Bycatch

Deutsch: Beifang / Español: Captura incidental / Português: Captura acessória / Français: Prise accessoire / Italiano: Cattura accessoria

Bycatch refers to the unintended capture of non-target species during commercial fishing operations. It represents a significant ecological and economic challenge in marine resource management, as it often involves juvenile fish, endangered species, or organisms with no commercial value. The phenomenon is closely linked to fishing gear selectivity, spatial-temporal fishing patterns, and regulatory frameworks governing fisheries.

General Description

Bycatch occurs when fishing gear, such as trawls, gillnets, longlines, or purse seines, captures species that are not the primary target of the fishing operation. These incidental catches may include fish, marine mammals, sea turtles, seabirds, and benthic organisms. The composition and volume of bycatch vary depending on the fishing method, gear type, and geographic region. For example, shrimp trawling in tropical waters is notorious for high bycatch rates, often exceeding the weight of the target shrimp by a factor of five to ten (see FAO, 2020).

The ecological consequences of bycatch are profound. Non-target species may suffer high mortality rates, either directly from the fishing process or indirectly due to stress, injury, or delayed release. Endangered species, such as sea turtles or certain shark populations, are particularly vulnerable, as even low levels of bycatch can impede recovery efforts. Additionally, bycatch can disrupt marine food webs by removing key predators or prey species, leading to cascading effects on ecosystem structure and function. Economically, bycatch represents a loss of potential revenue for fishers, as well as increased operational costs due to the need to sort, discard, or process unwanted catches.

Technical Details

Bycatch is quantified using metrics such as the bycatch-to-landing ratio, which compares the weight or number of non-target species to the target catch. Another key indicator is the discard rate, which measures the proportion of the total catch that is returned to the sea, often dead or dying. The Food and Agriculture Organization of the United Nations (FAO) defines discards as "that portion of the catch which is not retained on board during fishing operations and is returned to the sea" (FAO, 1996). Bycatch mitigation strategies focus on improving gear selectivity, modifying fishing practices, and implementing spatial or temporal closures to protect vulnerable species.

Gear modifications, such as turtle excluder devices (TEDs) in shrimp trawls or circle hooks in longline fisheries, have proven effective in reducing bycatch of specific taxa. For instance, TEDs can reduce sea turtle bycatch by up to 97% in shrimp trawl fisheries (see NOAA Fisheries, 2019). Similarly, acoustic deterrent devices (pingers) have been used to reduce marine mammal bycatch in gillnet fisheries. However, the effectiveness of these measures depends on proper implementation, enforcement, and adaptation to local conditions.

Norms and Standards

International agreements and regional fisheries management organizations (RFMOs) have established frameworks to address bycatch. The FAO Code of Conduct for Responsible Fisheries (1995) provides voluntary guidelines for reducing bycatch and discards, while the United Nations Convention on the Law of the Sea (UNCLOS) obligates states to protect and preserve the marine environment. Regional bodies, such as the International Commission for the Conservation of Atlantic Tunas (ICCAT) or the Western and Central Pacific Fisheries Commission (WCPFC), set binding measures for member states, including bycatch limits and gear restrictions.

Abgrenzung zu ähnlichen Begriffen

Bycatch is often conflated with terms such as "discards" or "incidental catch," but these concepts are not synonymous. Discards refer specifically to the portion of the catch that is returned to the sea, regardless of whether it was targeted or not. Bycatch, in contrast, encompasses all non-target species captured, including those retained for sale or personal use. Incidental catch is a broader term that may include bycatch but also covers unintended captures in non-fishing contexts, such as entanglement in marine debris.

Application Area

• Commercial Fisheries: Bycatch is a critical issue in large-scale fisheries, particularly those targeting shrimp, tuna, or groundfish. High bycatch rates can lead to regulatory interventions, such as gear restrictions or seasonal closures, to protect vulnerable species.
• Small-Scale and Artisanal Fisheries: While often perceived as more sustainable, small-scale fisheries can also generate significant bycatch, particularly when using non-selective gear like gillnets. Community-based management approaches are increasingly used to address bycatch in these contexts.
• Recreational Fisheries: Bycatch in recreational fishing, such as the capture of undersized or non-target fish, can contribute to localized depletion of stocks. Catch-and-release practices and size limits are common mitigation measures.
• Research and Monitoring: Bycatch data are essential for assessing the health of marine ecosystems and the effectiveness of fisheries management measures. Observer programs, where trained personnel monitor fishing operations, are a key tool for collecting bycatch data.

Well Known Examples

• Shrimp Trawling in the Gulf of Mexico: Shrimp trawls in this region are associated with high bycatch rates, including juvenile red snapper and sea turtles. The implementation of TEDs has significantly reduced sea turtle bycatch, but concerns remain about the sustainability of the fishery.
• Longline Fisheries for Tuna and Swordfish: These fisheries are known for bycatch of seabirds, sea turtles, and sharks. Mitigation measures, such as setting lines at night or using bird-scaring lines, have reduced seabird bycatch by up to 80% in some regions (see ACAP, 2021).
• Gillnet Fisheries in the Baltic Sea: Bycatch of harbor porpoises in gillnets has been a long-standing issue in this region. The use of pingers has reduced porpoise bycatch, but enforcement and compliance remain challenges.
• Purse Seine Fisheries for Tuna: The use of fish aggregating devices (FADs) in purse seine fisheries increases bycatch of juvenile tuna, sharks, and other species. FAD-free fishing zones and time-area closures have been implemented to mitigate these impacts.

Risks and Challenges

• Ecological Impacts: Bycatch can lead to the depletion of non-target species, including endangered or protected species. For example, the vaquita, a critically endangered porpoise, is threatened by bycatch in gillnet fisheries in the Gulf of California.
• Economic Costs: Bycatch reduces the efficiency of fishing operations by increasing fuel consumption, labor costs, and gear wear. It can also lead to market restrictions or bans if non-target species are protected under international agreements.
• Regulatory Complexity: Bycatch management requires coordination among multiple stakeholders, including fishers, scientists, policymakers, and conservation organizations. Conflicting priorities and limited enforcement capacity can hinder effective implementation of mitigation measures.
• Data Limitations: Accurate bycatch data are often lacking, particularly in small-scale or data-poor fisheries. Observer programs and electronic monitoring systems are expensive and logistically challenging to implement, leading to gaps in knowledge.
• Climate Change: Shifting species distributions due to climate change may alter bycatch patterns, making it difficult to predict and manage incidental catches. For example, warming waters may increase the overlap between target and non-target species in certain regions.

Similar Terms

• Discards: The portion of the catch that is returned to the sea, either dead or alive. Discards can include both target and non-target species and are often driven by market conditions, regulatory requirements, or size limits.
• Incidental Catch: A broader term that encompasses bycatch but also includes unintended captures in non-fishing contexts, such as entanglement in marine debris or collisions with vessels.
• Ghost Fishing: The capture of marine organisms by abandoned, lost, or discarded fishing gear. Unlike bycatch, ghost fishing occurs independently of active fishing operations and can persist for years or decades.
• Target Catch: The species or group of species that a fishing operation is intentionally designed to capture. Target catch is the primary focus of fisheries management and is subject to quotas, size limits, and other regulatory measures.

Summary

Bycatch is a multifaceted issue that poses significant ecological, economic, and regulatory challenges in marine fisheries. It encompasses the unintended capture of non-target species, including fish, marine mammals, sea turtles, and seabirds, and is influenced by fishing gear selectivity, spatial-temporal fishing patterns, and management frameworks. Mitigation strategies, such as gear modifications, spatial closures, and observer programs, have shown promise in reducing bycatch, but their effectiveness depends on proper implementation and enforcement. Addressing bycatch requires a collaborative approach involving fishers, scientists, policymakers, and conservation organizations to balance the needs of fisheries with the preservation of marine ecosystems.

--