A Bird’s Eye View of Discard Reforms: Bird-Borne Cameras Reveal Seabird/Fishery Interactions

Commercial capture fisheries produce huge quantities of offal, as well as undersized and unwanted catch in the form of discards. Declines in global catches and legislation to ban discarding will significantly reduce discards, but this subsidy supports a large scavenger community. Understanding the potential impact of declining discards for scavengers should feature in an eco-system based approach to fisheries management, but requires greater knowledge of scavenger/fishery interactions. Here we use bird-borne cameras, in tandem with GPS loggers, to provide a unique view of seabird/fishery interactions. 20,643 digital images (one min 21) from ten bird-borne cameras deployed on central place northern gannets Morus bassanus revealed that all birds photographed fishing vessels. These were large (>15 m) boats, with no small-scale vessels. Virtually all vessels were trawlers, and gannets were almost always accompanied by other scavenging birds. All individuals exhibited an Area-Restricted Search (ARS) during foraging, but only 42% of ARS were associated with fishing vessels, indicating much 'natural' foraging. The proportion of ARS behaviours associated with fishing boats were higher for males (81%) than females (30%), although the reasons for this are currently unclear. Our study illustrates that fisheries form a very important component of the prey-landscape for foraging gannets and that a discard ban, such as that proposed under reforms of the EU Common Fisheries Policy, may have a significant impact on gannet behaviour, particularly males. However, a continued reliance on 'natural' foraging suggests the ability to switch away from scavenging, but only if there is sufficient food to meet their needs in the absence of a discard subsidy.

The survival of discardedSepia officinalisin the English Channel

Cuttlefish are currently the highest yielding cephalopod group harvested in the north-east Atlantic. English Channel cuttlefish show seasonal migrations to and from deep offshore wintering grounds, which results in a large number of smaller cuttlefish within the offshore stocks, some of which are caught by trawlers. Discarding small cuttlefish from trawls may give them the opportunity to migrate inshore and spawn, but only if they survive. This study examined survival rates of small (<15-cm dorsal mantle length) cuttlefish caught on board a commercial beam trawler. Overall, 31% of the small cuttlefish caught remained alive by the time they reached the sorting table (immediate survival rate). This survival rate dropped to 16% after specimens were subsequently held in an on-board aquarium system for up to 72 h (short-term survival rate). Measures that reduce the capture of small cuttlefish in the first place and/or increase their survival could potentially benefit the stocks.

The survival of discardedSepia officinalisin the English Channel

Cuttlefish are currently the highest yielding cephalopod group harvested in the north-east Atlantic. English Channel cuttlefish show seasonal migrations to and from deep offshore wintering grounds, which results in a large number of smaller cuttlefish within the offshore stocks, some of which are caught by trawlers. Discarding small cuttlefish from trawls may give them the opportunity to migrate inshore and spawn, but only if they survive. This study examined survival rates of small (<15-cm dorsal mantle length) cuttlefish caught on board a commercial beam trawler. Overall, 31% of the small cuttlefish caught remained alive by the time they reached the sorting table (immediate survival rate). This survival rate dropped to 16% after specimens were subsequently held in an on-board aquarium system for up to 72 h (short-term survival rate). Measures that reduce the capture of small cuttlefish in the first place and/or increase their survival could potentially benefit the stocks.