How can killing smallmouth bass increase smallmouth populations? What about catch and release?

This may not make any logical sense but today I came across an interesting study done in 2008 on a small lake in upstate New York name Little Moose Lake.

Killing smallmouth bass

Smallmouth bass were introduced to this lake in the 1940s and have grown in numbers to the point that they are dominating other native species.  They are considered the invasive species.  As a result, an intensive, 7 year program of electrofishing and removing smallmouth bass was implemented in an effort to reduce their effect on native fish such as Lake Trout.

From the year 2000 to 2007, 53,947 young and adult bass were removed from the lake, typically in the spring before spawning and in the fall.

Despite removing these massive numbers of fish, the number of bronzebacks increased. The overall biomass of smallies decreased, meaning if you were to weigh the smallmouth bass population, it would be less but there was a growing young smallmouth bass population. Because there were less adult, larger bass, 6 native species did increase in their numbers.

The determination of the study was that to have a lasting effect, harvesting of smallmouth bass would need to be continued indefinitely.

In the case of Little Moose Lake, the smallmouth bass population may be regulated by competition among adults, based
on slow growth rates and low levels of recruitment prior to the initiation of removal (Weidel et al. 2000). Analysis of
diet data from the Little Moose Lake population showed that the ratio of adult to juvenile ingestion rates (defined as q by
De Roos et al. (2007)) was less than one and has decreased since the onset of the removal (unpublished data), which further implies that adult competition may be an important factor driving the overcompensatory response of the yearling and juvenile stages. The model presented by De Roos et al. (2007) predicted that in a reproduction-regulated population, harvesting any or all stages of the population could result in an increase in juvenile biomass (as was observed empirically with respect to abundance).  Source

So what does this mean?

At least in this lake, removing a large amount of the bronzebacks changed something in the lake, allowing for more smallmouth bass to be produced. It also means that things aren’t always as simple as they seem and when your try to mess with mother nature, you never know what is going to happen, despite us things we are so smart.

There are several explanations for this unexpected change. The one that the researchers thought was most likely was that there was less competition in reproduction so spawning was much more successful than when the population was dense. Other explanations could be less competition for food as a large number of adult bass were harvested.

Is catch and release BS?

When we look at fisheries were there is poor smallmouth bass reproduction, this study must be considered. Is there too much competition in some fisheries that is actually decreasing the number of young bass? Would harvesting more smallies improve the fisheries? These are questions that I can’t answer.

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