While pole and line fishing is highly sustainable and minimizes bycatch, its primary disadvantages include low economic efficiency, high labor intensity, and reliance on live bait, which can lead to overfishing of smaller bait species. Additionally, it is less productive than industrial methods and can cause localized stock and reef damage due to bait harvesting. Only 7% of all tuna caught globally can be attributed to pole and line fishing.
Key Disadvantages of Pole and Line Fishing:
• Low Efficiency and High Cost: Compared to industrial methods like purse seining, pole and line fishing has lower catch volumes, making it less economically viable. The labor-intensive nature means higher costs per unit of fish.
• Live Bait Dependency: The method relies on harvesting large amounts of live bait (e.g., sardines) from coral reefs, causing stress on reef ecosystems and potential depletion of baitfish populations.
• Environmental Impact (Gear & Pollution): While generally eco-friendly, broken or discarded, non-biodegradable fishing lines can create marine pollution and endanger marine life.
• Operational Challenges: Increased fuel costs and the need for large, specialized, and often expensive vessels can make operations difficult in fluctuating markets.
• Skill Dependence: It requires high skill and physical stamina from the crew, making it less productive for inexperienced operators.
• Social Conditions on board: The small scale pole and line boats hardly ever have proper crew quarters, or sanitary facilities. This creates a problem during multi-day trips.
• Lack of Freezing Facility: smaller pole and line vessels typically have no freezing facilities, but chill the fish right after the catch in ice. This can lead to higher chances of histamine development.
No onboard observer : due to the high amount of small scale vessels, it is no possible to have independent onboard observers, which is common on larger industrial purse seiners.
Purse Seining on FADs
Fishing on floating objects (FADs or natural logs) generally yields higher non-tuna catch rates. Globally, the non-tuna catch rate is estimated at 1.4% of the target catch (dropping to 0.92% if minor tunas and bonitos are excluded). Although this percentage is low for an industrial fishery, it still involves vulnerable or Endangered, Threatened, and Protected (ETP) species that require mitigation.
Sea Turtles
Turtles are encountered in both FS and FAD sets. Observer data indicates catch rates of:
• FADs: 0.046 turtles per set.
• Free Schools: 0.037 turtles per set.
Actual mortality is very low, as turtles caught alive are easily released—a primary mitigation measure required by RFMOs. However, “ghost fishing” (entanglement in abandoned gear) remains a risk if FADs use netting. To eliminate this, RFMOs have implemented prohibitions on netting in FAD construction.
Sharks and Rays
FAD operations capture several shark species, including silky and oceanic whitetip sharks, which have shown declining abundance. While the shark-to-tuna ratio is small (less than 0.5% by weight), shark catches on floating objects are two to six times higher than on free schools.
• Total Composition: Sharks and rays make up 0.19% to 0.44% of total FAD catches.
• Rays: Interestingly, mobulid rays are more frequently caught in free-swimming school sets than in FAD sets.
• Mitigation: Best practice release techniques are applied to both fishing modes. Prohibiting large-mesh netting in FAD designs further prevents shark entanglement.
Other Non-Target Species
• Seabirds: Mortality in FAD operations is almost nonexistent.
• Finfish: FAD fishing results in significant catches of bonitos and minor tunas. These species are generally resilient and productive, so their abundance is not currently threatened. The primary concern is waste; except in parts of the Atlantic where they are sold locally, these fish are often discarded at sea to save storage space for more valuable tuna.
Overview of Purse Seine Fishing
Purse seining is the primary method for tuna fishing globally, focusing largely on tropical species: skipjack, bigeye, and yellowfin. While bluefin tuna are also caught this way, they represent less than 1% of the total purse seine catch.
Fishing strategies generally fall into three categories:
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FAD Sets: Utilizing Fish Aggregating Devices (both drifting and anchored).
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Free-Swimming School (FS) Sets: Targeting unassociated schools of tuna.
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Tuna-Dolphin Associations: Specific to certain regions where tuna and dolphins congregate.
Most fleets operate opportunistically. A vessel specializing in FADs will still set on a free school if the chance arises during transit, and vice versa. Under the current MSC Fishery Standard, “compartmentalization”—the practice of excluding specific set types from a Unit of Assessment (UoA)—is not permitted. Consequently, the combined impact of all set types is evaluated during certification.
Purse Seining on Free Schools
Setting on free-swimming schools typically results in lower bycatch rates of non-target species. The nature of these sets often depends on regional and seasonal factors:
• Regional Differences: In the Atlantic and Indian Oceans, FS sets often target larger yellowfin. In the Western Central Pacific Ocean (WCPO), FS sets on skipjack are more common due to specific oceanographic conditions.
• Seasonality: Usage of FS sets fluctuates based on natural tuna availability or regulatory requirements, such as mandatory seasonal FAD closures imposed by Regional Fisheries Management Organizations (RFMOs).
While both FAD and FS strategies result in some bycatch, data from independent scientific observers show that FAD sets consistently have higher impacts. In some regions, the catch of non-tuna species in FAD sets is two to four times higher than in FS sets.
Bycatch Comparison (By Weight)
|
Ocean Region |
Free School (FS) Bycatch |
FAD Bycatch |
|
Western Pacific |
0.3% |
1.1% |
|
Eastern Pacific |
0.7% |
1.4% |
|
Indian Ocean |
0.8% |
3.0% |
|
Atlantic Ocean |
1.8% |
7.4% |