Module 8

Predator-Prey & Leopard Seal

Polar seals occupy multiple trophic levels: crabeater seals filter-feed on krill, leopard seals hunt penguins and other seals, and orcas — using the famous wave-washing coordinated hunting technique — prey on ice-bound Weddell seals. This module covers the trophic network and the charismatic predation cases.

1. Orca Wave-Washing

Pitman & Durban 2012 (Mar. Mamm. Sci.) documented coordinated groups of 3–5 Type B orcas (Antarctic) generating standing bow waves that wash seals off small ice floes. The orcas approach in a tight formation, accelerate in unison, then dive beneath the floe; the resulting wave tips the floe and dislodges the seal. Observed success rate ~70%. The behaviour requires cultural transmission and is specific to populations that specialise on ice-bound seals.

2. Leopard Seal Predation

Leopard seals (Hydrurga leptonyx) are the Antarctic apex predator of warm-blooded prey: penguins (principally Adélie and gentoo), seal pups (crabeater and Weddell), fish, and squid. Ambush strategy from pack-ice edge waiting for penguins to enter water. Hunting range overlaps with every Antarctic penguin colony. Hiruki 1999 and Rogers 2009 catalogued prey composition and hunting methods.

3. Crabeater Filter-Feeding

The crabeater seal’s multi-cusp postcanine teeth form a sieve unique among pinnipeds. The seal opens its mouth, takes in a volume of krill-laden water, closes and compresses; water is expelled through the tooth interstices while krill is retained. King 1983 documented the dental anatomy; more recent work (Churchill 2014) has re-examined tooth microwear to confirm the filter function. A single crabeater consumes ~40 kg of krill per day.

Simulation: Wave-Washing & Diet

Python

script.py52 lines

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

# Wave-washing orcas: 3-5 coordinated orcas generate wave that slides seal off floe
# Physics: bow wave from coordinated swimming; amplitude scales with swim speed
v = np.linspace(2, 8, 100)
wave_amp = 0.08 * v**1.5        # m
mass_seal = np.linspace(50, 300, 6)

# Energy required to dislodge seal (friction + gravity)
mu_ice = 0.03
def energy_to_slide(m, amp):
    return m * 9.81 * (mu_ice + amp/3.0)

fig, axes = plt.subplots(1, 3, figsize=(17, 5), facecolor='#0a0a1a')
for ax in axes:
    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)

ax = axes[0]
ax.plot(v, wave_amp*100, color='#60a5fa', lw=2.5)
ax.axhline(15, color='#fbbf24', ls='--', label='Wave amplitude to dislodge ~15 cm')
ax.set_xlabel('Orca swim speed (m/s)', color='#cbd5e1')
ax.set_ylabel('Wave amplitude (cm)', color='#cbd5e1')
ax.set_title('Coordinated orca bow wave',
             color='#e0f2fe', fontweight='bold')
ax.legend(facecolor='#1e293b', edgecolor='#334155', labelcolor='#cbd5e1')

ax = axes[1]
# Crabeater teeth schematic as Fourier series
x = np.linspace(0, 2*np.pi, 200)
y = 0.5 + 0.4*np.cos(4*x) + 0.2*np.cos(8*x)
ax.fill_between(x, 0, y, color='#f472b6', alpha=0.6, edgecolor='#e0f2fe')
ax.set_title('Crabeater postcanine sieve tooth', color='#e0f2fe', fontweight='bold')
ax.set_xlabel('Tooth cross-section (sideview)', color='#cbd5e1')
ax.set_ylabel('Height', color='#cbd5e1')

# Leopard-seal prey size distribution
prey_cats = ['Krill', 'Fish', 'Squid', 'Penguins', 'Seal pups']
freq = [15, 10, 20, 45, 10]
ax2 = axes[2]
ax2.bar(prey_cats, freq, color='#f87171', edgecolor='#e0f2fe')
ax2.set_ylabel('% of stomach contents', color='#cbd5e1')
ax2.set_title('Leopard seal diet', color='#e0f2fe', fontweight='bold')
plt.setp(ax2.get_xticklabels(), rotation=20, ha='right')

plt.tight_layout()
plt.savefig('output.png', dpi=120, bbox_inches='tight', facecolor='#0a0a1a')
print('Wave-washing: documented 4-5 orcas, 70% success dislodging seals (Pitman 2012)')
print('Crabeater filter teeth are the only pinniped specialisation for filter-feeding')

Click Run to execute the Python code

Code will be executed with Python 3 on the server

4. Synthesis

Polar seals span krill filter-feeders at one end of the food web and apex predators at the other. The Southern Ocean’s exceptional productivity feeds ~30 million seals; Arctic ringed seals in turn sustain polar bears. Climate- driven sea-ice loss (see polar-bears M6) disproportionately threatens ice-dependent species: ringed seal, ribbon seal, harp seal, crabeater. Krill decline compounds the pressure on filter-feeders. The eight modules of this course outline the biology that determines how each species responds.

Key References

• Pitman, R. L. & Durban, J. W. (2012). “Cooperative hunting behavior, prey selectivity and prey handling by pack ice killer whales.” Mar. Mamm. Sci., 28, 16–36.

• Hiruki, L. M. et al. (1999). “Diet of leopard seals.” Can. J. Zool., 77, 959–964.

• Churchill, M. et al. (2014). “Origin of the penguin-like teeth of crabeater seals.” Proc. R. Soc. B, 281, 20133130.

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

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