use in the area. The beginning of the year's heavy 

 rains in late September could have served as a vec- 

 tor for an agrochemical. Also, a fish mortality of 

 unknown cause in Lake Arenal, located approx- 

 imately 45 km NE of the upper Gulf and draining 

 adjacent lands, occurred simultaneously with the 

 sciaenid mortality, killing primarily Cichlasoma 

 nicaraguense (J. Cabrera^). However, in neither case 

 were there reports of dead fishes or invertebrates 

 in nearby rivers that might serve to transport an 

 agrochemical. Tests detecting the presence of possi- 

 ble pollutants were not available. The possibility that 

 the sciaenid deaths were caused by toxins from red 

 tides that occurred in parts of the gulf between April 

 and November (Vi'quez 1985; R. Viquez^) cannot be 

 ruled out. Likewise, disease cannot be discounted, 

 although attempts to isolate any infectious agents 

 (bacteria, fungi) from fresh specimens were unsuc- 

 cessful. 



The near specificity for sciaenids remains a 

 mystery, and we are not aware of any other fish kill 

 specific at the family level. Cardeilhac et al. (1981) 

 reported acute deaths of large red drum (a sciaenid) 

 in Florida, which they attributed to metal poison- 

 ing resulting from ingestion of contaminated prey. 

 Gulf of Nicoya sciaenids are generally bottom fishes 

 known to consume a variety of benthic fishes and 

 invertebrates (Araya 1984). Their benthic distribu- 

 tions or food habits alone do not explain their suscep- 

 tibility because a large number of benthic fishes with 

 similar food habits are common in the gulf (Leon 

 1973). The wide size range of sciaenids affected also 

 argues against the specificity being due to consump- 

 tion of common prey. 



No measure of total number of fishes killed in this 

 mortality is available. However, we estimated that 

 at its height (mid-October), a thousand fishes could 

 be sighted along a few hundred meter stretch of a 

 flotsam windrow. Since the mortality, fishermen 

 reported no noticable decline in the catch of sciae- 

 nid species. Although no mortalities of this nature 

 have been reported in the past, their recurrence 

 could endanger the livelihood of Gulf of Nicoya 

 fisheries. 



Acknowledgments 



We thank R. Viquez and her assistants for help 

 with collections; M. Arce and C. Villalobos for tech- 



nical assistance; A. Le6n for drafting the figure; and 

 W. Bussing and two anonymous reviewers for com- 

 menting on drafts of the manuscript. W.A.S. thanks 

 R. J. Lavenberg, M. M. Murillo, W. A. Bussing, M. 

 L L6pez, and D. Perry for invaluable assistance 

 while working in Costa Rica, and acknowledges 

 logistic and financial support by the ARCS Founda- 

 tion of Southern California, the University of South- 

 ern California, the Los Angeles County Museum of 

 Natural History, and the Centro de Investigacion 

 en Ciencias del Mar y Limnologi'a (CIMAR), Univer- 

 sidad de Costa Rica. 



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William A. Szelistowski 

 Centro de Investigaci&n en Ciencias del Mar y 



Limnologia (CIMAR) 

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Juan Garita 



Escuela de Ciencias Biologicas 

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365 



