WHITE and CHITTENDEN: AGE DETERMINATION OF ATLANTIC CROAKER 



difficult to read, possibly because the fish were 

 collected in tropical waters of southern Florida 

 where temperature changes are not as extreme as 

 further north. Only six fish from Texas had scales 

 with four marks. In contrast, scales from some 

 Chesapeake Bay fish had six marks (Figure 

 6c). Croaker that live in the Carolinian Province 

 south of Cape Hatteras live only 1 or 2 yr (see 

 General Discussion) and, therefore, tend to have 

 comparatively few marks on their scales. These 

 fish might be easier to age than croaker that live 

 north of Cape Hatteras. The latter fish apparently 

 survive longer and, therefore, probably tend to 

 have more marks on their scales. 



Times of Mark Formation 



The time when each annuluslike mark formed 

 was determined by plotting for each month the 

 distance from the scale margin to the last mark. 

 Distance was measured across the lateral field of 

 the scale (Figure 5a). Croaker generally form two 

 marks per year except during their first year. 

 Scales with no marks had the smallest distance 

 between the scale margin and focus in May (Fig- 

 ure 7). The radius increased from May to October 

 as scales grew during that period. Therefore, 

 apparently no mark is formed during the first 

 winter; and some croakers form no mark during 

 the first year of life if 15 October is defined as their 

 hatching date. Scales with one mark had the mark 

 closest to the scale edge in warmer months. In 

 March the mark was far removed from the scale 

 margin, suggesting that the first mark normally 

 forms in warm months. Apparently this mark 

 formed on some fish throughout the period May to 

 at least October. The increment between the scale 

 margin and the first (or third) mark did not in- 

 crease with time, but the reason for this is not 

 clear. Scales with two marks showed the second 

 mark closest to the scale margin in March. The 

 increment between this mark and the scale edge 

 increased until June and then remained nearly 

 constant through November. Therefore, the sec- 

 ond mark apparently forms during the colder 



FIGURE 6. — Top. Scale from a 305-mm croaker showing marks 1, 

 2, 3, and 4. This was an age 11+ fish when it was captured off 

 Florida in March. Middle. Scale from a 293-mm croaker showing 

 marks 1 and 2. This fish was approaching age II when it was 

 captured in Chesapeake Bay in July. Bottom. Scale from a 

 508-mm croaker showing marks 1, 2, 3, 4, 5, and 6. This fish was 

 approaching age IV when it was captured in Chesapeake Bay 

 during July. 



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