A review of the impacts of fisheries on open-ocean ecosystems

Due to the expansion of fishing practices, fish catches have become stagnant while global fishing efforts continue to grow, ultimately leading to major stresses on marine resources. Fisheries impacts on both coastal and deep-sea ecosystems are well understood and documented; however, the biological and ecological impacts of fishing on open-ocean systems are not well studied or documented.

A new article co-authored by Nereus Program Fellows Guillermo Ortuño Crespo and Daniel Dunn in ICES Journal of Marine Science addresses the knowledge gap of the ecological impacts of fishing practices in coastal & deep-sea ecosystems and open-ocean systems. Understanding the biological impacts of fishing on open-ocean systems will provide insights towards open-ocean management strategies, which will have implications on marine ecosystem services and food security. Failing to take action for high seas governance and management will pose significant risks to open ocean ecosystem services and integrity.

Current limitations to our understandings of the impacts of fishing practices on open-ocean ecosystems inhibits our ability to manage and conserve these systems, which could jeopardize their functionality and capacity to provide ecosystem services. Image: “Portree Harbour, United Kingdom” by Blair Fraser.

This research considers the impacts of fisheries on open-ocean system dynamics at 3 ecological scales:
(1) species
(2) biological community
(3) ecosystems

It was found that top-down control mechanisms dominate at species and community scales for open-ocean systems; however, further investigation and research should be completed at the ecosystem scale. At the species level, fishing can reduce abundance and alter physiology and life traits, thus impacting the functionality of the species within the biological community. Additionally, fishing may induce changes to open-ocean community trophodynamics and reduce the biodiversity and resilience of these ecosystems.

Given these results indicating the impacts of fishing operations on open-ocean ecosystems, monitoring mechanisms should be implemented in order to maximize sustainability and preserve the integrity of the functionality for open-ocean ecosystems, which will rely on coordination between the Global Ocean Observing System, fishing industry, and academia. This research may help inform the review of the United Nations Fish Stocks Agreement (UNFSA) and the biodiversity beyond national jurisdiction (BBNJ) negotiations.

Open‐ocean fisheries expanded rapidly from the 1960s through the 1980s, when global fish catches peaked, plateaued and possibly began to decline. While catches remain at best stagnant, fishing effort globally continues to increase (Anticamara, J. A., Watson, R., Gelchu, A., and Pauly, D. 2011. Fisheries Research, 107: 131–136; Merrie, A., Dunn, D. C., Metian, M., Boustany, A. M., Takei, Y., Elferink, A. O., Ota, Y., et al. 2014. Global Environmental Change 27: 19–31). The likelihood of ecosystem impacts occurring due to fishing is related to fishing effort and is thus also expected to be increasing. Despite this rapid growth, ecological research into the impacts of fisheries on open‐ocean environments has lagged behind coastal and deep-sea environments. This review addresses this knowledge gap by considering the roles fisheries play in controlling the open-ocean at three ecological scales: (i) species (population or stock); (ii) biological community; and (iii) ecosystem. We find significant evidence for top-down control at the species and community scales. While evidence of ecosystem-level impacts in the open-ocean were not explicit in the literature, we provide examples of these impacts in several marine pelagic systems and encourage further research at this ecological scale. At the species level, fishing can reduce abundance, and alter physiology and life history traits, which, in turn, affect the functional role of the species within the biological community. Fishing may also induce changes to open-ocean community trophodynamics, and reduce biodiversity and resilience in open-ocean ecosystems. Our ability to manage open-ocean ecosystems has significant implications for provisioning of ecosystem services and food security. However, we posit that the monitoring required to assure the sustainability of open-ocean ecosystems is not being undertaken, and will require coordination with the Global Ocean Observing System, industry, and academia.