1025 



Abstract.— A two-ship sur\-ey of the 

 I'astern tropical Pacific collected sur- 

 face plankton samples during El Nino 

 in August-November 1987. Although 

 the diversity of cephalopods in these 

 samples was low, cephalopod abun- 

 dance was extremely high. Most of the 

 cephalopods collected were rhyncho- 

 teuthion paralarvaeof an ommastrephid 

 squid, either Doscidicus gtgas or Stheno- 

 tciitlus oualaniensis. High abundances 

 (hundreds of paralarvae in a 15-min 

 tow) were concentrated in a band par- 

 allel to the coast, 740-900 km off Cen- 

 tral America. This band of high abun- 

 dance was approximately coincident 

 with the 29 = C surface isotherm. Maxi- 

 mum abundance (>12.000 rhyncho- 

 teuthions in a 15-min tow) was four 

 orders of magnitude greater than back- 

 ground levels and an order of magni- 

 tude greater than any other report of 

 cephalopod abundance. Based on flow- 

 meter readings from the sampler, the 

 anomalous abundance was not a sam- 

 pling artifact. Size-frequency analysis 

 indicates that this patch cannot be ex- 

 plained as a result of recent hatching 

 from an egg mass. This abundance may 

 have resulted from warm El Nino wa- 

 ters, aggregation by convergence of sur- 

 face currents, or the interaction of these 

 factors during the squid's spawning 

 season. 



Extraordinary abundance of squid paralarvae 

 in the tropical eastern Pacific Ocean 

 during El Nino of 1987 



Michael Vecchione 



Systematics Laboratory 



National Marine Fisheries Service 



National Museum of Natural History 



Washington, DC 20560 



E-mail address vecchione michaeliSinmnh si edu 



* Manuscript accepted 26 October 1998. 

 Fish. Bull. 97:1025-1030 ( 1999). 



Reports of the effects of El Nino/ 

 Southern Oscillation have been 

 widespread in both scientific litera- 

 ture and popular news media. Shifts 

 in distribution and decreases in 

 abundance of marine animals re- 

 sulting from El Nino have received 

 much attention. Cephalopods are 

 important components of the ma- 

 rine food web, as well as the targets 

 of commercial fisheries. I report 

 here on the serendipitous collection 

 of squid paralarvae during El Nino 

 1987 at abundances an order of 

 magnitude higher than any previ- 

 ously known. 



Materials and methods 



A two-ship survey for a visual cen- 

 sus of marine mammals was con- 

 ducted in the eastern tropical Pa- 

 cific Ocean during August-Novem- 

 ber 1987. During four cruise legs, 

 the NOAA Ship David Starr Jordan 

 surveyed the area between the 

 equator— 19°N and 79-121°W, 

 while the NOAA Ship MacArthin\ 

 also in four legs, covered the region 

 westward of the Jordan survey to 

 148 -W and southward to 11°S. Sur- 

 face plankton samplers (Manta 

 nets; Brown and Cheng, 1981) were 

 towed by both ships almost every 

 day after sunset to collect fish lar- 

 vae. Surface temperature was mea- 

 sured by bucket thermometer con- 

 currently with each plankton tow. 

 The distance of each tow was esti- 



mated by a flow meter mounted be- 

 low the net. Extremely high num- 

 bers of cephalopod paralarvae were 

 found in some of these samples 

 when they were sorted for ichthyo- 

 plankton after the conclusion of the 

 cruises. 



Results 



The diversity of cephalopods in 

 these samples was quite low; only 

 15 species were identified and >99% 

 of the 15,052 cephalopods collected 

 were a single species of the squid 

 family Ommastrephidae (Table 1). 

 Ommastrephid paralarvae are dis- 

 tinctive and are referred to as rhyn- 

 choteuthions because the two ten- 

 tacles (as opposed to the eight arms) 

 are fused throughout the early life 

 history. Throughout the entire sur- 

 veyed region, abundance of para- 

 larval ommastrephids, measured as 

 number of rhvnchoteuthions collected 

 per 15-min tow, generally was 0-10 

 squids per tow. Maximum abundance 

 (22 stations with 20->100 rhyncho- 

 teuthions/tow) was found about 

 740-900 km offshore in a band par- 

 allel to the coast of Central America 

 (Fig. lA). Within this band at three 

 stations during two separate legs, 

 379. 461, and 12,354 rhynchoteu- 

 thions were collected, respectively. 

 Although most of the stations in this 

 band were sampled by the Jordan, 

 the northeasternmost MacArthur 

 stations were in the eastern end of 



