336 



Abstract.-The tautog fTautoga onitis ) 

 is one of two temperate labrid species 

 commonly inhabiting the coastal marine 

 and estuarine waters of the mid-Atlan- 

 tic coast of the United States. To delin- 

 eate population structure throughout its 

 primary range, we examined samples 

 collected from three sites ( Rhode Island, 

 Delaware, Virginia). Five regions of the 

 mitochondrial genome (COI, ATPase 6, 

 cyt 6, ND2 and control region) and one 

 nuclear intron were amplified by PCR 

 and screened for sequence variation 

 with a battery of restriction enzymes 

 (RFLP analysis), or by denaturing gra- 

 dient gel electrophoresis (DGGE). 



With RFLP analysis an average of 

 129 restriction sites per individual were 

 revealed and 5.32 bases per individual 

 were surveyed. Polymorphisms were 

 observed in the ND2 and control region 

 fragments, but not in the COI, ATPase 

 6, or cyt 6 fragments. Mean within- 

 sample haplotype diversity was 0.690.5 

 (±0.00184), within the range of values 

 reported for other marine species. How- 

 ever, mean nucleotide diversity was 

 0.000782, one of the lowest values re- 

 ported for a marine teleost. Corrected 

 nucleotide divergence between samples 

 was essentially zero, suggesting the 

 absence of population structuring along 

 the mid-Atlantic Coast. DGGE analy- 

 ses of COI, cyt b. and a lactate dehy- 

 drogenase (LDH) intron revealed little 

 additional variation; each product pos- 

 sessed a single common haplotype and 

 occasional rare variants. 



The low level of genetic diversity ob- 

 served in the tautog may reflect a small 

 effective population size resulting from 

 historical population bottlenecks or large 

 variance in reproductive success. The 

 apparent absence of geographic differen- 

 tiation suggests that tautog from Rhode 

 Island to Virginia form a single genetic 

 stock; data from additional genetic poly- 

 morphisms are needed to confirm or dis- 

 prove this conclusion. 



Genetic structure of tautog iTautoga onitis) 

 populations assayed by RFLP and DGGE 

 analysis of mitochondrial and nuclear genes 



Elizabeth A. Orbacz 



Patrick M. Gaffney 



College of Marine Studies 



University ol Delaware 



Lewes, Delaware 19958 



E-mail address (for P M Gaffney, contact auttior) pgaffney a udel edu 



Manu.script accepted 27 September 1999 

 Fish. Bull. 98:336-344 (2000). 



The tautog iTautoga onitis) is one 

 of two temperate labrid species 

 commonly inhabiting the coastal 

 marine and estuarine waters of the 

 mid-Atlantic coast of the United 

 States. Although the species range 

 extends from the outer coast of Nova 

 Scotia to Georgia, tautog are most 

 abundant from Cape Cod to Chesa- 

 peake Bay (Bigelow and Schroeder, 

 1953). They are generally found in 

 high relief, reeflike habitats such as 

 those associated with jetties, break- 

 waters, and wrecks (Auster, 1989). 



In the northern part of the their 

 range, adult tautog generally over- 

 winter in a state of torpor in shel- 

 tered areas in deep water offshore 

 and move inshore during the spring 

 to spawn in estuaries and near- 

 shore waters (Cooper, 1966; 011a 

 et al., 1974). Some tautog remain 

 offshore throughout the year, par- 

 ticularly in the southern part of 

 their range (011a and Samet, 1977; 

 Eklund and Targett, 1991). Those 

 that migi'ate offshore do not always 

 return to the same sites to over- 

 winter (011a et al., 1979). Juve- 

 niles and some adults have been 

 found to overwinter at inshore sites 

 off Virginia (Hostetter and Munroe, 

 1993) and Delaware (Eklund and 

 Targett, 1991). In a tagging study, 

 Cooper (1966) found that adult 

 tautog tagged in Narragansett Bay 

 tended to return to the same spawn- 

 ing site each year, and adult move- 

 ment into and out of the area was 

 negligible. In general, tautog do not 



appear to undergo extensive along- 

 coast migration (Cooper, 1966; 011a 

 etal., 1974;Briggs, 1977). 



Tautog spawn between mid-May 

 and mid-August; spawning activ- 

 ity peaks in June (Colton et al., 

 1979). Eggs are buoyant and gen- 

 erally confined to coastal waters. 

 Hatching occurs in 42-45 hours at 

 20-22°C, and pelagic larval dura- 

 tion is approximately 20-30 days 

 (Victor, 1986), Although spawning 

 occurs primarily in estuaries, off- 

 shore spawning has been reported 

 (Eklund and Targett, 1990; Hostet- 

 ter and Munroe, 1993). 



Tautog support important recre- 

 ational and small commercial fisheries 

 throughout their range. After peak- 

 ing in 1986, annual hai-vests have 

 declined, and the species is believed 

 to be overexploited, particularly in the 

 northern part of its range, between 

 New York and Massachusetts.' 



Despite the economic importance 

 of tautog, little infomiation is avail- 

 able regarding stock structure of 

 the species. Tagging studies suggest 

 that there is little mixing of adult 

 fish between geographical regions 

 (Cooper, 1966; Briggs, 1977). Hostet- 

 ter and Monroe ( 1993) reported lati- 

 tudinal variation in size-at-age; fish 

 from Virginia were found to grow 



' Atlantic States Marine Fisheries Commis- 

 sion. 1996. Fishery management plan for 

 tautog, April 1996. Fishery Management 

 Report 25 of the Atlantic States Marine 

 Fisheries Commission. 1444 Eye Street, 

 N.W., 6"^ Floor, Washington D.C. 20005. 



