378 



Fishery Bulletin 100(2) 



and SS'/r were juveniles. At 100 m (tow 4) only one north- 

 ern lampfish (44 mm FL) was captured. Northern smooth- 

 tongue were also captured at depths of both 10-15 m (tow 

 1) and 100 m (tow 4), and both catches consisted of 39'^( 

 adults and 61% juveniles. 



Among all stations, oceanic parameters measured at the 

 depth of fishing had the following ranges: temperature 

 (4.3-8. 2°C), salinity (26.3-32.1 ppt), density (20.7-25.3 

 kg/m'), turbidity (7.3-15.1 FTU), and chlorophyll concen- 

 tration (0.9 - 25.4 pg/L). Vertical profiles of water temper- 

 ature (°C), salinity (ppt). and density (kg/m'^) at sites 1 and 

 2 indicated that the thermocline, halocline, and pycnocline 

 occurred at depths <10 m. The upper 10 m of the water 

 column at site 2 had the lowest average surface salinity 

 (26.3 ppt) and the highest turbidity of any of the 34 sta- 

 tions sampled in our study. Turbidity values at site 2 were 

 >15 FTU from 3 to 16 m and >10 FTU to depths of 41 

 m; turbidity at site 1 was low and ranged from 7.8 to 8.7 

 FTU (Fig. 3). At site 2 the maximum chlorophyll concen- 

 tration (16.1 pg/L) occurred at 5 m; whereas at site 1 the 

 chlorophyll concentration peaked (24.7 vig/L) at 12 m and 

 remained high (>10 pg/L) to 28 m. 



Discussion 



Prior to sunset, juvenile and adult mesopelagic fishes were 

 found at depths of 10 to 15 m near Muir Glacier in Glacier 

 Bay, Alaska. Diel migrations of northern lampfish may 

 be a response to light intensity (Paxton, 1967; Pearcy et 

 al., 1977) or be stimulated by hunger (Pearcy et al.. 1977; 

 Cailliet and Ebeling, 1990). In the spring-summer period, 

 when daylight hours increase in the Bering Sea, vertical 



migrations of northern lampfish and northern smooth- 

 tongue had smaller amplitudes and were not as distinct 

 iSobolevsky et al., 1996). Phytoplankton blooms and fog 

 banks can reduce the depth to which light can penetrate, 

 also causing northern lampfish to migrate higher in the 

 water column (Barham. 1957). 



Turbidity in the upper water layer next to Muir Glacier 

 was higher than anywhere else in this study (15 FTU), 

 and this high turbidity corresponded with the shallowest 

 occurrence of mesopelagic fishes. In contrast, in Icy Strait 

 at site 1, where the turbidity was lower, northern lampfish 

 were captured at 90 m depth during daylight hours (Table 

 1, Fig. 3). High turbidity from glacial silt at Muir Glacier 

 may significantly reduce light penetration and account for 

 the presence of northern lampfish and northern smooth- 

 tongue at 10-15 m depth prior to actual sunset. 



Although these mesopelagic fishes are more commonly 

 distributed along the continental slope, both northern 

 lampfish (Shimada, 1948; Taylor. 1968) and northern 

 smoothtongue (Mason and Phillips. 1985) also occur in 

 deep, nearshore waters from the eastern Gulf of Alaska 

 to Puget Sound. Washington. Northern lampfish were ob- 

 served in Icy Strait and Lower Glacier Bay. Alaska, pre- 

 viously.' but not as far inland as Muir Glacier. Northern 

 smoothtongue have not been obsei-ved previously in the 

 same area. Their occurrence along the inside waters and 

 ijords of Southeast Alaska makes them available to a suite 

 of predators that otherwise might feed upon them only off- 

 shore. 



' Wing. B. 2000. Personal commun. National Marine Fish- 

 eries Sei-vice, Auke Bay Laboratory, 11305 Glacier Highway. 

 Juneau, Alaska. 99801 . ' 



