necroplankton relative to communities in the northwestern part 

 of the Bering Sea were, at the outer continental shelf, 20% of 

 the total number; at the frontal zone over the 100-m isobath, 8% 

 of the total; and 7% of the total in the cold water mass of the 

 central shelf area. These regions are joined either by extreme 

 characteristics of the plankton community in the North Bering 

 Sea Shelfand Pacific basin or in the extremely low temperature 

 conditions of the water, which are near freezing. 



In the deep water area of the Bering Sea, the condition of 

 the major oceanic populations were normal. The average of 



total dead specimens was 5% of total numbers. On the outer 

 and northwestern shelf of the Bering Sea, the population of 

 oceanic species appeared here together with Anadyr Curtent 

 waters. As a result of the impact of unfavorable factors and 

 intensive illumination, it is necessary to note that there is a high 

 level of dead organisms of both oceanic and neritic types 

 associated with the Anadyr Current. In the Chukchi Sea, 

 necrozooplankton were at background levels with low mean 

 values found during the entire period of study. 



5.2.4 Carbon Isotope Ratios in Zooplankton as 

 Markers of Aging and Habitat Usage for 

 the Bowhead Whale (Balaena mysticetus) 



DONALD M. SCHELL, NORMA HAUBENSTOCK, and KIMBERLY A. VINETTE 



Institute of Marine Science. University of Alaska. Fairbanks. Alaska. USA 



Introduction 



The Third Joint US-USSR Bering & Chukchi Seas 

 Expedition was used to obtain zooplankton samples from the 

 two seas for stable isotope abundance studies. This paper 

 presents the d"C and d'^N data acquired from the cruise on 

 board the Soviet research vessel Akademik Korolev, in context 

 with pre vious data on stable isotope values in arctic zooplankton. 

 Although the nitrogen isotope data are also listed, we have 

 confined the discussion to the more comprehensive carbon 

 isotope data. Recent findings have shown that distinctive 

 gradients exist in the stable isotope ratios of carbon in 

 zooplankton from the Bering to the eastern Beaufort Seas. 

 With increasing latitude, the heavier isotope is less abundant in 

 the phytoplankton and this "signature" is passed up the food 

 chain. We have been using these natural tracers to determine 

 critical feeding habitats for bowhead whales (Balaena 

 mysticetus) and to aid in separating US and USSR polar bear 

 stocks that commingle in the Chukchi Sea during the winter 

 months. The work on bowhead whales has been described in 

 Schell et at. (I989a,b) and Saupe et al. (1989). The study on 

 polar bears is still in progress. 



Isotope Ratios in Food Web Studies 



Ecosystem studies involving biochemical systems usually 

 depend upon two approaches. One approach is to construct 

 budgets or mass balances of a key element and attempt to 

 determine which fluxes dominate these budgets. The second 

 approach measures the key rates or processes within the system 

 and then attempts to relate the findings to the overall goal. 

 Although ideally the two approaches should be complementaiy 

 and finally coalesce into abetter understanding of the ecosystem, 

 this goal is usually difficult to attain. There may be mismatches 



between time and space scales of the two approaches or 

 processes that cannot be determined to the required accuracy. 

 Many of these quandaries are evident in any attempt at estimating 

 the feeding requirements of bowhead whales. Because stable 

 isotope ratios can contribute both source (tracer) information 

 and process information, they are ideally suited for the 

 measurement of elemental movements, which in this case is 

 carbon. 



The field of stable isotope tracers has steadily expanded 

 and a wealth of information on terrestrial and aquatic applications 

 is now available. Fry and Shert (1984) and Peterson and Fry 

 ( 1 987 ) review these applications and discuss the strengths and 

 weaknesses of the many studies. There will be no attempt here 

 to review all of these applications, but several pertinent findings 

 will be presented. Rundel et al. ( 1989) presented a series of 

 papers on various applications including several multiple isotope 

 tracer studies. 



The fidelity of consumers to the isotopic compositions of 

 diet underlies all ecological studies using stable isotopes. 

 DeNiro and Epstein ( 1 978 ) plotted diet versus consumer isotope 

 ratio and found that the transfer was conservative with regard 

 to the whole animal. A small enrichment occurs of about one 

 part per thousand per trophic step, typically slightly larger with 

 herbivores and less with carnivores. This has been documented 

 in both field and laboratory studies (see review by Peterson & 

 Fry, 1987; McConnaughey & McRoy, 1979). A succinct 

 report by Jones et al. (1981) documents the change in isotope 

 ratios of cattle fed C-3 plants, then changed to C-4 plants, and 

 then switched back again. Within 70 days, newly grown hair 

 had reached equilibrium with the new diet after each change. 

 Since the hair required several days to reach the surface of the 

 skin following shaving, actual response was faster than the 

 isotope ratios in the shavings indicated. 



177 



