The Eastern Tropical Pacific (ETP), a large swath of the Pacific Ocean extending from Mexico to Peru, is the only region in the world where large pods of dolphins are prevalent above schools of tuna, accompanied by flocks of seabirds.
This gathering makes it possible to visually locate large schools of tuna by searching for the seabirds, which closely track the tuna.
Once the dolphins are sighted closer to the ocean surface, they are chased and encircled with purse seines to capture the schools of tuna underneath them.
A purse seine is a large surrounding net that hangs vertically in the water with its bottom edge held down by weights and its top edge buoyed by floats. Once the school of tuna is encircled, the net is “pursed” at the bottom, capturing the dolphins that follow the tuna.
Tuna and dolphins
It has been estimated that more than 7 million dolphins were killed by ETP tuna purse seiners since the late 1950s, and this is just due to entanglement. Research suggests that chase and encirclement may also have many other negative impacts on dolphins, such as increased fetal and calf mortality, separation of nursing females and their calves, decreased fecundity, increased predation, disruption of mating and other social systems, and ecological disruption.
In the mid-1960s, the high dolphin mortality in the ETP tuna purse seine fishery came to widespread public attention in the United States, resulting in calls on the government to take action that ultimately led to the Marine Mammal Protection Act (MMPA) being enacted in 1972 with the goal of reducing dolphin mortality to “insignificant levels approaching zero”.
Since dolphin mortality continued to be high after the passage of the MMPA, the legislation was tightened in subsequent amendments that led many US vessels to register under flags of other countries or to fish for tuna in other geographic regions, using other methods.
Modifications to purse-seine fishing methods were identified relatively early to reduce dolphin mortality from entanglement.
They range from simple solutions such as using swimmers and divers to disentangle and release dolphins and using high-intensity floodlights to illuminate dolphins in the nets at night, to more technical solutions. For example, the “backdown”, whereby the vessel is run in reverse after the seine has been pursed and approximately two-thirds of the net brought on board the vessel, which releases the dolphins while the tuna tend to remain below the dolphins in a deeper part of the net.
Sawing a “dolphin safety” panel of relatively small mesh netting into the purse seine to surround the apex of the backdown area where dolphins are most likely to gather has also proven very effective.
As US vessels left the ETP fleet due to the stringent MMPA requirements, vessels from other countries entered in larger numbers, so that the number of vessels using purse seines in the ETP continued to increase.
The 1984 amendments to the MMPA introduced embargoes on tuna imports from fleets with dolphin mortality above that of the US fleet, due to concerns that US gains in lowering dolphin mortality were being offset by increased mortality from non-US vessels.
In 1988, dolphin mortality requirements on tuna imports were further tightened.
At the same time, environmental public opinion pressure led to voluntary action by the three largest US tuna canners to buy only tuna caught using methods other than purse seine fishing.
The US embargo on the sale of tuna caught with purse seine nets was lifted in 1997 after challenges by Mexico and other nations under the General Agreement on Tariffs and Trade (GATT).
Meanwhile, a 1990 amendment to the MMPA established the “dolphin-safe” label, which mandated that during the entire trip for which tuna were captured no purse seines were deployed that targeted dolphins at the sea surface, as verified by a certified observer.
The labels, combined with environmental activism to pressure major US retailers, effectively excluded tuna caught on dolphins from the large and lucrative US market.
Mexico challenged the dolphin-safe label multiple times under the WTO non-discrimination rule and the WTO’s appellate body ruled against the US in 2012 and 2015, arguing that the label did not take into account the risk to dolphins of other tuna fishing methods.
After the US adapted the label, the appellate body upheld the measure in 2019 and ruled that it is fully consistent with WTO rules.
In the early 1990s, before the embargo on non-MMPA compliant tuna was lifted, the foreign fleets’ desire to re-enter the US market formed the basis for a series of multilateral initiatives.
In 1992, with the La Jolla Agreement, 10 fishing countries (including the US and Mexico) established the International Dolphin Conservation Program with a focus on comparability of dolphin mortality to the US fleet under the MMPA and the dolphin-safe label.
The agreement introduced two key features: the non-transferable Dolphin Mortality Limit (DML) per vessel, whereby once a vessel reached its own DML, it was required to cease purse seine fishing targeting dolphins, and a vessel changing flags would still retain its DML; and an International Review Panel (IRP) tasked with the review of cases of apparent non-compliance with the La Jolla Agreement based on fisheries observer reports.
In addition to representatives of the Parties to the Agreement, the IRP included elected industry and NGO representatives, thus increasing transparency and accountability.
In 1995, the Declaration of Panama was signed by 12 nations. It reaffirmed a commitment to reduce dolphin mortality to levels approaching zero, declared the nations’ intention to formally establish strict stock-specific DMLs on a per-vessel basis, and agreed to place fisheries observers on every large purse-seine vessel to verify dolphin mortality.
Finally, in 1998 features of the La Jolla Agreement and the Declaration of Panama were formally incorporated into the Agreement on the International Dolphin Conservation Program (AIDCP), a legally binding multilateral agreement with three primary objectives:
- Progressively reduce incidental dolphin mortalities in the tuna purse-seine fishery in the Agreement Area to levels approaching zero, through the setting of annual limits.
- Seek ecologically sound means of capturing large yellowfin tunas not in association with dolphins with the goal of eliminating dolphin mortality in this fishery.
- Ensure the long-term sustainability of the tuna stocks in the agreement area, as well as that of the marine resources related to this fishery, taking into consideration the interrelationship among species in the ecosystem.
Tuna and dolphins
The AIDCP also made periodic attendance of informational seminars to educate fishing captains on bycatch mitigation a requirement for certification to engage in purseseine fishing under the agreement.
Together, these institutional, market, and technological drivers reduced dolphin mortality due to entanglement by more than 99%. However, it is unclear whether and to what degree dolphin populations have recovered.
That is because conducting comprehensive repeated surveys to derive rigorous estimates of dolphin populations requires significant funding, not to mention the logistical challenges of such a large and remote area, and the multinational nature of the fishery, which complicate data collection, regulation, and enforcement.
Multilateral action is needed to monitor the biophysical outcomes of countries’ joint action.