Ryan Koenigs, Winnebago Sturgeon Biologist, May 29, 2013
The 2013 sturgeon spawning migration was met with expectations of a short, yet intense run. The ice broke loose on the Wolf River on April 6, which is two weeks after sturgeon began spawning in 2012, but air temperatures through the first few April weeks stayed cool and therefore water temperatures warmed very slowly. The slow warming led to sturgeon spawning later this year than on average, because spawning is strongly correlated to water temperature and peak spawning typically takes place at water temperatures of 54-60°F. The Wolf River reached this temperature range on the weekend of April 27, which cued spawning and the first sturgeon spawning activity was observed at the Sturgeon Trail in New London on the afternoon of April 28, 2013. Warm temperatures during that time period led to water temperatures throughout the Wolf River that were in the optimal spawning range and the fish responded. During the short period from April 28-May 1 there were sturgeon spawning simultaneously at spawning sites spread from New London to Leeman on the Wolf River with fish also being observed spawning in Berlin and Princeton on the upper Fox River and numerous sites along the Little Wolf and Embarrass Rivers. As expected, the spawning run went very fast and by the afternoon of May 2 (just 4 days following the onset of spawning) there was very little spawning activity taking place and the first run of the 2013 sturgeon spawning migration was completed.
As observed in most years, there was indeed a second spawning run of sturgeon documented on the Wolf River. Fish were observed spawning at Bamboo Bend in Shiocton on May 16 and at the Shawano Dam on the afternoon on May 17. Similar to most 2nd runs, this run did not contain nearly as many fish as the first run and likely was comprised of a hand full of late-spawning females at each site. When ripe females return the near shore rock habitat to spawn, the males pick up on the cues and will once again come back in and spawn with those females. Following spawning activity, males typically stay in deeper water adjacent to spawning sites until all prospects of spawning activity have diminished.
My crew and I did not venture out to tag sturgeon during the 2nd run, but we were very successful handling spawning fish during 4 days of the first run. In total we handled 208 females (150 newly tagged fish and 58 recaptures), 802 males (512 newly tagged fish and 290 recaptured males), and 2 fish of unknown sex. Our goal each spring is to handle and mark as many untagged fish as we can during spawning assessments, but our benchmark goal is 150 new female marks. Even with the shortened spawning run this spring we were able to meet this goal. We knew we were going to have a shortened window to tag spawning fish and thus worked longer hours to maximize our tagging opportunities.
Similar to what we have observed over the last 5-10 years, numerous “trophy” sized sturgeon were handled this year. In fact, 19% of the adult females that we handled this spring were larger than 70”, with the largest fish being an 82” female that was handled below the Shawano Dam on May 1