A First for the Solent: Osborne Bay Voluntary No Anchor Zone Installed

18 April 2024

Osborne Bay hosts an expansive seagrass bed that is showing signs of damage from anchoring and mooring pressures. Surveys indicate a high level of this activity in the bay. Reducing and removing these pressures will allow the seagrass bed to naturally recover and flourish. Natural England led the introduction of a Voluntary No Anchor Zone (VNAZ), which was successfully installed in March 2024.

Figure 1. Photos of seagrass in Osborne Bay by Tim Ferrero

Figure 1. Photos of seagrass in Osborne Bay by Tim Ferrero

Osborne Bay on the northeast coast of the Isle of Wight is home to a beautiful and expansive seagrass bed extending from the intertidal zone to around 400m offshore, protected as part of the Solent Maritime SAC (Figure 1). This sheltered bay is also a popular destination for people, with both locals and tourists venturing there via boat.

Seagrass as a habitat is vitally important to improving biodiversity, increasing carbon storage and reducing coastal erosion, however it is also very vulnerable to damage from anthropogenic pressures such as beach activity, water sports and anchoring.

 

Figure 2. Bar graph of the average number of vessels anchoring in the seagrass bed per survey (1-hour periods) at each of the 5 locations. Draft data shown for 2021, 2022 and 2023 surveys collected during Recreational Activity Surveys coordinated by the Hampshire & Isle of Wight Wildlife Trust, currently unpublished

Figure 2. Bar graph of the average number of vessels anchoring in the seagrass bed per survey (1-hour periods) at each of the 5 locations. Draft data shown for 2021, 2022 and 2023 surveys collected during Recreational Activity Surveys coordinated by the Hampshire & Isle of Wight Wildlife Trust, currently unpublished

This process started with recreational activity surveys, which through the LIFE Recreation ReMEDIES project, have been conducted between July and September at seagrass beds across the Solent Maritime SAC. These identified Osborne Bay as an area of above average boating pressure with 5.3, 8.5 and 9 boats on average anchoring inside the seagrass zone per survey (1-hour periods) in 2021, 2022 and 2023 respectively (draft data collected on surveys coordinated by Hampshire & Isle of Wight Wildlife Trust). Comparison with the other sites (Figure 2) highlights the significant difference between pressure in Osborne Bay and the other sites.

 

Figure 3. Photos of seagrass in Osborne Bay by Caitlin Napleton. (a and d. healthy seagrass, b and c. scoured seagrass)

Figure 3. Photos of seagrass in Osborne Bay by Caitlin Napleton. (a and d. healthy seagrass, b and c. scoured seagrass)

This has also been seen on site, the photos in Figure 3 were taken on the same day and show the variation from the healthy and dense areas of seagrass (a and d) to sparse seabed (b and c).

Now that Osborne Bay had been recognised as a hotspot of recreational activity potentially damaging to seagrass, the next step was to determine the best measures to prevent further damage and allow the bed to recover.

The ReMEDIES project had done work previously on Voluntary No Anchor Zones (VNAZs) in the Plymouth Sound SAC and Fal and Helford SAC, and through internal discussion this option was identified as the best solution. VNAZs are areas marked out around protected areas such as seagrass beds. They are intended to inform people of sensitive habitats or infrastructure in the area and often use buoys on the water to provide a visual marker.

Discussions with the landowner, English Heritage, were key from an early stage. From this, the plan for the VNAZ was established: 8 marker buoys to delineate the area of seagrass, using Advanced Mooring Systems (AMS) to prevent any further scour on the seabed. The AMS set up to be used was a helical screw and chain riser with floats to keep it off the seabed (more information on AMS can be seen here). As well as this, we discussed with other projects who have worked on VNAZs to learn from them, including the Studland Bay Partnership. This highlighted the importance of a community led approach.

Therefore, the next step, before beginning to think about installation of the VNAZ, was to present this proposal to the local community to hear any feedback, suggestions, or concerns. A series of community conversations took place to achieve this; one at East Cowes Sailing Club, one at Hill Head Sailing Club and one online. The results of these are summarised in Figure 4 below. Overall, the attendees mostly agreed with the VNAZ proposal outlined and most were not concerned about the potential impacts on boaters. Where there were concerns, these discussions gave an opportunity to understand and find solutions that worked for everyone.  These conversations were crucial to the process and demonstrated one of the key barriers to overcome is a lack of awareness on where seagrass is and the importance of it as a habitat.

Figure 4. Pie charts showing the breakdown of responses to 3 survey questions asked of attendees to the community conversations on the VNAZ proposal

Figure 4. Pie charts showing the breakdown of responses to 3 survey questions asked of attendees to the community conversations on the VNAZ proposal

Next up was the installation of the VNAZ itself. This involved discussion with the relevant authorities and securing the required licences before the buoys went in on 21-22nd March 2024. The installation was undertaken by ABC Subsea Consortium and was a huge success with all 8 marker buoys going in well. They tested a new method for installing AMS, intended to make the process easier and more accessible. As well as this, 4 traditional moorings were removed, and the buoys re-used in the VNAZ. The buoys sit outside the seaward edge of the seagrass bed, with signs marking the area as a VNAZ (Figure 5).

Figure 5. Photos from the installation of the VNAZ marker buoys in Osborne Bay by ABC Subsea Consortium

Figure 5. Photos from the installation of the VNAZ marker buoys in Osborne Bay by ABC Subsea Consortium

Although the VNAZ is now in place, the work does not end here, monitoring and engagement will continue to determine the impact of the VNAZ. This will be done through the 2024 recreational activity surveys, providing a direct comparison with anchoring data before the VNAZ was in place.

It is important to note that the intention is not to stop anchoring in this area, Osborne Bay is a beautiful area and should be enjoyed. The VNAZ will ensure boaters are aware of the seagrass bed and allow them to make an informed decision on where to anchor.

This is a big step for seagrass in the area, being the first VNAZ to go into the Solent and will hopefully help to reduce and remove some of the key pressures on the seagrass bed in Osborne Bay, allowing it to naturally restore and flourish.

If you have any questions regarding the VNAZ please let us know through our website enquiry form.