What San Francisco Bay Taught Us About Selenium in Sturgeon
We never get bored of studying the lakes at IISD Experimental Lakes Area (IISD-ELA), but sometimes we take the tools that we have developed here to help others better understand their aquatic systems.
That was precisely what motivated Lee Hrenchuk and me to travel to the San Francisco Bay area from February 3-6 to participate in some exciting and innovative studies of local white sturgeon at the Original Sturgeon Derby. The Derby provided us with an excellent opportunity to study the health of these amazing prehistoric fish.
This was the third year of our collaborative studies with the San Francisco Estuary Institute (SFEI), an independent science body that works to assess and improve the health of the waters, wetlands, wildlife and landscapes of the San Francisco Bay and beyond. SFEI works with the local Foundation Sportsman’s Club, at Bay Point, which has been organizing the Original Sturgeon Derby for more than 33 years.
Why are we concerned with the health of white sturgeon in San Francisco Bay? Studies of these fish have found elevated concentrations of selenium—an element that is required in small amounts as a nutrient but that can impair reproduction at high concentrations in animals that lay eggs, including fish, birds and amphibians. Several sources have contributed to elevated selenium levels in San Francisco Bay, including current agricultural runoff and historic discharges from local petroleum refineries. Sturgeon feed primarily on an invasive species of clam, and because of the clams’ efficient bioaccumulation of selenium, the sturgeon are also susceptible to relatively high exposures. You can imagine that local anglers, state authorities and conservation groups all have an interest in ongoing monitoring of the resident population.
One of the attributes that make sturgeon a unique species is the many years it takes them to mature. In general, males can take 10 to 20 years to reach maturity, and females usually spawn only after they are 15 to 25 years old. Managing a species that takes so long to reproduce is a challenge because fishing pressure can significantly reduce the numbers of actively reproducing fish. Obtaining information on the health of the population can also be difficult, and environmental managers may be reluctant to use lethal sampling techniques for fear of further negatively affecting population numbers.
So why did we choose to study these fascinating fish at the Original Sturgeon Derby? During the Derby, a relatively large number of white surgeon are brought in to be measured at the central headquarters at McAvoy Harbour, and in many instances the anglers will be allowed to keep their fish to eat. This year this provided an opportunity for SFEI and IISD-ELA scientists to obtain samples that would otherwise not be available.
In addition to determining current concentrations of selenium in the muscle, blood, liver and ovaries of these fish, we were also able to collect other tissues like pectoral fin rays and muscle biopsies. These last two sample types are being used to develop methods that can be used by SFEI—and by others in the future—to non-lethally assess the health of sturgeon and their exposure to selenium.
The pectoral fin rays from sturgeon are cut into thin sections and mounted on glass slides (left). Under a microscope (right), annual growth rings allow us to accurately age the fish. But we can also get information about what each fish was exposed to over the course of its life. To do this, we use a technique called laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS). Briefly, this technique uses a very fine laser to vapourize small amounts of bone material as it moves continuously in a thin line across the pectoral fin ray. You can see the laser’s trace just below the arrows that indicate the direction of the laser’s travel in the picture at right above. As the laser travels across the fin ray, the vapourized material is drawn into a sensitive instrument, and concentrations of elements that were in the water where the fish lived, or in its diet, are determined in real time. Because the elements are preserved in the bone structure of the fin ray, we can find out what the fish was exposed to for each year of its life.
Needless to say, we will continue to develop these non-lethal sampling tools and apply them to study fish in lakes at IISD-ELA. In fact, we have already innovated some interesting ways to track the health of our fish without sacrificing them. Watch this space to learn more—you will be the first to hear about it!