Historical Baselines for Key Fish Stocks in Tasmania

Bastard trumpeter in kelp forestEstablishing Historical Baselines for Key Recreational and Commercial Fish Stocks in Tasmania, by Sven Frijlink and Jeremy Lyle, a report by the Institute for Marine and Antarctic Studies (IMAS) was published in November 2013. The project was funded by the Fishwise Community Grants Scheme - your licence fees at work.

Download the full report here (6 MB).

The study analysed historical documents dating back to early settlers, historical catch data and influences of exploitation levels, technological adaptations, management changes and recent climate change mediated temperature increases. An important component is the collation of anecdotal observations of change through semi-structured interviews with 'old time fishers'. Understanding the historical abundance and average size (length) may provide benchmarks or baselines from which subsequent changes can be evaluated and an understanding of how fish stocks have responded to varying degrees of fishing or environmental change.

This study contributes to a better understanding of changes in fish populations through time. Understanding the past state of fish stocks, particularly their abundance, provides a benchmark or baseline from which subsequent changes can be evaluated. This long-view approach to understanding the past state of a fishery can not only help to contextualise current stock levels but may have implications for the sustainable management of the fishery.

Five species were investigated in this study - Southern Sand Flathead (Platycephalus bassensis), Blue Warehou (Seriolella brama), Greenback Flounder (Rhombosolea tapiri), Bastard Trumpeter (Latridopsis forsteri) and Southern Rock Lobster (Jasus edwardsii).

The study analysed historical documents dating back to early settlers, historical catch data and influences of exploitation levels, technological adaptations, and management changes. Collated anecdotal observations of change through semi-structured interviews with 'old time fishers'.

The findings for each species from the Executive Summary of the published report are as follows:

Southern Sand Flathead

Historical fishery report cover pageIn Tasmania, Southern Sand Flathead are primarily targeted by recreational fishers: the species currently comprises around two thirds of all fish (by number) caught recreationally. While comparatively small quantities of Southern Sand Flathead are landed by the commercial fishery relative to the Tiger Flathead, commercial catch returns have generally not differentiated flathead catches by species and thus a reliable time series of Southern Sand Flathead catches is not available. Flathead (assumed to be primarily Southern Sand Flathead) were described from catches made from early explorers and catches and attitudes towards this species provided insights into the former states of flathead stocks. Prior to the second half of the 20th century the species was generally unpopular among Tasmanian consumers and had little commercial importance. This unpopularity was due to its 'ugly' appearance, its ubiquity ('commonness') and its reputation as a scavenger. Largely due to these perceptions, Southern Sand Flathead stocks were likely to have been in an unfished state up until the last 60 or so years. Based on interviews with fishers, it appears that stocks of legal-sized Southern Sand Flathead have declined considerably in both abundance and average size through time. Most fishers also reported that whereas the species tended to be widely distributed in large numbers, the distribution has become increasingly patchy in recent years.

Bastard Trumpeter

Unlike flathead, Bastard Trumpeter were very popular among Tasmanians soon after colonisation. These fish were abundant around inshore reefs and were generally caught using gillnets. Harvesting reduced densities of fish closest to populated areas, particularly Hobart. By 1916, most nearby areas had been fished and the average size of fish declined. Effort then expanded into unfished areas, particularly to the south west and west coasts and record volumes of the species were caught. By around 1940 however, few unfished areas remained and commercial catch rates and catches declined until the mid-1980s, when successive successful recruitment pulses appeared to increase their abundance. Catch rates declined again in the mid-1990s and catches over the past decade or so have remained low, in part linked to low market demand. Recently, recreational catch has exceeded the commercial catch. Fisher interviews suggest that, since the 1940s, catch rates may have declined as much as ninefold. They also report the increasing relative scarcity of the larger 'whitefish' and the lack of variation in size classes.

Blue Warehou

Blue Warehou, often called 'snotty trevally' or 'snotties', are known to be highly mobile with high inter-annual variation in their availability within Tasmanian waters. This variation in abundance was noted as early as the first half of the 19th century. When available, they were caught commercially by the gillnet fishery, which commenced in the south east and gradually spread to other areas. They have also been historically popular among recreational fishers, caught on line and with gillnets. Until around the 1980s, catch rates were good, suggesting that fishing activities to this date had little impact on this relatively fast growing species. However, overfishing in the Commonwealth managed commercial fishery during the 1980s and 1990s had a large impact on fish numbers, including the size of schools migrating into Tasmanian waters. Some fishers interviewed recalled catching upwards of 100 fish per net-set and would often restrict set times to avoid catching too many. Currently, catches are low and sporadic. The Commonwealth have implemented a stock rebuilding strategy.

Greenback Flounder

Flounder (assumed to be primarily Greenback Flounder) were often mentioned in the journals of early explorers who frequently caught them using seine nets off sandy beaches in Tasmania's south east. However, decades later, this method was responsible for the reduction of flounder numbers in the Derwent and Tamar estuaries, which were important sources of seafood for the fledgling colonies of Hobart and Launceston. This decline in local stocks eventually prompted remedial measures including the implementation of area closures and gear restrictions. The spread of the fishery to neighbouring waters and the rising prominence of other fisheries also shifted effort away from local flounder stocks at the time. Interview information suggests that although flounder stocks have in general not experienced the same degree of decline as some other species, localised depletions have occurred more recently. However, each of fishers interviewed held the view that the average size of legal-sized fish had not changed through time.

Southern Rock Lobster

Some early explorers and new colonists made explicit references to the abundance of Southern Rock Lobster on Tasmanian inshore reefs. In unfished or lightly fished
waters, dozens of fish could be captured in a short time using hoop nets (cray rings) or by wading in knee-deep water. Their abundance promoted a commercial fishery in the south east using hoop nets. Originally destined for local markets, Southern Rock Lobster began to be exported interstate from the 1870s, where they obtained higher prices. In Tasmania, they were not highly regarded by consumers. Nonetheless, sufficient local and interstate demand existed such that localised changes in density became apparent by the late 19th century. However, it was not until the legalisation of lobster pots in 1925 that catches escalated, primarily in response to growth in demand from interstate markets. The fishery expanded to unfished areas and many scalefishers transitioned into the more lucrative Rock Lobster fishery. By the mid-1940s, catch rates fell while catches continued to rise. The average size of fish caught also declined over time and plateaued in the 1960s. By this time, management measures were implemented to address the decline in Southern Rock Lobster stocks.

While robust commercial data for the fishery has been available for many years, information collected through interviews with fishers has provided a supplementary view from which to assess changes in Rock Lobster stocks, particularly in shallow inshore areas. Over time, interviewees reported travelling further and fishing deeper whilst catching fewer and smaller Rock Lobster. While data vary between regions, and are limited in terms of respondent numbers, overall recalled catch rates (legal sized Rock Lobster per pot-lift) declined from 5.9 in the 1950s to a current average of 0.7 Rock Lobster. This decline in recalled information is greater than was recorded in catch and effort data over the same period although consistent in general trend. Over the same period, fishers reported a 25% reduction in the average weight of legal-size Rock Lobster.

Concluding Remarks

Despite important differences between species in terms of fishing methods, ecological characteristics, sectoral utilisation and patterns of exploitation, this research suggests that abundances of each of the study species has declined considerably since European settlement. While this is expected, and is a natural consequence of fishing, the indications of the scale and speed of the declines for some species is of interest. Research needs have been indicated throughout this report to address knowledge gaps - particularly for species and/or regions for which additional information would facilitate a more accurate and complete picture of past and present fishery trends. Comparisons between Local Ecological Knowledge and commercial catch rate data for the Southern Rock Lobster fishery suggests that while interviewees accurately perceived the direction of abundance trends they have tended to overestimate their scale, particularly changes that occurred prior to 1995. It is possible that factors apart from recall bias may help explain these discrepancies, such as fishery scale effects and differences in fishing behaviour between recreational and commercial fishers. In recognising these uncertainties, catch rate trends reported by interviewees and their inferences about patterns of abundance and stock status need to be considered as being indicative of the direction rather than magnitude of change. In spite of these uncertainties, many of the observations in this report will serve as a useful reference for fishers, managers and researchers as they seek to understand the past states of fish stocks and set management targets.

Further Information:

Contact: IMAS
Institute for Marine and Antarctic Studies
Private Bag 129
Phone: 03 6226 6379
Email: imas.sandybay.reception@utas.edu.au


Recreational Fishing Enquiries
Recreational Fisheries Section
Level 3, 134 Macquarie St
Hobart TAS 7001
Phone: 03 6165 3233, 1300 720 647
Email: fishing.enquiries@dpipwe.tas.gov.au

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