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Good Intent Gone Bad: A History of Intentional Releases and Invasive Alien Species

Invasive alien species (IAS) pose one of the most significant global threats to biodiversity today. These species are introduced, frequently through human action, into an ecosystem outside their natural geographic range, and have a demonstrable environmental or socio-economic impact. Although they may have been deliberately introduced to control other invasive species (e.g., mongoose to control rats), IAS can have devastating effects throughout ecosystems. Of the top 10 countries with the highest recorded IAS, 60% are in the Pacific.

Invasive alien species (IAS) poses one of the most significant global threats to biodiversity today (Early, 2016). IAS include species introduced through human action into an ecosystem outside their natural geographic range, with a demonstrable environmental or socio-economic impact, which are capable of sustaining a self-replacing population (Turbelin, 2017; IUCN 2000). The CBD Aichi Biodiversity Target 9 addresses IAS (CBD, 2020).


A 2017 study on the patterns of IAS pathways revealed important data on the patterns of the invasions of these species (Turbelin, 2017). Of the top 10 countries with the highest recorded IAS, 60% of the of the countries / territories are located in the Pacific or Oceania: U.S. including Hawai‘i, New Zealand, Australia, French Polynesia, New Caledonia, and Fiji. When taking a closer look at how these species came to be released in these remote ecosystems, the most common methods are the following:


  • Ignorant possessions or stowaways, traded via road vehicles, trains, boats, planes;

  • Horticulture, nursery trade, ornamental purposes; and

  • Intentional release.


The following are examples of how the intentional releases of IAS have severely impacted the Pacific and Oceania.



Rats have caused devastation throughout ecosystems across the Pacific. The Pacific rat (Rattus exulans) is pervasive across the region, which occurs in 13% of all Pacific countries, causing environmental destruction in many of them.


There are four rodent species in Hawai‘i today. The Polynesian rat (Rattus exulans), known in the Hawaiian language as the ‘iole, arrived first.  As mention above, the species is a prevalent IAS throughout the islands of the Pacific, having migrated out from its native range in continental Asia. It has been shown that the Pacific rat traveled with the traditional Polynesian voyagers who first settled the islands of the Pacific (Matisoo-Smith and Robins 2009; Rick et al. 2013). 


Rattus exulans arrived in Hawai‘i around 1000 AD with Native Hawaiians (Athens et al. 2002, Athens 2009).  Despite extensive unsubstantiated speculation that the species was intentionally introduced by Polynesians, the actual reasons for the widespread co-occurrence of the Polynesian rat with the first settlers of Pacific islands are unknown and undocumented.  Although Hawaiians may have intentionally introduced the species along with other food animals, R. exulans are also infamous stowaways and pests. 


While their natural range is Asia, Norway and black rats spread throughout Europe, then North America, and finally the Pacific via western explorers (Atkinson 1973, McNeill 1994). These pests brought with them a wide range of diseases that proved devastating to the native population of the islands (Tomich et al. 1984, Ikeda 1985, Stenseth et al. 2014, Kosoy et al. 2015). 



Mongooses were deliberately introduced on some oceanic islands, including Hawai‘i, by plantation owners in 1883 with the intent to control invasive rodents (Tomich, 1986). Yet, rather than controlling or eradicating rodent populations, mongooses have coexisted with rats and mice, and instead caused the decline or extinction of native bird, amphibian, reptile and mammal species (Seaman and Randall 1962, Nellis and Small 1983, Roy et al. 2002, Watari et al. 2008). Having little to no understanding of the species, the businessmen failed to understand they were introducing nocturnal predators to hunt diurnal prey. As the mongoose has no predators in Hawaii, the mongoose population thrived in the islands and continues to cause widespread devastation

to native species and ecosystems. 

Research into Hawaiian language newspapers reveals that Native Hawaiians knew the foreign introduced species to be a pest and many efforts existed throughout the islands to kill and eradicate the species shortly after its arrival to the islands. These articles by indigenous writers also speak about the carelessness of their introduction to the islands (Ka Nupepa Kuakoa, 1915, Ka Nupepa Kuokoa, 1907, Ka Nupepa Kuakoa, 1913).  

Today, failing to impact their intended prey with any significance, mongooses in Hawai‘i instead feed on a wide variety of prey and locally available food, feeding upon and adversely impacting live terrestrial vertebrates (reptiles, birds, rodents, amphibians), invertebrates (insects, spiders, crabs), and carrion and small fruits in lesser amounts (Baldwin et al. 1952). 




Researchers with the University of Hawai‘i intentionally introduced Gorgilla Ogo (Gracilaria salicornia) into the nearshore coastal areas of Kāne‘ohe and Waikīkī off the Island of O‘ahu for aquaculture purposes. The species quickly grew out of control and severely damaged coral ecosystems into which it had been intentionally introduced. Since introduction, conservation groups and community groups have spent millions of dollars trying to control and remove the species from the foreign waters.

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