Jm Lyle

The mid-slope demersal fish community off southeastern Australia

Abstract The mid-slope (800–1200 m) demersal fish community off southeastern Australia was sampled at 376 random, depth-stratified trawl stations. The mean density of demersal species was 4.82 g m −2 . Thirty-seven families and 111 species of demersal fish were represented in the catch. The density of mid-slope fishes off southeastern Australia was comparable to that observed in the Northern Hemisphere. However, landings and acoustic and egg surveys of orange roughy ( Hoplostethus atlanticus ) indicate that densities of that species alone are an order of magnitude higher than the total fish density indicated by trawl surveys. Water-column productivity over the mid-slope region appears insufficient to support the higher range of density estimates, implying a significant flux of energy into the region either from offshore or downslope. The dominant mid-slope demersal fishes appear to comprise an identifiable community within a biogeographic province that extends at least from the Great Australian Bight to the Chatham Rise (New Zealand), a distance of ∼5000 km. Distinct assemblages of demersal fish were found at upper (500 m) and mid-slope (800–1200 m) depths off southeast Australia. The mid-slope community could be sub-divided into assemblages by depth (shallow, intermediate and deep) and area (east and west Tasmania), which were statistically robust although with considerable overlap of species composition. There was no overlap in species composition of the southeast Australian mid-slope demersal fish community with fish communities at similar latitudes and depths in the North Pacific, but there were affinities with those in the North Atlantic. These biogeographic patterns, which appear consistent with oceanic circulation at intermediate depths, provide strong evidence that negates the recent hypothesis that deepwater fish communities cannot be defined over broad areas and are only random assemblages ( Haedrich and Merrett , 1990, Progress in Oceanography , 24 , 239–250).

Stock assessment of the blue grenadier Macruronus novaezelandiae resource off south-eastern Australia

The fishery can be divided into two subfisheries (‘spawning’ and ‘non-spawning’). Commercial catch rates for the ‘non-spawning’ subfishery declined from the late 1980s to 1997, whereas those for the ‘spawning’ subfishery exhibit no obvious temporal trend. An ‘Integrated Analysis’ assessment, of the feasibility of reconciling these differing trends, uses catch (landed and discarded), catch rate, length-at-age, and catch-at-age data and estimates of absolute abundance based on the egg-production method. It emphasizes uncertainty due to model assumptions and the data included in the assessment. Use of the discard data allows more precise estimation of the magnitude of recent recruitments. Spawning biomass is estimated to have declined from a peak in 1989–91 to 1999 although fishing mortality has consistently been <6%for each subfishery. One main reason for the reduction in population size is the weakness of year-classes spawned from 1988 to 1993. Differences in catch rates between the two subfisheries can therefore be explained by interactions between the components of the population harvested by the two ‘subfisheries’, and the trends in year-class strength. A risk analysis is used to evaluate the consequences of different future levels of harvest for different assessment assumptions. Overall, the spawning biomass is predicted to increase over the next five to ten years as a result of the strong 1994 and 1995 year-classes, although the extent of this increase remains uncertain.

Validation of age and growth in a long-lived temperate reef fish using otolith structure, oxytetracycline and bomb radiocarbon methods

Generating age estimates for long-lived fish requires particular attention to validation because they are usually difficult to age owing to narrow increment structure. A robust validation of the accuracy and precision of banded morwong, Cheilodactylus spectabilis, sampled from Tasmanian waters, was undertaken. Age at the first enumerated increment was established from analysis of juvenile cohorts, and the timing and periodicity of increment formation was established using a quantitative model from oxytetracycline (OTC) mark-recaptures at liberty for periods of up to 8 years. The accuracy of age estimates was examined independently by comparing radiocarbon values in the otolith region corresponding to the first year of growth against the south-western Pacific calibration curve. C. spectabilis is very long-lived, with males and females living to over 90 years of age. Growth modelling revealed a fast initial growth phase, terminating in an abrupt plateau near the asymptotic length. This species displays substantial sexual dimorphism in growth, with males growing to larger sizes than females.

High survivorship after catch-and-release fishing suggests physiological resilience in the endothermic shortfin mako shark (Isurus oxyrinchus)

We used satellite tags and blood based analyses to examine the impacts of catch and release angling on the shortfin mako shark. We report high survivorship seemingly unaffected by fight time or physiological stress and recommend that circle hooks should be used to reduce physical damage to these sharks.

Scale- and context-dependent selection of recreational harvest estimation methods: the Australasian experience.

Abstract Fisheries managers are becoming increasingly aware of the need to quantify all forms of harvest, including that by recreational fishers. This need has been driven by both a growing recognition of the potential impact that noncommercial fishers can have on exploited resources and the requirement to allocate catch limits between different sectors of the wider fishing community in many jurisdictions. Marine recreational fishers are rarely required to report any of their activity, and some form of survey technique is usually required to estimate levels of recreational catch and effort. In this review, we describe and discuss studies that have attempted to estimate the nature and extent of recreational harvests of marine fishes in New Zealand and Australia over the past 20 years. We compare studies by method to show how circumstances dictate their application and to highlight recent developments that other researchers may find of use. Although there has been some convergence of approach, we suggest th...

Super Trawler Scuppered in Australian Fisheries Management Reform

ABSTRACT In response to an intense social media campaign led by international conservation groups, Green politicians, and recreational fishers, the Australian government imposed a moratorium on the operations of a large factory trawler. This moratorium overrode the governments own independent fisheries management process by making amendments to its key environmental legislation just days prior to the commencement of fishing by this vessel. Concurrently, the government announced a comprehensive review of Australias fisheries management legislation. Whereas science is usually deployed in support of conservation in natural resource conflicts, in this case science-based fisheries management advice took a back seat to vociferous protest by interest groups, perpetuated by the media (in particular social media), ultimately culminating in a contentious political decision.

Effects of hooking damage and hook type on post-release survival of sand flathead (Platycephalus bassensis)

This study examined post-release survival in sand flathead (Platycephalus bassensis) and whether there were survival benefits from the use of circle hooks over conventional hook patterns. Anatomical hooking location was the major factor contributing to mortality, with an almost 100% survival rate for fish hooked in the lip, mouth or eye (shallow-hooked) compared with around 64% for fish hooked in the throat or gut (deep-hooked). Mortality in deep-hooked fish was generally associated with injuries to vital organs (gills, heart, liver) and survival was significantly lower if bleeding was associated with injury (54% compared with 85% for non-bleeders). Circle hooks resulted in significantly lower deep-hooking rates (1%) compared with conventional hook types (4-9%) and, based on catch rates, were at least as effective as conventional hook patterns. Estimated survival rates for line-caught sand flathead were high, over 99% for circle hooks and between 94 and 97% for conventional hooks. These findings support the efficacy of management strategies based on size and bag limits and the practice of catch-and-release fishing for sand flathead, as well as a potential conservation benefit from the use of circle hooks.

Rapid changes in life-history characteristics of a long-lived temperate reef fish

Banded morwong, Cheilodactylus spectabilis, a long-lived sedentary temperate reef fish, has undergone rapid changes in its growth and maturity characteristics along the east coast of Tasmania, Australia. Over a period of 10 years, growth of young males and females has consistently accelerated, such that in 2005, 3-year-old fish were up to 40 mm or 13% longer compared with 1996, and age at 50% maturity for females had declined from 4 to 3 years. The magnitude and speed of the observed changes were unexpected given the species’ longevity (maximum age of over 95 years). The underlying mechanisms for the changes remain unclear but density-dependent responses to changes in population size and age composition, possibly mediated through reduced competition for shelter and intra-specific interactions, may have been contributing factors. Increasing sea surface temperatures over part of the period of change does not appear to have been a major driver and a genetic response to fishing seems unlikely. Notwithstanding any uncertainty, C. spectabilis populations have become more productive in recent years, challenging the general approach towards stock assessmentwhere life-history characteristics are assumed to remain stable across contrasting levels of stock abundance and environmental conditions.

Characterisation of the recreational fishery for southern rock lobster Jasus edwardsii , in Tasmania, Australia: implications for management

Abstract Southern rock lobster (Jasus edwardsii) support significant commercial and recreational fisheries in Tasmania, Australia. Since the mid 1990s the number of persons holding recreational lobster licences increased by over 80%, with c. 15 500 persons licensed in 2002/03. Assessment of the recreational fishery has been undertaken periodically since 1996 using a telephone‐diary survey method. The fishery was concentrated off the south‐east and east coasts of Tasmania and characterised by strong seasonality in catch and effort, which peaked markedly early in the fishing year (November‐January). Although pots were the most popular fishing method, daily catch rates by divers were more than double those for pots. Divers selectively harvested larger lobsters than those taken by pots and more frequently attained the daily bag limit of 5 lobsters. The estimated recreational harvest increased significantly since 1996/97 and in 2002/03 effectively reached a management trigger level of 10% of the total allowable commercial catch, flagging a review of recreational management arrangements.

Long-term patterns in estuarine fish growth across two climatically divergent regions

Long-term ecological datasets are vital for investigating how species respond to changes in their environment, yet there is a critical lack of such datasets from aquatic systems. We developed otolith growth ‘chronologies’ to reconstruct the growth history of a temperate estuarine fish species, black bream (Acanthopagrus butcheri). Chronologies represented two regions in south-east Australia: South Australia, characterised by a relatively warm, dry climate, and Tasmania, characterised by a relatively cool, wet climate. Using a mixed modelling approach, we related inter-annual growth variation to air temperature, rainfall, freshwater inflow (South Australia only), and El Niño–Southern Oscillation events. Otolith chronologies provided a continuous record of growth over a 13- and 21-year period for fish from South Australia and Tasmania, respectively. Even though fish from Tasmania were sourced across multiple estuaries, they showed higher levels of growth synchronicity across years, and greater year-to-year growth variation, than fish from South Australia, which were sourced from a single, large estuary. Growth in Tasmanian fish declined markedly over the time period studied and was negatively correlated to temperature. In contrast, growth in South Australian fish was positively correlated to both temperature and rainfall. The stark contrast between the two regions suggests that Tasmanian black bream populations are more responsive to regional scale environmental variation and may be more vulnerable to global warming. This study highlights the importance of examining species response to climate change at the intra-specific level and further validates the emerging use of growth chronologies for generating long-term ecological data in aquatic systems.