Seasonal Distributions of Larval Flatfishes 



(Pleuronectif ormes ) on the Continental Shelf 



Between Cape Cod, Massachusetts, and 



Cape Lookout, North Carolina, 1965-66 



W. G. SMITH. J. D. SIBUNKA, and A. WELLS' 

 ABSTRACT 



Larval flatfishes, representing 4 families, 17 genera, and 15 species, were identified from collections 

 taken during a 1-yr survey designed to locate spawning grounds and trace dispersion of fish eggs and larvae 

 on the continental shelf. Most flatfishes began spawning in the spring, a time of marked seasonal tempera- 

 ture change. The seasonal distribution of larvae indicated that: 1) bothids had longer spawning seasons than 

 pleuronectids; 2) pleuronectids spawned largely in the northern half of the survey area during the spring; 

 3) most bothids spawned in the southern half, beginning in spring and continuing through early fall; 4) 

 although cynoglossids spawned incidentally off North Carolina, most of their larvae were transported into 

 the survey area from spawning grounds south of Cape Lookout; 5) the few representatives of the family 

 Soleidae originated south of Cape Lookout; 6) spawning that began in the spring proceeded from south to 

 north as the season progressed, but spawning that began in the fall proceeded from north to south, 

 suggesting that the onset of spawning is triggered by spring warming and fall cooling; 7) most species 

 spawned within a relatively narrow range of temperature; 8) salinity had no apparent influence on 

 spawning. 



INTRODUCTION 



Recruitment is a major factor determining the size of 

 heavily exploited fish populations such as those found along 

 our eastern seaboard. Unfortunately, we lack the needed 

 scientific information about the life histories of most coastal 

 fishes to relate numbers of adults to numbers of young and, 

 in turn, relate numbers of young to the sequence of 

 biological and environmental events that lead to a successful 

 year class. The sound management policies that seem so 

 essential during this period of increased foreign and 

 domestic fishing pressure will follow the enormously 

 important task of understanding life histories in their 

 entirety; not just that part dealing with adults but with all 

 stages of development. 



In 1965, biologists at Sandy Hook began a 2-yr survey of 

 young fishes on the continental shelf between southern New 

 England and Florida. The first year we sampled from Cape 

 Cod, Mass., to Cape Lookout, N.C.; the second year from 

 New River, N.C., to Palm Beach, Fla. We planned initially 

 to determine spawning areas and trace the distributional 

 patters of eggs and larvae after spawning, with a view 

 toward assessing the importance of the estuarine zone as a 

 nursery ground for juvenile fishes. In this paper, we discuss 

 the seasonal distribution and relative abundance of flatfish 

 larvae, belonging to 17 genera and 15 species, collected 

 during the year of sampling along the Middle Atlantic Bight, 

 i.e., that portion of the continental shelf between Cape 

 Cod, Mass., and Cape Hatteras, N.C. To assess the 

 contribution of ichthyoplankton to the Middle Atlantic Bight 

 from waters south of Cape Hatteras, we sampled to Cape 

 Lookout. 



' Middle Atlantic Coastal Fisheries Center Sandy Hook Laboratory, 

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



The Middle Atlantic Bight, hereafter referred to as the 

 bight, is inhabited by an arctic-boreal group of flatfishes, 

 largely pleuronectids, whose center of abundance lies north 

 of Cape Cod; and a warm-temperate group, mostly bothids, 

 that range southward to Florida and, for some species, into 

 the Gulf of Mexico, the Caribbean Sea, and the South Atlan- 

 tic Ocean (Topp and Hoff 1972). Some of the pleuronectids 

 escape unsuitably warm inshore water in the bight by 

 moving offshore to cool deep water in summer. Conversely, 

 many of the bothids favor the warm inshore water in 

 summer and some move offshore in winter, where bottom 

 temperatures are warmer than those inshore. Despite their 

 seasonal movements, members of both groups possess the 

 temperature tolerance characteristic of most coastal fishes 

 found at temperate latitudes. 



METHODS 



We conducted nine cruises during the survey, sampling at 

 92 stations situated along 14 transects (Fig. 1). The 

 sequence of sampling varied, depending largely on existing 

 weather conditions. With the exception of the September 

 cruise, which was twice delayed and subsequently re- 

 scheduled after sampling the four northernmost transects, 

 nearly all cruises were completed. Rough weather 

 precluded our sampling along transects A and B on the first 

 cruise in December, and at six stations on the second cruise 

 in January (Table 1). 



Sampling procedures, equipment, hydrographic data, and 

 laboratory procedures are described by Clark et al. (1969). 

 Two Gulf V nets (Arnold 1959) were towed for 30 min in a 

 step oblique pattern to collect plankton. Net 1 fished for 5 

 min each at six 3-m depth intervals from the surface to 15 m; 

 the other, net 2, at six intervals from 18 to 33 m. At depths 

 less than 33 m, we decreased the number of towing depth 



