Critical habitat

1. Introduction

  • Lecture focuses on critical habitats of sharks and rays, why they matter, and how they relate to conservation and assessment work.

  • Content is important for assessments, especially practical and project work.

  • Core topics:

    • Definition of critical habitat

    • Approaches for identifying critical habitat

    • Nursery areas (concepts & criteria)

    • Case studies

    • Human impacts on critical habitats

2. What is Critical Habitat?

2.1 General Definition

  • A widely used conservation term across taxa.

  • Refers to areas prioritised because they are crucial for survival or recovery of a species or ecological group.

  • Think of triage: critical habitat = top conservation priority.

2.2 Application Across Taxa

  • Well-established in birds, biodiversity hotspots, and increasingly in marine taxa.

  • Examples:

    • IMMA: Important Marine Mammal Areas

    • EBSAs: Ecologically or Biologically Significant Areas

2.3 Why It Matters

  • If an area is designated as critical:

    • More likely to receive legal protection

    • Influences environmental consultancy work, e.g., when evaluating impacts from:

      • Oil and gas developments

      • Construction and coastal modification

    • Under US Endangered Species Act, critical habitat designation legally restricts activities in that area.

3. Life Stages and Critical Habitat

  • Ideally, conservation would cover all life stages of sharks and rays.

  • In rare cases (e.g., Magellan skate, micro-endemic), this is possible.

  • For most species (99.9%), life stages occur across large geographic ranges and political boundaries.

  • Conservation focuses on key life-history activities, e.g.:

    • Gestation

    • Mating

    • Feeding

    • Migration

  • Not all behaviours fit neatly in these categories (e.g., seabird “loafing”), but they provide a conservation framework.

4. Important Shark and Ray Areas (ISRAs)

4.1 Overview

  • Developed by the IUCN Shark Specialist Group.

  • Global framework similar to IMMA.

  • Website contains atlas and maps of designated areas.

  • NE Atlantic (including Welsh coast & Caernarfon Bay) has recent ISRA designations.

4.2 Criteria for ISRA Designation

To prevent over-designation, strict scientific criteria are used:

(1) Vulnerability

  • Species listed as CR, EN, or VU on IUCN Red List.

  • Must be combined with other criteria.

(2) Range Restriction

  • Species that occur in only one or two Large Marine Ecosystems (LMEs).

  • LMEs = coastal ocean areas with similar oceanography, biology, and ecological processes.

  • Range-restricted species = high extinction risk.

(3) Life-History Traits

  • Presence of:

    • Large aggregations

    • Pregnant females

    • Mating sites

    • Feeding hotspots
      → Areas where sharks & rays are especially vulnerable to disturbance.

(4) Diversity Hotspots

  • Areas with higher-than-average species richness (e.g., certain Amazon tributaries with stingray diversity peaks).

(5) Special Natural Features

  • Natural cleaning stations, aggregations, etc.

  • Excludes human-created aggregation points (e.g., artificial shark feeding).

5. How Do We Identify Critical Habitat?

5.1 No Perfect Method

  • Must combine multiple approaches due to species behaviour, cost, and logistical challenges.

5.2 Fisheries-Independent Surveys

  • Planned scientific sampling (e.g., trawling, longline surveys).

  • Pros:

    • Quantitative abundance & density estimates

    • Repeatable

  • Cons:

    • Very expensive

    • Limited habitat access (e.g., can't trawl reefs)

    • Rare species often not detected

    • Lethal impacts in some cases

5.3 Visual Approaches

BRUVs (Baited Remote Underwater Videos)

  • Used in your practicals.

  • Good for:

    • Coral reefs

    • Scavenger/predator species

  • Limitations:

    • Ineffective for planktivores (e.g., manta rays)

    • Limited spatial coverage

Drones & Aerial Surveys

  • Good for shallow, clear waters and surface-oriented species.

  • Limited by:

    • Visibility

    • Depth
      (sharks do not always stay near surface)

5.4 Tagging

  • Produces highly detailed movement data (e.g., White Shark Café).

  • Pros:

    • Identifies migratory corridors, deep-water use, aggregation areas

  • Cons:

    • Extremely expensive

    • Small sample sizes

    • Requires specialised training

    • Mostly used for large charismatic species (white sharks, whale sharks)

5.5 Ecological Knowledge, Citizen Science, Historical Data

  • Underused but very powerful.

  • Includes:

    • Fishers’ knowledge

    • Beach records

    • Historical naturalist logs

    • Social media photos

    • Museum specimens

  • Example: Angel Shark Project Wales

    • Combined citizen science + historical records

    • Identified Cardigan Bay as a long-term core habitat

6. Nursery Areas in Sharks

6.1 Why Nursery Areas Matter

  • Concept >100 years old.

  • Intuitive: protect the young → protect the population.

  • BUT: often misidentified due to:

    • Single juvenile sightings

    • Storm displacement

    • Random occurrence

Problem

  • Mislabelled nurseries → misallocated conservation resources.

6.2 Heupel et al. (2007) Nursery Criteria

To classify a true nursery, the area must meet all three criteria:

  1. Higher abundance of young-of-the-year (YOY) than other areas

  2. Residency (juveniles stay for extended periods)

  3. Repeated use over multiple years

6.3 Case Studies

Bull Sharks (Gulf of Mexico)

  • 30 years of gillnet surveys

  • 5,000 individuals

  • Identified Matagorda Bay as a strong nursery area.

  • BUT surrounding bays also important → scale matters.

Bull Sharks in Iraq / Persian Gulf

  • Very limited research possible.

  • Combined museum, historical, social media, and fish market data.

  • Satisfied 2 of 3 criteria (no residency data).

  • Supported designation of ISRA for Iraq & Kuwait.

7. Egg Case (Oviparous) Nurseries

  • ~40% of sharks & rays lay eggs.

  • Vulnerable to:

    • Bottom trawling

    • Dredging

    • Coastal development

  • UK Shark Trust eggcase database useful.

  • Localised diver/ROV surveys reveal:

    • Distinct egg vs juvenile habitat zones

      • Example (Alaska): eggs laid on steep slopes; juveniles closer inshore.

8. Key Habitats

8.1 Common Misconception: Coral Reefs

  • Only ~5% of elasmobranch species rely on coral reefs.

  • Globally, soft sediment habitats and open water are more important.

8.2 Intertidal Zones

  • Extremely important and underappreciated.

  • Used by ~90 species from 25 families.

  • Includes:

    • Requiem sharks

    • Stingrays

    • Hammerheads

    • Critically endangered sawfish

Life-history functions in intertidal zones

  • Feeding (stingrays, juvenile sharks)

  • Predator refuge (e.g., blacktip juvenile sharks avoiding hammerheads)

  • Reproduction:

    • Warmer water speeds gestation in live-bearing species

  • Nursery habitat (e.g., Bimini mangroves for lemon sharks)

8.3 Pelagic Habitat

  • Often incorrectly seen as uniform and featureless.

  • Actually structured by:

    • Fronts

    • Gyres

    • Eddies

    • Oxygen/temperature layers

  • These create predictable hotspots for pelagic sharks (e.g., blue sharks, oceanic whitetips).

Vertical dimension matters

  • Some species forage deep at night or on the seafloor (e.g., scalloped hammerheads at 1,000 m).

  • DSL (Deep Scattering Layer) important as prey source.

9. Human Impacts on Critical Habitat

9.1 Loss of Intertidal Habitat

  • Massive global declines since at least the 1980s.

  • Major causes:

    • Coastal development (ports, housing, tourism)

    • Sediment disruption from agriculture, damming, dredging

    • Erosion from hard coastal structures

Example: UAE coastline

  • Once prime sawfish/guitarfish habitat → now artificial islands and coastal property.

9.2 Development Impacts on Juvenile Sharks

  • Bimini example:

    • Juvenile lemon sharks in developed areas had lower growth rates

    • Likely due to:

      • Reduced prey

      • Higher turbidity

      • Stress/nutrient changes

9.3 Pelagic Impacts

Climate change threats

  • Temperature shift → species pushed poleward

  • Oceanographic breakdown → fronts and eddies disrupted

  • Prey changes → affects predators

  • Deoxygenation:

    • Global O₂ decline predicted 1–7% by 2100

    • Expanding oxygen minimum zones (OMZs)

    • Creates a “triple whammy”:

      1. OMZ pushes sharks upward

      2. Warming surface waters limit inhabitable area

      3. Higher concentration of sharks → increased bycatch risk

9.4 Deep-Sea Mining

  • Emerging threat due to demand for minerals.

  • Risk of:

    • Sediment plumes disrupting bioluminescent communication and hunting

    • Vertical movement barriers

    • Unknown large-scale impacts on pelagic ecosystems

10. Summary

  • Critical habitats are essential for targeted conservation.

  • Identification requires multiple data sources: scientific surveys, tagging, citizen science, historical records.

  • Nursery areas must meet strict criteria to avoid misallocation of conservation effort.

  • Intertidal, pelagic, and soft-sediment habitats are especially important.

  • Human impacts (coastal development, climate change, deoxygenation, mining) are rapidly altering critical habitats.

  • Protecting these areas is crucial for elasmobranch survival.