Differences in the occurrence and abundance of batoids across an oceanic archipelago using complementary data sources: Implications for conservation

Abstract

Batoids, distributed from shallow to abyssal depths, are considerably vulnerable to anthropogenic threats. Data deficiencies on the distribution patterns of batoids, however, challenge their effective management and conservation. In this study, we took advantage of the particular geological and geomorphological configuration of the Canary Islands, across an east-to-west gradient in the eastern Atlantic Ocean, to assess whether patterns in the occurrence and abundance of batoids varied between groups of islands (western, central, and eastern). Data were collected from shallow (<40 m, via underwater visual counts and by a local community science program) and deep waters (60-700 m, via ROV deployments). Eleven species of batoids, assessed by the IUCN Red List of Threatened Species, were registered, including three "Critically Endangered" (Aetomylaeus bovinus, Dipturus batis, and Myliobatis aquila), three "Endangered" (Gymnura altavela, Mobula mobular, and Rostroraja alba), two "Vulnerable" (Dasyatis pastinaca and Raja maderenseis), and two "Data Deficient" (Taeniurops grabata and Torpedo marmorata). Also, a "Least Concern" species (Bathytoshia lata) was observed. Overall, batoids were ~1 to 2 orders of magnitude more abundant in the central and eastern islands, relative to the western islands. This pattern was consistent among the three sources of data and for both shallow and deep waters. This study, therefore, shows differences in the abundance of batoids across an oceanic archipelago, likely related to varying insular shelf area, availability of habitats, and proximity to the nearby continental (African) mass. Large variation in population abundances among islands suggests that "whole" archipelago management strategies are unlikely to provide adequate conservation. Instead, management plans should be adjusted individually per island and complemented with focused research to fill data gaps on the spatial use and movements of these iconic species.

Distribution and population structure of the smooth‐hound shark, Mustelus mustelus (Linnaeus, 1758), across an oceanic archipelago: Combining several data sources to promote conservation

“…In addition to this, and regarding conservation implications, our results suggest that, because of the large differences in abundance of this shark among the Canary Islands, management of the species should be adapted to the specific peculiarities of each island, rather than adopting a management policy at the entire archipelago‐scale. This strategy reinforces the idea of taxon specificities, that is, taxon dependencies, when depicting conservation actions on coastal elasmobranchs in the Canary Islands (Tuya et al, 2021). This should be underpinned by more research into the species' habitat, ecology, distribution, and behavior.…”

“…416 km from the African coast (Fernández‐Palacios & Martín Esquivel, 2001). Differences in the composition and abundance of marine biodiversity across the entire archipelago have been previously reported for macroalgae (Tuya & Haroun, 2009), reef fishes (Tuya et al, 2004) and rays (Tuya et al, 2021). In general, species of temperate affinities are limited (e.g., Sparus aurata ) or more abundant (e.g., Coris julis and Serranus papilionaceus ) in the easternmost islands, while species of tropical affinities are limited (e.g., Corniger spinosus and Gymnothorax miliaris ) or more abundant (e.g., Aulostomus strigosus and Heteropriacanthus fulgens ) in the westernmost islands (Brito et al, 2001).…”

“…Lanzarote and Fuerteventura, including islets north of Lanzarote, were categorized as the “eastern islands.” The “central islands” include Gran Canaria and Tenerife, old to middle‐age islands with moderately large, and independent, insular shelfs. Finally, the islands of La Gomera, La Palma and El Hierro, that is, the “western islands,” are the youngest islands, particularly El Hierro and La Palma, which are characterized by small and abrupted insular shelfs (Table 1, Tuya et al, 2021). Three marine protected areas are found across the archipelago, including “Punta La Restinga‐Mar de Las Calmas” (El Hierro Island, from 1996), “Isla de La Graciosa e islotes del norte de Lanzarote” (northern Lanzarote Island, from 1998) and “La Palma” (La Palma Island, from 2001) (Tuya, García‐Díez, et al, 2006).…”

Black coral forests enhance taxonomic and functional distinctiveness of mesophotic fishes in an oceanic island: implications for biodiversity conservation

“…Briefly, divers counted and identified, to the lowest possible taxonomic level (minimum genus level), all fish individuals within the transect area while swimming at a constant speed (Table S1 ), with fishes entering the field of view from behind the divers excluded to minimize double-counting. Sharks and rays (class Chondrichthyes) were excluded from the analyses due to their highly vagrant behavior and patchy distributions that challenge their population assessment via UVC 65 (only representing 6% of the species initially recorded and 0.01% of the total abundance). Also, they have, markedly distinct life history, morphological, and ecological traits 66 that might represent outliers in the multidimensional functional space.…”

The Status of Marine Megafauna Research in Macaronesia: A Systematic Review

“…Many basic biological questions relevant to fisheries management remain unanswered regarding the life-history, reproduction, and drivers of distribution of many chondrichthyes in the region. For example, the scarcity of research conducted on batoids from Madeira and Cabo Verde, with only recent advancements from the Canary Islands (see Tuya et al, 2021), remains a particularly concerning hindrance to the management of these species. Furthermore, there is some evidence of pupping and potential nursery grounds in Macaronesia [e.g., blue shark Prionace glauca, Azores (Vandeperre et al, 2014(Vandeperre et al, , 2016; smooth hammerhead shark Sphyrna zygaena, Azores (Santos et al, 1995;Das and Afonso, 2017) and Madeira (Freitas and Biscoito, 2018); angelshark, Canary Islands (Meyers et al, 2017;Jiménez-Alvarado et al, 2020)], yet there is little information generally on biologically sensitive areas, including nursery grounds, inshore and offshore aggregation, and deep-water skate and ray egg deposition sites.…”