NO. 3537 SHARK GENUS ISURUS — GARRICK 671 



in methods of measurement rather than to real differences. To what 

 extent this is true cannot be assessed, for only a few of the many 

 accounts which were abstracted to provide data used in the figures 

 and table give any indication of the measuring methods used. Ex- 

 amples of the growth change and variation shown in the figures and 

 table are as follows. The height of the first dorsal fin undergoes a 

 very significant proportional increase with growth (fig. 3) while its 

 base remains a constant proportion (table 1, A). The ensuing re- 

 lationship of first dorsal height to base® with growth is as in figure 4. 

 Prepectoral length shows no obvious change with growth but is rather 

 variable (table 1, B). Comparing prepectoral length with first 

 dorsal height relative to total length gives the plot shown in figure 5. 

 The distance between the pectoral axil and the pelvic fin origin 

 increases proportionately with growth (table 1, E). The distance 

 between the pectoral fin origin and the first dorsal fin origin does not 

 show growth change but is variable at all sizes (table 1, D); the 

 relationship of this distance to the length from the posterior of the 

 eye to the first gill opening is summarized in table 1, H. Various 

 other proportions which have been used by Bigelow and Schroeder 

 (1948) and Smith (1957) are given in table 1, C, F, G, I, and J; these 

 similarly show growth change and variation but need not be discussed 

 further here. 



One other character which has been thought to be of prime diag- 

 nostic significance is the shape of the first dorsal fin apex. A broadly 

 rounded apex has been regarded as a character of /. glaucus, while a 

 more angular or acutely angled apex has been ascribed to /. oxyrinchus 

 and /. tigris. This character, Hke that of first dorsal fin height, is 

 profoundly altered with growth. All juvenUe makos have broadly 

 rounded first dorsals, and in all the apex becomes increasingly angular 

 with growth. The same phenomenon occurs in nearly all sharks. 

 Figm-e 6 illustrates a range of fin shapes, Avith growth, in four New 

 Zealand makos, plus an Atlantic embryo which has the "/. glaucus," 

 i.e.. Pacific, type of fin. According to contemporary accounts, the 

 New Zealand makos illustrated here would be variously identified as 

 /. glaucus, I. oxyrinchus, and /. tigris. 



Comparing the diagnostic criteria used by Bigelow and Schroeder 

 (1948) and by Smith (1957, 1958) with my data shows that the species 



6 Krumholz' report (Copeia, 1957, no. 4, p. 302) of a large mako, 3,023 mm. 

 long, from the Bahamas, gives its first dorsal height and base as 8.2 percent and 

 10.1 percent of total length respectively — dimensions that are quite unlike those 

 of any large mako I have seen. Kodachromes of the Bahama mako, kindly 

 loaned by Dr. Krumholz, clearly show that the quoted dorsal fin dimensions are 

 in error — perhaps transposed — because the first dorsal height is noticeably 

 greater than the base, rather than the reverse as stated in Krumholz' account. 



