Good News from the Zero Tolerance Area in late 2022: Less illegal gillnetting and more evidence of vaquita survival

By Kristin Nowell, Cetacean Action Treasury


In 2022 there was a major new development in the Zero Tolerance Area (ZTA), the 225 km2 polygon inside Mexico’s Vaquita Refuge in the Upper Gulf of California. The ZTA, which was delineated to encompass all recent vaquita sightings and acoustic detections, has been designated as a no-fishing and no-entry zone since September 2020. However, there is strong evidence of lax enforcement: fishing skiffs (pangas) were observed inside the ZTA on 88% of observation days from October 2021 to May 2022. In response to persistent violations, the Mexican Navy developed a radical proposal to deter the use of illegal gillnets which have driven the precipitous decline of the Critically Endangered vaquita population. Between July 8 and September 30 (normally a season of low fishing activity), a grid of 193 gillnet-deterrent structures was installed on the ZTA seabed. They were lowered by crane into the water and placed in a grid about 1.1 km apart. The structures are concrete blocks a meter square, with two 3.5 m tall, 1 ½ inch diameter iron rebar hooks protruding from the top, intended to entangle gillnets as they drift with the tides (Figure 1).

Figure 1 – Gillnet deterrent structures being deployed in the Zero Tolerance Area

Anti-trawl structures have been used by other countries to stop trawl nets from operating in protected areas (such nets are dragged along the seafloor), but this approach has never been tried against gillnets outside of shallow waters (ZTA depths range from 10-30 m). Counts of fishing pangas in the ZTA from Sea Shepherd Conservation Society (SSCS) and scientific vaquita surveys were used to determine if there were any initial deterrent impacts (see full report for details).

The highest-ever recorded count of pangas in the ZTA in recent years (117) was in the fall 2021 shrimp season. To try to prevent a repeat in the fall 2022 shrimp season, Cetacean Action Treasury’s Mexican partner organization, Pesca ABC, with support from the International Conservation Fund of Canada, made five posts on its Facebook page in September through October, providing the ZTA coordinates and offering to assist fishers to input them into their GPS. Over a dozen fishers came to Pesca ABS’s office in San Felipe for assistance, and overall the posts garnered nearly 18,000 views.

It is well known locally that gillnetters prefer to work in spring tides (strong tidal fluctuations associated with the full and new moons, with approximately two such tidal periods per month). Maximum daily panga count data for 2021 and 2022 were grouped and averaged for consecutive spring tides (days when the difference between consecutive tide peaks – high or low – are over 350 cm). Although panga counts were not available for all spring tide days due to occasional absence of SSCS ships from the area, comparing consecutive tides for the two years suggests a significant reduction in gillnetting in the ZTA in 2022 subsequent to the first major fishing effort in the second October spring tide (Table 1). In other words, many fishers with gillnets apparently began to avoid the area.

Table 1. Reduction in average maximum daily count of pangas in the ZTA over consecutive bi-monthly spring tides in 2022 compared to 2021

Monthly spring tide cycle Oct – #2 Nov – #1 Nov – #2 Dec – #1
2021 27.6 74.5 42.5 41.6
2022 21.3 14.8 11.0 5.8
Reduction 33% 81% 74% 86%


On November 16, Pesca ABC warned the community in its social media that they knew of fishers getting their nets stuck on the structures. On January 11 2023, another San Felipe CAT partner organization (MAREM) asked fishers on Facebook to share coordinates of lost nets to aid in their removal. Although the only public comment on the post was “Nobody wants to cooperate” (which is illustrative of local non-compliance with the December 8 2021 requirement to report lost fishing gear within 24 hours), ultimately eight sets of coordinates were provided by fishers. Two sets were outside the ZTA, but all six sets reported inside the ZTA coincided with coordinates of deterrent structures, suggesting that the structures had been at least partially effective at snagging gillnets.

Active deterrence actions by the Mexican Navy increased significantly in fall 2022 compared to the previous year. SSCS ships assisted compliance monitoring by sending situation reports (SITREPs) of gillnetting in the ZTA; Navy actions are described in SSCS daily Scientist reports. The Navy was generally responsive to SSCS SITREPs during the spring tides of 2022, and was observed to “drive pangas out of the ZTA” on multiple occasions, with several instances where gillnets were seized or fishers were directed to remove them. In contrast, although Navy patrol boats were present during the 2021 fall vaquita survey (first two spring tides in Table 1), no interaction with pangas was observed.

The reduction of illegal gillnetting may have contributed to an observed increase in the rate of vaquita acoustic encounters after installation of the deterrent structures (Armando Jaramillo-Legorreta, pers. comm.). Eight acoustic sampling exercises (see here for background on Mexico’s acoustic monitoring program), supported by CICESE and CONANP and facilitated by community fishers associated with Pesca ABC and MAREM, were carried out in neap tide periods in 2022 (when few gillnetters would be expected to be present, thus minimizing the potential for loss of or tampering with monitoring equipment). Vaquitas were detected in every sampling exercise, indicating that at least some individuals were consistently present in the ZTA. Based on distance between encounters and maximum potential swimming speeds, 11.7% of 77 total encounters in 2022 were considered likely to have been detections of different individuals or groups of individuals. Comparing five exercises with comparable sampling effort, the number of vaquita encounters per day (number of acoustic detections >30 minutes apart) increased noticeably after installation of the deterrent structures was completed (Table 2). An increased acoustic encounter rate could reflect a change in vaquita behavior (vaquitas generally echolocate when hunting prey) associated with reduced gillnetting in the ZTA, but does not signify a change in population trend, which is still declining (A. Jaramillo-Legorreta, pers. comm.).

Table 2. Rate of vaquita acoustic encounters/day in the ZTA increased in late 2022

Sampling exercise Vaquita acoustic encounters/day Ending date
Installation of gillnet deterrent structures underway
4 0.057 20/09/2022
Installation of gillnet deterrent structures completed
5 0.045 04/10/2022
6 0.183 20/10/2022
7 0.248 18/11/2022
8 0.122 18/12/2022

Source: A. Jaramillo-Legorreta pers. comm., research supported by CICESE/CONANP


The Navy and CONANP had been warned in advance that pangas with gillnets would likely concentrate around the ZTA, creating an edge effect and increasing the risk to vaquitas that move outside the ZTA, which they certainly do. Since early February 2023, SSCS has been conducting panga counts in a one nautical mile buffer zone around the ZTA, and hopefully the Mexican Navy will be as responsive to reports of illegal gillnetting around the ZTA as inside it. Time-bound compliance processes in 2023 under CITES and the USMCA will further increase the pressure on Mexico to enforce its gillnet ban more effectively in the Upper Gulf of California. Unfortunately, a program to frequently inspect and clean the deterrent structures of entrapped or snagged net material, which could pose an entanglement risk to vaquitas, has not yet been implemented. There will be continued urgency to prevent fishers with other types of gillnets from entering the ZTA as the fishing seasons change in spring from shrimp to commercial finfish fishing and totoaba poaching. Some types of finfish and totoaba gillnetting usually do not involve setting on the bottom, as shrimp gillnets are, and these other types of gillnetting may not be deterred by the seabed concrete structures. Therefore, security for vaquitas during the coming months will depend on increased voluntary compliance by the fishing community and enforcement actions by authorities.