1. Marine protected areas (MPAs) are used as fisheries management and conservation tools. Well-enforced no-take zones allow the rebuilding of natural populations of exploited species; however, there is still controversy on the role of buffer zones.
2. The effectiveness of MPAs could be underestimated, as fish population assessments depend largely on traditional methodologies that have difficulties in detecting predatory fish because of their low abundances, their patchy distribution, and their reaction to the presence of divers.
3. The performance of different census methods was compared in assessing the protection benefits for large predatory fishes under different protection levels (i.e. no-take and buffer zones) in five Mediterranean MPAs. Specifically, conventional strip transects (CSTs, 50 × 5 m²) and tracked roaming transects combined with distance sampling (TRT + DS, variable lengths) were compared, including a series of TRT-derived estimators with variable transect lengths and fixed widths of 20, 10, and 6 m (TRT20, TRT10, and TRT6, respectively). Additionally, the effectiveness of the MPAs studied and protection levels for conserving large predatory species was evaluated.
4. Transects covering larger areas (i.e. TRT + DS and TRT20) allowed the detection of a greater number of species and yielded more accurate estimates of density and biomass than transects of narrower fixed widths, particularly the CSTs, which were associated with the lowest richness detection capability, accuracy, and precision. On average, both no-take zones and buffer zones appeared effective for the conservation of predatory fishes, indicating that multiple protection areas were ecologically effective. Differences between MPAs were also observed, however, probably arising from both local environmental and management factors.
5. We suggest the implementation of methodologies with larger transects for the study of large predatory fish, combined with CSTs for the rest of the fish community, in order to avoid biases in predatory population assessments, which are key indicators of MPA effectiveness.

中文翻译：

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捕食性鱼类保护效益的检测取决于普查方法

1. 海洋保护区 (MPA) 被用作渔业管理和保护工具。严格执行的禁捕区允许重建被开发物种的自然种群；然而，缓冲区的作用仍然存在争议。
2. 海洋保护区的有效性可能被低估，因为鱼类种群评估主要依赖于传统方法，由于捕食性鱼类丰度低、分布不均以及对潜水员存在的反应，传统方法难以检测捕食性鱼类。
3. 在评估五个地中海海洋保护区在不同保护水平（即禁捕区和缓冲区）下对大型掠食性鱼类的保护效益时，比较了不同普查方法的性能。具体而言，比较了常规带状断面（CST，50 × 5 m ²）和跟踪漫游断面结合距离采样（TRT + DS，可变长度），包括一系列具有可变断面长度和固定宽度 20 的 TRT 衍生估计量、10 和 6 m（分别为 TRT20、TRT10 和 TRT6）。此外，还评估了所研究的海洋保护区的有效性和保护大型掠食性物种的保护水平。
4. 覆盖更大面积的横断面（即 TRT + DS 和 TRT20）允许检测更多的物种，并且比固定宽度较窄的横断面更准确地估计密度和生物量，特别是与最低丰富度检测能力相关的 CSTs ， 准确度和精度。平均而言，禁捕区和缓冲区似乎都对掠食性鱼类的保护有效，表明多个保护区在生态上是有效的。然而，也观察到海洋保护区之间的差异，这可能来自当地的环境和管理因素。
5. 我们建议对大型掠食性鱼类的研究采用具有更大横断面的方法，并结合其他鱼类群落的 CST，以避免在掠食性种群评估中出现偏差，这是 MPA 有效性的关键指标。