5  Extinction Risk

Extinction risk scoring translates a species’ conservation status into a numeric weight that reflects its vulnerability to population-level impacts. The MST integrates protections from three US federal regulatory frameworks and the international IUCN Red List to assign each species a score from 1 to 100.

5.1 Regulatory Framework

5.1.1 Endangered Species Act (ESA)

The Endangered Species Act (1973) provides protections for species listed as Endangered (EN) or Threatened (TN) by either NMFS (for marine species) or FWS (for terrestrial/coastal species).

  • Endangered (EN): species in danger of extinction throughout all or a significant portion of its range
  • Threatened (TN): species likely to become endangered within the foreseeable future

ESA listings are the primary driver of extinction risk scores for US-listed species, with Endangered receiving the maximum score (100) and Threatened receiving a score of 50.

5.1.2 Marine Mammal Protection Act (MMPA)

The Marine Mammal Protection Act (1972) protects all marine mammals in US waters regardless of their ESA status. This includes whales, dolphins, porpoises, seals, sea lions, walruses, sea otters, polar bears, and manatees.

Because MMPA provides blanket protection, all marine mammals receive a minimum spatial floor score of 20 in cells where they are present — even species classified as Least Concern under IUCN. This ensures that the legal protection afforded to marine mammals is reflected in the sensitivity analysis.

The MMPA floor is intentionally higher than the MBTA floor because the MMPA imposes a stronger statutory standard: it affirmatively requires that all marine mammal populations be maintained at Optimum Sustainable Population levels and mandates active population recovery, whereas the MBTA is primarily a prohibitive take statute. Marine mammals also tend to have lower reproductive rates and longer recovery times than most seabirds, making them intrinsically more sensitive to disturbance.

5.1.3 Migratory Bird Treaty Act (MBTA)

The Migratory Bird Treaty Act (1918) protects migratory birds, which includes most seabird species. Similar to MMPA, all migratory birds receive a minimum spatial floor score of 10 in cells where they are present.

5.1.4 IUCN Red List

The IUCN Red List of Threatened Species provides internationally recognized conservation status assessments used for species not listed under US federal laws:

Table 5.1: IUCN Red List categories used in extinction risk scoring.
Category Abbreviation Description
Critically Endangered CR extremely high risk of extinction in the wild
Endangered EN very high risk of extinction in the wild
Vulnerable VU high risk of extinction in the wild
Near Threatened NT close to qualifying for a threatened category
Least Concern LC widespread and abundant
Data Deficient DD inadequate information to assess

5.2 Scoring Methodology

Extinction risk scores are computed by msens::compute_er_score(), which implements a two-track scoring system depending on whether the species is listed under US federal law.

5.2.1 US-listed Species

For species with NMFS or FWS ESA listings, the score is the maximum across three components:

\[ \text{er\_score} = \max(\text{ESA base}, \text{MMPA floor}, \text{MBTA floor}) \tag{5.1}\]

Table 5.2: US-listed species scoring components. The final score is the MAX across applicable components.
Component Score
ESA Endangered (EN) 100
ESA Threatened (TN) 50
ESA not listed (LC) 1
MMPA protected 20
MBTA protected 10

Examples:

  • ESA Endangered whale (MMPA): max(100, 20) = 100
  • ESA Threatened seabird (MMPA + MBTA): max(50, 20, 10) = 50
  • Non-ESA marine mammal (MMPA only): max(1, 20) = 20
  • Non-ESA migratory bird (MBTA only): max(1, 10) = 10

5.2.2 Species not federally listed (IUCN)

Species not federally listed or mentioned by NMFS (Species Directory | NOAA Fisheries ) or FWS (Species | U.S. Fish & Wildlife Service ) fall back to an extinction risk score based on their IUCN Red List category:

IUCN-based extinction risk scores for US species not listed or mentioned by NMFS or FWS
IUCN Category Score
Critically Endangered (CR) 50
Endangered (EN) 25
Vulnerable (VU) 5
Near Threatened (NT) 2
Least Concern / Data Deficient / other 1

Species with no matching extinction risk code (i.e., unmatched taxa) receive a default score of 1.

5.2.3 Scale Note

Scores range from 1 to 100, representing a percentage scale (1–100%). Integer storage is used for computational efficiency; conceptually the scale represents a 0–1 probability-like weight where 100 = 1.0 (maximum extinction risk) and 1 = 0.01 (minimum baseline).

5.3 Implementation

The scoring function is implemented in the msens R package:

msens::compute_er_score(
  extrisk_code,          # e.g., "NMFS:EN", "FWS:TN", "IUCN:CR"
  is_mmpa = FALSE,       # MMPA protection flag
  is_mbta = FALSE        # MBTA protection flag
)

The extrisk_code field follows the format AUTHORITY:STATUS where:

  • Authority: NMFS, FWS, or IUCN
  • Status: ESA codes (EN, TN, LC) or IUCN codes (CR, EN, VU, NT, LC, DD)