Aquaculture, non‐native salmonid invasions and associated declines of native fishes in Northern Patagonian lakes

Abstract

1. Even though intensive aquaculture production of salmonids in lakes occurs in many locations around the world published studies on the survival and reproductive success of escaped cultured salmonids in freshwater ecosystems are not common. A recent expansion of aquaculture in Chile has led it to become the world's second largest producer of cultured salmonids. 2. We document the recent history of escaped and self-sustaining salmonid populations over a wide spatial scale and a long temporal scale in Chilean Patagonian lakes. Our hypotheses are that salmonid density in lakes will be higher where there is intensive aquaculture, due to greater numbers of potential escapees. Secondly, if non-native salmonids have adverse impacts on native fishes, increases in the abundance of non-native species should be associated with decreases in relative abundance of native species. Finally, if the first two hypotheses are correct we anticipate that diets of salmonids may show evidence of predation on native fishes, diet overlap with native species, and evidence of the influence of feed from aquaculture operations in the diets of salmonids and native fishes. 3. We sampled six lakes with gill nets from 1992 to 2001. Our results show that the relative abundance of free-living salmonids is closely related to the level of fish farming production. Salmonids are the top predators and in lakes with fish farming the main prey item is native fishes. The relative abundance of native fishes has decreased, most likely due to predation by salmonids. 4. Our study contributes to the understanding of the effects of non-native salmonids in oligotrophic lakes, and it provides a starting point to judge the establishment of new fish farming sites in lakes around the world.

Estudios Limnológicos en Lagos Y Lagunas Del Parque Nacional Torres Del Paine (51° S, Chile)

“…Una situación totalmente inversa a la propuesta por ambos autores, sucedería en la Patagonia de Argentina, donde en condiciones de oligotrofia existiría baja actividad zooplanctónica (Balseiro et al 2001, Modenutti et al 2003, lo cual sería similar a lo observado en los grandes lagos estudiados en el presente trabajo (Tabla 1, Fig. 2b) Un factor importante, en grandes lagos de la Patagonia es el efecto de la presencia de salmónidos asilvestrados (Soto et al 1994, Becker et al 2007, Pascual et al 2007, Arismendi et al 2009). Aunque en el presente estudio no se cuantificaron sus poblaciones, y no está demostrado un efecto potencial directo o indirecto de estas poblaciones de peces sobre zooplancton en lagos chilenos, es muy probable en sitios con poblaciones de salmónidos existan especies zooplanctónicas de menor tamaño corporal (Soto et al 1994), por desaparición de grupos de gran tamaño como cladóceros y copépodos (Modenutti et al 1998, Reissig et al 2006.…”

“…Aunque en el presente estudio no se cuantificaron sus poblaciones, y no está demostrado un efecto potencial directo o indirecto de estas poblaciones de peces sobre zooplancton en lagos chilenos, es muy probable en sitios con poblaciones de salmónidos existan especies zooplanctónicas de menor tamaño corporal (Soto et al 1994), por desaparición de grupos de gran tamaño como cladóceros y copépodos (Modenutti et al 1998, Reissig et al 2006. De igual modo existiría una serie de interacciones del tipo efecto cascada, donde los salmónidos podrían depredar sobre peces nativos o compartir sus nichos tróficos , Arismendi et al 2009), lo cual no está del todo claro en cuanto a sus efectos sobre el zooplancton. Una situación diferente sucedería en presencia de peces nativos como puyes (Galaxias sp.…”

Native and exotic fishes in a Patagonian reservoir with rainbow trout cage culture: spatial and trophic resource use

“…The strong spatial segregation between P. trucha and rainbow trout intensified in Alicurá reservoir following the onset of aquaculture 25 years ago, also characterized by the almost total absence of O. hatcheri in littoral captures . This outcome may be a consequence of negative interactions taking place between the native fish and farm escapees, as has been argued for Chilean lakes (Arismendi et al, 2009).…”

“…Two studies in Norwegian sea fjords reported numerous indigestible items in ERT stomach contents with less than a year in the wild, but not farm pellets or wild food (Rikardsen and Sandring, 2006;Skilbrei, 2012). Wild food and farm pellets, but not indigestible items, were found in ERT with probably more than a year since escape time in Chilean sea fjords (Soto et al, 2001) and lakes (Arismendi et al, 2009). In a semi-enclosed estuarine habitat in Tasmania, ERT consumed mainly farm pellets and indigestible items, but also small amounts of wild food, depending on time since escape (Abrantes et al, 2011).…”

“…Salmonid escapees are expected to have long-term environmental effects on the receiving communities, given their high dispersion capacity and longevity, in addition to the high frequency and massive nature of escape events (Podemski and Blanchfield, 2006;Arismendi et al, 2009;Bourret et al, 2011;Patterson and Blanchfield, 2013). Ecological impacts include predation, competition and species replacement (Habit et al, 2010;Johnston and Wilson, 2014).…”