Hostetter and Munroe: Age, growth, and reproduction of Tautoga onitis 



55 



tautog is a long-lived species that reaches relatively 

 large sizes slowly. Seasonal growth, reflected by annu- 

 lar growth increments on opercles (Fig. 3), is one of 

 rapid somatic growth following spawning, with maxi- 

 mum yearly growth achieved from July to December. 

 Slower rates of somatic growth during January to 

 March may be attributed to decreased feeding during 

 colder winter temperatures (Cooper 1966, Olla et al. 

 1974). From March to June, the rate of somatic growth 

 is less than that observed in other seasons and most 

 likely results from energy expenditure associated with 

 gonadal maturation and spawning. 



In Virginia and Rhode Island, annual growth in 

 length was rapid during the first three years (-33% 

 and 38% of the total in Virginia and Rhode Island, 

 respectively) and declined steadily with increasing age. 

 Except for age-1, annual growth increments between 

 populations were roughly similar to about ages 12-13, 

 after which yearly increments (TL) in Rhode Island 

 fish declined rapidly; whereas growth rates for tautog 

 of the same age-groups from Virginia's coastal waters 

 did not diminish as rapidly. In fact, from about ages 

 12-13 onward, annular growth increments of tautog 

 from Virginia were nearly double those of their coun- 

 terparts from Rhode Island (compare Tables 4&5 with 

 Cooper 1967). Other differences between this study 

 and Cooper's (1967) are that tautog in Virginia reach 

 twice the TL of those in Rhode Island at time of first 

 annulus formation. Annular growth estimated by back- 

 calculations indicated that in tautog from Virginia, the 

 greatest average yearly increment in growth occurred 

 during the first year. In contrast, Cooper found that 

 both sexes had their largest yearly increase in TL dur- 

 ing their second year of life. Observed differences in 

 first-year growth of tautog from Virginia and Rhode 

 Island result either from our missing the first annu- 

 lus, or from differences in environmental factors be- 

 tween study areas. We discounted missing the first 

 annulus, because we believe we had adequate num- 

 bers offish in these younger age-groups (n=204), from 

 both seasonal and size perspectives, to consider this a 

 reasonable estimate of opercle size at age-1. Addition- 

 ally, back-calculated lengths-at-age-1 for all tautog aged 

 closely matched actual observations of TL at the end 

 of the first year (compare Tables 2,3 and 4,5). 



Observed differences in first-year growth between 

 tautog occurring in Virginia and Rhode Island may 

 result from environmental factors in more southern 

 waters that favor growth over a longer season 

 (Fig. 10). For example, temperatures in shallow-water 

 areas below which juvenile tautog become inactive 

 (-10° C) occur earlier and persist longer in inshore 

 coastal waters of Narragansett Bay, Rhode Island than 

 in the lower York River in Chesapeake Bay. On aver- 

 age, water temperatures in springtime remain below 



35 

 30 

 25 



n 20 



o 



» 15 - 



V 



a> 



cj- 10 - 



Q 



5 - 

 - 



-5 



Virginia 

 Rhode Isl 



X 



6 7 



Month 



10 11 12 



Figure 1 



Average monthly water temperatures ( 1979-86 ) for lower York 

 River, Virginia (VIMS oyster pier, taken lm below surface at 

 2.0-2.5m depth; G. Anderson, Coll. William & Mary, VIMS, 

 Gloucester Point VA, pers. commun.), and for bottom-water 

 temperatures at Fox Island, Narragansett Bay, Rhode Island 

 iH.P. Jeffries, Univ. Rhode Island, Grad. School Oceanogr., 

 Narragansett RI, pers. commun.). Solid squares and open 

 triangles represent mean monthly values for York River and 

 Narragansett Bay, respectively. 



10° C nearly a full month longer in Narragansett Bay 

 (not until mid- April) than in the York River (usually 

 mid-March). And in the fall, temperatures again de- 

 cline below 10° C during mid- to late October in 

 Narragansett Bay, whereas in Virginia temperatures 

 remain above 10° C usually well into mid-November or 

 early December. These temperatures, which are con- 

 ducive for somatic growth in juvenile tautog, are ex- 

 tended seasonally in coastal waters of Virginia com- 

 pared with those of more northern areas. Recently, 

 D.L. Martin and T.E. Targett (Grad. Coll. Mar. Stud., 

 Univ. Delaware, Lewes DE 19958, unpubl. data) found 

 in laboratory growth experiments that young-of-the- 

 year tautog from high-latitude populations (Rhode Is- 

 land) show no genetic compensation for a shorter grow- 

 ing season when compared with tautog from Delaware 

 Bay and Virginia waters. These data further support 

 our hypothesis that observed differences in growth of 

 young tautog from northern (Rhode Island) and south- 

 ern (Virginia) areas of the species range are due pri- 

 marily to environmental factors between the two ar- 

 eas (i.e., duration of optimal temperatures for growth 

 is longer in Virginia coastal waters compared with those 

 of coastal areas in the northern end of the species 

 range ). 



Estimated values of L„ for tautog from Virginia are 

 also considerably higher than those estimated for tau- 

 tog from Rhode Island (Table 8). A calculated L„ of 

 733mmTL (data for sexes combined; 733mm for fe- 

 males, 732 mm for males) as derived from the von 

 Bertalanffy equation in our study is close to the ob- 

 served maximum TL of 765 mm. Growth equations es- 



