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Fishery Bulletin 92(2). 1994 



insufficient to examine important details, and 

 Okiyama's study is a general overview of exisitng 

 information. The utility of early life stages of 

 Coryphaena in examining previous phylogenetic 

 hypotheses and evolutionary interrelationships of 

 echeneoids (i.e. Coryphaenidae-Rachycentridae- 

 Echeneididae) is discussed by Johnson (1984). Our 

 objectives are 1) to describe and compare early lar- 

 val development of common dolphin and pompano 

 dolphin using the dynamic approach to larval de- 

 scription (Berry and Richards, 1973) and 2) to de- 

 scribe the spatial and temporal distribution and 

 abundance of early life stages of dolphinfishes in the 

 northern Gulf. 



Materials and methods 



Seasonal occurrence, distribution, and abundance of 

 dolphinfish larvae were determined primarily from 

 814 neuston net collections taken during Southeast 

 Area Monitoring and Assessment Program 

 (SEAMAP) ichthyoplankton surveys of the Gulf be- 

 tween 1982 and 1984 (1982-276 stations, 1983-260, 

 1984-278). These years represent the first time in- 

 terval for which a complete set of data was currently 

 available. SEAMAP collections were made with an 

 unmetered 1x2 m net (0.947-mm mesh) towed at the 

 surface for 10 minutes at each station. The 

 SEAMAP effort also involved the collection and pro- 

 cessing of about 1,819 bongo net stations between 

 1982 and 1986 (1982-384 stations, 1983-288, 1984- 

 409, 1985-272, and 1986-466) (SEAMAP 1983- 

 1987) 2 . Bongo nets (60-cm net, 0.333-mm mesh) 

 were towed obliquely to the surface from within 5 

 m of the bottom or from a maximum depth of 200 

 m. Sampling during April and May was primarily 

 beyond the continental shelf, and that during March 

 and from June to November was primarily over the 

 shelf at stations <180 m depth. No samples were 

 taken during January and February. Tows were 

 made during both day and night depending on when 

 the ship occupied the station. Latitude 24°30'N was 

 the southern boundary of our survey area in the 

 eastern Gulf and latitude 26°00'N the southern 

 boundary of the central and western Gulf (Appen- 

 dix Fig. 1). These coordinates approximate the U.S. 

 Exclusive Economic Zone (EEZ)/Fishery Conserva- 

 tion Zone (FCZ). Additional information on tempo- 

 ral and spatial coverage of SEAMAP plankton sur- 

 veys are found in Stuntz et al. ( 1985), Thompson and 



2 SEAMAP. 1983-1987. (plankton i. ASCII characters. Data for 

 1982-1986. Fisheries-independent survey data/National Ma- 

 rine Fisheries Service. Southeast Fisheries Center: Gulf States 

 Marine Fisheries Commission, Ocean Springs, MS (producer!. 



Bane (1986, a and b), Thompson et al. (1988), and 

 Sanders et al. (1990). 



Ichthyoplankton collections were also examined 

 from riverine/oceanic frontal zones off the Missis- 

 sippi River delta. These collections were from sur- 

 face-towed 1x2 m neuston nets (0.947-mm mesh, 10- 

 min. tows, sample rc=311) and were obtained from 

 the National Marine Fisheries Service (NMFS), 

 Panama City, Florida (i.e. May 1988 [55 neuston 

 samples]; August 1988 [71]; September 1986 [46], 

 1987 [68], and 1989 [35]; and December 1988 [36]). 



A detailed examination of dolphinfish larvae was 

 made to describe developmental morphology. We 

 examined 25 common dolphin and 19 pompano dol- 

 phin larvae between 3.5 and 15.0 mm SL for differ- 

 ences in pigmentation, developmental morphology, 

 and head spination, but only cursorily discuss fin 

 development because of a thorough review of these 

 structures by Potthoff ( 1980). Body measurements 

 were made to the nearest 0.1 mm with a dissecting 

 scope and ocular micrometer following Hubbs and 

 Lagler (1958) and Richardson and Laroche (1979). 

 We follow Leis and Trnski's (1989) criteria for de- 

 fining length of preopercular spines, body depth, 

 head length, and eye diameter. We consider noto- 

 chord length in preflexion and flexion larvae synony- 

 mous with standard length (SL) in postflexion lar- 

 vae and report all lengths as SL unless otherwise 

 noted. Specimens were field-fixed in 10% formalin 

 and later transferred to 70% ethyl alcohol. We used 

 a compound scope to examine origin and location of 

 epithelial spicules and the maxillary spine. Juve- 

 niles are those >25 mm, when specimens usually 

 have developed a full complement of rays in all fins 

 and scales (Johnson, 1984). Representative speci- 

 mens were illustrated with a camera lucida (Figs. 

 1 and 2). Only three pompano dolphin <4 mm were 

 collected and these were in too poor a condition to 

 illustrate. 



Estimates of larval catch (number of larvae/neus- 

 ton tow) were calculated for each station. Mean 

 catch estimates by month and season were calcu- 

 lated by dividing the sum of larvae (by species) by 

 the total number of stations sampled within each 

 category (month, season, etc.) and multiplying the 

 result by 10 (number of larvae/10 neuston tows). 

 Mean catch more closely reflects the abundance of 

 larvae throughout the area by including total sam- 

 pling effort in calculations. Catch was combined by 

 month and by season across years. Seasons were 

 defined as follows: spring=March to May; sum- 

 mer=June to August; and fall=September to Novem- 

 ber (Appendix Fig. 2). 



Nonparametric tests were used to evaluate diel, 

 seasonal, and overall differences in catch of common 



