Spawning-site and natal-site fidelity by northern pike in a large lake: Mark-recapture and genetic evidence

We supplemented physical-tagging data with genetic data to provide evidence for spawning-site and natal-site fidelity by two spawning populations of n orthern pike Esox lucius in Kabetogama Lake, Minnesota. A mark-recapture st udy supported previous reports that individual northern pike and other esoc ids tend to return to the spawning grounds that they used in previous years . Of 1,900 northern pike marked at two spawning sites in the first year of the study, 23% were recaptured on spawning grounds one to three times over the next 4 years. Of these recaptured fish, only 1.3% and 4.8%, respectivel y, of those marked at the two spawning sites were recaptured at the other s ite. Tag returns from anglers showed that the year-round ranges for fish fr om the two sites overlapped, so that lack of dispersal could not completely explain the high fidelity to spawning sites. Significant allele frequency differences at five microsatellite DNA loci between the 1983 (P = 0.03) and 1985 (P = 0.002) spawning populations indicated low levels of gene flow be tween the populations. This reproductive isolation would only be expected i f most individuals first spawn at the site of their own birth and subsequen tly return to that site. We therefore conclude that northern pike in Kabeto gama Lake exhibit both natal-site and spawning-site fidelity. Management on the basis of discrete spawning populations within lakes may thus be approp riate for a larger number of species and locations than commonly practiced.