Alien fish risk increases in heavily populated areas

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The denser the population in England, the more likely an alien fish species will be introduced in the area.

This is the central argument of a paper by Gordon Copp, Lorenzo Vilizzi and Rodolphe Gozlan published in the most recent issue of the journal Aquatic Conservation: Marine and Freshwater Ecosystems.  

It has been known for some time that the incidence of pet fishes in the wild has been linked to the proximity of roads, fish markets, pet shops and areas with high human population density for marine species.  

The aim of the study was to carry out a statistical analysis (spatial modelling) to examine spatial relationships between alien fish occurrence and the demographic factors associated with propagule pressure (i.e. the quality, quantity and frequency of invading organisms) and to test whether the demographic factors are reliable predictors of the incidence of non-native fishes, and as such, surrogate estimators of propagule pressure.  

The study was carried out at the intermediate scale for all of England, dividing it up into 1500 squares of 10 square kilometres each.  

The authors used the following sets of data for their analyses:

  • non-native freshwater fish occurrences in the wild;
  • the numbers of non-native fishes imported; and
  • demographic information (i.e. numbers of humans, pet shops, garden centres, and fish farms per unit area). 

The results of the analyses showed that spatial distributions of non-native species in England were significantly related to human population density, garden centre density and fish farm density. The authors identified human population density and the number of fish imports as the best predictors of propagule pressure.

The authors conclude that: "…data on human population density can be used as a surrogate for predicting likely areas of non-native fish introductions. Used in conjunction with fish movements, where available, human population densities can be used to support biological invasion monitoring programmes across Europe and to inform management decisions on which areas should have priority for the control of non-native fish introductions."

For more information, see the paper: Copp, GH, L Vilizzi and RE Gozlan (2010) The demography of introduction pathways, propagule pressure and occurrences of non-native freshwater fish in England. Aquatic Conservation: Marine and Freshwater Ecosystems 20, pp. 595–601.