Nocomis

Nocomis l. bellicus

Mobile Bay

147

1,111

Pascagoula Bay

12

185

Pearl River

48

248

Mississippi River tributaries

33

433

Tennessee River

4

23

Subtotal

244

2,000

TOTAL

1,322

20,789

Methods

The methods used in counting meristic characters and measuring structures and body proportions were similar to those discussed by Lachner and Jenkins (1971). All references to body length are to standard length (SL) in millimeters, unless stated otherwise. The preliminary data of various morphometric characters as well as meristic characters were segregated by size, sex, and river system. The initial tabular data for each character were taken from samples of from ten to twenty specimens when available, and the samples were selected over the range of a population within a river system insofar as possible. When preliminary analysis of the data revealed no major divergence within or among certain river populations, collation was by river drainage or by subspecies.

The cephalic tubercle counts were easily made, almost always without the use of any great magnification, because the developed tubercles, spots, buds, or scars are very large, comparatively few in number, and are readily discernible. There is no difficulty in obtaining accurate counts, unlike the problem in counting the smaller, numerous tubercles of members of the Nocomis micropogon group. The areas of the head referred to in tubercle distribution and location are given designations similar to those presented by Lachner and Jenkins (1971), such as: transverse anterior internasal line (AIN); posterior internasal (PIN); anterior interorbital (AIO); mid-interorbital (MIO); posterior interorbital (PIO); anterior occipital (AOC); mid-occipital (MOC); and posterior occipital (POC). The posterior development of tubercles was recorded as the line nearest the most posterior tubercle (or tubercles). The supraorbital tubercles were not considered in the above designations since they have a comparatively similar development in all three forms, and are independent of the progressive development of the principal head tubercles with increase in body length.

The distribution and number of head tubercles are the two main characters involved in the separation of the subspecies of N. leptocephalus. These two characters were also of primary importance in the differentiation of the species of the micropogon group. A detailed discussion of tuberculation in Nocomis is presented by Lachner and Jenkins (1971). The total number of head tubercles for N. l. leptocephalus in the northern part of its range is summarized by size groups in Table 1. Because significant differentiation in the number of head tubercles occurred in each of the two southern river populations of N. l. leptocephalus (Pee Dee and Santee), these are summarized separately by size groups in Tables 2 and 3. No notable differences were observed in total number of head tubercles for the new subspecies in the Savannah, Altamaha, and Chattahoochee (Apalachicola) river drainages, and the data in Table 4 were combined and summarized by size groups; the same was done in Table 5 for similar tubercle data for N. l. bellicus from the Alabama River westward to tributaries of the Mississippi River. The allometric relationship of increase in tubercle number with increase in body size for these five diverged populations is shown in Figure 1. The curves were drawn to best fit the means of the body-length groups. The data for these curves are based on a sample of 2,467 specimens, including 196 N. l. bellicus; 663 N. l. interocularis; and 843 Santee, 160 Pee Dee, and 605 northern specimens of N. l. leptocephalus.

The total number of cephalic tubercles of specimens ranging in size from juveniles to adults and segregated by subspecies, intergrades, and major river drainages is summarized in Table 6. This summary shows the difficulty in identifying juvenile specimens, particularly those involving the subspecies N. l. leptocephalus and N. l. interocularis. Because of the allometric growth relationship of the number of tubercles with body length, specimens 90 mm SL and larger are compared by subspecies, intergrades, and river drainages in Table 7. Most specimens of the bluehead chub are mature at about 90 to 100 mm, and at this size the full complement of tubercles is present in all populations except for N. l. leptocephalus in the Santee-Pee Dee drainages (see Figure 1). Figure 2 shows the mean (Av.), range, standard deviation (SD), and the mean ± two standard errors for the total number of tubercles in the five populations. The values are illustrated for two size groups, 70 to 79 mm SL and all specimens 90 mm SL or greater. The statistical data for this graph are given in Table 11. The differences are much less in the smaller size group, and only the adult or subadult specimens are of practical systematic importance in this problem.

In order to demonstrate the sharp breaks in tubercle numbers among the three subspecies, the southern drainage populations of N. l. leptocephalus are compared with N. l. interocularis and N. l. bellicus in specimens greater than 65 mm, but excluding the supraorbital tubercles (Table 8). Supraorbital tubercles vary somewhat by subspecies, averaging notably fewer in N. l. bellicus.

Frequency distributions comparing the occurrence of tubercles posteriorly on the head, segregated by subspecies and river drainages, are given in Table 9. The relationship between body length and the extent of posterior development of head tubercles is summarized by size groups for the Santee River drainage in Table 10.

Vertebral numbers, pharyngeal dentition counts, and circumferential and lateral-line scale numbers are compared by subspecies and by various drainages in Table 12, 13, and 14.

Because of the large number of specimens examined and identified, only the river drainage and the museum catalog number are given in the “Appendix: Specimens Studied” (pages 34–35) for N. l. leptocephalus and N. l. bellicus. “Appendix: Specimens Studied” (pages 30–34) for N. l. interocularis includes the collections for each river system grouped by state and county. Also given are museum catalog number, date of collection, number of specimens (in parentheses), tributary, and locality. Type material is designated only from the Savannah River drainage. Collection data pertaining to the intergrades are listed separately on page 35.

Nocomis l. interocularis

Savannah

190

2,275

Ogeechee

3

8

Altamaha

56

1,011

Chattahoochee

62

789

Subtotal

311

4,083

Nocomis leptocephalus intergrade

interocularis × leptocephalus

Edisto

5

155

Nocomis is a genus of cyprinid fish native to North America. There are currently seven described species in this genus.