Zealand Hoki Research Articles

Modelling recruitment in a spatial context: A review of current approaches, simulation evaluation of options, and suggestions for best practices

Many, if not most, stocks of fish and invertebrates subject to commercial, recreational or subsistence harvesting exhibit some degree of spatial heterogeneity. This can be due to a lack of complete movement within a single biological population or due to the assessed region consisting of multiple sub-stocks. In principle, assessments for stocks for which the assumption of homogeneity is violated should be based on population dynamics models that are spatially-explicit. There are, however, relatively few stocks for which multi-stock/multi-area assessments are conducted. However, the number of assessments in which space is explicitly represented in the population dynamics model has been increasing in recent years and such models are available for fish stocks such as New Zealand hoki and canary rockfish off the US west coast, as well as invertebrates such as the rock lobsters off southern Australia and New Zealand. A challenge within such spatially-explicit assessments pertains to how recruitment and movement are modelled. This paper reviews assessments for fish and invertebrate stocks that are based on spatially-explicit models, identifying the challenges associated with modelling recruitment caused by increased model and parameter estimation complexity, and the available solutions. A set of illustrative simulations are undertaken to evaluate the consequences of different assumptions regarding spatial recruitment and movement, and hence develop some recommendations for best practice guidelines.

Physicochemical Properties and Bioactivity of Extracts from the Roe of New Zealand Hoki and Southern Blue Whiting

ABSTRACTVarious physicochemical properties of New Zealand hoki and southern blue whiting (SBW) roes and the biological activities of their extracts were investigated. Protein, moisture, and ash contents in both roes were similar; however, the lipid content of hoki roe was higher (p < 0.05) than SBW roe (11.0 ± 0.9 and 2.5 ± 0.1, respectively). Both fish roe extracts contained active protease inhibitors toward trypsin and papain. Neither of the roe extracts agglutinated erythrocytes, indicating the absence of lectins. Both fish roe extracts at 5 mg/mL concentration exhibited slight inhibitory effects on the proliferation of breast cancer cells, but neither of the roe extracts exhibited RNase or antifungal activity.

Coincident recruitment patterns of Southern Hemisphere fishes

Three dominant recruitment patterns were identified across 30 stocks from Australia, New Zealand, Chile, South Africa, and the Falkland Islands using data from 1980 to 2010. Cluster and dynamic factor analysis provided similar groupings. Stocks exhibited a detectable degree of synchrony among species, in particular the hakes and lings from Australia, New Zealand, Chile, and South Africa. We tested three climate indices, the Interdecadal Pacific Oscillation (IPO), Southern Annular Mode (SAM), and Southern Oscillation Index (SOI), to explore their relationship with fish stock recruitment patterns. The time series of IPO and SOI showed the strongest correlation with New Zealand hoki (blue grenadier, Macruronus novaezelandiae) and Australian jackass morwong (Nemadactylus macropterus) (r = 0.50 and r = –0.50), and SAM was positively related to Australian Macquarie Island Patagonian toothfish (Dissostichus eleginoides) (r = 0.49). Potential linkages in recruitment patterns at sub-basin, basin, and multibasin scales and regional and global climate indices do account for some of the variation, playing an important role for several key Southern Hemisphere species.

Improvements in estimating an acoustic target strength–length relationship for hoki (Macruronus novaezeladiae)

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=24.5log10(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 93cm 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 ±1.5dB 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.

Purification of Alaskan walleye pollock (Gadus chalcogrammus) and New Zealand hoki (Macruronus novaezelandiae) liver oil using short path distillation.

The beneficial health effects of a diet rich in n-3 long chain polyunsaturated fatty acids (n-3 LC-PUFA) have been extensively researched in recent years. Marine oils are an important dietary source of n-3 LC-PUFA, being especially rich in two of the most important fatty acids of this class, EPA (eicosapentaenoic acid; 20:5n-3) and DHA (docosahexaenoic acid; 22:6n-3). Oils rich in n-3 LC-PUFA are prone to oxidation that leads to loss of product quality. Alaskan pollock (Gadus chalcogrammus Pallas, 1814) and New Zealand’s hoki (Macruronus novaezelandiae Hector, 1871) are the highest volume fisheries of their respective countries. Both produce large quantities of fishery byproducts, in particular crude or unrefined n-3 LC-PUFA containing oils. Presently these oils are used as ingredients for animal feed, and only limited quantities are used as human nutritional products. The aim of this research was to investigate the applicability of short path distillation for the purification of pollock and hoki oil to produce purified human-grade fish oil to meet quality specifications. Pollock and hoki oils were subjected to short path distillation and a significant decrease in free fatty acids and lipid oxidation (peroxide and para-anisidine values) products was observed. Purified oils met the Global Organization for EPA and DHA Omega-3 (GOED) standard for edible fish oils.

Chemical modification of New Zealand hoki (Macruronus novaezelandiae) skin gelatin and its properties

Chemical modifications of gelatin from New Zealand hoki (Macruronus novaezelandiae) skins were carried out using three different cross-linking agents, namely, genipin, glutaraldehyde and caffeic acid, at different concentrations. The chemically modified gelatins exhibited better physical properties, such as higher gel strength, melting point, and rheological properties than did the uncross-linked gelatin. Gelatin cross-linked with glutaraldehyde had higher gel strength and melting point (231g, 21.9°C) than those cross-linked with caffeic acid (229g, 21.6°C) and genipin (211g, 20.5°C) at concentrations of 0.133, 0.111, and 0.044M, respectively. The elastic modulus (G′) and the loss modulus (G″) of chemically cross-linked gelatins were higher than those of the uncross-linked ones. These improved physicochemical properties of gelatin could lead to the development of products in the food industry that meet consumer demands.

Optimization of gelatine gel preparation from New Zealand hoki (Macruronus novaezelandiae) skins and the effect of transglutaminase enzyme on the gel properties

Response Surface Methodology (RSM) was adopted to optimize the preparation of NZ hoki (Macruronus novaezelandiae) gelatine gels treated with Transglutaminase (TGase) and some of the rheological properties were characterized. The optimum concentration of the enzyme [X1] was 3.33 mg/g, incubation time, [X2] was 30 min, and incubation temperature, [X3] was 37 °C. The calculated gel strength achieved by RSM was in very good agreement with the experimental value. The addition of TGase to hoki gelatine at the optimum concentration of increased the gel strength from 197 ± 5 g to 278.2 ± 0.19 g and the melting point from 21.4 ± 0.8 °C to 25.9 ± 0.1 °C. The increase in the G' values with the addition of TGase indicated the formation of firmer gels and the changes in G' and G" values with increase in temperature showed increase in melting point.

In situ measurements of target strength with optical and model verification: a case study for blue grenadier, Macruronus novaezelandiae

Abstract 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.

Flavour development in dairy cream using fish digestive lipases from Chinook salmon ( Oncorhynchustshawytscha) and New Zealand hoki ( Macruronusnovaezealandiae)

Digestive lipases from Chinook salmon and New Zealand hoki were evaluated as flavour modifying agents in dairy products. Cream was incubated either with fish lipase or commercially available lipases used in dairy flavour development – calf pregastric esterase (Renco™ PGE) and microbial lipase (Palatase® 20,000 L). The fish enzymes were more similar to calf PGE in terms of the total amount and types of fatty acids released over the course of the reaction. Like the pregastric esterase, the fish enzymes released mainly short chain fatty acids. The highest specificity was towards the key dairy product flavour and odour compounds, butanoic and hexanoic acids. The odour intensity of hexanoic acid produced by the salmon lipase, as measured by SPME–GC–MS, was similar to that produced by both Palatase® and PGE. Free fatty acid composition, together with sensory characteristics of lipase-treated creams, demonstrated the potential for flavour enhancement in dairy products using fish lipases.

Diet and dietary variation of New Zealand hoki Macruronus novaezelandiae

The diet of hoki was determined from examination of stomach contents of 1992 fish of 26–112 cm total length (TL) sampled at depths of 209–904m on Chatham Rise, New Zealand, from summer research trawl surveys and seasonal commercial fishing trawls, during 2004–2008. Prey was predominantly euphausiids, mesopelagic fishes and natant decapods. Multivariate analyses using distance-based linear models, non-parametric multi-dimensional scaling and similarity percentages indicated that the best predictors of diet variability were the position of the fish in relation to the subtropical front (STF), fish size and longitude. Pasiphaeids were more important to the north of the STF, and sternoptychid fishes and euphausiids more important in the STF convergence area. Euphausiids and sternoptychid fishes were important for smaller hoki (26–55 cm TL), myctophid fishes and natant decapods for larger hoki, and macrourids for the largest hoki (>84 cm TL). The longitudinal effect was characterised by pasiphaeids, euphausiids and sternoptychids to the west, and myctophids in the centre of Chatham Rise. Feeding activity was analysed using generalised additive models, and was found to vary with time of day, sample source (research or commercial), longitude, hoki size and depth. The variability in diet suggested hoki forage opportunistically within their preferred habitat and biological limits.

Catch-quota balancing in mixed-fisheries: a bio-economic modelling approach applied to the New Zealand hoki (Macruronus novaezelandiae) fishery

Managing adequately the exploitation of commercial species subject to technical interactions is a key step towards the ecosystem approach to fisheries. We evaluate here, using a bio-economic modelling approach building on the ISIS-Fish simulation platform, the relative impact of total allowable commercial catches (TACC) and of taxes appli- cable to over-quota landings (deemed value) on the sustainability of a selection of species exploited by the New Zealand hoki (Macruronus novaezelandiae) fishery. We investigate some aspects of the hoki mixed fisheries, consisting of four fleets and nineteen metiers, by considering the technical interactions between hoki and Southern hake (Merluccius aus- tralis). The dynamics of effort allocation were modelled using gravity model, using value per unit of effort (VPUE) as attractivity coefficient. Several management scenarios, based on different levels of TACC, effort limits and deemed value have been defined. The impact of these strategies on spawning biomass and catches has been investigated. The results confirm that the deemed value may, in combination with TACC, be an efficient management tool. By increasing the hoki deemed value, we could somehow limit the decrease in the hoki TACC needed to harvest Western hoki sustain- ably. Constraining hoki fishing also restricts Southern hake fishing in the Chatham Rise and in the West Coast South Island, but leads to increased targeting of this species in the Sub-Antarctic area. The relative costs of renting/buying quota or paying the deemed value are most constraining when the hoki TACC is at relatively low level and when the hoki deemed value is more than 1.5 times the current value.

Unreported bycatch in the New Zealand West Coast South Island hoki fishery

Abstract There are recognised benefits to managing fisheries by individual transferable quotas (ITQs), but ITQs may increase incentives to discard fish. Trawl data from government-observed trawlers in the New Zealand hoki fishery were used to predict catches of unobserved vessels. These predictions were compared with the catches unobserved vessels reported. Unobserved vessels’ reported catches were significantly different to observed vessels’ catches. There was clear evidence of misreporting in the hoki fishery. Misreporting deprives stakeholders of rentals, distorts catch statistics, and threatens the integrity of ITQ systems. If reporting is similarly biased in other fisheries, the issue cannot be safely ignored.

Links between climate and recruitment of New Zealand hoki (Macruronus novaezelandiae) now unclear

We investigated the relationship between climate variation and year‐class strengths for hoki (Macruronus novaezelandiae) in New Zealand waters. Our analyses extended those of a previous study, by using an additional 6 years’ data and considering some additional predictands (total year‐class strength and proportion migrating) relating to an alternative stock‐structure hypothesis, and also updated them, by using revised versions of some predictors and year‐class strengths. Predictors considered were based on the Southern Oscillation Index, weather patterns, sea‐surface temperatures, wind speeds, and modelled mixed‐layer depths and nutrient concentrations. In contrast to the earlier analyses we found little or no predictive power for either year‐class strength or proportion migrating. The substantial correlations found in the earlier study were greatly reduced. Such reversals are not uncommon in the climate‐recruitment literature.

Extraction of Collagen from Fish Skins and Its Use in the Manufacture of Biopolymer Films

ABSTRACT The aim of this study was to extract collagen from fish skins and investigate the physical properties of the biodegradable films formed from the extracted fish collagen. Extraction of collagen using hydrogen peroxide or enzymatic methods proved to be unsuccessful. A white collagen substance was successfully extracted using a hydrochloric acid extraction method; however, it was unsuitable for the formation of edible films. An acetic acid extraction process successfully yielded a collagen substance, which could be used to form biodegradable collagen films. Differences in the mechanical film properties, tensile strength, Young's modulus, elongation and water vapor permeability were found between collagen films from different fish species. Films formed from collagen of New Zealand (NZ) hoki and NZ ling had greater elongation (%EL), tensile strength (TS) and elasticity in comparison with similar films from Irish (IRL) fish species. The addition of plasticizer to the collagen films had an effect on the mechanical properties of the films.

Using fish-processing time to carry out acoustic surveys from commercial vessels

Abstract In some fisheries large factory freezer trawlers have periods of down time as the catch is processed. By utilizing this time, scientific acoustic surveys can be carried out between commercial-fishing operations without compromising fishing success. Examples are presented from three acoustic surveys for hoki (Macruronus novaezelandiae) in New Zealand waters during 2002 and 2003 conducted from a commercial vessel fitted with a scientifically calibrated SIMRAD ES-60 echosounder. These surveys confirmed the presence of a new spawning area for hoki and provided biomass estimates from known fishing grounds. The approach described works well for small-scale acoustic surveys adjacent to areas of high catch rates and is cost-effective because the vessel “pays for itself” by fishing commercially. The major limitation is that the boundaries of the survey area are determined by the time available during processing, which is related to the size of the catch and the time required to search for a suitable location for the next commercial trawl. In the New Zealand hoki surveys, processing time was typically 3–8 h, which was sufficient to carry out about 10–70 km of acoustic transects. Acoustic research was also limited to periods of relatively good conditions by the use of a hull-mounted transducer.

HIERARCHICAL MODELS IMPROVE ABUNDANCE ESTIMATES: SPAWNING BIOMASS OF HOKI IN COOK STRAIT, NEW ZEALAND

It is often difficult to estimate abundance for a dynamic population, i.e., one that is moving through the survey area or in which birth or mortality rates are high. One approach is to estimate the proportion of animals present during each survey, using a model that estimates the dynamics of the survey proportion of the population. However, this can increase the uncertainty of the estimates if the dynamics parameters are not well estimated. Here we approached this problem by developing methods using hierarchical model structures, which allow us to share information on the dynamics parameters across years. We applied this modeling approach to the estimation of residence time and spawning biomass for New Zealand hoki (Macruronus novaezelandiae) in Cook Strait spawning grounds. By sharing parameters across years, we obtained better parameter estimates than by the traditional assumption that the dynamics in one year are independent of those of other years. By integrating the estimation of residence time into a dynamic model using simulated maximum likelihood methods, we also were able to calibrate acoustic estimates of spawning biomass for the fact that not all individuals are on the grounds at the time of the acoustic survey. We discuss alternative model formulations for the application of hierarchical methods to stage‐structured data and the analysis of data from acoustic surveys of spawning fish.

Determining species composition in mixed-species marks: an example from the New Zealand hoki (Macruronus novaezelandiae) fishery

Abstract A model-based method has been developed for partitioning acoustic backscatter from mixed-species marks. This method uses catch-composition data to partition the echo integral, but allows for differences in trawl catchability and acoustic vulnerability between species. It was applied to estimate the biomass of New Zealand hoki (Macruronus novaezelandiae) from trawl and acoustic surveys on the Chatham Rise and Campbell Plateau in 2001. Mixed-species layers containing up to 20 different species were present in both survey areas. A total of 224 bottom-trawl surveys (123 on Chatham Rise and 101 on Campbell Plateau) were carried out to determine the species composition and relative densities. Simultaneous acoustic recordings made during each of these trawls were used to estimate vulnerability ratios for the two methods, i.e. acoustic as opposed to trawl surveys, (acoustic:trawl) by non-negative, least-squares minimization. The best-fit model for each survey attributed 14–22% of the backscatter in mixed layers within 10 m of the bottom to hoki. This produced hoki biomass estimates 1.3–1.8 times higher than the standard approach, which divides the echo integral in proportion to the catch assuming equal trawl catchability. The precision of the estimated acoustic:trawl vulnerability ratios depended on the contrast in trawl catch composition, and the ratios for the same species differed between areas. A major problem on the Chatham Rise was the acoustic contribution of small mesopelagic species, which are not caught by the bottom trawl. Despite these difficulties, the model-based approach has good potential for determining the biomass of the target species in a mixed-species mark when the different species cannot be discriminated acoustically.

Links between climate variation and year class strength of New Zealand hoki (Macruronus novaezelandiae): An update

Hoki (Macruronus novaezelandiae Hector) year class strength (YCS) varies substantially from year to year. We examined associations between YCS and climate variables including the Southern Oscillation Index (SOI), satellite sea surface temperatures (SSTs), synoptic weather patterns, wind speeds, and the depth of the west coast, South Island, New Zealand, mixed layer. We evaluated the predictions of a model developed 2 years ago to predict YCS of the western and eastern New Zealand hoki stocks from similar climate variables. New predictive models were developed using updated data. Strong year classes of the western hoki stock were associated with cooler SSTs, a negative SOI, and westerly or south‐westerly flow along the west coast of the South Island. We accordingly predict a moderately strong 1997 year class and weak 1998 and 1999 year classes for the western stock of hoki. The current model cannot predict eastern stock year class strengths with confidence.

Links between climate variation and the year class strength of New Zealand hoki (Macruronus novaezelandiae) Hector

Hoki (Macruronus novaezelandiae) Hector year class strength (YCS) varies substantially from year to year. In this study, potential links between hoki YCS estimates for western and eastern stocks, and time series of the Southern Oscillation Index (SOI), satellite sea surface temperatures (SST), synoptic weather patterns, depth of the mixed layer (western stock only), and wind speeds are explored. The results indicate that favourable recruitment in the western stock is correlated with a negative SOI and associated conditions such as lower SSTs, early onset of deep water mixing and synoptic weather patterns that result in a higher incidence of southwest (SW) flow. Favourable recruitment in the eastern stock appears to be correlated with periods of westerly flow, particularly from the SW, but also the north‐west (NW). Regression studies showed that when inter‐correlation was minimised, 95% of the variation in YCS of the western stock was explained by four variables—SOI in autumn, the onset of winter mixing, SST in spring, and NW spring weather patterns. In the eastern stock, 88% of the variation in YCS was explained by SW and NW winter weather patterns and the average speed of SW winds in winter through Cook Strait. Although the underlying mechanisms are not proven, the climate variables which appear to be linked to favourable recruitment for both western and eastern stocks, also favour upwelling and the physical transportation of larval hoki from the spawning grounds into their respective inshore nursery areas.

Analysis of vessel movements and strategies using commercial catch and effort data from the New Zealand hoki fishery

Analysis of vessel movements and strategies using commercial catch and effort data from the New Zealand hoki fishery