Elasmobranchs in Tunisia: Status, Ecology, and Biology

*Samira Enajjar, Bechir Saidi and Mohamed Nejmeddine Bradai*

#### **Abstract**

The authors have compiled published information on taxonomy, distribution, status, statistics, fisheries, bycatch, biologic, and ecologic parameters mainly on food and feeding habits and reproductive biology of elasmobranchs along the Tunisian coasts. This bibliographic analysis shows that cartilaginous species, including sharks and rays are by far the most endangered group of marine fish, with 63 species, about 53% of all are critically endangered, endangered, or vulnerable. Overfishing, fishing practices, and habitat degradation are leading to dramatic declines of these species. Biologic parameters concern a few species primarily in the Gulf of Gabes. Therefore, recommendations to fill gaps in order to protect and manage elasmobranchs stocks are proposed in this chapter.

**Keywords:** status, elasmobranchs, Tunisia, bibliographic analysis

#### **1. Introduction**

The Mediterranean Sea is known to be an important habitat for elasmobranchs with at least 48 sharks and 38 batoids species [1]. However, the region is a hotspot of extinction risk [2]. It has been demonstrated that sharks in the Mediterranean Sea have declined by more than 97% in number and "catch weight" over the last 200 years [3]. This situation driven a regional and a global rising concern about shark conservation and management [4].

Tunisian coasts (Central Mediterranean Sea) are characterized by their sharks and rays diversity [5, 6]. The region is known to be an important habitat for this group and a breeding grounds for many species such as the sandbar shark (*Carcharhinus plumbeus*) [7–9]. Like the rest of the Mediterranean, Elasmobranchs in Tunisia are subject to an increasing pressure due to the anthropogenic activities mainly fisheries [10]. The emerging picture illustrates a decline of several elasmobranch populations [11]. Nevertheless, investigation on management and conservation on elasmobranch have received little attention [12].

Elasmobranchs are vulnerable to fishing mortality owing to their life histories characteristics, such as low fecundity, late maturity, and slow growth rates [1]. Accordingly, information on biology, ecology, fishery, distribution, and population structure is required for suitable management and conservation of this group. Unfortunately, the investigations research related to these creatures is quite recent, it started by the end of the 1990s when landings declined, and some species became threatened [6].

Along Tunisian coasts, research interested on elasmobranch has started in early 1970. Although the studies relating to this group of fish are maintained until today, several gaps still exist for an adequate management of catches and sustainable conservation.

The aim of the present chapter is to review and analyze the research publications relating to elasmobranch species along the Tunisian coasts in order to appreciate the main gathered information and gaps. In addition, this analysis will guide our future research in order to acquire the essential information indispensable for an adequate conservation of this group.

#### **2. Study area**

Tunisia, with 2290 km of coastline, constitutes a transition zone between the eastern and western basins of the Mediterranean [13]. The Tunisian marine coasts include the FAO-GFCM Geographical Sub Areas (GSA) 12, 13, and 14 (**Figure 1**).

The northern coasts (GSA 12) are characterized by a turbulent underwater morphology, an alternation of hard, and soft bottom and a steeply sloping continental shelf. This diversity of biotopes gives them a high biodiversity. Among the 327 fish species listed in Tunisian waters, 270 were recorded in the Northern coast [5].

**Figure 1.** *GFCM geographic subareas off Tunisian coasts.*

The eastern region of Tunisia (GSA 13), corresponding to the Gulf of Hammamet, begins with a narrow continental shelf (the -50 m isobath is located quite far from the coast), bordered by the Siculo-Tunisian channel and gradually widening from north to south of this region. The seabed of the area provides a transition between the northern and southern Tunisia [14, 15].

The GSA14, corresponding sensu lato to the Gulf of Gabes, represents the southern part of the Tunisian coast [16]. This region is characterized by a significant tidal phenomenon and an extended continental shelf. The presence of extensive seagrass meadows and the ease of access to fishing areas rich in species of high commercial value makes this region one of the most important maritime fishing areas in Tunisia.

The area is a high spot for marine biodiversity of regional importance. It constitutes a preferential habitat for several emblematic vertebrates: a wintering and feeding area for the Loggerhead Sea Turtle (*Caretta caretta*) [17], a nursery for several species of elasmobranchs, some of which are threatened [9–12], and a favorable area to several fish such as the groupers and tunas. Cetaceans, especially bottlenose dolphin (*Tursiops truncatus*) and the fin whale (*Balaenoptera physalus*), are regularly encountered [18, 19].

#### **3. Elasmobranchs landing**

In Tunisia, the elasmobranchs species are caught as bycatch. Nevertheless, some species such as the sandbar shark and the smooth hound are targeted by a small artisanal fishery in the southern coast of the country during the summer [20]. This fishery uses a specific gill nets locally called "Garracia" and "Gattatia".

Elasmobranchs represent an average of 2% of the national landing [21]. According to FAO Statistic, a mean of 2370 tons' year is landed during the last 20 years (2000– 2020). The production shows an increasing trend, although some exceptional decrease is noted during 2012 and 2017 (**Figure 2**)**.**

**Figure 2.** *Tunisian elasmobranchs production according to FAO statistics from 2000 to 2020.*

#### *Sharks - Past, Present and Future*

The Gulf of Gabès region (GSA 14) is known to be the most important area for sharks and rays in Tunisia, contributing by more than 60% in the landing of elasmobranchs [10]. However, during the last years, the statistics data provided by the General Directorate for Fisheries and Aquaculture (GDFA) between 2008 and 2020 show an increase in landing of elasmobranch of the Eastern region (GSA 13) (**Figure 3**). This area contributed in 2020 by more than 49% in the Elasmobranchs national production.

Along the Tunisian costs, elasmobranchs are landed mainly by small-scale vessel using gillnets, trammel nets, and longlines followed by bottom trawl (**Figure 4**)**.**

**Figure 3.** *Tunisian elasmobranchs production by GSA according to GDFA statistics from 2008 to 2020.*

**Figure 4.** *Tunisian elasmobranchs production by fishing gear according to GDFA statistics from 2008 to 2020.*

#### **4. Diversity and status**

The list of elasmobranchs species occurring in Tunisian waters is established mainly by the authors and bibliographic analysis over the last 20 years. Species are classified according to four categories: very common, common, rare, and very rare. The analysis of data shows the occurrence of 63 elasmobranchs species in the area: 37 sharks belonging to 17 families and 26 batoids belonging to eight families (**Table 1**). This number reflected the specific richness on species in the area (71.6% of species signaled in the Mediterranean Sea).

Four species cited in the literature are not considered in this list because their record seems to be doubtful or not observed during the study period: the cuckoo ray (*Leucoraja naevus*)*,* the African ray (*Raja Africana*), the spiny dogfish (*Squalus acanthias*), and the porbeagle (*Lamna nasus*). However, three species were observed for the first time in the area during the study period: the shortnose spurdog (*Squalus megalops*) [22]*,* the little sleeper shark (*Somniosus rostratu*s) [23], and the bigeye thresher (*Alopias superciliosus*) [24].

The spinetail devil rays (*Mobula japonica*) signaled in the area in 2015 [25] are not considered in this list because it was assessed by many authors as a junior synonym of the devil fish (*Mobula moblar*) [26, 27]. No proofs to support the hypothesis of two different species were demonstrated.

Among elasmobranchs species occurring in Tunisian coast, only three species were very common in all sub-area; species caught very frequently throughout the region along the year; the smooth hound (*Mustelus mustelus*), the common torpedo (*Torpedo torpedo*), and the thornback ray (*Raja clavata*). Five species were common; species captured in more or less abundant quantities in at least one sector of the region and during a period of the year; the shortfin mako (*Isurus oxyrinchus*)*,* the marbled electric ray (*Torpedo marmorata*)*,* the brown ray (*Raja miraletus*)*,* the round stingra (*Taeniura grabatus*) and the blackspotted smooth-hound (*Mustelus punctulatus*).

The southern waters of Tunisia were characterized by the presence of costal species: the blackchin guitarfish (*Glaucostegus cemiculus),* the common guitarfish (*Rhinobatos rhinobatos*), and the spiny butterfly ray (*Gymnura altavela)*, whereas deep species were found mainly in northern zone: the Velvet belly (*Etmopterus spinax*), the kitefin shark (*Dalatias licha*)*,* and the little gulper shark (C*entrophorus cf. uyato).*

The number of species recorded in each GSA are almost comparable: 51 species in GSA 12 and 14 and 52 in GSA 13.

According to IUCN red list, more than 52% of elasmobranch species observed in Tunisian waters were threatened (Critically endangered, endangered, and threatened). Thirteen species were data deficient, not evaluated, or not applicable (**Figures 5** and **6**).

#### **5. Available data on elasmobranchs (Bibliographic analysis)**

Two hundred and fifty-four references concerning elasmobranch species off Tunisia were published between 1971 and 2022. The temporal distribution of publications indicated that attention on elasmobranch has started in 1970. However, there is a lack of studies in the area during the period from 1980 to 1999. Since 2000, an interest in research on elasmobranchs is noticed in the area (**Figure 7**), following the emergence of an international concern for the conservation of this group of fish. However, studies concern mainly species of the southern (GSA 14) and northern coasts of the





#### **Table 1.**

*Diversity and status of elasmobranchs species occurring in Tunisian water during the last 20 years.*

country (GSA 12). Only 10 publications covered the Eastern coast (GSA12) (**Figure 8**). Some studies concern all Tunisian coasts because of the uses of samples from all the countries without distinction between GSA.

Studies concern essentially biology (sexual maturity size, reproductive cycle, size at birth fecundity, etc.), ecology (diet composition, frequency of prey, etc.), and growth (Von Bertalanffy growth parameters, age at maturity, , etc.). Recently, an attention to the impact of fishery, bycatch, and systematic were observed [11–20, 28–30] (**Figure 9**).

*Elasmobranchs in Tunisia: Status, Ecology, and Biology DOI: http://dx.doi.org/10.5772/intechopen.108629*

**Figure 5.** *Species status according to IUCN red list classification.*

**Figure 6.**

*Some vulnerable species captured accidentally in Tunisia. 1:* Isurus oxyrinchus*; 2:* Gymnura altavela*; 3:* Alpoias vulpinus*; 4:* Aetomylaeus bovinus*; 5:* Raja radula.

#### **5.1 Available data on reproduction**

Elasmobranchs are a vulnerable group because of their life histories including the late maturity, the low fecundity, and a long reproductive cycle [31]. Reproductive parameters are crucial to develop conservation strategies and management plan. In Tunisia, data on reproductive parameters are available for 39 species (**Table 2**). However, recent data concern only 16 species. Among them, six species are listed in annex II and III of the of the SPA/BD Protocol to the Barcelona Convention. Reproductive studies related to GSA 13 are scare. The main reproductive parameters are listed in **Table 2**.

**Figure 7.**

*Temporal distribution of the number of published papers dealing with elasmobranchs in Tunisia.*

**Figure 8.**

*Geographic distribution of elasmobranchs paper in Tunisia according to GFCM sub-area (1971–2022).*

#### **5.2 Available data on age and growth**

The age and growth parameters of a population are very important for conservation and management plans [34]. The parameters are used for the determination of natural mortality and longevity and, ultimately for the calculation of vital rates in demographic models [35].

**Figure 9.**

*Distribution of elasmobranchs paper by topic in Tunisia (1971–2022).*

For age determination of elasmobranchs in Tunisia, vertebral sections and dorsal spines are used (**Figure 10**). These structures tend to accumulate calcified growth material as they age, thus producing concentric areas that often have characteristics reflecting the time of year in which this material is being deposited [36].

The age and growth studies in Tunisia are recent. They concern the south coast of the country (GSA 14). Age and growth data presented in this section include parameters of the Von Bertalanffy growth model (VBGM) (von Bertalanffy 1938) of eight species: three viviparous species and five oviparous species (**Table 3**).

#### **5.3 Available data on food and feeding habits**

Studies of feeding habits are essential to understand the functional role of fish in the ecosystem. Data on feeding can provide information on species distribution and its position in food webs.

Sharks are considered top predators and have an important role in the marine ecosystems. Information about the food habits is essential to appreciate the species biology and ecology, since the quality and quantity of food directly affect species maturation and growth.

In Tunisia, available data on food and feeding habits concern 24 species. Among them 16 species were subject of recent studies mainly in Gabes Gulf (GSA 14). Information on diet composition are summarized in **Table 4**.

#### **5.4 Available data on fishery and by catch**

The studies on fisheries and bycatch of elasmobranchs in Tunisia are recent. The first study back to 2003 [113] (**Figure 11**)**.** The low economic value of this group's products compared to bony fishes, crustacean, and mollusk has resulted in a lower priority for research and conservation of these species in Tunisia. It is to highlight that


*Elasmobranchs in Tunisia: Status, Ecology, and Biology DOI: http://dx.doi.org/10.5772/intechopen.108629*


#### **Table 2.**

*Reproductive parameters of elasmobranch species in Tunisia. TL: Total length, disk width.*

some other projects studying bycatch are currently in execution in Tunisia as the "Medbycatch" project.

In Tunisia, elasmobranchs are caught accidentally by all fishing gear (trawl, trammel net, longline, purse senne, etc.) and as a targeted species during the summer by a specific gill nets in the southern coast (GSA 14).

#### *5.4.1 Bycatch of elasmobranchs by longline*

In the frame of ACCOBAMS-GFCM Project on mitigating interactions between endangered marine species and longline fishery in Zarzis (GSA 14), developed with the collaboration of the RAC/SPA and a substantial financial support from the MAVA foundation, results show that 46% of the production of the bottom longline targeting groupers are elasmobranchs. Eight sharks and nine batoids are caught by bottom longline. Among elasmobranchs species captured the blackchin guitarfish (*Glaucostegus cemiculus*), the hound sharks (*Mustelus spp*.), the Shortnose spurdog (S. megalops), the sandbar shark (*C. plumbeus*) and the stingray *(Dasyatis spp.*) were the most caught [114, 115] (**Figure 12**).

Elasmobranchs represent more than 90% of the capture of pelagic longline in the southern coast of Tunisia. Nine elasmobranch species were captured by this gear (Sandbar shark, spinner shark, shortfin mako shark, smooth hound, pelagic stingray, blackchin guitarfish, bull rays, round stingray, and thornback ray). The captures were dominated by the sandbar shark accounting about 82.5% of capture [11, 114, 115] (**Figure 13**)**.**

#### *5.4.2 Bycatch of elasmobranchs by trammel nets*

Landing monitoring of boat using shrimp's trammel nets in Sfax port during May, June, and July 2009 shows that seven species elasmobranchs (*M. mustelus*, *Mustelus*

#### **Figure 10.**

*A thin-section of a longnose spurdog spine and a blackchin guitarfish vertebra from the Gabes Gulf (GSA 14).*

*punctulatus*, *Dasyatis pastinaca*, *Dasyatis marmorata,T. torpedo, C. plumbeus*, and *Carcharhinus brevipinna*) were caught as by-catch in GSA 14. Elasmobranch by-catch was dominated by sharks (90.3%). The smoothhound sharks *Mustelus spp.* being by far the most important (88.9%) and reflecting their abundance in the area; 58% of the sets caught at least one specimen. Captures were composed essentially of neonate and juvenile sharks, while the batoids were dominated by mature individuals [28].

#### *5.4.3 Bycatch of elasmobranchs by trawl*

Monitoring of trawler fishery in the Gulf of Gabes during 2009 shows that Elasmobranchs are commonly caught as by-catch by bottom trawlers in the Gulf of Gabes (GSA 14). A total of 31 elasmobranch species was recorded in trawl captures, among them 14 sharks and 17 batoides representing 64.58% of elasmobranch species observed in the area. Elasmobranch bycatch averaged 5.42% of the total landing

*Elasmobranchs in Tunisia: Status, Ecology, and Biology DOI: http://dx.doi.org/10.5772/intechopen.108629*


#### **Table 3**

*Von Bertalanffy growth model (VBGM) parameters: L*∞*: cm (TL), k: (year-1), t0 (years); tmax: oldest fish (years), Amat: age at maturity (years).*

(1.7% sharks and 3.7% batoides). The CPUE was estimated at 0.8 Kg/haul for all elasmobranchs. Sharks represented 0.27 Kg/haul and batoides constituted 0.54 Kg/haul. Specimens caught were mainly juveniles [116].

#### *5.4.4 Bycatch of elasmobranchs by purse seine*

The purse seine caught a very low proportion elasmobranch especially pelagic sharks and rays. *Mobula mobular*, *I. oxyrinchus*, and *Alopias vulpinus* were the most reported species [117, 118].

#### *5.4.5 Specific fishery*

From March to August and between Jerba Island and Zarzis (Southern Tunisia, GSA14) adults of the blackchin guitarfish, the smouth-hound shark, and the sandbar shark are targeted by a little flotilla of small-scale vessel using specific gillnets called locally "Gattatia" and "Garracia"; "Gattatia" for smouth-hound sharks and "Garracia" for Blackchin guitarfish and sandbar shark. Gillnets are in polyamide monofilament netting with a stretched mesh size of 120–160 mm for the first one and 300–400 mm for the second gillnet type. These nets are used at 5–30 m depth. Size composition of captures varied by species, but usually mature, mainly gravid females were abundant [20] (**Figure 14**).

#### *Sharks - Past, Present and Future*


*xxx: Main preys, xx: Secondary preys, x: Accessory preys, \*: Accidental preys, fish: Teleost fishes, chon: Chondrichtyens, Mol: Mollusks, an: Annelids, Cr: Crustaceans, other: Other invertebrates.*

#### **Table 4.**

*Diet composition of elasmobranch species from Tunisia.*

#### **6. Critical area**

Elasmobranch nurseries are areas characterized by the presence of neonates, small juveniles, and pregnant females. This area offers a better source of food and protection against predation; overall, they are located in coastal, shallow, and highly productive waters. At least four elasmobranch species were perceived use the coastal water of the southern coast of Tunisia (GSA 14) as nursery (**Figure 15**)**.** *C. plumbeus*, *M. mustelus, R. rhinobatos,* and *Rhinobatos cemiculus* use the area as a year-round primary and secondary nursery, with juveniles remaining in it up to the size at maturity [7–9].

**Figure 11.** *Temporal distribution of published papers dealing with fishery and bycatch of elasmobranchs in Tunisian coast.*

#### **Figure 12.**

*Elasmobranchs catch rates in the bottom longline in Zarzis zone.*

#### **7. Regulations for the protection of elasmobranchs in Tunisia**

Tunisia ratified many international conventions dealing with cartilaginous fishes and biodiversity in general (**Table 5**) and adopted the GFCM recommendations on the management and conservation of sharks and rays in the GFCM area of application (Rec. GFCM/36/2012/3; Rec. GFCM/42/2018/2).

The protection of elasmobranchs species is ensured at the national level by the decree n° 94–13 on July 31, 1994 and the decree of September 28, 1995 of the Minister

**Figure 13.** *Catch composition of pelagic longline in Zarzis zone [33].*

**Figure 14.** *Length-frequencies distribution of elasmobranch species caught by gillnet [20].*

*Elasmobranchs in Tunisia: Status, Ecology, and Biology DOI: http://dx.doi.org/10.5772/intechopen.108629*

#### **Figure 15.**

*Nursey area of some elasmobranchs in Gabes Gulf.*


#### **Table 5.**

*International conventions ratified by Tunisia.*

of Agriculture regulating the practice of fishing activities. The former one is currently being amended to mainly consider the conventions ratified by Tunisia and the recommendations of the CGPM.

#### **8. Recommendations**

Sharks and rays occupy a high level in the trophic webs and are characterized by a K-strategy. This determines a high sensibility to fishing pressure. To conserve the biodiversity of this emblematic groups, many actions should be ensured in Tunisia and in the Mediterranean as many species are migratory.

To overcome this situation, it is necessary to improve data collection at sea and at land for a global map of species distribution and for effective landing statistics in all

Tunisian coast; statistic data must be done by species or at least by group of species. For this, it is necessary to focus on species identification trainings and to develop studies on systematic, launched a monitoring to delimit critical area for elasmobranchs in the area and to determine the discard quantity of elasmobranchs by different fishing gear. Experimentation of mitigation measures must be enlarged.

Developing of stock assessment studies; some knowledge on biologic parameters is now available and on fishery; at regional levels because of the urgent need for protection of these groups. Likewise, undertake studies on migration and exchange between populations by satellite tracking.

#### **9. Conclusions**

Elasmobranchs represent an average of 2% of the Tunisian national fish production. According to FAO statistics, a mean of 2370 tons per year is landed during the last 20 years. They are landed mainly by small-scale vessels using gillnets, trammel nets, and longlines followed by trawling.

Two hundred and fifty-four references, dealing with elasmobranchs in Tunisia, were analyzed in this chapter.

This analysis shows that 63 elasmobranchs occurred in the area during the last 20 years: 37 sharks belonging to 17 families and 26 batoids belonging to eight families. Three species were observed for the first time in the area during the considered period: *S. megalops, S. rostratus*, and *A. superciliosus.* The southern waters of Tunisia were characterized by the presence of costal species, whereas deep species were found mainly in northern zone. More than 52% of elasmobranchs species observed in Tunisian water were criterial endangered, endangered, or threatened. The Gabes Gulf represents an important area for elasmobranchs, four species use the coastal water of the area as a nursery.

In Tunisia, information on reproduction is available for 40 species. However, recent data concern 16 species. Studies on age and growth concerned only species from the south coast of the country (GSA 14). Von Bertalanffy parameters are available for eight species. Concerning food habits, recent data concern 16 species. Therefore, it is urgent to initiate the study of the age and growth of other species.

Bycatch has become one of the issues to be considered in any development of fisheries. Elasmobranchs which are considered mainly as bycatch are very sensitive given their particular biological characteristics. In Tunisia, trammel nets and trawl in the area cause the capture of juveniles while specific gillnets engender the capture of adults and mainly pregnant females.

*Elasmobranchs in Tunisia: Status, Ecology, and Biology DOI: http://dx.doi.org/10.5772/intechopen.108629*

#### **Author details**

Samira Enajjar<sup>1</sup> \*, Bechir Saidi<sup>2</sup> and Mohamed Nejmeddine Bradai<sup>1</sup>

1 National Institute of Science and Technology of the Sea, R16INSTM02 Marine Biodiversity Laboratory, Carthage University, Sfax, Tunisia

2 Faculty of Sciences and Techniques of Sidi Bouzid, Kairouan University, Sidi Bouzid, Tunisia

\*Address all correspondence to: enajjarsamira@yahoo.fr

© 2022 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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#### **Chapter 2**

## Overview of the Genus *Squalus* in the Mediterranean Sea

*Sondes Marouani, Sami Karaa and Othman Jarboui*

#### **Abstract**

In the Mediterranean Sea, in addition to the two historically known species belonging to the *Squalus* genus (*Squalus blainville* and *Squalus acanthias*), a third species, *Squalus megalops*, has been reported. This last specie is a subject of debate between authors. *S. acanthias* is quite distinct from the other species of the genus *Squalus*, while S. *blainville* and *S. megalops* are very similar morphologically. This similarity has resulted in considerable confusion over their taxonomy. The lack of a well-preserved holotype for *S. blainville*, misidentifications in databases and in the literature, description, and figure of Risso (1827) not conforming to any known species of *Squalus* are impediments to the proper taxonomic identification and the potential revision of the genus. This chapter aims to clarify the state of the species of the genus *Squalus* in the Mediterranean Sea, taking into account all the studies carried out on this subject.

**Keywords:** sharks' misidentification, *squalus* genus, *Squalus blainville*, *Squalus acanthias*, *Squalus megalops*, Mediterranean Sea

#### **1. Introduction**

The Mediterranean Sea is a semi-enclosed sea covering less than 1% of the surface of the global oceans, even though it constitutes a general richness hotspot of total species on a global scale [1, 2]. This richness of cartilaginous and bony fishes is likely the result of the recolonization of the Mediterranean basin after the Messinian crisis. As demonstrated for the great white shark [3], pulses of species immigrations occurred during the glacial and interglacial periods of the quaternary [4].

It is a heterogeneous biogeographic area that shows a high level of biological diversity. This sea constitutes a complex marine ecosystem within which elasmobranchs play a basic role in controlling trophic relationships [5]. This is related to multiple factors from its geological history to its peculiar oceanographic and ecological features [6].

The Mediterranean Sea is considered a Chondrichthyes-rich basin. Recently, a total of 88 chondrichthyan species were listed, representing 30 families and 48 genera in the area [6]. This list includes 48 species of sharks, belonging to 18 families and 27 genera, 38 species of batoids, belonging to 11 families and 19 genera, and two chimeras belonging to two different genera.

Despite its richness, it encloses the highest proportion of threatened species in the world [7], in the Mediterranean Sea, where at least 53% of the species are classified

by the IUCN as vulnerable, endangered, and critically endangered [8, 9]. Quite a large proportion of species (13%) are still classified as data deficient [8].

There are information gaps with respect to species richness and abundance of elasmobranchs in the Mediterranean Sea. These gaps often make it hard for international organizations to assess the conservation status of populations. Either the knowledge of the abundance and richness of this group, which has played a crucial ecological part in Mediterranean trophic webs, is also significant to any future strategic plan for the conservation of marine biodiversity in the region [10, 11].

The gaps are due to many reasons, the most important of which is the misidentification of species in databases and in the literature. Generally, elasmobranchs have suffered major taxonomic constraints that have led to misidentification issues related to by-catch and fisheries, which were usually solved by grouping data at higher taxonomic levels, such as genus or family [12, 13], or to morphological and biological similarities among some species, which have led to considerable confusion over their taxonomy such the case of the *Squalus* genus species [14].

Dogfish are scientifically classified as the Squalidae family, categorized under the squaliform order, which encompasses seven families in total, including Squalidae. The latter, more commonly known as dog sharks or spiny dogfish, have two dorsal fins different in shape with long spines without grooves and anal fin, with a cylindrical body and a small mouth. Their jaws are furnished with powerful cutting teeth and sometimes present only on the lower jaw; the upper jaw plays, in this case, only the role of holding the prey. The species of this family are generally small sharks, which frequently generally more or less accentuated bottoms except for the spiny dog *S. acanthias,* which does not descend below 150 meters.

Some species are highly valued and important as a major fish resource for food and liver oil. Some species are threatened due to overfishing and because of their biological characteristics, namely a long lifespan, late maturity, and low fecundity, as is the case with all elasmobranchs.

The Squalidae family itself contains two separate genera: *Cirrhigaleus* and *Squalus*, numbering together 37 species, and has the most species in the group, including *Squaliolus laticaudus*, one of the smallest known sharks with a size of 15 cm.

The genus *Squalus* Linnaeus, 1758 is distributed worldwide [15]. Until 2013, 25 species were known: 14 species documented as valid and 11 species added latterly from the western Indo-Pacific ocean [16–18]. But, this number has recently increased due to the resurrection of *Squalus acutipinnis* (Regan 1908) from South Africa and the description of four new species (*S. albicaudatus*, *S. bahiensis*, *S. lobularis,* and *S. quasimodo*) from the southwest Atlantic [19–21].

It was stated that the species diversity within the group is still poorly characterized [22]. For instance, 20 species have been described or resurrected in the last decade in the Indo-Pacific region [23–25] and the south Atlantic [19, 20].

In fact, cryptic speciation among elasmobranchs is very common [26, 27] and the number of new descriptions, redescriptions, and resurrections of species is growing with the increasing application of molecular tools and integrated taxonomic methodologies. Thus, the number of valid species in the genus was doubled and a significant amount of "hidden" diversity in the group has been revealed. Consequently, about 50% of the *Squalus* species are considered data deficient consistent with the International Union for the Conservation of Nature (IUCN) red list of threatened species [22].

The *Squalus* species inhabit the waters of the continental shelf and upper slope, between 300 and 700 m of depth [28–30], as well as some seamounts and the waters around oceanic islands [22, 31]. They have been divided into four assemblages based on *Overview of the Genus* Squalus *in the Mediterranean Sea DOI: http://dx.doi.org/10.5772/intechopen.108977*

their morphology: the "*acanthias*" group, the "*blainville*" group, the "*megalops cubensis*" group, and the "*asper-barbifer*" group [32–34]. However, members of the "*asperbarbifer*" group are assigned to the genus *Cirrhigaleus* [17]. Nevertheless, in recent years, different genetic studies have attempted to identify *Squalus* species using mitochondrial COI and NADH2 genes [22, 35–37]. Generally speaking, three well-defined groups within the genus have been described: group I, including *Squalus* suckleyi and *S. acanthias*; group II, including *S. blainville/S. megalops/Squalus raoulensis/Squalus brevirostris*; and a third group, "the *Squalus mitsukurii* complex" including *Squalus edmundsi*, *Squalus japonicus*, *Squalus grahami*, *Squalus clarkae*, *and S. mitsukurii* [22, 38–40].

In the Mediterranean, in addition to the two historically known species the longnose spurdog *S. blainville* (Risso, 1827) and the spiny dogfish *S. acanthias* (Linnaeus, 1758), a third species, the shortnose spurdog *S. megalops* (Macleay, 1881), has been reported [40–43].

In the following, we try to clarify the state of the species of the genus *Squalus* in the Mediterranean Sea taking into account all the studies carried out on this subject.

#### **2. Status of** *squalus* **genus in the Mediterranean Sea**

#### **2.1 Ecobiology**

As many elasmobranchs, Squalidae are K-selected species with slow growth rates, low fecundity, and late sexual maturation; those species tend to aggregate by sex and size [31, 44, 45]. These features make such a taxon greatly vulnerable to overfishing. Thus, increased understanding of their ecobiology is crucial to develop an assessment for conservation strategies and developing effective fisheries management.



#### **Table 1.**

*Studies on* Squalus blainville*,* S. megalops*, and* Squalus acanthias *reproduction carried out in the Mediterranean Sea.*

In the Mediterranean Sea, many investigations on the life history traits of Squalidae were conducted toward filling the information gap and to develop practical conservation strategies for those species in the area. As shown in **Tables 1**–**4**, a survey of the available published literature was carried out through a bibliographic study.

Until now, the historical traits of the Mediterranean population of *S. megalops* remained poorly studied, which may be attributed to its taxonomic problem in the area.

Generally speaking, Squalidae species are aplacental viviparous, with a long gestation, estimated up to 2 years for *S. acanthias* [81]. Their uterine fecundity was estimated to be from 1 to 12 embryos per litter. Females reach maturity at up to 70 cm,


#### **Table 2.**

*Studies on* Squalus blainville*,* S. megalops*, and* Squalus acanthias *diet carried out in the Mediterranean Sea (−; +; ++; +++: Increasing gradient of prey importance according to the calculated IRI%/ Chond.: Chondrichthyes; Teleo.: Teleosteans, crus.: Crustaceans; moll.: Mollusks; Ann.: Annelids; Echino.: Echinoderms; Oth.: Others).*

56.41 cm, and 88 cm total length (TL), whereas males matured at up to 55.0 cm, 44.39 cm, and 70.0 cm TL for *S. blainville*, *S. megalops,* and *S. acanthias,* respectively (**Table 1**). The estimated size at maturity differed between males and females confirming the marked sexual size dimorphism of those species.

Concerning the food habits of those species, they are active predators, which feed on similar preys but with different importance according to the index of relevant importance of each prey item consumed (IRI%) calculated (**Table 2**). Species are reported to feed mainly on bony fishes, cephalopods, and crustaceans.

Sexual size and mass dimorphism were observed, with females attaining larger TL and greater mass than males (**Table 3**). This pattern is common among viviparous



#### **Table 3.**

*Studies on squalus blanville, S. megalops, and Squalus acanthias mass-lenght relationship, carried out in the Mediterranean Sea (N: Number of individuals; M: Male; F: Female; L: Lenght; W: Weight; GT: Growth type; I: Isometry; (+): Positive allometry; (−): Negative allometry).*

sharks since for females, due to their more energetically demanding reproductive mode, there is a strong selection pressure for larger body size [82].

Squalidae are long-lived animals, with females attaining greater age than males, as it is typical of most elasmobranchs. Using the von Bertallonfy model, the investigations were conducted to confirm this pattern of differential growth between males and females (**Table 4**). The maximum ages observed for males were 22 years, 26 years, and 23 years and for females were 28 years, 29 years, and 36 years of *S. blainville*, *S. megalops,* and *S. acanthias,* respectively.

#### **2.2 Geographic distribution**

*S. acanthias* and *S. blainville* are mostly found in the northern part of the Mediterranean Sea and the Adriatic, including the Black Sea [30, 83–85]. Some authors have reported the spiny dogfish (*S. acanthias*) to be one of the most frequent shark species captured in the Mediterranean [30, 86, 87]. Whereas, its congener *S. blainville* is stated to be one of the most important species of the demersal assemblages in the eastern Ionian Sea [88], as well as throughout the basin, principally in its central-western part (eastern Corsica and southern Sicily) and the eastern Ionian and Aegean seas [87]. The species was found to be more abundant on the slope than on the shelf [89].

The reason for this replacement between those sharks could be related to taxonomic problems afflicting the *Squalus* genus in different areas of the Mediterranean [38, 84]. Indeed, recent studies [53] highlight that *S. acanthias* showed a limited geographic distribution in the past, suggesting an inaccurate classification of these two species [90].

To clarify the real presence of the *Squalus* species in the Mediterranean Sea, numerous scientific studies, such as MEDITS trawl survey, have been conducted. *Overview of the Genus* Squalus *in the Mediterranean Sea DOI: http://dx.doi.org/10.5772/intechopen.108977*


 *Studies on* Squalus blainville*,* S. megalops*, and* Squalus acanthias *age, carried out in the Mediterranean Sea (VBGM Von Bertallonffy; L∞: The asymptotic length at which growth is zero; K is the growth rate; T0: Constant value).* According to those studies, *S. acanthias* and *S. blainville* are mostly found in the northern part of the Mediterranean Sea, Adriatic, and Black Sea [25, 84, 85, 91].

Concerning *S. megalops,* it is recorded from the northern coasts of the Canary Islands, Morocco, and southern Spain (Malaga), but it is present mainly along the African coasts of Tunisia [41].

#### **2.3 Catches**

Fundamental problems in accurately identifying and classifying species have hampered the collection of robust biological and ecological data. This fact, together with erroneous reports of reported catches (usually lower than actual catches; [30, 92]) makes stock estimates for these fish difficult to assess. This situation is of particular concern in elasmobranchs taken as targets or as bycatch in several fisheries around the globe, as their conservative life history strategies make them extremely vulnerable to overexploitation [93].

Worldwide, Indonesia and Spain remain the top three shark catchers in the world [94]. In the Mediterranean Sea, countries, contributing more to the elasmobranch landings during the last years, are Tunisia and Libya, which contributed more than 70% of production. Tunisian landings did not show any distinguished variations from 1980 to 2015. Those from Libya appear for the first time in FAO statistics and seem to be significant. Turkey and Italy register a dramatic decrease in catch after being known to be the major elasmobranch-fishing countries within the Mediterranean, between 1980 and 2008. It should be noted that the Mediterranean landings of carcharhiniformes, the most represented group among the elasmobranchs and the most commercially fished, recorded a notable decrease [92]. The most commonly caught species are skates (Rajidae) and catsharks (*Scyliorhinus spp.* and *Galeus spp.*) [95, 96]. Different species of pelagic sharks, as well as eagle rays (Myliobatidae) and stingrays (Dasyatidae), are bycatch of pelagic and demersal fisheries [97, 98].

Squalidae, it represents one of the most commercially targeted families among elasmobranchs [24]. Capture production for Squalidae in the Mediterranean and the Black Sea during the last decades is illustrated in **Figure 1** [99].

#### **Figure 1.**

*Capture production for Squalidae in the Mediterranean and Black Sea during the last decades.*

Indeed, several species belonging to this family are landed by up to 50 countries in direct fisheries or as bycatch [24]. The genus *Squalus* is highly represented in bycatch and several studies have focused on the mitigation of the fishery impact on this group [100–102].

In the Mediterranean Sea*, S. blainville* constitutes an important landing from bottom trawlers, longlines, and gill nets [103, 104]. Moreover, the presence of *S. megalops* and *S. blainville* was reported on African coasts of Tunisia in bycatch of bottom trawl and longline fisheries [41, 92].

Although longlines are considered selective, they bring several nontarget species, including *S. acanthias* [92]*.* In fact, a significant decline in the bycatch of the former species is perceived according to the fishermen's perception on the evolution of shark populations in the northern Catalan coast (north-western Mediterranean Sea) [105]. The low presence of the piked dogfish (Annex III of the Barcelona Convention) in the subregion's bycatch composition could confirm the recorded decrease in biomass of this species.

The bycatch of elasmobranchs is an issue of global concern, particularly in highseas pelagic longline fisheries, where 25% of the catch is nontarget sharks and rays [106]. Thus, in order to keep the populations of these fishes in balance, incisive management programs are required to guarantee stability for the populations. Among these management measures, the elimination or at least the reduction of the bycatch cannot be missing.

#### **2.4 Taxonomic status**

Dependable data on species richness are crucial for any biodiversity study and conservation policies, even though it is every so often difficult to discriminate a species based on extremely similar morphological characters [107]. Therein, reliable species identification is the principal step for the application of conservation policies and maintainable exploitation of natural resources [108], all the more so considering the currently elevated biodiversity crisis induced by human activities [109].

Overall, sharks belonging to the *Squalus* genus exhibit conserved body morphology, making identification based entirely on morphological characters complicated, leading to misidentifications [110]. This complexity is amplified even similarly *via* the high overlap of morphological characters among species, as identification is often based on limited and insufficiently consistent characters, like the number of vertebrae and morphometric data [10, 16, 20, 38, 111, 112]. In fact, morphological and biological similarities among squalids have led to considerable confusion over their taxonomy [14]. Some taxonomic and nomenclatural problems affect the group of species in question. Excluding *S. acanthias*, easily recognizable thanks to its specific pattern, characterized by the presence of white spots on the back or narrowly round to acutely angular rear tips and inner margins of the pectoral fins, which permits an easier identification and discrimination from the other two species [84], and the correct identification of the other two species, which do show a very similar morphology, requires the observations of the dermal denticles, meristic features, or even genetic analysis.

Compared with *Squalus acanthias* and *S. asper*, a close similarity between *S. blainville* and *S. megalops* was pointed out [113, 114]. Moreover, despite that the relationships between the snout tip and nostril distance and the distance from the nostril to the preoral clefs were proposed as the best features for discriminating between species of the genus *Squalus*, and it is proved that they were of little use [115].

The taxonomic status of *S. blainville* is problematical as there are no extant types and the original description and figures do not correspond to any known species of

*Squalus* [42, 116]. Consequently, in a review of the Australian species of *Squalus*, *Squalus griffini* and *Squalus fernandinus* (Molina, 1782) were incorrectly synonymized with *S. blainville* [32]. However, in a review of Japanese *Squalus*, *S. blainville* was defined as a species with high dorsal fins and long dorsal-fin spines [116]. The same review revealed that *Squalus*, referring to *S. fernandinus* and *S. blainville* by some authors, had short dorsal-fin spines and were more similar to *S. mitsukurii* from Japan, and suggested that nominal *S. blainville* from New Zealand could be identical to *S. mitsukuri* [112, 117]. It was also noted that dogfish resembling *S. mitsukurii* occurred in Australia and New Zealand [31]. Outside its main distributional area (Mediterranean Sea and eastern Atlantic), *S. blainville* has also been recorded erroneously in Australia and New Zealand [112]. It was thought to be widespread in the Atlantic, Indian and Pacific Oceans [34, 117] as well as in Japan [116]. The distribution of *S. blainville* was restricted to the Mediterranean Sea and eastern Atlantic, and its records in the Pacific records were questioned [17]. The confusion is due largely to the poor original description and the lack of type material.

Taxonomic research on the genus *Squalus* conducted in the Tunisian waters revealed that *S. blainville* in this zone is not characterized by its high first dorsal fin and spine as was well thought-out by some authors, but rather it is a short-spine species [31, 116]. Comparing their data for *S. blainville* with the measurements of the same species in different regions, they noted that data generally agree despite there being some differences in the morphometrics between populations, and that Tunisian *S. blainville* specimens examined and the specimens studied by some authors [41–43, 114, 115, 118] have similar vertebral counts.

Recently, according to the studies conducted in other areas of the Mediterranean Sea and based on morphological and genetic (COI sequences) analyses, only one spurdog species, *S. blainville*, occurs in the Ionian, Libyan, Aegean Seas, and the Sardinian waters [38, 119].

These findings spotlighted the stretch of sea between Tunisia, southern Sicily, Malta, and Libya, known as the Strait of Sicily, as a more interesting area for spurdog species. The presence of *S. blainville* in the Maltese waters was assessed through the use of the DNA barcoding approach [84]. In the same region, some authors [37] collected and analyzed individuals belonging to the nominal *S. blainville* and genetically clustering within clade B [22], while three individuals were classified as *Squalus* sp. by the authors as clustering in the genetic clade C [22].

Regarding *S. megalops*, it is described for the first time in the Mediterranean in 1984 [43]; its occurrence is still debated and several scientific studies contributed to clarifying the real presence of this species in the area [21, 22, 37, 39, 41, 42, 84, 85, 119].

It was suggested that the southern Australian *S. megalops* might be endemic to Australia [91]. However, the tale can be even extra complex. Morphological research has proven that more than a single form of this species exists in Australian seas [28].

Recently, few research within the context of integrative taxonomy had been successfully accomplished in the genus *Squalus* aiming at the integration of new molecular taxonomy techniques to more classical morphological analyses with the purpose to make clear taxonomic ambiguities among some of the species [41, 84].

To highlight the taxonomic uncertainties in relation to the occurrence of *Squalus* species in the central Mediterranean Sea, a study including other morphometric characters and a molecular study was carried out to confirm that *S. megalops* occurs as a valid species in the Mediterranean Sea [41]. In fact, two species of spurdog of the genus *Squalus* occur in the Gulf of Gabès (southern Tunisia and central Mediterranean): *S. blainvillei* and *S. megalops cubensis* group. Morphometric and

meristic data as well as genetic analyses (DNA inter-simple sequence repeat markers and molecular barcoding methods) support the assignation of this short-snout spurdog to *S. megalops*.

The Tunisian *S. megalops* species are consistent for characters typifying the "*megalops-cubensis*" group and fit the description of *S. megalops* from Australian waters [23], as well as the eastern Atlantic-Mediterranean [42] and Mediterranean waters [43]. Specimens described from other areas clearly agree with the Tunisian samples of *S. megalops* for most of the morphometric characters and had similar vertebral counts to those studied by other authors (Indo-Pacific, [118]; South Africa, [115]; Mediterranean coasts of Spain, [34]; east Atlantic, [42]; south western Australia, Queensland [23]).

Some authors stated that the number of chondrocranial lateral processes is the most important character to discriminate between *S. blainville* and *S. megalops* [34, 42], but they can be discriminated also based on other morphological features, such as teeth and dermic denticles morphology. These findings have been confirmed in the Gulf of Gabès through morphometric, meristic, and genetic analyses, suggesting that S. *megalops* could be even more common than *S. blainville* in these waters (**Figures 2** and **3**) [41]. In addition to the differences cited between those species, the study of their traits of the life history in the area revealed that they differ also in those terms [50, 51, 63, 66, 77].

Differently from the former study [41], a study on the intraspecific morphological variability in *S. blainville* did not identify diagnostic features (e.g., dermal denticles), which could effectively discriminate between *S. blainville* and *S. megalops*. The authors asserted that species identification based only on morphological characteristics can easily lead to taxonomic misidentifications, especially when multiple anatomical characters (e.g., skull and teeth morphology) are used [84].

To aid in clarifying the taxonomic status of *Squalus* species in the eastern Atlantic and Mediterranean, some authors assessed species diversity at the molecular level and evaluated the consistency in species identification in the region [22]. They confirmed unreliable species identification in the eastern Atlantic and Mediterranean *Squalus* and reinforced the need to revise the status of *S. megalops* and *S. mitsukurii* as they may include several distinct species distributed around the world. Nonetheless, the results provided by those authors suggest that a different species from the "true Australian" *S. megalops*, which remains unidentified, can occur in the eastern Atlantic and Mediterranean waters [22].

In any case, specimens of *S. megalops* for which the identification is considered feasible were rarely reported in the catches [38, 51]. Most of the catches of these species are recorded from the northern coasts of Canary Islands, Morocco, and southern Spain (Malaga). However, the real presence of *S. megalops* is still unclear not only for the Mediterranean Sea but also for the neighboring Atlantic area [18, 22] and some evidences confirm the inconsistency of the species identification keys to distinguish between the Atlantic and Mediterranean *Squalus*, concerning *S. blainville* and *S. megalops* [22].

Studies conducted in the Sardinian waters showed that morphological and genetic analysis revealed the presence only of *S. blainville* in the region, despite the observation of chondrocranial lateral processes initially allowing the investigated specimens to be subdivided into two groups. Indeed, the comparison of chondrocranial and body morphology of the specimens examined indicated that none of the considered measurements could differentiate the two squalid groups [38].

They noted that considering the brief half-life and fast replacement rate of the dermal denticles [120]. In fact, the different development stages of denticles observed

#### **Figure 2.**

*Squalus blainville (adult female 96 cm TL) off Tunisian waters (a: Lateral view, b: unicuspid flank denticles, c: teeth with a single cusp deeply notched and outward end strongly oblique d: bent claws and massive spurs, e: two cartilaginous processes in the basal plate, f: sharpen palatoquadrate).*

*Overview of the Genus* Squalus *in the Mediterranean Sea DOI: http://dx.doi.org/10.5772/intechopen.108977*

#### **Figure 3.**

*Squalus megalops (adult female 76 cm TL) off Tunisian waters (a: lateral view, b: unicuspid flank denticles, c: teeth with a single cusp deeply notched and outward end directed strongly laterally, d: bent claws and massive spurs, e: two cartilaginous processes in the basal plate, f: sharpen palatoquadrate).*

in the analyzed skin portion could explain this particular aspect [120]. Moreover, dermal denticles, teeth, and dorsal fin spines were reported as common diagnostic morphological structures, which could vary in shape with the ontogenetic development [121, 122]. Consequently, the morphology of the dermal denticles should be further investigated before it can be properly used as a suitable classification tool, as also suggested particularly for the genus *Squalus* [84]. The same authors stated that considering the finding of sporadic divergent sequences [22, 38, 41, 119] different from *S. blainville* and *S. acanthias* but also *S. megalops* from Australia, the occurrence of a third species in the Mediterranean (apart from *S. acanthias* and *S. blainville*) cannot be ruled out.

Similar efforts were undertaken recently for those species [39]; it was noted that *S. megalops* does not occur in the eastern Atlantic and Mediterranean waters and that individuals composing clade C [22] should be considered a new species that needs formal description and proper taxonomic assessment [22, 123]. Besides, the species described as short-snout spurdog by other authors was considered a rare species and an occasional visitor with high morphological similarity to the *S. megalops* and *S. blainville* but is genetically distinct from both [39].

According to some authors [32], molecular data alone do not replace traditional taxonomy in the delimitation of species [124]. This integrative approach has been used over the years and has proven to be quite effective in elasmobranchs [124, 125] and in other groups of organisms [125, 126]. However, because of the difficulty of morphologically defining *Squalus* species, many sequences available in genetic databases indicate misidentifications or identifications only at the genus or family levels, making them not very useful for molecular identification purposes.

On their part, some authors stated that despite *S. acanthias* is the type species of the genus and is one of the most easily distinguished species of *Squalus* some sequences of Mediterranean specimens originally recognized as *S. acanthias* clustered in clade B. This misidentification is surprising but reveals the confused state of *Squalus* taxonomy in the region [22].

These findings further support current inconsistencies in species identification within the genus *Squalus* and the need for an accurate redescription of *Squalus* species, especially in the Mediterranean Sea, to stabilize the systematic and facilitate specimens' identification.

#### **3. Conclusions**

The Mediterranean Sea represents some of the most intensively studied regions of the world's oceans; however, this wealth of information does not translate into a good understanding of the species diversity and raises additional concerns regarding accurate identification of elasmobranchs. This concerns, among others, the genus *Squalus,* which the taxonomic confusion on it, is intrinsically related to difficulties in morphologically separating congeners and to incessant applications of synonyms due to the lack of appropriate taxonomic scrutiny with disregard for detailed morphological assessments that are essential for understanding possible variations and defining species.

In conclusion, since the first comprehensive revision on the genus in Africa [115] and after over 40 years gap, it is clear thus that an integrative approach includes both morphological and genetic tools with rigorous participation of taxon experts in the systematics of elasmobranch fishes still need to be strengthened to reduce this "taxonomic obstacle" and to faster actions in conservation and management of target species that were formerly unknown. Therefore, the establishment of a coordinated international effort to implement a comprehensive and integrated taxonomic assessment of this genus which represents an irreplaceable component of the biodiversity of the area is welcomed.

### **Acknowledgements**

The authors gratefully acknowledge the Regional Activity Center for Specially Protected Areas (SPA/RAC) for its contribution in funding the cost of editing this chapter.

### **Author details**

Sondes Marouani\*, Sami Karaa and Othman Jarboui National Institute of Marine Science and Technology (Sfax Center), Sfax, Tunisia

\*Address all correspondence to: sondes.marouani@instm.rnrt.tn

© 2023 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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