Communication

Demographic impacts of fisheries on three species of Mediterranean seabirds

  • Bycatch mortality from fisheries is clearly among the most serious global threats for marine ecosystems, affecting a wide range of top predators.
  • Here we estimate for the first time both bycatch mortality rates and their population-level effects on three endemic and vulnerable Mediterranean taxa: scopoli’s shearwater, mediterranean shag and audouin’s gull.

 

 

Foto: (1) Audouin’s gull. (2) Scopoli’s shearwater (Autor: Pep Arcos).

 

Esporles, 31 de marzo de 2017. Fisheries have an enormous economic importance but reconciling their socio-economic features with the conservation and sustainability of marine ecosystems presents major challenges

 

Bycatch mortality from fisheries is clearly among the most serious global threats for marine ecosystems, affecting a wide range of top predators. Recent estimates report ca. 200,000 seabirds killed annually by bycatch in European waters. However there is an urgent need to rigorously estimate actual mortality rates and quantify effects of bycatch on populations. The Mediterranean Sea is one of the most impacted regions.

 

Here we estimate for the first time both bycatch mortality rates and their population-level effects on three endemic and vulnerable Mediterranean taxa:

  • scopoli’s shearwater
  • mediterranean shag
  • audouin’s gull

that die in different types of fishing gears:

  • longlines
  • gillnets
  • sport trolling

 

We use multi-event capture-recapture modeling to estimate crucial demographic parameters, including the probabilities of dying in different fishing gears. We then build stochastic demography models to forecast the viability of the populations under different management scenarios.

 

Longline bycatch was particularly severe for adults of Scopoli’s shearwaters and Audouin’s gulls (ca. 28% and 23% of total mortality respectively) and also for immature gulls (ca. 90% of mortality).

 

Gillnets had a lower impact, but were still responsible for ca. 9% of juvenile mortality on shags.

 

Sport trolling only slightly influenced total mortality in gulls.

 

Bycatch mortality has high population-level impacts in all three species, with shearwaters having the highest extinction risk under current mortality rates. Different life history traits and compensatory demographic mechanisms between the three species are probably influencing the different bycatch impact: for shearwaters, urgent conservation actions are required to ensure the viability of their populations. Results will be very useful for guiding future seabird conservation policies and moving towards an ecosystem-based approach to sustainable fisheries management.

 


Font: IMEDEA (UIB-CSIC)

More information: Varying demographic impacts of different fisheries on three Mediterranean seabird species