COMMERCIAL SCALLOP DIVE FISHERY PORT PHILLIP BAY Scallop

COMMERCIAL SCALLOP DIVE FISHERY - PORT PHILLIP BAY Scallop Dive (Port Phillip Bay) Fishery Results of the Fishery-Independent Dive Survey 31 August – 28 September Report to Port Phillip Bay Scallops Survey completed by Professional Marine Science Services (PMSS) Report prepared by David Gwyther (Picton Group Pty Ltd) Cover photo - PMSS

Background • This report provides the results of the 2015 independent dive survey and an estimate of the abundance of harvestable scallops (Pecten fumatus) in the areas accessible to the commercial dive fishery • The work was undertaken as described in the Commercial Scallop Dive Fishery (Port Phillip Bay) Baseline Management Arrangements (2013) (BMA) • It is the second annual fishery-independent survey since the hand dive fishery was established

Methods – Management Zones • • Bay divided into six strata Coincide as far as practicable with: – current fishery Port Phillip Bay commercial catch reporting grids and – the strata used for previous diver surveys during the historical dredge fishery • Zone 3 divided into 3 a (east) and 3 b (south) • The fishery does not operate in zones 2 (central Port Phillip Bay) and 6 (Corio Bay)

Methods – Sampling sites

Methods – Analyses • The abundance of scallops (total numbers, and available scallops of 90 mm and above) and the weight of available scallops was recorded for all sites and the means (numbers and biomass) per 100 m 2 calculated for each zone • The estimate of available biomass was determined from the mean weight of available scallops per 100 m 2 in each zone scaled up by the total area of that zone (i. e. , within the depth range 10– 20 metres, but without the exclusion areas) • An estimate of precision or coefficient of variation (as for 2014 survey as standard error/mean x 100%) • The distribution of scallop densities (numbers / 100 m 2) were plotted for each sampling site • Length frequencies of all scallops measured were graphed for each zone

Results – Numbers and Biomass Table shows: Numbers and weights of scallops sampled during the 2015 survey and estimates of available scallop biomass in the fishable areas of Port Phillip Bay

Results – Length Frequency • Scallop length frequency distributions of all scallops >25 mm in Zones 1, 3, 4 and 5 Length frequencies for zones 3 a and 3 b were combined as only 10 scallops in total were recorded from zone 3 a • Population distinctly bimodal • Pre-recruit cohort of modal size around 4060 mm Larger size class of modal length 85 -90 mm Similar structure in 2014, although numbers were much less Pre-recruits indicate a strong potential for recruitment, particularly in Zones 4 and 5 • • •

Summary of Numbers and Biomass • • • Numbers and mean weights of scallops /100 m 2 were higher in all zones than for the equivalent 2014 data. The total available biomass result of 11, 065 tonnes from 116 million scallops indicating a strong population which has substantially increased since last year’s estimate. The proportion of available scallops (i. e. , scallops of 90 mm or above) was highest at 57. 4% and 63. 0% in zones 1 and 5 respectively The average individual weight was 94. 7 g, calculated from the combined weight of 195. 9 kg of all 2069 available-sized scallops sampled Greatest abundances at sites on the north western and western parts of Port Phillip Bay, predominantly in zones 5, the western part of zone 1 and zone 3 b