Summary
As part of a Strategic Environmental Impact Assessment of oil activities in the Disko West area, the spatiotemporal distribution of marine organisms and ecosystem processes in the marginal ice zone was studied in spring 2006. The study had two main objectives: 1) identifying key areas for biodiversity at this highly dynamic time of year, and 2) evaluating factors affecting the spatial distribution of key species and groups. Two surveys were carried out simultaneously in Disko Bay and south-eastern Baffin Bay: an aerial survey of seabirds and marine mammals, and an oceanographic cruise combined with transect surveys. On the cruise, physical and biological data were recorded at 116 stations situated approx. 10 km apart, and seabirds and marine mammals were surveyed between stations. Thick-billed murres were collected at sea to assess their diet. Where appropriate, remote sensing data were used to supplement the in situ measurements and observations.
Vertical profiles of salinity and temperature showed that stratification progressed over the three-week study period, with some spatial variation. Nutrient concentrations were generally high, and conditions for a phytoplankton spring bloom were thus in place. Accordingly, in situ measurements of fluorescence as well as remote sensing data showed a gradual increase in chlorophyll concentration. The bloom seemed to occur earlier on Store Hellefiskebanke in the southern part of the study area, perhaps because the shallow depth allowed phytoplankton to remain in the photic zone before stratification was established, i.e. when the water column was fully mixed.
Mesozooplankton biomass in the upper part of the water column was dominated by Calanus copepods (64%), barnacle larvae (nauplii, 16%) and shrimp larvae (12%). Larger planktonic organisms were not sampled adequately by the available gear. Copepods were dominant in all areas except on Store Hellefiskebanke, where barnacle nauplii were most abundant. Total zooplankton biomass showed a high spatial variability, with few clear patterns. Statistical modelling showed that ice concentration affected the distribution of all three key groups, with a weak avoidance of ice by copepods and shrimp larvae, and a strong preference for ice by barnacle nauplii, which also preferred areas where stratification was weak. All fish larvae observed were sand lance, and these were mainly found around Store Hellefiskebanke.
Abundance estimates based on the aerial survey showed that about one million seabirds used the study area in spring. The most numerous species were thick-billed murre (430,000) and king eider (400,000), followed by northern fulmar (89,000), black-legged kittiwake (77,000) and black guillemot (21,000). King eiders were concentrated on Store Hellefiskebanke and common eiders near coastlines, areas that are shallow enough to allow them access to their benthic prey. The spatial distribution of the other common species was much more complex, partly because the study period was relatively long and birds probably redistributed themselves as food and ice conditions changed. Statistical modelling based on the ship survey data showed that northern fulmars and black-legged kittiwakes were more likely to occur in areas where the spring bloom was well developed, whereas thick-billed murres preferred deep waters and black guillemots preferred shallow waters. None of these relationships were very strong. Further statistical analyses of the spatial distribution of seabirds based on the aerial surveys are planned, using newly developed methods.
Many thick-billed murres had empty stomachs, and among the remainder invertebrates (amphipods and squid) were more common than fish. Capelin was the only fish species positively identified in murre stomachs.
Abundance estimates of marine mammals were based on the aerial survey. These showed that the most numerous species in the study area were ringed seal (4600), beluga (1400), bearded seal (1200), bowhead whale (450) and walrus (420). However these estimates were very imprecise and almost certainly too low, because they were not corrected for submerged animals.
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