DIEL MOVEMENTS OF LARVAL YELLOWTAIL FLOUNDER, 



LIMANDA FERRUGINEA, DETERMINED FROM 



DISCRETE DEPTH SAMPLING 



W. G. Smith, J. D. Sibunka, and A. Wells ^ 



ABSTRACT 



A 72-h study to investigate diel movements of yellowtail flounder larvae indicated that they exhibited 

 pronounced vertical movements that were repetitious from day to day. Collections at 3-h intervals with 

 20-cm bongo nets revealed that larvae were near the surface at night, and mostly at a depth of 20 m 

 during the day. Ascent and descent occurred largely at sunset and sunrise, respectively. Thermal 

 gradients at 10 to 20 m and 30 to 40 m had no apparent influence on the vertical movements. Amplitude 

 of the movements increased with the size of larvae. Recently hatched larvae remained near the shallow 

 thermal gradient. Intermediate sized larvae migrated from middepths during the day to surface and 

 near-surface at night. Large larvae moved throughout the water column. The incidence of feeding was 

 low but a daily feeding pattern was evident. Most larvae with gut contents were collected from 1900 to 

 0100 h on the first day; from 1600 to 2200 h on the second day; and from 1600 to 0100 h on the third day. 

 The near-absence of gut contents in larvae caught during morning daylight hours suggests that the 

 onset of feeding is triggered by something other than, or in addition to, light. Wind driven circulation 

 near the surface was thought to transport larvae at night, when they moved towards the surface. 

 Subsurface circulation was sluggish and ineffective as a transporting mechanism. 



Diel migrations by larval fishes play an important 

 but largely unexplored role in dispersion during 

 planktonic development. We became cognizant of 

 the need to investigate this role after our initial 

 ichthyoplankton survey, a series of cruises in the 

 Middle Atlantic Bight to determine when and 

 where coastal fishes spawn and to trace the disper- 

 sal of planktonic eggs and larvae (Clark et al. 

 1969). Despite a full schedule of field work, the 

 survey was only partially successful. We learned 

 where and when many fishes spawn and recog- 

 nized seasonal shifts in spawning areas (see Smith 

 1973; Fahay 1974; Kendall and Reintjes 1975; 

 Smith et al. 1975), but we were unsuccessful in 

 tracking disperson away from the spawning 

 grounds. 



After realizing the shortcomings of the survey, 

 we began to speculate on the significance of diel 

 migrations and how they might interact with cir- 

 culation to affect dispersion, especially where the 

 water column is thermally stratified and surface 

 and subsurface currents differ in velocity. We 

 theorized that a study of the diel movements offish 



'Northeast Fisheries Center Sandy Hook Laboratory, Na- 

 tional Marine Fisheries Service, NOAA, Highlands, NJ 07732. 



Manuscript accepted June 1977. 



FISHERY BULLETIN: VOL. 76. NO. 1, 1978. 



larvae, when related to our survey data and to 

 known circulation patterns, might provide us with 

 better information on larval transport than we 

 could obtain from continued surveys. In June 1972 

 we conducted a 72-h study of the diel movements of 

 larval yellowtail flounder, Limanda ferruginea 

 (Storer), an important species in the New England 

 trawl fishery, and the most abundant flatfish lar- 

 vae collected during our survey of the Middle At- 

 lantic Bight. Our primary objectives were to de- 

 termine whether the young flatfish undergo diel 

 migrations, whether the migrations are repeti- 

 tious in time and extent, and how they interact 

 with circulation to affect dispersion. 



Yellowtail flounder range from the Gulf of St. 

 Lawrence to Chesapeake Bay. Their center of 

 abundance lies between the western Gulf of Maine 

 and southern New England (Bigelow and 

 Schroeder 1953). They spawn from March to Sep- 

 tember in the Middle Atlantic Bight. Spawning 

 progresses from south to north as the season ad- 

 vances. The peak of the season in the bight occurs 

 in early May with heaviest spawning off New 

 York and northern New Jersey. Based on the catch 

 of larvae <4 mm. Smith et al. (1975) determined 

 that most spawning takes place between 4° and 

 9°C. 



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