Editor’s Choice 59:7 The key to seabird conservation – mitigating bycatch from industrial fisheries and eradicating invasive species

Associate Editor, Maria Paniw, introduces this month’s Editor’s Choice article by Dasnon et al., which presents some good news for seabird conservation: combined efforts of avoiding bycatch from commercial fisheries and reducing impacts of invasive species can effectively boost population sizes of vulnerable marine pelagic species.

Industrial fishing activities can cause substantial damage, not only to fish stocks but also to pelagic vertebrate predators that die as a result of accidental bycatch of fishing activities. Indeed, fisheries bycatch led to a dramatic decline of seabird populations in the 1980s, triggering investment in bycatch mitigation measures worldwide.

However, assessing the consequences for seabird populations is challenging because their population dynamics are impacted by various factors aside from accidental bycatch deaths, and the contribution of all of these must be considered when trying to tease apart the relative role of bycatch mortality on population trends. In addition, although studies have shown positive short-term effects of bycatch mitigation of seabird abundances, long-term datasets are necessary to understand whether such effects persist. 

In their article, Dasnon and coauthors explore how different biotic and abiotic factors affect survival, reproduction, and population dynamics of the white-chinned petrel on Possession Island, one of the most bycatch impacted species. The study capitalizes on 30 years (1986-2917) of capture-recapture and abundance datasets to parameterize a multievent capture-recapture model.

Their model assesses stage-specific survival and reproduction in different time periods marked by different degrees of demographic impacts by fisheries and invasive black rats that prey on petrel eggs and chicks. The authors also examine the relative role of different fisheries practices and environmental variables on the demographic rates. Matrix population models parameterized from these rates and projected under various, cleverly designed scenarios of bycatch intensity were then able to shine a light on the threats and opportunities for population recovery of petrels.

Stochastic population growth rate of white-chinned petrels at Possession Island according to six different management scenarios. Error bars are 95% confidence intervals.

The results, which could be robustly compared to empirical population trends before and after the implementation of bycatch mitigation and rat poisoning measures, are encouraging. They show that, as expected, bycatch mitigation measures have been successful in increasing the survival of adults, which is the demographic rate that contributes most strongly to population dynamics.

Interestingly though, the eradication of invasive black rats, which have largely affected breeding success, has also contributed substantially to prevent population extinction of this vulnerable marine pelagic species. From an applied perspective, this work therefore highlights the importance of holistic approaches to the conservation of pelagic species.

As the authors point out, their study is one of the few that directly assesses the effects of fisheries bycatch mitigation on the demography and dynamics of threatened seabird population. It applies sophisticated modelling tools to a dataset that represent a common empirical sampling method in seabird studies. As such, the holistic approach presented in this work can be applied to other systems.   

Read the full paper Fisheries bycatch mitigation measures as an efficient tool for the conservation of seabird populations in Journal of Applied Ecology.

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