bioRxiv preprint doi: https://doi.org/10.1101/2020.12.09.417493; this version posted December 9, 2020. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under aCC-BY 4.0 International license. 1 A first assessment of the distribution and abundance of large 2 pelagic species at Cocos Ridge seamounts (Eastern Tropical 3 Pacific) using drifting pelagic baited remote cameras 4 Marta Cambra1,2*, Frida Lara-Lizardi3, , Cesar Peñaherrera3, Alex Hearn3,4, James 5 T. Ketchum3,5, Patricia Zarate3,6, Carlos Chacón7, Jenifer Suárez-Moncada8, Esteban 6 Herrera9 and Mario Espinoza2, 10 7 8 1. Postgraduate Program in Biology, Universidad de Costa Rica, San Pedro, San José, Costa 9 Rica. 10 2. Centro de Investigación en Ciencias del Mar y Limnología, Universidad de Costa Rica, San 11 Pedro, San José, Costa Rica. 12 3. MigraMar, Sir Francis Drake Boulevard, Olema, California, United States of America 13 4. Galapagos Science Center, Universidad San Francisco de Quito, Quito, Ecuador. 14 5. Pelagios Kakunjá. Sinaloa, Las Garzas, La Paz, Baja California Sur, México. 15 6. Division de Investigación Pesquera, Instituto de Fomento Pesquero, Valparaíso, Chile. 16 7. Fundación Pacífico, Sabana Norte, San José, Costa Rica. 17 8. Dirección del Parque Nacional Galápagos, Isla Santa Cruz, Ecuador. 18 9. Área de Conservación Marina Cocos, Heredia, Costa Rica 19 10. Escuela de Biología, Universidad de Costa Rica, San Pedro, San José, Costa Rica. 20 21 * Corresponding author: [email protected] 1 bioRxiv preprint doi: https://doi.org/10.1101/2020.12.09.417493; this version posted December 9, 2020. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under aCC-BY 4.0 International license. 22 Abstract 23 Understanding the link between seamounts and large pelagic species (LPS) is critical 24 for guiding management and conservation efforts in open water ecosystems. The 25 seamounts along the Cocos Ridge in the Eastern Tropical Pacific (ETP) are thought to play 26 a critical role for LPS moving between Cocos Island (Costa Rica) and Galapagos Islands 27 (Ecuador). However, to date, research efforts to understand pelagic community structure 28 beyond the borders of these oceanic Marine Protected Areas (MPAs) have been limited. 29 This study used drifting-pelagic baited remote underwater video stations (BRUVS) to 30 characterize the distribution and relative abundance of LPS at Cocos Ridge seamounts. Our 31 drifting-pelagic BRUVS detected a total of 21 species including sharks, large teleosts, 32 small teleosts, dolphins and one sea turtle, of which 4 are threatened species. Relative 33 abundance and richness of LPS was significantly higher at shallow seamounts (<400m) 34 compared to deeper ones (>400m) suggesting that seamount depth could be an important 35 driver structuring LPS assemblages along the Cocos Ridge. Our cameras provided the first 36 visual evidence of the schooling behaviour of S. lewini at two shallow seamounts outside 37 the protection limits of Cocos and Galapagos Islands. However, further research is still 38 needed to demonstrate a positive association between LPS and Cocos Ridge seamounts. 39 Our findings showed that drifting pelagic BRUVS are an effective tool to survey LPS in 40 fully pelagic ecosystems of the ETP. This study represents the first step towards the 41 standardization of this technique throughout the region. 42 2 bioRxiv preprint doi: https://doi.org/10.1101/2020.12.09.417493; this version posted December 9, 2020. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under aCC-BY 4.0 International license. 43 Introduction 44 Quantifying the spatial distribution and abundance of pelagic species is critical to 45 effectively manage and protect their populations in open oceans [1]. Overexploitation of 46 these highly productive regions is driving many large pelagic species (LPS) such as 47 elasmobranchs, large teleosts, sea turtles and cetaceans to dangerously low levels [2,3], 48 raising global concerns about the potential top-downs effects on marine ecosystems [4,5]. 49 Seamounts have been recognized as productive and unique features in open water-systems 50 where highly migratory LPS tend to aggregate, thus becoming highly vulnerable areas to 51 overfishing [6,7]. Understanding the link between seamounts and LPS is critical for 52 identifying regional hotspots of biological production, and guiding management and 53 conservation efforts in open water ecosystems [8]. 54 The Cocos Ridge is a chain of seamounts in the Eastern Tropical Pacific (ETP) that 55 connects Cocos Island (Costa Rica) and the Galapagos archipelago (Ecuador) [9]. These 56 two oceanic island groups are considered biodiversity hotspots in the ETP because of the 57 high biomass of apex predators they harbor [10,11]. They are also Marine Protected Areas 58 (MPAs) and UNESCO World Heritage Sites [12,13]. Previous studies have shown a higher 59 degree of movement connectivity between Cocos and Galapagos Islands relative to other 60 regions of the ETP, suggesting that LPS may be using this area as a migratory corridor 61 [14–18]. Cocos Ridge seamounts are thought to be sites of ecological importance where 62 LPS aggregate during these migrations [18]. However, most research effort on LPS in the 63 ETP have concentrated inside MPAs [19–22] and therefore, the biological diversity and 64 community structure associated to seamounts have still not been described. 3 bioRxiv preprint doi: https://doi.org/10.1101/2020.12.09.417493; this version posted December 9, 2020. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under aCC-BY 4.0 International license. 65 As LPS continue decreasing in the ETP [19,21,23], there is a greater need to survey 66 the open ocean to effectively guide marine spatial planning [24]. Information outside the 67 protection boundaries of Cocos and Galapagos Islands is scarce and restricted to fishery 68 dependent data [25–27] or to movement studies on sharks [14–17,28], teleosts [29] and sea 69 turtles [30,31]. Despite the valuable information acquired from biotelemetry devices to 70 understand individual habitat preferences, movements and migrations, this technique relies 71 on the catch of a high number of individuals from various species in order to understand 72 pelagic community structure and identify aggregation sites in the open ocean [32]. 73 Furthermore, such studies can be invasive, expensive and logistically challenging [33]. 74 Fisheries data also present some limitations as they are usually biased by temporally and 75 spatially uneven sampling effort, gear selectivity and lack of robust reports [34,35]. 76 Drifting-pelagic baited remote underwater video stations (BRUVS) have 77 demonstrated a promising potential for studying pelagic wildlife in open water ecosystems 78 [36–38]. Drifting-pelagic BRUVS are an adaptation of the benthic BRUVS where an 79 anchoring system is no longer needed, thus enabling dynamic sampling over deep and 80 topographically complex pelagic areas [37]. The odor of the bait triggers bait-search 81 behavior in nearby fish assemblages, increasing the probability of detecting predatory 82 species in the vicinity of the BRUVS [39]. A reduced amount of zeros derived from bait 83 use increases the statistical power of BRUVS compared to traditional survey techniques 84 [40–42]. Although the drifting-pelagic version of BRUVS has received little attention to 85 date [43], it offers a powerful framework to overcome the difficulties associated to 86 effectively survey pelagic assemblages [36]. For example, drifting-pelagic BRUVS units 87 can be simultaneously deployed reducing the survey effort while generating permanent 4 bioRxiv preprint doi: https://doi.org/10.1101/2020.12.09.417493; this version posted December 9, 2020. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under aCC-BY 4.0 International license. 88 high definition images on species composition, behavior and relative abundance at 89 different depth levels and for long periods of time [37]. Additionally, they are affordable 90 and easy to operate allowing the participation of stakeholders into the field work. In this 91 study, we used drifting-pelagic BRUVS for the first time in the ETP to characterize the 92 distribution and relative abundance of LPS at Cocos Ridge seamounts. This study might 93 serve as an important reference on the future use of drifting-pelagic BRUVS at a regional 94 level. 95 96 Methodology 97 Study area 98 The Cocos Ridge is an underwater mountain range located in the northwestern 99 Panama basin of the ETP, which originated more than 30 million years ago as a result of 100 volcanic activity from the Galapagos Ridge hot spot [9]. The Cocos Ridge rises about 2000 101 m above the seafloor and extends more than 1000 km from the Galapagos Islands to Cocos 102 Island, and from Cocos Island to the south pacific coast of Costa Rica [9,44,45]. Although 103 the depth and total number of seamounts along the Cocos Ridge is not available on global 104 bathymetric databases, there are at least 14 seamounts that have been identified in this 105 region [18,44]. All the seamounts along the Cocos Ridge are located within the 200 Nm 106 mile Exclusive Economic Zones (EEZs) of either Ecuador or Costa Rica (Fig 1).