An Examination of Inconnu Life History Strategies through Use of Radiotelemetry and Otolith Microchemistry

A radiotelemetry study of inconnu (Stenodus leucichthys) conducted during 2007-2015 in the Kuskokwim River drainage in Alaska has expanded our understanding of life history strategies.  Four spawning areas have been identified and examined: Big and Tonzona rivers, and the South and Middle forks.  Inconnu arrived at their spawning areas during late July through mid-September and spawned during late September through early October.  Post-spawning outmigration occurred during 1-1.5 weeks in mid-October.  Most of the radio-tagged inconnu overwintered in the lower Kuskokwim River and the brackish upper Kuskokwim Bay.  After spring ice out many of these fish swam upriver and spent summers feeding at the mouths of major tributaries.  However, some inconnu spent the entire summer in the lower Kuskokwim River and others spent the entire winter in the middle and upper Kuskokwim River, with year to year variations for individual inconnu.

Strontium:Calcium (Sr:Ca) levels were examined in thin-sectioned otoliths, encompassing all annuli over the fish’s lifetime.  Various degrees of anadromy were detected, which corroborated with the radiotelemetry data.  Sr:Ca is positively correlated with salinity, with freshwater environments having lower Sr:Ca values than marine.  Some otoliths showed clear evidence of anadromy with others illustrating limited exposure to salt water.