Fish assemblages on the continental shelves of Freycinet and Huon Marine Parks: Insights from stereo BRUV and ROV surveys

Our comprehensive Baited Remote Underwater Stereo Video (stereo BRUV) and Remote Operated Video (ROV) surveys in the Huon and Freycinet Marine Parks (HMP and FMP, respectively) have significantly improved the understanding of the benthic/demersal fish assemblages of shelf to shelf-break habitats in these waters, particularly on mesophotic and rariphotic rocky reefs. Extensive surveys were conducted across different management zones, habitats, and depths, both inside and outside of the FMP and within the HMP. These datasets provide a robust quantitative baseline for monitoring future changes to fish communities and the abundance and size structure of key benthic and demersal fish species in the parks. For the FMP, these allowed for comparison of relative changes between zones (Multiple use Zone – MUZ, and Recreational Use Zone – RUZ), and between the FMP zones and adjacent habitats outside the park. Further, this information provides a solid quantitative reference point to assess the effectiveness of Marine Park zoning in the future, including protection from benthic trawling (both parks) and protection from commercial fishing in the Recreational Use Zone (RUZ) of the FMP.
Importantly, the outcomes from these studies provide robust information on the current abundance and size structure of key recreationally and commercially targeted species, including jackass morwong (Nemadactylus macropterus), striped trumpeter (Latris lineata) and ocean perch (Helicolenus percoides) in both parks, as well as rock lobsters (Jasus edwardsii), in the HMP where lobsters were particularly abundant on the complex dolerite reef systems of the inner shelf. For all the targeted species above, there were sufficient individuals recorded and with sufficient length measurements made, to underpin future monitoring programs aimed to detect biologically meaningful change through time and between habitats and park zones.
The most significant patterns in overall fish communities observed within the parks were strongly driven by habitat features rather than zoning. Generally, the distinct reef systems, including Joe’s Reef and the shelf-break reefs in the FMP, the extensive inner-shelf reef systems in the HMP, and the complex reef in the northern fished area outside the FMP, all had markedly differing fish communities to the adjacent soft sediments, or the extensive dune-like features found throughout much of the FMP. As Joe’s Reef is the only significant complex reef structure in the shelf waters within the MUZ of the FMP, and the only habitat to extend into the mesophotic zone, it is not surprising that it also hosts a unique fish assemblage, characterised by large numbers of planktivorous species like butterfly perch. Likewise, the shelf-break reefs within the MUZ in FMP constituted only a small proportion of reef habitat in this region, but also had distinct communities, including rock lobsters and large numbers of eastern orange perch, that were observed utilising small holes in the mudstone reef on the Remote Operated Vehicle (ROV) transects. Several handfish individuals were also observed on rubble adjacent to these reefs, raising the potential importance of these shelf-break systems to some rare and unique species.
The survey design employed for the stereo BRUV and ROV surveys, which covered both mesophotic (30 - 70 m) and rariphotic (70 – 200 m) depths has allowed quantification of fish communities across important environmental gradients that exist in these Marine Parks, both with respect to depth and key habitat types. In the HMP many species were shown to have strong reef affinity (including striped trumpeter, butterfly perch (Caesioperca lepidoptera) and rosy wrasse (Pseudolabrus rubicundus)), while others like jackass morwong had a clear reef affinity but were also distributed more widely. Notably though, in the FMP where reef outcrops were rare, the widespread dune-like features that cover most of the rariphotic shelf waters of the park hosted moderate abundances of both striped trumpeter and jackass morwong in places, demonstrating the importance of this distinct habitat type to several commercially targeted species.
As well as establishing a sound baseline for future monitoring, an initial comparison of fish on the shelf was also undertaken between the Multiple Use Zone (MUZ) and the RUZ in the FMP. While some small differences were observed between zones, it appears that most differences observed were primarily driven by habitat rather than protection-related differences within the park. Likewise, a comparison was made between soft bottom habitat inside and outside of the FMP as trawling is not permitted in the FMP. This showed a markedly greater abundance of jackass morwong within similar habitat in the park relative to adjacent fished areas, although in the absence of baseline studies when the park was established, this cannot conclusively be attributed to protection effects.
A key component of this study was to trial the use of a remotely operated vehicle (ROV) to inventory and monitor shelf fish communities across the two AMPs with the aim of comparing to results generated by baited remote underwater stereo-video (stereo BRUV). While ROV-based sampling was primarily targeted at reef communities, the results demonstrate that this quantitative sampling method has a significant role to play in future inventory and monitoring studies. ROV sampling increased the range and number of fish species seen that are not attracted to bait, including rare species such as handfish, as well as providing more fine scale information on species/habitat associations. However, stereo BRUV sampling yielder greater numbers of length measurements per deployment, important when tracking biomass and size structure changes in response to protection levels. Overall, the two methods are highly complementary and would ideally be utilised in initial inventory and baseline studies such as this.
As this study, coupled with prior multibeam mapping programs (Nichol et al. 2009b, Heaney and Davey 2019), has yielded a significant amount of new information on the distribution of fish species and their preferred habitats within both parks, it is important for management agencies such as Parks Australia to be aware of the likely impact of such new knowledge on future fishing pressure. Locations such as Joe’s Reef and the shelf-break reef habitat within the Freycinet Marine Park are some examples of spatially constrained high value habitats that may need additional spatial protection in the future if such information drives an increase in use. We note, that from our ROV footage of the shelf-break reef systems we surveyed, there was already an extensive coverage of snagged ropes and fishing lines, due to these systems being spatially small, but high value targets.