The impacts of fishing on the foraging behaviour of African penguins

Abstract

A unique field experiment in South Africa has provided the opportunity to study the Critically Endangered African penguin Spheniscus demersus and their prey with and without localised fishing activity. The aim of this experiment was to understand the impact of the local purse-seine fishery on the penguin population declines.

This PhD uses a long-term biologging dataset to determine whether fishing results in changes in prey acquisition in the African penguin. I quantify the level of overlap between the purse-seine fishery and the foraging grounds of the penguins and found that overlap was lowest when prey biomass was low, suggesting that competition with the fishery is exacerbated when conditions are poor. I then investigated how the presence of the fishery may result in changes in penguin foraging and prey schooling behaviour using simultaneous prey acoustic surveys with penguin biologging data. Schools were smaller in height and length, and penguins carried out 10% fewer foraging dives when the fishery was present. Consequently, fishing intensity, particularly when the fishery was harvesting sardine, was found to impact penguin foraging effort. Acceleration data also suggested more foraging behaviour occurs when prey biomass is high. Finally, a bioenergetics model was developed to determine the proportion of breeding penguins that are returning from a foraging trip with sufficient energy to successfully rear chicks. Breeding penguins were found to be at their energetic limit with only 50% of individuals expecting to return from foraging trips in an energy surplus. Through simulating a reduction in fishing, the median net energy increased by over 1000 kJ and a further 12% of individuals were in an energy surplus after the 2-day period.

This thesis highlights the effects of fishing on the foraging behaviour of the Critically Endangered African penguin. Fishing and changes in prey availability significantly impacted the amount of foraging behaviour carried out by penguins.

Date of Award	2 Jul 2025
Original language	English
Awarding Institution	University of St Andrews
Supervisor	Debbie JF Russell (Supervisor), Andrew Stuart Brierley (Supervisor), Richard Sherley (Supervisor) & Roland Hudson Proud (Supervisor)