421 



Periodicity of increment formation in otoliths 

 of overwintering postlarval and prejuvenile 

 Atlantic menhaden, Brevoortia tyrannus 



Dean W. Ahrenholz 



Beaufort Laboratory, Southeast Fisheries Science Center 



National Manne Fishenes Service, NOAA 



101 Pivers Island Road 



Beaufort, North Carolina 28516-9722 



e mail address: dean ahrenholza'noaa gov 



Deborah D. Squires 

 James A. Rice 



Stephen W. Nixon 



Department of Zoology, North Carolina State University 



PO Box 7617 



Raleigh, North Carolina 27695-7617 



Gary R. Fitzhugh 



Panama City Facility, Southeast Fishenes Science Center 

 National Manne Fisheries Service, NOAA 

 3500 Delwood Beach Road 

 Panama City, Florida 32408-7403 



Hypotheses of fishery recruitment 

 processes often have as their foun- 

 dation studies of incremental oto- 

 Hth growth (e.g. Methot, 1983; Rice 

 etal., 1987). Conclusions from these 

 studies, however, are only as robust 

 as their baseline otolith validation 

 work. This is especially true for in- 

 vestigations on Atlantic menhaden 

 {Brevoortia tyrannus), an estua- 

 rine-dependent, marine-migi-atory 

 clupeid ranging from southeastern 

 Florida to Nova Scotia (Reintjes, 

 1969; Ahrenholz, 1991). The spawn- 

 ing season for Atlantic menhaden 

 is protracted, occurring wherever 

 fish of spawning age are found 

 (Judy and Lewis, 1983). Spawning 

 is probably greatest from October 

 to March (Higham and Nicholson, 

 1964). The spawning activity that 

 occurs in south coastal U.S. waters 

 normally occurs within this time 

 period, usually peaking during mid- 

 to late winter (Wilkens and Lewis, 



1971; Nicholson, 1972). Owing to 

 the extended spawn and seasonal 

 movement of spawning adults, prog- 

 eny from different temporal spawn- 

 ing periods experience different 

 environmental conditions during 

 similar early life history stages. 



Daily age validation studies have 

 been conducted on late lai-vae and 

 juvenile Atlantic menhaden (Ahr- 

 enholz et al., 1995), but none of 

 the specimens were reared in a 

 water temperature regime that 

 typified conditions experienced by 

 fall-spawned lai-vae. Fall-spawned 

 larvae enter inshore nurseries when 

 estuarine waters are cooling, yet 

 still warm enough for moderate 

 somatic growth and development. 

 These young fish then endure the 

 coldest winter temperatures in a 

 partially transformed condition, i.e. 

 in a postlarval-prejuvenile stage. 

 In contrast, larvae of winter and 

 early spring spawnings ingi'ess into 



relatively cold, but progressively 

 warming waters, from late winter to 

 midspring; although they probably 

 do not enter during extreme winter 

 cold spells (Reintjes and Pacheco, 

 1966). Differences in growth pat- 

 terns in the otolith microstructure of 

 larvae and juveniles from these dif- 

 ferent spawning periods are detect- 

 able (Fitzhugh et al., 1997). 



Validation of the otolith daily 

 aging technique should take into 

 account the environmental condi- 

 tions experienced by field-sampled 

 specimens (Jones, 1986), especially 

 when some field conditions affect the 

 daily periodicity of otolith growth 

 increments. The sagittal growth in- 

 crements for the fall-spawned Atlan- 

 tic menhaden are disproportionately 

 narrower (±1 pm) during the cold- 

 est overwintering months. Moreover, 

 increments <1 jim potentially indi- 

 cate less than daily increment for- 

 mation (Campana etal., 1987). Less 

 than daily increment deposition 

 associated with cold water and slow 

 growth rates has been observed for 

 juvenile summer flounder (Paralich- 

 thys dentatus), another estuaiine- 

 dependent, marine-migi-atory species 

 (Szedlmayer and Able, 1992). 



Previous otolith microstructure 

 validation studies for larval Atlan- 

 tic menhaden have used larvae 

 collected in the field during April 

 or laboratory-reared specimens 

 spawned in February (Ahrenholz 

 et al., 1995). Test conditions were 

 set at higher salinities than are 

 normally associated with larval to 

 juvenile transformation. Hence, we 

 designed a study to specifically 

 address the periodicity of otolith 

 increment formation in over-win- 

 tering, fall-spawned Atlantic men- 

 haden postlarvae and prejuveniles 

 under the thermal and salinity con- 

 ditions they experience in North 

 Carolinian estuaries. 



Manuscript accepted 26 November 1999. 

 Fish. Bull. 98:421-426 (20001. 



