Fisheries bycatch mitigation measures as an efficient tool for the conservation of seabird populations
Résumé
1. The impact of industrial fisheries on marine biodiversity is conspicuous in large
pelagic vertebrate's fisheries bycatch. In seabirds, this led to the decline of many
populations since the 1980s following the rise of global fishing effort. Bycatch
mitigation measures were implemented since the 2000s, but their effects on the
concerned seabird populations remain poorly quantified and understood.
2. We studied the effects of bycatch mitigation measures on the demography of
the white-chinned petrel, one of the most bycatch impacted seabirds whose
populations suffered dramatic declines before the implementation of mitiga-
tion measures. To do so we (a) built multi-event capture–recapture models to
estimate the demographic parameters of a population from Possession Island
(southern Indian Ocean) over 30 years, (b) assessed the effect of climate and
fishery covariates on demographic parameters, (c) built a population matrix
model to estimate stochastic growth rate according to the management in fish-
eries bycatch and (d) estimated changes in breeding population density using
distance sampling data.
3. The population declined from the 1980s to the mid-2000s, while trawl and
longline fisheries occurred with no bycatch mitigation measures. The negative
effects of fishery bycatch through additive mortality and of rat predation on
breeding success were likely the main drivers of this decline.
4. Both modelled population growth rate and observed breeding densities showed
an increase since the mid-2000s. We explained this trend by the improvement
in survival probability following implementation of fishery bycatch mitigation
measures and in breeding success probability with the local control of the rat
population and changes in sea ice conditions on foraging grounds.
5. Synthesis and applications. We provide a holistic approach to assess the effects of
management measures by analysing datasets from sampling methods commonly
employed in seabird studies. Our conclusions should encourage the eradication
of invasive predatory species in seabird breeding areas and the strengthening
of bycatch mitigation measures for the vulnerable seabird species, especially in
international waters, but also the development of such measures considering the other marine large pelagic species threatened by fisheries bycatch (sharks,
rays, turtles and marine mammals) since it could be crucial to avoid populations'
extinction.