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Mortality Rate-Electro-Fishing

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#1 Guest_pylodictis_*

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Posted 08 June 2011 - 08:31 PM

Guys, when backpack shocking in small creeks what kinds of mortality rates do you get on average?

#2 Guest_gerald_*

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Posted 08 June 2011 - 09:00 PM

Do you mean the fish or the field technicians?

#3 Guest_Newt_*

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Posted 08 June 2011 - 09:36 PM


Pylodictis- Mortality rates of a darter project I've been working on have been low (0-5%) during cool weather, but higher in hot weather (probably about 15%). Don't quote me on those numbers, it's a colleague's project and I don't have the data in front of me. These fish were not only shocked, but also anesthetized and injected with elastomer dye before being released, so the extra stress and handling time undoubtedly increases mortality. Certain fish (silversides, for example) are especially delicate and often succumb when shocked or even netted. Breeding male stonerollers and striped shiners seem to have high mortality too, perhaps due to already deteriorated condition from putting all their energy into sex-related issues.

Precautions you can take to minimize mortality:

Keep handling time short

If you're hanging onto fish for a while, as for photography, keep them as cool and well-aerated as possible (set bucket or cooler in the shade or partly submerged in stream, and use battery-powered air pumps)

Do not overcrowd bucket or cooler

Use the lowest voltage setting on the shocker that effectively stuns fish (this will depend on the conductivity of the water; a higher setting is needed in soft than in hard water)

Some people add salt or commercial electrolyte solutions to the water in the cooler/bucket to help reduce stress; I haven't tried this but it seems reasonable.

#4 Guest_UncleWillie_*

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Posted 09 June 2011 - 05:01 PM

Everything Newt said is spot-on, and doesn't just apply to backpack shocking small streams. Although I have experienced higher mortality rates when backpack shocking small streams than I experience when in larger rivers while boat electrofishing. In larger electrofishing boats, I essentially observe zero mortality (from the shocking itself - I'm not counting holding fish in tubs for hours in the middle of August temperatures in middle Georgia). However, all of my stream experience seems to result in higher mortality from the shocking itself (e.g., sometimes the amperage is too much for the fish physically, and results in death. The tiny fish in small streams can certainly be more prone to breaking it's own spine than the larger fish (in my experience).

Of course, species does matter. Each species has a unique body shape and size, and some get shocked "harder" than others, and are more sensitive to handling. Think about the difference body shapes (surface area) of sunfish vs. gar vs. shad etc.

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