Monday, March 11, 2013

Long term monitoring: An electrified subject

In the spirit of Florida’s recent AFS symposium on long term monitoring, I would like to reflect on my personal experiences with freshwater fish community monitoring. Electrofishing is a common method employed to assess fish communities and is used extensively by state and federal officials. Data from electrofishing transects are compared to historical results, which were (hopefully) obtained in the same manner. However, electrofishing can be a fickle beast, producing different results based on a myriad of factors. Operator error is one of the most common sources of variability in results. Inexperienced researchers, even when trained, often lack the field knowledge needed to respond appropriately to different environmental variables. For instance, depth and conductivity change the efficacy of electrofishing. On the flip side, inexperienced dippers (those who net the fish at the front of the boat) can miss fish more often than those seasoned biologists with a trained eye.A good example is the case of high macrophyte coverage trapping fish unseen and/or reducing the effective output.
                To confound the results derived from this monitoring tool even further, there is ample evidence that electrofishing can be species and size selective. Adjusted settings can compensate for size selectivity (given proper training and experience), but little can be done for those species which are notoriously hard to shock. While some monitoring efforts have changed the protocol for longer “pedal down” time over a constrained regions, one has to ask if this data is comparable to data collected using traditional catch-per-unit-effort protocol. Even given that  comparisons of fish communities across years is relative, any true relative changes may be hard to tease apart from sampling error.
                Multiple studies have been conducted to compare different gear: which is another potential confounder. There are many types of electrofishing gear; from high powered boat electrofishing units to small backpack units. Studies aimed at quantifying differences show different, sometimes conflicting results. And each study focuses on a single variable of change or limited set of factors (e.g.,5.0 GPP vs. 9.0 GPP,  effect of driver). The variation resultant from unit, operator and environmental variables combined, make detecting change induced by these various factors difficult to pinpoint.
                One option for ensuring consistent results is to use different gears in conjunction with electrofishing. Seine nets or Zippin depletion sampling are excellent ways of comparing results. While seine netting can also be size selective, true depletion sampling is generally accurate when conducted properly. One downfall to using multiple methods is the time and resources needed. Multiple gears can become a costly endeavor. With funding reduced for state and federal agencies, this becomes an unlikely way to test the gear or compensate for errors in electrofishing.
                Perhaps the most important method of reducing sampling error is through comprehensive, standardized training. Some standardization of methods exists, but little training is offered on how to respond to different environmental variables which may skew results. My personal experience working for an agency taught me that current training on the theory of electrofishing is lacking the “what-to-do-if…” component. I believe this portion of the training could use more detailed standardization, coupled with a period of apprenticeship for hands on experience.
                Electrofishing can be a good tool for community monitoring, given training on the finer details of the art of electrofishing. Knowing the limitations to the gear is also essential. While electrofishing is a good relative comparison, it is not suitable for true population estimates, and monitoring efforts would benefit substantially from the use of multiple gears.

1 comment:

  1. I totally agree with your statement about the variability among researchers that have training and experience.

    In fact, because of these potential sources of error our lab (Rehage lab @ FIU) has developed a pretty rigorous training program for boat drivers and dippers. We have also built a very detailed protocol to make electrofishing a cook book procedure. The training and protocol has helped tremendously in keeping consistency among different crews.