|
The Identification of Pike
by Means of Characteristic Marks by Neville J. Fickling The markings of pike (Esox lucius L.) were found to be specific to individual fish. The subsequent recapture of pike after 2 years of growth, indicated that the markings could be used for the positive identification of specific pike. Marking or tagging studies have frequently been employed to study the movement and growth of a variety of fish species. A variety of tag types, subcutaneous dye injections, fin clips and freeze brands have been used with success in such studies. It is however, unfortunately true that many tag types will retard growth (De Roche, 1963; Christensen, 1961; Eschmeyer, 1959; Shetter, 1967). Tags are also prone to loss due to either removal by natural causes or by anglers. Mutilation caused by fin clipping is not acceptable in many fisheries, while freeze branding demands constant access to a supply of liquid nitrogen. This is obviously impractical for small scale studies. Dye marks are generally satisfactory, but restricted in application, due to the limited number of permutations available for the identification of the individual. It is suggested that the markings of the pike (Esox lucius L.) are very specific for individual fish and a method of identification of individual pike by these markings is described. One-hundred and eighty-seven photographs of pike were examined (length 838-1118 mm; age 5-14 years), Eighteen individuals were photographed from both sides enabling comparison between sides. Key areas were selected on the flanks of the pike, these areas being those where markings were distinct and easily examined. One area of fin was also selected as a key area. These key areas are identified in Fig. 1, Initially the markings of individual pike were compared, one side against the other. The criteria of similarity was noted as when three key areas showed similarity, between pike being compared. In practice when three key areas were found to be similar, all other key areas were also similar. Comparison of the two sides of a pike showed that the markings, though similar in size and shape, were not necessarily similar in position. It was therefore concluded that comparisons of markings were only valid for pike photographed from the same side. A standard method of photography was therefore employed. All pike which were either hand held or laid on the ground were photographed with the head of the pike facing the right of the picture. This was in effect, with the pike's head facing left from the holder's point of view. |
|
|
The photographs of 187 pike, all viewed from the same side were then studied. The types of marking varied considerably depending on the origin of the pike. Considerable differences in markings were also noticed in pike from the same habitat. Three basic types of marking were noted, all typical of mature pike (small pike tend to have transverse bar markings, which disappear with increasing growth). These are shown in Fig. 2 and can be described as:
|
|
|
Oval spots tend to vary in size, from 10 to 25 mm depending on the locality and size of the pike. Round or stellate spots vary similarly. The longitudinal bar pattern is very typical of pike of Irish Loughs. It is uncommon for pike to display more than one pattern type in one particular environment. However, examples of all three patterns have been noted by the present author in one of the Fenland Drains. In order to establish the unique nature of the markings of all the pike examined, each were compared with each other. In no case was more than one key areas similar between individual pike. Often the difference in spot pattern was enough to signify `no similarity'. A small number of pike were dye marked and photographed. Recaptures of four different fish were made 2 years later. Each fish was found to be similar on the basis of at least three key areas being comparable. This indicated that the markings remain similar for at least two years. A large number of other fish, (860-1120 min) which have been at liberty for up to one year were also found to retain the same markings. Figs 3 and 4 shows one such fish captured from Loch Lomond (A.), on four occasions in 1978 and 1979. Figure 3 shows the fish as captured in 1978 and Fig. 4 as captured in 1979. The caudal area of this fish has particularly characteristic marks. Growth increments of dye marked pike were up to a maximum length increment of 50 mm and weight increase of 2.75 kg. Table 1 presents the weights, age & fork lengths of the four pike noted above.
|
|
|
TABLE 1. Weights, lengths and ages of four pike recaptured after 2 years
|
|
|
The method of identifying individual pike requires the use of photography, a relatively inexpensive method, easily available for the study of pike. The method does not disfigure, mark or otherwise harm the fish-an important point if the aesthetic qualities of catching and returning fish in good condition are to be preserved. The method has been found to be suitable for the identification of pike of 500 mm and larger which have shown percentage length increases of 5.4% and percentage weight increases of 31.3% over a period of 2 years. Caution should be shown when attempting to apply this method to very young pike. Rapid growth results in the addition of more spots or marks and it is therefore likely that the marks change beyond recognition. Pike are at present under a prolonged investigation, with particular reference to changes in markings with growth. The result of this study will be presented at a later date. I would like to thank Mr D. Plummer for the photograph used in Fig. 3 and pike angling friends who supplied photographs of pike. Christensen, J.M. (1961) Survey of the Danish sole tagging experiments with notes on the growth rate. Conseil permanent internationale pour I'Exploration de la Mer, 1961 Meeting Northern Seas Committee Paper, No 126 14pp.. De Roche, S.E (1963) Slowed growth of lake trout following tagging. Transactions of the American Fisheries Society, 92, 185-186. Eschmeyer, P.H. (1959) Survival and retention of tags, and growth of tagged trout in rearing ponds. Progressive Fish Culturist, 21, 17-21. Shetter, D.S. (1967) Effects of jaw tags and fin exision upon growth, survival and exploitation of hatchery rainbow trout fingerlings in Michigan. Transactions of the American Fisheries Society, 394-399. This article first appeared in Fish Management (1982) 13, No. 2 - on this website 25/06/06 |
|
|