The Life History and Trophic Relationship of the Ninespine Stickleback, Pungitius Pungitius, in the Apostle Islands Area of Lake Superior

The ninespine stickleback is an important food of juvenile lake trout in the Apostle Islands area. It is the most numerous fish of the area and is distributed in deep waters during the winter and in shallow waters during the summer. Females grow fastel than males. reaching an average total length of 80 mm at age 5. Males live to age 3 and attain an average length of hh mm. Annulus formation on otoliths is complete by mid-July. Seasonal growth is more than half complete by early August: growth of mature females ·is delayed until after spawning. Both sexes mature over a period of 3 yr. Spawning occurs from mid-June to late July. Males apparently do not live as long as females. possibly because of a post-spawning mortality. Egg number is a linear function of fish length. although this relationship is different for fish from two separate areas. Environmental differences between these areas. which may affect spawning time. possibly cause the differences in fecundity. Significant quantities of maturing eggs atrophy just prior to spawning. a phenomenon which changes the fecundity relationship. Sticklebacks eat a variety of invertebrates. particularly the crustaceans Mrsis re!icra and Pontoporeia alfinis. Food eaten by the stickleback and slimy sculpin is similar. bill the adaptability of both species tends to eliminate serious competition. The lake trout is the only serious predator of stickleback. Investigations were made by the Bureau of Commercial Fisheries (BCF) on the biology of the fishes of Lake Superior from the early 1960's. These studies have been primarily life history studies on economically valuable species such as the lake trout, Sa{velil/lls l/amayclIsh (Walbaum), various coregonids, and the smelt, o.~II/('rUS morda.1" (Mitchill). Some of the more comprehensive of these include Bailey (1964), Dryer (1963), and Dryer and Beil (1964). When it became apparent that these fish stocks were being rapidly modified by exotic species, particularly the sea lamprey, Pcfl'o1 This work is a result of research sponsored in part by . the Minnesota Agricultural Experimental Station. Umversity of Minnesota. SI. Paul, MN 55101. 2 Northeast Fisheries Center, National Marine Fisheries Service, NOAA, Woods Hole. MA 02543; present address: OhIO Cooperative Fishery Unit, Department of Zoology, OhIO State University. 1735 Neil Ave., Columbus. 01-1 43210. U aOepartment of Entomology, Fisheries and Wildlife. mversity of Minnesota, SI. Paul, MN 55101. Manuscript accepted March t973. FISHERY BULLETIN: VOL. 71, NO.4. 197.1. myzo/I maril/lls L" additional emphasis was placed on ecological studies of noncommercial fishes whose life histories are interrelated with the exploited ones. One of these, the ninespine stickleback, occurs in BCF index trawl samples in greater numbers than any other. However, prior to the study presented in this paper, its ecological significance in these waters was largely unknown. This study was designed to investigate the life history of the ninespine stickleback in the Apostle Islands region of Lake Superior and determine the importance of its relationships to the economically important fish species of the area. The ninespine stickleback is one of the most widely distributed northern fishes, occurring in freshwater, estuarine, and coastal saltwater environments (Bigelow and Schroeder, 1953). It is abundant in cool-water habitats similar to Lake Superior throughout the Northern HemiRphere. In middle western United States, it is found in all the Great Lakes except Lake Erie