Lead Poisoning of Reef Cover from Lead Sinkers.

Citizen Science Protecting Conserving the Reef.

When the Strandloper Project began research into the impact of snagged recreational fishing tackle on reef cover and biodiversity, the core focus was on ghost fishing.

Expanded Fields of Study

Ghost fishing is the untargeted capture and killing of marine fauna by lost and snagged fishing tackle. Studies by the Strandloper Project have documented the incident of 11 species of fish killed by ghost fishing caused by snagged recreational fishing tackle.

With ongoing survey dives it became apparent that lost fishing tackle has a raft of detrimental impacts on the reef habitat of which Lead Poisoning was the most sinister.

Sections of reef cover surrounding lead sinker accumulations were either unhealthy, dead or entirely absent depending on the density of accumulated sinkers.

This site, of 6m2, contained 100 lead sinkers and lacked any reef cover, an indication of the impact of lead poisoning on reefs.

The accumulated mean sinker density over 4 years of reef cleanup dives is higher than 5 sinkers/m of reef, with some sections greater than 30 sinkers/m of reef.

Most of the snagging occurs when the sinker wedges in a crack in the reef, resulting in the line breaking off and leaving the hook drifting free. If the hook is still baited, it can result in ghost fishing, the indiscriminate catching and killing of marine fauna. In 4 years the Strandloper Project has documented 11 species of fish killed by ghost fishing caused by snagged and lost recreational fishing tackle.

95% of the tackle snags on the edge of the intertidal shelf with one rock in particular along the transect accounting for approximately 18% of all snagged recreational fishing tackle that is recovered. The rock is located in the center of the high cast zone used by most sports and recreational fishermen at this site.

In the areas of high density accumulation of lead sinkers, the reef lacks algal diversity and is either bare reef or stunted coralline algae with muted brown olive colour compared to the usual mauve pink colour of this group of algae. The area is devoid of any other reef cover.

In addition to lead poisoning, the process of reeling in fishing tackle to check the condition of the bait caused physical damage to surface cover of the reef. The video below provides a clear comparison of the difference in reef cover condition between the high cast zone and the areas beyond fishing.

Healthy Reef

Reef assessment demonstrates that in areas that no snagging occurs and where there are no sinkers, the reef cover is vibrant and species rich and attracts shoals of a variety of bait species, an indication of a productive reef.

Most of the intertidal reef in the Garden Route presents in two distinct zone. The upper surface of the reef hosts a cover of red, green and brown algae, Red Bait (Pyura stolonifera) and coralline algae, which combined, yield a muted brown to purple tone. Beneath the overhangs in the intertidal zone, a profusion of colour from sea fans, sponges, sea stars, feather-duster worms, hydroids and numerous other organisms is on display. From approximately 4m to 5m, depending on the directional aspect of the reef, sea fans and sponges start to grow on the reef exposed to sunlight.

After 4 years of cleaning sections of the reef at our Gericke’s Point dive transect, we are starting to witness a recovery of reef cover, especially outside the high cast zone.

Reef Regeneration

To complement our reef surveys, the Strandloper Project has conducted Fixed Point Photography (FPP) to monitor for any transformations in reef cover condition. At our primary site at Gericke’s Point we have documented a phenomenal reestablishment of reef cover, primarily by Sea Fans (Alcyonacea), at the site. In 2014 the reef was almost barren with two sponges beneath the overhang and sparse stunted coralline algae growth on the upper surface pf the rock in the center of the site.

In October 2014, the site lacked any sea fans and only had sparse stunted coralline algae growth.

By December 2019, the site had been colonized by Sea Fans. Our assessment of the causes for the lack of reef cover suggest that agri-chemicals flowing into the ocean from the Swartvlei Estuary prior to October 2014 was the main cause.

FPP Site #1 : This image was capture on in November 2021 and clearly shows that the reef has reestablished compared to the the above image taken in 2014. This site was almost barren in October 2014 with a few small tufts of coralline algae on the upper surface and two sponges under the overhang. The colonization of sea fans was first recorded in December 2019, showing that, with right conditions (removal of toxic chemicals), the reef can reestablished rapidly.

The cause for the reestablishment of the reef with Sea fans is due to a drought cycle and low rainfall between 2014 and 2020 which resulted in the sand bar that regulates the open/closed status of the estuary mouth being closed for extended periods of time.

The duration of the phases of being open and closed reversed from being closed for between 3 and 6 weeks and open for between 18 and 22 months, to being open for a mere 3 to 6 weeks and closed for between 6 and 12 months. With lower rainfall and extended periods of the estuary mouth of being closed, less agri-chemicals flowed into the ocean, allowing the reef cover to grow.

Lead Alternatives

A local entrepreneur has graded and sorted two weight categories of stones and created natural alternatives to lead sinkers in and effort to reduce the loss of lead during shore based fishing. While it is a start, more effort is required to produce a viable alternative to lead for fishing sinkers.

Based on our preliminary findings, the Strandloper Project is convinced that the recreational fishing industry needs to investigate alternatives to lead for sinkers for sustainable reef health and fish productivity.

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