Review On The Current Effect Of Discarding On Fish Stocks And Marine Ecosystems; On Data, Knowledge And Models Of Discarding; And Identification Of Knowledge Gaps In All Case Studies

• Main Authors: Feekings, Jordan, Savina, Marie, Ulrich, Clara
• Format: Report
• Language: English
• Published: Zenodo 2017
• Subjects: discards; Landing Obligations; Common Fisheries Policy; Canada; New Zealand; Norway; Iceland
• Online Access: https://dx.doi.org/10.5281/zenodo.1204308; https://zenodo.org/record/1204308

Discards are defined as the part of the catch that is brought on deck only to be returned to the sea. This Deliverable is the result of an extensive litterature review on the state of knowledge regarding the biological, ecological and technical aspects of the discard issue. Additionally, factsheets have been collated for the various DiscardLess case studies regarding the more specific knowledge available for the various regions. The main findings are summarized as follows: Discarding occurs for a number of reasons including low or no commercial values, undersized fish, or the absence of quota. Discards are driven by a variety of factors (sociological, technical, legislative, environmental and biological) which form a complex network of often interwoven causes and effects, and are highly species, fisheries, and areas specific. However, the root cause is the lack of selectivity of fishing gears or operations, notably in trawl fisheries. Methods for reducing discards are often fishery, fleet, or area specific. They can be grouped into two categories: - Improvements to gear selectivity. For trawls, most of the selection happens in the codend, and modifying mesh size and/or shape is the simplest and most commonly used measure to improve size selection. Additional techniques aiming at sorting the catch in the codend according to morphology include selective grids and square mesh panels (or escape windows). Alterations of other parts of the trawls are also explored, as are the use of deterrent such as physical, acoustic, and electronic modifications. In the case of multi-species fisheries, the range of minimum landing sizes (implemented to protect smaller immature individuals) cannot be all harmonised with the selectivity of fishing gears. Short-term economic losses due to reduced marketable catch are identified as the main reason discouraging the uptake of more selective gears. - Temporal and spatial closures. The main objectives are to avoid areas of high juvenile abundance or high by-catch species abundance. While effective, spatial closures can have side effects (e.g. increase of the fishing effort in other places) and low acceptance (do not affect all fishers equally depending on their home ports, preferred fishing grounds or countries). Real Time Closures, i.e. triggered by information gained in real time aboard fishing vessels, provide more flexibility than permanent or seasonal closures, and account for the variability in the timing and location of large bycatch of juveniles. It requires a strong collaboration between managers and the industry, and efficient dissemination of information to fishers. In general, the use of closures is becoming less prescriptive and more incentive based. Discard bans have been implemented in several countries (Norway, Iceland, New Zealand and Canada). In Europe, the obligation to land catches of regulated species is the cornerstone of the 2013 Reform of the Common Fisheries Policy, to be gradually implemented between 2015 and 2019. The retention of discards include additional costs for the industry, related to sorting, storage and landing of unwanted fish, therefore a discard ban should theoretically encourage fishers to develop fishing techniques and strategies to become more selective. Implemented together with a strong monitoring program, it also ensures that more accurate catches are recorded, and subsequently allows more accurate total allowable catches being set. If currently discard size classes are counted against the available species quota, a decrease in overall fishing pressure may also result from such a ban. However, a discard ban will only be effective with extensive monitoring, which may not be economically viable. It might also develop, if not carefully set up, a new market for discards and therefore establish incentives for their capture. Finally, although selective fishing benefits the fisheries (through reduced sorting time, simpler catch handling and processing , and more space on-board for higher valued commercial species), and reduces the overall target species fishing mortality (through reduced catch of the juvenile stages), there is no experimental or theoretical evidence showing that highly selective fishing is the best or least harmful way to extract a sustainable harvest from an ecosystem. It is argued that selective fishing alters the existing community structure, spectrum of biodiversity, and species and size diversity. The question of the desirability and the feasibility of unselective fishing (i.e. ‘balanced harvesting’) is still a highly debated case. Mortality of discarded fish can represent a significant portion of total fishing mortality. Discarded fish can die from damages inflicted during the fishing process (gear, handling on deck…), from predation by seabirds, or midwater/bottom dwelling scavengers, or from the impossibility to return to a suitable habitat. The survival rate of discarded fish varies depending on the species and the fishing technique and is generally unmeasured. It subsequently represents a large source of uncertainty in estimates of fishing mortality worldwide. The effect of discarding on fish population logically depends on the survival rate of discarded individual. Solutions to mitigating discards mortality have been explored, however, the escape of unwanted organisms before hauling should be promoted during fishing, as the mortality of escapees are considerably lower than of discards for a majority of species. There are indications that discarding has altered the ecosystem functioning of some seabirds communities and has negative effects on charismatic and endangered species (such as sea turtles and marine mammals). A reduction in discards may lead to a food shortage for seabirds as well as some scavenger species and possible shifts in species composition. The effect of this shortage depends on the ability of the seabirds and scavengers to compensate by switching to other food sources. This may limit the direct effects on these species, but may also cause unpredictable cascading effects on other species through increased predation and/or competition. Recent and current research focus on the identification of the main scavenging species feeding on discards, and estimate consumption rates using traps or video surveys. In EU, the collection of discards data has been framed in the Data Collection Framework and national sampling program have evolved accordingly. Data are shared and used through the STECF and the ICES. In spite of the resources allocated by the EU and Members states, less than 1% of the fishing trips are sampled because of the high cost of sampling programs. Therefore the discard estimates used in the assessment and management advice for European stocks are considered the best available knowledge, but they remain highly uncertain. In the ICES areas, the integration of discards in stock assessment has improved, and in 2013, 26 stocks included discards in their assessment. ICES has generalised the basis of advice as being catch advice, instead of the previously used landing advice, and advice sheets include a mention on discard estimates either quantitative or qualitative. In the context of the DiscardLess project, ecosystem models allow to study the interactions between the effect of the removal of the flow of discards to the ecosystem, as well as the effect of new fishing strategies on fish stocks. Five types of models will be used in the project: Osmose, Ecopath w Ecosim, Atlantis, StrathE2E and ISIS-Fish, distributed over 7 Case studies. They differ in their assumption and settings as well as in their representation of the discarding process and the fate of discards.