Twenty Years of Research on Demersal Communities Using the Delta Submersible in the Northeast Pacific

Abstract

Visual surveys of demersal fishes and their associated habitats are being conducted regularly in deep water (i.e., 30-365 m) off Alaska and the West Coast of North America by numerous research groups using quantitative transect methods from the research submersible Delta. The use of Delta has been applied primarily to the characterization of fish habitats, with increasing applications to improve stock assessments, evaluate gear impacts, and identify new species. Using Delta is no longer an unproven concept, but rather an accepted survey tool as demonstrated in more than 85 peerreviewed publications since 1988. Maps of seafloor substrata and bathymetric data are commonly used to identify and quantify survey sites, which serves both to increase the costeffectiveness of the submersible and provide the frame within which to distribute sampling effort. In turn, direct observations from Delta can be used to validate the interpretation of such habitat maps. Values that are commonly measured or estimated during Delta dives include the number and length of organisms, distance to a fish, and distance along a transect, from which habitat-specific species density, total abundance, and biomass can be calculated. In this paper we review the research that has been conducted using Delta during the last twenty years, and consider some potential sources of methodological bias as well as the advantages and some strategies for conducting visual surveys using Delta.

Evidence of stability in a chondrichthyan population: case study of the spotted ratfish Hydrolagus colliei (Chondrichthyes: Chimaeridae)

“…Size‐specific patterns of H. colliei aggregation were assessed by qualitative video analysis of visual strip‐transect surveys conducted by the delta submersible (Yoklavich & O’Connell, 2008). These data provided information that was unobtainable from the fishery‐independent groundfish surveys because of the risk of getting trawl gear snagged on high‐relief rock habitat.…”

Demersal fish assemblages in the Southern California Bight based on visual surveys in deep water

“…This method, direct observations of fish assemblages from the Delta submersible, has been used extensively to characterize both fish diversity and their ontogenetic movements (Yoklavich and O'Connell 2008).…”

Environmental factors that influence the distribution, size, and biotic relationships of the Christmas tree coral Antipathes dendrochristos in the Southern California Bight

“…However, characterizing cold-water coral habitats is inherently difficult because of the complex nature of marine ecosystems in which multiple factors affect coral−habitat associations, the range of spatial and temporal scales over which habitat features are relevant, and the practical difficulties of sampling deep-sea habitats. Increased use of manned submersibles and remotely operated vehicles to survey deep-sea fisheries habitat has provided unique and valuable data sets that have been gleaned from archived video (Yoklavich & O'Connell 2008). These spatially explicit data include numerous species of fishes and invertebrates, their sizes, densities, and associated habitat components.…”