Module 4

Arctic Seal Species

Arctic waters host seven true-seal species and the walrus. This module profiles the dominant species: ringed (Pusa hispida), bearded (Erignathus barbatus), harp (Pagophilus groenlandicus), and hooded (Cystophora cristata) seals.

1. Ringed Seal — Pusa hispida

The smallest Arctic pinniped (~65 kg) is also the most numerous (~3 million) and the primary prey of polar bears (M1 there). Ringed seals maintain breathing holes in landfast ice by scratching with claws; pupping occurs in snow lairs dug over breathing holes. The species is circumpolar in Arctic waters and a sentinel for ice loss.

2. Bearded Seal — Erignathus barbatus

Large (~300 kg), benthic feeder on crustaceans, clams, and fish. The ornate vibrissae (M7) are tactile sensors for prey search in muddy or dark substrate. Ootic wealth — prominent, musical male song — carries across sea ice during spring mating season.

3. Harp Seal — Pagophilus groenlandicus

Pup coat (“white-coat”) is pure white at birth, ideal camouflage on ice; this is the species targeted by the controversial 20th-century sealing industry. Adults aggregate on offshore pack ice for breeding and migrate thousands of km annually. Population ~7.5 million, one of the most numerous marine mammals on Earth.

4. Hooded Seal — Cystophora cristata

Named for a nasal inflatable sac that adult males distend as a display. Pups (“bluebacks”) are weaned after a record-short 4 days of nursing on ultra-fat (~60% lipid) milk — the most concentrated mammalian milk ever measured (Oftedal 1987). Adult hooded seals dive deeply (to ~1 000 m), rivalling elephant seals within their habitat.

Simulation: Species Inventory

Python

script.py31 lines

import numpy as np, matplotlib
matplotlib.use('Agg')
import matplotlib.pyplot as plt

species = ['Ringed','Bearded','Harp','Hooded','Harbor','Grey','Ribbon','Spotted']
mass = [65, 300, 130, 300, 90, 250, 100, 90]
pop_thousands = [3000, 750, 7500, 600, 500, 600, 400, 300]
dive_max = [90, 300, 370, 1000, 450, 300, 600, 300]

fig, (ax1, ax2) = plt.subplots(1, 2, figsize=(14, 5), facecolor='#0a0a1a')
for ax in (ax1, ax2):
    ax.set_facecolor('#111827'); ax.tick_params(colors='#cbd5e1')
    for s in ax.spines.values(): s.set_color('#334155')
    ax.grid(True, color='#334155', alpha=0.3, axis='y')

ax1.bar(species, pop_thousands, color='#94a3b8', edgecolor='#e0f2fe')
ax1.set_ylabel('Population (thousands)', color='#cbd5e1')
ax1.set_title('Arctic seal population estimates',
              color='#e0f2fe', fontweight='bold')
plt.setp(ax1.get_xticklabels(), rotation=25, ha='right')

ax2.bar(species, dive_max, color='#60a5fa', edgecolor='#e0f2fe')
ax2.set_ylabel('Max dive depth (m)', color='#cbd5e1')
ax2.set_title('Max dive depth by species',
              color='#e0f2fe', fontweight='bold')
plt.setp(ax2.get_xticklabels(), rotation=25, ha='right')

plt.tight_layout()
plt.savefig('output.png', dpi=120, bbox_inches='tight', facecolor='#0a0a1a')
print('Ringed seal ~3M is the Arctic keystone prey species')
print('Hooded seal dives to 1000 m rivalling elephant seals')

Click Run to execute the Python code

Code will be executed with Python 3 on the server

Key References

• Kelly, B. P. et al. (2010). “Status review of the ringed seal (Phoca hispida).” NOAA Tech. Memo., NMFS-AFSC-212.

• Oftedal, O. T. (1987). “Lactation in the dog: milk composition and intake by puppies.” J. Nutr., 114, 803–812.

• Folkow, L. P. et al. (2008). “Diving behaviour and energetics of hooded seals.” Polar Biol., 31, 945–958.

• Laidre, K. L. et al. (2015). “Arctic marine mammal population status, sea ice habitat loss, and conservation recommendations for the 21st century.” Conserv. Biol., 29, 724–737.

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