View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Aquila Digital Community Northeast Gulf Science Volume 13 Article 6 Number 2 Number 2 12-1994 Winter Mass Mortality of Animals in Texas Bays Lawrence W. McEachron Texas Parks and Wildlife Department Gary C. Matlock National Marine Fisheries Service C.E. Bryan Texas Parks and Wildlife Department Phil Unger Jones and Stokes Associates, Inc. Terry J. Cody Texas Parks and Wildlife Department et al. DOI: 10.18785/negs.1302.06 Follow this and additional works at: https://aquila.usm.edu/goms Recommended Citation McEachron, L. W., G. C. Matlock, C. Bryan, P. Unger, T. J. Cody and J. H. Martin. 1994. Winter Mass Mortality of Animals in Texas Bays. Northeast Gulf Science 13 (2). Retrieved from https://aquila.usm.edu/goms/vol13/iss2/6 This 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 Science by an authorized editor of The Aquila Digital Community. For more information, please contact [email protected]. McEachron et al.: Winter Mass Mortality of Animals in Texas Bays Northeast Gulf Science Vol. 13, No. 2 December 1994 · p. 121-138 WINTER MASS MORTALITY OF ANIMALS IN TEXAS BAYS Lawrence W. McEachron Texas Parks and Wildlife Department Coastal Fisheries Division 702 Navigation Circle Rockport, Texas 78382 and Gary C. Matlock National Marine Fisheries Service 1315 East-West Highway Sliver Spring, Maryland 20910 and C. E. Bryan Texas Parks and Wildlife Department Coastal Fisheries Division 4200 Smith School Road Austin, Texas 78744 and Phil Unger Jones and Stokes Associates, Inc. 2600 V Street, Suite 100 Sacramento, California 95818 and Terry J. Cody and Joe H. Martin Texas Parks and Wildlife Department Coastal Fisheries Division 702 Navigation Circle Rockport, Texas 78382 ABSTRACT: The Texas coast experienced three unusually cold weather periods In the 1980's, one In 1983 and two In 1989, that caused massive fish kills. Identification of organisms killed and estimation of the number of estuarine fishes and Invertebrates killed was accomplished through a systematic standardized approach utilizing airplanes, ground qualitative observations and quantitative counts, and trawling. Of 159 species Identified, 103 were fishes, 45 were Invertebrates, and 11 were.vertebrates other than fishes. About 14 million fishes were killed In December 1983, 11 million In February 1989 and 6 million In December 1989; number of Invertebrates killed ranged from 13,000 In February 1989 to 1,000,000 In 1983. These assessments are the largest In area and most comprehensive to be documented In the literature with known levels of precision. Methodology used provides reasonably precise estimates which managers can use to assess extensive widespread kills and subsequent Impacts on affected populations. It Is recommended that managers consider reducing fishing mortality on the remaining economically Important populations after extensive kills to speed recovery of those populations. Mortality of marine organisms due to so recovery to pre-event levels is slow to events such as cold temperatures can occur. Information on mass mortalities have dramatic Impacts on population are required by fishery managers to en­ abundance. Severe mortalities could sure that subsequent fishing mortality lower recruitment from loss of spawners does not jeopardize long-term viability of 121 Published by The Aquila Digital Community, 1993 1 Gulf of Mexico Science, Vol. 13 [1993], No. 2, Art. 6 122 McEachron, L W., G. C. Matlock, C. E. Bryan, P. Unger, T. J. Cody, and J. H. Martin populations. With knowledge of these with some modification, to estimate the · natural mortalities, fisheries managers number of fish killed in mass mortality can enact measures to reduce fishing events. These procedures were applied to mortality which speeds recovery of the 3 mass mortalities that occured in the population. 1980's. This paper documents methods Polar cold fronts have pushed into used to estimate mortality of fJshes in a Texas and crossed the Gulf of Mexico to freeze in 1983 and two in 1989, and pro­ as far south as Nicaragua (Gunter ahd vides estimates of animals reported HildebFand 1951). The near-shore Gulf of killed. Mexico and adjacent waters are vulnerable to periodic mass mortalities of MATERIALS AND METHODS fishes due to cold temperatures because of limited openings between land masses A stepwise, standardized approach separating shallow bays from the Gulf, was used to estimate numbers of animals especially when water temperature killed in catastrophic cold kills along the decreases rapidly (Bartlett 1856; Higgins Texas coast (Fig. 1); over 100 persons par­ and Lord 1927; Anonymous 1931; Storey ticipated in each survey. First, extensive and Gudger 1936; Storey 1937; Gunter reconnaissance of shoreline areas that 1941, 1945, 1952; Baughman 1947, 1951; were accessible by vehicle were made Gunter and Hildebrand 1951; Simmons daily to 1) measure water temperatures; 1957, 1962; Moore 1976; Holt and Holt 2) determine when organisms began to 1983). Impact of cold fronts on fish sur­ die; and 3) record general observations for vival is lessened if the front is preceded areal documentation of the kill so future by gradually decreasing water tempera­ ground counts could be made. Second, tures which allow poikilothermic animals when dead organisms were observed, to acclimate or move offshore (Gunter airplane flights were initiated to identify and Hildebrand 1951, Springer and Wood­ burn 1960, Dahlberg and Smith 1970). Cold also can affect size of fishes killed (Gunter 1947). Methods used to estimate the magnitude of freeze mortalities were not well documented prior to 1983-84; preci­ sion of estimates was not determined. Generally, qualitative observations were made; few quantitative counts were made over a broad area. Estimations of kills were extrapolated to sections of the coast with little documentation of areal extent of a kill. As a result, reliable quan­ titative comparisons of the impacts of freezes are impossible. The Texas Parks and Wildlife Department (TPWD) im­ plemented procedures in the 1970's to estimate numbers of fish killed during rotenone collections in Texas bays (Matlock et al. 1982). These procedures were sufficiently general for application, Figure 1. Texas bay systems. https://aquila.usm.edu/goms/vol13/iss2/6 2 DOI: 10.18785/negs.1302.06 McEachron et al.: Winter Mass Mortality of Animals in Texas Bays Winter Mortality in Texas Bays 123 concentrations of dead organisms within lected subsample was taken so a total each bay system. Third, based on these area count estimate could be made. findings, bay systems were stratified into The same site (in 1983) or grid (in areas of high and low animal concentra­ 1989) system previously described was tions, which in turn were divided into also used for trawls. Sites or grids were shoreline and open water areas. In 1983, selected at random in identified kill areas. organisms were found to be distributed Trawls were pulled for 10 minutes in pre­ throughout the bay systems, so there was selected grids without replication to no stratification into high-low areas. estimate numbers of dead animals in Shoreline areas were accessed by boat or water >1 m deep; one 10 minute pull with vehicle, and the number of dead animals a 6.1-m trawl covered 0.35 ha. All dead in pre-selected random segments were animals were identified to 'species and counted. In the final phase, dead animals counted; up to 19 individuals of each were collected on the bottom in open species in each 10 minute collection were water areas using trawls after shoreline measured. counting began. Distribution of fish among sites (in In 1983, count (N = 242) or trawl (N 1983) or grids (in 1989) was highly skewed. = 100) sites were selected from existing Numbers at a few sites or grids were shoreUne and open water TPWD sample relatively high, whereas most sites or stations, whereas for 1989, shoreline grids had few or no fish. The skewed counts (N = 118 February; 124 December) distribution and large number of zeroes and trawl sites (N = 78 February; 107 precluded using the raw data to compute December) were selected from a 1-minute unbiased~ estimators for the mean and latitude by 1-minute longitude grid system standard error; log transformation failed in each bay .•Within each site or grid, three to normalize the data. Therefore, Penn­ count areas, 30.5 m long, were randomly ington's (1986) estimators,' which are un­ selected. To obtain the most precise biased for skewed distributions with estimates of numbers of dead fish, many zeroes, were used to com put~ mean sampling was stratified (Cochran 1977) and standard error of the number of among bays and within each bay by organisms per site or grid for each observed high- and low-kill density areas. stratum. All sites had roughly equal This procedure was used to select lengths and grids had approximately shoreline grids for sampling during 1989, equal areas, so it was not necessary to whereas in 1983 simple random sampling standardize numbers collected for length was used to estimate numbers for each or area sampled. bay; in 1983 bays were treated as strata Total numbers and 95% confidence to estimate coastwide totals. At each intervals of dead individuals of each shoreline area sampled, all dead fish and species, and total number and 95% con­ macro-invertebrates along shore, floating fidence interval for all species combined in the water or visible on bottom out to were computed for each bay and for the 15.2 m offshore were identifieo to species entire coast as follows (Scheaffer et al. and counted; "other" animals were iden­ 1979): tified and recorded. Up to 19 randomly Total :I:NX = I I selected individuals of each species were 95% C.