Midwater Invertebrates from the Southeastern Chukchi 



Sea: Species and Abundance in Catches Incidental to 



Midwater Trawling Survey of Fishes, 



September-October 1970 



BRUCE L. WING and NANCY BARR' 



ABSTRACT 



Midwater invertebrates were collected in the southeastern Chukchi Sea. A 1.8-m Isaacs-Kidd 

 midwater trawl was used at 20 stations to collect 81 semiquantitative samples; a :!-m otter trawl was 

 used at one station to collect two qualitative samples. Data tables list the species collected and their 

 numbers, size range, and displacement volumes for the midwater trawl stations and a species list only 

 for the otter trawl station. One hundred three species of invertebrates were identified from the mid- 

 water trawl samples, and ,33 species were identified from the otter trawl samples. Amphipods were the 

 most diverse group (40 species) and decapod shrimps the next most diverse (14 species). Numbers of 

 species in a sample varied from 4 to 40 (mean 17). After removal of jellyfishes, the most important con- 

 tributors in numbers and volume to the catches were euphausiids and mysids. 



INTRODUCTION 



The Western Beaufort Sea Ecological Cruises (WEB- 

 SEC) were a sequence of oceanographic cruises spon- 

 sored by the U.S. Coast Guard to assess the Alaskan arc- 

 tic marine environment and biota before major indus- 

 trial development. The Coast Guard enlisted the efforts 

 of federal, state and university research groups for the 

 program, and the National Marine Fisheries Service con- 

 tributed to the first three cruises with studies of 

 zooplankton, midwater invertebrates, and fishes. 



The intent of the first cruise, WEBSEC-70, which took 

 place during September and October 1970, was to ex- 

 amine the arctic coast from Barrow eastward to Barter 

 Island. Extremely heavy ice conditions in mid-Septem- 

 ber 1970 prevented the Icebreaker Glacier from working 

 in the Beaufort Sea; therefore, an alternative area, the 

 southeastern Chukchi Sea between Point Lay and Cape 

 Lisburne (Fig. 1) was surveyed between 25 September 

 and 17 October. Preliminary results of physical, 

 chemical, geological, and biological investigations for 

 WEBSEC-70 were reported by Ingham et al. (1972); and 

 reports were later published by Quast (1974) and Wing 

 (1974). 



This report presents data on the invertebrates taken in 

 midwater trawls made to collect fishes from 25 Septem- 

 ber to 17 October 1970. The data are presented in tabular 

 form and are not interpreted, although some apparent 

 sampling anomalies are discussed. The tables provide a 

 list of species found, numbers of individuals taken, and 

 linear size range and displacement volume of the 



'Northwest and Alaska Fisheries Center .Auke Bay Laboratory, National 

 Marine Fisheries Service, NOAA. P.O. Box 155, Auke Bay, AK 99821. 



specimens of each species. These data are the first 

 attempts to quantitatively assess macroplanktonic and 

 niicronektonic invertebrates in the southeastern Chuk- 

 chi Sea. 



METHODS 



A 1.8-m Isaacs-Kidd midwater trawl was used to 

 sample at 20 stations for a total of 81 tows (Fig. 1, Ap- 

 pendix Table 1). The trawl had a forward section of 38- 

 mm bar mesh, a rear section of 6-mm bar mesh, and a 

 cod end of 3-mm bar mesh. Cross-sectional areas were 

 calculated to be 2.87 m' at the mouth, 1.55 m' at the 

 beginning of the 6-mm mesh, and 0.13 m- at the begin- 

 ning of the 3-mm mesh. The depth of tow was recorded 

 by a bathykymograph attached to the bottom of the 

 depressor. Tows were standardized for a length of 3.7 km 

 at an estimated vessel speed of 4 knots. At least four tows 

 were made at each of the 20 stations, two on one bearing 

 and two on the reciprocal bearing. Trawling was general- 

 ly done at night in areas relatively free of ice. The choice 

 of sampling depths was dependent on water depths and 

 on whether or not the samples were intended to be 

 replicates or were to examine depth distributions (Quast 

 1974). 



At one station (No. 8— Fig. 1) two trawls were made 

 with a 3-m, 38-mm mesh otter trawl (shrimp try net) to 

 collect bottom fishes and invertebrates. 



Large scyphomedusans and most hydromedusans 

 taken in the trawls were discarded in the field after the 

 sizes and numbers of each species of scyphomedusan and 

 the volumes of hydromedusans had been recorded. The 

 other invertebrates were preserved in 5'"c Formalin. 



In preparation for examining the invertebrates in the 

 laboratory, formalin was washed from the samples and 



