flushed, and then sealing them. Samples were fixed 

 with manganous sulphate reagent and alkaline 

 iodide solution as soon as the submersible had sur- 

 faced and was recovered at the end of each dive, 

 and dissolved oxygen concentrations were deter- 

 mined later using a modified Winkler titration pro- 

 cedure (Strickland and Parsons 1972). Ambient 

 water temperature was recorded continuously 

 during each dive. On 14 October 1986, a more com- 

 prehensive set of oceanographic measurements 

 (temperature, salinity, and dissolved oxygen [DO2]) 

 was obtained by University of British Columbia 

 (UBC) oceanographers 1 km from the study 

 area. 



Results 



Substrate type was a soft, light-brown flocculent 

 ooze at the bottom of the inlet up to a depth of about 

 60 m, when it became more gravelly. The floor of 

 the inlet was relatively flat, changing to a slope of 

 30-60° at the walls up to a depth of about 100 m, 

 at which point 5-10 m vertical rock cliffs often oc- 

 curred. The slope then lessened at approximately 

 70 m depth to 20-30°, with frequent rock outcrop- 

 pings observed up to the minimum depth (20 m) 

 surveyed. 



Salinity and temperature below 20 m ranged from 

 30.0 to 31.4^00 and from 8.0° to 11.2°C, respec- 

 tively, throughout the study. During the first two 

 days of observations, measured DO2 levels were 

 >1 mL • L"^ at depths above 20 m. Between the 

 afternoon and evening dives of the third day (8 Octo- 

 ber), an abrupt decrease in DO2 concentration to 

 between 0.76 and 0.92 mL • L"^ was detected at 

 depths of 75-77 m. However, at nearby depths of 

 71-73 m, DO2 levels remained above 1 mL • L~^ 

 (1.29-2.00 mL • L'^). 



Dissolved oxygen (DO2) measurements obtained 

 during the last two days of our study show a similar 

 profile to those obtained four days later in the center 

 of the inlet by the UBC team (Fig. 1). In both cases, 

 a region of low DO2 (<1 mL • L"^) was seen in 

 waters of intermediate depth, although the depth 

 at which this lens of low DO2 occurred differed by 

 about 20 m. Minimum DO2 level recorded during 

 our dives was 0.76 mL  L"' at 77 m on 8 October, 

 while on 14 October in the center of the inlet, the 

 lowest value noted was 0.44 mL • L"^ at 110 m. 

 Since low DO2 levels normally occur in the deepest 

 waters of the inlet (Pickard 1975; Burd and Brink- 

 hurst 1984), these results indicated that there had 

 recently been intrusions of denser, more oxygenated 

 water over the sill into the deeper regions of the 



inlet, displacing the low DO2 layer upwards or ad- 

 vecting low DO2 water into the study area. 



There were clear differences in depth ranges in- 

 habited by species commonly observed in the study 

 area (Fig. 1). The species we observed were pri- 

 marily benthic in habit, although some epibenthic 

 species such as spotted ratfish, Hydrolagus colliei 

 (Lay and Bennet, 1839); spiny dogfish, Squalus 

 acanthias Linnaeus, 1758; and Pacific cod, Gadus 

 macrocephalus Tilesius, 1810, were periodically 

 observed, usually at depths below 80 m. Various 

 rockfish (Sebastes sp.) were observed around rock 

 outcroppings. 



The most abundant benthic invertebrate species 

 observed below 60 m were four species of shrimp 

 {Spirontocaris holmesi Holthuis, 1947; S. sica Rath- 

 bun, 1902; pink shrimp, Pandalus jordani Rathbun, 

 1902; and prawn) and munids. A few Dungeness 

 crab, Cancer magister (Dana, 1851) were observed 

 at 40-80 m depth. Greatest densities of prawns 

 generally occurred between 70 and 85 m depth, 

 although their observed range was from 20 to 159 m 

 (Table 1). There was no obvious difference in the 

 depth range of major prawn concentration (70-85 

 m) between afternoon and night dives on the same 

 day. However, more prawns were observed in the 

 depth range of 20-70 m at night than during the 

 day, but these were relatively few in comparison to 

 those at 70-85 m depth (Table 1). During the latter 

 part of the study, most prawns were in a narrow 

 band between 70 and 79 m depth. An amphipod, Or- 

 choTnene ohtusa (Sars, 1890), was common on the 

 substrate from 80-210 m water depth. Major con- 

 centrations of pelagic amphipods were observed at 

 depths of 45-75 m and 23-90 m during the day and 

 night, respectively. Euphausiids were most abun- 

 dant at 90-135 m during the day and at 50-90 m 

 at night. 



Munids were not observed above the main prawn 

 concentration at 70-85 m. A wide size range of 

 munids was observed, ranging from recently settled 

 juveniles to adults of about 3 cm carapace length. 

 In general, large individuals were found below 

 100 m whereas small munids were found from 80 

 to 120 m depth. Munids were observed down to the 

 deepest depth surveyed (209 m). 



On the evening dive of the third day, 8 October, 

 dying and dead prawns, the latter covered with 

 swarms of amphipods, were observed between 82 

 and 90 m depth, with most between 85 and 90 m 

 (Table 1). Some live prawns showing disoriented 

 behavior were also observed. Examination of col- 

 lected live prawns observed to be in poor condition 

 when sampled showed no evidence of disease or 



603 



