Abstract
Fisheries bycatch continues to drive the decline of many threatened marine species such as seabirds, sharks, marine mammals, and sea turtles. Management frameworks typically address bycatch with fleet-level controls on fishing. Yet, individual operators differ in their fishing practices and efficiency at catching fish. If operators have differing abilities to target species, they should also have differing abilities to anti-target bycatch species. We analyse variations in threatened species bycatch among individual operators from five industrial fisheries representing different geographic areas, gear types, and target species. The individual vessel is a significant predictor of bycatch for 15 of the 16 species-fishery interactions, including species that represent high or low costs to fishers, or have economic value as potentially targeted byproducts. Encouragingly, we found high performance operators in all five fishing sectors, including gears known for high bycatch mortality globally. These results show the potential to reduce negative environmental impacts of fisheries with incentive-based interventions targeting specific performance groups of individuals. Management of threatened species bycatch Incidental catch of marine animals in fishing gear ("bycatch") has been recognized as a serious problem for several decades. Despite widespread efforts to address it, bycatch remains one of the most pressing issues in fisheries management today, especially for threatened or protected species such as sea turtles, seabirds, elasmobranchs, and marine mammals1,2. The most common approaches to reducing bycatch have been command-and-control measures implemented across the entire fleet or industry, such as technology requirements or total allowable catch for particular bycatch species3,4. These conventional approaches have been far from universally successful, and have often performed worse in practice than models and trials suggested, even when the same approach is translated to a similar fishery5. The Skipper Effect Managing bycatch is a problem of fishing efficiency. Although management frameworks typically treat fishing fleets as a unit, several studies suggest that the skill of individual operators (the "skipper effect") could be a driver of important and unexplained variations in fishing efficiency. A skipper's skill is some combination of managerial ability, experience and knowledge of the environment, ability to respond to rapidly changing information and conditions at sea, and numerous other factors that are difficult to describe or record6. There is ongoing debate about the key components of operator skill and its importance in different contexts, such as different gears or technical advancement of fisheries7–10. Yet, numerous studies show consistent variation in target catch rates among anglers, skippers, or fishing vessels that is not explained by environmental variables or economic inputs7,11−13. This includes technically advanced and homogeneous fleets where a skipper's skill would seemingly be less important14. Previously, the skipper effect has been explored in relation to fishing efficiency and profitability (effort and target catch). However, if fishers have differing abilities to catch species they want, it follows that they would also have variable skill at avoiding unwanted species. Untangling the skipper effect is difficult without very detailed data, which are often not available for target catch and are extremely rare for bycatch. We capitalize on a rare opportunity to compare multiple high-resolution fisheries datasets that have information about both target and bycatch. We use fisheries observer data from five Australian Commonwealth fisheries sectors to answer three key questions: 1) Is there significant and predictable variation among operators in their target to bycatch ratios? We hypothesize that there are characteristics at the operator level that lead some vessels to perform worse than others on a consistent basis, and that operator skill is an important factor driving variations in bycatch across fishing fleets; 2) Does the pattern hold across species, gear types, and fisheries? We predict that, irrespective of the bycatch context, there are high performing operators that are able to avoid bycatch while maintaining high target catch; and 3) Does skipper skill transfer across species?” We posit that certain types of bycatch are inherently more difficult to avoid but expect to find correlations between bycatch rates, indicating that a skipper's ability to avoid one species extends to other types of bycatch. If these hypotheses hold true, then there exists untapped potential to reduce bycatch without imposing additional controls on fishing effort and gear. This would support an alternative approach to framing management questions such as those around threatened species bycatch. It may be that it is not a random event across a fishery, but in fact is an issue of particular low performance operators. In this case, measures aimed directly at those individual operators could be an opportunity to make considerable progress towards reducing threatened species bycatch, at potentially much lower cost than common whole-of-fishery solutions.
What affects fisheries in African lakes: Climate change or fishing effort? A case study from Lake Kariba