Module 1

Weddell Seal Diving

Kooyman’s 1966 Antarctic work on Leptonychotes weddellii founded the modern physiology of diving. Weddell seals routinely dive 20–40 min and record dives exceed 90 min — durations that require oxygen stores, bradycardia, and anaerobic metabolism to manage. This module quantifies the aerobic dive limit (ADL) and the physiological toolkit.

1. Oxygen Stores

Total body O₂ stores in diving seals are 3–5× human mass-specific values. Three compartments:

Blood O₂ — elevated blood volume (20–25% body mass), high haemoglobin (~25 g dL^-1). Splenic contraction releases stored erythrocytes at dive onset.
Muscle myoglobin — 4–7 g per 100 g muscle, 10× human. Elevated positive surface charge prevents protein aggregation at the high concentrations (Mirceta 2013 Science).
Lung O₂ — small; lungs collapse at depth and are not the primary store.

2. Dive Reflex & Bradycardia

Heart rate falls from ~70 bpm surface to ~10 bpm during deep dives. Selective vasoconstriction shunts blood away from muscles and viscera, preserving oxygenation of brain and heart. Lactate accumulates in peripheral tissue during the dive and is cleared rapidly on surfacing (Scholander 1940 definitional work). The reflex is triggered by apnoea + facial-water submergence.

Simulation: ADL & Dive Distribution

Python

script.py46 lines

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

# Kooyman 1966 Weddell seal aerobic dive limit
# O2 stores
mass = 450    # kg
# Blood: ~200 ml/kg, Hb 25 g/dL -> O2 capacity
blood_O2 = mass * 0.21 * 1.34 * 25 * 0.9 / 100   # L O2
# Muscle: myoglobin 5 g/100g; skeletal muscle 35% mass
muscle_O2 = mass * 0.35 * 0.05 * 1.34 * 0.9      # L O2
# Lungs: collapse during deep dive -> not relied on
lung_O2 = 2.0
total_O2 = blood_O2 + muscle_O2

# Dive VO2: resting ~3 ml O2/kg/min * mass
VO2_rest = 3 * mass / 1000    # L/min
ADL_min = total_O2 / VO2_rest

# Dive duration distribution observed
durations = np.array([5, 15, 25, 40, 55, 72, 96])
frequencies = np.array([45, 30, 12, 7, 3, 2, 1])   # % observations

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)

ax1.bar(['Blood','Muscle','Lung'], [blood_O2, muscle_O2, lung_O2],
        color=['#dc2626','#f97316','#60a5fa'], edgecolor='#e0f2fe')
ax1.set_ylabel('O2 store (L STPD)', color='#cbd5e1')
ax1.set_title(f'Total O2 {total_O2:.1f} L; ADL {ADL_min:.0f} min',
              color='#e0f2fe', fontweight='bold')

ax2.bar(durations, frequencies, color='#94a3b8', edgecolor='#e0f2fe')
ax2.axvline(ADL_min, color='#dc2626', ls='--', label=f'Calc ADL {ADL_min:.0f} min')
ax2.axvline(96, color='#fbbf24', ls='--', label='Max observed 96 min')
ax2.set_xlabel('Dive duration (min)', color='#cbd5e1')
ax2.set_ylabel('% of dives', color='#cbd5e1')
ax2.set_title('Kooyman 1966 dive distribution', color='#e0f2fe', fontweight='bold')
ax2.legend(facecolor='#1e293b', edgecolor='#334155', labelcolor='#cbd5e1')

plt.tight_layout()
plt.savefig('output.png', dpi=120, bbox_inches='tight', facecolor='#0a0a1a')
print(f'Calc ADL {ADL_min:.0f} min; 96 min extreme dives require anaerobic extension')

Click Run to execute the Python code

Code will be executed with Python 3 on the server

3. Under-Ice Navigation

Weddell seals maintain breathing holes by cutting through fast ice with their canines and incisors, scratching channels several metres deep. They hold exclusive access to individual holes through social dominance; subordinates must find alternate routes, often travelling kilometres under ice. Echolocation is not used; the seals rely on residual bioluminescence, vision in dim light, and whisker-based proprioception to navigate back to breathing holes (M7).

Key References

• Kooyman, G. L. (1966). “Maximum diving capacities of the Weddell seal.” Science, 151, 1553–1554.

• Scholander, P. F. (1940). “Experimental investigations on the respiratory function in diving mammals and birds.” Hvalradets Skrifter, 22, 1–131.

• Mirceta, S. et al. (2013). “Evolution of mammalian diving capacity traced by myoglobin net surface charge.” Science, 340, 1234192.

• Williams, T. M. et al. (2015). “Exercise at depth alters bradycardia and incidence of cardiac anomalies in deep-diving marine mammals.” Nat. Commun., 6, 6055.

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