Open Veterinary Journal, (2026), Vol. 16(4): 2114-2127

Research Article

10.5455/OVJ.2026.v16.i4.15

Quantitative morphometric assessment of shark pectoral fins for taxonomic differentiation along the Mediterranean coast of Libya

Osama M. El-Barasi^1*, Ahmad M. Azab² and Mohamed A. M. El-Tabakh²

¹Department of Zoology, Faculty of Science, Derna University, Derna, Libya

²Department of Zoology, Faculty of Science, Al-Azhar University, Cairo, Egypt

*Corresponding Author: Osama M. El-Barasi. Department of Zoology, Faculty of Science, Derna University, Derna, Libya. Email: o.mofftah [at] uod.edu.ly

Submitted: 18/01/2026 Revised: 03/03/2026 Accepted: 16/03/2026 Published: 30/04/2026

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ABSTRACT

Background: This study presents the first morphometric examination of the pectoral fins of 19 shark species in the Libyan Mediterranean Sea using 88 specimens collected from November 2023 to November 2024.

Aim: The observed morphometrics successfully differentiate between benthic Squatiniformes, demersal Squalidae, triakis, and pelagic lamnids and carcharhinids.

Methods: Statistical analysis revealed significant interspecific variation (p < 0.05) in different calculated ratios, with the highest level of discrimination power being shown by PL/PF and PA/PB. Multivariate data analyses also supported unique morphological groupings of ecologically and phylogenetically close members.

Results: The present study also recorded significant biogeographical information with five shark species being first reported in Libyan waters: Heptranchias perlo (Bonnaterre, 1788), Squalus megalops (Macleay, 1881), Carcharhinus altimus (Springer, 1950), Carcharhinus obscurus (Lesueur, 1818), and Squalus mitsukurii (Jordan and Snyder, 1903). It is noteworthy that S. mitsukurii was first reported in the entire Mediterranean Sea, a considerable expansion of its known range.

Conclusion: These results are important to emphasize the ecological significance of the area and make further observations to improve our knowledge of shark diversity and distribution in the southern Mediterranean. In addition, the present findings help to underline the high diagnostic significance of pectoral-fin morphometrics and the usefulness of the present methods for species identification and shark biodiversity in the southern Mediterranean Sea.

Keywords: Libya, Mediterranean, Morphometric analysis, Pectoral fins, Shark species.

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Introduction

The Mediterranean sea is a semi-enclosed sea defined by a relatively narrow continental shelf. It is believed to be the most prominent intercontinental sea, and it is located in the region between the three ancient continents, namely, Europe, Asia, and Africa. It is situated between 6-° W-36-° E and 30° to 46° N, covering an approximate area of 2.5 million square kilometers (UNEP, 1989). The Libyan coast stretches approximately 2,000 km and is one of the longest coasts in the Mediterranean Sea because it covers nearly 3.9% of the southern coast of the Mediterranean Sea. Bathymetrically, three regions can be identified in the Libyan coast, which is closely linked to some significant structures of the African continent (Zupanovic and El-Buni 1982).

Elasmobranchii (a class of Chondrichthyes) are unique species that contain cartilaginous skeletons, unlike Osteichthyes (bony fishes). Elasmobranchii and Holocephali have been almost existent since 400 1000000 years ago. (Sobhana, 2025).

There are 57 families, 219 genera, and more than 1,280 living species of Chondrichthyes; sharks and batoids (skates and rays), as well as chimeras (Ebert and Stehmann, 2013; Last et al., 2016; Scharpf and Lazara, 2019). The fauna of chondrichthyans is also quite diverse in the Mediterranean Sea, with at least 89 species (about 7% of the total living chondrichthyans species) (Serena and Barone, 2023).

Over the last few years, the discussion of the diagnostic usefulness of fin morphology as an effective method of shark species identification in areas lacking adequate taxonomic knowledge has increased. However, Azab et al. (2019) found that morphometric ratios of the dorsal fin are statistically significant enough to identify interspecific differences in sharks living in the Egyptian Mediterranean, proving that fin-based characters can effectively address taxonomic ambiguities. Likewise, Shaban and El-Tabakh (2019) demonstrated that there is significant morphometric variation in pectoral fins that can dependably distinguish between species when compared through standardized measurements and ratios, indicating the considerable potential of these body structures to successfully distinguish those species without disturbing their environment.

Recently, Al-Khatib et al. (2025) presented additional proof of using fin morphometrics to distinguish the species in the family Carcharhinidae in the Suez Gulf, Red Sea. Highlighted the effectiveness of morphometric studies in improving shark identification, particularly in regions where entire body specimens are not provided or in situations where standard morphological keys are not easily implemented.

Regardless of these developments, no similar kind of fin-based morphometric study has been conducted in Libyan Mediterranean waters. It is an especially worrying knowledge gap in the view of the fact that most of the shark species around the globe have been shown to be in decline due to the pressure of fishing (and because of their biological vulnerability) (Chuang et al., 2016), and many considered as Vulnerable, Endangered, or Critically Endangered according to the IUCN Red List (2018), or the data being deficient which create a big gap in biodiversity knowledge.

The current research seeks to quantitatively study the morphology of the pectoral fin in sharks in the Libyan Mediterranean Sea to determine whether these structures exhibit adequate species-specific morphological differences to the extent that they could be used as reliable taxonomic traits. This question would potentially aid in correct species identification and offer more primary data to enhance conservation evaluation in this unexplored area of the Southern Mediterranean.

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Materials and Methods

Samples collection

A total of 88 shark specimens were collected, belonging to 19 species (2 of Heptranchias perlo, 7 of Squalus megalops, 1 of Squalus mitsukurii, 2 of Squalus blainvillei, 8 of Squatina squatina, 4 of Squatina aculeate, 1 of Squatina oculata, 4 of Isurus oxyrinchus, 1 of Alopias superciliosus, 1 of Carcharias taurus, 2 of Scyliorhinus stellaris, 4 of Mustelus asterias, 27 of Mustelus mustelus, 3 of Mustelus punctulatus, 5 of Carcharhinus altimus, 1 of Carcharhinus brevipinna, 1 of Carcharhinus falciformis, 2 of Carcharhinus obscurus, and 12 of Carcharhinus plumbeus).

Between November 2023 to November 2024, shark specimens were obtained from commercial fish markets located at landing sites along the Libyan Mediterranean coast, specifically At-Tamimi, Derna, Susa, Al-Bayda, Benghazi, Bin Jawad, and Sirte (Fig. 1). The sampling collection process was extended over 352 days. Immediately after collection, shark specimens were freshly examined. All photographs were captured using a Canon EOS 90D professional DSLR camera. The right pectoral fins of each shark were processed using ImageJ V1.46r software to calculate the morphometric measures. Each morphometric feature for the pectoral fins was measured three times in three separate sessions, and the average and standard division were calculated to eliminate any possible errors during the measurement process (Table 1 and Fig. 2). Each pectoral fin belonging to one of the species investigated has been fully described, and their diagnostic features have been highlighted.

Fig. 1. Map showing the land markets along the eastern Libya coast of the Mediterranean Sea.

Fig. 2. Diagrammatic representation of morphometric measurements of shark pectoral fins.

Table 1. Morphometric measurements of the pectoral fin of sharks.

Some sharks were preserved in 10% formalin solution and transported to the laboratory of the Zoology Department, Faculty of Science, Derna University, Libya, for later examinations. Sharks were identified in the laboratory according to FAO (2005) and the following studies

Data analysis

Data were coded and entered using SPSS V.22 (Al-Khatib et al., 2025). Data were tested to satisfy the assumptions of parametric tests, and continuous variables were subjected to Shapiro–Wilk, and Kolmogorov–Smirnov test for normality. The probability and percentile data were standardized for normality using the arcsine square root. Data are presented as mean and standard deviation. One-way analysis of variance analyses were performed for pectoral morphometric ratios; post hoc analysis was evaluated using Tukey pairwise comparison; p-values 0.05 were considered significant at < 0.05 (Hamada et al., 2024). Data were visualized when possible by using R studio V 2022.02.4 (Abo-Taleb et al., 2020; Shehata et al., 2024). A two-way cluster (heat map) was created using a Euclidean (Pythagorean) distance measure with the wards group linkage method. PAST V4.12 software was used for analysis. The correlation cross-products matrix was used to obtain Principal component analysis (PCA). The value of the ratios was computed using a distance-based biplot. Species represented by a single specimen (n=1) were not used for variance-based statistical inference (e.g., analysis of variance). However, they were intentionally retained in the dataset and multivariate analyses to reflect the actual structure of shark assemblages along the Libyan Mediterranean coast, as low sample sizes of these heavily exploited and threatened taxa represent ecological reality rather than sampling bias.

Ethical approval

The National Subcommittee for Bioethics College of Medical Technology, Derna, Ministry of Technical and Vocational Education, Libya, granted ethical approval for this research (Approval No. NBC.017.A.24.1; approved on September 09, 2024).

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Results

This study documented 19 shark species from Libyan waters between November 2023 and November 2024, including five species recorded for the first time in Libya (Heptranchias perlo, S. megalops, Carcharhinus altimus, and Carcharhinus obscurus), in addition to Squalus mitsukurii, which represents a new record in the Mediterranean Sea basin. According to global IUCN assessments, 12 of the recorded species (63%) fall within the threatened category. The Vulnerable (VU) group constitutes the largest proportion (32%), followed by Critically Endangered (CR) species (26%), while Endangered (EN) species account for only 5%.The remaining 37% are listed as Near Threatened (NT), least concern (LC), or Data Deficient (DD), indicating lower immediate risk but also highlighting significant knowledge gaps, especially for DD species. Species facing varying levels of extinction risk dominate the recorded shark community in Libyan waters (Table 2).

Table 2. List of examined shark species, collected from Eastern Libya between November 2023 and November 2024 with notes on their orders, families, and specimen numbers.

The pectoral fin measurements presented in Table 3 indicate evident species-level differentiation (p < 0.05). The non-overlapping and highly contrasting values showed that pectoral-fin morphometrics are highly diagnostic between broad benthic fin-type species, intermediate demersal fin-type species, and high-aspect pelagic species.

Table 3. Measurements (cm) of pectoral fins of shark species collected from Eastern Libya from November 2023 to November 2024.

All calculated ratios (PL/PF, PA/PB, PDh/PH1, PL/PE, PJ/PI, PL/PK, PH2/PH1, PAh/PE, PEh/PH1, and PBh/PI) were significantly different (p < 0.05), indicating significant interspecific variations in the structure of pectoral fins. PL/PF and PA/PB had the highest levels of separation, resulting in the highest H values and effect sizes, and were therefore considered the most responsive measures of morphological differentiation. There were considerable differences (p < 0.05) in the intermediate ratios (PDh/PH1, PL/PE, and PJ/PI) and rather mild but still significant divergence (p < 0.05) in PH2/PH1, PAh/PE, PEh/PH1, and PBh/PI. High interspecific variation in the pectoral fin ratios makes it a significant diagnostic feature.

The ratios of these differences are shown in Figure 3, in which the grouped bar chart shows how the species cluster in terms of the proportional pectoral-fin profile. A central group of the Carcharhinidae family: C. altimus, C. falciformis, C.s obscurus, C. plumbeus, and C. brevipinna, have relatively stable PL/PE, PL/PK, and PA/PB ratios, indicating that the fin geometry is conserved in the family.

Fig. 3. Grouped bar chart of pectoral fin morphometric ratios of sharks collected from Eastern Libya from November 2023 to November 2024.

The heat map represents the pectoral fin ratios (Fig. 4), offering an orthogonal perspective of the ratios, indicating evident gradients of proportional variation across all 19 species. The most notable differences are within A. superciliosus, where the values of PL/PF and PA/PB are the highest, and I. oxyrinchus and the squatinid species, which all have large fin spans compared with the body length. In contrast, the homogeneous and moderate ranges of carcharhinid species ratios are centrally located. The triakid and squalid groups are in inferior proportional bands, demonstrating the conservatory aspect of their fin structure. This visualization highlights the morphological differences between the major families.

Fig. 4. Heat map of pectoral fin morphometric ratios (Species × Ratios) of sharks collected from Eastern Libya from November 2023 to November 2024.

The additional development of these connections is depicted in Figure 5, in which the clustered heatmap demonstrates two primary fin morphology assemblages. The former consists of A. superciliosus, I. oxyrinchus, and a squatinid (S. squatina, S. oculata, and S. aculeata) with enlarged laterally extended pectoral fins. The second group includes the carcharhinid, triakid, and squalid groups, which have proportionately smaller and more compact fins. In this latter group, C. taurus and H. perlo are found as transitional forms between the two major groups’ structural gaps. This dendrogram pattern is reflective of taxonomic affinity, indicating that the morphology of a pectoral final is a good indicator of an evolutionary historical trajectory as well as adaptive functionality.

Fig. 5. Two-way clustered heat map of pectoral fin morphometric ratios (Species × Ratios) of sharks collected from Eastern Libya from November 2023 to November 2024.

Figure 6 represents the PCA biplot, with the initial two PCs explaining almost 95% of the total variance. It is evident that A. superciliosus and I. oxyrinchus are isolated on PC1 as they have remarkably high PL/PF and PA/PB ratios. Squatinids exhibit extended bases of the fins (PH2/PH1, PL/PE). (PH2/PH1, PL/PE). Carcharhinid and triakid species constitute a small (morphologically conservative) core cluster, and Squalidids are clustered around the lower axis (proportional uniformity). Carcharias taurus and H. perlo fall in the in-between space again, confirming their transitional morphology between pelagic and benthic.

Fig. 6. Principal component analysis (PCA biplot) of pectoral fin morphometric ratios of sharks collected from Eastern Libya from November 2023 to November 2024.

Plate I. Photographs of the pectoral fin of the studied shark species.

The morphological variations of the investigated shark species are represented in Plate (I), which is significantly different by shape, color, and dimensions. There are visible differences among the study shark species in their overall shape, relative size, outline, and margin setup. The pectoral fin of H. perlo is short and broad in form and is rounded at the distal margin and large at the base of the insertion. The pectoral fins of S. megalops, S. mitsukurii, and S. blainvillei are triangular in form, medium in length, pointed at the apex, and slightly rounded at the posterior margins. S. squatina, S. aculeata, and S. oculata have conspicuously wide and flattened pectoral fins that are laterally expanded and wing-like in appearance with broadly rounded outer margins. The pectoral fins of C. taurus are large, triangular, and have a broad base and a sharp end. S. stellaris has smooth pectoral fins that are comparatively slender and rounded at their ends. In the pectoral muscles of I. oxyrinchus and A. superciliosus, the pectoral fin is long, narrow, and distinctly falcate, with pointed apices and straight to slightly curvy edges. Mustelus species (M. asterias, M. mustelus, and M. punctulatus) have relatively wide-ranged triangular-shaped pectoral fins with rounded to slender apices. The pectoral fins of representatives of the genus Carcharhinus (C. altimus, C. brevipinna, C. falciformis, C. obscurus, and C. plumbeus) are well developed, triangular to slightly falcate, with pointed apices and distinct anterior and posterior margins.

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Discussion

According to Shakman et al. (2023), shark records along the Libyan coast constitute a compilation of published literature, unpublished data, and results from two specific surveys. Early studies such as Tortonese (1939), Sogreah (1977), and Zupanovic and El-Buni (1982) established the historical baseline for these species, followed by later contributions from Lamboeuf et al. (1995) and Tobuni et al. (2016). Shakman et al. (2023) expanded this inventory to include newly recorded species. These records demonstrate that the Libyan coast supports a rich diversity of shark species across multiple orders and families, highlighting the region as an ecologically significant biodiversity hotspot in the southern Mediterranean.

The morphometric ratios of pectoral fins in this study show a clearly defined interspecific differentiation among investgated species, which is statistically sound and follows the trends of earlier Mediterranean studies. Allometric adjustment was not applied because calculating robust species-specific coefficients requires larger sample sizes than those available for these rare taxa. Instead, standard morphometric ratios, which remain practical and widely accepted for field identification, were used.

The low-aspect benthic flattened fins of Squatina squatina and S. aculeata are similar to the morphology previously recorded by Cavallaro et al. (2015). Triakid species, including Mustelus mustelus and M. punctulatus, had greater ratios of fin length, consistent with Eryilmaz et al. (2011). The tallest and highest-aspect fins were observed in pelagic predatory species (Isurus oxyrinchus and C. falciformis), as described by Shaban and El-Tabakh (2019). A further taxonomic separation was based on shape-based traits, including the length of the free rear-tip (PA/PB), which was extremely long in S. megalops and short in Alopias. superciliosus, as well as concavity indices that differentiated Squatinidae species.

The diagnostic value of these characters was statistically different (p < 0.05), and those with the greatest discriminative power and the highest proportion of effect (epsilon squared) were PL/PF and PA/PB, whereas median ratios (PJ/PI, PL/PE, PDh/PH1) represented the difference in curvature and fin height functionality. The statistical results of this research showed a significant difference (p < 0.05) in interspecific character in all pectoral-fin ratios and a high discriminatory power of PL/PF and PA/PB, which were completely similar to the data presented by Shaban and El-Tabakh (2019). These results confirm that pectoral fin data are strong predictors of species-specific fish fin morphology along the Libyan coast.

This study reports the first Mediterranean record of S. mitsukurii and the first Libyan record of S. megalops based on pectoral fin morphometrics. It is important to emphasize that recent molecular evidence definitively supports these morphological identifications. A parallel molecular analysis (DNA barcoding) conducted by our research team has confirmed the presence of both species in the region (El-Barasi et al., 2026).

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Conclusion

The current work shows that pectoral-fin morphometrics is a solid and quantitative instrument that can be used to differentiate shark species along the Libyan Mediterranean coast. Interspecific variance was observed in all measured ratios, with fin-length proportions (PL/PF) and free rear-tip (PA/PB) being the most informative diagnostic measures. The multivariate patterns also clearly identified the obvious segregation between benthic, demersal, and pelagic groups, illustrating the ecological and taxonomic significance of fin-based characteristics. These results have the best part in bridging a critical area of knowledge in Libyan waters and highlighting the potential of fin morphometrics to aid in species identification and add to conservation efforts of the region with numerous threatened species of sharks and inadequately documented ones.

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Acknowledgments

None.

Conflict of interest

The Authors declare that there are no conflicts of interest.

Funding

This study received no external funding.

Authors’ contributions

Conceptualization, Ahmad M. Azab; Osama M. El-barasi; Databarasi; Data curation, Mohamed A. M. El-Tabakh; Osama M. El-barasi; Formal analysis, Mohamed A. M. El-Tabakh; Osama M. El-barasi; Investigation, Mohamed A. M. El Tabakh; Osama M. El-barasi; Ahmad M. Azab; Mohamed A. M. El-Tabakh; Osama M. El-barasi. All authors have read and agreed to the publication of this manuscript.

Data availability

The datasets used and analyzed in this study are available on reasonable request from the corresponding author.

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