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Zoology in the Middle East
ISSN: (Print) (Online) Journal homepage: https://www.tandfonline.com/loi/tzme20
Fisheries bycatch and conservation priorities of
young sharks (Chondrichthyes: Elasmobranchii) in
the Eastern Mediterranean
Deniz Erguden, Hakan Kabasakal & Deniz Ayas
To cite this article: Deniz Erguden, Hakan Kabasakal & Deniz Ayas (2022): Fisheries bycatch
and conservation priorities of young sharks (Chondrichthyes: Elasmobranchii) in the Eastern
Mediterranean, Zoology in the Middle East, DOI: 10.1080/09397140.2022.2051916
To link to this article: https://doi.org/10.1080/09397140.2022.2051916
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Published online: 10 Mar 2022.
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Zoology in the Middle East, 2022
http://dx.doi.org/10.1080/09397140.2022.2051916
*Corresponding author. Email: deniz.erguden@iste.edu.tr
© 2022 Taylor & Francis
Fisheries bycatch and conservation priorities of young sharks
(Chondrichthyes: Elasmobranchii) in the Eastern Mediterranean
Deniz Ergudena,*, Hakan Kabasakalb and Deniz Ayasc
aMarine Sciences Department, Marine Sciences and Technology Faculty, İskenderun Technical
University, İskenderun, Hatay, Turkey; bIchthyological Research Society, Ümraniye, İstanbul,
Turkey; cFaculty of Fisheries, Mersin, Turkey
(Received 16 June 2021; accepted 15 February 2022)
Sharks are one of the most threatened groups of marine animals because of high exploi-
tation rates coupled with low resilience to fishing pressure. We provide information on
the current status of the young sharks caught in fishing nets in Iskenderun and Mersin
Bays in the eastern Mediterranean, based on fishery-dependent surveys conducted be-
tween 2010 and 2021. Sharks were found in bycatches in trawling nets, trammel nets,
bottom longlines and fishing lines. Incidental captures of young-of-the-year or juvenile
specimens (n=269) included 15 species and the data indicate that İskenderun and Mersin
Bays may serve as a nursery ground for the new-born and young individuals especially
for the Blackmouth Catshark (Galeus melastomus), the Lesser Spotted Dogfish (Scylio-
rhinus canicula), and the Velvet Belly (Etmopterus spinax). If necessary measures are
taken, bycatch can be reduced to a certain limit, or even eliminated for shark species in
the Mediterranean Sea.
Keywords: Turkey; cartilaginous fish; Blackmouth Catshark; Lesser Spotted Dogfish;
Velvet Belly; neonate; fishing pressure, conservation
Introduction
Elasmobranchs constitute an essential group in marine ecosystems, andmost elasmo-
branchs invest more into juvenile survival and growth (Frisk et al., 2001) rather than fe-
cundity (Cortés, 2002). Being apex predators, sharks play an essential role in the structure
and function of marine ecosystems, from higher to lower trophic levels (Camhi et al.,
1998). They are characterised by a k-selected life-history with slow growth rates, late
sexual maturity, low fecundity and a long life, resulting in low population increase rates
(Holden, 1974; Casey et al., 1985).
Generally, sharks are one of the most threatened groups of marine animals, as high
exploitation rates coupled with low resilience to fishing pressure have resulted in popu-
lation declines throughout the world. In many species, it can take years to recover when
their population decreases. Overfishing, habitat degradation, and slow recovery rates are
known potential factors that lead to dramatic declines of shark species (Dulvy et al.,
2014), especially in areas such as the Mediterranean Sea, where fishing activities have
long been a way of life and continue to be intense.
The ability to recover after population depletion depends on a combined effect of size
and preferred habitat. It was reported to be highest for small coastal sharks, intermediate
for pelagic, and minimal for large coastal species (Smith et al., 1998). From this perspec-
tive, the conservation of nursery areas are widely considered to be essential
Published online 10 Mar 2022
2 D. Erguden et al.
Figure 1. Locations (black triangle) of the occurrences of young shark specimens in Iskenderun and
Mersin bays.
(Heithaus, 2007; Heupel et al., 2007). Since shark nurseries have been defined as essential
habitats for breeding of a given shark species (Heithaus, 2007), the development of ap-
propriate management for nursery areas relies on the ability to accurately identify areas
of most significant importance (Heupel et al., 2007).
Since commercial or recreational fisheries are a major concern in some areas, partic-
ularly in nursery grounds, and there is a need for greater awareness that such bycatch
should be returned to the water alive (Fowler et al., 2005), identification and mapping of
such nursery grounds is of great significance before initiating efforts to raise public
awareness and implementation of conservation measures. Furthermore, according to
Fowler et al. (2005), due to the magnitude of the elasmobranch catch in commercial fish-
eries, there is a critical need for assessments to understand the multi-species nature of
multiple gear types. Therefore, this study is a first attempt to provide data both for under-
standing the implications of commercial fisheries on young populations of regional sharks
and the distribution of such individuals in Iskenderun and Mersin bays in the eastern
Mediterranean. We also attempt drawing attention to possible nurseries of shark species
in the region. This information should help understanding the fishing pressure on these
species and developing practical management plans for their conservation.
Material and Methods
Study area (Figure 1). Iskenderun Bay is located in the northern end of the Levant part of the
Mediterranean Sea with an area of approximately 2275 km2 and a width of 35 km. The bay has a
very wide continental shelf, and the depth within this region does not exceed 90 m (Erguden &
Turan, 2013). The bottom structure of the western parts of the Iskenderun Bay is primarily sandy
and muddy, while the eastern parts have a more rocky habitat. The topography of the coastline is
rich of several streams and rivers, where Asi and Ceyhan rivers are the major sources of freshwater
supplies into Iskenderun Bay. This area is rich in biodiversity and fisheries resources.
Mersin Bay is situated between Taşucu (36°18′N, 34°02′E) in the west and Karataş (36°32′N,
35°22′E) in the east. The total water surface is about 2300 km2. The deepest point is 365 m. The
western region of the bay is slightly deeper than the eastern region. The bay is the spawning and
breeding area for many fish species due to the wide continental shelf. The biodiversity of the Taşucu
and Yeşilovacık coast is affected by the migration of the fish species. Both areas are surrounded by
littoral shores, while sandy beach is located inside. These areas are covered with the sandy, muddy
sediment on the seafloor of the bay. At the same time, these areas have an anticyclonic gyre opposite
the cyclonic gyre, which is the main gyre of the Mediterranean Sea.
Zoology in the Middle East 3
Figure 2. Examples of young shark specimen, Alopias supercilious; which was incidentally cap-
tured off Turkish coast of eastern Mediterranean.
Sampling of shark individuals. Samples were collected through fishery-dependent surveys con-
ducted between 2010 and 2021. The regional commercial fisheries is characterised by the use of
different type of nets (trawling nets, trammel nets, bottom longlines and fishing lines). Trawl fishery
surveys were carried out on a commercial trawler (18–24 m and 420–480 hp main engines) during
daytime in stable weather and sea conditions. Catches of commercial trammel-netters, bottom long-
liners and hand-liners, landed at regional fishing ports were also examined on an opportunistic basis
to collect data on by-caught neonate and young sharks. This commercial fishery-dependent study
is a kind of opportunistic research, which is based on dead animal sampling, for methodological
details was given by Jessup (2003). The sampling process was not carried out in a regular time
interval. Juvenile sharks were collected by boat personnel or by an observer on the fishing vessel
and sent to the first author.
Definition of neonates, juveniles and nurseries. Following Castro (1993), neonates are post-
hatching or post-birth, free-swimming young bearing fresh, unhealed, or healing umblical scars in
the case of placental species, or those at or near birth size in the case of a placental or ovoviviparous
species. Juveniles are all the post-neonatal individuals prior to sexual maturation (Castro, 1993) and
nursery areas (nurseries) are geographically discrete parts of the species range where the gravid
females deliver their young or deposit their eggs, and where the young spend their first weeks,
months, or years. Size at birth and maturity of examined shark species are presented in Supplemen-
tary Table S1, based on Compagno (1984).
The identification and taxonomic nomenclature of juvenile sharks were carried out following
Serena (2005, 2020), Bariche (2012) and Kabasakal (2020). These records constitute the young
records of these shark species in the eastern Mediterranean coast of Turkey (Iskenderun and Mersin
Bays) (Figure 2).
Results
A total of 269 young shark specimens, representing 15 species in 11 families (Hexanchi-
dae, Lamnidae, Cetorhinidae, Alopiidae, Penthanchidae, Scyliorhinidae, Carcharhinidae,
Dalatiidae, Etmopteridae, Oxynotidae, and Squalidae) were obtained from fishing nets in
Iskenderun and Mersin Bays (Figure 2, Table 2). The most abundant species reported was
the Lesser Spotted Dogfish, Scyliorhinus canicula (n=134), comprising 49.8% of all spec-
imens, followed by the Velvet Belly, Etmopterus spinax (27.1%), the Blackmouth Cat-
shark, Galeus melastomus (11.9%), the Angular Rough Shark, Oxynotus centrina (2.2%),
Longnose Spurdog, Squalus blainvillei (1.8%), the Shortfin Mako, Isurus oxyrinchus
(1.8%), the Bluntnose Sixgill Shark Hexanchus griseus (1.8%), and the Sandbar Shark,
4 D. Erguden et al.
Table 1. Young sharks caught in Iskenderun and Mersin Bays in 2010 and 2021. Gear: FL = fishing
line; T = trawl; L = longline; TN = trammel net. MB = Mersin Bay, IB = Iskenderun Bay. TL: Total
length (in cm), Av: Average.
Family Species Nos. Date Gear Depth
(m)
TL Locations
Hexanchidae Heptranchias perlo 1 27.06.2014 T 601 105.0 MB: off Erdemli
Hexanchidae Hexanchus griseus 1
2
27.06.2014
20.03.2018
25.02.2019
T 300
200
90.0
350.0
N/A
MB: Taşucu coast-
Dana Island
1 12.01.2021 T 200 210.0 MB: Taşucu coast
Lamnidae Isurus oxyrinchus 2
25.03.2010-
30.03.2016
L 55-65
59.0-
69.8
IB: Samandağ coast
1 12.04.2018 L 73 75.0
MB: Taşucu coast-
Dana Island
1 05.02.2020 L 67 70.0 MB: Taşucu coast
1 10.02.2021 L 70 73.0
MB: Taşucu coast-
Dana Island
Cetorhinidae Cetorhinus maximus 1 20.03.2014 TN 25
245.0 MB: off Yeşilovacık
Alopiidae Alopias vulpinus 1 09.03.2019 TN 38 250.0 MB: Erdemli coast
Alopias superciliosus 1 02.01.2020 TN 25 240.0 MB: Taşucu coast
Penthanchidae Galeus melastomus 14
17.05.2014 T 500
32.5-
67.0
MB: off Erdemli
1 May 2018 T 641 19.0 MB: off Erdemli
17 13-
15.05.2020
T 450
18.5-
24.5
MB: off Erdemli
Scyliorhinidae Scyliorhinus canicula 49 17.05.2014 T 500 28.0-
42.5
MB: off Erdemli
85 May 2018 T 641 30.0-
33.5
MB: off Erdemli
Carcharhinidae Carcharhinus altimus 1 20.07.2019 L 25 65.2 MB: Göksu
C. brevipinna 1 Feb. 2019 L 20 115.0 MB: Göksu
C. plumbeus 2
1
25.10.2014
26.12.2019
L 42
40
62.0-
65.0
IB: Arsuz coast
Dalatiidae Dalatias licha 1
11.06.2016 L 40 118.0 IB: Çevlik coast
Etmopteridae Etmopterus spinax 60
2
17.05.2014
25.06.2014
09.07.2019
T 601
595
15.0-
30.5
MB: off Erdemli
11 14-
17.05.2018
T 641
Av.
17.25
cm
MB: off Erdemli
Oxynotidae Oxynotus centrina 4 17.05.2014
25.06.2014
T 600
40.3-
46.0
MB: off Erdemli
1 05.10.2018 FL 25 39.0
MB: Göksu River
estuarine
1 13.05.2020 T 450 50 MB: off Erdemli
Squalidae Squalus blainvillei 5 17.05.2014
25.06.2014
T 301
27.5-
65.0
MB: off Erdemli
Zoology in the Middle East 5
Figure 3. Occurrence of incidentally captured young sharks by families, examined in the present
study.
Figure 4. Bathymetric distribution of incidentally captured young sharks, with respect to numbers
of specimens.
Carcharhinus plumbeus (1.2%). Other sharks (Table 1) were represented at the rate of as
0.4%.According to these bycatch data, the family with the highest number of young in-
dividuals is Scyliorhinidae (n=134, 49.8%) (Figure 3).
In bottom trawl fishery, 254 individuals of 7 species were accidentally caught with
trawl nets. Hexanchus griseus was caught at 200–300 m depth contour range (N=4), Squa-
lus blainvillei at a depth of 301 m (N=5), Oxynotus centrina at depths of 450 m (N=1)
and 601 m (N=4), the latter together with one individual of Heptranchias perlo; two in-
dividuals of Etmopterus spinax were caught at 595 m, 60 at 601 m and 11 at 641 m
10 5315
81
6
158
0
20
40
60
80
100
120
140
160
180
0-50 51-100 101 -200 201-300 301-400 401-500 501-600 >601
Number of Individuals
Depth (m)
6 D. Erguden et al.
Figure 5. Global Red List status of the shark species found in the Eastern Mediterranean coast.
Categories are abbreviated as: EN- Endangered; NT- Near Threatened; VU-Vulnerable; LC-Least
Concern; DD-Data Deficient.
depth contour; 17 individuals of Galeus melastomus were caught at 450 m, 14 at 500 m
depth and one at 641 m depth. Forty-nine individuals of Scyliorhinus canicula were
caught at 500 m depth and 85 at 641 m depth contour (Figure 4).
Eleven sharks belonging to five species were obtained in the long-line fishery: Isurus
oxyrinchus (N=2 at 55-65 m), Carcharhinus plumbeus (N=3 at 40-42 m), Dalatias licha
(N=1 at 40 m); I. oxyrinchus (N=3 at 67-73 m), C. altimus (N=1 at 25 m) and C. brevi-
pinna (N=1 at 20 m) (cf. Figure 4).
In the gill-net fishery, one individual of Cetorhinus maximus was accidentally caught
at 25 m depth, one individual of Alopias superciliosus at a depth of 25 m, and one indi-
vidual of A. vulpinus at 38 m depth. Regarding Oxynotus centrina, one individual was
hooked at the Göksu River mouth (Mersin Bay) (Figure 4).
Based on Global Red List status of the examined species (IUCN, 2021), 40 percent of
the incidentally captured young sharks are considered as “Vulnerable” species (n=6), fol-
lowed by “Near Threatened (20%; n=2)”, “Least Concern (20%; n=2)”, “Endangered
(13%; n=2)” and “Data Deficient (7%; n=1)” species (Figure 5).
Discussion
There is no targeted fishery for shark species in Iskenderun and Mersin bays and all sharks
examined were incidentally caught by trawlers or bottom long-liners.
Yaglioglu et al. (2015) reported seven shark species (Carcharhinus plumbeus, C. al-
timus, Isurus oxyrinchus, Mustelus mustelus, Scyliorhinus canicula, S. stellaris, Squatina
squatina) in bottom trawl fishery in the Iskenderun Bay at depths between 50 and 100 m
for. However, they sampled S. canicula and S. stellaris from greater depths than in the
present study and they also reported that Oxynotus centrina and Galeus melastomus were
recorded in trawl catches, hauled at depths >100 m.
Elasmobranch bycatch in fisheries has become one of the main sources of population
declines. Juvenile sharks are caught in large numbers in longline, purse seine and trawl
Zoology in the Middle East 7
fisheries, contributing to long-term declines in populations that may not be immediately
apparent (Campbell & Corwell 2008; Damalas & Vassilopoulou, 2011; Favaro & Coté,
2015). The actual amount of shark bycatch in fisheries is difficult to determine due to a
lack of reporting or underreporting at both the fishermen and national levels, even in reg-
ulated fisheries. According to Dulvy et al. (2021), overfishing is the sole threat for 67.3%
of elasmobranch species, and science-based limits on fishing, effective marine protected
areas, and approaches that reduce or eliminate fishing mortality are urgently needed to
minimize mortality of threatened species.
From a biological perspective, large sharks are characterised by K-selected life history
traits, including slow growth, late onset of sexual maturity, low fecundity and remarkable
longevity, all of which leading to low rates of population increase (Fowler et al., 2005).
Such fragile life histories make large sharks highly vulnerable to overexploitation, which
was recently demonstrated in a large-scale Mediterranean case study (Ferretti et al.,
2008). Thus, once their populations depleted, recovery may take several decades or
longer. Besides, these species are extremely vulnerable to habitat degradation and to-
gether with overexploitation, this may result in dramatic declines in their populations
(Frisk et al., 2002; Ferretti et al., 2008; Bradley & Gaines, 2014; Peristeraki et al., 2020).
Myers and Worm (2005) estimated that sharks had twice the risk of extinction in fishing
operations compared to bony fish. Many sharks and rays are being considered vulnerable,
threatened, endangered, or critically endangered in the Mediterranean waters (Otero et
al., 2019). Among the 85 species known in the Mediterranean, only 73 were assessed
within the framework of the International Union for Conservation of Nature (IUCN) Red
List. Despite this high biodiversity, the Mediterranean Sea shows more significant con-
servation concern for chondrichthyans than the rest of the world, as reported by the last
IUCN Regional Red List assessment, which listed more than half of the 73 evaluated
species as threatened (Dulvy et al., 2016). In addition, 16 species (13 shark and three ray
species) are still considered data deficient “DD” (Otero et al., 2019).
Historically, many sharks have low commercial value and are not regularly recorded
in fishing statistics. For this reason, detailed capture or survey data are often lacking
(Dulvy & Reynolds, 2002; Clarke et al., 2006), and also population changes are not well
documented for many shark species in Mediterranean waters.
Traditional commercial fisheries have exploited many small bottom-living coastal
sharks and skates, and have recently increased their exploitation efforts of deep-water
sharks, both as target and utilised bycatch in multi-species fisheries. This situation is es-
pecially serious for shark species that are regarded as vulnerable to exploitation.
Iskenderun Bay and the neighboring Mersin Bay are important fishing grounds with
regards to pelagic swordfish drift lines and drift nets, and demersal trawl fisheries. At
least for the last decade, the importance of the region with regards to marine aquaculture
has been significantly rising. Recently, newborn and young-of-the-year (YOY) speci-
mens of several elasmobranch species were recorded in previous studies (Basusta et al.,
2021; Erguden et al., 2020).
Bycatch is one of the most significant issues in the management and conservation of
global fisheries and has been known as one of the leading causes of shark population
declines (Hall et al., 2000; Lewison et al., 2004; Peristeraki et al., 2020). Up to date, the
Eastern Mediterranean is not in a good state of conservation due to the high effects of
fishing (target and bycatch), which causes a significant decline in the number of sharks
day by day. Therefore, the present study contains important data in terms of focusing on
the incidental captures of young sharks in the region by fishing activities and reconsider-
ing fishing regulations in the region.
8 D. Erguden et al.
Based on the data on the incidental captures of young-of-the-year and juvenile speci-
mens (n=269; 15 species), between 2010 and 2021, it was suggested that İskenderun and
Mersin bays may serve as a nursery ground for several shark species. Since nursery
grounds are essential habitats, and may serve as a growing and feeding ground for juve-
niles until maturity, a long-term monitoring program is required to provide the necessary
conservation for sharks in this valuable nursery area and to detect spatio-temporal
changes. Cooperation between policymakers, fishers, conservationists, and researchers
are necessary to significantly reduce the threat of bycatch and help sharks gain a chance
at recovery.
Supplementary Material
Supplementary Material is given as a Supplementary Annex, which is available via the “Supple-
mentary” tab on the article’s online page.
Acknowledgements
The authors thank the boat captain and staff for their friendly cooperation during field surveys and
sampling.
Disclosure Statement
No potential conflict of interest was reported by the authors.
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