Chittenden, Mark E., Jr.

Pavela, John S.

Ross, Jeffrey L.

English

Aquila Digital Community

Northeast Gulf ScienceVolume 6Number 2 Number 2 Article 1110-1983Sharp Reductions in Abundance of Fishes andBenthic Macroinvertebrates in the Gulf of MexicoOff Texas Associated with HypoxiaJohn S. PavelaTexas A&M UniversityJeffrey L. RossTexas A&M UniversityMark E. Chittenden Jr.Texas A&M UniversityDOI: 10.18785/negs.0602.11Follow this and additional works at: https://aquila.usm.edu/gomsThis Article is brought to you for free and open access by The Aquila Digital Community. It has been accepted for inclusion in Gulf of Mexico Scienceby an authorized editor of The Aquila Digital Community. For more information, please contact Joshua.Cromwell@usm.edu.Recommended CitationPavela, J. S., J. L. Ross and M. E. Chittenden Jr. 1983. Sharp Reductions in Abundance of Fishes and Benthic Macroinvertebrates in theGulf of Mexico Off Texas Associated with Hypoxia. Northeast Gulf Science 6 (2).Retrieved from https://aquila.usm.edu/goms/vol6/iss2/11Northeast Gulf Science Vol. 6, No. 2 October 1983 167 SHARP REDUCTIONS IN ABUNDANCE OF FISHES AND BENTHIC MACROINVERTE· BRATES IN THE GULF OF MEXICO OFF TEXAS ASSOCIATED WITH HYPOXIA1 Natural depletion of dissolved ox-ygen (D.O.) to hypoxic (<2.0 mg/1) or anox-ic levels in bottom waters of the con-tinental shelf of the northwestern Gulf of Mexico (Gulf) has been recognized since the mid-1930's (Conseil Perm. Interna-tional pour !'exploration de Ia mer, 1936). Subsequent, but primarily unpublished, studies suggest this is a recurrent hydrographic feature off Louisiana (Far-rell, 1974; Harris eta/. 1976, Brent eta/. 1979, Fotheringham and Weissberg, 1979; Bedinger et a!., 1980; Reitsema, 1980), and po.ssibly off Texas (Harper and McKinney, 1980; Slowey, 1980; Harper et a/., 1981). Little has been published about the effects of natural hypoxia on fishes, shrimps and other macroinvertebrates in the northwestern Gulf despite its ap-parent frequency and the valuable fisheries in that region. Ragan et a/. (1976), and Fotheringham and Weissberg (1979) reported sharp declines in the abundance of fishes, anthozoans, polychaetes, bivalves, and crustaceans under hypoxic and/or anoxic conditions. Data on reduced abundance of benthic infauna during hypoxia have been presented by Harper eta!. (1981) but no data have been published for fishes and shrimps (Penaeus spp.). This paper documents sharply reduced abundance and the elimination of both fishes and shrimps coincident with hypoxia off Texas and presents general observations about decreases in common benthic macroinvertebrates. MATERIALS AND METHODS A total of 2;880 trawl tows was made on 71 monthly or twice monthly cruises from October 1977 through August 1981 along a transect from 5-47 m in the Gulf off Freeport, Texas (Figure 1). Cruises were made by day prior to December 1978. Thereafter, a night cruise and a day cruise normally were made each month. Collections were made from a commer-cial shrimp trawler using twin 10.4 m shrimp trawls with tickler chains and 4.4 em stretch mesh in the cod ends at sta-tions in depths of 5, 9, 13, 16, 18, 22, 24, 27, 36, and 47 m. Two tows of ten minutes duration (bottom time) were usually made at each depth. However, we em-phasize that 8-12 tows were made at the 16 m isobath and 24 tows were usually made at the 22m isobath. This extensive trawling was conducted within an area where hypoxia occurred (Harper et a/., 1981). All fishes and shrimps were iden-tified and enumerated by species; the other more abundant macroinvertebrates 'Technical article 17991 from the Texas Agricultural Figure 1. Location and depths (meters) of trawl sta-Experiment Station. tions off Freeport, Texas. 1Pavela et al.: Sharp Reductions in Abundance of Fishes and Benthic MacroinvertebPublished by The Aquila Digital Community, 1983168 Short papers and notes were simply identified. Bottom water samples were col-lected with a Kemmerer bottle at each depth between the 5-36 m isobaths from August 1979-1981 to determine dissolv-ed oxygen using the Alsterberg (azide) modification of the Winkler Method (American Public Health Association, 1976). However, we collected no D.O. data concurrent with trawling prior to August 1979; D.O. values presented for May, June and July 1979 were obtained from other cited researchers working in our study area. RESULTS AND DISCUSSION Fishes and shrimps normally are abundant between the 5-47 m isobaths off Freeport when D.O. levels are high during the summer. Mean catch per tow (C/f) of fishes and shrimps generally was high throughout this bathymetric range from May through August or. September in 1980 and 1981 (Figures 2 & 3) and in May, early June, August and September 1979 (Figure 4, panels A, B, F & G) when D.O. levels were above 2.0 mg/1. Similar-ly, C/f generally was high from May through September 1979 between the 5-9 m isobaths in the white shrimp (Penaeus setiferus) community and between the 24-47 m isobaths in the brown shrimp (P. aztecus) community (Figure 4) delineated by Hildebrand (1954) and Chittenden and McEachran (1976). The primary exceptions to these generalizations are: 1) the generally low catches of shrimps during day cruises bet-ween the 18-47 m isobaths. This is normal and reflects the fact that Catch per Tow Catch per Tow Calch per Tow ~ § ~ § ~ ~ g g 8 g g g 1 ) { .... t i bcbbbb Dissolved Oxygon lmg/1) § g p ill :il g ~ = ~ ~ §~ g~ ~ § ~ § § ~ ~ § §~ gg ~ p ~ ~ c ;;;; = ~ z ~ / ·· . ., rn ,.., ,. • .1'~~ ,:., .. ~ c <.:. ;;;; ~ ·· .... 0 ~ \ , ..... ~ ··········~ .. , b ~ ~ ~ b b b b Dissolved Oxygen lmg/11 ~ ~ ;;; ~a; S:a; :§: ~ 11 ':! !;\ ;: g ~ § § ~ ~ ~ §~ 8 g l,l I g g g g 8 gl I "" ··r = f ~ i ~ 1 l j l ( .... = m p ~ 0 0 ~ .·••· !" ~ ~ c ~ "' m 0 i b ~ ~ ~ b ~ b b Dissolved Oxygen lmg/11 Figure 2. Mean catch per tow of shrimps (Penaeus spp.) and fishes in relation to D.O. and station depths, May-September 1980. 2Gulf of Mexico Science, Vol. 6 [1983], No. 2, Art. 11https://aquila.usm.edu/goms/vol6/iss2/11DOI: 10.18785/negs.0602.11Northeast Gulf Science Vol. 6, No. 2 October 1983 169 Catch per Tow Catch per Tow ~ ~ ~ § § g § ~ ~ 8 § g g I "' i fi" ~ .:______ ... ~ .. · ··.). --==- ···:: .. . I ; , I i Catch per Tow ~ ~ ~ § g § ~ ~~ c '< b~bbbbb~ Dissolved Oxygen (mg/IJ p p ~ ' i I "' = Dissolved Oxygen (mg/1) b~bbbbbb Dissolved Oxygen (mg/1) Figure 3. Mean catch per tow of shrimps (Penaeus spp.) and fishes in relation to D.O. and station depths, May·August 1981. greater catches of most Penaeus spp. are made at night (Williams, 1955; Perez-Farfante, 1969; Wickham and Minkler, 1975). Penaeus aztecus predominates in this bathymetric range in our study area, but they are rarely cap-tured there during the day even when night catches in the same month are large (Chittenden eta!., 1980; 1982). 2) the often relatively low catches of fishes and shrimps between the 18-47 m isobaths. This is normal and reflects decreased nekton abundance off Freeport with in-creasing depth and distance from shore; catches between the 5-9 m isobaths often are much greater than those in deeper water (Chit-tenden et a/.1980; 1982). Unusually low abundance or the total elimination of both fishes, shrimps, and other macroinvertebrates, occurred in bottom waters between the 13-24 m isobaths during June and July 1979 associated with hypoxic conditions. Catches increased dramatically at these depths in late August 1979 when D.O. levels recovered. Data from four cruises document these changes: 1) Unusually low abundance was first evident in the field between 21-24 June 1979 when hardly any fishes or shrimps were captured in ten tows at 13 and 16m (Figure 4, panel C). A distinct decline was also observed in catches of other typically abundant macroinverte-brates including penaeid shrimps Trachypenaeus spp., Sicyonia brevirostris, S. dorsalis and 3Pavela et al.: Sharp Reductions in Abundance of Fishes and Benthic MacroinvertebPublished by The Aquila Digital Community, 1983170 Short papers and notes Catch per Tow ~ § § ~ ~ § § 8 g g g g g g Catch per Tow g ~ ~ ~ § ~ g g g Dissolved Oxygen !mg/IJ ~~ ~~ 0.[ i Catch per Tow ~ g S'r· ~ / " " ' ;;j ~ ~ g g ~ ~ ""·, ..,., ........................... , ~r--·)r~~~ i ~ ~> ~ ~···················~ ; \ ~ ~ /'. ~ § g ~~+-+-+-+-+-~·~ g ~ ~ ··,i r······ .fs:~ ~ H·/~ i • • ., <0 ~:: ................................. .,~~ " N ~ ~ ';:! ......... :a. "' 01 ;: Dissolved Oxygen !mg/11 ~~bb:bb Dissolved Oxygen !mg/IJ b ~ c ~ ~ Figure 4. Mean catch per tow of shrimps (Penaeus spp.) and fishes in relation to D.O. and station depths, May-September 1979. Collection dates are indicated when D.O. measurements were not taken concur-rent with trawling. Xiphopenaeus kroyeri; brachyuran crabs, Ca/linectes sapidus, C. simi/is, Libinia dubia, L. emarginata, Ca/appa flammea, C. su/cata, Hepatus epheliticus, Por-tunus spp., P. spinicarpus; mantis shrimp, Squilla empusa, and squid, Lol/iguncu/a brevis. Harper et a/. (1981) and Slowey (1980) found hypoxic bottom water (0.7-2.0 mg/1) at 16-22 m along our station transect on 25-30 June 1979 which is only a few days after we observed sharply re-duced nekton abundance. 2) The area that exhibited unusually low C/f broadened by 5-9 July 1979 to include the 13-22 m isobaths where few or no fishes, shrimps (Figure 4, panel D) or macro-invertebrates were captured in 28 tows. Harper et at. (1981) re-corded bottom D.O. levels of 0.8-2.1 mg/1 between 9-33 m during our cruise. 3) We captured no fishes or shrimps in 27 tows between the 13-24 m isobaths on 19-22 July 1979 (Figure 4, panel E); our entire catch included only dead and decaying brachyuran and anomuran crabs, mantis shrimp and the anthozoan Renilla renifor-mis. No D.O. data exists for this period but Harper et at. (1981) and Slowey (1980) found hypoxic bot-tom water (1.6-3.3 mg/1) still pre-sent at 18-22 m the following week (28 July-2 August 1979). 4) Fish and shrimp abundance in-4Gulf of Mexico Science, Vol. 6 [1983], No. 2, Art. 11https://aquila.usm.edu/goms/vol6/iss2/11DOI: 10.18785/negs.0602.11Northeast Gulf Science Vol. 6, No. 2 October 1983 171 creased tremendously between the 13-22 m isobaths on 23-25 August 1979 (Figure 4, panel F). Abundance of macroinvertebrates was also much greater than July and no dead or decaying organisms were observed in the catch. Increased abundance was most conspicuous between the 13 and 16 m isobaths where sharp declines in abundance were first noted in late June. The resurgence in nekton abundance coincided with high bottom D.O. levels (2.9-6.0 mg/1) that we measured between the 13-24 m isobaths. The sharp reduction and elimination of nekton from bottom waters between the 13-24 m isobaths off Freeport during late June and July 1979 was probably due to natural hypoxia. Although we did not collect D.O. data concurrent with our trawling, Harper eta/. (1981) and Slowey (1980) document the presence of hypox-ic bottom water in our study area at about the same times we observed great-ly reduced -or absent- nekton. In con-trast, nekton C/f: 1) was consistently high and seemed normal under non-hypoxic conditions during these same months in 1980 and 1981 and just prior to the onset of hypoxia in 1979, 2) was high just in-shore and offshore of the hypoxic area in 1979, and 3) increased greatly in late August 1979 between the 13-24 m isobaths just after hypoxic conditions passed. Reductions in nekton abundance due to hypoxia might be a recurrent phenomenon off Freeport. A similar though less severe decline in nekton C/f occurred in June 1978 between the 9-16 m isobaths. Harper et a/. (1981) noted decreased diversity and abundance of benthic invertebrates in the same area at the same time. Unfortunately, neither we nor Harper et a/. have D.O. data to establish hypoxia as the cause on that occasion. Hypoxic conditions also ex-isted between the 7-20 m isobaths dur-ing early June 1982 (R. E. Randall, Dept. of Civil Engineering, Ocean and Hydraulic Engineering Div., Texas A&M Univ., College Station, TX 77843, pers. commun.). However, this occurred after we ceased collections in that depth range. The ecological impact of natural hypoxia on nekton dynamics in the north-western Gulf is not clear but could be important because a large region may be affected. Our data indicate hypoxic bot-tom waters greatly reduced nekton abun-dance in a cross-shelf band of at least 15 km between the 13-24 m isobaths during some periods of summer 1979. Harper and McKinney (1980) estimated that hypoxia in early July 1979 off Texas ex-tended along the coast from Sabine Pass to Matagorda Bay (130 km) and across the shelf from 9-33 m (50 km). Although hypoxia in the bottom water appears to greatly reduce the abundance of benthic and demersal nekton, it seemingly has little effect on larger pelagic fishes near the surface and might even benefit them. On 19-22 July 1979, when we captured only dead and decaying specimens within the 13-24 m isobaths, we observed many pelagic fishes swimming at the surface including sharks, (Carcharhinus spp.), pompano dolphin, (Coryphaena equisetis), little tuna, (Euthynnus alletteratus), crevalle jack, Caranx hippos, and mackerel (Scomberomorus spp.). It is not clear whether or not we observed an unusual abundance of larger pelagic fishes on this occasion. However, it is tempting to speculate that these fishes might have been attracted to or were held in the area by an exceptional food opportunity presented during June and July by an unusually vulnerable bottom fauna 5Pavela et al.: Sharp Reductions in Abundance of Fishes and Benthic MacroinvertebPublished by The Aquila Digital Community, 1983172 Short papers and notes distressed by hypoxia. ACKNOWLEDGMENTS We wish to thank R. Baker, M. Bur-ton, T. Crawford, M. Rockett, W. Slingerland, H. Yette and Captains P. Smirch and A. Smircic for their assistance in field collections. G. Stan-dard and M. Cuenca wrote and assisted with computer programs. We would also like to thank Dr. J. Slowey and L. Rice (Dept. of Civil Engineering, Texas A&M Univ.) for laboratory D.O. analyses and Dr. D. Harper (Texas A&M Univ. Marine Lab., Galveston) for providing additional D.O. data. Financial support was provid-ed in part, by the Texas Agricultural Ex-periment Station; by the Strategic Petroleum Reserve Program, Department of Energy (Contract No. DE-FC96-79P010114); and by the Texas A&M University Sea Grant College Program, supported by the NOAA Office of Sea Grant, U.S. Department of Commerce. LITERATURE CITED American Public Health Association. 1976. Standard methods for the ex-amination of water and wastewater (fourteenth ed.): 433. Washington, D.C. Bedinger, C.A., J.W. Cooper, A. Kwok, R.E. Childers, and K.T. Kimball. 1980. Ecological investigations of petroleum production platforms in the central Gulf of Mexico. Volume 1: Pollutant fate and effects studies. Draft final report submirted to the Bureau of Land Management, Contract No. AA551-CT8-17. 149 p. Brent, C.R., H.P. Williams, W.A. Bergin, J.L. Tyroll, and T.E. Myers. 1979. Organic carbon, inorganic carbon and related compounds in offshore oil pro-duction areas of the northern Gulf of Mexico, p. 245-264. In: C. H. Ward, M.E. Bender, and D.J. Reish (eds.), Effects of oil drilling and prodt:Jction in a coastal environment. Rice Univ. Stud. 65(4&5):1-589. Chittenden, M.E., Jr., and J.D. McEach-ran. 1976. Composition, ecology and dynamics. of demersal fish com-munities on the northwestern Gulf of Mexico continental shelf, with a similar synopsis for the entire Gulf. Texas A&M Univ. Sea Grant Publ. TAMU-SG-76-208. ______ , J.S. Pavela, and J.L. Ross. 1982. Nekton, p. 4.1-4.155. In: R.W. Hann Jr. and R.E. Randall (eds.), Final report of 18 month postdisposal studies to the Department of Energy, Contract No. DE-FC96-79P010114. ______ , J.L. Ross, and J.S. Pavela. 1980. Nekton, p. 4.1-4.131. In: R.W. Hann Jr. and R.E. Randall (eds.), Evaluation of brine disposal from the Bryan Mound site of the Strategic Petroleum Reserve Program, Final report of predisposal studies to the Department of Energy, Contract No. DE-FC96-79P010114. Conseil Perm. International pour !'exploration de Ia Mer. 1936. Bull. Hydrographique pour I'Anee 1935, 89:101-102. Farrell, D. 1974. Benthic communities in the vicinity of oil producing wells on the shallow Louisiana continental shelf. Offshore Ecol. Invest., Gulf Univ. Res. Consortium. 52 p. Fotheringham, N. and G. Weissberg. 1979. Some causes, consequences and potential impacts of oxygen depletion in the northern Gulf of Mexico. Off-shore Tech. Cont. Proc. OTC 3611: 2205-2207. Harper, D.E., Jr., and L.D. McKinney. 1980. Benthos, p. 5.1-5.78. In: R.W. Hann Jr. and R.E. Randall (eds.), Evaluation of brine disposal from the Bryan Mound site of the Strategic 6Gulf of Mexico Science, Vol. 6 [1983], No. 2, Art. 11https://aquila.usm.edu/goms/vol6/iss2/11DOI: 10.18785/negs.0602.11Northeast Gulf Science Vol. 6, No. 2 October 1983 173 Petroleum Reserve Program, Final report of predisposal studies to the Department of Energy, Contract No. DE-FC96-79P01 0114. _____ , R.R. Salzer, and R.J. Case. 1981. The occurrence of hypoxic bot-tom water off the upper Texas coast and its effects of the benthic biota. Contrib. Mar. Sci. 24:53-79. 1981. Harris, A. H., J.G. Ragan, and J.H. Green. 1976. Oxygen depletion in coastal waters. Sea Grant Sum. Rep. Proj. No. R/BOD-1. 161 p. Hildebrand, H.H. 1954. A study of the brown shrimp (Penaeus aztecus lves) grounds in the western Gulf of Mexico. Univ. Tex. Pub!. lnst. Mar. Sci 3(2):1-366. Perez-Farfante, I. 1969. Western Atlantic shrimps of the genus Penaeus. Fish. Bull. U.S. 67(3):461-590. Ragan, J.G., A.H. Harris, and J.H. Green. 1976. Temperature, salinity and oxygen measurements of surface and bottom waters of the continental shelf off Loui-siana during portions of 1975 and 1976. Nicholls St. Univ. Prof. Pap. Ser. (Bioi.) (3): 1-9. Reitsema, L.A. 1980. Biological/chemical survey of Texoma and Capline sector salt dome brine disposal sites off Louisiana, 1978-1979. Vol. 2: Zoo-plankton. NOAA Tech. Mem. NMFS-SEFC-16. 133 p. Slowey, J.F. 1980. Water and sediment quality, p. 3.1-3.74. In: R.W. Hann Jr. and R.E. Randall (eds.), Evaluation of brine disposal from the Bryan Mound site of the Strategic Petroleum Reserve Program, Final Report of Predisposal studies to the Department of Energy, Contract No. DE-FC96-79P010114. Wickham, D.A., and F.C. Minkler. 1975. Laboratory observations on daily pat-terns of burrowing and locomotor ac-tivity of pink shrimp, Penaeus duorarum brown shrimp, P. aztecus and white shrimp, P. setiferus. Contrib. Mar. Sci. 19:21-35. Williams, A.B. 1955. Substrates as a factor in shrimp distribution. Limnol. Oceanogr. 3(3):283-290. John S. Pavela, Jeffrey L. Ross and Mark E. Chittenden Jr. Depart-ment of Wildlife and Fisheries Sciences, Texas A&M Universi-ty, College Station, TX 77843. Present Address: (J.L.R.) North Carolina Marine Resources Center, Airport Road, Manteo, NC 27954. 7Pavela et al.: Sharp Reductions in Abundance of Fishes and Benthic MacroinvertebPublished by The Aquila Digital Community, 1983

Sharp Reductions in Abundance of Fishes and Benthic Macroinvertebrates in the Gulf of Mexico Off Texas Associated with Hypoxia

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Sharp Reductions in Abundance of Fishes and Benthic Macroinvertebrates in the Gulf of Mexico Off Texas Associated with Hypoxia

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