Why Whales Beach Themselves and What We Know About Mass Strandings

Why Whales Beach Themselves and What We Know About Mass Strandings

Mass whale strandings — where dozens or even hundreds of whales beach themselves simultaneously — are among nature's most puzzling phenomena. Scientists have identified several contributing factors (naval sonar, disease, disorientation, social bonding), but no single explanation accounts for all strandings. The mystery persists despite decades of research, and strandings appear to be increasing worldwide.

The Scale

• 1,000+ strandings reported annually worldwide
• 300+ species of marine mammals have been documented stranding
• Largest mass stranding: 835 pilot whales, New Zealand (2017)
• Largest single species stranding: 400 pilot whales, Tasmania (2023)
• Strandings occur on every continent except Antarctica
• Annual increase: Strandings have increased 20% in the last decade

Species Most Commonly Affected

• Pilot whales: Account for 60% of mass strandings (highly social, follow leaders)
• Sperm whales: Deep divers that can get disoriented in shallow water
• Beaked whales: Extremely sensitive to naval sonar (ziphiids)
• Dolphins: Both solitary and mass strandings
• False killer whales: Social species prone to mass events

Known Causes

1. Naval sonar (strongest evidence):

• Mid-frequency active sonar (MFAS) used by military navies causes beaked whales to strand
• Sonar damages whale hearing and causes decompression sickness ("the bends")
• Beaked whales dive to 1,000-2,000m and surface slowly — sonar causes rapid ascent
• 2000: Mass stranding of beaked whales in the Bahamas coincided with US Navy sonar exercises
• 2002: NATO sonar exercises linked to strandings in the Canary Islands
• Multiple courts and scientific bodies have confirmed the sonar-stranding link
• But sonar explains only beaked whale strandings, not pilot whale mass strandings

2. Social bonding (explains pilot whales):

• Pilot whales form extremely tight social groups (pods of 20-100)
• If one whale (especially a matriarch) is sick or disoriented and beaches, the pod follows
• Their social instinct to stay together overrides individual survival instinct
• This is why mass strandings almost always involve the same species and pod
• Rescue efforts face a dilemma: Save one → the pod may restrand to rejoin it

3. Disease and parasites:

• Brain parasites (nematodes) can cause disorientation
• Bacterial and viral infections documented in stranded individuals
• Morbillivirus outbreaks have caused mass dolphin strandings
• Chronic illness may impair navigation ability

4. Navigational errors:

• Whales navigate using magnetic fields, sound, and seabed topography
• Gently sloping beaches can confuse echolocation (sound doesn't bounce back clearly)
• Rapidly changing seabed features (sandbars, channels) can trap whales
• Following prey into shallow water and becoming stranded

5. Climate change:

• Changing ocean temperatures alter prey distribution → whales follow into unfamiliar waters
• Shifts in migration routes → whales encounter new hazards
• Warming waters → increased disease susceptibility
• More frequent extreme weather → disorientation in storms

The Rescue Challenge

What happens during strandings:

• Whales suffer organ damage from their own weight on land (gravity compresses organs)
• They can survive only 24-48 hours out of water
• Sun exposure, overheating, and dehydration are immediate threats
• Rescuers must keep whales cool, wet, and upright

Rescue techniques:

• Keep whales upright and wet (sheets, water)
• Dig trenches around pectoral fins to relieve pressure
• Use boats to guide whales back to deeper water
• Herd non-stranded pod members to prevent them from beaching
• In some cases: Euthanasia is the only humane option (severe injuries)

The restranding problem:

• Rescued whales often restrand (30-50% restrand rate)
• Social instinct draws them back to stranded pod members
• Some rescuers euthanize stranded whales to prevent the pod from returning

New Zealand: The Stranding Capital

• New Zealand has the highest stranding rate in the world
• 3-4 mass strandings per year on average
• Farewell Spit (South Island) is a global stranding hotspot
• Shallow, gently sloping beaches confuse whale echolocation
• New Zealand has one of the world's best stranding response networks
• 2023: 40 pilot whales euthanized after restranding at Farewell Spit

The Takeaway

Whale strandings remain one of nature's great unsolved mysteries. Naval sonar clearly causes strandings in beaked whales. Social bonding explains why pilot whales strand in mass groups. Disease, disorientation, and climate change contribute. But no single explanation fits all cases. What we know is that strandings are increasing, the causes are complex and overlapping, and the rescue efforts — while heroic — face an impossible dilemma: saving one whale may doom its entire pod to restrand. The best long-term solution may be reducing the human activities (sonar, ocean noise, pollution) that contribute to disorientation, while accepting that some strandings are natural phenomena we can't prevent.