The fishery for western lobster (Panulirus cygnus) has supported an annual catch of about 10,500 tonnes per annum over the last twenty years and is worth between $200-300 million per annum. The fishery has been experiencing increasing exploitation rates over time and estimates in the early 1990s were suggesting that the brood stock had declined to between 15-20% of unfished levels. These low levels were considered to pose a serious risk to future recruitment and resulted in a number of management measures being introduced in the 1993/94 season aimed at \raising the levels of the brood stock.

In the past, the state of egg production in the stock has been estimated using data obtained from the commercial fishery. Data from this source can introduce possible bias, in that it is possible for fishers to avoid certain areas where there are large numbers of female animals in a breeding state and which under the new management measures are now required to be returned to the sea Furthermore, the effect of increases in fishing power on commercial fishing effort due to changes in gear technology, can lead to the spawning stock index being over estimated if valid measures of the increases in effectiveness are.pot available.

The only way of avoiding the potential biases of using commercial data, is by conducting a sampling programme independent from commercial fishing data. Such a pilot programme was undertaken at Fremantle and the Abrolhos Islands in 1991, was expanded to include Dongara and Jurien in 1992 and with the assistance of FRDC funding was continued and expanded to include Lancelin and Kalbarri from 1993 to 1996 (FRDC project 93/091). The project was further extended under FRDC funding from 1996 to 1998 (this project), in order to increase the confidence of the results and to examine the breeding stock indices over the full term of the current management package. The results from this latter survey form the basis of this report.

Commercial lobster fishing boats were chartered to do research fishing in five areas on the coast and a research vessel was assigned to the Abrolhos Islands. Fishing took place at each of these areas over ten days during the last new moon prior to the start of the commercial fishing season in mid-November. Standard commercial pots were set on the same GPS positions each year in areas that had previously been identified as localities which consistently yielded large numbers of spawning animals. All lobsters caught were measured, sexed and in the case of females particular attention was paid to their reproductive state. Environmental parameters (bottom and surface temperature, salinity, swell size) were recorded daily in each area. Egg production indices (expressed as the mean number of eggs per pot lift) were calculated annually for each area separately and for the areas combined, based on the number of mature female animals in the catch. Analysis of the results at all the coastal sites showed significant increases in egg production since the surveys first commenced. All the survey areas have shown an upward trend in egg production since 1993 when the management changes came into effect.

Other analyses showed that there were substantial inter-annual differences in swell size as well as bottom temperature. These environmental factors did not significantly increase or decrease the egg production indices in anyone year, but the analysis did suggest that swell size has an influence on the index.

The need to optimise spawning success and survival of offspring by fishes has resulted in the evolution of a vast array of reproductive strategies, such as spawning aggregations. A spawning aggregation is defined by Domeier and Colin (1997) as, “a group of con-specific fish gathered for the purpose of spawning with fish densities or numbers significantly higher than those found in the area of aggregation during non-reproductive periods”. However, Mackie et al. (2009) noted that this is not always the case, as individuals of a species may aggregate to spawn in numbers lower than those found in schools of the same species, at the same location, outside of spawning times. A more pertinent description of an aggregation from a management perspective is that reproductively active fish are grouped together in a manner which increases their vulnerability to fishing. 

Over-fishing of spawning aggregations is often associated with the collapse of the fisheries they supported. Management of fisheries that exploit such aggregations has become a crucial element in sustaining such resources. To effectively assess the biomass, distribution, behaviour and ecological importance of spawning aggregations, techniques are required which are non-invasive, incite as little behavioural bias as possible, can repetitively acquire high-resolution data for periods up to entire spawning seasons and are comparatively easy and cost effective to deploy. Conventional sampling techniques, such as video census (for example, Diver Operated Video surveys or Baited Remote Underwater Video systems), egg tows or catch related sampling often offer only a snapshot-in-time of the aggregation and in some cases suffer from sampling bias induced by the method itself. No sampling method is exempt from bias; however, the integration of a suite of techniques pertinent to the biological and behavioural characteristics of the species can provide complementary data sets that allow a better understanding of their biases.

Although not without limitations, acoustic techniques offer unique, complementary methods to other sampling techniques. Sound waves propagate efficiently through water, allowing acoustic ‘observation’ of sound-producing marine animals over considerably greater distances and ranges of conditions than visual techniques. Over 800 species of fish reportedly produce sound, many during spawning and the recording of these vocalisations is being increasingly used to acquire information on species that aggregate. The lack of human interaction during the recording of fish calls means that passive acoustics offers a non-extractive method of monitoring vocal fish. Sound pressure levels (SPLs) of fish choruses have been shown to be related to the number of calling fish present and provide important information on likely ecological (environmental or anthropogenic) correlates behind the timing, spatial distribution and relative size of aggregations and the behaviours associated with them.

The proposal for this project was developed in liaison with the Department of Fisheries, Western Australia (DoFWA); Aquaculture Development Unit (ADU) at Fremantle Challenger Institute of Technology; the Shark Bay Ecosystem Research Project (SBERP); the Department of Parks and Wildlife (DPaW) and; the Curtin Aquatic Research Laboratory (CARL), who have all provided in-kind support to various areas of the project. Recreational and commercial fishing groups including Recfishwest, Recfishing Research and Western Australia Fishing Industry Council (WAFIC) were consulted for advice and support. The Swan River Trust was also consulted to identify the benefits this project could offer towards their current objectives, and have provided in-kind support in the form of access to a substantial environmental dataset for the Swan River to compare environmental variables with sound production levels. 

One of the primary objectives of this project was to quantify the spatial and temporal variations in sound production of mulloway at various aggregation sites.  In addition, at the beginning of this project no reports of sound production by WA dhufish, snapper and black bream existed; thus, the project aimed to determine whether these species are vocal and, if so, whether their vocalisations are of use as a fisheries-independent monitoring tool. Deployments have been successfully completed along the WA coastline from Augusta to Shark Bay to record vocalisations by the four target species.  In excess of 1.84 Tbytes of data have been collected during the course of the project, comprising a total of 9015 hrs (375 days) of recordings over a total deployment period of 818 days. Analysis from a further nine datasets, comprising 894 days deployment (287 days of recording in total), provided from affiliated projects has helped investigate a variety of fish calls and choruses off Western Australia.

Keywords: Sound production, spawning aggregation, fisheries management, propagation, mulloway, dhufish, snapper, black bream, Western Australia.

The study estimates the benefits and costs of the beam trawl fishery to the Queensland economy in each of four study areas. Benefits are values of catches and costs include catching costs and costs imposed on the recreational and otter trawl fisheries, through by-catch, congestion and habitat disturbance in the case of the recreational fishery, and through competition for prawn stocks in the case of the otter trawl fishery. Chapter 2 of the study provides a comprehensive review of the beam trawl fishery. Chapters 3 and 4 deal with the interactions between the beam trawl fishery and the recreational fishery. Chapter 5 models these interactions together with the interaction with the otter trawl fishery. Chapter 6 summarises the study and presents the conclusions.

Three surveys were conducted of the beam trawl and related fisheries: a survey of the recreational boat and shore fishery in areas nominated by the Project Steering Committee; a beam trawl by-catch survey; and an income, costs and returns survey of beam and otter trawl vessels. Using the results of these surveys, together with those of previous surveys, information about the prawn fisheries available in published articles and reports, and vessel logbook data, a simulation model of the beam trawl fishery and its interactions with the recreational and otter trawl fisheries was constructed. The model was used to estimate the net contribution of the beam trawl fishery to the economy in each of four study areas: Area 1 between 27°S and the NSW border,  and Areas 2, 3 and 5. The net contribution is measured as prawn revenues less all variable, annual and capital costs, and less the costs imposed by beam trawling on the recreational and otter trawl fisheries.