Terwilliger and Munroe: Age, growth, longevity, and mortality of Symphurus plogiusa 



357 



Etropus microstomus (to ca. 159 mm TL), small-size 

 species that are not commercially or recreationally 

 exploited and ones that complete their life cycles 

 within the Bay. Virtually nothing is known concern- 

 ing age and growth of smallmouth flounder, espe- 

 cially within the Bay system; therefore further com- 

 parisons of its life history with those of sympatric 

 flatfishes are limited. The flatfish fauna of the Bay 

 also includes summer flounder [Paralichthys dentatus), 

 southern flounder (Paralichthys lethostigma ), window- 

 pane (Scophthalmus aquosiis), and winter flounder 

 (Pseudopleuronectesamericanus), species that do not 

 necessarily complete their life cycles entirely within 

 Chesapeake Bay and ones that are heavily exploited 

 both commercially and recreationally. The remain- 

 ing species of flatfishes recorded from the Bay are 

 transient species that occur only irregularly within 

 the Bay and will not be discussed further. The diver- 

 sity in size and growth parameters represented 

 among those flatfishes occurring in Chesapeake Bay 

 which have been studied provides an interesting 

 opportunity for investigating comparative life histo- 

 ries of sympatric members of an estuarine benthic 

 fish assemblage with somewhat similar lifestyles 

 (Table 5). 



Few published age-growth studies exist for 

 noncommercially exploited flatfishes, especially for 

 those species occurring in temperate estuaries of the 

 western North Atlantic. Von Bertalanffv growth pa- 

 rameters for species other than blackcheek tongue- 

 fish were taken from data found in the literature 

 ! (Miller et al., 1991; Desfosse, 1995). These data re- 

 ' veal that among this assemblage, blackcheek tongue- 

 fish have the highest value for growth parameter K 

 (Table 51, and therefore reach asymptotic length 

 faster than sympatric counterparts (Francis, 1996). 

 Of sympatric flatfishes occurring in Chesapeake Bay, 

 only hogchokers display growth parameters and 

 maturation schedules (some males mature at end of 

 first year, most of both sexes mature by age 2; Koski, 

 1978) similar to those observed for blackcheek 

 tonguefish. In contrast, summer and southern floun- 

 ders mature at ages 2-3, windowpane flounders 

 mature at ages 3 or 4, and winter flounders mature 

 at ages 2-5. Later age at maturation in these spe- 

 cies reflects a different life history pattern, and one 

 that allows for energy allocation favoring increased 

 somatic growth during several years prior to the on- 

 set of maturation. Because these other species ma- 

 ture at later ages than do blackcheek tonguefish and 

 hogchoker, growth in length for these fishes would be 

 relatively rapid over the course of several years during 

 the early part of their lives (Fig. 11). 



Estimates of asymptotic length, reflecting average 

 maximum length attained by a species, also varies 



considerably among members of this assemblage. 

 Asymptotic lengths for summer flounder (859 mm 

 TL ) and southern flounder ( to 760 mm ) greatly exceed 

 those for blackcheek tonguefish and hogchoker ( 192 and 

 210 mm, respectively). In fact, these fishes grow more 

 during their first year than do blackcheek tonguefish 

 and hogchokers in a lifetime. Windowpane and winter 

 flounder (383 and 376 mm, respectively) attain asymp- 

 totic lengths intermediate to these other two groups of 

 sympatrically occurring estuarine flatfishes. 



Estimates of instantaneous total mortality based 

 on blackcheek tonguefishes caught within Chesa- 

 peake Bay during this study are also relatively higher 

 when compared with those for most other estuarine 

 dependent species of northwestern Atlantic Pleuro- 

 nectiformes (Table 6). In this comparison, blackcheek 

 tonguefish are among the shortest-lived species and 

 therefore have one of the higher rates of instanta- 

 neous total mortality. Relatively few individuals 

 within Chesapeake Bay are older than three years. 

 Extrapolating mortality rates for a possible seventh 

 year class (age 6+ ), which may be found on the inner 

 shelf region, provides an instantaneous total mor- 

 tality estimate comparable to those for hogchokers 

 and southern flounder caught in Chesapeake Bay. 



Blackcheek tonguefish exhibit the youngest age at 

 first maturity, the highest growth coefficient, the 

 youngest known maximum age, and the smallest 

 asymptotic length when compared with sympatric 

 pleuronectiforms from Chesapeake Bay. Blackcheek 

 tonguefish exhibit rapid growth until maturity, af- 

 ter which growth rate declines markedly. Munroe 

 (1990, 1998) indicated that eight dwarf species of 

 Symphurus reach sexual maturity between 28 and 

 45 mm SL. Small size and presumably early age at 

 maturation may be characteristic of species in this 

 genus (Munroe, 1988); even S. jenynsi, the largest 

 species in the genus (reaching ca. 350 mm TL), ma- 

 tures at a relatively small size (about 132 mm TL). 

 More ageing studies on fishes of this genus are re- 

 quired to test this hypothesis. Other cynoglossid flat- 

 fishes, although they attain a relatively large size 

 before reaching sexual maturity, are only 1 or 2 yr 

 old when first maturing. According to available data, 

 it is quite possible then that tonguefishes in general 

 have an age dependent maturity schedule. Roff ( 1982) 

 indicated that age, and not size, would appear to be 

 most important in fish species that mature early. 

 Data for tonguefishes support that finding. 



When compared with estimates for sympatric flat- 

 fishes, blackcheek tonguefish caught during this 

 study exhibit the highest rates of instantaneous to- 

 tal mortality. Other species inhabiting the Bay sys- 

 tem also mature at larger sizes, have larger asymp- 

 totic lengths, and slower growth rates. Interesting 



