Module 5

Antarctic Seal Species

The Southern Ocean hosts one of the planet’s great mammalian radiations. Crabeater seals alone number ~15 million — the most abundant large mammal after humans. Four phocid species plus Antarctic fur seal dominate the pack-ice and shelf-edge habitats. This module profiles each.

1. Crabeater Seal — Lobodon carcinophaga

Despite the name, crabeater seals eat krill — >95% of the diet is Euphausia superba. Specialised multi-cusp postcanine teeth form a sieve when jaws close: the seal opens its mouth, takes in a volume of krill-laden water, closes to expel the water through the tooth sieve, and swallows the retained krill. This is the only pinniped filter-feeding apparatus (King 1983). Population ~15 million make crabeaters the most abundant large mammal on Earth.

2. Weddell Seal — Leptonychotes weddellii

The southernmost breeder and the subject of M1’s diving physiology. Circum-Antarctic fast-ice resident; population ~800 000. Unique among mammals for its tolerance of continuous exposure to −50 °C air during winter breeding.

3. Leopard Seal — Hydrurga leptonyx

Apex Antarctic predator; eats penguins, crabeater pups, and fish. Adult females reach 600 kg and 3.5 m, larger than males. Robust jaw musculature, long canines, and ambush strategy from pack-ice edges. Rogers 2009 resolved the acoustic repertoire that underwater hydrophones reveal as a near-constant chorus during breeding.

4. Ross Seal — Ommatophoca rossii

The least-known and most solitary Antarctic seal. Large eyes adapted for mesopelagic squid foraging; deep-diving specialist (to ~600 m). Population estimate ~130 000. Rarely observed directly; the species was named by Sir James Clark Ross during his 1840 expedition.

5. Southern Elephant Seal & Fur Seals

Southern elephants are the largest pinniped (males to 4 t) with the most extreme sexual dimorphism of any mammal. They breed on sub-Antarctic islands and forage across the Southern Ocean. Antarctic fur seals (Arctocephalus gazella) recovered from near-extinction by 20th-century sealing to ~4 million today.

Simulation: Species Inventory

Python

script.py40 lines

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

species = ['Crabeater', 'Weddell', 'Leopard', 'Ross', 'S. Elephant', 'Antarctic Fur']
mass = [230, 450, 350, 220, 2200, 140]
pop_M = [15, 0.8, 0.22, 0.13, 0.65, 4.0]
diet = {'Krill':      [95,  0, 15, 45,  0, 30],
        'Fish':       [ 3, 50, 10, 30,  5, 55],
        'Squid':      [ 1, 40, 20, 25, 90, 15],
        'Penguins':   [ 0,  0, 45,  0,  0,  0],
        'Seals':      [ 0,  0, 10,  0,  0,  0]}

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_M, color='#60a5fa', edgecolor='#e0f2fe')
ax1.set_ylabel('Population (millions)', color='#cbd5e1')
ax1.set_title('Antarctic seal populations', color='#e0f2fe', fontweight='bold')
plt.setp(ax1.get_xticklabels(), rotation=25, ha='right')
for i, (v, n) in enumerate(zip(pop_M, species)):
    ax1.text(i, v+0.3, f'{v} M', ha='center', color='#e0f2fe')

bot = np.zeros(len(species))
cols = {'Krill':'#f472b6','Fish':'#60a5fa','Squid':'#fbbf24','Penguins':'#f87171','Seals':'#dc2626'}
for cat, vals in diet.items():
    ax2.bar(species, vals, bottom=bot, color=cols[cat], edgecolor='#e0f2fe', label=cat)
    bot = bot + np.array(vals)
ax2.set_ylabel('Diet composition %', color='#cbd5e1')
ax2.set_title('Dietary partitioning', color='#e0f2fe', fontweight='bold')
ax2.legend(facecolor='#1e293b', edgecolor='#334155', labelcolor='#cbd5e1', fontsize=8)
plt.setp(ax2.get_xticklabels(), rotation=25, ha='right')

plt.tight_layout()
plt.savefig('output.png', dpi=120, bbox_inches='tight', facecolor='#0a0a1a')
print('Crabeater seal ~15M: most abundant large mammal on Earth')
print('Leopard seal: apex predator, eats penguins and other seals')

Click Run to execute the Python code

Code will be executed with Python 3 on the server

Key References

• King, J. E. (1983). Seals of the World, 2nd ed. British Museum.

• Rogers, T. L. (2009). “Age-related differences in the acoustic characteristics of male leopard seals.” J. Acoust. Soc. Am., 122, 596–605.

• Siniff, D. B. et al. (2008). “Opinion: projecting the effects of environmental change on Antarctic seals.” Antarct. Sci., 20, 425–435.

• Southwell, C. et al. (2008). “Estimating population status under conditions of uncertainty: the Ross seal in East Antarctica.” Antarct. Sci., 20, 123–133.

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