Biodiversity

1. Introduction

  • Lecturer’s background:

    • Conducted PhD research on shark and ray diversity and fisheries in Kuwait (Arabian Gulf).

    • Member of IUCN Shark Specialist Group (~20 years).

    • Involved in global conservation strategies, including sawfish conservation.

    • Experience identifying hundreds of sharks and rays from fish markets worldwide.

  • Images shown were from fish markets illustrating the high biodiversity in subtropical fisheries.

2. High-Level Classification of Fishes

Three main fish groups

  1. Osteichthyes (bony fish) – ~30,000 species (not the focus).

  2. Chondrichthyes (cartilaginous fish) – ~1250 species

    • Sharks + Rays (Elasmobranchii)

    • Chimaeras (Holocephali / Chimaeriformes)

  3. Agnathans (jawless fishes: hagfish, lamprey)

Chondrichthyes overview

  • ~1,250 species of sharks, rays, and chimaeras.

  • Divided into:

    • Elasmobranchs → Sharks & Rays

    • Holocephalans → Chimaeras (rabbitfish, ghost sharks)

Chimaeras

  • Small group (~50 species), mostly deep-sea, poorly studied.

  • Increasing number of new species found with deeper sampling.

3. Sharks vs Rays: Key Diagnostic Differences

Fundamental distinguishing feature:
✅ Gill slits & pectoral fin attachment

Group

Gill Position

Pectoral Fin Attachment

Sharks

Lateral (side of head)

Not fused to head

Rays (Batoids)

Ventral (underside)

Pectoral fins fused to head

Shape is NOT reliable

  • Some sharks are flattened (e.g., angel sharks, wobbegongs).

  • Some rays look shark-like (sawfish, wedgefish).

Common confusion:

  • Sawfish = rays

  • Sawsharks = sharks

  • Swordfish = bony fish (completely unrelated)

4. Major Groups Within Rays (Batoids)

  1. Electric rays (Torpediniformes)

    • Understudied, cryptic, variable size.

  2. Wedgefish & Guitarfishes

    • Some of the most valuable species in the global fin trade.

    • Includes sawfish (largest rays; up to 7 m).

  3. Skates (Rajiformes)

    • Dominant in cold/temperate waters; many UK species.

  4. Stingrays (Myliobatiformes)

    • Includes small benthic stingrays → large manta rays.

    • ~200+ species.

5. Major Groups Within Sharks

  1. Angel sharks – flattened benthic predators; one critically endangered species in Wales.

  2. Sawsharks – small group; distinctive toothed rostrum.

  3. Dogfish & catsharks (Carcharhiniformes)

    • ~140 species; highly similar → difficult to ID.

  4. Cow sharks / frilled sharks (Hexanchiformes)

    • Ancient, few species; “primitive” morphology.

  5. Carcharhiniformes (ground sharks)

    • Largest order; includes most reef sharks, catsharks, tope.

  6. Lamniformes

    • Includes mako, porbeagle, threshers, basking shark, megamouth.

  7. Orectolobiformes

    • Includes whale shark and carpet sharks.

  8. Heterodontiformes

    • Bullhead sharks; distinct small group.

6. Evolutionary Distinctiveness

  • Sharks and rays are an ancient lineage (400+ million years).

  • Despite few species, they represent huge evolutionary history per species.

  • Example: A deep-sea guitarfish species represents 188 million years of unique evolutionary heritage.

EDGE (Evolutionarily Distinct & Globally Endangered)

  • Combines evolutionary distinctiveness + threat level.

  • Highest scoring chondrichthyan: Big-mouth guitarfish.

  • Sawfishes also rank extremely highly.

7. Taxonomy: Why It Matters

Taxonomy = formal classification of organisms
Identification = applying taxonomy to identify real specimens

Key reasons taxonomy is essential:

  • Fisheries management

  • Conservation prioritisation

  • Biogeographic studies

  • Forensic identification in illegal trade

  • Accurate population assessments

Misidentification = ineffective or invalid management.

Example: The Flapper Skate

  • Once thought to be one species ("common skate").

  • Later discovered to be two species:

    • Flapper skate (very large)

    • Blue skate (smaller)

  • Both heavily exploited and misidentified for decades.

This changed conservation status and management drastically.

8. How New Species Are Described

  • Based on morphological characters:

    • Measurements

    • Fin positions

    • Tooth shape

    • Vertebral counts

  • Increasing use of molecular methods (DNA barcoding).

  • Requires:

    • Formal peer-reviewed description

    • Designation of a holotype (museum specimen representing the species)

New species are still being found:

  • Hammerheads

  • Deep-sea species

  • Entirely new families identified through genetics

9. Challenges of Identification

Identification is difficult because:

  • Many species have conservative body shapes

  • Markings can be ambiguous or misleading

  • Overlapping morphological features across species

  • Need combinations of characteristics:

    • Fin proportions (heights, lengths)

    • Fin positions (distance between dorsal fins)

    • Spircule (spiracle) presence

    • Tooth visibility

    • Body ratios

    • Colour patterns (rarely sufficient on their own)

Example: Mistaking a Pig-eyed Shark for a Bull Shark

  • Both are heavy-bodied, blunt-snouted

  • Only reliable difference: relative height of dorsal fins

  • Requires measurement, not visual judgement

Fisheries observer misidentification

Study in northern Australia:

  • Even experienced observers misidentified similar species.

  • E.g., blacktip shark complex; pig-eye vs bull shark.

  • Confirmed using genetic validation.

10. Importance of Accurate ID in Conservation & Enforcement

  • Essential for:

    • Identifying endemic species

    • Recognising threatened populations

    • Distinguishing similar species in the shark fin trade

    • Correctly mapping distribution hotspots

Example:
A rare species (Smith’s guitarfish) occurs alongside very similar widespread species → must be identified correctly to focus conservation efforts.

11. Biogeography & Global Distribution Patterns

Distribution ≠ random

Driven by:

  • Evolutionary history (deep time)

  • Plate tectonics

  • Oceanographic barriers

  • Temperature regimes

  • Depth & habitat structure

Analogy: Why marsupials are only in Australia

  • Historical separation + barriers to dispersal = unique fauna.

12. Global Diversity Patterns in Sharks & Rays

✅ Greatest Diversity = Indo-West Pacific (Coral Triangle region)

Warm-temperate meets tropical → highest overlap of species.

Patterns mirror:

  • Corals

  • Mangroves

  • Marine fishes
    → High species richness in same central Indo-Pacific region.

13. Major Biogeographic Barriers for Sharks & Rays

1. Isthmus of Panama closure (~3 million years ago)

  • Separated Atlantic & Pacific faunas.

  • Explains near-identical “sister species” pairs:

    • Grey reef shark (Indo-Pacific) vs Caribbean reef shark (Atlantic)

    • Lemon shark vs Sicklefin lemon

    • Nurse shark pairs

2. Pacific Barrier (~5000 km of deep water)

  • Shallow-water species cannot cross vast ocean distances.

  • Deep-water or pelagic species sometimes can.

3. Benguela Upwelling (cold water off South Africa)

  • Prevents warm-water Indian Ocean species from entering the Atlantic.

Result:
Parallel species in each ocean basin.

14. Regional Examples: Arabian Peninsula

  • Region has three distinct water bodies:

    1. Red Sea

    2. Gulf of Aden / Arabian Sea

    3. Persian/Arabian Gulf

  • Persian Gulf:

    • Shallow, extremely hot, almost no coral.

    • Low species richness is natural (not due to overfishing).

  • Important for interpreting absence/presence patterns correctly.

15. Distribution Patterns by Habitat

Pelagic species (blue shark, silky shark)

  • Wide-ranging

  • Cross ocean basins

  • Can traverse temperature barriers

Coastal/shelf-associated species

  • Restricted by:

    • Temperature

    • Depth

    • Shelf continuity

  • Example: Lemon shark stays within continental shelves (<100 m).

Micro-endemic species

  • Tiny ranges → far higher extinction risk.

  • Examples:

    • Sleeping rays (Gulf of Aqaba)

    • Maugean skate (2 estuaries in Tasmania)

  • Vulnerable to:

    • Pollution

    • Localised habitat loss

    • Marine development

16. Key Takeaways

  • Sharks & rays form a small but evolutionarily important vertebrate lineage.

  • Taxonomy and identification are fundamental to research, conservation, fisheries, and trade enforcement.

  • Many species are extremely similar → require careful morphological measurement or genetics.

  • Global diversity patterns shaped by geological and oceanographic barriers.

  • Highest global richness is in the Indo-West Pacific.

  • Many species have tiny ranges, making them highly vulnerable.

  • Misidentification can undermine conservation management.