FISHERY BULLETIN: VOL. 75, NO. 1 



peak spawning period as a denned hatching date 

 upon which year class and age group terminology 

 is based. Using an October hatching date, the year 

 class would pertain to the fall calendar year and 

 would include any fish of that spawning cycle 

 hatched in the following winter and spring. A 

 virtual annulus would be designated as of October. 



Characteristics of Scale Markings 

 Used to Determine Age 



The first mark is typically a more or less in- 

 distinct mark formed in warm periods. It is 

 characterized by cutting over in the lateral field, 

 but it has little or no differential spacing of circuli 

 before and after the mark (Figure 5a). This mark 

 is often difficult to distinguish after the heavier 

 second mark is formed. The typical second mark is 

 formed in cold periods. It is the most diagnostic 

 feature for age determination in croaker, and its 

 recognition is the basis for our method. This mark 

 is characterized by heavy cutting over of circuli 

 and differential spacing of circuli in the lateral 

 field (Figure 5b). Generally, circuli are closely 

 spaced before the second mark and more widely 

 spaced after it. When the first mark is absent or 

 difficult to see, the typical second mark is readily 

 distinguished. The third mark is typically formed 

 in warm periods and is similar to the first mark 

 (Figure 5c). We examined only six fish whose 

 scales had the fourth mark, and its criteria may 

 need modification. However, the fourth mark 

 apparently forms in cold periods and apparently, 

 resembles the second mark in having heavy cut- 

 ting over and differential spacing of circuli (Figure 

 5c). 



Croaker from a broad geographical range 

 seemingly can be aged by the method proposed, 

 although further work is needed to establish this. 

 Scales offish from Mississippi, Fort Pierce (Figure 

 6a), and Chesapeake Bay (Figure 6b, c) showed 

 markings similar to those on scales from Texas 

 fish. Croaker scales from Florida generally had 

 more or less indistinct cutting over and seemed 



FIGURE 5. — Top. Scale from a 190-mm croaker showing mark 1. 

 This fish was approaching age I when it was captured off Texas in 

 September. The axis depicted shows how measurements were 

 made to determine when each mark formed. Middle. Scale from a 

 255-mm croaker showing marks 1 and 2. This fish was ap- 

 proaching age II when it was captured off Texas in August. 

 Bottom. Scale from a 310-mm croaker showing marks 2,3, and 4. 

 This was an age 11+ fish captured off Texas in March. 



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