Reassessment of intertidal macroalgal communities near to and distant from salmon farms and an evaluation of using drones to survey macroalgal distribution
University of Tasmania (UTAS)
Christine D. Crawford
The proposed expansion of salmon farming to new sites in south eastern Tasmania earlier this year has already elicited opposition from some neighbouring residents, wild abalone fishers and environmental groups, which has been well displayed in the media. One of their major concerns is lack of information on whether salmon farms are affecting intertidal and subtidal macroalgae, and no ongoing monitoring of these habitats. This highlights the importance of repeating the survey eleven years later to assess changes in intertidal macroalgal abundance and species composition around salmon farms. Drones are increasingly being used to record agricultural environments, including salmon farms. However, methods to quantitatively assess coastal environmental change using drones, such as macroalgal distribution and abundance have not been assessed. The effectiveness of this technique to monitor salmon farms is needed to maximise usage of this data and before it can be incorporated into monitoring programs. This project will provide information important to several FRDC Strategic Priority Areas. • Program 1: Environment: Themes 2 and 4: Habitat and Ecosystem Protection and Ecologically Sustainable Development, especially providing information to the community to demonstrate improvements in the aquaculture industry’s environmental performance and quantifying the environmental carrying capacity of aquaculture operations. • Program 2: Industry: Theme 6 and 7: Resource Access and Allocation, and Production, Growth and Profitability, especially increasing knowledge among diverse groups of stakeholders about each other’s expectations for resource access and allocation, and increase and diversify opportunities for the aquaculture sector. • Program 3: Communities: Theme 10: Resilient and Supportive Communities, especially understanding and influencing the community perceptions about the fishing and aquaculture industry and improving interactions between them, and increasing the community’s capacity to accept and incorporate higher levels of aquaculture activity.
1. To repeat the assessment of intertidal macroalgal composition and abundance near to and distant from salmon farms in the Huon and D’Entrecasteaux Channel region eleven years after the initial assessment.
2. To evaluate the potential of using Unmanned Aerial Vehicles (drones) to monitor macroalgal distribution.
The salmon farming industry has significantly expanded in South-eastern Tasmanian both in production and in number and location of farms. Along with this expansion has been an increasing concern from the general community about the effects of salmon farms on the environment. This includes a reported spread of ‘nuisance’ algae in the intertidal zone; however, this has not been verified scientifically. As one of the main effects of salmon farming is an increase in nutrients to the environment from waste products, a possible flow-on effect could be a proliferation of macroalgal beds near salmon farming operations. However, a survey of intertidal areas in the Huon and D’Entrecasteaux Channel region in 2002/03 found no clear patterns of macroalgal abundance with distance from salmon farms, (Crawford et al 2006), and it was recommended that any future studies focus on surveying the abundance of key species in the intertidal, Ulva spp and Hormosira banksii, which are widely distributed and readily identified.
In this project researchers from the Institute for Marine and Antarctic Studies at the University of Tasmania repeated the survey of intertidal macroalgae conducted in 2002/03 to assess whether abundances have significantly changed at these sites. We also investigated monitoring macroalgal abundance at a larger spatial scale using Unmanned Aerial Vehicles (UAVs), commonly known as drones. Since the previous survey in 2002/03, the technology for UAVs has significantly advanced and they are now a much more cost effective option. However, the techniques and quantitative analyses required to monitor intertidal algal assemblages using drones have not been assessed.
Although the percentage cover of all species of intertidal algae in the quadrats was recorded, the analysis focussed on the two dominant species types Ulva spp and Hormosira banksii. Similar to the previous surveys conducted in 2002/03, there were no clear patterns in abundance of Ulva or Hormosira with distance from salmon farms, even though production from salmon farms has increased substantially over this time. However, the abundance of Hormosira in 2015 and 2016 was significantly lower than in 2002/03. This species had almost disappeared from the mid tide region at nearly all sites in 2015-16, whereas the percentage cover of Ulva was significantly higher. These results suggest that factors other than nutrients from salmon farms were also influencing the abundance of intertidal algae, as the results were consistent across sites, regardless of distance from salmon farming operations.
The drone survey in December 2016 produced over 1500 photographs but only a portion of these were suitable for orthomosaic processing due to the system failing to deal with refraction issues in deep water during the image matching stage. Although boundaries of Macrocystis beds were visible and could be mapped, the refraction effects with water depth would likely hinder change analysis if the beds were mapped at a later date. Similarly, the drone surveys in March 2016 were not that successful because even at low tide sections of the intertidal were covered with water, and a depth of only 1 cm was found to severely limit camera recordings, including poor colour definition.
Keywords: intertidal algae, salmon aquaculture, nutrients, environmental monitoring, drones, unmanned aerial vehicles