By Patrick Cooney, Certified Fisheries Professional

Scientists at hatcheries are cutting the faces off of fish as part of a program to improve the health of rivers, but why?  Read on, and you will realize that this rather barbaric act makes scientific sense.

Video by Patrick Cooney

What do gardens and rivers have in common?

Every year, Spring arrives and flowers blossom.  Accordingly, vegetable gardeners and lawn aficionados make their annual migration to home improvement stores to stock up on fertilizer.  They do this because the nutrients in fertilizer play a critical role in the overall yield of a garden and the health of a lawn.

Rivers and streams are not much different from gardens and lawns when it comes to needing a proper balance of nutrients to thrive.  Give a garden or a river too few nutrients, and they will quickly become unproductive.

What acts as fertilizer and nutrients for a stream?

Fish carcasses make great fertilizer, and over human history, people have tilled massive amounts of fish into soil in order to increase land crop productivity.

Just the same in streams, fish carcasses decompose and fertilize the production of small insects and plants that support the bottom of the food chain.

How are dams, hatcheries, and anglers interrupting nutrient cycles in streams?

Every upstream migrating fish that is blocked by a dam or removed from the river is one less “packet” of marine derived nutrients reaching upstream habitats.  The continuous exclusion and removal of migratory fish carcasses has subsequently led to reduced production in rivers because of nutrient poor conditions.

How do fisheries scientists know which streams are experiencing declining numbers of fish carcasses and associated marine derived nutrients?

Every year, fisheries scientists embark on journies into streams and rivers to complete “carcass surveys”.  The goal of a carcass survey is to walk or boat along a stream and count dead fish carcasses.  The number of dead fish counted gives scientists an indication of the quantity of naturally spawning adults that returned from the sea.

Once a carcass is found and counted, biologists modify the carcass in a way that ensures that it is not counted on any subsequent surveys.  A popular method of quickly modifying a carcass is to cut it in half with a machete.  On any subsequent carcass counts, any carcasses cut in half is not recounted.

What are fisheries scientists doing to supplement stream nutrients?

Anadromous fish around the globe spend a majority of their lives at sea, growing big and fat on marine organisms.  When migrating inland to spawn, anadromous fish bring marine derived nutrients into freshwater rivers and streams.

Unfortunately, anadromous fish have been systematically blocked from upstream migration by dams and habitat fragmentation.

As anadromous fish are blocked by dams or their populations are reduced by overfishing, the number of fish carcasses in streams also decline.  Streams depleted of adult fish carcasses and related marine nutrients are more recently receiving supplemental nutrients from biologists.

To supplement stream nutrients, scientists are taking surplus dead fish carcasses from hatcheries and dispersing them in streams where the dead bodies decompose.

So why are scientists at hatcheries cutting the faces off of the fish?

Fisheries scientists modify the carcasses of the hatchery salmon before dumping them in rivers in order to not double count a carcass.  A preferred method for permanently marking fish at hatcheries is the “fish face guillotine”.   Although it is rather gruesome at first site, this device is serving a rather useful and novel purpose.

While cutting off your nose to spite your face generally seems like an overreaction to a problem, this time around it seems like a rather appropriate solution.

 

Learn more about fish derived nutrient subsidies.