The fishery for black scabbardfish ( Aphanopus carbo Lowe, 1839) in the Portuguese continental slope

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


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


123

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


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


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)


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


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


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


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


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


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


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)


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


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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The fishery for black scabbardfish ( Aphanopus carbo Lowe, 1839) in the Portuguese continental slope

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