Inshore demersal fish stocks in Australia’s north-west face increased exploitation pressure by an ever increasing number of recreational fishers in direct competition with an adjacent commercial fishing industry. There is, therefore, an urgent need to determine the species distribution and the composition of demersal scalefish resources in the inshore region of north-western Australia in waters outward from the shoreline to depths of 30 metres, including the documentation of the abundance and diversity of any significant finfish by-catch of prawn trawlers operating within the region, as a basis for formulating rational management plans for the exploitation of the demersal scalefish resource among user-groups.
The sharing of the inshore demersal fish resource in this region will require careful future management to ensure sustainability and avoid conflict among these user groups. This project will provide baseline information on the species composition and relative abundance of the inshore fishes of Australia’s north-west and identify possible nursery areas of species of commercial and recreational fishing significance which may need protection, possibly as nursery closures, in the future. Furthermore, in order to facilitate sagacious management plans and to safeguard the interests of commercial and recreational fishers, the baseline information on the nearshore fishery resources of the north-west provided by this study can be used to assess the impact of any possible access restrictions that may be imposed in areas nominated as future marine reserve sites in north-western Australia.
The catches of the main fish species obtained by commercial, recreational and charter boat fishers along the Pilbara and Kimberley coasts have been determined by analysing the Department of Fisheries Western Australian Catch and Effort Database System (CAES), the results of a recreational creel survey and the statutory monthly reports of catch and effort by charter boat operators.
The weight of finfish caught by nearshore and inshore commercial fishers along this coast during 2002 was approximately 590 tonnes. The total annual recreational fishing effort along the coast between Onslow and Broome in 2002 was estimated as 190,000 fisher days, which yielded approximately 320 tonnes of fish. The 111 licensed charter boat operators in the Pilbara and Kimberley undertook 3628 tours in 2002, during which they caught 53 tonnes of fish. Thus, the total catch from all three sources approached 1000 tonnes.
Nearshore, shallow waters on beaches and in mangroves and intertidal pools in three regions along the Pilbara and Kimberley coasts were sampled during the wet and dry periods of two consecutive years. Data derived from the resultant catches were used to determine the ways in which fish species use the different habitat types and how the characteristics of the fish faunas varied with latitude, habitat type and season.
The fish catches from all habitat types collectively yielded 170 species representing 66 families. Fifty three of these species are fished commercially and recreationally along the Pilbara and Kimberley coasts, and a further 17 fish species are caught solely by recreational fishers. The most abundant species included the blue and king threadfin salmons, salmon-tailed catfish, the blue-spot and large-scale mullets, queenfish, western school whiting, Quoy’s garfish, Moses snapper and estuary rockcod.
Some species, such as the two threadfin salmons, spend the whole of their life cycle in nearshore, shallow waters, whereas others, such as Moses snapper and estuary rockcod, use those waters solely as a nursery area. Species such as the two threadfin salmons and also whiting species were caught predominantly over bare sand, whereas species such as the large-scale mullet and the nervous shark were obtained mainly from mangroves, and Moses snapper and estuary rockcod were collected almost exclusively from intertidal pools.
The species compositions of the fish assemblages were influenced not only by habitat type, but also by season and region and also apparently the extent of tidal action and thus turbidity. Differences between the compositions in the extreme wet and dry periods found in the region were attributable to emigrations and immigrations of large numbers of particular species at certain times. For example, mature catfish aggregate in nearshore, shallow waters during the wet period.
This project has synthesised the available data from commercial, recreational and charter boat fisheries with baseline survey data throughout the region. In order to build on the outcomes of this project a number of priority areas for research in this nearshore zone have been identified.
These priority areas of research include; estimation of biological parameters of key species for the purposes of fisheries management (a list of key species is provided in the Further Development Section of this Report); evaluation and assessment of recreational and aboriginal netting activities in the Pilbara and Kimberley region of north-western Australia; determination of the genetic stock structure of the key species of commercial and recreational fishing significance in the nearshore areas throughout north-western Australia to define the appropriate spatial scale for fisheries management; and refinement of commercial and recreational data collection programs in the Pilbara and Kimberley region of north-western Australia.
Keywords: Tropical, commercial, recreational, nursery habitats, nearshore reefs, estuaries, beaches, intertidal, rockpools.
There is clearly a concern in the Tasmanian lobster industry about the status of inshore component of the stock. Catch has declined in a number of areas, despite improvements in catch rates. In the Northeast, catch is at record lows, but CPUE has remained stable, which is a possible indicator of hyper-stability or false stability. The apparent stability in catch rates occurs because aggregations containing a major proportion of the population are fished down, as the fleet moves from one area of good catch rates to the next, resulting in a serial depletion of the aggregations, which is masked by the apparent stability in the fishing block. This can result in a very sudden decline in biomass once the entire block is depleted, posing a serious and immediate risk to the inshore component of the stock. There are two potential sources of this problem. Firstly, the scale of the current assessment model, of eight inshore areas (64m) and three offshore areas (>64m) is not be fine enough to detect localised changes in the CPUE or biomass. Secondly there are changes in fishing practices that have increased effort on inshore stocks, and it is unclear whether the extra effort in these practices is adequately recorded in estimates of CPUE. There has been a recent increase in potting effort, commonly referred to as double night fishing, whereby fishers set and haul their pots twice a night, compared to the standard practice of emptying pots once at dusk and/or once during the day. Currently we have no data on the composition of the catch in double night shots, and what proportion of captured lobsters are handled and released, and in fact what consequence this handling has on the overall health of the fishery.
There is a critical need for information to support management decisions about inshore fisheries resources, and to address rising industry, conservation and public concern about the impact of net fishing on sustainability and biodiversity of the ecosystem and habitats associated with the fishery. The theory of measuring changes in biodiversity have yet to be applied in net fisheries. This project will be a test case for the practical application of determining net fishing effects on biodiversity.
Information on the effect of net fishing on bycatch and biodiversity in Australia is extremely limited. While some data exist on the marketed catch, the quantity and nature of bycatch remains virtually unknown. There is little information on the total catch characteristics of net fisheries, the proportions of species caught, and the proportion of the resource harvested each year. Similarly little is known about the fate of fish discarded from nets which would help to characterise the impact of net fishing on biodiversity.
This project will address the urgent need for information on the: total catch composition from net fishing, fate of discarded fish bycatch, impact on protected species and impact on biodiversity. Baseline data collected through both fishery dependent and independent methods will provide a basis for long term monitoring of the fishery and will enhance the interpretation of existing commercial catch records. These data will help meet the requirements of the ‘National Strategy for Conservation of Australia’s Biological Biodiversity’ of a) improving the knowledge base of fisheries, b) improving fisheries management and c) assessing and minimising the impact of commercial fishery practices on non-target and bycatch species, ecosystems and genetic diversity.
In Tasmania, there is a paucity of information on the life-history, population parameters and habitat requirements of fish associated with inshore soft-sediment habitats, particularly seagrasses. Clearly, such information is needed before stock assessment models can be developed, recruitment processes understood, key habitats identified and appropriate management measures developed to minimise impacts on these habitats. In order to examine the structure of fish communities in coastal soft-sediment habitats around Tasmania, the demersal and larger mobile fish fauna were routinely sampled from three areas-Norfolk Bay, Georges Bay and Prosser Bay. In each area, representative unvegetated (mud and sand) and seagrass habitats between 1 and 12 m deep were sampled seasonally.
In Tasmania, there is a paucity of information on the life-history, population parameters and habitat requirements of fish associated with inshore soft-sediment habitats, particularly seagrasses. Clearly, such information is needed before stock assessment models can be developed, recruitment processes understood, key habitats identified and appropriate management measures developed to minimise impacts on these habitats. In order to examine the structure of fish communities in coastal soft-sediment habitats around Tasmania, the demersal and larger mobile fish fauna were routinely sampled from three areas-Norfolk Bay, Georges Bay and Prosser Bay. In each area, representative unvegetated (mud and sand) and seagrass habitats between 1 and 12 m deep were sampled seasonally.
The fish fauna associated with Heterozostera seagrass and unvegetated habitats were compared in all three areas. Seagrass sites had a significantly higher abundance of demersal fish and a distinct community compared to unvegetated sites in Norfolk Bay and Georges Bay. In contrast, neither abundance or community composition differed between habitats in Prosser Bay. This pattern may be attributed to the patchy distribution of seagrass beds that result from the higher degree of exposure of the bay and the significant loss of beds over the past 20-30 years. Demersal fish in seagrass beds were dominated by small resident species, while those in unvegetated habitats were dominated by juveniles of larger species. Few larger more mobile species showed a distinct habitat preference. Unvegetated habitats were found to be more important than seagrass as a nursery area for juveniles of commercially important finfish species.
