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Gobies associated with a scattering layer off southwest Africa
Deep-Sea Research, 1969, Vo] 16, pp 105 to 106 PergamonPress Printedm Great Britain
LETTER
TO
THE
EDITORS
Gobies associated with a scattering layer off southwest Africa* RICHARD T
BARBER'~ and RICHARD L
HAEDRICH'~
(Recewed 24 October 1968) A DISTINCT Sound scattering layer was observed in waters over the continental shelf adjacent to Southwest Africa during Cruise 42 of the R V Atlantis H A portion of the 12 kHz Precision Graphic Recorder record showing the sound scattering layer is reproduced in Fig 1, this section was recorded at R V Atlantis H Sta 1223 (24 ° 36'S, 14° 23E'), about 12 miles~: west of Hollam's Bird. Island An oblique tow with a three-quarter-meter plankton net through the layer caught three fish The three specimens, 47-50 m m in standard length, belong to the species Gobtus btbarbatus von Bonde 1923 The diagnostic character is the presence of two small barbels on the chan The counts-Dorsal VI, I 13-14, Anal I 12-13, Pectoral 21-22, lateral hne scales (dafficult to count) 59-61--are approprmte for the species, and in other respects, particularly the stlk-hke rays of the upper part of the pectoral and the two pores in the medaan line of the mterorbital, they agree almost completely with the description gwen by BARNARD(1927) All three are juvemles with the gonads just forming Gobius btbarbatus is known to reach 130 mm in length The previously known dmtnbuUon of thas speoes Is St Helena Bay, Saldanha Bay, and St Sebastlen Bay in 28-50 fms Our record represents a range extension of some 540 redes to the north Whale there ~s no conclusive ewdence that the gob~es were the scattering organisms, the absence o f other potentml scatterers m the tow and the presence of large, than-walled swim bladders m the captured specimens provide clrcumstantml evidence that they are indeed responsible for the strong sound scattering layer observed The net catch, whale rich m copepods, planktonic larvae, and phytoplankton, contained no slphonophore fragments or other fishes The obhque zooplankton net tow did catch several hters of a colomal diatom m whach the valves are umted by the entwe valve face forming long flat ribbons Thas diatom, almost certainly a member of the genus Fragtlarla Lyngbye (HENDEY, 1964), was the most abundant species at thas station and contributed most to the hagh particulate carbon and chlorophyll values (Table 1) Intact frustules of the rlbbon-hke colomes of the Fragdarla dmtom as well as large Coscmodtscus frustules were present m the stomachs of the gobles, whale no crustacean parts or other ammal remains were found The particulate carbon and chlorophyll data (Table l) indicate that large amounts of organic matter were present at the depth
Table 1 Phystcal and chemtcal propertws at R V Atlantis II Sta 1223, about 12 miles west o f Hollam' s Bird Island Depth (m)
Temp (°C)
Sahmty (%0)
Density (crt)
09 (ml/l)
PO4 (/zg-at/1 )
NO 2 (/zg-at/1 )
Part C (/zg/l)
Chl a (/~g/1)
1 15 25 40 50 65
13 48 1343 13 32 13 11 12 62 1267
35 35 35 35 35 35
26 432 26446 26 469 26518 26 608 26599
4 59 441 3 98 281 0 43 023
l 79 1 90 3 01 296 2 09 249
8 36 823 6 20 1445 8 36 1636
757 970
28 3 292 24 2 15 3 4 75 1 75
154 158 159 167 159 157
530 176
*Contribution No 2216 from the Woods Hole Oceanographic Institution Research supported by Atomic Energy Commission Contract AT (30-1)-3862 (Ref No NYO-3862-10) "['Woods Hole Oceanographac Inshtutlon, Woods Hole, Mass 02543, U S A ~:1 mde = 1 853 18 km 105
106
Letter to the Edators
of the sound scattering layer Thin orgamc matter could potentially support large populahons of gobles if the gobles are grazing on phytoplankton as the stomach contents mdacated If the gobles are the sound scatterers, as we suggest, then our somc recordings indicate that large numbers of these fish are present m the nent~c waters off Southwest Africa The presence of these normally benthic fishes in a mid-water habitat may be related to the low oxygen content of the bottom waters in this area At 65 m 0 23 ml O2/1 was present (Table I) and between 65 m and. the bottom, oxygen content was certainly lower or completely absent Cores from thin area gave a distract hydrogen-sulfide odor gwmg further mchcahon of anoxlc cond~ttons along the bottom The lower edge of the scattering layer at approximately 55 m coincides ~lth the upper hm~t of the zone of low oxygen Other water properties (Table 1) do not show any particular relattonship to the vertical poslhon of the scattering layer REFERENCES
BARNARD K H (1927) A monograph of the marine fishes of South Afn~.a, Part II Ann S Afr .A4us, 21 (2), 419-1065 HENDEV N I (1964) An mtroductory account of the smaller algae of Brmsh coastal waters Part V Baclllarlophyceae (Diatoms) Ftsherv Investt, Lond, (Series IV), 317 p p , PI I-XLV YON BONDE C (1923) Shallow-water fishes procured by the S S Pwkle Rep Ftsh mw blo[ Surv Un S 4 f i , 3 (Spec Rep No 1), 1--40
75
50
25
m
0
Fig 1 Portion o f the 12 k H z Precision G r a p h i c R e c o r d e r record m a d e at R V A t l a n n s H Sta 1223 (24 36'S, 14 ~ 23'E), a b o u t 12 miles west o f H o l l a m ' s Bird Island T h e b o t t o m is indicated by the level trace at a p p r o x i m a t e l y 68 m , the m a r e scattering layer is s h o w n b e t w e e n 35 a n d 55 m
[/a~tng p 1061
LETTER
TO
THE
EDITORS
Gobies associated with a scattering layer off southwest Africa* RICHARD T
BARBER'~ and RICHARD L
HAEDRICH'~
(Recewed 24 October 1968) A DISTINCT Sound scattering layer was observed in waters over the continental shelf adjacent to Southwest Africa during Cruise 42 of the R V Atlantis H A portion of the 12 kHz Precision Graphic Recorder record showing the sound scattering layer is reproduced in Fig 1, this section was recorded at R V Atlantis H Sta 1223 (24 ° 36'S, 14° 23E'), about 12 miles~: west of Hollam's Bird. Island An oblique tow with a three-quarter-meter plankton net through the layer caught three fish The three specimens, 47-50 m m in standard length, belong to the species Gobtus btbarbatus von Bonde 1923 The diagnostic character is the presence of two small barbels on the chan The counts-Dorsal VI, I 13-14, Anal I 12-13, Pectoral 21-22, lateral hne scales (dafficult to count) 59-61--are approprmte for the species, and in other respects, particularly the stlk-hke rays of the upper part of the pectoral and the two pores in the medaan line of the mterorbital, they agree almost completely with the description gwen by BARNARD(1927) All three are juvemles with the gonads just forming Gobius btbarbatus is known to reach 130 mm in length The previously known dmtnbuUon of thas speoes Is St Helena Bay, Saldanha Bay, and St Sebastlen Bay in 28-50 fms Our record represents a range extension of some 540 redes to the north Whale there ~s no conclusive ewdence that the gob~es were the scattering organisms, the absence o f other potentml scatterers m the tow and the presence of large, than-walled swim bladders m the captured specimens provide clrcumstantml evidence that they are indeed responsible for the strong sound scattering layer observed The net catch, whale rich m copepods, planktonic larvae, and phytoplankton, contained no slphonophore fragments or other fishes The obhque zooplankton net tow did catch several hters of a colomal diatom m whach the valves are umted by the entwe valve face forming long flat ribbons Thas diatom, almost certainly a member of the genus Fragtlarla Lyngbye (HENDEY, 1964), was the most abundant species at thas station and contributed most to the hagh particulate carbon and chlorophyll values (Table 1) Intact frustules of the rlbbon-hke colomes of the Fragdarla dmtom as well as large Coscmodtscus frustules were present m the stomachs of the gobles, whale no crustacean parts or other ammal remains were found The particulate carbon and chlorophyll data (Table l) indicate that large amounts of organic matter were present at the depth
Table 1 Phystcal and chemtcal propertws at R V Atlantis II Sta 1223, about 12 miles west o f Hollam' s Bird Island Depth (m)
Temp (°C)
Sahmty (%0)
Density (crt)
09 (ml/l)
PO4 (/zg-at/1 )
NO 2 (/zg-at/1 )
Part C (/zg/l)
Chl a (/~g/1)
1 15 25 40 50 65
13 48 1343 13 32 13 11 12 62 1267
35 35 35 35 35 35
26 432 26446 26 469 26518 26 608 26599
4 59 441 3 98 281 0 43 023
l 79 1 90 3 01 296 2 09 249
8 36 823 6 20 1445 8 36 1636
757 970
28 3 292 24 2 15 3 4 75 1 75
154 158 159 167 159 157
530 176
*Contribution No 2216 from the Woods Hole Oceanographic Institution Research supported by Atomic Energy Commission Contract AT (30-1)-3862 (Ref No NYO-3862-10) "['Woods Hole Oceanographac Inshtutlon, Woods Hole, Mass 02543, U S A ~:1 mde = 1 853 18 km 105
106
Letter to the Edators
of the sound scattering layer Thin orgamc matter could potentially support large populahons of gobles if the gobles are grazing on phytoplankton as the stomach contents mdacated If the gobles are the sound scatterers, as we suggest, then our somc recordings indicate that large numbers of these fish are present m the nent~c waters off Southwest Africa The presence of these normally benthic fishes in a mid-water habitat may be related to the low oxygen content of the bottom waters in this area At 65 m 0 23 ml O2/1 was present (Table I) and between 65 m and. the bottom, oxygen content was certainly lower or completely absent Cores from thin area gave a distract hydrogen-sulfide odor gwmg further mchcahon of anoxlc cond~ttons along the bottom The lower edge of the scattering layer at approximately 55 m coincides ~lth the upper hm~t of the zone of low oxygen Other water properties (Table 1) do not show any particular relattonship to the vertical poslhon of the scattering layer REFERENCES
BARNARD K H (1927) A monograph of the marine fishes of South Afn~.a, Part II Ann S Afr .A4us, 21 (2), 419-1065 HENDEV N I (1964) An mtroductory account of the smaller algae of Brmsh coastal waters Part V Baclllarlophyceae (Diatoms) Ftsherv Investt, Lond, (Series IV), 317 p p , PI I-XLV YON BONDE C (1923) Shallow-water fishes procured by the S S Pwkle Rep Ftsh mw blo[ Surv Un S 4 f i , 3 (Spec Rep No 1), 1--40
75
50
25
m
0
Fig 1 Portion o f the 12 k H z Precision G r a p h i c R e c o r d e r record m a d e at R V A t l a n n s H Sta 1223 (24 36'S, 14 ~ 23'E), a b o u t 12 miles west o f H o l l a m ' s Bird Island T h e b o t t o m is indicated by the level trace at a p p r o x i m a t e l y 68 m , the m a r e scattering layer is s h o w n b e t w e e n 35 a n d 55 m
[/a~tng p 1061