For the past several seasons CSRP biologists have intensively and meticulously tracked female pallid sturgeon to their spawning locations. All this attention on females is because biologists can easily tell when a female spawns by the presence or absence of eggs. When the female is tagged with eggs, migrates, then stops, and is recaptured without any eggs it is easy to conclude that she must have spawned. Knowing where these spawning sites are is critical to understanding why there are so few young pallid sturgeon being added to the population each year. But finding the “spot” on the map where spawning happens is only part of the story. What are the males doing while females are migrating upstream and what part do males play in when and where females stop to spawn? Spawning locations are defined by where a female deposits her eggs, but which sex really chooses the spot on the map, and why?
For the first time in the Lower Missouri River, CSRP biologists documented a small aggregation of reproductive male pallid sturgeon this spring. On May 22, 2013 CSRP biologists set out to recapture telemetered male pallid sturgeon PLS08-048, near the Platte River, Nebraska at rivermile 594.7. Biologists were curious to know if the male was reproductive and ready to spawn with nearby females. A trammel net was drifted over the tagged fish several times, but the targeted fish was not captured on that day. Instead, four different male pallid sturgeon without telemetry tags were caught. Three out of these four males were in reproductive condition at the time of capture. The following day, May 23rd, a fourth reproductive male pallid was captured just upstream of the male aggregation recorded the previous day.
CSRP researchers have previously documented loose aggregations of males in the Yellowstone River, North Dakota a few miles upstream of the confluence with the Missouri River (see previous post Just One of the Guys). These aggregations of males in the Yellowstone have occurred near suspected spawning locations. Biologists are hoping to learn if male pallid sturgeon are selecting spawning locations early in the season before females with eggs arrive. They want to know the factors that male sturgeon use to select spawning sites and whether or not females are selecting spawning sites using the same factors or if they are relying on the judgment of the males who have already arrived. If biologists can determine which sex is selecting spawning sites, and what factors are preferred as “good” spawning habitat, then it is possible to determine how much spawning habitat is available and maybe predict spawning success.