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Spatiotemporal patterns of catch and discards of the Israeli Mediterranean trawl fishery in the early 1990s: Ecological and conservation perspectives

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Spatiotemporal patterns of catch and discards of the Israeli Mediterranean trawl fishery in the early 1990s: Ecological and conservation perspectives

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The spatiotemporal patterns of discards and catch composition of Israeli trawlers were examined using a 4-year (1990-1994), 324 haul dataset. Haul depth was found to be the main grouping variable for hauls, although significant seasonal differences were also found. 28.3% of the total catch was discarded, and there was a 40.1% discard percentage in shallow hauls. According to these figures, annual discards for the Israeli trawl fleet for the study period are estimated at ca. 440 to 700 t. Both the biomass and the number of discarded specimens peaked in summer, as well as the percentage of juvenile fish of commercial species. These findings suggest that a summer moratorium on trawling would reduce discards. The percentage of specimens of Indo-Pacific origin decreased from 51% in depths shallower than 37 m to 24% between 38 and 73 m, and 8% in deeper strata. Discards along the Israeli coast were comparable to those observed elsewhere in the Mediterranean. The findings presented here are the first quantitative account of fish community assemblages in the nearshore waters of the easternmost part of the Mediterranean, and thus provide valuable information for comparisons with more current datasets that are currently being assembled.
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Spatiotemporal patterns of catch and discards of the
Israeli Mediterranean trawl fishery in the early 1990s:
ecological and conservation perspectives
DOR EDELIST 1, OREN SONIN 1,2, DANIEL GOLANI 3, GIL RILOV 4
and EHUD SPANIER 1
1 Department of Maritime Civilizations and The Leon Recanati Institute for Maritime Studies, The Leon H. Charney
School for Marine Sciences, Faculty of Natural Sciences, University of Haifa, Mount Carmel, Haifa 31905, Israel.
E-mail: blackreefs@gmail.com
2 Ministry of Agriculture and Rural Development, Department of Fisheries and Aquaculture The Agricultural Center P.O.
Box 30, Beit Dagan 50250, Israel.
3 Department of Evolution, Systematics and Ecology, The Hebrew University of Jerusalem, 91904 Jerusalem, Israel.
4 Israel Oceanographic and Limnological Research. Tel- Shikmona, P.O.B. 8030, Haifa 31080, Israel.
SUMMARY: The spatiotemporal patterns of discards and catch composition of Israeli trawlers were examined using a
4-year (1990-1994), 324 haul dataset. Haul depth was found to be the main grouping variable for hauls, although signicant
seasonal differences were also found. 28.3% of the total catch was discarded, and there was a 40.1% discard percentage
in shallow hauls. According to these gures, annual discards for the Israeli trawl eet for the study period are estimated at
ca. 440 to 700 t. Both the biomass and the number of discarded specimens peaked in summer, as well as the percentage of
juvenile sh of commercial species. These ndings suggest that a summer moratorium on trawling would reduce discards.
The percentage of specimens of Indo-Pacic origin decreased from 51% in depths shallower than 37 m to 24% between
38 and 73 m, and 8% in deeper strata. Discards along the Israeli coast were comparable to those observed elsewhere in the
Mediterranean. The ndings presented here are the rst quantitative account of sh community assemblages in the nearshore
waters of the easternmost part of the Mediterranean, and thus provide valuable information for comparisons with more
current datasets that are currently being assembled.
Keywords: bottom-trawl, Israel, discards, catch composition, Lessepsian migration, shery management.
RESUMEN: Patrones espacio-temporales de la captura y los descartes de pesquería de arrastre mediterránea
israelí al inicio de la década de los noventa: perspectivas ecológicas y de conservación. – Se analizaron los
patrones espacio-temporales de los descartes y la composición de la captura de la flota de arrastre de Israel utilizando datos
de 4 años (1990-1994), 324 caladas. La profundidad resultó ser el principal factor en la agrupación de las caladas, si bien se
encontraron asimismo diferencias significativas entre estaciones. Se descartó el 28.3% de la captura total, alcanzándose el
40.1% en las caladas realizadas en las aguas más someras. Según estos porcentajes, se estimó una captura anual descartada
por la flota de Israel en ese período de 440-700 t. La biomasa, el número de ejemplares descartados, así como el porcentaje
de juveniles de especies comerciales fue mayor en verano. Estos resultados sugieren que una veda de arrastre en verano
favorecería la disminución de la captura descartada. El porcentaje de ejemplares de origen indo-pacífico descendió desde
51% en aguas de una profundidad inferior a 37 m, al 24% entre 38-73 m y al 8% en el estrato más profundo. Los descartes
en la costa israelí fueron similares a los observados en otras zonas del Mediterráneo. Se presentan por primera vez resultados
cuantitativos relativos a comunidades de las aguas costeras del extremo oriental del Mediterráneo, aportándose información
para su comparación con datos más recientes que en la actualidad están siendo obtenidos.
Palabras clave: arrastre de fondo, Israel, descartes, composición de la captura, migración lessepsiana, gestión de pesquerías.
Scientia Marina 75(4)
December 2011, 641-652, Barcelona (Spain)
ISSN: 0214-8358
doi: 10.3989/scimar.2011.75n4641
642D. EDELIST et al.
SCI. MAR., 75(4), December 2011, 641-652. ISSN 0214-8358 doi: 10.3989/scimar.2011.75n4641
INTRODUCTION
It is considered that marine communities have been
altered by multiple human stressors. One of the most
influential of these stressors is fishing, specifically bot-
tom trawling (Alverson et al., 1994, Hall et al., 2000,
Jackson et al., 2001, Pauli et al., 2002). Trawling was
criticized for its low selectivity and damaging effects
on the benthic habitat as early as the 18th century
(Sacchi, 2008). Low selectivity leads to large portions
of the catch being discarded at sea due to the species
being unmarketable or too small. These discards are
an important measure of the impacts of fishing on ma-
rine stocks (Alverson et al., 1994). The present study
deals with discards, rather than bycatch. It argues that
bycatch may be a misleading term for the spatially
and temporally heterogeneous multi-species Mediter-
ranean trawl fishery. Whereas bycatch is a loosely
defined term, discards are unanimously defined as the
part of the catch which is brought onto the deck and
then thrown back into the sea (Alverson et al., 1994,
Hall et al., 2000, Tsagarakis et al., 2008).
Alverson et al. (1994) did not specifically address
discards in the Mediterranean; however, Kelleher
(2005) assigned the Mediterranean and Black Sea
fisheries (excluding the Levant) a mere 4.9% discard
ratio based on an analysis of 24% of the total catch.
Davies et al. (2009) took a more thorough approach
and estimated Mediterranean discards at 306000 tons,
or 21.1% of the total catch. 85% of these discards
originated in the trawl fisheries, which were esti-
mated to have a 45-50% discard ratio. Various other
studies (Stergiou et al., 1998, Machias et al., 2001,
D’Onghia et al., 2003, Sánchez et al., 2004, 2007)
have assigned discard ratios of 20-50% to various
trawl fisheries in the western and central Mediterra-
nean. El-Mor et al. (2002) and Alsayes et al. (2009),
however, found that only 15-25% of the catch was
discarded in Egypt. Recently, in two extreme cases,
local discards were found to exceed 70% in Portugal
(Esmeralda Costa et al., 2008) and Turkey (Soykan
and Kincigil, 2006). Discard practices vary annu-
ally and seasonally throughout the Mediterranean
(Machias et al., 2001, Lleonart and Maynou, 2003,
Sánchez et al., 2004). For some commercial species,
this is because fishermen adjust the actual minimum
landing size to match market demand rather than to
comply with the Minimum Landing Size (MLS) regu-
lations. For other species (most notably goatfishes)
this means that juvenile specimens are consistently
landed and marketed. MLS regulations in Israel have
been arbitrarily set for several prominent commercial
species but are not enforced.
Depth and fishing season were found to be the ma-
jor factors contributing to the discard rate and catch
composition in many Mediterranean trawl fisheries
(Stergiou et al., 1998, Machias et al., 2001, D’Onghia
et al., 2003, Sánchez et al., 2004, 2007). These find-
ings have been used to justify and manage seasonal
trawl closures and minimal trawling depth limitations.
The time of day was also shown to have significant ef-
fects on catch composition, but mostly as a confound-
ing factor with depth (Wassenberg et al., 1997). There
are also spatial differences between different trawling
zones. In order to understand these, it is important to
determine the characteristics of and variation in local
fishing practices (Sánchez et al., 2007).
The Levantine ecosystem differs from the rest of
the Mediterranean in phenomena such as Levantine
Nanism, in which organisms are smaller and reproduce
earlier. This phenomenon was hypothesized by Por
(1989) and demonstrated by Sonin et al., 2007 for the
red mullet Mullus barbatus. The Levant is also consist-
ently invaded by Indo-Pacific species (e.g. Spanier and
Galil, 1991, Rilov and Galil, 2009). This bioinvasion is
particularly reshaping the shallow shelf fauna, mainly
due to the shallowness of the main invasion vector
the Suez Canal (Rilov and Galil, 2009).
The present study analyzes catch, discard and as-
semblage composition data for the Israeli trawl fishery
for the years 1990-1994. This analysis is the first quan-
titative study of Israeli trawl catches and the first to
describe the spatio-temporal patterns of the demersal
fish community in the Levant. It focuses on the propor-
tion of discarded specimens, a measure which has thus
far been overlooked in Mediterranean trawl catch stud-
ies, most of which focus on discarded biomass alone.
From a conservation perspective, these data are vital
for an understanding of the rates of change vectors and
how they are reflected through the fishery. They can
serve as a baseline for future comparisons of the status
of fish and fisheries in the rapidly changing eastern
Mediterranean, and as such assist in ecosystem-based
management of the trawl fishery.
MATERIALS AND METHODS
Description of the fishing fleet, study area and
typical catch and effort
Israeli trawling fleets operate along 170 km of
coastline, up to 20 km offshore. Some additional, small-
scale activity took place near the coast of northern Si-
nai until the mid 1990s. Trawling occurs in two main
geographic areas (Fig. 1), and the same fishing gear
is used in both areas. South of Haifa, trawling lanes
run parallel to the shore and maintain the haul depth
along the isobaths. The wide, shallow continental shelf
of southern Israel means that more shrimp trawling,
generally performed between 20 and 40 m, is carried
out than in the northern fields. The narrower northern
shelf and curvature of Haifa Bay often dictate curved
or semi-circular trawling lanes. The primary target fish
species have traditionally included high priced species
such as prawns, mullids and groupers, common sea
breams (such as bouge and pandoras) and lizard fish.
Hake are also targeted, but at greater depths (Snovsky
and Shapiro, 1997).
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The present study refers to data collected in the
early 1990s, when 30-34 vessels, each with a mean
engine power of 214-228 hp, were spending a total of
5152-6214 days at sea each year (Snovsky and Shapiro,
1997). The fleet size was frozen at 30 licenses in 1995
and today only 23 out of the 30 vessels are active, pos-
sibly due to rising fuel prices and declining catches.
This fleet size limit has not proven effective in halting
declines in CPUE (catch per unit effort; Fig. 2). A 45-
day summer trawling moratorium was established in
1998-99, but the policy was discontinued the follow-
ing year despite encouraging interim results, including
increasing catches and larger specimens of commercial
species (Pisanty et al., 2000). Currently, the fleet trawls
all year round, spending only ca. 4000 days/year at
sea. It is important to note that this reduction in fish-
ing effort is mitigated by an increase in mean engine
power (currently 294 hp), which allows increased effort
per sea-day. Before 2004-5, the fleet trawled for hake
in the spring, and also for rose shrimps Parapenaeus
longirostris and red shrimps Aristeus antennatus and
Aristeomorpha foliacea. In recent years stocks have
dwindled, and now the fleet operates almost exclusively
on the continental shelf between 15 m (the minimum
depth allowed by law) and 150 m. This trend towards
shallower trawls is in opposition to the efforts in other
Mediterranean fisheries, for which regulation of shal-
low trawling has led to the development of deep-sea
trawl fisheries (D’Onghia et al., 2003, Esmeralda-Costa
et al., 2008). Such spatial changes in fishing effort alter
species compositions, and therefore more Lessepsian
migrants are caught by trawlers fishing in the shallows
(see Results). The gear has changed very little since
1990, and 40-48mm (at the cod end) diamond-mesh nets
are still used by all trawlers. Annual catches in the early
1990s fluctuated between 1107 and 1757 t, with a mean
of 1409 t; in the last 3 years, catches did not exceed
1227 t per year. While catches of hake, grouper, goat-
fish and meagre have sharply declined in recent decades
(Scheinin, 2010), increases were noted for Chondrich-
thyes and for the invasive tiger prawn Marsupenaeus
japonicus. Since shrimp trawling is more fuel efficient,
today almost all vessels target M. japonicus in the shal-
lows (15-40 m) at night.
Data collection
Data were collected from 324 commercial trawl
hauls carried out between April 1990 and December
1994 by the Israel Fishery Department. These surveys
Fig. 1. – Map of the study site, with the main locations and isobaths mentioned in the text. The dark grey area represents the study area, cover-
ing all the trawling grounds on the Israeli coast in the study period.
Fig. 2. – Declines in CPUE (catch per unit effort) of Israeli trawl-
ers based on data collected by the Department of Fisheries in the
Ministry of Agriculture since 1948. The effort unit used was engine
horsepower per day at sea, as used by Garcia and Demetropoulos
(1986).
644D. EDELIST et al.
SCI. MAR., 75(4), December 2011, 641-652. ISSN 0214-8358 doi: 10.3989/scimar.2011.75n4641
took place onboard trawlers fishing the Israeli conti-
nental shelf, between latitudes 31º20’ N and 33º05’
N. Depths ranged between 15 and 300 m. The gross,
discarded and landed catch weights were estimated for
173 out of the 324 hauls in which two or more of these
variables were recorded, and therefore total catch anal-
ysis was possible. A sample of ca. 5% of the biomass
(2.7-12.5 kg with a mean of 5.5±2.4 kg per haul) was
extracted from each haul. While this partial-sampling
method may miss rare species, it allows nearly all
the fauna in the nets to be properly sampled and the
time-consuming length measurements to be carried out
onboard. Fish were taxonomically identified to species
level, except for several cases in which only the genus
was noted. Fish Total Length (TL), cephalopod Mantle
Length (ML) and crustacean Carapace Length (CL for
crabs, eye to telson length for shrimps) were measured
to the closest 0.5 cm interval. The discard lengths de-
fined in the present study are described in Table 1 and
were subsequently used to differentiate between the
two discarded fractions: non-commercial species and
juveniles of commercial species. These lengths were
determined empirically, i.e. they were estimated based
on observations of onboard sorting practices, fisher-
men’s experience and minimum landing size (MLS),
rather than on the actual onboard sorting of specimens,
which may vary considerably due to factors such as
season, abundance, and market considerations (Machi-
as et al., 2001, Demestre et al., 2008).
Data analysis
Four factors (season, depth, time of the day and
geographical trawling area) were tested for their ef-
fects (Wilcoxon signed rank test, P<0.05) on discard
proportions of both the biomass (expressed in kg per
hour) and number of discarded fish, which were clas-
sified as either undersized commercial specimens or
non-commercial species. Other variables examined
included mean species richness (S), Shannon (H’) and
Simpson diversity and evenness (Pielou’s J) as well as
the mean proportion of Lessepsian migrants in hauls.
Seasons were defined as four equal three-month
periods. The time of day was defined as either day or
night. Depths of hauls were divided into 3 depth strata.
The 37 m isobath was chosen to separate the shallow
from medium depth due to bottom type: sandy to 37 m
and muddy in deeper strata. This depth is the median
point of the 25-50 m sand-mud transition zone de-
scribed by Sandler and Herut (2000). The 83 m isobath
was chosen as the transition point between medium
and deep strata because it approximates the median
depth for hauls deeper than 37 m. The two study areas,
north of Hadera vs. south of Hadera, span the entire
trawling range of the Israeli fleet. Though the two areas
are adjacent, they were analyzed independently in this
study because they are trawled by two different groups
of trawlers (which use similar fishing techniques).
Haifa-based trawlers operate north of Hadera, while
fields south of Hadera are mostly fished by trawlers
that dock in Jaffa and Ashdod (see Fig. 1). We compare
the northern and southern areas to test our hypothesis
of a higher Lessepsian migrant abundance in the south.
Catch composition analysis was performed using the
PRIMER-E v6 statistical software package (Clarke and
Warwick, 2001) as follows: For clustering of hauls and
Multi Dimensional Scaling analysis (MDS), data was
log x+1 transformed (to allow for the expression of less
common species in the assemblage) and then ordered
in a Bray-Curtis similarity matrix. The PERMANOVA
routine in PRIMER was used to test the significance of
differences and the interactions between factors. This
application tests the simultaneous response of variables
to factors in an ANOVA design using permutations.
The SIMPER routine in PRIMER was used to identify
the most dominant species in each stratum, defined as
the species which contributed most to the Bray-Curtis
similarity. To this end, sample data was square-root
transformed in order to weight the more abundant spe-
cies (e.g. Clarke and Warwick, 2001).
RESULTS
A total of 145 species (or genera, where specific
identification was uncertain) belonging to 75 families
was identified in surveys (Table 1). Of 124 bony fish
species, Sparidae (17 species) and Carangidae (8 spe-
cies) were the most dominant families. Seven cartilagi-
nous fish species, 10 crustacean species and 6 species/
genera of cephalopods were recorded. Sixty-two spe-
cies were consistently discarded, 52 were commercial,
and 40 were assigned a minor commercial value due
to their scarcity, low price or both (Table 1). Bony fish
accounted for 69.4% of the total number of specimens.
Crustaceans, despite being represented by only 10 spe-
cies, accounted for 28.3% of all specimens. The total
landed biomass harvest rate was 19.7 kg h-1, while 7.74
kg h-1 were discarded, culminating in a total discard
mean per-haul of 28.2% of the biomass. Of all the sam-
pled specimens, 46.7% were discarded. For bony fishes
only, this figure was slightly higher at 52.3% (Table 1).
All four factors were found to have significant
effects (Wilcoxon, P<0.05) on the discarded propor-
tion of the catch, and the factors ‘depth’ and ‘season’
generally had lower p values. Depth and season also
had significant effects on Shannon’s H’, Pielou’s J and
Simpson’s D, as well as species richness. The time of
day and geographic area did not however have signifi-
cant effects on evenness.
The highest seasonal biomass discard ratio was
recorded in summer (38.6%; Fig. 3a) and almost
doubled that of spring or winter. It coincided with a
very high summer proportion of discarded specimens
(61% of bony fish; Fig. 4a). Furthermore, during sum-
mer 74% of these were undersized juveniles of com-
mercial species. In no other season did any of the last
two parameters exceed 52%. Shannon’s diversity and
species richness significantly decreased from means of
CATCH AND DISCARDS OF THE ISRAELI TRAWL FISHERY • 645
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Table 1. – List of species recorded in surveys, their origin, commercial value and abundance in 324 trawl samples, as well as their landed and
discarded fractions in the catch. N, number of specimens; Minor, minor commercial value; Com., commercial; Disc., discarded; * Lessepsian
migrant; ** discard size was set according to MLS regulations; *** species were not separated in samples and were recorded as one taxa.
Species Family Value N Discard No. Discard %
Size in mm Landed
Bony Fishes
Pagellus erythrinus Sparidae Com. 7284 110** 1918 73.6
Upeneus moluccensis* Mullidae Com. 6230 90 4524 27.3
Boops boops Sparidae Com. 5469 130 1979 63.8
Mullus barbatus Mullidae Com. 4774 90 3624 24.1
Callionymus filamentosus* Callionymidae Disc. 3631 - 0 100
Leiognathus kluzingeri* Leiognathidae Disc. 3569 - 0 100
Mullus surmuletus Mullidae Com. 3501 90 2525 27.9
Spicara smaris Centracanthidae Minor 2491 130 139 94.4
Pagellus acarne Sparidae Com. 2483 120 1402 43.5
Dentex macrophthalmus Sparidae Com. 2093 110 328 84.3
Saurida undosquamis* Synodontidae Com. 1796 160** 1289 28.2
Trachurus mediterraneus Carangidae Com. 1795 130 833 53.5
Engraulis encrasicolus Engraulidae Minor 1573 110 25 98.4
Lepidotrigla cavillone Triglidae Disc. 1525 - 0 100
Merluccius merluccius Merlucciidae Com. 1090 140 849 22.1
Macrorhamphosus scolopax Macrorhamphosidae Disc. 838 - 0 100
Sardina pilchardus Clupeidae Minor 764 110 200 73.8
Lithognathus mormyrus Sparidae Com. 763 110** 546 28.4
Citharus linguatula Citharidae Minor 731 150 86 88.2
Alepes djedaba* Carangidae Com. 729 110** 547 24.9
Serranus hepatus Serranidae Disc. 600 - 0 100
Upeneus pori* Mullidae Com. 583 90 481 17.5
Sphyraena chrysotaenia* Sphyraenidae Com. 515 150 494 4.1
Trachinus draco Trachinidae Disc. 453 - 0 100
Stephanolepis diaspros* Monacanthidae Disc. 450 - 0 100
Bothus podas Bothidae Disc. 427 - 0 100
Spicara maena Centracanthidae Minor 406 130 42 89.6
Trachurus picturatus Carangidae Com. 342 130 186 45.6
Trachurus trachurus Carangidae Com. 332 130 240 27.7
Capros aper Caproidae Disc. 325 - 0 100
Sardinella aurita Clupeidae Com. 319 110** 217 32.0
Sphyraena sphyraena Sphyraenidae Com. 286 150 268 6.3
Arnoglossus sp. Bothidae Disc. 213 - 0 100
Uranoscopus scaber Uranoscopidae Disc. 203 - 0 100
Scomber japonicus Scombridae Com. 197 110 172 12.7
Pagrus coeruleostictus Sparidae Com. 186 110 116 37.6
Diplodus sargus Sparidae Com. 165 110** 144 12.7
Synodus saurus Synodontidae Com. 159 160** 108 32.0
Ariosoma balearicum Congridae Disc. 152 - 0 100
Trigloporus lastoviza Triglidae Disc. 149 - 0 100
Diplodus annularis Sparidae Com. 138 110** 87 36.9
Trigla lyra Triglidae Disc. 130 - 0 100
Caranx rhonchus Carangidae Minor 123 130 110 10.5
Serranus cabrilla Serranidae Disc. 113 - 0 100
Gobius niger Gobiidae Disc. 110 - 0 100
Sillago sihama* Sillaginidae Com. 90 130 73 18.8
Spicara flexuosa Centracanthidae Minor 86 130 16 81.4
Helicolenus dactylopterus Scorpaenidae Disc. 85 - 0 100
Epinephelus aeneus Serranidae Com. 79 150 53 32.9
Lagocephalus suezensis* Tetraodontidae Disc. 78 - 0 100
Seriola dumerili Carangidae Com. 76 130 70 7.9
Scomberomorus commerson* Scombridae Com. 73 140 67 8.2
Lepidorhombus whiffiagonis Scophthalmidae Minor 71 150 0 100
Trichiurus lepturus Trichiuridae Minor 64 300 47 26.6
Solea spp. Soleidae Minor 60 150 24 0.6
Diplodus vulgaris Sparidae Com. 57 110** 48 15.8
Chlorophthalmus agassizii Chlorophthalmidae Disc. 56 - 0 100
Pomadasys incisus Haemulidea Minor 55 130 45 18.2
Atherina spp. Atherinidae Disc. 49 - 0 100
Trachinus araneus Trachinidae Disc. 48 - 0 100
Apogon imberbis Apogonidae Disc. 44 - 0 100
Gnatholepis mystax Congridae Disc. 38 - 0 100
Phycis phycis Gadidae Disc. 37 - 0 100
Dussumieria elopsoides* Clupeidae Minor 36 110** 36 0
Herklotsichthys punctatus* Clupeidae Minor 34 110 0 100
Pagrus pagrus Sparidae Minor 33 110 1 96.9
Coelorhynchus Coelorhynchus Macrouridae Disc. 25 - 0 100
Zeus faber Zeidae Minor 25 120 4 84.0
Oxyuirichthys petersi* Gobiidae Disc. 24 - 0 100
Caranx crysos Carangidae Com. 21 130 15 28.6
Lagocephalus spadiceus* Tetraodontidae Disc. 21 - 0 100
Siganus rivulatus* Siganidae Minor 20 130 5 0.75
Sargocentron rubrum* Holocentridae Minor 18 140 17 5.5
646D. EDELIST et al.
SCI. MAR., 75(4), December 2011, 641-652. ISSN 0214-8358 doi: 10.3989/scimar.2011.75n4641
Table 1 (cont.). – List of species recorded in surveys, their origin, commercial value and abundance in 324 trawl samples, as well as their landed
and discarded fractions in the catch. N, number of specimens; Minor, minor commercial value; Com., commercial; Disc., discarded; * Lessep-
sian migrant; ** discard size was set according to MLS regulations; *** species were not separated into samples and were recorded as one taxa.
Species Family Value N Discard No. Discard %
Size in mm Landed
Diplodus puntazzo Sparidae Com. 17 110** 17 0
Ophiodon barbatum Ophidiidae Disc. 17 - 0 100
Balistes capriscus Balistidae Com. 16 130 14 12.5
Microchirus ocellatus Soleidae Disc. 14 - 0 100
Dactylopterus volitans Dactylopteridae Minor 13 130 2 84.6
Oblada melanura Sparidae Com. 13 110** 12 7.7
Cynoglossus sinusarabici* Cynoglossidae Disc. 11 - 0 100
Terapon puta* Terapontidae Disc. 10 - 0 100
Liza aurata Mugilidae Com. 9 200** 5 4.44
Dentex gibbosus Sparidae Minor 8 110 8 0
Aspitrigla cuculus Triglidae Disc. 7 - 0 100
Conger conger Congridae Disc. 7 - 0 100
Dentex dentex Sparidae Minor 7 110 2 71.4
Dentex maroccanus Sparidae Minor 7 110 1 85.7
Hoplostethus mediterraneus Trachichthyidae Disc. 6 - 0 100
Sparus aurata Sparidae Com. 6 110 6 0
Xyrichthys novacula Labridae Disc. 6 - 0 100
Blennius ocellaris Blenniidae Disc. 5 - 0 100
Epinephelus haifensis Serranidae Minor 5 150 4 0.2
Alectis alexandrines Carangidae Minor 4 150 0 100
Apogon pharonis* Apogonidae Disc. 4 - 0 100
Pempheris vanicolensis* Pempheridae Disc. 4 - 0 100
Siganus luridus* Siganidae Minor 4 130 0 100
Trachinus radiatus Trachinidae Disc. 4 - 0 100
Trigla lucerna Triglidae Disc. 4 - 0 100
Dicentrarchus punctatus Moronidae Minor 3 150 3 0
Hyporamphus affinis* Hemiramphidae Minor 3 160 3 0
Lepidopus caudatus Trichiuridae Minor 3 300 3 100
Liza ramada Mugilidae Minor 3 200 2 33.3
Lophius budegassa Lophiidae Minor 3 200 3 100
Torquigener flavimaculosus* Tetraodontidae Disc. 3 - 0 100
Anguilla Anguilla Anguillidae Disc. 2 - 0 100
Argyrosomus regius Sciaenidae Com. 2 150 2 0
Etrumeus teres* Clupeidae Com. 2 150 2 0
Hemiramphus far* Hemiramphidae Minor 2 160 2 0
Muraena Helena Muraenidae Minor 2 - 0 100
Phycis blennoides Gadidae Disc. 2 - 0 100
Pomatomus saltator Pomatomidae Com. 2 150 2 0
Argentina sphyraena Argentinidae Minor 1 - 0 100
Echelus myrus Ophichthidae Disc. 1 - 0 100
Echeneis naucrates Echeneididae Disc. 1 - 0 1
Epinephelus costae Serranidae Minor 1 150 1 0
Lepidotrigla dieuzeidei Triglidae Disc. 1 - 0 100
Microchirus variegates Soleidae Disc. 1 - 0 100
Mugil cephalus Mugilidae Com. 1 200 1 0
Pagrus auriga Sparidae Com. 1 110 1 0
Panturichthys fowleri Heterechelyidae Disc. 1 - 0 100
Scorpaena notate Scorpaenidae Disc. 1 - 0 100
Scorpaena scrofa Scorpaenidae Disc. 1 - 0 100
Symphurus nigrescens Cynoglossidae Disc. 1 - 0 100
Cartilagenous Fishes
Torpedo torpedo Torpedinidae Minor 30 170 14 53.3
Rhinobatos rhinobatos Rhinobatidae Com. 8 300 3 62.5
Raja miraletus Rajidae Com. 7 250 0 100
Squalus blainvillei Squalidae Minor 3 500 2 33.3
Torpedo marmorata Torpedinidae Minor 3 170 2 33.3
Dasyatis pastinaca Dasyatidae Com. 2 250 1 50
Mustelus mustelus Triakidae Minor 1 500 0 100
Cephalopods
Loligo vulgaris Loliginidae Com. 1481 100 233 84.3
Sepia ofcinalis Sepiidae Com. 242 60 189 21.9
Octopus/Eledone sp. Octopodidae Com. 134 20 100 25.4
Illex coindeti Ommastrephidae Com. 63 100 20 68.2
Crustaceans
Parapenaeus longirostris Penaeidae Com. 14773 60 4253 71.5
Marsupenaeus japonicus* Penaeidae Com. 3707 60 3637 1.9
Charybdis longicollis* Portunidae Disc. 3595 - 0 100
Aristeomorpha foliacea/
Aristeus antennatus*** Aristeidae Com. 2940 60 2270 22.8
Erugosquilla massavensis*/
Squilla mantis*** Squillidae Disc. 252 - 0 100
Portunus pelagicus* Portunidae Com. 30 70 30 0
Penaeus semisulcatus* Penaeidae Com. 41 60 41 0
Pontocaris cataphracta Crangonidae Disc. 12 - 0 100
Metapenaeus monoceros* Penaeidae Minor 8 60 8 0
CATCH AND DISCARDS OF THE ISRAELI TRAWL FISHERY • 647
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H’=1.96 and S=18.17 species per haul in the summer
to values of 1.77 and 15.72 respectively in winter.
The discard ratio was also found to be highest in
shallow fishing fields (Fig. 3b; 40.1%) and discards
were comprised mostly of unwanted species (Fig. 4b).
In deeper strata, discard proportions were lower but
were comprised mostly of juveniles of commercial
species. Diversity and richness were negatively cor-
related with depth, and decreased from 1.92 and 17.94
for shallow hauls (<37 m deep) to 1.56 and 14.98 spe-
cies per haul in deep hauls respectively.
The predominance of night hauls in shallow waters
(80 out of 114 shallow hauls were nocturnal; Fig. 5)
caused the depth and time of day to be confounding.
The time of day factor was therefore nested within the
depth factor in the permutational analysis of variance
(PERMANOVA) design, which tested for interactions
between factors. The PERMANOVA model results
(Table 3) indicate that depth and time of day nested
within depth had the most significant effects on catch
Fig. 3. – Mean landed and discarded biomass ± standard error, recorded in 173 trawl hauls for the 4 study factors: a, season; b, depth; c, time
of day; and d, area.
Table 2. Number of hauls used for the analysis of sample data
(total n=324) and biomass (recorded in 173 hauls). Note that several
hauls may have exceeded a single time of day, depth or area and
were thus omitted from the respective analysis.
Sample analysis Biomass analysis Details Factor
(Total n=324) (Total n=173)
78 40 Oct.-Dec. Autumn
100 53 Jan.-Mar. Winter
40 17 Apr.-Jun. Spring
106 63 Jul.-Sep. Summer
55 38 >84m Deep
147 72 38-83m Medium
114 57 <37m Shallow
162 90 Daylight Day
158 82 Darkness Night
199 106 North of Hadera North
116 60 South of Hadera South
Table 3. – A permutation analysis of variance (PERMANOVA)
designed to test interactions of the study factors - depth, time of day
(nested in depth), area and season, and their interactions. P(perm)
indicates the statistical significance of the interaction. *P<0.05
**P<0.005
Factor df Pseudo-F P(perm) perms
Depth 2 4.1055 0.018* 999
Area 2 1.5092 0.145 998
Season 3 2.8254 0.102 997
Time of day (Depth) 3 4.3359 0.001** 999
Depth×Area 3 1.4737 0.134 999
Depth×Season 6 2.0571 0.079 999
Area×Season 5 1.5973 0.219 998
Area×Time of day(Depth) 4 1.5736 0.008* 999
Season×Time of day(Depth) 7 1.7061 0.001** 996
Depth×Area×Season 5 1.3105 0.302 999
Area×Season×Time of day (Depth) 3 1.4126 0.04* 997
Residual 274 4.1967E5
Total 324 8.1654E5
648D. EDELIST et al.
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species composition. Towing area and season had no
significant effects on composition, except when they
interacted with the time of day nested in depth, which
suggests a complex set of influences on species com-
positions. After it was determined that depth was the
dominant factor affecting catch composition, a SIM-
PER analysis was performed separately for each of the
3 depth strata. Higher similarity (Table 4) was recorded
for hauls in deep and medium strata than in shallow
hauls. The porgy Pagellus erythrinus was found to
be the most dominant species in shallow and medium
depths. Commercial penaeid prawns were among the
dominant species in both shallow and deep hauls, with
P. longirostris and M. japonicus ranking first and third
respectively in these strata.
Several trends were found to differentiate between
trawling areas: northern hauls showed higher landed
catches (by 9 kg h-1; Fig. 3d) and lower biomass discard
percentages (by 6%) than southern hauls. However,
these discards were comprised mainly of juveniles of
commercial species (Fig. 4d).
Migrants accounted for 29.2% of the total landed
biomass in surveys. Out of 26 Lessepsian bony fish
species, 7 were commercial, 6 were of minor com-
mercial value and 13 were always discarded (Table 1),
whereas 4 out of the 6 Lessepsian crustacean species
were of commercial value. In The SIMPER analysis,
4 out of the 7 most dominant species in the shallow
stratum were Lessepsian migrants (Table 4). In depths
exceeding 37 m, the dominant Lessepsian species were
Fig. 4. – Mean proportion of the two fractions comprised in the discarded portion of the fish in 324 haul samples: undersized juveniles of
commercial species and specimens of unwanted, non-commercial species ± standard error, for the 4 study factors: a, season; b, depth; c, time
of day; and d, area.
Fig. 5. – MDS of the species composition of 324 haul samples ac-
cording to haul depth (top) and time of day (bottom); n, night; d,
day.
CATCH AND DISCARDS OF THE ISRAELI TRAWL FISHERY • 649
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the goatfish U. moluccensis and the lizardfish S. undos-
quamis (Table 4). In shallower waters, where migrants
proliferate, the penaeid prawn M. japonicus was the
prominent commercial species. It also accounted for
the bulk of shallow landings. Other common migrants
were mostly non-commercial species such as the in-
shore pelagic pony fish L.klunzingeri, the shallow wa-
ter dragonet C. filamentosus and the swimming crab C.
longicollis. Proportions of migrants in the catch varied
significantly (Wilcoxon, P<0.05) with season, depth
and area, peaking in the autumn, shallows and south
respectively (Fig. 6). No statistically significant differ-
ences were found for the time of day. In total, 43.9% of
all Indo-Pacific specimens were discarded; slightly less
than the 47.3% noted for indigenous specimens.
DISCUSSION
Discards and catch composition
This is the first fully quantitative study of demersal
fish communities in the Levant. Despite its delayed
publication, this dataset provides a crucial reference
point for the assessment of change vectors. It also dem-
onstrates the magnitude of the effects of trawling on the
Levantine ecosystem via discards, which is a prime con-
servation issue. Discards in the present study amounted
to 28.2% of the total catch, or 330-550 t of the 1107-
1757 t y-1 caught by Israeli trawlers during the study
period (Snovsky and Shapiro, 1997). It is estimated,
however, that >90% of trawling in Israel is performed
at depths shallower than 83m, where discard rates are
closer to 40% (Fig. 3b). This leads to a total discards
estimate of 440-700 t per annum for the Israeli fleet.
The 28.2% figure for total discards in the present study
is considerably lower than the 40-45% figure used by
Davies et al. (2009) for the entire Mediterranean, but
higher than the 15-25% values suggested by El-Mor
et al. (2002) and Alsayes et al. (2009) for Egyptian
trawlers. The high discard ratios described here clearly
support the use of more selective trawl nets, such as
the 40mm square mesh nets mandated by the General
Fisheries Commission for the Mediterranean (GFCM)
for Mediterranean fleets by 2012. Mesh size regulations
in Israel today are still similar to those used during the
study period. We therefore recommend making further
changes, as well as establishing MPAs and a summer
moratorium on trawling as precautionary measures.
Table 4. – Results of a nonparametric SIMPER procedure based on a square root transformed Bray-Curtis similarity index of the number
of specimens per hour of trawling. The contribution of the dominant species to the similarity % (Contrib%) of the 3 depth strata is described
for the 7 dominant species of each stratum. Other parameters include the average contribution to abundance, similarity, similarity/standard
deviation and cumulative similarity.
Species Av.Abund Av.Sim Sim/SD Contrib% Cum.%
Shallow stratum (15-37 m) average similarity: 30.31
Pagellus erythrinus 1.50 6.30 1.25 20.77 20.77
Callionymus filamentosus* 1.30 5.41 0.97 17.84 38.61
Marsupenaeus japonicus* 1.26 4.86 0.70 16.05 54.66
Boops boops 0.68 2.17 0.78 7.15 61.81
Saurida undosquamis* 0.52 1.33 0.66 4.39 66.19
Lithognathus mormyrus 0.50 1.32 0.67 4.36 70.55
Upeneus pori* 0.45 1.26 0.69 4.17 74.72
Medium stratum (38-83 m) average similarity: 34.06
Pagellus erythrinus 1.46 6.01 1.72 17.65 17.65
Upeneus moluccensis* 1.51 5.21 0.98 15.28 32.93
Mullus barbatus 1.20 3.25 0.79 9.54 42.48
Boops boops 1.16 3.18 0.86 9.33 51.81
Mullus surmuletus 0.99 2.27 0.64 6.68 58.49
Pagellus acarne 0.88 1.60 0.50 4.70 63.19
Saurida undosquamis* 0.62 1.51 0.59 4.43 67.62
Deep stratum (>84 m) average similarity: 33.09
Parapenaeus longirostris 2.77 12.63 1.13 38.18 38.18
Merluccius merluccius 1.09 4.33 1.01 13.07 51.25
Dentex macrophthalamus 1.23 3.54 0.66 10.69 61.93
Boops boops 0.85 1.94 0.60 5.87 67.80
Mullus barbatus 0.62 1.77 0.75 5.35 73.15
Macrohamphosus scolopax 0.77 1.48 0.53 4.47 77.62
Aristeomorpha foliacea 0.77 1.24 0.28 3.73 81.35
Fig. 6. – Mean Lessepsian migrant proportion ± S.E. for the 4 study
factors in the 324 haul samples.
650D. EDELIST et al.
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Israeli gross catch rates fluctuated seasonally
between 19.9 and 32.2 kg h-1, while discards varied
between 3.7 and 9.9 kg h-1 (Fig. 3). Despite the poor
Levantine fishery suppositions made in various studies
(Por, 1989, Sonin et al., 2007), these values are compa-
rable to catch and discard rates reported for the central
Mediterranean (Machias et al., 2001, D’Onghia et al.,
2003, Sánchez et al., 2007). Discarded biomass alone,
however, cannot represent the full extent of the impact
of trawling on future year classes. The spatiotemporal
variance in discards, as shown in Fig. 4, reveals the
motive for discarding and also the potential commer-
cial losses incurred. We suggest that these datasets
may compensate slightly for the absence of proper
stock assessments in the region. Nearly 60% of all fish
were discarded in the present study, with juveniles of
commercially exploited species representing >60% of
these discards.
97 species appeared in both Machias et al. (2001)
and the present study. Out of these, 30 taxa were mar-
keted in Greece but discarded in Israel. An example
of these taxa (which abound in catches but are seldom
sold) is the genus Spicara (n=2978 in Table 1). Mem-
bers of this genus comprise up to 50% of the commercial
catch of trawls in Cyprus (Garcia and Demetropoulos,
1986), while they are normally discarded in every size
in Israel, and only acquire a minor commercial value
when catches are especially poor. Other such species
include congers, ophiodons and other eels, gurnards,
some flatfishes, such as B. podas or C. linguatula,
scorpion fishes, weavers and stargazers. Some crus-
taceans with commercial potential are also discarded
in Israel, most notably the stomatopod Squilla mantis,
which is landed consistently, and seldom discarded in
Balearic and Adriatic trawl fisheries (Sánchez et al.,
2007, Demestre et al., 2008). The Israeli fishing fleet
is thus wasting a potentially valuable resource, as these
species can be landed and sold if a suitable market can
be found. However, when this issue is addressed the
smaller size of Levantine organisms (i.e. Nanism), may
limit the commercial potential of these genera. This
dwarfing phenomenon has been suggested to be the
result of lower productivity in the region (Sonin et al.,
2007) and is speculated to affect most of the Levantine
fauna (Por, 1989, Sonin et al., 2007).
For several species, most noticeably goatfishes, the
observed discard length differed greatly from MLS.
The MLS of goatfish is 11 cm; however, due to the
high prices obtained for goatfish regardless of size,
specimens as small as 9 cm were consistently landed
and this was the length actually used as the maximum
discard size. This led to fairly low discard rates of
17.5-27.3% for the 4 mullid species. An examination
of the most commonly caught commercial and minor-
commercial species in Table 1 reveals two distinct sub-
groups. One subgroup includes species which exhibit
low discard rates (less than 30%) such as the 4 mullid
species, lizardfish and hake (due to their high com-
mercial value and small discard sizes), rock-dwelling
sea breams (most of which are adults caught foraging
slightly off their rocky habitat) and pelagic or semi-
pelagic families such as Scombridae, Clupeidae or
Carangidae. The second subgroup is made up of species
for which 60-98% of the specimens were discarded.
This includes some of the most common species, such
as porgies, bouge, picarels, dentex and flatfishes. The
landing size for these species is substantially larger
than the mean size of caught specimens, which leads
to high discard rates. Esmeralda Costa et al. (2009)
found a similar trend as far west as Portugal, with less
than 30% discards for sardines, carangids, scombrids
and Diplodus spp., as opposed to >70% for porgies and
hake. It is evident from the small size of the fish caught
by Levantine trawlers (Table 1) that most individuals
have not reached reproductive maturity. This seriously
jeopardizes the sustainability of the fishery regardless
of whether juveniles are landed or discarded.
Spatial and temporal trends
Depth was found to be the main explanatory fac-
tor for both catch composition and discard percentage.
Higher landed and lower discarded biomass was found
deeper than 37 m (Fig. 3b). However, the proportion
of juveniles of commercial species within discards
in these deep strata was significantly higher (Fig. 4).
Shallow stratum discard proportions were higher (Fig.
3b); however, they were dominated by non-commercial
species, rather than commercial juveniles (Fig. 4b).
This finding may present a dilemma for fishery manag-
ers seeking to minimize discards via spatial exclusion:
although closing shallow waters to trawling will lead
to a richer and more diverse environment, shifting
the effort into deeper grounds will harm more com-
mercial juveniles. A trawl ban shallower than 50m (as
described by Sweeting et al., 2009) may not be suitable
for Israeli fishing fields, as it may displace trawling ef-
fort into deeper grounds, where juvenile recruits make
up a larger portion of the assemblage. In addition, a
50 m minimum trawl depth would eliminate the entire
M. japonicus catch, the most valuable commercial re-
source harvested by trawlers.
High summer discard proportions were accompa-
nied by increases in Shannon’s H’ and species richness.
As in shallow depths, summer discards were comprised
mostly of non-commercial species (Fig. 4a). A summer
trawling moratorium, as practiced in other Mediterra-
nean countries (Machias et al., 2001, D’Onghia et al.,
2003, Sánchez et al., 2004, Demestre et al., 2008) may
prove effective in raising CPUE and reducing discards.
An effective moratorium requires that fishing pressure
is not merely shifted to other seasons and that discard
practices remain consistent throughout the fishing sea-
son (Machias et al., 2001, Sánchez et al., 2007).
As in the present study, Sánchez et al. (2004) re-
ported that discarded biomass decreased with depth
on the shelf. Machias et al. (2001) and D’Onoghia et
al. (2003), working on the slope, found that discard
CATCH AND DISCARDS OF THE ISRAELI TRAWL FISHERY • 651
SCI. MAR., 75(4), December 2011, 641-652. ISSN 0214-8358 doi: 10.3989/scimar.2011.75n4641
percentages increased with depth. This may attest to a
spatial discarding pattern for the Mediterranean, where
discards are highest on the deep shelf and decrease to-
wards the shallower shelf from one end and the deeper
slope on the other.
Juveniles of the European squid L. vulgaris and the
rose shrimp P. longirostris were dominant among deep
strata discards. Whereas squids are consistently landed
when of size, rose shrimps are often discarded even at
legal sizes, mostly due to low market prices. Despite
the high abundance of rose shrimp, the high costs of
deep sea trawling often stop trawlers from targeting it.
Conversely, discarded crustaceans in shallow waters
included mostly the non-commercial swimming crab
C. longicollis. Along with several other species, this
crab was responsible for a high crustacean discard rate
in Levantine shallow waters (>5 kg h-1), which is un-
like the low ca. 1 kg h-1 crustacean discard rate noted
by Machias et al. (2001) in Greece.
Lessepsian migrants
The percent of Lessepsian migrant specimens in
trawl catches decreased from 51% in the shallows to
24% and 8% in the medium and deep strata respec-
tively. S. undosquamis and U. moluccensis were the
dominant Indo-Pacific species in the deeper grounds;
perhaps outlining the maximum bathymetric boundary
of migration. The niche partitioning pattern, (Golani,
1993) which suggests that native goatfishes domi-
nate deeper strata than migrants, is also evident in the
present data (Table 4).
While Lessepsian migrants remain poorly estab-
lished in the rocky littoral (Golani et al., 2007), this
study has found that they proliferate in highly (and
often) disturbed trawl grounds. This heavily exploited
environment only allows resilient species with rapid
population recovery rates and recolonization abilities
to persist. We therefore hypothesize that Lessepsian
migrants display good adaptive characteristics, which
have enabled them to migrate and colonize a new
ecosystem, and which have given them a selective ad-
vantage in a scheme of recurring and rapid exploitation
and recolonization like that imposed by trawling.
Lessepsian migrants were a significant and valu-
able portion of the Israeli trawl catch in the past (Ben-
Yami, 1955), and remain so today (Sonin et al., 2007).
Still, some studies argue that the cumulative effect of
migration is harmful (Galil, 2007). Ben-Tuvia (1973)
estimated that migrants constitute 21% of trawl yields,
slightly less than the landed migrant biomass propor-
tion found in the present study (29%). As expected,
migrants were most common in shallow grounds (Fig.
6). No substantial diurnal differences in migrant pro-
portions were observed; however, their composition in
catches varied between night and day. The SIMPER
analysis showed that typical nighttime migrants were
the dragonet C. filamentosus and the prawn M. japoni-
cus in the shallows. The main migrants contributing to
daytime assemblages in all strata were U. moluccensis,
S. undosquamis and L. klunzingeri. The first two spe-
cies were also responsible for high migrant percentages
in autumn and winter (Fig. 6). These species, along
with the indigenous B. boops and P. erythrinus, also
accounted for the high landings in autumn (Fig. 3a).
The present study has also found a significantly higher
proportion of Lessepsian migrants in the southern
trawling area (Fig. 6). We suggest that this is either the
result of its proximity to the Suez Canal or of the wider
continental shelf of southern Israel.
Today, the migrant prawn M. japonicus is a central
target species of the Egyptian, Turkish and Israeli trawl
fisheries (Galil, 2007). Its high market value and near-
shore habitat have reshaped local trawling and turned
the shallow strata into the most intensively trawled
habitat off the Israeli coast. Since its acceptance in the
local market in the 1970s, it has comprised more than
a fifth of the income of Israeli trawlers (Snovsky and
Shapiro, 1997). With increasing migration rates, soar-
ing oil prices and declines in deep fisheries, it stands
to reason that the market value and overall biomass of
migrant species will continue to rise in the future. More
research and time are required to determine whether
migrants can compensate for the loss of landings of
local species or the declines in CPUE shown in Fig. 2.
New trawl surveys are currently being conducted
along the Israeli coast. The present study serves as an
important spatial and temporal baseline for a detailed
comparison of the status of fish and fisheries over the
last two decades in the dynamic, quickly evolving
habitats of the Mediterranean.
ACKNOWLEDGEMENTS
The research was partially funded by a grant from
the Israeli Ministry of Agriculture and Rural Develop-
ment to E. Spanier and O. Sonin and the Maurice Hat-
ter Grant for Maritime Studies to D. Edelist. We also
wish to thank the editor and reviewers, as well as Mr.
Jonathan Liberzon for their useful comments, which
greatly improved this article.
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... Pomadasys bennetti: Diamant, 1977; Diamant, 1983 (Heb.); Diamant et al., 1986;Edelist et al. 2011a (Fish.). ...
... 75 (Syst.); Chervinski, 1975 (Aqu.); Zismann & Ben-Tuvia, 1975 (Juv.); Chervinski, 1976 (Gro.); Fischthal, 1980 (Parasit.); Ben-Yami, 1981 (Aqu.); Ben-Yami & Grofit, 1981 (Fish.); Golani & kredo, 1981 (Fish., Heb.); Zismann, 1981 (Syst.); Darom & Tsurnamal, 1992 (Heb.);Golani, 1996; Golani, 1997 (Heb.);Golani, 2003; Ethad, 2004 (Heb.);Golani, 2005;. Edelist et al. 2011a ;Levitt, 2012; ...
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This checklist of the Mediterranean fishes of Israel enumerates 469 species which is an addition of 62 species since the previous checklist of 2005. This new checklist includes 58 Condrichthys and 411 Osteicthys species. Most newly-recorded species are of Red Sea origin (Lessepsian migrants)—38 species, 25 species are from previously poorly investigated habitats, mainly deep water, while two species reached the Mediterranean most likely by ballast water and two are aquaculture escapees. The dramatic increase in the number of Lessepsian migrants (an average of 2.5 species per year) is most likely due to the increased water influx between the Red Sea and the Mediterranean, following the recent opening of the new parallel, 72 km, “new canal” and the enlargement of other parts of the Suez Canal.
... The removal of juvenile fish through discarding can alter food webs and the dynamics of fish communities, decrease adult populations occurring in open sea, and generate possible conflict among commercial fisheries (de Rezende, Ortega, and Dumont, 2019). Previous studies have recorded that fish are the most vulnerable group among bycatch in shrimp trawl fisheries in tropical regions (Edelist et al., 2011;Stobutzki et al., 2001;Watts and Pellegrin, 1982). ...
... Presently, discard studies related to some environmental variables have already emerged (Edelist et al., 2011;Pennino et al., 2014). Nonetheless, to date, physicochemical parameters have not yet been considered as variables that might affect discarding variations for the Celestun lagoon. ...
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... The information gaps were filled using catch data collected and analysed from three trawl surveys conducted in [1990][1991][1992][1993][1994]2000, and 2008-2011 along with reconstructed catch data (Corrales et al., 2017a). and fishing efforts (Edelist et al., 2011. Catch data for the recreational sector were obtained from a survey of recreational fishers (Schulz et al., 2011) and extrapolated by Scheinin et al. (2013). ...
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... These penaeid shrimps are commercially exploited and highly prized worldwide with an impressive aquaculture farming production (Tsoi et al. 2014). In the eastern Mediterranean, P. pulchricaudatus has been an important target of fisheries that significantly contributes to local economy (Mehanna et al. 2005(Mehanna et al. , 2011Galil 2007b;Duruer et al. 2008;Edelist et al. 2011;Otero et al. 2013;Corsini-Foka et al. 2015;Ulman et al. 2015;Katsanevakis et al. 2018;Ammar 2019;van Rijn et al. 2020). Pond aquaculture of the species has also been developed around various locations of the Mediterranean (Galil and Zenetos 2002;Savini et al. 2010;Otero et al. 2013;Manfrin et al. 2018). ...
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... In the Mediterranean, MTC based on landings has been found to increase between 1970 and 2010 by 0.56, 1.05, and 0.29 °C per decade in the western, central, and eastern sub-basins, respectively (Tsikliras and Stergiou 2014), by 0.25 °C per decade in the northeast Aegean (Keskin and Pauly 2014), by 1.01 °C, and 1.17 °C per decade for the Aegean and Ionian Seas, respectively (Tsikliras et al. 2015), and by 0.48 °C per decade in the northern part of the Levantine Sea (Keskin and Pauly 2018). These estimates were made without considering the non-indigenous tropical Lessepsian species, although they now constitute a significant proportion of the fish population, especially in the eastern Mediterranean (CIESM 2021; Edelist et al. 2013Edelist et al. , 2011 and their inclusion in the calculation would probably have increased the estimated MTC. Although our results show a decrease in MTO when non-indigenous species are excluded from the calculation for the Holocene death assemblages, this decrease is very small due to rarity of Lessepsian species in these assemblages compared to native taxa. ...
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Evaluation of the impact of climatic changes on the composition of fish assemblages requires quantitative measures that can be compared across space and time. In this respect, the mean temperature of the catch (MTC) approach has been proven to be a very useful tool for monitoring the effect of climate change on fisheries catch. Lack of baseline data and deep-time analogues, however, prevent a more comprehensive evaluation. In this study, we explore the applicability of the mean temperature approach to fossil fish faunas by using otolith assemblage data from the eastern Mediterranean and the northern Adriatic coastal environments corresponding to the last 8000 years (Holocene) and the interval 2.58–1.80 Ma B. P. (Early Pleistocene). The calculated mean temperatures of the otolith assemblage (MTO) range from 13.5 to 17.3 °C. This case study shows that the MTO can successfully capture compositional shifts in marine fish faunas based on variations in their climatic affinity driven by regional climate differences. However, the index is sensitive to methodological choices and thus requires standardized sampling. Even though theoretical and methodological issues prevent direct comparisons between MTO and MTC values, the MTO offers a useful quantitative proxy for reconstructing spatial and temporal trends in the biogeographic affinity of fossil otolith assemblages.
... A positive correlation between the discarded fraction and depth was found by D' Onghia et al. (2003) in the Ionian Sea. On the contrary, Edelist et al. (2011) found a decreasing trend with increasing depth off the Israeli coast. Despite the effects of depth are known, the relationship between the discarded fraction and depth can be modified through the operational pattern of fishing. ...
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In the Mediterranean Sea, the catch of bottom trawl fisheries is composed of a complex mix of fish and invertebrates with a considerable amount of discards. Seasonal composition of catches and discards of bottom trawls operating at different depths in the central Tyrrhenian Sea were investigated from October 2014 to October 2015. The mean total catch per unit effort (CPUE) ranged between 30.93±8.43 and 27.52±9.88 kg/h in shallow and deep fishing grounds, respectively. The discarded fraction of the catch was 39.9% in shallow and 43.3% in deep fishing grounds. The mean CPUE of commercial target species were similar in shallow and deep trawling (10.81+5.82 vs 8.92±3.16 kg/h). The commercial bycatch was lower in shallow (6.66±1.25 kg/h) than in deep grounds (8.24±2.91 kg/h), whilst the discards were lower in deep (10.43±5.14 kg/h) than shallow grounds (13.43±5.29 kg/h). Overall, 246 species were caught during fishing operations, out of which 209 were included in discards. The number of species recorded in shallow grounds (199 caught species with 166 discarded) was higher than that recorded in deep grounds (116 caught species with 102 discarded). Fish were the most represented taxa in the shallow discards, followed by echinoderms and crustaceans, and were the main discarded taxa in deep water. Depth was the main factor affecting both commercial catches and discards composition, whereas the season affected the CPUE of main target species only. The results confirmed that discards were higher in shallow than in deep trawling, suggesting that the latter is more efficient than the former in catching fishery resources for human consumption. Understanding the factors that affect discarding is the starting point for adopting management measures to mitigate negative impacts of trawl fisheries on marine resources and benthic communities.
... For example, in the Mediterranean Sea, the opening of the Suez Canal in 1869 facilitated the widespread introduction of numerous alien marine taxa. The speed of invasion and range of Lessepsian IAS have been increasing ever since, owing to a number of factors such as currents, climate change, removal of high and low-salinity barriers, overexploitation of native fish, etc (Lasram et al. 2008(Lasram et al. , 2010Raitsos et al. 2010;Edelist et al. 2011Edelist et al. , 2013Vergés et al. 2014). Indeed, for marine taxa, recorded species introductions into the Mediterranean Sea significantly exceed the numbers of species introductions in other European seas, with the eastern Mediterranean possibly the most heavily impacted (Edelist et al. 2013;Galil et al. 2014). ...
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Invasive alien species (IAS) negatively impact the environment and undermine human well-being, often resulting in considerable economic costs. The Mediterranean basin is a culturally, socially and economically diverse region, harbouring many IAS that threaten economic and societal integrity in multiple ways. This paper is the first attempt to collectively quantify the reported economic costs of IAS in the Mediterranean basin, across a range of taxonomic, temporal and spatial descriptors. We identify correlates of costs from invasion damages and management expenditures among key socioeconomic variables, and determine network structures that link countries and invasive taxonomic groups. The total reported invasion costs in the Mediterranean basin amounted to $27.3 billion, or $3.6 billion when only realised costs were considered, and were found to have occurred over the last three decades. Our understanding of costs of invasions in the Mediterranean was largely limited to a few, primarily western European countries and to terrestrial ecosystems, despite the known presence of numerous high-impact aquatic invasive taxa. The vast majority of costs were attributed to damages or losses from invasions ($25.2 billion) and were mostly driven by France, Spain and to a lesser extent Italy and Libya, with significantly fewer costs attributed to management expenditure ($1.7 billion). Overall, invasion costs increased through time, with average annual costs between 1990 and 2017 estimated at $975.5 million. The lack of information from a large proportion of Mediterranean countries, reflected in the spatial and taxonomic connectivity analysis and the relationship of costs with socioeconomic variables, highlights the limits of the available data and the research effort needed to improve a collective understanding of the different facets of the costs of biological invasions. Our analysis of the reported costs associated with invasions in the Mediterranean sheds light on key knowledge gaps and provides a baseline for a Mediterranean-centric approach towards building policies and designing coordinated responses. In turn, these could help reach socially desirable outcomes and efficient use of resources invested in invasive species research and management.
... Nonindigenous species in the Mediterranean now total above 950 (Zenetos et al. 2010) and are of particular concern in the eastern Mediterranean, where a large migration of Red Sea species followed the opening of the Suez Canal in 1869 (Galil 2009;Golani and Appelbaum-Golani 2009;Ben Rais Lasram and Mouillot 2009;Rilov and Galil 2009). These nonindigenous species constitute as much as 50-90% of total fish biomass in some habitats in the eastern Mediterranean (Goren and Galil 2005;Edelist et al. 2011;Buba et al. 2017). The current rate of nonindigenous species invasion and the consequent changes in species composition far exceed those in any other open marine system (Edelist et al. 2013). ...
Chapter
Nonindigenous species are considered among the major threats to biodiversity. A deep understanding of the processes underlying invasion is impeded, among others, by insufficient taxonomic and distributional knowledge. The Mediterranean Sea is experiencing a large invasion by Red Sea species as a result of the opening of the Suez Canal, at a rate which far exceeds those in any other open marine system. Here, we focus on a potential Red Sea marine invader into the Mediterranean, the mytilid Brachidontes pharaonis, as a case study, and review alternative explanations for its present distribution in the Mediterranean, Red Sea, and the Indo-Pacific. A previous study showed a significant difference in haplotype composition among the Mediterranean and the northern Red Sea and that most Mediterranean Sea haplotypes were unique (up to 80%). We present updated analyses using mitochondrial DNA (mtDNA) samples from the Persian Gulf (Arabian Sea) and compare them to populations in the Mediterranean, Red Sea, and Sri Lanka. We found that haplotypes collected in the southern Red Sea, Qatar, and Sri Lanka were significantly distinct from all those sampled in the eastern Mediterranean and northern Red Sea. In contrast, the haplotypes from Abu Dhabi, a large, active port, clustered within those from the Mediterranean Sea and the northern Red Sea. Together, the Persian Gulf and the Indian Ocean do not seem to be the sources of the Mediterranean and northern Red Sea populations. The presence of many haplotypes within the Mediterranean and northern Red Sea that are not traceable to other populations (apart from Abu Dhabi) suggests that B. pharaonis is not truly a nonindigenous to the Mediterranean but, rather, is a previously undetected indigenous species. The establishment of the Suez Canal may have brought together divergent lineages and resulted in an admixture of populations, but this scenario alone cannot explain the rich assembly of unique haplotypes in the Mediterranean Sea. Our results lead to a better understanding of the genetic structure of this species. The results of our study suggest that detailed empirical and careful evaluations are needed in order to resolve the correct origin of those classified as nonindigenous species.
... Both are thus difficult to intercept in visual censuses or trawl surveys, which have provided most of the data on benthic fishes on the Israeli shelf (e.g. Edelist et al., 2011Edelist et al., , 2013. ...
Article
The eastern Mediterranean marine ecosystem is undergoing massive modification due to biological invasions, overfishing, habitat deterioration, and climate warming. Our ability to quantify these changes is severely hindered by the lack of an appropriate baseline; most ecological datasets date back a few decades only and show already strong signatures of impact. Surficial death assemblages (DAs) offer an alternative data source that provides baseline information on community structure and composition. In this study, we reconstruct the marine fish fauna of the southern shallow Israeli shelf before the opening of the Suez Canal based on fish otoliths. We quantify the age of the otolith DAs by radiocarbon dating, and describe its taxonomic composition, geographic affinity, and trophic structure. Additionally, we test by radiocarbon dating the hypothesis that Bregmaceros, a presumed Lessepsian invader with continuous presence in the Mediterranean throughout the late Cenozoic, is a relict species. The otolith DA dates back to the mid-Holocene because 75% of the dated otoliths of the native species are older than the opening of the Suez Canal in 1869, suggesting that the DA is a proper baseline for quantifying modern impacts. Consistently, 97% of the otoliths and 88% of the species we collected belong to native Mediterranean species. The native anchovy Engraulis encrasicolus dominates the DAs, although gobiids are the most diverse group (14 species, 28%). The DAs show similar trophic structure to present-day pristine Mediterranean coastal fish assemblages. Two non-indigenous species are recorded here for the first time in the Mediterranean Sea, Amblygobius albimaculatus and Callogobius sp., highlighting the importance of DAs for detecting non-indigenous species. Finally, Bregmaceros otoliths are modern, not supporting the previous hypothesis that the taxon is a Pleistocene relict.
Article
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Of the 452 multicellular non-indigenous species (NIS) recorded off the Israeli Mediterranean coast, nearly 90% are considered to have been introduced through the Suez Canal (Erythraean NIS). The Israeli shelf serves as an important way station and breeding ground for Erythraean NIS, with 260 and 91 species already recorded in the greater Levant Sea and Central Mediterranean, respectively. The positive relationship between time since first record and spread indicates that Erythraean NIS populations may not be at equilibrium and are likely to spread further. Thus, the greater NIS numbers recorded in the past half century augur a sizable invasion debt. A review of the policy of the State of Israel concerning marine NIS, as reflected in recent official documents and regulations, reveals how these enhance their establishment, proliferation and spread in Israeli waters and in waters under the jurisdiction of other Mediterranean States. The continued role of the enlarged Suez Canal as corridor for invasion, and the increasing temperature of Mediterranean seawater , portend unceasing propagule pressure and likely rising establishment success of species not yet introduced. Recognition that factors driving the introduction and establishment of marine NIS are increasing, and the large-sized accrued invasion debt, impel us to urge the Contracting Parties to Barcelona Convention to undertake prevention and control measures to curb marine introductions into the Mediterranean Sea.
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Data on discards were collected during deep-water bottom seasonal trawling surveys targetting red shrimps (Aristeus antennatus and Aristaeomorpha foliacea) in the Ionian Sea (Eastern-Central Mediterranean). The performance of 3 codends, with stretched mesh sizes of 40, 50 and 60 mm, was tested. A cover with a stretched mesh of 20 mm was employed on each codend. The discarded catch constituted an important fraction of the total catch (20–50%). This was almost exclusively due to unwanted fish species, while discards of the target species and other commercial species were negligible. Discard rates increased with total catch and depth. No substantial differences were seen in the overall performance of the codends used. Differences were only detected in the biomass of the escaped fraction of the catch (both marketable and discards) and in the size selectivity. The 40 mm mesh size was not selective in Aristeus antennatus. Larger mesh size codend (50 and 60 mm) allowed a higher number of small specimens to escape. The 50% retention sizes increased according to the mesh size in all examined species.
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– After a general presentation of the characteristics of Mediterranean trawling, the principal problems raised by this technique are exposed, in particular in terms of selectivity and discards of exploited species, but also of protected species. Negative impact of trawling on the habitats, as well as increasing difficulties for the profitability of the trawlers, which require great power consumption, are also tackled. The second part of the paper presents the available solutions for improvement, in particular those upheld by the European Commission and the GFCM, associating technical and management measures for the fisheries. The conclusion insists more particularly on the need for establishing a stock management strategy taking account of the impact on the ecosystem and integrating the analysis of the problems arising in all fishing activities. RESUME – "Le chalutage en Méditerranée. Problèmes et options de sélectivité". Après une présentation générale des caractéristiques du chalutage méditerranéen, les principaux problèmes que pose cette technique sont exposés, notamment en termes de sélectivité et de rejets d'espèces exploitées, mais aussi d'espèces protégées. L'impact négatif du chalutage sur les habitats, ainsi que les difficultés croissantes pour la rentabilité des chalutiers qu'entraîne leur grande consommation énergétique, sont abordés. La seconde partie de l'article expose les solutions d'amélioration disponibles, notamment celles retenues par la Commission Européenne et la CGPM, associant mesures techniques et d'aménagement des exploitations. La conclusion insiste plus particulièrement sur la nécessité d'établir une stratégie de gestion des ressources tenant compte de l'impact sur l'écosystème et intégrant l'analyse de la problématique de l'ensemble des activités de pêche.
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The study was carried out in two fishing grounds on the Mediterranean continental shelf: one in the Adriatic Sea and one in the Catalan Sea. Samplings on board otter trawlers were performed from November 2002 to December 2003 in the Catalan Sea and from February 2003 to January 2004 in the Adriatic Sea. The Adriatic fishing ground was affected by high fishing intensity from January to June, while the Catalan area was highly exploited from September to February. Fishing activity in the Adriatic area was closed for 45 days, and 62 days in the Catalan area; both periods were in summer. Totals of 92 and 88 species were collected in the Adriatic and Catalan fishing grounds respectively. The species composition of the retained and discarded fractions showed close agreement between the two areas. Mullus barbatus showed very low discard fates in both areas, as well as Loligo vulgaris in the Catalan Sea and Merluccius merlaccius in the Adriatic Sea. In both fishing grounds Squilla mantis showed high catch rates with low discards, except in March in the Catalan area. In the Adriatic Sea Liocarcinus depurator was characterized by large discard fractions. In both fishing grounds the retained fraction was slightly higher in the high fishing intensity periods than in the low intensity ones (Adriatic Sea: 0.613 vs 0.524; Catalan Sea: 0.597 vs 0.539), even though the Kruskall Wallis test revealed significant differences (p<0.05) only for the Adriatic Sea.
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The opening of the Suez Canal unintentionally initiated an important event — the joining of two biogeographical provinces. For over 120 years, Red Sea species, migrating through the canal, have been colonizing the Mediterranean. The recent proliferation of a Red Sea jellyfish along the Levant coast highlights the profound changes in the indigenous biota.
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As part of two research projects for analysing bycatch and discards, we quantified catch composition, catch rates, bycatch and discards in two important commercial bottom trawl fisheries (crustacean and fish trawls) off the southern coast of Portugal (Algarve). Stratified sampling by onboard observers took place from February 1999 to March 2001 and data were collected from 165 tows during 52 fishing trips. Commercial target species included crustaceans: blue and red shrimp ( Aristeus antennatus ), deep-water rose shrimp ( Parapenaeus longirostris ), Norway lobster ( Nephrops norvegicus ); and fishes: seabreams ( Diplodus spp. and Pagellus spp.), horse mackerels ( Trachurus spp.) and European hake ( Merluccius merluccius ). The trawl fisheries are characterised by considerable amounts of bycatch: 59.5% and 80.4% of the overall total catch for crustacean and fish trawlers respectively. A total of 255 species were identified, which belonged to 15 classes of organisms (137 vertebrates, 112 invertebrates and 6 algae). Crustacean trawlers had higher bycatch biodiversity. Bony fish (45.6% and 37.8%) followed by crustaceans (14.6% and 11.5%) were the dominant bycatch components of both crustacean and fish trawlers respectively. The influence of a number of factors (e.g. depth, fishing gear, tow duration and season) on bycatch and discards is discussed.
Book
The book provides a historical sequence of events leading to the present-day Levantine biogeographical province with its impoverished freshwater and highly specific marine flora and fauna. A chapter on geological events in the Levant's early formative history is followed by one on Pleistocene changes (tectonics, chronology, marine biogeography, pluvials and interpluvials, and shifting rivers). The remainder of the book then examines the eastern Mediterranean (oceanography, zoobenthos and zooplankton, other biota, the Lessepsian migrants, and the impact of the Aswan high dam); the biota of the northern Red Sea and the Gulfs of Aqaba and Suez; halmyric or changing salinity environments; hydrology and limnology of the continental waters (the Jordan valley, Dead Sea, oasis springs, Lake Kinneret, river basin separation, Mesopotamia, the River Orontes, Ethiopia, Palearctic inftlux, the Lebanese rivers, Lake Hula, ephemerous waters, polluted and manmade waterbodies, etc). -J.W.Cooper
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The trash catch of an Egyptian Mediterranean trawling net was analyzed. The catch amounted to approximately 15-20 kg per haul, composed of three categories: Juveniles of commercially important species (86.5%), Low-value small size fish species (5.5%) and non-edible species (7.9% of the total trash catch). In the catch, 35 species were identified representing 22 families. Among these, 11 species are known to be of Red Sea origin. The amount of trash catch constituted about 15-20% of the total landing of trawling net. Three species, Diplodus annularis (recruit in July and August), Dicentrarchus punctatus (recruit in June and July) and Sardinella aurita (recruit in September and October) were the most abundant fish species representing 20.5%, 18.9% and 17.9% of the total trash respectively.
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A majority of the known Red Sea migrant fish species which colonized the eastern Mediterranean via the Suez Canal occupy a shallow sandy or muddy habitat in their target area. In the present work, the fish assemblage of the comparable habitat in the Red Sea was studied in order to assess whether there are criteria characterizing the source population of the colonizing species. The fish assemblage of the Red Sea sandy shore near Eilat was sampled repeatedly over a period of 2 years. Out of sixty-two species sampled, seventeen (27.4%) were among those colonizing the Mediterranean (`Lessepsian migrants'). The relative importance (IRI) of each of the sixty-two species in this assemblage was determined using frequency of occurrence and gravimetrical and numerical percentage in the samples. The Lessepsian migrant fish species were found to have high IRI values in the sandy shore which they inhabit throughout all their life stages, these characteristics being considered pre-adaptation for successful colonization of their target area, the eastern Mediterranea.