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