KENDALL and WALFORD SOURCES AND DISTRIBUTION OF BLUEFISH 



ern area (18'-26'C and 30-32°/„o). Bluefish larvae 

 have been reported by other authors in this area 

 from May through September, but mostly in July 

 and August (Table 5). Larvae have also been re- 

 ported in the more saline areas of several estuaries 

 of the Middle Atlantic Bight (Table 5). Although 

 some juveniles from the Middle Atlantic Bight 

 spawning inhabit estuaries in late summer, more 

 seem to remain along the shore. Nevertheless, all 

 appear to move southward and out of the bight in 

 midfall. Their distribution in late fall and winter 

 is still unknown. 



From the scarcity of juveniles (i.e., fish 50-150 

 mm SL) in our samples at sea, and the abundance 

 of these fish in estuarine collections, it appears 

 that bluefish depend chiefly on estuaries for 

 habitat during this stage. Their dependence is de- 

 termined by the time and place of their spawning. 

 Those from the spring spawning spend most of 

 their first summer in estuaries, while those from 

 the summer spawning spend at most about a 

 month there. Both changes in temperature and 

 seasonal photoperiod influenced the activity and 

 distribution of adult bluefish at least under 

 laboratory conditions (011a and Studholme 1971, 

 1972 1. Thermal edges may act as barriers affecting 

 the distribution of juvenile bluefish, as shown in 

 recent laboratory work (OUa'). These factors, and 

 possibly others, probably trigger movements of 

 juveniles from the open ocean to estuaries and 

 back to the open ocean. 



In order to assess the relative proportions of the 

 two major spawning areas to the total recruitment 

 of bluefish on the Atlantic coast in any given year, 

 it would be necessary to sample repeatedly during 

 the spring south of Cape Hatteras and during the 

 summer in the Middle Atlantic Bight. 



Our" present limited understanding of early life 

 history contributes to several other facets of 

 bluefish biology. Population differences of bluefish 

 on the U.S. Atlantic coast have been studied using 

 meristic characters (Lund 1961), migratory pat- 

 terns, morphometries, and scale morphology 

 ( Wilk see footnote 6). All of these studies indicate 

 that more than one population exists. Scale 

 studies defined two groups of bluefish by the size of 

 fish when the first annual ring forms in May. One 

 group, which reaches about 260 mm by the end of 



'B. L- 011a. Northeast Fisheries Center Sandy Hook Laborato- 

 ry. National Marine Fisheries Service. NOAA. Highlands. N-J 

 07732, pers. commun. August 1978. 



its first winter, evidently represents fish spawned 

 in spring south of Cape Hatteras. The other group, 

 which reaches only about 1 20 mm by the end of its 

 first winter, represents fish spawned in the sum- 

 mer in the Middle Atlantic Bight. Body propor- 

 tions of these two groups of fishes are statistically 

 different (Wilk see footnote 6). 



Precise information on adult bluefish migration 

 is not available, but general patterns are known 

 ( Wilk see footnote 6). Some mature bluefish spawn 

 near the inner edge of the Gulf Stream as they 

 migrate northward from their wintering grounds 

 off Florida. To a lesser extent some bluefish also 

 spawn in the same area in fall and winter, pre- 

 sumably on their return migration. Adult bluefish 

 migrate to coastal waters off the Middle Atlantic 

 Bight in spring and feed there until they migrate 

 south coincident with fall cooling. During their 

 stay in the Middle Atlantic Bight, bluefish spawn 

 on the shelf, and to some extent in mouths of the 

 larger estuaries (Norcross et al. 1974). Although 

 spawning can take place as soon as the adults 

 arrive in the area in May, most seems to occur in 

 July and August, while some continues into Sep- 

 tember. From the apparent annual variations in 

 timing and amount of this spawning, it is depen- 

 dent on a combination of several features of the 

 environment including temperature, salinity, 

 photoperiod, and food for the adults. 



If each mature fish spawns in both areas and in 

 all seasons, this would indicate that there is a 

 single stock of bluefish on the east coast of the 

 United States. If each fish spawns in only one area, 

 separate populations must exist. Our early life 

 history information is consistent with other in- 

 formation that indicates that there are separate 

 populations. Southern and northern spawnings 

 take place under quite different hydrographic 

 conditions and in quite different current regimens 

 to assist the young fish in movements to nursery 

 grounds. In time these conditions could allow 

 genetically distinct populations to become estab- 

 lished. Tagging and fecundity studies would show 

 to what extent this has happened. 



Since year-class strength of fishes is determined 

 mainly during their young stages, it is important 

 to understand the factors influencing survival of 

 these stages. In bluefish, the eggs and larvae 

 occur at the surface of the ocean and the juveniles 

 occur in estuaries, areas affected by annual varia- 

 tions in weather-related phenomena and, to an 

 increasing extent, affected by man's activities. It 

 is thus important to monitor these influences and 



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