Staff from the Status of Stocks and Multispecies Assessment (SSMA) Program's
Fisheries Interaction Team (FIT) led NMFS's first dedicated fish survey of the Beaufort Sea this summer (30 July to 30 August).
The survey was funded by the Minerals Management Service (Department of the Interior). Participating institutions included the University of Alaska and the University of Washington. The goals of the survey were to provide a baseline for analysis of the impacts of future oil and gas development in the Beaufort Sea and for the study of climate change. The results from the survey also will provide information for the Arctic Fisheries Management Plan currently under development by the NPFMC.
The survey was conducted on the chartered vessel Ocean Explorer in shelf waters (20 to 500 m depth) between 155°W and 152°W. The species composition, distribution, and abundance of benthic fish and invertebrates were assessed with standard bottom trawl methods.
Pelagic fish were surveyed with fisheries acoustics and midwater nets. In addition, oceanographic data and zooplankton samples were collected to assess water column properties and the prey available to fish. Scientists also recorded marine mammal observations and conducted transect surveys for seabird distribution and abundance.
The cruise was a success. One challenge was the presence of sea ice during the transit from Dutch Harbor and in the study area. The vessel encountered fairly heavy ice around Pt. Barrow, requiring approx. 24 hours of slow and careful steaming to work through it (Fig. 1). When the vessel arrived on the survey grounds on 6 August, dense sea ice covered the inner- and midshelf areas (20-100 m) and persisted for 6 days. Only the deepest stations could be sampled during that time (100-500 m depth).
After 6 days it was possible to trawl at midshelf stations (less than 100 m water depth), although it required navigating through ice to reach open water, and fishing operations were conducted within 0.5 to 3 nmi of the ice. However, the next day (13 August), the midshelf region was mostly clear of ice, and ice was not encountered in densities requiring a change in survey plans for the remainder of the cruise.
A total of 26 bottom trawls and 27 midwater trawls were conducted. Seven approximately 30-nmi acoustic transects were surveyed (Fig. 2). Fish comprised 6% of the total weight captured in the bottom trawls of which 38 species of fish were identified. Of the total weight of fish captured in the bottom tows, 80% was Arctic cod (Boreogadus saida); several species of eelpouts (Lycodes spp.) made up 13% of the total weight.
Figure 4. An adult polar bear (presumably female) and two cubs on the ice near Pt. Barrow. Photo courtesy of Joao DoMar.
Collections of other species resulted in extensions of known distributional ranges. For example, Bering flounder (Hippoglossoides robustus), walleye pollock (Theragra chalcogramma), Pacific cod (Gadus macrocephalus), marbled eelpout (Lycodes raridens), salmon snailfish (Careproctus rastrinus) and bigeye sculpin (Triglops nybelini) were not formerly known to inhabit Beaufort Sea waters (pending species confirmation with voucher specimens).
Invertebrates comprised 94% of the total weight captured in the bottom tows of which approximately 174 species were identified. Of the invertebrates, Ophiura sarsi (brittlestar) made up 41%, and Chionoecetes opilio made up 10% of the total weight. The pelagic fish community, as assessed with acoustics and midwater nets, was dominated by Arctic cod.
Data on the distribution and abundance of seabirds were collected during the transit to and from Dutch Harbor and during the acoustic transects when conditions allowed. Arctic terns, black-legged kittiwakes and phalaropes were the most abundant seabirds in the study area. Figure 3 shows the distribution of these three species. Terns appeared to be distributed primarily in offshore depths (approx. 100-500 m), whereas kittiwakes were most abundant in mid- and inner-shelf depths (20-100 m). Phalaropes were very patchy and observed in high abundances at just two locations in the midshelf area.
Opportunistic marine mammal sightings were recorded in collaboration with the Platforms of Opportunity program at the National Marine Mammal Laboratory. Highlights included an adult polar bear (presumably female) and two cubs on the ice near Pt. Barrow (Fig. 4). A swimming polar bear was also observed in the same area. Large numbers of gray whales were observed during the transit to and from the study area, in the Chukchi Sea/Bering Strait area. They appeared to be feeding. No confirmed bowhead whale sightings were made during the transit or in the study area.
Temperature-depth data were collected with a trawl-mounted microbathythermograph (MBT) on all trawls. Figure 5 shows bottom temperature at all bottom trawl locations. Bottom temperatures ranged from -1.4° to 1°C. The coldest bottom water appeared to be found at depths ranging from around 70 m to 300 m, with warmer water inshore and offshore of those depths.
