Discarded fishing gear can pose a significant entanglement risk.
Most people will be familiar with the threat macroplastic debris poses to pinnipeds — asphyxiation, choking, blocking the digestive tract, open wounds (tightening around growing animals or pulled tight by drag in the water) and/or impairing the ability to forage successfully. However, while emotive images of individuals suffering from encounters with plastic are well known, the potential impact on populations are not.
In their study, Perez-Venegas et al. (2021), investigate the impact of macroplastic debris on the population growth of South American fur seals. Using modelling and assuming an otherwise stable population of around 2950 individuals, Perez-Venegas et al. forecast population growth over a 30 year period in five different scenarios:
- Zero entanglement
- The reported entanglement rates for the study population (lowest)
- The reported entanglement rates from other pinniped colonies around the world
They found that even the lowest rate of entanglement they used had a significant effect on population growth, reducing it by around 20%. More shockingly, the highest reported entanglement rate reduced population growth by just over 90%. As such their findings suggest that modelling entanglement rates should form a part of any pinniped conservation management plan and likely policy to protect any marine species affected by plastic entanglement. The authors acknowledge that their method has some limitations but offer that it gives a “straightforward and potentially useful approach for the standardized prediction of impacts at a population level of different rates of plastic pollution and entanglement and could be applied in distinct populations of the same species around the world.”
The paper “Towards understanding the effects of oceanic plastic pollution on population growth for a South American fur seal (Arctocephalus australis australis) colony in Chile” by Diego Joaquín Perez-Venegas, Andrés Valenzuela-Sánchez, Felipe Montalva, Héctor Pavés, Mauricio Seguel, Chris Wilcox and Cristóbal Galbán-Malagón, 15 June 2021 is published in Environmental Pollution available through the ELSEVIER.
by Andrew Pollard