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This study presents inter-annual variability of otolith growth from 1993 to 2011 and cohort specific sex ratios from 1976 to 2011 in blue grenadier Macruronus novaezelandiae on the west coast of Tasmania. Length-at-age data highlighted that M. novaezelandiae females grow larger than males with mean length-at-age statistically diverging by three years of age and remaining separated thereafter. Statistical differences in both cumulative, and age specific otolith increment widths-at-age between sexes were detected at earlier ages, but these effects were variable and not consistent with the sexual dimorphism observed for mean length at age. No differences between sexes were evident for the ages 8–14 or 7–11 for cumulative increment widths or age specific otolith increment widths-at-age respectively. Inter-annual variation in mean otolith increment widths for the first five increment zones (juvenile zones) showed a trend of declining increment widths from 2006 to 2010. Inter-annual cohort sex ratio variation across year-of-birth was also significant displaying a similar trend to the first-year otolith increment growth profiles. Regression analysis of birth year sex ratio with mean otolith increment widths indicated a significant negative relationship for first year growth with increasing numbers of male offspring. The inter-annual variation in cohort specific sex ratio suggests that environmental factors may be involved with sex determination. When coupled with climate change these influences could have long term consequences for the fitness of the stock and corresponding flow-on effects into the stock assessment process and future management of the stock. [ABSTRACT FROM AUTHOR]

An industry-based acoustic observation program was developed and applied to the austral winter spawning blue grenadier fishery from 2002. Blue grenadier has the highest Total Allowable Catch (TAC) among fished stocks of Australia’s Southern and Eastern Scalefish and Shark Fishery (SESSF). High recruitment variability and stock size uncertainty motivated development of an industry-based cost-effective acoustic monitoring program in 2002 to optimise harvest while ensuring sustainability. The development of industry-based acoustic methods resulted in “routine” surveying being carried out by skippers on industry vessels since 2006. During this time an incentive based management approach was introduced by allocation of research quota to assist in the long term implementation and delivery of the biomass indicator. The survey strategy of the industry-based method differed significantly from chartered vessel based surveys; fishers were tasked with recording the maximum biomass during the spawning season. This monitoring method shifted the “burden of proof” to industry and reinforced the need for both local and broad scale surveys to estimate the stock size. Survey results have been used for management advice by reducing uncertainty in stock size, inclusion in the stock assessment model and informing spatial planning for the region. An associated outcome was the confidence by industry that fishers’ observations of the spawning biomass were recorded and used in the stock assessment process for management of the fishery. [ABSTRACT FROM AUTHOR]

Hoki ( Macruronus novaezelandiae ) is New Zealand's largest fishery. Acoustic surveys of spawning hoki provide abundance indices for informing management of the stocks. For estimating fish abundance using acoustic methods, relationships between the acoustic backscatter from a single fish, commonly known as the acoustic target strength (TS), and fish length are required. Here we present in situ data on TS from individual live hoki, collected using a trawl-mounted acoustic-optical system (AOS). Deriving TS–length relationships from measurements of individual fish is complicated because of the very large stochastic variability in TS from the same fish, and from individual fish of similar length. A new TS–total length relationship of TS = 24.5log 10 (TL) − 83.9 was derived based on a weighted non-linear least-squares fit to acoustic backscattering cross-section measurements from 62 New Zealand hoki between 35 and 93 cm TL. It was necessary to use a weighted fitting method to appropriately account for variance, as not doing so can introduce a bias to the estimated mean TS. Using the new TS–TL relationship decreases absolute estimates of hoki abundance by 50–60% from those currently used in stock assessment, but has little impact on relative indices. Estimated 90% confidence intervals around the new TS–TL relationship based on bootstrapping suggested uncertainty in mean TS of ±1.5 dB at typical New Zealand hoki lengths, with resulting uncertainty in abundance estimates of up to 50%. Further in situ measurements and modelling are required to reduce this uncertainty and to investigate potential differences in TS between AOS-measured and ‘undisturbed’ fish. [ABSTRACT FROM AUTHOR]

Niklitschek, E. J., Secor, D., Toledo, P., Valenzuela, X., Cubillos, L., and Zuleta, A. 2014. Nursery systems for Patagonian grenadier off Western Patagonia: large inner sea or narrow continental shelf? – ICES Journal of Marine Science, 71: 374–390.Adjacent to Chile's long and narrow continental shelf, the Patagonian Inner Sea (PES) is among the largest and most complex estuarine systems in the world. The PES harbours high concentrations of juveniles and adults of important groundfishes, which spawn within or in near proximity to it. A dominant view is that recruitment primarily originates here rather than in adjacent coastal regions. We used otolith stable isotopes to evaluate the relative contribution of several PES and continental shelf regions to recruitment of Patagonian grenadier, one of the most abundant groundfishes in the area. Seawater chemistry confirmed that δ13C and δ18O differentiated these nursery and feeding regions. Estimated recruitments from PES nurseries to adult feeding regions were important (10–35%), but lower than dominant contributions from shelf nurseries (64–85%). Stable isotope differences within otoliths indicated, however, that most adults had previously used PES habitats as subadults. Adults exhibited stronger homing to feeding habitats in the PES than to shelf regions, suggestive of seasonal site fidelity or partial migration behaviours. The proximity of principal spawning areas to the bifurcation of the West Wind Drift Current may cause large interannual and decadal variations in larvae transport and the relative contribution of different shelf and PES nurseries to recruitment. [ABSTRACT FROM PUBLISHER]

Abstract: The aims of the present study were to investigate the protozoan and metazoan parasite fauna of hoki Macruronus magellanicus in the Southwest Atlantic and Southeast Pacific and to identify parasites of potential value as biological tags for stock identification and migrations. In 2007 a total of 76 hoki were examined from three locations, two off the coast of Chile and one off the Falkland Islands. Two further samples were taken in 2009, one of 32 hoki taken from a position off the coast of Chile between those sampled in 2007 and one of 42 juvenile hoki taken off the Falkland Islands. Seventeen different parasite taxa were recorded, including eight identified to species. Seven were new host records for hoki, and at least three, and possibly as many as five, are new species. The most promising tag parasites for hoki stock identification are the long-lived larvae of the cestodes Hepatoxylon trichiuri and Pseudophyllidea gen. sp. and of the nematode Anisakis sp. Three others – the myxosporean Myxidium baueri, the nematode Pseudascarophis sp. and the acanthocephalan Echinorhynchus longiproboscis – were identified as potentially useful for following seasonal migrations of hoki and for estimating the proportions of fish of different origin in mixed samples. [Copyright &y& Elsevier]

Kloser, R. J., Ryan, T. E., Macaulay, G. J., and Lewis, M. E. 2011. In situ measurements of target strength with optical and model verification: a case study for blue grenadier, Macruronus novaezelandiae. – ICES Journal of Marine Science, 68: 1986–1995.In situ measurements of target strength (TS) of isolated fish surrounding dense schools need to be representative of the schooling fish to calculate their echo-integrated biomass. Using synchronous optical and acoustic measurements from a pelagic fishing net, the standard length (81 cm, n = 128), tilt-angle (−9°), and net-disturbed in situ TS (−34.4 dB) of Australian Macruronus novaezelandiae (blue grenadier) were confirmed at depth. In situ drift experiments of assumed undisturbed but dispersed blue grenadier recorded a mean TS of −31.8 dB (CI −33.1 to −30.9 dB) with attributed fish standard lengths of 83 cm (s.d. 7.5 cm) and weight 2.5 kg. Modelling the gasbladder showed that uncertainties in fish length, orientation, and gasbladder size could explain the differences observed. Blue grenadiers have negative buoyancy because the cavity size of their gasbladder is smaller than the volume of gas required for neutral buoyancy at depth. For the same species and length, New Zealand hoki weigh less and have smaller gasbladders than Australian blue grenadier, suggesting a conversion factor of 1.10 in length for comparative measurements. Net-attached acoustic and optical measurements indicate that model and drift in situ measurements are biased high by 2.9 and 1.0 dB, respectively. Net-attached acoustic and optical measurements are a cost-effective method of monitoring TS routinely at depth for changes in species length and weight. [ABSTRACT FROM PUBLISHER]

A monthly characterization of Chilean hoki aggregations was done using acoustic records obtained with SIMRAD EK60 and ES60 devices aboard three multipurpose vessels that operated in the centralsouthern fishery unit during 2003; this considered morphological and bathymetric descriptors. The wide morphological variation of the aggregations was explained by their cohesion level and tendency to form large horizontal aggregations whereas, bathymetrically, 90% of the aggregations were located between 300 and 450 m. Evidence of associations between various descriptors was found, and these were, in turn, associated with other factors such as mean size, water temperature, latitude, and month, allowing an adequate description of the shape of the aggregations and their location in the water column. The relevant relationships were: aggregation depth with regard to bottom depth (r = 0.55), aggregation altitude with regard to bottom depth (r = 0.72), aggregation altitude with respect to the relative depth index (r = -0.98), and aggregation depth with respect to mean size (r = 0.66). [ABSTRACT FROM AUTHOR]