Distribution and abundance of fishes and saips in ...
Melville and K. Daly participated aboard the icebreaker Westwind. This work was supported by National Science Foundation grant DPP 82-18784 with contributions of equipment and resources from the Northwest and Alaska Fisheries Center and National Oceanic and Atmospheric Administration. References Ainley, D.B., and W.R. Fraser. 1984. AMERIEZ 1983: Oceanographic factors affecting seabird occurrence in the Scotia and Weddell Seas. Antarctic Journal of the U.S., 19(5). Brinton, E. 1984. Observations of plankton organisms by bongo nets during the November-December 1983 ice-edge investigations. Antarctic Journal of the U.S., 19(5). Erickson, A.W. 1984. Aerial census of seals, whales, and penguins in
Distribution and abundance of fishes and saips in relation to the marginal ice zone of the Scotia Sea, November and December 1983 J. J. TORRES, T. M. LANCRAFT, B. L. WEIGLE, and T. L. HOPKINS Department of Marine Science University of South Florida St. Petersburg, Florida 33701
the pack ice of the northwestern Weddell Sea, November 1983. Antarctic Journal of the U.S., 19(5).
Johannesson, K.A., and R.B. Mitson. 1983. Fisheries acoustics, a practical manual for aquatic biomass estimation. (FAO technical paper no. 240. FIRIvIIT240.) Macaulay, M. 1977. Acoustic estimation of zooplankton (Doctoral dissertation, University of Washington). Macaulay, M.C. 1981. Distribution and abundance of krill in the Scotia Sea as observed acoustically, 1981. Antarctic Journal of the U.S., 16(5), 166-167. SCAR. 1981. Calculations of the constants needed to scale the output of an echo integrator. (BIOMASS Handbook 7.) Torres, J.J., T.M. Lancraft, B.L. Weigle, T.L. Hopkins, and B.H. Robison. 1984. Distribution and abundance of fishes and saips in relation to the marginal ice-zone of the Scotia Sea: November and December 1983. Antarctic Journal of the U.S., 19(5).
with a 9-square-meter-mouth-area, mouth-closing Tucker trawl made of 6 millimeter knotless nylon mesh with a nested 0.75 meter, 163-micron, plankton net in the mouth. A thermal-turbulence protecting cod end (Childress et al. 1978) was used to enhance survival of captured specimens for respiration measurements. The considerable saip biomass encountered in the study area usually (90 percent of all trawls) necessitated taking a volume measurement then subsampling the catch. We used the volume measurements of the total catch to estimate saip biomass by assuming that the total volume consisted of salps and that 1 liter of saips weighed 1,050 grams. All fishes were removed from each catch. We have identified and measured 99 percent of captured fishes. We calculated fish biomass from size/weight
B. H. R0BIsON Marine Science Institute University of California Santa Barbara, California 93106
As part of the AMERIEZ (Antarctic Marine Ecosystem Research at the Ice Edge Zone, see Sullivan and Ainley, Antarctic Journal, this issue) expedition to the Scotia Sea, we investigated the distribution, abundance, and metabolism of zooplankton and micronekton in the top 1,000 meters of the open water north of the marginal ice zone (figure 1). Our research program was designed to assess latitudinal variation in species composition and biomass as related to the marginal ice zone and to describe for the first time the vertical distributions of mesopelagic fauna in the Scotia Sea. Frozen and preserved specimens were returned to our home laboratories for analysis of diet, proximate and elemental compositions, growth, reproductive state, and intermediary metabolic enzyme activities. Metabolic rates of dominant micronektonic species were determined at sea and are reported in a separate article (Torres, Weigle, and Lancraft, Antarctic Journal, this issue). All references to study area in this paper refer only to the cruise track of the iIv Melville (figure 1). Twenty-nine midwater trawl samples (including a complete day-night vertical series and several 0-1,000 meter oblique tows) were taken going away from most of the Melville hydrostations. Sampling was done 1984 REVIEW
17j 11
83-9
\I-
59
883_e)4)M8329 j1183_10
30 11 20 /
L
M83-14 20/111 I 83 83
N883-2
Figure 1. Location of midwatertra 's taken on the A/V Mel vllleduring AMERIEZ 1983. Dashed line is cruise track; solid lines indicate location and duration of trawls. Numbers refer to trawls only and not to hydrostations.
117
regressions for that species or similar species; we weighed rarer species separately. As sample analysis progresses the absolute numbers reported here may change slightly; trends will remain unaltered. The study area is best characterized as a low diversity, high biomass system in the midst of a saip bloom (mean saip biomass for the study area was 23.9 kilograms per 100 square meters for the upper 600 meters). Saips, dominated by Salpa thorn psoni, were the dominant micronektonic organisms in the upper 500 meters of the water column. The dominant fishes in the upper 500 meters were Electrona antarctica and Gymnoscopelus braueri (Myctophidae) and Notolepis coatsi (Paralepididae). Dominant fishes in the lower 500 meters of the water column were Bathylagus antarcticus (Bathylagidae) and Cyclot hone rnicrodon (Gonostomatidae). Mean fish biomass for the upper 1,000 meters of the study area was 327 grams per 100 square meters, a figure somewhat lower than that found by Frost and McCrone (1979) for the subarctic-transitional waters off Washington (450 grams per 100 square meters for myctophids only) but considerably higher than that found in the tropical-subtropical systems studied by Maynard, Riggs, and Walters (1973; 214 grams per 100 square meters, Hawaii) and Hopkins and Lancraft (in press; 212 grams per 100 square meters, Gulf of Mexico). Piscivorous fishes were extremely rare in the study area; two specimens of Neoscopelarchoides elongatus (Scopelarchidae) and four specimens of Paradiplospinosus antarcticus (Trichuridae) represent the entire predatory fish catch in 29 midwater trawls. There was a clear trend of increasing biomass moving from south to north away from the marginal ice zone followed by a
sharp drop in biomass north of 58°S (figure 2). The biomass peak corresponded to a pronounced phytoplankton bloom found in the vicinity of 59°S during the eastern transect in the early portion of the AMERIEZ cruise (see Nelson, Smith, and Gordon, Antarctic Journal, this issue). There was a pronounced temporal component in our trawl data that mirrors the results obtained by Nelson, Smith, and Gordon (Antarctic Journal, this issue) when superimposed on observed latitudinal trends. There was a marked increase with time in both fish and saip biomass in the southern portions of the study area. The increase corresponded to an intensifying phytoplankton bloom identified at the ice edge during the western transect. This suggests a gradual southward displacement of mobile micronektonic species in response to the increased production of the ice-edge bloom and its associated increase in prey species. In the case of saips it suggests an increased population size through reproduction. Eight species of mesopelagic fishes were sufficiently common to determine their diel vertical distributions (figure 3). Six of the eight species exhibited diel vertical migrations: Electrona antarctica, Gyrnnoscopelus braueri, Protornyctophurn anderssoni, Protorn yctophurn bolini (Myctophidae); Notolepis coatsi (Paralepididae); and Bathylagus antarcticus (Bathylagidae). Neither of the Gonostomatid species Cyclothone surniaen or Cyclothone microdon exhibited an upward vertical migration at night. Only one species, E. antarctica, was captured above a depth of 100 meters. The rest of the myctophids and N. coatsi remained below 100 meters and B. antarcticus remained below 250 meters. Salpa thorn psoni showed no evidence of diel vertical migration; however, there was a distinct trend toward finding larger num-
500 450 400 CY
E
350
0 300
co 200 0
150 100 50
6 1 0 FISHES SALPS TOTAL 60 0
FISHES SALPS TOTAL
(9 .102) (g.102 )
590
FISHES SALPS TOTAL 580 FISHES SALPS TOTAL (9.102) (g.10 2) (g.102)(g.102)
570
(9.102) (9 .102)
SECTOR OF STUDY AREA (°S) Figure 2. Biomass of fishes and saips in the upper 1,000 meters of the water column for each 1 degree of latitude of the AMERIEZ study area. Results from all trawls taken within each 1 degree of latitude of the study area were combined to produce the histogram. The figure is designed to show trends from one sector to the next only and does not Imply anything about trawl location within that sector. The approximate northern extent of the marginal ice zone is indicated to orient the reader. Note that biomass of saips and total biomass are 100 times the figures shown on the ordinate. ( 11 g100 m 2 " denotes grams per 100 square meters; "g•10 2 " denotes that saips and total are 100 times the figures shown on they axis.) 118
ANTARCTIC JOURNAL
to the highest reported in the literature (cf. Wiebe etal. 1979). • Beyond 300 kilometers north of the marginal ice zone there is a sharp drop off in biomass. This could be due to the absence of ice-edge influence, water mass effects, or patchiness. The latter possibility is unlikely. • There was a trend toward increased fish biomass and numbers of species in the southern portions of the study area with increasing time in the study area. This trend mirrored the observed intensification of an ice-edge bloom in the southern portion of the study area. The authors gratefully acknowledge the help of Bob Wilson of the Scripps Institution of Oceanography for technical assistance beyond the call of duty. Captain Haines and the fine crew of the Wv Melville all went the extra mile to make our cruise an extremely successful one. This research was supported by National Science Foundation grant DDP 82-10437.
100 200 300 E
400 500 600 700 800
References
900 1000
18 16 14 12 10
10 12 14 lb
its
Nos. of Fish 10,000 m3 Figure 3. DIel vertical distribution for all fishes in the Scotia Sea. Each box in the figure represents the depth stratum sampled and the number of fish captured in a single trawl. The dashed line represents a trawl with an extraordinarily large catch. ("m" denotes meter; "Nos. of Fish 10,000 r n -3" denotes number of fish per 10,000 cubic meters.)
bers of saips deeper in the water column as the study progressed. Our data at the present stage of analysis suggest the following conclusions concerning the micronekton of the study area: • The area up to 300 kilometers north of the marginal ice zone is a biologically rich area with wet weight biomass comparable
AMERIEZ 1983: Oceanographic factors affecting seabird occurrence in the Scotia and Weddell Seas D. C. AINLEY and W. R. FRASER
Point Reyes Bird Observatory Stinson Beach, California 94970
It is becoming increasingly clear that pelagic seabirds, even with their great powers of mobility, are constrained as are many 1984 REVIEW
Childress, J.J., A.T. Barnes, L.B. Quetin, and B.H. Robison. 1978. Thermally protecting cod ends for the recovery of living deep sea animals. Deep-Sea Research, 25, 419-422. Frost, G.W., and L.E. McCrone. 1979. Vertical distribution and abundance of some mesopelagic fishes in the eastern subarctic Pacific Ocean in summer. Fishery Bulletin, 76, 751-770.
Hopkins, T.L., and T.M. Lancraft. In press. The composition and standing stock of mesopelagic micronekton at 27N 86°W in the eastern Gulf of Mexico. Contributions to Marine Science of the University of Texas.
Maynard, S.D., F.V. Riggs, and J.E Walters. 1973. Mesopelagic micronekton in Hawaiian waters: Faunal composition, standing stock and diel vertical migration. Fishery Bulletin, 73, 726-736. Nelson, D.M., W.O. Smith, and L.I. Gordon. 1984. Phytoplankton dynamics of the marginal ice zone of the Weddell Sea: NovemberDecember 1983. Antarctic Journal of the U.S., 19(5). Sullivan, C.W., and D.G. Ainley. 1984. Antarctic marine ecosystem research at the ice-edge zone. Antarctic Journal of the U.S., 19(5). Torres, J .J. , B.L. Weigle, and T.M. Lancraft. 1984. Metabolism of two antarctic mesopelagic fish species. Antarctic Journal of the U.S., 19(5).
other marine organisms to specific, physically defined water masses and water types. It is also becoming more clear that within respective ranges, seabird occurrence is affected strongly by those oceanographic phenomena which increase prey availability (for example, environmental discontinuities such as fronts). Previous work in the Antarctic has indicated the existence of two especially distinct assemblages of pelagic seabirds separated by a particularly obvious environmental discontinuity: the presence or absence of pack ice. Also indicated is a marked increase in the abundance of seabirds at the marginal ice zone. In conjunction with AMERIEZ, we studied the pack-ice/ open-water system in greater detail than ever before to determine whether occurrence patterns of seabirds were responses 119
Distribution and abundance of fishes and saips in relation to the marginal ice zone of the Scotia Sea, November and December 1983 J. J. TORRES, T. M. LANCRAFT, B. L. WEIGLE, and T. L. HOPKINS Department of Marine Science University of South Florida St. Petersburg, Florida 33701
the pack ice of the northwestern Weddell Sea, November 1983. Antarctic Journal of the U.S., 19(5).
Johannesson, K.A., and R.B. Mitson. 1983. Fisheries acoustics, a practical manual for aquatic biomass estimation. (FAO technical paper no. 240. FIRIvIIT240.) Macaulay, M. 1977. Acoustic estimation of zooplankton (Doctoral dissertation, University of Washington). Macaulay, M.C. 1981. Distribution and abundance of krill in the Scotia Sea as observed acoustically, 1981. Antarctic Journal of the U.S., 16(5), 166-167. SCAR. 1981. Calculations of the constants needed to scale the output of an echo integrator. (BIOMASS Handbook 7.) Torres, J.J., T.M. Lancraft, B.L. Weigle, T.L. Hopkins, and B.H. Robison. 1984. Distribution and abundance of fishes and saips in relation to the marginal ice-zone of the Scotia Sea: November and December 1983. Antarctic Journal of the U.S., 19(5).
with a 9-square-meter-mouth-area, mouth-closing Tucker trawl made of 6 millimeter knotless nylon mesh with a nested 0.75 meter, 163-micron, plankton net in the mouth. A thermal-turbulence protecting cod end (Childress et al. 1978) was used to enhance survival of captured specimens for respiration measurements. The considerable saip biomass encountered in the study area usually (90 percent of all trawls) necessitated taking a volume measurement then subsampling the catch. We used the volume measurements of the total catch to estimate saip biomass by assuming that the total volume consisted of salps and that 1 liter of saips weighed 1,050 grams. All fishes were removed from each catch. We have identified and measured 99 percent of captured fishes. We calculated fish biomass from size/weight
B. H. R0BIsON Marine Science Institute University of California Santa Barbara, California 93106
As part of the AMERIEZ (Antarctic Marine Ecosystem Research at the Ice Edge Zone, see Sullivan and Ainley, Antarctic Journal, this issue) expedition to the Scotia Sea, we investigated the distribution, abundance, and metabolism of zooplankton and micronekton in the top 1,000 meters of the open water north of the marginal ice zone (figure 1). Our research program was designed to assess latitudinal variation in species composition and biomass as related to the marginal ice zone and to describe for the first time the vertical distributions of mesopelagic fauna in the Scotia Sea. Frozen and preserved specimens were returned to our home laboratories for analysis of diet, proximate and elemental compositions, growth, reproductive state, and intermediary metabolic enzyme activities. Metabolic rates of dominant micronektonic species were determined at sea and are reported in a separate article (Torres, Weigle, and Lancraft, Antarctic Journal, this issue). All references to study area in this paper refer only to the cruise track of the iIv Melville (figure 1). Twenty-nine midwater trawl samples (including a complete day-night vertical series and several 0-1,000 meter oblique tows) were taken going away from most of the Melville hydrostations. Sampling was done 1984 REVIEW
17j 11
83-9
\I-
59
883_e)4)M8329 j1183_10
30 11 20 /
L
M83-14 20/111 I 83 83
N883-2
Figure 1. Location of midwatertra 's taken on the A/V Mel vllleduring AMERIEZ 1983. Dashed line is cruise track; solid lines indicate location and duration of trawls. Numbers refer to trawls only and not to hydrostations.
117
regressions for that species or similar species; we weighed rarer species separately. As sample analysis progresses the absolute numbers reported here may change slightly; trends will remain unaltered. The study area is best characterized as a low diversity, high biomass system in the midst of a saip bloom (mean saip biomass for the study area was 23.9 kilograms per 100 square meters for the upper 600 meters). Saips, dominated by Salpa thorn psoni, were the dominant micronektonic organisms in the upper 500 meters of the water column. The dominant fishes in the upper 500 meters were Electrona antarctica and Gymnoscopelus braueri (Myctophidae) and Notolepis coatsi (Paralepididae). Dominant fishes in the lower 500 meters of the water column were Bathylagus antarcticus (Bathylagidae) and Cyclot hone rnicrodon (Gonostomatidae). Mean fish biomass for the upper 1,000 meters of the study area was 327 grams per 100 square meters, a figure somewhat lower than that found by Frost and McCrone (1979) for the subarctic-transitional waters off Washington (450 grams per 100 square meters for myctophids only) but considerably higher than that found in the tropical-subtropical systems studied by Maynard, Riggs, and Walters (1973; 214 grams per 100 square meters, Hawaii) and Hopkins and Lancraft (in press; 212 grams per 100 square meters, Gulf of Mexico). Piscivorous fishes were extremely rare in the study area; two specimens of Neoscopelarchoides elongatus (Scopelarchidae) and four specimens of Paradiplospinosus antarcticus (Trichuridae) represent the entire predatory fish catch in 29 midwater trawls. There was a clear trend of increasing biomass moving from south to north away from the marginal ice zone followed by a
sharp drop in biomass north of 58°S (figure 2). The biomass peak corresponded to a pronounced phytoplankton bloom found in the vicinity of 59°S during the eastern transect in the early portion of the AMERIEZ cruise (see Nelson, Smith, and Gordon, Antarctic Journal, this issue). There was a pronounced temporal component in our trawl data that mirrors the results obtained by Nelson, Smith, and Gordon (Antarctic Journal, this issue) when superimposed on observed latitudinal trends. There was a marked increase with time in both fish and saip biomass in the southern portions of the study area. The increase corresponded to an intensifying phytoplankton bloom identified at the ice edge during the western transect. This suggests a gradual southward displacement of mobile micronektonic species in response to the increased production of the ice-edge bloom and its associated increase in prey species. In the case of saips it suggests an increased population size through reproduction. Eight species of mesopelagic fishes were sufficiently common to determine their diel vertical distributions (figure 3). Six of the eight species exhibited diel vertical migrations: Electrona antarctica, Gyrnnoscopelus braueri, Protornyctophurn anderssoni, Protorn yctophurn bolini (Myctophidae); Notolepis coatsi (Paralepididae); and Bathylagus antarcticus (Bathylagidae). Neither of the Gonostomatid species Cyclothone surniaen or Cyclothone microdon exhibited an upward vertical migration at night. Only one species, E. antarctica, was captured above a depth of 100 meters. The rest of the myctophids and N. coatsi remained below 100 meters and B. antarcticus remained below 250 meters. Salpa thorn psoni showed no evidence of diel vertical migration; however, there was a distinct trend toward finding larger num-
500 450 400 CY
E
350
0 300
co 200 0
150 100 50
6 1 0 FISHES SALPS TOTAL 60 0
FISHES SALPS TOTAL
(9 .102) (g.102 )
590
FISHES SALPS TOTAL 580 FISHES SALPS TOTAL (9.102) (g.10 2) (g.102)(g.102)
570
(9.102) (9 .102)
SECTOR OF STUDY AREA (°S) Figure 2. Biomass of fishes and saips in the upper 1,000 meters of the water column for each 1 degree of latitude of the AMERIEZ study area. Results from all trawls taken within each 1 degree of latitude of the study area were combined to produce the histogram. The figure is designed to show trends from one sector to the next only and does not Imply anything about trawl location within that sector. The approximate northern extent of the marginal ice zone is indicated to orient the reader. Note that biomass of saips and total biomass are 100 times the figures shown on the ordinate. ( 11 g100 m 2 " denotes grams per 100 square meters; "g•10 2 " denotes that saips and total are 100 times the figures shown on they axis.) 118
ANTARCTIC JOURNAL
to the highest reported in the literature (cf. Wiebe etal. 1979). • Beyond 300 kilometers north of the marginal ice zone there is a sharp drop off in biomass. This could be due to the absence of ice-edge influence, water mass effects, or patchiness. The latter possibility is unlikely. • There was a trend toward increased fish biomass and numbers of species in the southern portions of the study area with increasing time in the study area. This trend mirrored the observed intensification of an ice-edge bloom in the southern portion of the study area. The authors gratefully acknowledge the help of Bob Wilson of the Scripps Institution of Oceanography for technical assistance beyond the call of duty. Captain Haines and the fine crew of the Wv Melville all went the extra mile to make our cruise an extremely successful one. This research was supported by National Science Foundation grant DDP 82-10437.
100 200 300 E
400 500 600 700 800
References
900 1000
18 16 14 12 10
10 12 14 lb
its
Nos. of Fish 10,000 m3 Figure 3. DIel vertical distribution for all fishes in the Scotia Sea. Each box in the figure represents the depth stratum sampled and the number of fish captured in a single trawl. The dashed line represents a trawl with an extraordinarily large catch. ("m" denotes meter; "Nos. of Fish 10,000 r n -3" denotes number of fish per 10,000 cubic meters.)
bers of saips deeper in the water column as the study progressed. Our data at the present stage of analysis suggest the following conclusions concerning the micronekton of the study area: • The area up to 300 kilometers north of the marginal ice zone is a biologically rich area with wet weight biomass comparable
AMERIEZ 1983: Oceanographic factors affecting seabird occurrence in the Scotia and Weddell Seas D. C. AINLEY and W. R. FRASER
Point Reyes Bird Observatory Stinson Beach, California 94970
It is becoming increasingly clear that pelagic seabirds, even with their great powers of mobility, are constrained as are many 1984 REVIEW
Childress, J.J., A.T. Barnes, L.B. Quetin, and B.H. Robison. 1978. Thermally protecting cod ends for the recovery of living deep sea animals. Deep-Sea Research, 25, 419-422. Frost, G.W., and L.E. McCrone. 1979. Vertical distribution and abundance of some mesopelagic fishes in the eastern subarctic Pacific Ocean in summer. Fishery Bulletin, 76, 751-770.
Hopkins, T.L., and T.M. Lancraft. In press. The composition and standing stock of mesopelagic micronekton at 27N 86°W in the eastern Gulf of Mexico. Contributions to Marine Science of the University of Texas.
Maynard, S.D., F.V. Riggs, and J.E Walters. 1973. Mesopelagic micronekton in Hawaiian waters: Faunal composition, standing stock and diel vertical migration. Fishery Bulletin, 73, 726-736. Nelson, D.M., W.O. Smith, and L.I. Gordon. 1984. Phytoplankton dynamics of the marginal ice zone of the Weddell Sea: NovemberDecember 1983. Antarctic Journal of the U.S., 19(5). Sullivan, C.W., and D.G. Ainley. 1984. Antarctic marine ecosystem research at the ice-edge zone. Antarctic Journal of the U.S., 19(5). Torres, J .J. , B.L. Weigle, and T.M. Lancraft. 1984. Metabolism of two antarctic mesopelagic fish species. Antarctic Journal of the U.S., 19(5).
other marine organisms to specific, physically defined water masses and water types. It is also becoming more clear that within respective ranges, seabird occurrence is affected strongly by those oceanographic phenomena which increase prey availability (for example, environmental discontinuities such as fronts). Previous work in the Antarctic has indicated the existence of two especially distinct assemblages of pelagic seabirds separated by a particularly obvious environmental discontinuity: the presence or absence of pack ice. Also indicated is a marked increase in the abundance of seabirds at the marginal ice zone. In conjunction with AMERIEZ, we studied the pack-ice/ open-water system in greater detail than ever before to determine whether occurrence patterns of seabirds were responses 119
