2004 Lake Sturgeon Research

2004 Field Season Highlights & Review
When it Rains it Pours

By Patrick Forsythe, Graduate Student, Michigan State University

Adult lake sturgeon were captured on the spawning grounds to provide a continual (now 4 year) evaluation of the annual spawning stock abundance, sex ratios, size and age class structure and movement patterns. The first adult sturgeon was captured on May 1st and the last was captured on May 29th. At least two different spawning runs were observed in 2004. However, the exact number of runs remains unclear due to several flood events and treacherous water conditions that precluded us from netting. Despite the harsh river conditions, we were successful at capturing a total of 101 lake sturgeon (75 males, 25 females and 1 undetermined). On average, male sturgeon weighed 45.6 pounds and were 53 inches long; females weighed 81.8 pounds and were 66 inches long. Eight of the 25 females captured this year topped the scale at over 100 pounds!

All adult sturgeon were marked (tagged) using both external and internal methods. Tagging information from each of the past four years (2001-2004) will be used to estimate the number of fish that are currently of spawning age in Black Lake. Nearly half of all fish (48%) in the 2004 spawning run had been captured during one of the three previous field seasons. More specifically, of the 25 females captured, 15 were untagged (new fish) and 10 had been tagged during previous field seasons (old fish). Of the 75 males captured, 37 were untagged and 38 had been handled previously. Several particularly virile males have been captured during three or all four years that we have been handling spawning fish. Estimates of the total population size, coupled with information on spawning frequencies and spawning stock abundance, is critical to the future management of Black Lake sturgeon.

Several other research objectives implemented during this past field season were to 1) test the success of alternate methods of gamete collection and 2) estimate the sources and magnitude of mortality during the egg stage. We were successful at capturing approximately 1000 naturally produced eggs directly from the water column on modified filter pads positioned downstream from the spawning group. From this subsample of eggs, it appears that fertilization rates are quite high regardless of the number of spawning adults. However, additional sampling is required for more conclusive results. Experiments involving the sources and magnitude of egg predation will need to be continued next field season.

The last objective of the season was to determine the chronology and abundance of naturally produced out-migrating larval sturgeon. Larval sampling was conducted on the Upper Black River over the course of 22 nights beginning at the end of May and ending in late June. Unfortunately, several extended periods of rain during the sampling period prevented us from obtaining a continual estimate of larval abundance and an accurate picture of the larval drift profile. Sampling was conducted during a 5-hour time period, beginning at dusk (9:00 pm) and ending in the early morning (2:00 am). Majority of the larval fish were captured during several "peak" hours (between 11:00 pm and 1:00 am) within a particular sampling evening. Even though a few larval sturgeon were observed every evening over entire sampling period, majority of the fish this spring were captured during several consecutive evenings of "peak" drift activity occurring in mid-June. In total, 448 lake sturgeon larvae were collected. All larvae were transported to Wolf Lake Fish Hatchery for rearing and the survivors will be returning to the Upper Black River later this fall.

The information obtained on each of the research objectives outlined above is critical to understanding factors that are potential barriers to lake sturgeon reproductive success. I would like to thank members of Sturgeon For Tomorrow for providing continual support and encouragement for this research project, the Michigan DNR for providing funding and assistance in the field and PIE&G for contributions.

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