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



341 



investigated factors influencing recruitment (Miller 

 et al., 1991); and some have described daily growth 

 rates of juveniles in Georgia estuaries (Reichert and 

 van der Veer, 1991). The minimal amount of pub- 

 lished information on this species (summarized in 

 Munroe, 1998) may be due in part to the relatively 

 small size of the fish. It reaches a maximum size of 

 approximately 210 mm total length (TL) (Wenner and 

 Sedberry, 1989), but fish smaller than 165 mm TL 

 are those most commonly taken in Chesapeake Bay 

 by otter trawl (Terwilliger, 1996; Geer et al., 1997). 

 Small size and benthic microinvertebrate feeding 

 habits (Stickney, 1976; Reichert and van der Veer, 

 1991; Toepfer and Fleeger, 1995) render this species 

 inaccessible to most recreational and commercial 

 [l fishing gears used in Chesapeake Bay. 



Few age and growth studies using bony structures 

 or otoliths exist for species of the Cynoglossidae. This 

 relatively large gap in knowledge for approximately 

 150 species of tonguefishes was recently noted in a 

 compilation of flatfish life history parameters (Miller 

 etal., 1991). Although several studies have described 

 growth for species of Cynoglossiis from the eastern 

 Atlantic (Chauvet, 1972), western Pacific (Lin, 1982; 

 Meng and Ren, 1988; Zhu and Ma, 1992), and In- 

 dian Ocean (Seshappa, 1976, 1978, 1981; Ramana- 

 than et al., 1980; Seshappa and Chakrapani, 1984), 

 no growth studies using bony structures or otoliths 

 have been performed on species oi^ Symphurus. Pre- 

 vious work describing the age structure of blackcheek 

 tonguefish in Chesapeake Bay using length frequen- 

 cies offish taken by otter trawl (Bonzek et al., 1993) 

 is limited because this type of analysis requires sub- 

 jective interpretation of modal frequencies in the 

 data, which, given the difficulty of distinguishing 

 modal groups at older ages, renders the interpreta- 

 tion unreliable (Chauvet, 1972; White and Chitten- 

 den, 1977; Jearld, 1983; Barbieri, 1993). Such limi- 

 tations in interpretation of age from length-frequency 

 distributions are particularly evident in data from 

 Koski's ( 1978) study on hogchokers from the Hudson 

 River estuary, where the first of bimodal peaks in a 

 frequency distribution of hogchoker lengths corre- 

 sponded to age-1 fish, whereas the second peak rep- 

 resented combinations of length distributions for 

 fishes age 2-6 yr. Chauvet's (1972) data for C. 

 canarlensls off West Africa also show a similar pattern 

 of overlapping sizes among fishes of different ages. 



Syr7iphurus plagiusa is a good candidate for an age 

 and growth study. It is unique among the Cynoglos- 

 sidae in that it is the only species of this family that 

 inhabits estuarine environments in the seasonally 

 dynamic region of north temperate latitudes. Most 

 other cynoglossid species occur in the tropics and are 

 difficult to age from hard parts because environmen- 



tal constancy precludes the formation of interpret- 

 able annular growth marks on these structures 

 (Qasim, 1973). Other species of symphurine 

 tonguefishes that occur in temperate waters gener- 

 ally are small-size, deep-water forms that are diffi- 

 cult to catch in abundance (Munroe, 1998). 



This study was undertaken to determine age struc- 

 ture, growth rate, longevity, and mortality for a popu- 

 lation of S. plagiusa residing in Chesapeake Bay, 

 Virginia. Knowledge about life history parameters 

 for this species provides a window of understanding 

 into the biology of the Cynoglossidae, as well as in- 

 sights into age, growth, and longevity of other small- 

 size, estuarine-dependent flatfishes. 



Materials and methods 



Blackcheek tonguefishes were collected by 9.14-m 

 semiballoon otter trawl with a 38.10-mm stretch 

 mesh body, 6.35-mm mesh codend liner, and attached 

 tickler chain (Bonzek et al., 1993). Fish were collected 

 from April 1994 through August 1995 during the Vir- 

 ginia Institute of Marine Science (VIMS) Juvenile 

 Finfish and Blue Crab Stock Assessment Program's 

 trawl survey. The survey employs a monthly, ran- 

 dom-stratified design of the lower Chesapeake Bay 

 and fixed-station mid-channel transects in each of 

 three major Virginia tributaries; the York, James, 

 and Rappahannock rivers (Fig. 1). Details of sam- 

 pling design were provided in Geer et al. (1993). 



Samples of blackcheek tonguefishes selected fi-om 

 trawl catches were brought to the laboratory, measured 

 for total length (TL) to the nearest millimeter and for 

 total weight (TW) taken to the nearest hundredth of a 

 gram. When samples were small, all fish were used in 

 age analyses; however, fish were randomly selected for 

 age analyses from relatively large samples. Regressions 

 were fitted to the length-weight data, and regressions 

 on log-transformed data for male and female blackcheek 

 tonguefish were compared by using analysis of covari- 

 ance (ANCOVA). The formula to convert SL to TL for 

 blackcheek tonguefish provided by Jorgenson and 

 Miller ( 1968: 1 1 ) was used when comparing length data 

 (reported as SL) from other studies. 



All fish were sexed macroscopically, and then gonads 

 were removed and preserved for later histological analy- 

 sis to determine maturity stages (Terwilliger, 1996). 

 Males were classified as either immature or mature 

 according to the absence or presence of spermatozoa in 

 the testes; females were considered mature if they 

 showed any evidence of developing oocytes or previous 

 spawning, e.g. thickening of the ovarian membrane. 



Both sagittal otoliths were removed, cleaned, and 

 stored dry for later processing. Otolith maximum 



