Gertzen

Quantifying Invasion Pathways: Fish Introductions from the Aquarium Trade

Abstract

  • Introduction to Issue: Introduced species can cause significant economic and environmental harm. Therefore, researchers have developed risk assessment models based on biological characteristics of exotic species.
  • Gap in Research: Few studies have quantified propagule pressure, despite its significance in determining species establishment.
  • Focus of Study: This study specifically examines fishes introduced via the aquarium trade, which transports thousands of species worldwide.
  • Objective: Develop a method to estimate propagule pressure by:
    • Identifying and quantifying aquarium fishes sold.
    • Determining fish owner behaviors and disposal practices.
    • Quantifying uncertainty in the measurements.
  • Model System: The St. Lawrence Seaway.
  • Findings:
    • Only one non-established species, Tanichthys albonubes, with a propagule pressure of 117 per year, was likely capable of invasive potential in the region.
    • Over 10,000 fishes are released annually from Montreál (Quebec, Canada) alone.
  • Implications: The aquarium trade poses a significant risk in warmer habitats and should be assessed explicitly to inform population models estimating species establishment probabilities.

Introduction

  • Global Context: The world is experiencing increased international trade leading to the spread of biological organisms beyond their native ranges.
  • Role of Human Activity: Human actions have facilitated the introduction and spread of nonindigenous species (NIS) at an accelerated rate compared to past events (Mills et al. 1992; Hochberg and Gotelli 2005).
  • Consequences: Significant impacts include:
    • Economic damage estimated at 137 billion dollars annually in the US due to NIS (Pimentel et al. 2000).
    • Declining ecosystem functions and decreased global biodiversity (Miller 1989; Pimentel 2005).
  • Invasion Mechanism: NIS are a major driver in global biodiversity loss, surpassed only by habitat loss (Wilcove et al. 1998; Levine and D’Antonio 2003).
  • Risk Quantification: Proper management of NIS necessitates quantifying invasion risks through rigorous risk assessments integrating the complete invasion process:
    • Transport
    • Introduction
    • Establishment
    • Spread
    • Impact (Kolar and Lodge 2001).
  • Propagule Pressure Importance: Propagule pressure indicates the number introduced. The likelihood of successful invasion relates directly to propagule numbers (Kolar and Lodge 2001; Williamson 1996).

Research Gap

  • Previous studies have primarily concentrated on biological characteristics of NIS for risk assessments (Mandrak 1989; Kolar 2004; Copp et al. 2005) rather than quantifying introduction rates.
  • Assessing risk involves knowing species introductions through various pathways that necessitate focus on prevention strategies (Ricciardi and Rasmussen 1998; Kolar and Lodge 2002).
  • Identifying pathways of introduction is critical, with notable examples including:
    • Ballast water (Ricciardi and Rasmussen 1998; Rixon et al. 2005)
    • Aquarium releases, escape from aquaculture, live food markets, and intentional releases (Mills et al. 1992).

Methodology

  • Study Area: Montreál and the St. Lawrence Seaway, significant entry points for NIS into the Great Lakes (Environment Canada 1996).
  • Aquarium Trade Overview: Over 5,000 fish species traded internationally are typically non-native to the Great Lakes (Welcomme 1984; Chapman et al. 1997).
  • Data Collection Methods:
    • Store Inventories: Survey of aquarium and pet stores in Montreál to quantify fish species sold:
    • Visited over 75% of stores (18 total) from February to May 2006.
    • Derived counts through standing stock populations recorded at beginning and end of period.
    • Store Owner Surveys: Interviewed 20 store owners about unsold fish policies, confirming that unsold fish were either kept for sale or returned to distributors.
    • Customer Surveys: Conducted interviews with 86 customers outside 11 stores in October and November 2005 to explore fish ownership and disposal behaviors.

Data Analysis

  • The methodology integrated data from customer behavior into a propagule pressure model based on:
    • Overall Propagule Pressure Calculation:
      overallextpropagulepressure=MimesP(I)imesNimesP(R∣I)overall ext{ propagule pressure} = M imes P(I) imes N imes P(R|I) with parameters defined as follows:
    • M: Total number of households owning fish.
    • P(I): Probability that a person is a releaser.
    • N: Average number of fishes owned.
    • P(R|I): Probability that a fish is released given it is owned by a releaser.
  • Bayesian Statistical Approach: Used to incorporate uncertainty in estimates due to sample size (P(I), N, P(R|I)).
  • Model for Species-Specific Propagule Pressure: species−specificextpropagulepressure=MimesP(I)imesNimesP(R∣I)imesr<em>ximescimess</em>xspecies-specific ext{ propagule pressure} = M imes P(I) imes N imes P(R|I) imes r<em>x imes c imes s</em>x with variables defined as:
    • r_x: Relative rate of release due to species characteristics.
    • c: Correction factor.
    • s_x: Relative proportion of fishes of a certain species.
  • Results:
    • Total number of fish sold: 46,722 over 30 days across sampled stores.
    • Most sold species identified and their respective attributes analyzed for propagule pressure:
    • Species List Includes:
      • Goldfish (Carassius auratus)
      • Guppies (Poecilia reticulata)
      • Neon tetras (Paracheirodon innesi)
      • Others as listed in the study.

Results Analysis

  • Propagule pressure for each type of fish derived from customer surveys revealed:
    • 6.98% of respondents reported releasing fish into the wild (P(I)).
    • Average release rate of 5.1% among those who have released fish into the wild (P(R|I)).
    • Aggressive behaviors and large size were significant factors influencing the proportion of disposed fishes based on survey data.

Conclusion

  • This study illustrates a simple method to quantify propagule pressure from the aquarium trade, emphasizing human behavior as a critical determinant.
  • Notable findings highlight that over 10,000 fishes are released annually from the Montreál aquarium trade, emphasizing environmental risks.
  • Recommendations for future studies to include comprehensive analyses on additional pathways of introduction and behaviors across different regions susceptible to invasions from the aquarium trade are critical moving forward.

Acknowledgments

  • Research funding from the Canadian Aquatic Invasive Species Network (CAISN) and contributions from Fisheries and Oceans Canada alongside academic collaborators provided necessary support for this project.

References

  • Complete references can be found at the end of the original document, providing a comprehensive bibliography of all cited works for further research.