Does trawl fisheries affect the diet of fishes? A stable isotope analysis approach^*

* Originally presented at the Stable Isotope Summer School 2018 ‘Stable isotopes in ancient and contemporary environments’, 15–19 April 2018, University of Konstanz, Germany.

ABSTRACT

Trawling is the main fishing practice worldwide and its ecosystem effects have been raising concern over the past decades. Long-term impacts can be monitored through changes in the trophic structure, and several studies evaluated trophic level (TL) shifts in fish populations between trawled and untrawled environments. However, published results are contrasting. We performed a metanalysis integrating all available studies that evaluated TL shifts in fishes between trawled and untrawled environments and conducted a local study comparing several features of the trophic ecology in two species of fishes. According to the metanalysis, TL does not change significantly with trawling. In contrast, the local study showed higher TLs and broader isotopic niches in the trawled environment. Diet reconstruction indicated a potential consumption of hake, the main discard component, at the trawled environment. All the studies used in the metanalysis were conducted in the Northern Hemisphere, whereas the local study represents the first data available from the Southern Hemisphere. As industrial commercial fisheries in Argentina are relatively recent, it is possible that our data are capturing the initial stage of ecological changes induced by trawling, compared with the historical fisheries located at the Northern Hemisphere.

KEYWORDS:

• Bycatch consumption
• carbon-13
• fisheries impact
• isotope ecology
• metanalysis
• nitrogen-15
• reef fish
• Patagonia
• trophic position

Acknowledgments

The authors would like to thank Leo Venerus and Alejo Irigoyen for their support provided at fieldwork, and again Leo Venerus, Pablo Yorio and Mariana Viglino for their important comments on the manuscript.

Disclosure statement

No potential conflict of interest was reported by the authors.

ORCID

Manuela Funes http://orcid.org/0000-0002-7825-8664

Notes

* Originally presented at the Stable Isotope Summer School 2018 ‘Stable isotopes in ancient and contemporary environments’, 15–19 April 2018, University of Konstanz, Germany.

Additional information

Funding

This work was supported by the Rufford Foundation [grant number 20709-1]. Samples obtained at the research cruise were part of Pampa Azul initiative, Golfo San Jorge Campaigns 2016 and 2017. Authors’ scholarships are granted by Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET).