Summary

Authors: Chris Rooper, Mike Sigler, Pam Goddard, Pat Malecha, Rick Towler, Kresimir Williams, and Rachel Wilborn

Institution: Alaska Fisheries Science Center

Abstract: In summer 2014 we conducted a survey of the eastern Bering Sea slope and outer shelf using an underwater stereo camera at 250 randomly selected transects. The objective of this survey was to verify distribution models of coral, sponge, and sea whips that were based on bottom trawl survey data that had been presented to the North Pacific Fishery Management Council in June 2013. Additionally, we collected data on invertebrate density, height, and fish associations and documented the presence of fishing gear and damage to invertebrates. Presence or absence models of coral, sponge and sea whips were also constructed from the camera survey data and were compared to previous coral, sponge, and sea whip models constructed from bottom trawl survey data. The model of coral presence or absence based on bottom trawl survey data was generally accurate in predicting coral presence or absence in the camera survey. The bottom trawl survey models were also accurate in predicting sponge and sea whip presence or absence, but to a lesser degree than for coral. Corals were found at 32 of 250 transects, most of which were located in Pribilof Canyon and the slope area to the northwest. Overall, the densities of corals were low, averaging 0.005 individuals*m-2 and ranging from 0 to 0.28 individuals*m-2. The low densities were consistent with the absence of hard substrates for coral attachment in most areas of the eastern Bering Sea. Densities of corals were generally highest in Pribilof Canyon and corals were largest in the slope area to the northwest of Pribilof Canyon. For sponges, densities and heights were highest surrounding Pribilof Canyon, north of Bering Canyon, and in some locations in Zhemchug Canyon. Sea whip densities and heights were highest on the outer shelf between Pribilof and Zhemchug Canyon and in an area to the south of Pribilof Canyon. There were significant positive relationships between fish density and the presence of coral and sponge for some rockfish species and king crabs. There were significant negative relationships for grenadiers and Chionoecetes crabs. Direct evidence of fishing gear occurred at 12.8% of transects. Individual demosponges (0.3%), Isididae corals (2.9%) and sea whips (9.0%) were observed to be damaged. Vulnerability of benthic invertebrates was estimated from the field data on invertebrate density and height and was modeled for the entire eastern Bering Sea outer shelf and slope. Based on height and density, the areas that appeared to be most vulnerable for coral occurred in narrow areas of the two arms of Pribilof Canyon and in deeper areas to the northwest along the slope. For sponge and sea whips, the most vulnerable areas were centered around the shelf break and extended from Pribilof Canyon to the north for sponge and from Bering Canyon to the north for sea whips. Although combining the bottom trawl survey models and the camera survey models only exhibited some improvement over bottom trawl survey data-based models alone, the combined models were able to integrate both bottom trawl and camera data into a single map of the probability of invertebrate presence and from this a prediction of density of invertebrates for the eastern Bering Sea slope and outer shelf.

This report is a deliverable of DSCRTP's Alaska Fieldwork Initiative (FY12-14).

 
Category:
  • Technical Report
Type: DSCRTP Supported Date: 2015
Region(s):
  • North Pacific Council
Location(s):
  • Eastern Bering Sea