36 Rock Lobster Habitat Assessment Figure 20. Nine Mile Reef video survey sites (see Table 4 for biota codes). a. NMR01a low profile reef, sessile invertebrates. d. NMR03a low profile reef, sessile invertebrates. b. NMR02a low profile reef, sessile invertebrates. e. NMR05a high profile reef, sessile invertebrates. c. NMR03a low profile reef, sessile invertebrates. f. NMR06a low profile reef, sessile invertebrates. Rock Lobster Habitat Assessment 37 g. NMR06a low profile reef, sessile invertebrates. i. NMR09a low profile reef, sessile invertebrates. h. NMR08a High profile reef, sessile j. NMR09a low profile reef. invertebrates. Figure 21. Nine Mile Reef video still images. Rock Lobster Habitat Assessment 38 Rock Lobster Habitat Assessment Figure 22. Torquay and Ocean Grove (western area) video survey sites (see Table 4 for biota codes). 39 40 Rock Lobster Habitat Assessment Figure 23. Torquay and Ocean Grove (eastern area) video survey sites (see Table 4 for biota codes). a. OGT05a low profile reef, sessile invertebrates. d. OGT12a patchy low profile reef, sessile invertebrates / E. radiata b. OGT06a patchy low profile reef. e. OGT16a low profile reef, E. radiata / Cystophora spp. c. OGT11a high profile reef, E. radiata. F. OGT17a sediment, A. antarctica. Rock Lobster Habitat Assessment 41 g. OGT18a patchy low profile reef, Cystophora j. OGT24a patchy low profile reef, sessile spp. invertebrates (Butterfly perch). h. OGT22a low profile reef, E. radiata / Cystophora k. OGT27a patchy low profile reef ‐ cobble. spp. i. OGT23a low profile reef, E. radiata. l. OGT30a patchy low profile reef, E. radiata. Rock Lobster Habitat Assessment 42 m. OGT32a low profile reef, Cystophora spp. p. OGT37a patchy low profile reef, E. radiata / Cystophora spp. n. OGT33a low profile reef, Cystophora spp. / E. q. OGT39a low profile reef, E. radiata. radiata. o. OGT35a low profile reef, E. radiata / Cystophora r. OGT39a low profile reef, E. radiata. spp. / Sargassum spp. Figure 24. Ocean Grove‐Torquay video still images. Rock Lobster Habitat Assessment 43 approximately 48 m and was often the dominant Summary of Video Observations species. Cystophora spp. was observed up to a The depth distribution of video sites at the rock depth of approximately 44 m typically growing lobster fixed sites is summarised in Figure 25. with E. radiata. A change from the dominant There was some overlap between the depths large brown macroalgae (kelps) to sessile across the fixed sites, but they broadly fell into invertebrates occurred at the 60–80 m depth the following three depth groups: range (Figure 28). This was highlighted by the change from E. radiata dominance at Big Reef to • shallow (<20 m): Warrnambool West and sessile invertebrates at Nine Mile Reef (Figure Warrnambool South 27). Durvillaea potatorum was observed in the • intermediate (21–60 m): Discovery Bay, inshore region up to a depth of approximately Portland, Port Fairy West, Warrnambool 14 m. East, Big Reef and Nine Mile Reef and Ocean Grove‐Torquay • deep (61–120 m) Discovery Bay Deep and Port Fairy Deep. While Portland, Port Fairy West, Warrnambool East and Ocean Grove‐Torquay were predominantly at intermediate depths, they represented a transition from the shallow to intermediate depth group. Nine Mile Reef was at the transition from the intermediate to deep depth group. Dominant substratum types across the fixed sites did not appear to be related to depth (Figure 26). Low profile reef was the most common substratum type and dominated most of the video sites. Warrnambool West was the exception to this, and the only site with predominantly high profile reef. Discovery Bay Deep had a more even spread of substratum types. Low profile patchy/cobble reef dominated at Port Fairy Deep and was also common at the Ocean Grove–Torquay site. The rock lobster fixed sites were typically dominated by a single dominant biota or canopy species and this reflected the depth group of each site (Figure 27). Portland, Port Fairy West and Ocean Grove‐Torquay had the greatest range of dominant biota types. The deepest sites at Discovery Bay Deep, Port Fairy Deep and Nine Mile Reef were entirely dominated by sessile invertebrates. Ecklonia radiata was the dominant species at the majority of the other sites. Phyllospora comosa on its own or growing with E. radiata was an important component of the biota at Portland, Warrnambool, Warrnambool West, Port Fairy West and Ocean Grove–Torquay. The mean percentage cover of dominant biota or canopy species showed a depth zonation across the sites (Figure 28). Phyllospora comosa was observed up to a depth of approximately 29 m and was typically growing with E. radiata. Ecklonia radiata was observed up to depth of Rock Lobster Habitat Assessment 44 0–20 m 21–40 m 41–60 m 61–80 m 81–100 m 101–120 m 100 90 80 70 60 50 40 30 20 Percentage of video sites 10 0 West Deep Portland Big Reef East West Port Fairy Port Fairy Port South Deep Torquay Warrnambool Warrnambool Warrnambool Ocean Grove- Nine MileReef Discovery Bay Discovery Bay Discovery Rock lobster fixed site Figure 25. Depth distribution of video sites (quadrats) at rock lobster fixed sites. High Profile Reef Low Profile Reef Low Profile Reef - Patchy/Cobble Sediment 100 90 80 70 60 50 40 30 Percentage of video sites 20 10 0 West Deep Portland Big Reef East West Port Fairy Port Fairy Port South Deep Torquay Warrnambool Warrnambool Warrnambool Ocean Grove- Nine Mile Reef Discovery Bay Discovery Bay Discovery Rock lobster fixed site Figure 26. Substratum types at video drops (quadrats) at rock lobster fixed sites. Rock Lobster Habitat Assessment 45 E. radiata E. radiata & P. comosa P. comosa E. radiata & Sessile invertebrates Sessile invertebrates Cystophora spp. 100 90 80 70 60 50 40 30 20 Percentage of video sites video of Percentage 10 0 West Deep Portland Big Reef East West Port Fairy Port Fairy Port South Deep Torquay Warrnambool Warrnambool Warrnambool Ocean Grove- Nine Mile Reef Mile Nine Discovery Bay Discovery Bay Discovery Rock lobster fixed site Figure 27. Dominant canopy species on video transects at rock lobster fixed sites. E. radiata P. comosa D. potatorum Cystophora spp. Sessile invertebrates 80 70 60 50 40 30 Mean Percentage Cover 20 10 0 0–20 21–40 41–60 61–80 81–100 101–120 Depth range (m) Figure 28. Depth zonation and mean percentage cover of dominant canopy species in video quadrats. Rock Lobster Habitat Assessment 46 Hydro‐acoustic Survey – Warrnambool West The video surveys of the Warrnambool West fixed site showed that it was predominantly high‐profile reef (Figure 26) and this site was selected for the hydro‐acoustic survey. The sidescan sonar data mosaic of the survey area within the Warrnambool West fixed site overlayed with single‐beam sounder and video data is shown in Figure 29. The seabed habitat classification mapping from the sidescan sonar data is shown in Figure 30. Standardised catch data from the fixed site for 2002–07 is overlayed on the habitat classification in Figure 30. This shows a pattern of fishing effort clustered around the boundary of the high profile reef. Figure 30 does not show the location of pots with zero catches as these were not included in the rock lobster fixed site database. The boundary between the high profile reef and sediment at the eastern end of the mapping area is highlighted in Figure 31. The high profile reef video site at the centre of Figure 31 is site WW02a (Figure 12a). Rock Lobster Habitat Assessment 47 48 Rock Lobster Habitat Assessment Figure 29. Sidescan sonar, single‐beam sounder and video data at Warrnambool West rock lobster monitoring area. Rock Lobster Habitat Figure 30. Habitat classification from sidescan sonar at Warrnambool West fixed site overlayed with standardised rock lobster catches 2002–07. Assessment 49 50 Rock Lobster Habitat Assessment Figure 31. Sidescan sonar data showing reef detail at Warrnambool West overlayed with standardised rock lobster catches 2002–07 Statistical Analysis Linking habitat and CPUE data The bubble plot overlaying mean cpue values on Catch data the ordination of all habitat parameters also The abundance of rock lobster as measured by showed a correspondence with the three main cpue differed between sites and between years. depth groups. The shallower sites had lower There was a general decline in cpue values over cpue values, and the intermediate and deeper the time period investigated at all sites except sites had higher cpue values, although there was for Warrnambool West and Torquay. While the only catch data from one of the deeper sites i.e. Warrnambool West site showed a general Nine Mile Reef (Figure 36). decline in cpue for the years 2002–06, the 2007 data indicated that the relative abundance of Examination of the other habitat parameters in rock lobster had returned to 2002 levels. In the form of bubble plots suggested that, apart Torquay, cpue values increased over the time from depth, there were seven variables that period, with the highest catch rates recorded in looked likely to be important in contributing to 2006. the observed pattern in the nMDS (Figure 34). These were percent cover of continuous rocky Catch per unit effort was generally higher at the reef (Figure 37), percent cover of high profile western (Discovery Bay sites) and eastern (Big reef (Figure 38), percent cover of understorey Reef, Nine Mile Reef, Torquay) sites, and lower canopy (Figure 39), percent cover of E. radiata in the central sites. The Ocean Grove site did not (Figure 40), percent cover of P. comosa (Figure fit with this pattern and cpue values recorded 41), percent cover of mixed red algae from this site were consistently low. It should be understorey (Figure 42) and percent cover of noted that the Ocean Grove and Torquay fixed sessile invertebrates (Figure 43).