Grass pickerel (Esox americanus vermiculatus) COSEWIC assessment and status report: chapter 5

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Species information

• Name and classification
• Description
• Designatable units

Name and classification

In the Fifth Edition of the American Fisheries Society’s list of Common and Scientific Names of Fishes from the United States and Canada (Robins et al. 1991) two subspecies of Esox americanus were recognized, and listed, separately. For the sixth edition (Nelson et al. 2004), a decision was made not to list subspecies. As a result the only listing is "Esox americanus Gmelin 1789, redfin pickerel." Redfin pickerel is the common name of the nominate subspecies. Originally considered a full species (Cuerrier 1944, Legendre 1952), these pickerels have more recently been considered subspecies (Crossman 1962a, Lachance 2001). Writers will still have the freedom to refer separately to the valid subspecies (Crossman 1966, Reist and Crossman 1987, Nelson et al. 2004), to make it clear which populations are being discussed. This alternative was chosen for this Status Report, especially since the redfin pickerel subspecies does occur in Canada, with a limited distribution in Quebec (PQ) (see Lachance 1997, 2001).

As presently recognized, the family Esocidae has five species. However, Lopez et al. (2000) suggested including in it species presently in the family Umbridae. They would divide the family into two subfamilies--Esocinae, with Esox and Novumbra, and Dallinae with Dallia. They would restrict Umbridae to the three species in the genus Umbra. These results were confirmed using nuclear DNA (Lopez et al. 2004). For a considerable period, the family was placed in the suborder Esocoidei of the order Salmoniformes. As a result of the need to dismantle the order Salmoniformes, most workers have placed the pikes and related species in a separate order Esociformes.

As defined here, the family has a circumpolar distribution in the northern hemisphere. Only the amur pike, Esox reicherti, does not occur naturally in North America. The natural distribution of the smaller pickerels is limited to eastern North America.

Description

The grass pickerel (Figure 1) is often mistaken for the young of the northern pike, Esox lucius or, less often, for that of the muskellunge, Esox masquinongy. The original use of the English common name pickerel--the diminutive of the word pike--is the basis for the common names of the two smaller species: chain pickerel, Esox niger, and redfin and grass pickerels, Esox americanus. The grass pickerel has the usual pike-like body--long, relatively shallow, and cylindrical to subcylindrical. When considering individuals of the various species in the family at the same length, the small pickerels will be more cylindrical, and the others more laterally compressed (Crossman 1962a). Other distinguishing family characters include the posterior location of the dorsal and anal fins, the large mouth ("duck-billed snout"), well armed with teeth, and forked tail. In the grass pickerel, body colouration is variable, but usually consists of a green to brownish background, with 12 to 24 irregular, more or less vertical, narrow, dark bars, and a middorsal brownish stripe. Dark, preorbital, suborbital, and postorbital bars are obvious on the head. The fins lack strong colour and markings. Juveniles have a prominent pale lateral band that breaks up as the fish grows (see Figure 1, A, B, and C).

Figure 1. Grass pickerel, Esox americanus vermiculatus

A. Adult, 25.4 cm; B. juvenile, 16 cm; C. Young-of-Year, 10.2 cm TL. A and C from Crossman 1962a; B. Photo by E. Holm © ROM.

The grass pickerel is distinguished from the northern pike and muskellunge by: small adult size; less laterally compressed body; the possession of obvious, oblique, black, suborbital, preorbital and postorbital bars (the latter two are absent to inconspicuous in the larger species); fully scaled cheeks and opercula, vs. one or both half-scaled; fewer than 10 submandibular pores, vs. 10 or more; notched (cardioid) scales on flanks, other than those associated with the lateral line, and also between the pelvic fins; and 11 to 13 branchiostegal rays, vs. 13 to 19. It is distinguished from chain pickerel by its 11-13 branchiostegal rays, vs. 14-17, and the absence of the dark, chain-like pattern over a pale or yellowish background on the sides typical of the chain pickerel only. The grass pickerel is distinguishable from the redfin pickerel by a longer, narrower snout with a slightly concave dorsal configuration, vs. a shorter, broader snout with a flat, to convex upper surface; a branchiostegal ray formula of 4+7 or 4+8 (those on anterohyal+those on the posterohyal bones, see Crossman 1960), vs. 5+5 or 5+8; fewer than 5 cardioid scales in a vertical row of scales on the flank, vs. more than 5; fewer than 5 cardioid scales in the angle between the pelvic fins, vs. 5 or more; only yellow paired fins, vs. orange to red, at spawning time (Scott and Crossman 1973).

Designatable units

Crossman (1966) believed that the two subspecies intergraded across a broad front in the US tributaries to the Gulf of Mexico from the St. Johns River in Florida to the Biloxi River, Mississippi. In that area, individuals had a confusing array of character values. Recent genetic work (Butler, Crossman and Wilson, unpublished) indicated that the Atlantic (Esox americanus americanus) and Mississippian (Esox americanus vermiculatus) populations are genetically distinct using both nuclear and mtDNA marker systems. The intergrades represented a third unique form (M. Butler, Trent University, Peterborough, Ontario; personal communication). These results indicate that the grass pickerel and the redfin pickerel are evolutionary significant units and, therefore, qualify as designatable units of Esox americanus.

It has been suggested (P. Dumont, Quebec Natural Resources, Wildlife and Parks, Longueil, QC; personal communication 2005) that there are three populations in Quebec: Lac St-François, Coteau, and Lac Saint-Louis. These three sections of the St. Lawrence are effectively separated by a series of natural obstacles. The section between Lac Saint François and Lac Saint-Louis was closed between 1912 and 1958 by a series of dams and weirs; however, there is no genetic, or other evidence that suggests that these populations are reproductively isolated from each other or from those in Ontario, so at this time there are no eligible units below the sub-species level.