Pregnant giant devil ray ( Mobula mobular ) bycatch reveals potential Northern Gulf of California pupping ground

Sharks and rays are globally in peril because of overharvesting, with a quarter listed as threatened under the International Union for the Conservation of Nature (IUCN). Out of the seven most threatened families, five of them are families of rays (Dulvy et al. 2014). Two keys to their successful conservation are fisheries regulation and finding and protecting key nursery habitats for threatened or endangered species (Lawson et al. 2017). Although fishing regulation and enforcement has received the most attention and has generated international agreements, relatively little progress has been made in protecting pupping grounds. One of the greatest impediments to bringing protection of nursery habitats into multipronged conservation strategies is that for most shark and ray species, we simply do not know where females give birth (Stewart et al. 2018). Giant devil rays (Mobula mobular) occur in tropical and temperate oceans. Many of these populations face increasingly heightened pressure, as they are caught as bycatch in high numbers, threatened by low reproduction rates, and fished to meet the demand for their gill plates for traditional Chinese medicine (Acebes 2013, Lawson et al. 2017, O’Malley et al. 2017). Therefore, understanding giant devil ray ecology is critically important to the conservation of the species. Despite their global range and protection by international groups, there is still critical and basic information about the species that remains unknown (Notarbartolo di Sciara et al. 2015). For example, we have little knowledge of aggregation, pupping, and migration zones along with their reproductive biology, but this information would allow more targeted and effective protections and help halt overexploitation of this species. Here, I present a previously undocumented observation of dozens of pregnant devil rays with full-term pups caught in northern Sonora (Fig. 1). This new natural history understanding is significant for their future management and conservation, as it suggests the first potential documented pupping ground for the species. While taking a class and observing a small-scale fishing community at Old Kino Beach, I noticed dozens of mobulid rays caught as bycatch in gillnets on 12 April 2014. As a result of the rays’ immense size and weight, the fishers were unable to return them to sea and were forced to land them. Using photogrammetry, I estimated the disc width of two of the pregnant adult female rays to be 1.97 m and 2.17 m, and one of the pups to be 0.91 m. These sizes are similar to disc-width measurements of this species in the Philippines, with females reaching sexual maturity at an average of 2.18 m, and newborn pups at an average of 1.00 m (Rambahiniarison et al. 2018). I observed one captured sexually mature male, and every observed female ray being cut open was pregnant with one pup. I determined that the pups were full-term, as I revived one birthed into a net with the permission of the fisherman and it successfully swam away. Each boat landed multiple rays, suggesting that the nets were set out in a pupping zone for this species. The interaction between the rays and fishers was negative for both groups. The rays entangled in the fishermen’s nets drove away the desired catch, and earnings greatly decreased, as mobulid meat is not valuable in the Gulf of California, only earning them 3 pesos per kilo. In other parts of the world, their overexploitation is driven by demand for Peng Yu Sai, an ineffective but wellmarketed tonic in traditional Chinese medicine, which contains their highly valued gill plates (Lawson et al. 2017). At this time, mobulid rays are not targeted for their gill plates in the Gulf of California, but if a market opens up, this would significantly increase the pressure on their populations. Despite their size and expansive distribution, their full annual movement patterns and critical reproductive zones remain unidentified. Previously, pupping zones were hypothesized to occur offshore at islands or seamounts (Ebert 2003) or in the northern Mediterranean Sea (Notarbartolo di Sciara and Serena 1988). According to previous studies, giant devil rays are found in the