AGE AND GROWTH OF LARVAL GULF MENHADEN, 

 BREVOORTIA PATRONUS, IN THE NORTHERN GULF OF MEXICO 



Stanley M. Warlen' 



ABSTRACT 



Experiments on laboratory-spawned and -reared larval gulf menhaden, Brevoortia patronus , showed 

 that they formed one otolith growth increment per day and that the increments could be used to 

 estimate their age. Wild larvae from collections in the northern Gulf of Mexico along three transects 

 I Cape San Bias, Florida; Southwest Pass, Louisiana; and Galveston, Texas) were aged. Gompertz 

 growth equations were used to describe the relationship between age and standard length for larvae 

 collected at various locations, and in different seasons and years. MANOVA tests and subsequent 

 pairwise tests were used to test for differences among these growth curves. For the most extensive 

 data set (Southwest Pass, Louisiana), there were significant differences in growth between early 

 season (December) and late season (February) larvae. Early season larvae grew faster than late 

 season larvae. Growth of larvae also differed among December collections and among February 

 collections. The growth model for the pooled data for all wild larvae predicted that they grew from 2.4 

 mm SL at hatching to 20.4 mm SL at 62 days. 



Gulf menhaden, Brevoortia patronus , is the most 

 abundant commercial finfish in the Gulf of Mex- 

 ico and, with 883,500 metric tons (t) landed in 

 1985 (U.S. National Marine Fisheries Service 

 1986); it constitutes the largest fishery in the 

 United States. Some aspects of the oceanic early 

 life history of this clupeid are known and are re- 

 viewed by Turner (1969), Christmas and Waller 

 (1975), Lewis and Roithmayr (1981), Govoni et al. 

 (1983), and Shaw et al. (1985a). However, virtu- 

 ally nothing is known about the age and growth 

 of the larvae, much less how these parameters 

 vary spatially and temporally. Daily growth in- 

 crements on otoliths of larval fishes can be used 

 as an indicator of their age, and once the use of 

 this technique, first described by Pannella ( 1971 ), 

 is validated for the larvae of an individual spe- 

 cies, their ages can be estimated with confidence 

 and growth rates can be determined. Intraspecific 

 growth may be compared for larvae from different 

 areas and seasons (Lough et al. 1982), and from 

 this it may be possible to ascertain how biotic and 

 abiotic environmental variables affect larval 

 growth and survival. The objectives of this study 

 are to 1) validate the periodicity of increment for- 

 mation in otoliths of larval gulf menhaden, 2) 

 estimate larval growth rates, 3) compare growth 

 rates of larvae from different locations and times, 

 4) estimate spawning times, and 5) examine pos- 



•Southeast Fisheries Center Beaufort Laboratorv, National 

 Marine Fisheries Service, NOAA, Beaufort, NC 28516-9722. 



Manuscript accepted September 1987 

 FISHERY BULLETIN. VOL. 86, NO. 1, 1988. 



sible relationships between larval growth and 

 surface water temperature. This work was part of 

 a larger project designed to investigate the early 

 life history of several economically important 

 fishes and the marine planktonic food webs that 

 support their growth and survival in the northern 

 Gulf of Mexico. 



METHODS 



Spawning and Larval Rearing 



Adult gulf menhaden were collected near Gulf 

 Breeze, FL, and transported to the Beaufort Lab- 

 oratory, Beaufort, NC (Hettler 1983). After a pe- 

 riod of acclimation, adults were induced to spawn 

 in the laboratory. The resultant larvae were used 

 in experiments to validate the periodicity of in- 

 crement formation on their otoliths and the age at 

 first increment formation. 



Beginning February 1983, several thousand 

 newly spawned gulf menhaden eggs were trans- 

 ferred to a tank containing 90 L of filtered sea- 

 water. The static water in this tank, kept at 

 20.5° ± 0.5°C throughout the experiment, was 

 continuously aerated and the salinity maintained 

 at 31 ± 17cc. Photoperiod was 12 hours light:12 

 hours dark. A food concentration of 25 rotifers 

 (Brachionus plicatilis) mL"^ was maintained. A 

 green alga, Nanochloris sp., was added periodi- 

 cally as food for the rotifers and to aid in remov- 

 ing toxic metabolites. The otoliths of larvae sam- 



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