Influence of management practices and of scavenging seabirds on availability of fisheries discards to benthic scavengers

Furness, Robert W.; Edwards, Ann E.; Oro, Daniel

doi:10.3354/meps07191

Cited by 49 publications

(38 citation statements)

References 21 publications

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“…For these species, fishery waste often has higher energy content and digestibility than their natural prey ( Furness et al 2007). Some populations consequently become dependent upon fishery wastes, to the point that a reduction in industrial fishing effort can lead to breeding failures (Oro et al 1995).…”

Section: Discussionmentioning

confidence: 99%

A junk-food hypothesis for gannets feeding on fishery waste

et al. 2008

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Worldwide fisheries generate large volumes of fishery waste and it is often assumed that this additional food is beneficial to populations of marine top-predators. We challenge this concept via a detailed study of foraging Cape gannets Morus capensis and of their feeding environment in the Benguela upwelling zone. The natural prey of Cape gannets (pelagic fishes) is depleted and birds now feed extensively on fishery wastes. These are beneficial to non-breeding birds, which show reduced feeding effort and high survival. By contrast, breeding gannets double their diving effort in an attempt to provision their chicks predominantly with high-quality, live pelagic fishes. Owing to a scarcity of this resource, they fail and most chicks die. Our study supports the junk-food hypothesis for Cape gannets since it shows that non-breeding birds can survive when complementing their diet with fishery wastes, but that they struggle to reproduce if live prey is scarce. This is due to the negative impact of low-quality fishery wastes on the growth patterns of gannet chicks. Marine management policies should not assume that fishery waste is generally beneficial to scavenging seabirds and that an abundance of this artificial resource will automatically inflate their populations.

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Section: Discussionmentioning

confidence: 99%

A junk-food hypothesis for gannets feeding on fishery waste

et al. 2008

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“…seabirds (Furness et al 2007), fishes, crustaceans and gastropods. The composition of scavenger assemblages may vary considerably with habitat type (Ramsay et al 1997).…”

Section: Responses Of Scavengers To Fisheries Carrionmentioning

confidence: 99%

“…The outcome of interactions over carrion may be related to competitive ability that is also influenced by the background density of a particular species (Ramsay et al 1997). Accordingly, the responses of different scavenger species to increasing inputs of carrion may vary between habitats, and we might expect to see different population-level responses at a habitat scale that is smaller than the scale applying to scavenging seabirds (Furness et al 2007). …”

Section: Responses Of Scavengers To Fisheries Carrionmentioning

confidence: 99%

“…Nevertheless, there is significant bias introduced into studies that examine posttrawl survival in the absence of natural predators, which can lead to greatly under-estimated mortality rates . A large proportion of the discarded non-commercial or undersized fish is eaten by seabirds (Furness et al 1988, Camphuysen et al 1993, the number taken varying according to the species discarded, as most seabirds eat roundfish in preference to flatfish (Furness 1996, 2003, Furness et al 2007). It has been suggested that increases in the population sizes of some scavenging seabirds can be linked (in part) to increased food availability in the form of fisheries discards (Furness et al 1988).…”

Section: How Much Carrion Is Produced and Where Does It Go?mentioning

confidence: 99%

“…Those discards not eaten by seabirds will sink through the water column where some may be eaten by cetaceans and fishes (Hill & Wassenburg 1990); the remainder sink to the sea bed where they become available as food for benthic scavengers. In the North Sea, it is considered that approximately half of the discarded material from trawlers sinks to the seabed, but this varies from one region to another (Garthe et al 1996, Furness et al 2007.…”

Section: How Much Carrion Is Produced and Where Does It Go?mentioning

confidence: 99%

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Food subsidies from fisheries to continental shelf benthic scavengers

Kaiser¹,

Hiddink²

2007

Mar. Ecol. Prog. Ser.

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Fisheries generate carrion as a result of material discarded at sea from fishing boats, and as a result of the direct mortality of organisms on the seabed that is caused by the bottom trawling gears. It is unclear whether the increases in the population sizes in scavenging seabirds that have been partially attributed to discarding practices might be mirrored in populations of benthic scavengers. We used a previously published and field-validated, size-based model to calculate the effects of bottom fishing on benthic invertebrate production and production of invertebrate carrion at the seabed in the North Sea. This estimate was combined with previously published estimates of discarded fish carrion that reaches the seabed. Fishing decreases benthic biomass; this means that benthic production is also reduced. In this process, fishing increases production in the short term (2 to 3 d) by generating carrion. However, the production of carrion only compensates for 22% of the reduction in production. Calculations of ash free dry weight of carrion produced per unit area were similar to other previous estimates for the North Sea, which indicated that fisheries-generated carrion was sufficient to sustain benthic carnivores for only approximately 3 d yr

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Two lenses for exploring relationships between seabirds and fishers: Unveiling reciprocal contributions

Ojeda,

Morello,

Suazo

et al. 2024

People and Nature

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Reciprocal relationships between fishers and marine life have been documented in Indigenous fishing contexts, but there are few case studies that describe the mechanisms of such relationships, and even fewer that explore other contexts, such as that of artisanal fishers in Latin American countries. We studied the artisanal hake fishery in the sub‐Antarctic channels of Chilean Patagonia, a global hotspot for albatross and petrel diversity. We aimed to uncover nature's contributions to hake fishers and, reciprocally, the potential fishers' contributions to marine life with a particular emphasis on seabirds. We adopted a bifocal observational strategy. From a human perspective, ethnographic methods (e.g., semi‐structured interviews) are analysed with Nature's Contributions to People and reciprocal contribution frameworks. From the seabirds' view, we assessed offal consumption through experimental and observational methods. We randomly threw offal items into the sea and observed the seabird responses (whether they consumed offal). Hake fishers' relationships with the marine environment are multidimensional, particularly with seabirds. Based on fishers' perceptions, we identified four key contributions of seabirds to humans: they serve as value indicators of fishing distribution and concentration areas, offer companionship and recreation during fishing activities, enhance scenic emotionality through the presence of albatrosses and assist in the function of sea cleaning. In reciprocal contributions, artisanal fishers viewed hake offal as a beneficial food source for the seabirds, especially the liver. Fishers described that fishing in the right way can reduce bycatch and effort. The fishers' main contribution to seabirds is through offering them the offal of hake catches. We observed that seabirds consumed hake liver 99% of the time, while they consumed stomach less frequently (24%). We identified that southern giant petrels and black‐browed albatrosses consumed more liver, while kelp gulls ate more stomach. The liver comprises 51.6% fat, essential for high trophic level marine predators such as black‐browed albatrosses. Adopting reciprocal contributions and NCP served as a catalyst for understanding fishers' positive actions but also is a promoter to research multiple views of nature–human relationships in fishing settings. Values of nature, like reciprocity, could enrich ecosystem‐based management strategies. Read the free Plain Language Summary for this article on the Journal blog.

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Influence of management practices and of scavenging seabirds on availability of fisheries discards to benthic scavengers

Cited by 49 publications

References 21 publications

A junk-food hypothesis for gannets feeding on fishery waste

A junk-food hypothesis for gannets feeding on fishery waste

Food subsidies from fisheries to continental shelf benthic scavengers

Two lenses for exploring relationships between seabirds and fishers: Unveiling reciprocal contributions

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