Discards from fisheries are the most important predictable anthropogenic food subsidies (PAFS) that are being incorporated into marine ecosystems. Changes on their availability and predictability can help us to understand the role that food availability (i.e. an important indicator of the carrying capacity) plays at different ecological levels, from individual fitness to community dynamic and ecosystem functioning. For several reasons, seabirds are an excellent model for evaluating the ecological effects arising from a lack of discards: 1) they are one of the most important discard scavengers, 2) they are easy to monitor and 3) they are apical predators are globally distributed, which makes them suitable health indicators of ecosystems. Here we review the existing information on seabird-discard interactions to identify the main knowledge gaps and propose new challenges for improving our understanding of the general role of food availability. We conclude that the new policies on the ban of fishery discards that are being progressively implemented in the European Union, Norway, Chile and New Zealand offer a suitable experimental scenario for improving our understanding of how a large decrease in the carrying capacity may alter demographic parameters such as survival, dispersal and reproduction, the resilience of populations against perturbations and the role of individual specialization in the foraging process.
Los descartes pesqueros constituyen el recurso antropogénico predecible (PAFS) más importante que está siendo incorporado en los ecosistemas marinos. Cambios en su disponibilidad y predictibilidad pueden ayudar a entender mejor el papel ecológico de la disponibilidad de alimento (i.e. un importante indicador de la capacidad de carga) a diferentes niveles, desde la eficacia biológica individual hasta la dinámica de poblaciones o el funcionamiento de los ecosistemas. Las aves marinas constituyen un modelo excelente para estudiar los efectos ecológicos derivados de la falta de descartes por diversas razones: las aves marinas: 1) se encuentran entre los principales carroñeros de descartes, 2) son fáciles de monitorear y 3) son depredadores apicales globalmente distribuidos, lo cual las convierte en buenas indicadoras de la salud del ecosistema. En el presente estudio revisamos la información existente sobre las interacciones ecológicas entre las aves marinas y los descartes de la pesca, con el fin de identificar los principales vacíos de conocimiento y plantear retos futuros de cara a mejorar nuestra comprensión sobre el papel ecológico que tiene la disponibilidad de alimento. Concluimos que las políticas actuales en materia de prohibición de descartes que están siendo implementadas en la Unión Europea, Noruega, Chile o Nueva Zelanda, ofrecen un escenario ideal para mejorar nuestra comprensión sobre cómo una reducción de la capacidad de carga puede alterar parámetros demográficos tales como la supervivencia, la dispersión y la reproducción, la resiliencia de las poblaciones frente a perturbaciones y el papel de la especialización individual en el proceso de forrajeo.
The large amount of discards in the form of offal that are generated daily by industrial and artisanal fisheries and thrown into the sea constitutes one of the most important and predictable anthropogenic food subsidies (PAFS) that are being incorporated into marine ecosystems worldwide (
Changes in the availability and predictability of fishery discards as PAFS can help to understand the ecological role that food availability (i.e. carrying capacity) have at multiple ecological levels, including individual fitness, community dynamics and ecosystem functioning.
Seabirds constitute an excellent model for evaluating the ecological effects arising from a lack of PAFS for several reasons: seabirds are 1) one of the most important discard scavengers at a global level, 2) easy to monitor (because they breed on land) and 3) apical predators with a global distribution, which makes them suitable bioindicators of ecosystem health. The link between seabirds and fishery discards has been reviewed in several studies (
Here we review current knowledge on the global ecological interactions between seabirds and fishery discards in order to identify the main knowledge gaps and propose new challenges for improving our understanding of the ecological role that food availability has for populations, communities and ecosystems.
We considered the information available in SCI journals (6 June 2017) on the Web of Science platform (WOS; Clarivate Analytics). We first selected articles with concomitant terms: [(
A total of 166 studies addressing up to 15 different ecological effects arising from seabird-discard interactions were selected and subsequently reviewed (
Family | Diet | Foraging Ecology | Energy requirements | Bycatch | Competition | Reproduction | Population dynanmics | Body condition | Pollutants | Predatory interactions | Migration patterns | Parasitism | Survival | Ecosystem level | Resilience | Dispersal |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Laridae (102 spp.) | 25 | 12 | 13 | 11 | 15 | 4 | 9 | 3 | 6 | 3 | 0 | 4 | 1 | 0 | 2 | 1 |
Procellaridae (88 spp.) | 11 | 6 | 3 | 14 | 1 | 1 | 0 | 0 | 2 | 1 | 0 | 0 | 0 | 1 | 0 | 0 |
Diomedeidae (21 spp.) | 19 | 19 | 5 | 38 | 5 | 5 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
Sulidae (10 spp.) | 50 | 20 | 20 | 20 | 20 | 10 | 20 | 20 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
Stercorariidae (7 spp.) | 29 | 29 | 14 | 14 | 14 | 14 | 0 | 14 | 14 | 14 | 14 | 0 | 0 | 0 | 0 | 0 |
Phalacrocoracidae (37 spp.) | 5 | 0 | 3 | 3 | 3 | 0 | 0 | 0 | 3 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
Hydrobatidae (25 spp.) | 8 | 4 | 4 | 12 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
Fregatidae (5 spp.) | 40 | 0 | 0 | 0 | 20 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
Alcidae (24 spp.) | 17 | 0 | 17 | 0 | 0 | 0 | 0 | 0 | 0 | 8 | 0 | 0 | 0 | 0 | 0 | 0 |
Spheniscidae (19 spp.) | 0 | 0 | 0 | 5 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
Chionidae (2 spp.) | 0 | 0 | 0 | 50 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
Ardeidae (68 spp.) | 0 | 0 | 0 | 0 | 3 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
Cathartidae (7 spp.) | 0 | 0 | 0 | 0 | 29 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
Pelecanidae (8 spp.) | 13 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
Few studies quantified the effect of discards on seabirds’ ecology, and most (68%) focused on the amount/type of fishing discard in seabirds’ diet and on species attendance rate. In particular, we found that for the most important scavenger seabirds (
Fishery discards may have important ecological effects on demographic parameters and on the resilience of scavenger populations. However, these effects have never been evaluated for most of species scavenging on fishery discards. A few studies have shown that fishery discards, like other PAFS, can increase average individual survival and reproductive output in several scavenger species (
The availability of fishery discards could have important effects on dispersal of several species among breeding colonies, with potential consequences for the structure of communities and ecosystems. However, these effects remain unstudied for most species directly and indirectly associated with fishery discards.
Fishery discards may improve average breeding success in scavenger seabirds such as Larids (
Food availability is known to increase population resilience after perturbations (see e.g.
Individual specialization in foraging strategies may have important ecological implications by altering the dynamics of populations and the structure of communities and ecosystems (
A reduction in fishery discards is expected to cause a population decrease of marine scavenger organisms (including generalist seabirds), but they can also trigger cascading effects through a change in nutrients in the water column. The general lack of studies addressing the potential impacts of fishery discards at an ecosystem level makes it difficult to predict the real ecological consequences of a ban of discards. For example, a population decrease of scavenger seabirds would alter the soil composition and the structure of animal and plant communities in coastal regions (
Several large areas of the world where interactions between discards from fisheries and marine scavengers could be potentially important have received little or no attention. Furthermore, most important ecological effects that fishery discards have on marine ecosystems have never or seldom been studied. Considering this, the new policies on the ban of fishery discards, which are being progressively implemented in the European Union, Norway, Chile and New Zealand, offer a suitable experimental scenario for improving our understanding of how food availability (e.g. carrying capacity) can alter the dynamics of populations and the structure of communities and ecosystems. The example given at the Ebro Delta (e.g.
Funds for this study were supplied by the Spanish Ministry of Economy and by the European Social Fund (grant ref.: CGL2013-42203-R). The study also received funding from the European Commission’s Horizon 2020 Research and Innovation Programme under Grant Agreement no. 634495 for the project Science, Technology, and Society Initiative to Minimize Unwanted Catches in European Fisheries (MINOUW). MG and ASA are supported by postdoctoral contracts co-funded by the Regional Government of the Balearic Islands and the European Social Fund. Two reviewers helped to improve the manuscript.
The following supplementary material is available through the online version of this article and at the following link:
Table S1. – Seabird species identified as scavengers of fishery discards according to reviewed studies and number of studies considering each ecological effect derived from seabird-discard interactions.