Accidental capture in fishing nets
Accidental capture in fishing nets, also known as bycatch, is the leading cause of death in the vaquita, the world's smallest cetacean. This small porpoise lives only in the northern Gulf of California, Mexico. It becomes trapped in gillne...
What is it?
Accidental capture in fishing nets, also known as bycatch, is the leading cause of death in the vaquita, the world's smallest cetacean.
This small porpoise lives only in the northern Gulf of California, Mexico. It becomes trapped in gillnets set to catch other species, particularly the totoaba, a fish illegally sought for its swim bladder.
This cause of mortality is not a disease in the classical sense, but a severe traumatic accident. It is now considered the number one threat to the survival of the species, with only a handful of individuals remaining in the wild.
Commonly observed signs
These signs are neither exhaustive nor specific. Only a veterinarian can establish a diagnosis.
Related signs — each one links to its page:
When to consult without delay
This list does not replace veterinary advice. It gathers situations that justify a prompt consultation.
Causes and risk factors
The direct cause is prolonged submersion without the ability to rise and breathe, brought on by entanglement in a gillnet, particularly those used illegally for totoaba fishing.
The vaquita, like all cetaceans, breathes air at the surface. Caught in a fixed or drifting net, it cannot free itself and drowns within minutes to hours.
The presence of gillnets in the vaquita's highly restricted habitat, the Gulf of California, is the major risk factor.
Illegal totoaba fishing, pursued for the fish's swim bladder which is highly prized on certain Asian markets, uses nets particularly dangerous to vaquitas.
The small size of the remaining vaquita population means that each accidental capture has a disproportionate impact on the survival of the entire species.
Diagnosis and care
Diagnosis is the veterinarian's responsibility, based on clinical examination and laboratory tests. Care is decided case by case.
There is no standard veterinary diagnosis for this event: accidental capture is identified through direct observation by marine surveillance teams, or following discovery of a carcass washed ashore or caught in a net.
Necropsy examinations performed by marine wildlife specialists can confirm that drowning due to entanglement is the cause of death by looking for net marks, compatible internal injuries, and ruling out other causes of death.
Treatment
No medical treatment is possible once the animal has drowned.
If an animal is found alive but trapped, emergency rescue by teams specialized in marine mammals is necessary to free it from the net as quickly as possible.
In cases of superficial wounds on a rescued live animal, specialized veterinary care may include wound treatment and monitoring, but such interventions on the vaquita remain exceptional given its rarity and extremely shy nature.
Treatment depends on the cause and the animal's condition: it must be determined by a veterinarian. No self-medication.
Prevention
Prevention depends entirely on fisheries management measures, not on individual animal care.
This includes banning and effectively removing gillnets from areas frequented by vaquitas, stepped-up enforcement against illegal totoaba fishing, development of alternative fishing gear with no entanglement risk, and international cooperation to reduce illegal demand for totoaba swim bladder.
These actions depend on Mexican authorities and conservation organizations, not on a pet owner, since the vaquita is an undomesticated wild species.
Possible complications
Drowning is the most frequent and serious complication, causing death in a short time.
In a rescued live animal, deep wounds, secondary infections, and severe stress can compromise its survival over the longer term.
At the species level, each accidental capture brings the vaquita closer to extinction, with the total population estimated at an extremely low number of individuals.
When to see a veterinarian
Observation of a porpoise entangled in a fishing net in the Gulf of California.
Discovery of a small cetacean carcass washed ashore or caught in fishing gear.
Observation of an animal swimming abnormally or very weakened near a fishing area.
Any report should be made immediately to the competent Mexican authorities or local marine conservation organizations, never attempted alone without proper training.
Prognosis
The prognosis is very poor in cases of complete entanglement: the vast majority of vaquitas caught in nets drown before rescue is possible.
At the population level, the conservation prognosis for the species is extremely concerning. The vaquita is considered critically endangered, with the number of surviving individuals estimated below ten according to some recent assessments.
Without complete elimination of gillnets from its habitat, specialists believe the species could disappear in the very near future.
Frequently asked questions
Why is the vaquita so vulnerable to fishing nets? The vaquita is vulnerable to fishing nets for several reasons: 1. **Small size and habitat** – The vaquita is one of the smallest cetaceans (around 1.2–1.5 meters long) and lives in shallow waters of the Gulf of California, where gillnets are commonly used. 2. **Poor visibility** – Gillnets are nearly invisible in the water, and the vaquita's echolocation and vision are not effective enough to detect them in time. 3. **Slow movement** – Unlike faster dolphins and whales, vaquitas move slowly, reducing their ability to escape entanglement. 4. **Solitary behavior** – Vaquitas are shy and avoid boats, which paradoxically makes them less aware of fishing activities in their area. 5. **Limited range** – Their entire population is confined to a small area (about 3,500 square kilometers) in the Gulf of California, concentrating the risk. 6. **Illegal fishing** – Illegal gillnets for totoaba fish are the primary threat, as fishermen prioritize profit over the vaquita's survival. These factors combined have made the vaquita the world's most endangered marine mammal, with fewer than 10 individuals remaining.
It lives in a highly restricted area of the Gulf of California where fishing, particularly illegal fishing, uses gillnets. Its small size and discreet lifestyle do not protect it from entanglement, and like all cetaceans it must surface to breathe, which becomes impossible if it is trapped.
Can an injured vaquita be treated after being caught in a net?
In theory yes, if she is released alive and quickly taken care of by specialized teams. In practice, these interventions are very rare because the species is extremely wary and difficult to approach, and most trapped animals drown before any rescue is possible.
What can be done to prevent these accidental captures?
Mexico has established fishing exclusion zones for gillnets in vaquita habitat, with monitoring and removal of abandoned nets. These measures are primarily aimed at combating illegal totoaba fishing, whose nets are particularly deadly for the species.
How many vaquitas are left today?
The most recent estimates suggest an extremely low residual population, likely fewer than ten individuals, which places the species among the most threatened marine mammals in the world.
References
WOAH — Organisation mondiale de la santé animale (ex-OIE)
FAO — Organisation des Nations unies pour l'alimentation et l'agriculture
Content reviewed by the TunisieVet editorial team · Updated 03 September 2026
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