Shark and Ray Product Identification

A shark fin is not solid cartilage. Its internal framework consists of ceratotrichia: parallel, unsegmented protein rods (they are not true calcified cartilage but a specialized collagenous material) that run from base to tip. In a freshly removed fin, these rods are embedded in connective tissue and skin. In a dried 'fin needle' product prepared for the shark fin soup trade, the skin and connective tissue have been stripped, leaving the ceratotrichia exposed as translucent, pale needles. These same needles that are the commodity of the fin soup market are also the primary morphological substrate the analyst examines.

Ceratotrichia characteristics that vary between species include: total count at mid-fin cross-section, branching frequency (whether and how often they bifurcate toward the fin margin), and cross-sectional diameter. Reference data compiled from known-species fins allow analysts to compare these metrics against unknowns. Fin shape metrics are also used for whole-fin identification: the ratio of fin height to base length, the curvature of the trailing margin, and the presence of distinctive markings (such as the white-tipped coloration of Triaenodon obesus, the whitetip reef shark). Shape metrics are less reliable when fins have been trimmed during processing.

Dorsal fin spines, present anterior to the first and second dorsal fins in squaliform sharks (orders Squaliformes and related groups), add another morphological layer. The spiny dogfish (Squalus acanthias) and its relatives have distinctive spines whose cross-sectional histology, with concentric dentine lamellae, provides both species identity and an age estimate independent of vertebral analysis. Many species targeted in directed fin fisheries are not squaloids and lack dorsal spines, but spine presence is diagnostic when observed.

Drying and prolonged storage fragment DNA substantially. Standard COI barcodes (652 bp) and full-length cytochrome b amplicons (1140 bp) regularly fail on dried fin tissue that has been stored for months or traded commercially. The solution is to use mini-barcodes: short amplicons designed to span diagnostic regions within the longer gene, typically 100-250 bp. Several validated mini-barcode sets exist for elasmobranchs, targeting cytochrome b or NADH2, with published primers and positive species-identification results on commercially acquired dried fin samples.

1. Sample selection
   For a whole dried fin, the base tissue is preferred over the fin body; the base is better protected and retains higher DNA concentration. For fin needles, each needle represents a single fin; select material from multiple needles to account for mixture.
2. Extraction
   Small amounts (10-20 mg) of tissue are lysed using a prolonged proteinase K digestion adapted for desiccated collagenous material. Silica-column cleanup follows standard QIAGEN or equivalent protocols.
3. Mini-barcode amplification
   Short-amplicon primers targeting a diagnostic region of cytochrome b or NADH2 are used. PCR conditions use higher annealing temperature than standard barcoding to reduce non-specific amplification from degraded templates.
4. Sequencing and database matching
   Sanger sequencing or next-generation amplicon sequencing generates the target sequence. BLAST against GenBank or the BOLD elasmobranch database returns species-level identifications. For species with sparse database coverage, phylogenetic tree placement alongside reference sequences is more reliable than top-hit BLAST alone.

Manta and mobula ray gill plates present a related challenge. These structures, which filter zooplankton, are dried and traded as a traditional-medicine product in East Asian markets under the term peng yu sai. The gill plates are keratinous and retain DNA in the thin layer of tissue at their base. Cytochrome b and COI mini-barcodes distinguish Mobula birostris (oceanic manta ray, CITES Appendix II since 2013) from other mobulids and from reef manta rays (M. alfredi), both of which are CITES-listed.

CITES listings for sharks and rays expanded rapidly through CoP16 (2013), CoP17 (2016), and CoP19 (2022). The 2022 conference was particularly significant: it extended Appendix II coverage to all species within the family Carcharhinidae (requiem sharks, the large family that includes bull sharks, oceanic whitetip, and silky shark) and all Sphyrnidae (hammerheads). This broad family-level listing was intended to close the identification-difficulty loophole under which dealers could claim a regulated species was actually an unlisted relative.

The practical consequence of broad family-level listings is that the burden of identification has shifted from 'prove this is a protected species' to 'prove this is not one of the very few unlisted species.' For Carcharhinidae, effectively all common traded species are listed, so any requiem shark fin in commercial trade requires documentation. This makes rapid, port-level DNA screening tools (like lateral-flow assays for high-priority species and portable sequencers) increasingly important for customs enforcement.

Shark vertebrae are calcified but not ossified: they retain a cartilaginous core surrounded by concentric layers of calcified material deposited over the shark's lifetime. Under transmitted light or after staining with alizarin red, these layers appear as alternating opaque and translucent bands. In most well-studied species, one opaque-translucent pair is deposited per year, allowing age estimation from band count in a manner analogous to tree-ring dendrochronology. Periodicity has been validated by oxytetracycline injection studies, where a fluorescent time-stamp confirms the relationship between band count and elapsed time.

In forensic contexts, vertebral age rings contribute three kinds of information. First, individual age allows courts to assess whether a shark was killed before or after a protective measure came into force (though this is uncommon because vertebrae are rarely preserved in trade). Second, age-at-capture data from confiscated vertebral samples provides information about the size structure of the population being exploited, which informs non-detriment findings. Third, von Bertalanffy growth parameters derived from reference age-length studies allow body length estimation from a vertebra alone, establishing whether the individual was a juvenile, sub-adult, or adult and whether it had reached reproductive maturity.

The scale of the global shark fin trade has been estimated from multiple data sources. FAO landing statistics record reported catches but substantially undercount actual take because finning at sea and unreported landings are common. TRAFFIC and independent researchers have analyzed Hong Kong trade statistics (Hong Kong publishes detailed import-export data by commodity code) to estimate total fin volume. A widely cited 2013 study by Worm et al. in Marine Policy estimated 63-273 million sharks killed per year based on fin import data, substantially higher than FAO-reported figures. More recent analyses estimate the current global fin trade involves 26-73 million sharks per year, reflecting some decline from peak levels in the early 2000s but still at scales that are unsustainable for many populations.

The trade structure is important for understanding where forensic identification fits. Fins are removed at sea by fishing vessels, dried on board or ashore, bundled, and sold to first buyers who aggregate them into large mixed-species lots. These lots move through trading hubs (notably Hong Kong, Guangzhou, and Singapore) where they are processed, sorted, and distributed to wholesale and retail markets. By the time fins reach a market or restaurant, they are completely divorced from any documentation about the species, origin, or fishing vessel. Forensic identification is therefore the only method available to determine whether a traded product involves a CITES-listed species.

• TRAFFIC pangolin and shark seizure databases: compiled records of documented wildlife seizures including species composition and trade route information, used for prosecution support and trend analysis.
• FAO global fisheries statistics: reported shark landings by flag state, widely used for stock assessment despite known under-reporting.
• Hong Kong Census and Statistics Department trade data: the most detailed public dataset on fin trade volume; used to back-calculate total shark mortality estimates and to track shifts in species composition as listings take effect.

Manta and mobula rays are filter feeders, and their gill arches carry dense arrays of comb-like gill plates that strain zooplankton from the water. These gill plates have been marketed in parts of East Asia as a health product, driving a targeted fishery for manta and mobula rays that expanded rapidly in the 2000s. By 2013, manta rays (then genus Manta, now synonymized into Mobula) were listed on CITES Appendix II; subsequent CoP meetings extended coverage to all Mobula species.

Forensic identification of gill plates uses both morphology and DNA. Morphologically, gill plates differ in size, color, and filament density between species, but dried and processed material can be difficult to assign to species level by morphology alone. DNA from residual gill tissue at the base of the plate is the more reliable method. The same mini-barcode approach used for shark fins applies here. Species-level resolution is important because M. birostris (the oceanic manta, the largest and most valuable species in the trade) and M. alfredi (the reef manta) are both listed but have different population sizes and conservation status, making species distinction relevant to non-detriment findings.