Some Aspects of the Life Histories of Three Closely Related Crayfish Species, Orconectes Obscurus, O. Sanborni, and O. Propinquus

The life histories of three closely related species of crayfish, Orconectes obscurus (Hagen), Orconectes sanborni (Faxon) and Orconectes propinquus (Girard), which occupy separate rivers in northeastern Ohio, were studied and compared. Crayfish were collected from the same location, approximately bi-weekly, from April through October 1967. Major aspects of life histories of the three species are similar and can be summarized as follows. Mature crayfish mate in August and September; eggs are laid in April and May and young become independent in June. Growth and activity cease during the winter and resume in the spring. First-form males change to second form in the spring and in late summer revert back to first form. Immature individuals molt several times during the summer, each time increasing in carapace length by one mm, or sometimes by two mm or more. Males of Orconectes obscurus and 0. sanborni do not attain sexual maturity until their second summer, but many 0. propinquus males become sexually mature in their first summer. Attempts at interspecific mating in the laboratory yielded one successful mating, that between a male Orconectes propinquus and a female 0. sanborni. This female could not be kept, so it is not known whether viable young would have been produced. The pleura were clipped in different combinations for marking and recapture studies which were conducted during the summer of 1967. Rates of recapture of marked individuals were: Orconectes obscurus, 28%; 0. sanborni, 1%; and 0. propinquus, 14%. INTRODUCTION Although literature on crayfish systematics is extensive, relatively little information is available on life histories, and no one has published a comparative study of the life histories of closely related crayfish species using identical methods. This study compares the life histories of Orconectes obscurus (Hagen, 1870), Orconectes sanborni (Faxon, 1885) and Orconectes propinquus (Girard, 1852). Fitzpatrick (1967) revised the taxonomy of the Propinquus Group of Orconectes, after statistical and qualitative analyses of several characters, and proposed two subgroups, Sanborni and Propinquus. Orconectes obscurus and 0. sanborni are in the Sanborni Subgroup and 0. propinquus is in the Propinquus Subgroup. METHODS The studies of Orconectes obscurus were made in the West Branch of the Mahoning River, a tributary of the Ohio River, in Ravenna Township, Portage County, Ohio (north of Ohio Route 5); those of 0. sanborni were made in the Cuyahoga River, in Streetsboro Township, Portage County, Ohio (between Ohio Routes 14 A portion of a thesis submitted to the Kent State University Graduate School in partial fulfillment of the requirements for the degree of Master of Arts. Manuscript received April 20, 1970. 'Present address: R. D. 1, Maryland, New York 12116. THE OHIO JOURNAL OF SCIENCE 72(3): 129, May, 1972. 130 DOROTHY DAVIS FIELDER Vol. 72 and 303); and those of 0. propinquus were made in Morgan Township, Ashtabula County, Ohio (west of Ohio Route 45). Collections were always made at the same sites in each of the rivers; habitat areas in each of the rivers were approximately the same size. Water temperature was taken at each collection; the mean temperatures were 14.9°C for the West Branch, 16.0°C for the Cuyahoga, and 17.8°C for Bronson Creek. Substrate in the West Branch and Cuyahoga areas was cobbles and boulders (65 to 256 mm and up) composed predominantly of sandstone but some shale. The substrate of the Bronson Creek area was shale with some clay and was less firm than was that of the other two sites. The Cuyahoga River area was the only one having submergent vegetation, which consisted of species of Elodea, Vallisneria, Potamogeton, Myriophyllum, and Ceratophyllum. Collections were made about bi-weekly; the duration of each period of collecting was approximately one hour. At each collection the following was entered on a data sheet: time, date, specific geographical location, method of capture, collection zone (riffle or pool), type of banks, substrate (type and compaction), flow stability (intermittent or continuous), amount of current, width and depth of water, aquatic vegetation, temperature of the air and water, and general weather conditions. Crayfish were captured by use of a minnow seine (3̂ 4-inch mesh, 6-foot length), held downstream from rocks being overturned by foot in order to catch crayfish dislodged from under them. Sometimes the seine was supplemented by a dip net. The carapace length (the distance from the tip of the rostrum to the posterior border of the thoracic region), sex, and form (if male) of each crayfish were recorded and then the crayfish was returned to the water. (No distinction was made between juvenile and second-form males.) Record was made of crayfish that were ovigerous, about to molt, recently molted, or copulating. Age groups were determined from graphs, using the methods of Van Deventer (1937). From 13 July through 4 September 1967, all crayfish were marked by clipping the pleura in different combinations (Goellner, 1943). For example, in R12 L34, the clipped pleura would be the first and second on the right side and the third and fourth on the left side. In this way, records could be kept as to frequency of recapture, approximate time of molting, and growth per molt for individual crayfish. The scars from the clippings were distinct even after three molts, because regeneration was relatively slow and usually produced deformed pleura (Goellner, 1943). Mating experiments were conducted in the laboratory, first with members of the same species and then with individuals of two different species together, on 28 August and 31 August 1967, respectively. One or two individuals of each sex, of approximately equal size, were placed in fingerbowls, 20 cm in diameter. Seventeen pairs were used in the intraspecific experiment and eighteen pairs in the interspecific experiment. In the interspecific-mating experiment, all three combinations of species were tried. Pairs were observed every 15 minutes. The presence of a sperm plug was chosen as the criterion for a successful mating. All females were examined for sperm plugs before and after each experiment. RESULTS Composition of the Collections Population sampling was started during the first week of April 1967 and continued through October 1967, when growth for the year had ceased and sizes corresponded to those of individuals caught in April. (Freshly molted individuals of Orconectes obscurus and 0. sanborni were last observed on 30 September and of 0. propinquus on 7 October 1967.) Several general trends in the population size and composition were noted (figs. 1, 2 and 3). The early-spring and late-fall collections were the smallest, but the summer collections were relatively large, reflecting recruitment of young-of-theNo. 3 CRAYFISH LIFE HISTORIES 131 year. The major periods of form change occurred, during May and from the end of June through July and August. In May, most of the first-form males of all three species changed to second form (demonstrated best in fig. 1). During June, no first-form males of Orconectes obscurus were captured (fig. 1), but newly molted first-form males of 0. sanborni were captured beginning on 30 June, and of O. propinquus beginning on 24 June, thus identifying the beginning of the time of change to first form in these species (figs. 2 and 3). The first freshly molted firstform males of 0. obscurus were captured on 9 July. 2 23 30 14 28 S e p t . Oct. FIGURE 1. The relationship of abundance, form, and season in Orconectes obscurus, females; = first-form males; • • • • • = second-form males. 132 DOROTHY DAVIS FIELDER Vol. 72 Sex ratios of all three species were approximately 1:1 most of the time. The only departures from this ratio were in the fall samples of Orconectes sanborni (when the numbers collected were small), and in the collections of all species in April and May, at both times of which the ratio of females to males was 1:2. In the latter case, the difference was probably a result of inadequate sampling at a time when ovigerous females remain hidden.