Monday, May 20, 2013

Let the predatory fish do the work for you: a new early detection method for non-native fishes

    I am writing today about non-natives, early detection and BIASs.   Non-native fishes are causing serious problems to many aquatic systems. Carp for instance, can become so abundant in rivers and lakes,  that they crop much of  aquatic vegetation, taking away important juvenile habitat for freshwater fishes.

Hundreds of large herbivorous carp in a temperate river

    Likewise, in Florida, populations Orinoco sailfin catfish can dig thousands burrows in the sides of rivers, which reduces bank integrity, changing the structure of rivers.

Sailfin catfish borrows in the side of a tropical river bank

     Unfortunately, once non-native fishes reach the abundances of Orinoco sailfin catfish and carp in aquatic systems, there is not much managers can do to get rid of them.  But, if fisheries managers can find these critters when they just become introduced, then eradication is possible and managing these non natives becomes  a lot cheaper!  Therefore, much research has gone into developing effective methods that can find these alien fishes when they are rare or just become introduced.

      Over the last three years we have discovered a new early detection method for recently established non-natives.  The method is simple, just let predatory fishes find the non-natives for you. These BIASs (Biological Invasive Auto Samplers) or predatory fishes go about their daily business swimming around and eating other fishes. With some luck,  the predatory fishes find and consume recently introduced non-natives. All you have to do is catch BIASs remove their stomach contents and identify the new non-native species….. Seems easy enough.

    A recent anomalous weather event provided a unique opportunity for us to test whether or not BIASs can find recently established non-native fishes before other conventional methods.  In 2010, an extreme cold front virtually eliminated all of the tropical non-native fishes from the Everglades estuary, restarting species invasions.   The clean non-native slate in the Everglades estuary created an ideal natural experiment to test whether or not 5 common non-native species that were severely impacted by the cold front would first be detected with sampling BIASs or from another common early detection method, electrofishing, as the re-colonize the estuary.

     The five non-native species we chose to track are all tropical new and old world fishes (pictured below). Two are catfishes, brown hoplo and walking catfish, one eel species, peacock eel, and two spiny rayed fishes, the mayan cichlid and the African jewelfish.     And our focal BIASs were largemouth bass, common snook, and bowfin.

                                                     The non natives we tracked

Sure enough, the BIASs did a great job finding and consuming most of the non-natives. In fact, by sampling BIASs we found 2 non native species that were not even known to have colonized the estuary! These were the brown hoplo and the walking catfish. A large 20 pound snook ate the walking catfish (below),

and a bass was the first to eat the hoplo. 

Unlike the catfishes, jewelfish were found in bass diet samples and electrofsihing samples at nearly the same time. 

Peacock eels were also captured by both methods, however found in the diet of a bowfin about 2 years after we had first captued one via electrofishing. 

Last, Mayan cichlids have yet to be captured by either method following the cold front.

 Sampling with BIASs was quite successful in detecting non-native fishes. In fact, sampling predator diets detected two non-natives that were missed with conventional electrofishing techniques.  Unfortunately, one non native (peacock eel) was detected in the diets well after they were first detected by electrofishing equipment.  

In many active monitoring efforts such as electrofishing, seine netting etc. predators are often subsequently captured. Since they are already captured, sampling their diets does not take much extra training, time or money.   Thus, I believe that incorporating this sampling technique into early detection efforts can be very cost effective and may help identify and stop the spread of some nasty invading fish! 



  1. Neat research man! Very cool idea

  2. those are very small fish. try Reef fishing in Vanuatu. For sure you will ove to do it again and again.

  3. These are pretty small fish relative to whats on those reeefs. Trying to non-lethally remove the stomach contents of something like a massive dog tooth tuna would likely be more hassle than other methods. I am writing up this management brief now and will be adding a size limitation statement to the discussion... Thanks for the comment!