Year

2017

Degree Name

Doctor of Philosophy

Department

School of Biological Sciences

Abstract

Marine protected areas (MPAs) are an increasingly common management approach to assist in conserving marine biodiversity by limiting, avoiding or removing anthropogenic activities such as pollution, habitat destruction and fishing. Globally, a considerable proportion of the area under protection in MPAs comprises soft sediments. Research on rocky reefs and coral reefs has demonstrated that when MPAs are well designed and implemented, the abundance and biomass of targeted fish species can increase. However, demersal fish on marine soft sediments have been poorly studied and it remains unclear whether they respond in the same ways to protection as fish on other habitats. In this thesis, I aimed to assess (i) whether MPA protection in south-east Australia has affected the species composition, abundance and size of demersal marine soft sediment fishes among management zones and (ii) the degree of long-term residency shown by a key recreationally and commercially targeted species in relation to MPA size and zoning.

First, I used baited remote underwater videos (BRUVs) to sample the fish assemblages and test hypotheses about the effects of MPA management and implementation. My results revealed that in, shallow (10 m), deep (20 m) and offshore (50–60 m) waters, the demersal soft sediment fish assemblages were characterised by a few frequently occurring species. At all depths sampled the most common species were flathead (Platycephalus caeruleopunctatus & Platycephalus grandispinis). Shallow- and deepwater BRUV sampling was carried out between May and June in 2011, 2013 and 2015, within Jervis Bay Marine Park. At the assemblage level, no impact of MPA zoning was detected at either depth. There was also no difference between zones in total relative abundance (abundance of all species combined) or species richness at either depth. Abundances of individual species (those appearing on ≥ 25% of BRUVS samples) were also compared between zones; In shallow-water, there was a 32% greater abundance of Platycephalus spp. in no-take zones (NTZs) compared to partially protected areas (PPAs) over the study. In addition, abundances were more stable in NTZs across time. In shallow-water, Eastern fiddler ray (Trygonorrhina fasciata) and shovelnose ray (Aptychotrema rostrata), also had higher abundances in NTZs compared to PPAs in 2015. In deep-water there were no differences between zones for any individual species. There were no differences in length of flathead between zones at either depth. Offshore comparisons were carried out between August 3 and December in 2015, within Jervis Bay Marine Park, Batemans Marine Park and open access (OA) areas outside the two MPAs. Assemblages showed clear differences among NTZ, PPA, and fished OA areas. At the species level, on average, larger individuals of longspine flathead (P. grandispinis) were observed in NTZs than in both PPAs and OAs. There were also substantially higher abundances of ocean jackets (Nelusetta ayraudi) in NTZs. In offshore water there were no differences in abundances among zones for any other species or in species richness and total relative abundance.

Second, I tested the assumption that fish on soft sediments are unlikely to show residency by evaluating the movement patterns of the bluespotted flathead (P. caeruleopunctatus) in Jervis Bay Marine Park. Bluespotted flathead were acoustically tagged within a NTZ in spring 2014 (n=25), autumn 2015 (n=15), and summer 2015 (n=6). I then monitored the tagged fish for 625 days. Bluespotted flathead exhibited small-scale and long-term residency within the NTZ. Over the first 108 days post tagging most fish (74%) remained within a ~200 ha area of NTZ and were detected frequently. I observed residency of up to 600 days. Although close to two thirds of the tagged fish were only detected within Jervis Bay, the remainder were detected moving up to 155 km from where they were tagged. Generally, these fish had a prolonged period of site residency before making these large-scale movements. Importantly, range testing confirmed that acoustic tags in this habitat were detected with a high degree of confidence and reliability.

My findings demonstrate that temperate demersal fishes found on marine soft sediments can be influenced by protection within MPAs at a number of spatial scales. However, the response is highly variable among species with the majority showing no response, a relatively small effect size for those that do show a response and assemblage wide responses occurring in offshore waters but not within nearshore waters. In conclusion, marine soft sediments are an extensive habitat that harbour a unique demersal fish community. This habitat supports an important component of marine biodiversity and represents a rich fishery resource. This study provides a rare example of MPA effects on demersal soft sediment assemblages and presents substantial evidence of long-term residency by a demersal soft sediment associated fish within an NTZ.

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