Did she or didn’t she?

When the spring spawning migration finally ends and the tagged female is recaptured, all is not over.  The question on everyone’s mind is, “Did she spawn, or didn’t she?”

Using a portable ultrasound unit similar to those used in modern emergency rooms, biologist Sabrina Davenport scans the belly of the fish for any sign of the large mass of dark grey and black eggs that were there two months ago (see Catch Me If You Can blog post for a picture of Davenport performing an ultrasound on a pallid sturgeon). It only takes a few moments to confirm that all her eggs are gone and that only the thin filmy tissue of her ovaries remains.  She is taken out of the water and quickly weighed.  Female PLS11-008 lost 16% of her body weight when she released several thousand eggs on the bottom of the Missouri River in spring 2011.  See Female prerogative blog post for more information on PLS11-008.

Pre-spawn ultrasound image of PLS11-008: the green arrow points to ripe eggs visible as lighter specs in this side view of the abdominal cavity.

 

Post-spawn ultrasound image of PLS11-008: the green arrow points to the ovary in this side view of the abdominal cavity. The absence of eggs visible in the pre-spawn ultrasound image collected 2 months prior indicates PLS11-008 successfully spawned in 2011.

Davenport then places the female back into the shallow tank and proceeds to perform a minor surgical procedure to recover the data storage tag (DST).  The DST recorded the water temperature and depth of PLS11-008 at 30 minute increments during her entire upstream migration.  In conjunction with telemetry, the data from the DST helps biologists characterize her migration route, determine the spawning time frame, and document environmental conditions at the spawning location.   

Depth data from the DST (represented by the grey line on the graph) is highly variable when PLS11-008 is swimming upstream indicating the use of a variety of depths during migration. When stopped at her apex, or most upstream location, there is a period of little change in depth in relatively deep water. This pattern of a pronounced period of little change in depth over 24-36 hours usually in deep water after the rapid, frequent depth changes associated with upstream migration (weeks) is what biologists associate with spawning.

 Surgery also provides an opportunity to visually inspect the ovaries, or reproductive organs, for reproductive condition, abnormalities, or anomalies.  An incision roughly an inch long does not provide a very big window through which to observe the gonads, but it is usually enough to get a glimpse. 

 

An inch long incision in the abdomen of a sturgeon is big enough to implant and remove a DST tag and get a glimpse of the gonads.

 

Before PLS11-008 is slipped back into the river, biologists insert a fine gauge needle into her tail and take a blood sample.  Blood samples taken before and after spawning are analyzed for reproductive hormones.  Comparing profiles of reproductive hormones before and after spawning attempts help project scientists understand why some female sturgeon spawn successfully and others may not.  See Bloody business post for pictures and more information. 

PLS11-008 was released at her capture location and will continue to contribute to extensive telemetry studies looking at long term movements and reproductive cycles of known adult pallid sturgeon.

Completed with contributions by Aaron DeLonay.

About Emily Pherigo

Emily is no longer with the Comprehensive Sturgeon Research Project. When she was here, she was a biologist contracted to the Comprehensive Sturgeon Research Project. Most of her time was spent at a computer performing QA/QC on data or updating figures and graphs most used by Aaron DeLonay. However, she occasionally made it to the river, where she enjoyed seeing pallid sturgeon and was reminded why she entered the natural resources field.
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