Local forage fish abundance influences foraging effort and offspring condition in an endangered marine predator
Campbell, K; Steinfurth, A; Underhill, L; et al.Coetzee, J; Dyer, B; Ludynia, K; Makhado, A; Merkle, D; Rademan, J; Upfold, L; Sherley, R
Date: 20 May 2019
Journal
Journal of Applied Ecology
Publisher
Wiley
Publisher DOI
Abstract
1. Understanding the functional relationship between marine predators and their prey is vital
to inform ecosystem-based management. However, collecting concurrent data on predator
behaviour and their prey at relevant scales is challenging. Moreover, opportunities to study
these relationships in the absence of industrial fishing ...
1. Understanding the functional relationship between marine predators and their prey is vital
to inform ecosystem-based management. However, collecting concurrent data on predator
behaviour and their prey at relevant scales is challenging. Moreover, opportunities to study
these relationships in the absence of industrial fishing are extremely rare.
2. We took advantage of an experimental fisheries closure to study how local prey abundance
influences foraging success and chick condition of Endangered African penguins Spheniscus
demersus in the Benguela Ecosystem.
3. We tracked 75 chick-provisioning penguins with GPS-time-depth devices, measured body
condition of 569 chicks, quantified the diet of 83 breeding penguins and conducted 12 forage
fish hydro-acoustic surveys within a 20 km radius of Robben Island, South Africa, over three
years (2011–2013). Commercial fishing for the penguins’ main prey, sardine Sardinops sagax
and anchovy Engraulis encrasicolus, was prohibited within this 20 km radius during the study
period.
4. Local forage fish abundance explained 60% of the variation in time spent diving for 14
penguins at sea within 2 days of a hydro-acoustic survey. Penguin foraging effort (time spent
diving, number of wiggles per trip, number of foraging dives and the maximum distance
travelled) increased and offspring body condition decreased as forage fish abundance
declined. In addition, quantile regression revealed that variation in foraging effort increased as
prey abundance around the colony declined.
5. Policy implications. Our results demonstrate that local forage fish abundance influences
seabird foraging and offspring fitness. They also highlight the potential for offspring condition
and the mean-variance relationship in foraging behaviour to act as leading indicators of poor
prey abundance. By rapidly indicating periods where forage resources are scarce, these
metrics could help limit seabird-fisheries competition and aid the implementation of dynamic
ocean management
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