A Comparison of Approaches for Estimating Relative Impacts of Nonnative Fishes

Abstract

Lack of standard methods for quantifying impact has hindered risk assessments of high-impact invaders. To understand methodological strengths and weaknesses, we compared five approaches (in parentheses) for quantifying impact of nonnative fishes: reviewing documented impacts in a large-scale database (review); surveying fish biologists regarding three categories of impact (socioeconomic, ecological, abundance); and estimating frequency of occurrence from existing collection records (collection). In addition, we compared game and nongame biologists’ ratings of game and nongame species. Although mean species ratings were generally correlated among approaches, we documented important discrepancies. The review approach required little effort but often inaccurately estimated impact in our study region (Mid-Atlantic United States). Game fishes received lower ratings from the socioeconomic approach, which yielded the greatest consistency among respondents. The ecological approach exhibited lower respondent bias but was sensitive to pre-existing perceptions of high-impact invaders. The abundance approach provided the least-biased assessment of region-specific impact but did not account for differences in per-capita effects among species. The collection approach required the most effort and did not provide reliable estimates of impact. Multiple approaches to assessing a species’ impact are instructive, but impact ratings must be interpreted in the context of methodological strengths and weaknesses and key management issues. A combination of our ecological and abundance approaches may be most appropriate for assessing ecological impact, whereas our socioeconomic approach is more useful for understanding social dimensions. These approaches are readily transferrable to other regions and taxa; if refined, they can help standardize the assessment of impacts of nonnative species.

Appendices

Appendix 1. Example survey^a

• (1) The relative abundance of the species in suitable habitats in the drainage is:

  • a. () Generally abundant throughout the drainage

  • b. () Locally abundant somewhere in the drainage

  • c. () Not abundant anywhere in the drainage

• (2) Nuisance fishes are those species whose establishment has led to undesirable economical, social, or cultural impacts. Based on this definition, the species is a:

  • a. () Major nuisance.

  • b. () Moderate nuisance.

  • c. () Minor nuisance/not a nuisance.

• (3) Fishes having an ecological impact are those that have noticeably and negatively affected native species (including nonfishes), either directly or indirectly. Based on this definition, the species has had a:

  • a. () Major ecological impact.

  • b. () Moderate ecological impact.

  • c. () Minor or no ecological impact.

• (4) Please state the focus of your work/research:

  • a. Game fishes

  • b. Nongame fishes

  • c. Other ___________

Questions one to three were repeated for each species. Question four was given at the end of the survey.

Appendix 2

See Table 6 and Box 1.

Table 6 Nonnative fishes in the study region. Column headings are defined as follows: HUCs total number of HUC6 s in which a species is established, game game species listed as “yes”, GISD species found in the GISD listed as “yes.” For collection approaches with more than one sample, N sample size, R species’ rank based on mean rating, E species’ rank based on scanning electron microscopy rating. Highest-ranking species (i.e., 1) had the highest mean rating or SE

Box 1 Evaluating the tens rule