Derelict fishing line on fringing reefs of inshore groups of the GBR, 2007-2009 (NERP 8.2, JCU)

This dataset consists of site means of the density of derelict fishing line, the percent cover of major benthic categories on fringing coral reefs of the Keppel, Whitsunday and Palm Island groups, and the accumulation rate of fishing line at ten sites in the Palm Islands between 2007 and 2009.

Monofilament nylon fishing line is persistent in the marine environment and once entangled in the reef, it can remain in place for many years. Temporal monitoring of the relative number of fishing lines recorded at each site can be used as a proxy for fishing effort. During the last few years we have established a collaboration with ReefCheck Australia to enhance this aspect of the project. In 2007, volunteer divers were tasked with removing all derelict fishing lines from a subset of the monitoring sites in the Palm Islands. In the last few years, the rate of line re-accumulation has been monitored to gauge relative levels of fishing effort and zoning compliance.

Methods:

Underwater visual census (UVC) was used to survey derelict fishing lines at 30 sites in the Palm Islands, 42 sites in the Whitsunday Islands and 22 sites in the Keppel Islands during 2009. Within each island group, half of the sites (n = 47) were located on reefs within NTMRs and half (n = 47) were on reefs that are open to fishing (non-NTMR). A proportion of the NTMR sites in each island group were located within ‘old’ reserves (NTMR 1987) protected since 1987; while others were located within ‘new’ reserves (NTMR 2004) protected since 2004.

Five replicate 50 m x 6 m (300 m²) UVC transects were surveyed at each monitoring site by two observers using SCUBA. The total survey area at each site was 1500 m2. Transect tapes were deployed along reef slopes, parallel to the reef crest and at a depth between 4 m and 9 m depending on the reef slope topography at each site.
The benthic community was surveyed using a standard line intercept survey method every 1 m along each transect (50 points per transect). Hard corals were classified as live or dead and assigned into morphological categories (branching, digitate, plate, massive, foliose, encrusting). Other categories of benthos included soft coral, sponges, clams (Tridacna spp.), other invertebrates (such as ascidians and anemones), macro-algae, coral reef pavement, rock, rubble and sand. Reef structural complexity was estimated using a five-point scale for both reef slope angle and rugosity. Five independent structural complexity estimates were made for each transect. Underwater visibility was recorded on each transect and ranged from 6 m to 12 m. Surveys did not proceed if the visibility was less than 5 m.

Teams of volunteer divers from Reef Check Australia carried out the removal of derelict fishing lines at ten of the monitoring sites in the Palm Islands during April 2007. Five of the cleaned sites were located on reefs within NTMRs and five were on non-NTMR reefs. Four of the cleaned NTMR sites were located on the leeward side of Orpheus Island (NTMR 1987) and one site was at Curacoa Island (NTMR 2004). Of the cleaned non-NTMR sites, four were located on the leeward side of Pelorus Island and one was at Curacoa Island. The ten cleaned sites were randomly selected from a pool of eighteen sites that were in sheltered (leeward) locations and were identified as being readily accessible by fishers during calm to moderate (< 15 knots of wind) weather conditions.

At each site, divers removed all sighted derelict fishing lines and tackle (hooks, sinkers, wire leaders etc.) on reef slopes between 4 m and 12 m depth, for 200 m in both directions from a central GPS waypoint marking the site position. Transect tapes were deployed to measure the distance covered and increase the search efficiency so that very few, if any, derelict fishing lines remained after cleanup operations were completed. Derelict lines that were overgrown with hard coral or encrusting sponges, or partially embedded in the reef matrix were cut, and all of the exposed (visible) sections of line were removed. All collected fishing lines were recorded on data sheets before being placed in catch bags and taken back to the boat for later disposal.

Baseline UVC surveys of derelict fishing lines were conducted at each of the ten cleaned sites immediately prior to the removal of fishing lines in April 2007 and UVC surveys were subsequently repeated in December 2009, providing a 32 month period for fishing lines to re-accumulate on the reefs. The 2007 and 2009 UVC surveys on the 10 cleaned sites used the same methodology described in the survey methods section above.

We assumed that all of the fishing lines recorded and collected were lost at the same location in which they were found. The authors recognize that the removal of derelict fishing line from ten of the thirty sites in the Palm Islands prior to the 2009 surveys would have reduced the fishing line density estimates for the Palm Islands. However the magnitude of this effect was balanced between old and new NTMRs and non-NTMRs, as only one-third of the monitoring sites in each zone were cleaned.

Format:

The data are contained within two worksheets of an Excel file (20 kB). All benthic data is in % cover. Fishing line data are presented as both mean density (mean number of lines per 300 m2) and a total summed value for each site (total number of lines recorded per 1500m2). The first worksheet provides the site-level data for 2009. The second worksheet provides the accumulation rates of fishing lines at 10 monitoring sites in the Palm Islands between their removal in 2007 and the re-survey in 2009.

Data Dictionary:

Names in brackets correspond to those used in the shapefile equivalents of the spreadsheet data. These names were adapted to work within the 10 character attribute limitation of shapefiles.
- Fish Line_MEAN (FishLineMn) - mean number of lines recorded over 5 transects surveyed at each 300 m2 site.
- Fish Line_SUM (FishLinSum) - is the pooled number of lines recorded on the 5 transects surveyed at each site. It is the total number of lines found over the 1500m2 surveyed at each site.
- Line Accumulation Rate (LineAccRat) - number of lines accumulated per month.
- SCI_MEAN - Structural complexity Index.. An index (1-25) calculated by multiplying our visual estimates of reef slope angle (1-5) by reef slope rugosity (Complexity 1-5). These values are estimated for each 10m section of each 50m transect. 5 transects per site = 25 SCI estimates per site. The data provided is site means… i.e. the mean of those 25 values.
- %LHC_MEAN (LHC_MEAN) - Live hard coral cover (%), live hard coral only.

References:

Williamson D.H., Ceccarelli D.M., Evans R.D., Hill J.K., Russ G.R. (in press). Derelict fishing line provides a useful proxy for estimating levels of non-compliance with no-take marine reserves. PlosOne 2014

本数据集包含开普群岛（Keppel Islands）、圣灵群岛（Whitsunday Islands）与棕榈群岛（Palm Island groups）岸礁（fringing coral reefs）上的废弃渔线密度站点均值、主要底栖生物（benthic categories）盖度百分比，以及2007至2009年间棕榈群岛10个监测站点的渔线累积速率。

单丝尼龙渔线在海洋环境中具有极强的持久性，一旦缠绕于珊瑚礁上，可留存长达数年。对各监测站点记录的渔线相对数量进行时序监测，可作为捕捞努力量的替代指标。近年我们与澳大利亚珊瑚礁检查项目（ReefCheck Australia）建立合作，以强化本项目此方向的研究工作。2007年，志愿潜水员被指派移除棕榈群岛部分监测站点内的所有废弃渔线；近年则通过监测渔线重新累积的速率，以评估捕捞努力量的相对水平与分区合规性。

方法：
2009年，研究采用水下视觉普查（Underwater visual census, UVC）方法，对棕榈群岛30个、圣灵群岛42个以及开普群岛22个监测站点的废弃渔线开展调查。每个群岛组内，半数站点（n=47）位于禁捕海洋保护区（No-Take Marine Reserve, NTMR）内的珊瑚礁上，另一半（n=47）则位于允许捕捞的非禁捕海洋保护区（non-NTMR）珊瑚礁上。各群岛组内的禁捕海洋保护区站点中，一部分位于“老保护区”（NTMR 1987）——即1987年起实施保护的区域；其余则位于“新保护区”（NTMR 2004）——即2004年起实施保护的区域。

每个监测站点由两名使用水肺潜水（SCUBA）的观察员开展5次重复的50m×6m（即300㎡）UVC样带调查，单站点总调查面积为1500㎡。样带胶带沿礁坡布设，与礁脊平行，布设深度介于4m至9m之间，具体数值依各站点礁坡地形而定。

底栖生物群落调查采用标准的样带截线法，沿每条样带每1m设置1个采样点（每条样带共50个采样点）。硬珊瑚分为活珊瑚与死珊瑚，并按形态划分为分枝状、指状、板状、块状、叶状、皮壳状等类别。其他底栖生物类别包括软珊瑚、海绵、砗磲（Tridacna spp.）、其他无脊椎动物（如被囊动物与海葵）、大型藻类、珊瑚礁岩坪、岩石、碎石与泥沙。珊瑚礁结构复杂度通过5级评分法分别评估礁坡角度与粗糙度；每条样带独立开展5次结构复杂度评估。每条样带均记录水下能见度，范围介于6m至12m之间，若能见度低于5m则终止调查。

2007年4月，来自澳大利亚珊瑚礁检查项目的志愿潜水员团队对棕榈群岛10个监测站点开展废弃渔线清除工作。其中5个已清理站点位于禁捕海洋保护区内的珊瑚礁上，另外5个位于非禁捕海洋保护区珊瑚礁上。已清理的禁捕海洋保护区站点中，4个位于奥菲斯岛背风侧（NTMR 1987），1个位于库拉科阿岛（NTMR 2004）；已清理的非禁捕海洋保护区站点中，4个位于佩洛鲁斯岛背风侧，1个位于库拉科阿岛。这10个清理站点是从18个位于遮蔽（背风）区域、且在风力≤15节的温和至中等海况下便于渔民抵达的候选站点中随机选取的。

各站点的潜水员需在以站点GPS定位点为中心、向两侧各延伸200m的范围内，清除4m至12m深度礁坡上所有可见的废弃渔线与钓具（包括鱼钩、铅坠、钢丝引线等）。布设样带胶带用于测量作业覆盖范围，以提升搜索效率，确保清理作业完成后几乎无残留废弃渔线。对于被硬珊瑚或皮壳状海绵覆盖、或部分嵌入礁体基质的废弃渔线，潜水员需将其剪断，并移除所有裸露（可见）的渔线段落。所有收集到的渔线均需记录在数据记录表上，随后装入收纳袋带回船上以待后续处理。

2007年4月开展渔线清除作业前，研究人员已对这10个清理站点开展废弃渔线的基线水下视觉普查；随后于2009年12月再次开展普查，从而获得了32个月的渔线重新累积周期。针对这10个清理站点的2007年与2009年水下视觉普查，均采用前文所述的统一调查方法。

研究假设所有记录与收集的渔线均丢失于发现点位。研究团队意识到，2009年调查前对棕榈群岛30个监测站点中的10个开展废弃渔线清除作业，可能会降低棕榈群岛的渔线密度估算值，但由于每个分区仅三分之一的监测站点被清理，该影响在老禁捕海洋保护区、新禁捕海洋保护区与非禁捕海洋保护区之间保持均衡。

数据格式：
数据存储于一个Excel文件的2个工作表中（文件大小20KB）。所有底栖生物数据以盖度百分比形式呈现；渔线数据同时以平均密度（每300㎡的渔线平均条数）与单站点总计数（每1500㎡调查区域内记录的渔线总条数）两种形式展示。第一个工作表包含2009年的站点级数据；第二个工作表则展示了棕榈群岛10个监测站点在2007年渔线清除作业后至2009年重测期间的渔线累积速率。

数据字典：
括号内的名称对应电子表格数据对应的矢量形状文件（shapefile）中使用的字段名，这些名称为适配矢量形状文件10字符的属性限制而调整。
- 渔线平均密度（Fish Line_MEAN, FishLineMn）：单站点5条300㎡样带调查记录的渔线平均条数。
- 渔线总计数（Fish Line_SUM, FishLinSum）：单站点5条样带调查记录的渔线总条数，即该站点1500㎡调查区域内发现的渔线总数。
- 渔线累积速率（Line Accumulation Rate, LineAccRat）：每月累积的渔线条数。
- 结构复杂度指数均值（SCI_MEAN）：结构复杂度指数（Structural complexity Index）。该指数（取值范围1~25）由礁坡角度视觉评分（1~5级）与礁坡粗糙度视觉评分（1~5级）相乘得到。评分值按每条50m样带的每10m区段分别估算，单站点5条样带共可获得25个指数值，本数据集提供的为单站点25个值的均值。
- 活硬珊瑚盖度均值（%LHC_MEAN, LHC_MEAN）：活硬珊瑚盖度百分比，仅统计活硬珊瑚。

参考文献：
Williamson D.H.、Ceccarelli D.M.、Evans R.D.、Hill J.K.、Russ G.R.（已刊印），《废弃渔线可作为评估禁捕海洋保护区违规程度的有效替代指标》，《公共科学图书馆·综合》（PLOS ONE），2014年。