Counter-productive perspectives

Posted on March 23, 2016

A central aim of freshwater research is to understand the processes that regulate biological productivity. However, while lake-based investigations have focussed heavily on controls on primary production, river-based researchers have tended to concentrate more on production limits imposed by physical habitat requirements. If lake and river researchers think about production in different ways, and concentrate on different types of influential factors, these biases may affect our perceptions of the dominant processes that drive freshwater ecosystems. A team of American ecologists reviewed 564 papers on fish production in rivers and lakes published over a 46-year period. They focussed on salmonid species, which are common in both types of environment. Papers were classified according to the types of predictor variables studied (physical environment, system fertility, temperature, pollution and biotic factors). The analysis confirmed that there was a significant divergence in the approach taken by river and lake researchers. Papers on biotic variables (e.g., competition, predation) made up 51% of lake studies but only 29% of river studies, and system fertility was more often represented in lake (45%) than river (22%) publications. In contrast, papers on physical variables comprised 65% of river studies but only 25% of lake studies. Regardless of their lake or river focus, researchers were almost twice as likely to concentrate on one type of predictor than on multiple predictors, in spite of the fact that when multiple variables were examined they were all significant in 70-80% of cases. Therefore, it seems that ingrained assumptions about controls on fish production may have led both river- and lake-based researchers to miss the bigger picture. Contributing to the persistence of contrasting perceptions is the fact that relatively few studies have been experimentally-based, especially those in rivers, where 70% of production investigations have been correlative or descriptive in nature.

Reference: Wurtsbaugh, W.A. et al. 2015. Approaches for studying fish production: do river and lake researchers have different perspectives? Canadian Journal of Fisheries and Aquatic Sciences 72, 149–160.