Background to Lake Sturgeon Larval Stage
Lake sturgeon larvae begin feeding and emerge from the substrate during evening hours (21:00 to 02:00) to disperse downstream in search of nursery habitat. Similar to peaks associated with adults spawning, drifting lake sturgeon also occurs in peaks and the entire drift period may last 30 to 40 nights. Although it is not well documented, researchers believe that larval lake sturgeon inhabit natal rivers during this life period until they reach the first year or two of the juvenile period. Mortality at this life period is significant due to the lack of habitat which provides cover for drifting larvae from predators. Discharge is also a likely contributor to early mortality and may negatively affect year-class strength of lake sturgeon by either not providing enough water to, or pushing larvae beyond, critical nursery habitat areas.
Larval Sampling Methods
Each year in the Black River we use 5 D-frame drift nets to capture larval lake sturgeon as they migrate downstream from spawning areas. The sampling site is approx. 2 km downstream from the spawning areas.
Extreme inter-annual variation in larval production
Because the same gear is used in the same location each year, we can use the number of captured larvae as a measure of annual recruitment. Independent estimates of the efficiency of gear suggests that the number captured is approx. 13% of all larvae passing the collection nets. Even though the number of adults spawning does not vary greatly from year to year, the 40 fold difference in estimates of offspring recruiting to the larval stage suggests that environmental factors play a significant role in egg and larval mortality; especially considering that each female will release 100,000s of eggs.