Bathymetric distribution of the Chilean red sea urchin (Loxechinus albus, Molina) in the inner seas of northwest Patagonia: Implications for management

One of the primary invertebrates in Chilean benthic fisheries is the red sea urchin Loxechinus albus Molina, 1782. Currently, the main fishing grounds for this urchin are located in the inner seas of Patagonia, an area otherwise known as the southern channels and fiords. Anecdotal information supports the notion that this species of urchin lives between the surface waters and a depth of 340 m. Because of this supposed abundance, the fishery is in expansion. We used divers handling submarine cameras and a ROV-type LBV (Little Benthic Vehicle), operating between the surface and 105 m depth, to study the number and density per transect, substrate and depth strata of red sea urchin in fishing areas surrounding the Corcovado Gulf, to the South of Chiloé Island and in the Guaitecas Archipelago. Knowledge of the bathymetric and geographic distribution are important in quantitative assessments and the development of strategies to conserve marine resources, particularly for Loxechinus albus, which is the subject of intense exploitation in the continental seas of Chile. The results from this research show that the proportion of sea urchins inhabits in shallow waters (0–30 m) is 97.7% of the total observed population, and only 2.5% of the total sampled sea urchins was found in deeper waters (below 30 m) in the Guaitecas Archipelago. In the southern area of Chiloé Island, 76.6% was observed inhabits in shallow strata (0–30 m) and 23.4% was found deeper strata (>31 m). In each case, deep red sea urchins were significantly associated with hard bottoms (rocks, boulders and stones). The percentage living in deep waters is considered insufficient to replace the individuals removed by the shallow water fishery, and we suggest considering the bathymetric distribution in the Management Plan for this resource.

► Chilean red urchins were quantified in the channels of X and XI regions using a ROV.
► Statistically significant presence of urchins over rocky substrate was found.
► The density was highly variable as a result of aggregation over rocky substrate.
► Over 77% of the population inhabit in the first 30 m at the south of Chiloé.
► Over 98% live in the first 30 m at the Guaitecas Archipelago.