997, before an equal number of vessels left
the fleet in 1998, and the number of vessels that
remained in the fleet in consecutive years decreased
from 17 to 14 (Fig. 1). The vessels that entered the
fleet in 2002 and 2003 were larger, with tonnage,
engine power and LOA average values of 114 GT,
413 HP and 23 m, respectively. More than 95% of the
vessels are registered in Sesimbra, the remainder
Rev Fish Biol Fisheries (2009) 19:49–67 53
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being from Peniche (north of Lisboa) and Sines
(south of Sesimbra).
Using a total of 113 pairs of vessel per year, four
main groups of vessels (Fig. 2) were consistently
Table 1 Number of vessels and technical characteristics of the black scabbardfish fleet in the period 1984–2004
Year Number
of vessels
Tonnage Engine’s power (HP) Length-over-all (m)
Avg. Std. Avg. Std. Avg. Std.
Martins et al. (1994) 1984 15 16.6 – 128.3 – 11.2 –
1985 23 16.1 – 113.4 – 11.2 –
1986 28 16.1 – 116.9 – 11.3 –
1987 23 18.0 – 133.4 – 11.8 –
1988 27 (23)a 20.1 – 144.9 – 12.4 –
1989 27 (25)a 19.9 – 144.5 – 12.2 –
1990 27 (26)a 19.9 – 144.5 – 12.2 –
1991 28 (18)a 20.0 – 142.5 – 12.2 –
1992 27 (22)a 20.0 – 142.5 – 12.2 –
Present study 1995b 20 29.0 8.92 183.5 45.28 16.3 1.76
1996b 18 29.3 8.55 194.5 61.69 16.5 2.22
1997b 20 27.5 7.99 194.9 61.21 16.5 2.06
1998 17 26.5 8.65 186.6 51.02 16.0 1.84
1999 15 27.7 8.13 194.0 51.36 16.4 1.55
2000 17 27.8 10.27 195.7 50.44 16.1 1.66
2001 16 34.5 19.74 206.9 61.34 16.6 1.54
2002 15 45.1 29.62 236.5 83.86 17.2 2.44
2003 15 46.0 31.71 239.5 90.43 17.4 2.94
2004 15 43.3 26.50 238.6 82.65 17.3 2.68
No data was available for 1993 and 1994. For the period 1984–1992, tonnage is expressed in GRT (Gross Registered Tonnage),
whereas for the period 1995–2004 it is expressed in GT (Gross Tonnage). For further explanation on data sources see texta Re-calculated number of vessels based on monthly landings separated by vesselb 1995, 1996 And 1997 values were calculated based on 70%, 78% and 90% of the vessels, respectively
0
2
4
6
8
10
12
14
16
18
1996 1997 1998 1999 2000 2001 2002 2003 2004
Year
Nu
mb
er o
f ve
ssel
s
Continue Enter Leave
Fig. 1 Number of vessels which have entered, left or
continued (from previous year) to fish in the black scabbarfish
longline fleet in the period 1995–2004
Fig. 2 Hierarchical cluster analysis dendrogram showing four
groups of vessel per year pairs, from the period 1995–2004,
obtained using Centroids agglomeration method and the
Manhattan distance
54 Rev Fish Biol Fisheries (2009) 19:49–67
123
formed by the combinations distance/agglomeration
methods tested. The combination of the Manhattan
distance with the Centroids agglomeration method
gave the highest values for both the Cophenetic
correlation coefficient (0.903) and the Hubert Cstatistic (0.73). The first value points to a close
similarity between the distance matrix generated from
the dendrogram and the initial distance matrix gener-
ated from the dataset. The high value obtained for the
Hubert C statistic gives a good indication that the
groups formed are different from each other (Haldiki
et al. 2002). Groups G1 and G2 (Table 2) contain the
five larger vessels of the fleet that had engine power
values higher than 300 HP, whereas group G3 corre-
spond to the two smallest vessels with LOA values
below 13 m. Group G4 includes the majority of vessels
in the fleet and presents the largest variability on
technical characteristics values. These results shows
that the technical characteristics used in the analysis
were sufficient to form dissimilar groups of vessels in the
fleet that eventually exhibit different catching powers.
Fishermen interviews carried out in 1999 to the
black scabbardfish fishing community (all male)
indicated that 16% of the fishermen attended fishing
school and 9% completed the basic nine years of
formal education. In terms of age, 4% of the
fishermen were under 20 years old and 18% more
than 50. At least 80% of the skippers had more than
10 years experience in longline fishing and remained
operating with the same vessel.
There are usually two types of crew: land crew who
are responsible for preparing the gear and arrange
vessel provisions, and the sea crew who perform all the
operations onboard. The median number of fishermen
that compose each vessel’s crew is 6 (range 1–10) and
8 (range 7–12) for land and sea crews respectively.
Land crews are often smaller than sea crew because, in
some vessels, most of the latter carry out both land and
sea functions, which reduced the need to hire person-
nel to work on land-based operations.
Fishing gear and operation
The fishing method and gear used by the black
scabbardfish longline fleet developed soon after the
initial fishing trials off the Sesimbra coast by
fishermen from Madeira. Gear design has since been
modified from the traditional Madeira longline fish-
ing gears in order to catch the species in continental
waters—setting a horizontal bottom longline, where
alternating floats and weights occur at constant
intervals on the main line (Fig. 3). This aims to
match the intricate vertical distribution exhibited by
the species in the slopes and to prevent gear loss on
the hard grounds (Henriques 1997). The total number
of hooks used by fishing gear has increased over time.
At the beginning, longlines had 3,600–4,000 hooks
(Martins et al. 1989). Numbers of hooks ranged from
4,800 to 5,400 in 1996 (Henriques 1997) and were
between 4,000 and 10,000 in 2004 (present study).
The No. 5 Hook (Fig. 3) has been commonly used in
fishing gears since the beginning of the fishery,
however, some vessels have also tried No. 6 Hooks.
The most common bait of the gear is sardine (Sardina
pilchardus), though chub mackerel (Scomber japoni-
cus) can also be used when sardine is less available or
too expensive. The process of gear preparation,
including disentangling, baiting and coiling of the
Table 2 Descriptive
statistics of vessel technical
characteristics by group,
G1, …, G4
Indicated in brackets is the
number of vessels of each
group
Min Median Max SD Min Median Max SD
Vessel technical characteristics
G1 (n = 3) G2 (n = 2)
AGE 0.0 1.0 3.0 1.17 0.0 1.5 11.0 5.07
HP 340.0 357.0 369.0 14.57 424.0 434.5 445.0 –
GT 77.0 99.6 113.6 18.48 93.0 114.0 135.0 –
LOA 18.5 19.2 21.5 1.59 24.5 24.5 24.5 –
G3 (n = 2) G4 (n = 12)
AGE 0.0 3.5 9.0 3.09 0.0 4.0 26.0 6.21
HP 106.0 121.0 136.0 – 159.0 200.5 270.0 32.66
GT 13.9 14.0 14.1 – 21.6 31.6 74.4 12.13
LOA 12.3 12.4 12.6 – 15.2 16.3 18.8 1.20
Rev Fish Biol Fisheries (2009) 19:49–67 55
123
main line into the tubs, is carried out ashore either by
land crew or vessel crew (Henriques 1997). All the
work is done by hand and is very labour intensive.
The preparation of one single gear can take more than
half a day and involves at least four men. Fishing
operations usually start at dusk, when vessels leave
the port and steam offshore for 1–6 h. At the fishing
ground, two operations generally occur: 1) the newly
baited longline gear is deployed into the sea and set,
2) another longline gear previously set in the last
24–48 h (average around 38 h) is recovered with the
aid of a hauling winch. Fishing takes place on
hard bottoms along the slopes of canyons at
depths normally ranging from 800 to 1,200 m though
1,450 m has been reached in the last few years. If the
gear is set before week-ends or national holidays, the
fishing duration can exceed 70 h. Landings
occur immediately after vessels arrive, and could
last from early in the morning to the end of the
afternoon.
Fishing areas
At present, the fishery for black scabbardfish occurs in
three geographic areas of the Portuguese continental
slope (A, B and C in Fig. 4). During the early years of
the fishery (in the 1980s) only fishing grounds from
area A were targeted. In the mid 1990’s, new vessels
entering the fleet started targeting the grounds in area
C. In 2000, improvements in technical characteristics
(LOA, GT and engine power) allowed some vessels to
target grounds in area B located farther away
([65 nm) from Sesimbra port. Soon after these
vessels started to fish in area B, they moved to
Peniche port in order to reduce their steaming time.
The landings, however, continued to be marketed in
Sesimbra port. The fishing grounds within each of the
three areas do not change much through the year.
Fishermen usually adopt individual fishing grounds
where they can operate solely, thus, eliminating the
need to compete for the same resource and locations.
Fig. 3 Schematic diagram of the longline fishing gear used by the black scabbardfish fleet operating in the Portuguese continental
slope, adapted from Henriques (1997)
56 Rev Fish Biol Fisheries (2009) 19:49–67
123
Areas A and C present a more rugged sea-floor
than area B. From the anecdotal information collected
from skipper interviews, longline gears are usually
deployed along irregular bathymetric contours of
ground slopes. Regarding the type of sediment, 60%
of the inquired skippers report that they fish on mud
bottoms, while 20% operate on rocky bottoms.
According to 29% of the interviews, water
Fig. 4 Main fishing areas
(A, B and C) of the black
scabbardfish fleet on the
Portuguese continental
slope
Rev Fish Biol Fisheries (2009) 19:49–67 57
123
temperature at the bottom can also influence the
abundance of black scabbardfish.
Landings
More than 95% of the landings of black scabbardfish
(information from the period 1991–2001) occur in
Sesimbra port (Bordalo-Machado and Figueiredo
2002). In the period 2003–2005, almost 98% of the
landings on the species were registered in this port.
The first landing records of the black scabbardfish
longline fleet in mainland Portugal was a total of 69 t
at the end of 1983 in Sesimbra (Martins et al. 1989).
In the period 1984–1989, landings rapidly increased
from 676 to 3,828 t (Fig. 5). Between 1990 and 1993,
landings showed the largest increase, up to 4,520 t,
but decreased rapidly to nearly 3,400 t in 1994.
Whilst 95% of the fleet landed the species throughout
1993, one vessel stopped fishing in 1994 and others
(20%) only registered landings in 3–9 months.
In order to analyse how recent landings have
varied regionally, records from the period 2000–2004
were split by area (A, B, C). As expected, the
landings from area B increased between 2000 and
2002 (Fig. 5), reflecting the entry of larger vessels
and the exploitation of new fishing grounds. The
landings from area A continued the decreasing trend
observed for the period 1995–1999, although they
showed an increase in 2003 and 2004 as landings
from area B decreased.
The black scabbardfish fishery takes other deep-
water species as a by-catch, of which Portuguese
dogfish and Leaf-scale gulper shark accounted for the
major part during the period 1995–2004 (Fig. 6). In
this period, annual landings of Portuguese dogfish
ranged from 548 to 928 with a median value of 637 t,
while Leafscale gulper shark ranged from 386 to
612 t with a median value of 493 t (ICES 2006a).
Other by-catch species include Gulper shark
(Centrophorus granulosus), Bulls-eye (Epigonus
telescopus), Arrowhead dogfish (Deania profundo-
rum), Kitefin shark (Dalatias licha), Longnose velvet
dogfish (Centroscymnus crepidater), and Roughskin
dogfish (Centroscymnus owstoni).
The annual income from black scabbardfish land-
ings has increased from 1991 and peaked in 2000
(Fig. 7). The price per kilo also increased until 2000,
and has stabilised at around 2.5 €. Important revenue
was also obtained from the landings of both
Portuguese dogfish and Leaf-scale gulper shark,
which realised annual values of between 1.5 and
2.0 M€ during the last 6 years (Fig. 8). Different
revenues were obtained by fishing area in the period
2000–2004, with vessels operating in area B gaining
larger profits from black scabbardfish landings
0
1000
2000
3000
4000
5000
Year
To
ns
All landings
North fleet
South fleet
Central fleet
1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004 2006
Fig. 5 Annual landings
of black scabbardfish into
mainland Portugal since
the beginning of the fishery.
From 2000 to 2004,
landings are presented
separately by fishing area
0
20
40
60
80
100
1995 1996 1997 1998 1999 2000 2001 2002 2003 2004
Year
Per
cen
tag
e
Portuguese dogfish Leaf-scale gulper shark Other species
Fig. 6 Species composition in the annual by-catch landings of
the black scabbardfish fleet for the period 1995–2004
58 Rev Fish Biol Fisheries (2009) 19:49–67
123
(Fig. 9). The revenues from the southern fleet showed
some seasonality with quarter, with the highest
average values in the first quarter of the year.
Total length samples collected in Sesimbra’s
landing port ranged from 710 to 1,350 mm
(Fig. 10). Modal length decreased from 1,120 mm in
2000 to 1,040 mm in 2004. In 2005, the modal length
increased to 1,080–1100 mm. Apart from 2004,
length frequencies of juvenile black scabbardfish
(\1,000 mm) were always lower than adult frequen-
cies. Frequencies of length classes below 960 mm
usually presented lower variances (\1.0 9 1021) than
the observed on higher length intervals. This was not
so evident in 2000 and in 2005.
Fishing effort
Model 1 explained 45% of the total variance, while
model 2 explained 25%. All the coefficients of model
1 were significant, and the variable vessel’s age
contributed least to explain the response variable
variance (Table 3). Engine power caused very little
change in the deviance when the number of hooks
was used as nominal effort. Thus, it was not selected
by the stepwise procedure as an explanatory variable
of model 2. Considering the deviance and the
coefficient values obtained, the most important
explanatory variable for model 1 was LOA, whereas
for model 2 it was Tonnage. This latter was the only
explanatory variable to present a positive relationship
with LPUE in both models, possibly because Ton-
nage was the technical characteristic of the fleet that
presented the largest variation in the period 2000–
2004 (Tables 1). Vessel age, the second explanatory
variable in importance of model 2, also showed some
variation due to the entrance of new vessels to the
fleet after 2002.
Normal Q–Q plots showed some deviation from the
normal distribution of the residuals at the lower and
upper ends of both models, reflecting larger uncer-
tainty of very small and large LPUE estimates
(Fig. 11). These values correspond to vessels from
cluster analysis group 3 and 1, representing very small
and very large vessels, respectively. The quantile
residuals histograms for the two models showed a
distribution reasonably close to the gaussian curve.
Using the two log-normal GLM models, standard-
ized monthly effort estimates of the fleet were
calculated for the period 2000–2004 (Fig. 12). The
two effort curves, one for each model, presented
comparable shapes with no marked trend through the
analysis period. However, there seems to be some
0,0
0,5
1,0
1,5
2,0
2,5
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
Mill
ion
s o
f E
uro
s
0,0
0,5
1,0
1,5
2,0
2,5
3,0
Eu
ros
Annual Income Price/kg
Fig. 8 Annual income and price per kilo of Portuguese
dogfish and Leaf-scale gulper shark combined landings in the
period 1991–2005
0
1000
2000
3000
4000
5000
6000
1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4
Quarter-Year
Avg
erag
e in
com
e (E
uro
s)
North Fleet
Central fleet
South fleet
2000 2001 2002 2003 2004
Fig. 9 Average daily income of the black scabbardfish fleet by
quarter and fishing area in the period 2000–2004
0
1
2
3
4
5
6
7
819
91
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
Mill
ion
s o
f E
uro
s
0,0
0,5
1,0
1,5
2,0
2,5
3,0
Eu
ros
Annual Income Price/kg
Fig. 7 Annual income and price per kilo of black scabbardfish
landings in the period 1991–2005
Rev Fish Biol Fisheries (2009) 19:49–67 59
123
Fig. 10 Black scabbardfish
annual length frequencies
composition estimates and
respective variance from
Sesimbra port market
samples collected during
the period 2000–2005.
n represents the annual
number of specimens
measured
Table 3 Results from two
LPUE standardization
models fit by the GLM
approach
a Age values were
transformed as (AGE + 1)
to correct for invalid
numbers = 0, when a
vessel has less than
1 year-old
Response variable LPUE (Landed fish weight per no. trips)
Expl. variables d.f. Deviance A.I.C. Coefficients
Estimate eEstim. SE Pr([|t|)
Log-normal model 1
Log (TON) 1 156.82 978.49 0.703 2.020 0.0638 \2e-16
Log (LEN) 1 150.42 944.82 2.459 11.691 0.2685 \2e-16
Llog (POW) 1 147.83 930.78 -1.177 0.308 0.1421 5.0E-16
Log (AGE + 1)a 1 138.85 880.03 -0.089 0.915 0.0227 8.8E-05
\none[/(Intercept) 136.21 866.54 3.870 47.929 0.4686 6.1E-16
Null deviance 248.30
Log-normal model 2
Log (TON) 1 147.00 923.9 0.497 1.644 0.0531 4.08E-02
Log (AGE + 1)a 1 133.71 847.5 -0.054 0.947 0.0204 8.15E-03
Log (LEN) 1 133.25 844.7 -0.414 0.661 0.2020 4.08E-02
\none[/(Intercept) 132.55 842.5 -2.474 0.084 0.4334 1.60E-08
Null deviance 177.68
60 Rev Fish Biol Fisheries (2009) 19:49–67
123
Quantile residuals
Fre
quen
cy
-4 -3 -2 -1 0 1 2 3
050
100
150
-3 -2 -1 0 1 2 3
-4-3
-2-1
01
23
Normal Q-Q Plot
Theoretical Quantiles
Sam
ple
Qua
ntile
s
Quantile residuals
Fre
quen
cy
-4 -3 -2 -1 0 1 2 3
050
100
150
-3 -2 -1 0 1 2 3
-3-2
-10
12
Normal Q-Q Plot
Theoretical Quantiles
Sam
ple
Qua
ntile
s
Model 1
Model 2
Fig. 11 Quantile residuals
plots for the final models to
standardize black
scabbardfish LPUE
0
50
100
150
200
250
1 4 7 10 1 4 7 10 1 4 7 10 1 4 7 10 1 4 7 10
Month / Year
Mo
nth
ly la
nd
ing
s
0
100
200
300
400
500
600
700
Std
. mo
nth
ly e
ffo
rt
Tons
hooks x 10E4
trips
2000 2001 2002 2003 2004
Fig. 12 Landings and
standardized nominal effort
by month of the black
scabbardfish fleet in the
period 2000–2004
Rev Fish Biol Fisheries (2009) 19:49–67 61
123
seasonality, with the highest effort values occurring
in the last and first quarters of the year. The variation
of standardized effort from 2000 to 2004 follows a
very similar pattern to that of fleet landings of black
scabbardfish.
Discussion
The fishing operations of the longline fishing fleet
taking black scabbardfish in the Portuguese conti-
nental slope have changed very little since the fishery
began in 1984. At present, the preparation of the gear
is still entirely done by hand, and only the hauling of
the gear is mechanically assisted. Nevertheless, with
the entry of new vessels in the past 6 years, the
fleet’s gear size has increased substantially, and today
the number of hooks by gear is always C5,000.
Tonnage and LOA increased to 45 and 17 m on
average. Although this indicates an investment by the
fishermen to increase revenue from the fishery,
equipment such as autoline devices have not been
installed so far.
Cluster analysis has been commonly employed in
the scientific literature to help in the detection of
different fishing metiers (Garcia-Rodrıguez et al.
2006; Holley and Marchal 2004; Lewy and Vinther
1994). However, the longline fishery for black
scabbardfish shows little variability in vessels’ tech-
nical characteristics, gears, diversity of landed
species and fishing strategies. Consequently, the
multivariate analysis conducted was not further
refined to account for additional factors affecting
fishing activity nor were other robust methods, such
as Principal Components Analysis or Multi-Dimen-
sional Scaling, attempted. Three of the four groups
formed by cluster analysis show a clear affinity with
the main fishing areas of the fleet. Vessels belonging
to group 3 only fished in area A at short distances to
Sesimbra port, and include two small vessels that are
amongst the oldest of the fleet and are not able to
conduct long fishing trips away from Sesimbra.
Vessels from groups 1 and 2 only operated in fishing
area B where distances between fishing grounds and
landing port are larger. These bigger vessels entered
the fleet after 2000 and have higher steam power
and can target the more distant grounds of area B and
deploy large-size fishing gears. Group 4 is composed
of vessels with fishing grounds in all the three main
areas. However, only one third of these vessels have
fished in more than one area.
The delineation of the three main fishing areas
presented in this study was mainly based on the
interviews conducted to skippers and to a less extent
on the available VMS data. Therefore, these areas are
based solely on the knowledge of fishing activity and not
on information about resource distribution or dynamics.
This particularly relied on the fact that: (a) fleet vessels
have their fishing grounds confined to particular regions
of the slope that do not mingle and (b) the observation of
plotted VMS data of the fishery enabled the delimitation
of three distinct geographic groups of fishing grounds.
Black scabbardfish seems to occur more frequently in
areas of the Portuguese slope with irregular bathymetric
outlines, characterized by the existence of scarps and
steep landscapes. This was mentioned by skippers in
interviews and later confirmed by the superimposition of
VMS data on to a bathymetric chart. Evidence to support
this idea comes from an earlier exploratory fishing
survey on black scabbardfish conducted in the Portu-
guese continental slope, in which Leite et al. (1985)
found that only flat bottom slope areas located in the
south of Portugal did not yielded black scabbardfish.
There is a lack of recent information about environ-
mental variables, such as temperature, dissolved oxygen
or salinity, on fishing areas where the species is
generally caught, owing to the absence of systematic
oceanographic data collection programmes conducted
at great depths. Nevertheless, during research project
BASBLACK, an observer programme on board one
vessel operating in area C, from February 1999 to
January 2000, used a mini-log recorder attached to the
longline gear to collect data on fishing depth and
temperature (Santos 2000). The results showed that
temperatures at fishing locations were fairly constant
throughout the year, at around 11�C.
The laborious process of preparing and baiting
longline gears of several thousands of hooks dis-
suades black scabbardfish fishing crews from
conducting more than one haul per fishing trip. As
a consequence, vessels perform no more than three
hauls a week and soak times are high as gears usually
remain immersed for more than 24 h. There is no
study on the effect of soak-times in black scabbbard-
fish catch performance, though it is known that catch
rates of some tuna species can decrease at soak times
as long as 20 h (Ward et al. 2004). Another aspect to
consider is that baited longlines commonly catch fish
62 Rev Fish Biol Fisheries (2009) 19:49–67
123
that are searching for food from distances of several
hundred meters. This distance corresponds to the
length of the odour plume produced by the bait in
water (Bjordal and Løkkeborg 1996), which will
diminish as soak time increases. Regarding the
efficiency of the bait used in longlines, earlier studies
conducted by the Portuguese Fisheries Research
Institute, during exploratory fishing experiments
around Madeira island, indicated that orangeback
squid (Sthenoteuthis pteropus) produced higher catch
yields of black scabbardfish, though there were no
trials with other baits (INIP 1984).
Discards from the black scabbardfish longline fleet
were not investigated in the course of this study.
Although there is very little information, preliminary
studies conducted recently by IPIMAR showed a very
low percentage of discards—6% in number and 2% in
weight of the total catch—which did not include
black scabbardfish (Fernandes and Ferreira 2006).
The majority of vessels have been associated with
the fishery for more than 10 years without changing
skipper. If, at the beginning, fishing trips were mostly
of an experimental nature, today fishermen know
quite well where and how the species can be fished.
This has reduced the time spent in gear handling and
on the search of fishing grounds, even when part of
the fleet intended to move to the grounds of area B in
late 2000. IPIMAR has collaborated with the sector
by providing access to maps with the locations of
fishing grounds for black scabbardfish to the north of
Peniche. These maps were built soon after the
exploratory research surveys held by IPIMAR during
the mid 1980’s (Martins et al. 1987). The extensive
experience gained by fishermen enabled them to
allocate fishing locations individually among the
main areas where the species occurs, causing at the
same time difficulties to newcomers to the fleet. This
has contributed to the decrease of fleet size through
time: the fleet in 2004 was half the number at the
beginning of the 1990s. Following the EC regulation
no. 2347/2002, the Portuguese government intro-
duced new legislation during August 2004 (Anon.
2004) that makes the enrolment of new vessels to the
deep-water fishery even more difficult, by limiting
fleet capacity (20,390 GT and 23,303 HP), and
prohibiting the use of trawl gears.
Black scabbardfish landings have continuously
been reported (almost exclusively) in Sesimbra
landing port since the beginning of the fishery in
mainland Portugal. Species wholesalers also concen-
trate mostly on Sesimbra, raising the prospects of
gaining more profit from fishing. The connection of
the fishery to this port strengthened in the mid 1990’s,
when a fish producers organization was established to
acheive better prices in the Sesimbra auction market
and promote fish products in the global sale markets.
The fishery has remained profitable, supported by the
increased price per kilo attained by the species at the
auction market and its stability at around 2.5 € after
2000. As an additional revenue, fishermen could also
receive income from the by-catch of deep-water
sharks, at least until recently, when the council
regulation (EC) no. 2015/2006 has fixed restrictive
TAC’s for deep-water sharks of 381 and 254 t for
2007 and 2008, respectively, for Portugal.
Three major periods can be identified in the landings
trend from 1983 to 2005 (Fig. 5): The initial period
comprises the first 10 years where the expansion of the
fishery occurred. The second includes the years between
1994 and 1999, when the largest decline was observed,
down to 2,740 t, and a large number of vessels were
operating in areas A and C—20 in 1997, increasing
fishing intensity and causing individual fishermen’s
yields to decrease. As a consequence, six vessels left the
fleet between 1998 and 1999. Average fishermen’s
yields only rose in the third period when some vessels
experienced technological improvements and started
targeting the more northern grounds of area B.
Other European countries, mostly located between
parallels 44� and 60�, have reported landings on the
species over the last two decades. The majority of
these landings came from bottom trawl multi-species
fisheries operating in ICES sub-areas/divisions Vb,
VI, VII and XII (Fig. 13). The absence of longline
0
1000
2000
3000
4000
5000
6000
7000
1983
1985
1987
1989
1991
1993
1995
1997
1999
2001
2003
2005
Year
To
nn
es
VbVI+VIIXIIIX
Fig. 13 Black scabbardfish landings by ICES sub-area/divi-
sion in the period 1983–2005 (source: ICES, 2006)
Rev Fish Biol Fisheries (2009) 19:49–67 63
123
fisheries targeting black scabbardfish in those areas is
apparently because bottom trawl gears have been
more efficient to catch the species (Kelly et al. 1998;
Munoz and Roman 2001). French fisheries accounted
for almost 90% of the combined landings in sub-areas
VI and VII and 35% of the landings in Division Vb
for the period 1988–2005 (ICES 2006). Faroe islands
followed in importance for the same period with 62%
of the landings reported in Division Vb and 49% of
the landings from sub-area XII (ICES 2006a). For the
period 1999–2003, French bottom trawlers, fewer in
number than the Portuguese longliners operating in
the south, have reported a larger amount (nearly 50%
more) of black scabbardfish landings.
The length structure of the black scabbardfish
captured on the Portuguese continental slope was
relatively stable during the period 2000–2005, with
length frequency distributions that differ from those
observed in northern European waters, where they are
usually smaller. This variation was mentioned by
Figueiredo et al. (2003), who showed different length
ranges off NW Scotland (612–1,175 mm TL),
Sesimbra (667–1,365 mm TL) and Funchal, Madeira
Island (712–1,510 mm TL). More recently, bottom
trawl landings of the species in northern European
countries have been shown to have similar length
frequency distributions, ranging from 800–1,100 mm
TL, and are dominated by juveniles (ICES 2005).
These differences between northern and southern
regions could be partially explained by the different
size selectivity patterns of the fishing gears used;
trawl and longline (ICES 2006b).
The GLM analysis performed on this study
focused only on factors related with the technical
characteristics of fleet vessels, allowing the calcula-
tion of standardized effort estimates without vessel-
vessel differences variability. Several studies have
acknowledged the need to investigate the influence of
technical improvements in vessels’ fishing power
(e.g., Gulland 1956; Houghton 1977; Sanchez et al.
2004; Taylor and Prochaska 1986; Vignaux 1996).
This has implications for standardization of effort, as
sometimes the inputs of nominal effort remain
constant but an increase in the effective effort can
still be observed (Bordalo-Machado 2006). From the
results of the two models, tonnage was the most
important technical factor to explain the variability of
LPUE values of the fleet. This factor is decisive to the
fishery, as a larger vessel volume will permit not only
larger gears to be accommodated but also bigger fish
catches to be landed. Fishing-related instrumentation
like sonar or GPS was not included in effort
standardization analysis because all the vessels con-
sidered already used these type of equipment at the
beginning of the period 2000–2004. Since most of
the skippers remained with their vessels, the age of the
vessel was used in the models as a proxy of skipper
skill level and experience.
There was a large LPUE variability that was not
accounted for by the adjusted models, especially
model 2 which explained less than 30%. This is not
surprising, since factors linked to time and space
were not taken into consideration. These factors are
usually attributed to variations in the target resource
populations, when CPUE or LPUE is used as an
index of abundance (Hilborn and Walters 1992;
Vignaux 1996). Due to the particular behaviour of the
fleets, i.e. vessels do not change fishing grounds
locations much through time, a possible approach to
investigate fishery dynamics and also changes in the
abundance of the species would be a time-series
analysis (Park 1998; Zuur and Pierce 2004). As an
option, the residuals resulting from the GLM effort
standardization could be used instead of the LPUE
estimates, since in this case vessel characteristics
variability would have been removed.
Although the number of hooks could be considered
as the most visible expression of changes in the fishing
effort expended, there is some uncertainty associated
with hooks per fishing trip values from the present
study. Fleet skippers did not, until recently, fill in
logbooks with the number of hooks used, which has
resulted in a lack of data on this effort unit. The
monthly number of hooks used as nominal effort in the
calculation of LPUE values is, therefore, an approx-
imation of the real effort spent by a vessel. In this sense,
LPUE calculated as the ratio of landings per no. of trips
is an option to consider for effort standardization and
abundance studies, not only due to the data precision
but also to their better availability. Furthermore, the
model that used the number of trips as effort measure
yielded the most satisfactory results.
Conclusion
Fortunately for the fishing community of Sesimbra,
the fishery for black scabbardfish has been sustained
64 Rev Fish Biol Fisheries (2009) 19:49–67
123
for nearly 20 years, acting as an important source of
income for more than 300 families in the region
(Bordalo-Machado and Figueiredo 2002). This pop-
ulation has strived to maintain its identity as a
fishery-dependent community as defined by Brooke-
field et al. (2005), despite the expansion of seaside
tourist activities. This is of paramount importance, as
these areas will be the ones to gain more benefits
from European Union structural funds. A relevant
aspect that would help the continuity of the fishery by
maintaining high prices at the fish market is the
certification of the fish products as the one followed
by the project CEPROPESCA (Certification and
Promotion of Azorean Fisheries and Fisheries Prod-
ucts). Contrary to ports in the north of Europe, where
fish specimens are usually landed with the skin
missing from most of the body so that they appear
white, black scabbardfish are landed as whole fresh
fish in Sesimbra (Bordalo-Machado and Figueiredo
2002), thus increasing quality.
Besides the socio-economic aspect, it is also
crucial to the preservation of the fishery to have as
much information as possible about the fish stock
status. Monthly fishing effort variation did not show
any marked trend in the period analysed, and annual
landings and fleet size have remained quite stable.
However, it is not possible with the available
information to quantify the impact of the fishery
on the species’ stock. So far, the hypothesis of a
single stock in the NE Atlantic (Figueiredo et al.
2003; ICES 2006b) prevails as an assumption
for management measures in the ICES area. Not-
withstanding, the species experiences distinct
exploitation regimes within the NE Atlantic, and
there are differences in its length structure between
north and south regions. To assure a continuous
sustainable exploitation of the resource, further
investigation on the species stock structure and life
cycle is required to obtain scientific advice that will
help to formulate adequate fishing control measures
for this important fish resource.
Acknowledgements This work was supported by the
Portuguese Foundation for Science and Technology (FCT)
through the scholarship SFRH/BD/16037/2004. We thank Mike
Pawson (CEFAS) for the thorough review of an early version of
the manuscript. Thanks also go to Joaquim Parente, Rogelia
Martins and Victor Henriques from IPIMAR for the stimulating
conversations held during the preparation of this work.
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