Stream Variables Associated with Stream Entry and Initiation of Spawning
Many species use cues in their physical environmental to guide choices of when and where to reproduce. External cues are important because environmental variables that affect spawning site quality are related to offspring survival. Survival during early life stages is in turn often related to population levels of recruitment.
Covariates Measured in Black River
- 24 hr lagged temperature (Tlag)
- 24 hr lagged discharge (Dlag)
- 24 hr change in temperature (Tchange)
- 24 hr change in discharge (Dchange)
- Quadratic effect of temperature (Tquad)
Lunar cycle covariates:
- sin θ (peak at the first and last quarter)
- cos θ (peak occurring at full moon and new moon)
Dark Blue = Cosine
Light Blue = Sine
Temp. Hobo logger
Picture of the mouth of the Black River
757 total observations of upstream movement (2000-2002) by adults entering the Black River. Adults enter the river during twilight hours in the morning and in the evening. Day of entry appears to be related to periods of increasing river temperature and decreasing discharge.
Evidence for reproductive isolation due to differences in spawning time
Adult lake sturgeon spawn at different times during early (late April and early May), and later in May and early June. Adults spawning earlier in the season do so when the water temperatures are colder and when river flows are generally higher and more variable due to melting snow and spring rains.
Repeatability in the timing of spawning is high. Adults observed spawning during early and late portions of the spawning run are highly likely to spawn at approximately the same time in future years. Period of the lunar cycle, water temperature and declining periods of water discharge are positively related to timing of spawning.
Results of model predicting day of spawning.
Intervals between spawning events: generally males spawn more frequently
Individual-based analyses that included data from a large proportion of the adult lake sturgeon population in Black Lake revealed that variation in spawning periodicity (i.e., inter-annual duration between spawning events) was small, was shorter for males than females, and was unrelated to age. We also showed that intra-annual individual reproductive behaviors, such as relative spawning time within a season (i.e., early vs. late) and locations selected for breeding over 1.5 km (upstream vs. downstream), were consistent from spawn to spawn.
Inter-spawning interval differed between males (average 2.3 ± 0.08 years) and females (average 3.7 ± 0.16 years), but was not significantly related to age.
Probability of spawning in year t+x given you spawn in year t
*individuals likely missed once between captures
The location of spawning varies within a season and is repeatable on an individual basis. There are 6 areas within the upper Black River that are used for spawning. Typically, locations further upstream (sections 1-3) are used by spawning adults early in the season while locations further downstream (4-6) are used later in the year. There is more variation in use of downstream locations as indicated in the figure on the right by the variation about the means (grey and bars).