Silver Hake Research Articles

Diets of five hake species in the northeast United States continental shelf ecosystem

We examined the diets of 5 hake species in the continental shelf ecosystem of the northeast USA: offshore hake Merluccius albidus, silver hake M. bilinearis, white hake Urophycis tenuis, red hake U. chuss, and spotted hake U. regia. We conducted a multivariate analysis of stomach contents from bottom-trawl surveys to assess the major factors that determine diet composition, to compare and contrast diets between species, and to compare the trophic role of the hakes in the northwest Atlantic to hakes in other ecosystems. These fish consume pelagic invertebrates (e.g. euphausiids and other shrimps) and pelagic fish prey, including conspecifics. The incidence of piscivory generally increases with increasing size. Regional and temporal (seasonal and yearly) variation in hake diets generally reflects differences in prey availability. Hakes are among the most abundant predators in continental shelf ecosystems worldwide. Fish prey consumption by hakes can be high and may be a primary source of mortality for economically important pelagic species. Hake predation plays an important role in the dynamics of both the US northeast continental shelf ecosystem and generally on a global scale.

Apparent digestibility coefficients of raw ground, acid and fermented silver hake (Merluccius bilinearis) feedstuffs for mink and an evaluation of the storage stability of the silages

A 3 × 4 factorial design experiment was conducted to determine digestibility coefficients (DC) of dry matter (DM), crude protein (CP), crude fat (CF), gross energy (GE) and amino acids (AA) in raw ground silver hake (RGSH), acid (ASHS) and fermented (FSHS) silver hake silages for mink. The ASHS was prepared with the addition of 2.5% (wt:wt) formic acid (85% concentration) and 200 ppm antioxidant (ethoxyquin) to the raw ground fish. The FSHS was produced with the addition of 1% Marisil® (Finn Sugar), 15% extruded wheat and 1% (wt:wt) formic acid (conc. 85%) to the raw ground fish. Twelve mature standard type male mink were confined to metabolism cages during the digestibility trial, which consisted of three experimental periods comprised of a 6-d adjustment period, followed by a 5-d collection period. Based on the total collection (TC) method and with graded levels (0, 15, 30 and 45%) of the test feedstuffs in the experimental diets, nutrient digestibilities in the pure feedstuffs were determined using a mathematical regression technique. The apparent digestibility (AD) of DM, CP, CF and GE were RGSH: 88.4, 93.6, 99.2 and 94.7%; ASHS: 90.6, 85.8, 96.1 and 87.2% and FSHS: 77.7, 84.5, 99.2 and 86.1%, respectively. The AD of all the AAs, except proline, in the RGSH was significantly higher (P < 0.05) than that in the ASHS and FSHS. A quality evaluation of the silages was conducted in a completely randomized design with two replications to determine storage stability of the silages, on 10 different sampling days, (3 sampling days for AAs), over the storage period. Quality of the silages was stable up to 90 days for the ASHS and 180 days FSHS based on increases in pH and total volatile nitrogen (TVN) content and decreases in N and AA content. The silver hake feedstuffs would provide a good source of highly digestible nutrients for mink and should be considered as opportunity feeds for these animals. Key words: Apparent digestibility, fish by-products, mink, silage, silage quality, silver hake

Reactivity of the invariant cysteine of silver hake parvalbumin (Isoform B) with dithionitrobenzoate (DTNB) and the effect of differing buffer species on reactivity

Covalent and non-covalent homo- and hetero-dimerization has been implicated as a means of functional regulation in members of the EF-hand family of calcium-binding proteins, including oncomodulin, S100, troponin C and calmodulin. The presence of an invariant cysteine at position 18 in all β-lineage parvalbumins suggests an important function for this sulfhydryl-containing amino acid. The chemical reactivity of Cys-18 toward the thiol-directed reagent dithionitrobenzoate (DTNB) (in a variety of solvent systems) was examined in this study to obtain information on differences in reactivity of the group in the calcium-bound versus the metal-free protein. Under our experimental conditions, the purified parvalbumin isoform from the silver hake employed was shown to be a mixture of monomeric protein (with a free thiol at the Cys-18 position) and disulfide-linked `dimeric' protein. The monomeric protein, but not the disulfide-linked `dimeric' protein, proved to be reactive towards DTNB and it was determined that the reaction occurs at a significantly greater rate with protein in the presence of excess EDTA than with just the calcium-loaded protein, indicating a conformational change in the apo-protein which exposes the Cys-18 thiol to the sulfhydryl-directed reagent. This is in agreement with the observations of Clayshulte et al. (1990) on oncomodulin, and also with Donato and Martin (1974) in their work with carp β-parvalbumin, but in contrast to the observations of Mutus et al. (1988) also with oncomodulin. The experimental kinetic profiles associated with the reaction of DTNB and SHPV-B were fitted to a simple model containing multiple bi-molecular reactions. The results of molecular dynamics simulations, focused on the issue of solvent exposure of the Cys-18 thiol, are consistent with our interpretation of the kinetics. The reactivity of Cys-18 with DTNB predictably increased with pH, but, quite unexpectedly, the precise nature of the kinetic response was also found to depend rather dramatically on the nature of the buffer species employed. The buffer dependency of the reaction of DTNB with the Cys-18 sulfhydryl group is one of the more significant, and unexpected, findings of this study. The dramatic changes in Cys-18 modification kinetic profiles observed with buffers of different ionic character (NH 4HCO 3, Tris–HCl, piperazine) clearly demonstrate that buffer selection is not a trivial matter. Buffers that have significant metal ion complexing power can easily sequester trace metal ions, and protein thiol-disulfide kinetic studies performed in the presence of such buffers can exhibit dramatically altered kinetic behavior when compared to similar studies performed in metal-free buffer systems.

Evaluation of separator grates for reduction of bycatch in the silver hake ( Merluccius bilinearis) otter trawl fishery off Nova Scotia, Canada

The effectiveness of separator grates in reducing bycatches in the small-mesh otter trawl fishery for silver hake on the Scotian Shelf was examined in three experiments aboard a research and two commercial vessels. Different grate bar orientations, bar spacings, grate insertion angles, and guiding mechanisms were tested. The size selection and escapement levels resulting from these grate configurations are described. A grate with vertical bars spaced 40 mm apart inserted at 45–60°, and with a funnel or panel forward of the grate to direct fish to its base, released 85–98% by weight of pollock and haddock, and 48–70% of other species, while retaining 95% of silver hake. Commercial bycatches contained more small haddock than did experimental catches, and it is projected that commercial use of this grate would release 75–80% by weight of haddock encountered, and only 50% by number. Other grate configurations tested displayed poorer species selection characteristics.

Behavioral inferences from regulatory observer data: catch rate variation in the Scotian Shelf silver hake (Merluccius bilinearis) fishery

The detailed spatial and temporal data collected for the regulation of the silver hake (Merluccius bilinearis) fishery on the Scotian Shelf provide a unique opportunity to test hypotheses about variability in catch rates on the scale of individual trawls. I used these data to examine vessel interactions and long-term temporal trends in catchability. An index of course linearity, derived from observed positions, times, and speeds of fishing vessels, indicated that interference competition was present in the fishery. However, catch rate did not decline with local vessel density. This apparent contradiction is consistent with fleet dynamic theory and suggests that the direct examination of catch rates is a poor test for interference in the retrospective analysis of fisheries data. The study of extended periods of high, localized fishing activity revealed a cycle in catch rates with periods of about 6 days. Such periods may represent an interaction between tidal, diel, and (or) technological factors. Although more study is required to identify the cause of these cycles, their existence should be considered in the design of surveys and other population studies using catch and effort data.

Impacts of density-dependent growth and maturation on assessment advice to rebuild depleted U.S. silver hake (Merluccius bilinearis) stocks

We examined how density-dependent growth and maturation rates would affect scientific advice to rebuild U.S. silver hake (Merluccius bilinearis) stocks to a minimum biomass threshold (SSB50) using an age-structured stochastic projection model. Uncertainty in recruitment and initial stock sizes at age was incorporated to more realistically capture the stochastic nature of the stock's dynamics through time. Performance measures including spawning stock biomass (SSBt), risk (prob(SSBt< SSB50)), and fishery yields were examined under model assumptions of static life history parameters in contrast with density-dependent parameters for various constant fishing mortality rate (F) harvest policies. Model results indicated that unless compensatory mechanisms are accounted for, scientific advice may be too optimistic and lead to unrealistic expectations of F targets to achieve stock rebuilding, requiring longer rebuilding times and entailing more risk and unrealized sustainable yield. For instance, projected median southern stock SSBt exceeded the SSB50 of 104 000 metric tons (t) with 40% risk to the stock by year 20 from harvesting at F = 0.50. However, under the density-dependent assumption, median SSBt did not rebuild as expected, and after 20 years reached only 75 000 t with 85% risk to the stock. Also under this assumption, median yields increased from 9000 to 27 000 t by year 20 but were 30-40% lower than what would have been expected under density independence.

Bioeconomic Analysis of Alternative Selection Patterns in the United States Atlantic Silver Hake Fishery

In this paper a bioeconomic simulation of the U.S. fisheries for silver hake, Merluccius bilinearis, is presented. The model design combines elements of age-structured population and harvest yield models with economics of the silver hake fishery. The analysis evaluates both biological and economic effects of interest to managers, such as future yields or rebuilding of parental stock, as well as future revenues and net returns to vessels. The bioeconomic model is used to evaluate the economic implications of tradeoffs between alternative selection patterns in the U.S. Atlantic silver hake fishery. Throughout the study, a selection pattern is defined as the suite of age-specific selection coefficients that are applied to a fish population over time. The results indicate that shifting fishing pressure to younger age classes could result in short-run gains in economic value that may not be sustainable due to longer run declines in biomass, hence lowered fishery yield and value. By contrast, strategies to dela...

Impacts of density-dependent growth and maturation on assessment advice to rebuild depleted U.S. silver hake (<i>Merluccius bilinearis</i>) stocks

Impacts of density-dependent growth and maturation on assessment advice to rebuild depleted U.S. silver hake (<i>Merluccius bilinearis</i>) stocks

Pressure as a Limit to Bloater (Coregonus hoyi) Vertical Migration

Bloater Coregonus hoyi are one of the Great Lakes ciscoes, an incipient species flock of seven recognized fishes (Todd and Smith, 1992). The vertical migration of adult bloater has been documented in day-night catch-per-unit-effort comparisons on the lake bottom (Brandt et al., 1991; Argyle, 1992) and in hydroacoustic observations (Fleischer et al., 1997). Bloater stay on or near the bottom during the day, whereas at night, a portion of the population ascend in the water column (Brandt et al., 1991; Argyle, 1992). Vertical migrators with swimbladders cope with frequent buoyancy changes due to pressure-induced volume changes of the swimbladder. Maintaining neutral buoyancy by gas secretion and resorption is time consuming and not practical for daily vertical migrations (Jones and Scholes, 1985; Alexander, 1993). Frequent adjustments of swimbladder volume are also energetically expensive, especially in environments with low temperatures and high pressure gradients (Alexander, 1972, 1993; Jones and Scholes, 1985). Alexander (1972) suggested that vertical migrators with gas-filled swimbladders may cope with the problem of swimbladder adjustment by using their swimbladder for neutral buoyancy only at the shallowest depths of their migration, whereas at the deepest depths of their migration, Alexander (1972) hypothesized these fish would be negatively buoyant and either rest on the bottom or use another buoyancy mechanism such as hydrodynamic lift to remain above the bottom. Observations of Merluccius bilinearis

Characterization of a helix-loop-helix (EF hand) motif of silver hake parvalbumin isoform B.

Parvalbumins are a class of calcium-binding proteins characterized by the presence of several helix-loop-helix (EF-hand) motifs. It is suspected that these proteins evolved via intragene duplication from a single EF-hand. Silver hake parvalbumin (SHPV) consists of three EF-type helix-loop-helix regions, two of which have the ability to bind calcium. The three helix-loop-helix motifs are designated AB, CD, and EF, respectively. In this study, native silver hake parvalbumin isoform B (SHPV-B) has been sequenced by mass spectrometry. The sequence indicates that this parvalbumin is a beta-lineage parvalbumin. SHPV-B was cleaved into two major fragments, consisting of the ABCD and EF regions of the native protein. The 33-amino acid EF fragment (residues 76-108), containing one of the calcium ion binding sites in native SHPV-B, has been isolated and studied for its structural characteristics, ability to bind divalent and trivalent cations, and for its propensity to undergo metal ion-induced self-association. The presence of Ca2+ does not induce significant secondary structure in the EF fragment. However, NMR and CD results indicate significant secondary structure promotion in the EF fragment in the presence of the higher charge-density trivalent cations. Sedimentation equilibrium analysis results show that the EF fragment exists in a monomer-dimer equilibrium when complexed with La3+.

Distributional responses to small-scale habitat variability by early juvenile silver hake, Merluccius bilinearis

Early juvenile (0-year) silver hake, Merluccius bilinearis, occurred at higher densities on bottoms with greater amphipod tube cover at a 55 m deep site in the Middle Atlantic Bight. The size range of individuals at this site was 1.5–5 cm total length. Additional observations at other sites showed that 0-year silver hake only occurred on silt-sand bottom with amphipod tubes at bottom water temperatures of 8.7–11.4 °C. This distribution pattern could be the result of either selective settlement into appropriate habitats or differential predation with higher survivorship in more complex habitats. We posit that 0-year silver hake occur in patches of dense amphipod tube cover to avoid visual predators and co-occur with preferred prey (i.e., amphipods and shrimps).

Effects of high dietary levels of silver hake and Atlantic herring on growing-furring performance and blood clinical-chemistry of mink (Mustela vison)

An experiment was conducted with a total of 168 mink (Mustela vison) of the standard black genotype to determine the effects of dietary silver hake (Merluccius bilinearis), silver hake silage and herring (Clupea harengus) on the growing-furring performance. There were seven dietary groups. The control diet (CONTROL) contained 40% haddock offal, 8% poultry offal, 15% beef tripe and lungs, 5% corn gluten meal, 12% extruded wheat, 0.4% vitamin-mineral premix, and water. Test diets were made by replacing the fish offal with 15 or 30% hake (HAKE 15, HAKE 30), hake silage (SILAGE 15, SILAGE 30) or with 40% herring (HERRING 40). The last dietary group (HERR/CONT) was fed alternatingly with the CONTROL or the HERRING 40 diets. The animals in the HERRING 40 group developed anorexia after 2 wk on the test diet and were injected with vitamin B complex. The diet was supplemented with thiamin, 25 mg kg−1 feed. This restored appetite and supported normal growing-furring performance. Mink fed HAKE 30 diet had a lower weight gain from weaning until pelting (males 814 ± 58.0 g, females 366 ± 53.6 g) than the CONTROL (males 987 ± 61.9 g, females 429 ± 52.1 g)(P < 0.05). Blood haemoglobin (Hb) values for all groups were on average 178 ± 4.4 g L−1 in September and 184 ± 7.0 g L−1in October, i.e. well above the critical level to prevent the development of cotton fur. However, the total amount of iron stored in spleen and liver was lower for the HAKE 30 (562.1 ± 85.1 µg) and SILAGE 30 (435.9 ± 77.7 µg) groups than in the CONTROL (800.7 ± 77.7 µg) (P < 0.05) possibly indicating impaired absorption. No signs of poor pigment development were seen in the underfur of the winter pelage. Both silver hake and herring show good potential as alternative feedstuffs in growing-furring diets for mink. At high inclusion levels the effects of thiaminase enzyme in herring and the iron-binding trimethylamine oxide in silver hake should be accounted for. Key words: Mink, herring, thiamin, silver hake, fish silage, iron

Density‐dependent growth and sexual maturity of silver hake in the north‐west Atlantic

Stock abundance was the most important predictor of sexual maturation of age 2 and 3 silver hake in the north‐west Atlantic between 1973–1990. Growth at ages 1 and 2 in the southern stock was significantly and negatively correlated with stock abundance (r2>0.56, P<0.01). Sexual maturity may be mediated through competition and growth during the first and second years of life. In the northern stock, growth and stock abundance was not significantly correlated (P>0.05). Here, increased sexual maturity at ages 2 and 3 during 1973–1990 may have occurred without increased somatic growth, already near its maximum, due to the relatively cooler water temperatures of the Gulf of Maine. Logistic regression models indicated that maturation is dependent on age, stock density and an age‐density interaction.

Density-dependent growth and sexual maturity of silver hake in the north-west Atlantic

Stock abundance was the most important predictor of sexual maturation of age 2 and 3 silver hake in the north-west Atlantic between 1973–1990. Growth at ages 1 and 2 in the southern stock was significantly and negatively correlated with stock abundance (r2>0.56, P<0.01). Sexual maturity may be mediated through competition and growth during the first and second years of life. In the northern stock, growth and stock abundance was not significantly correlated (P>0.05). Here, increased sexual maturity at ages 2 and 3 during 1973–1990 may have occurred without increased somatic growth, already near its maximum, due to the relatively cooler water temperatures of the Gulf of Maine. Logistic regression models indicated that maturation is dependent on age, stock density and an age-density interaction.

The isolation of parvalbumin isoforms from the tail muscle of the american alligator ( Alligator mississipiensis)

Multiple parvalbumin isoforms have been detected in the tail (skeletal) muscle of the American alligator (Alligator mississipiensis). One of these isoforms (APV-1) has been highly purified and partially characterized. Protein purification involved mainly gel filtration and anion exchange chromatography, and characterization included gel electrophoresis, amino acid composition analysis, metal ion analysis, MALDI-TOF and ESI mass spectrometry, ultraviolet and fluorescence spectroscopy, and one- and two-dimensional 500 MHz proton NMR spectroscopy. The alligator isoforms are rich in phenyl-alanine and deficient in the other aromatic residues as is typical for parvalbumins. In fact, the one highly purified isoform that forms the basis of this study has only phenyl-alanine as an aromatic residue. Ion exchange chromatography further indicates that this isoform has a relatively high isoelectric point (pl ∼ 5.0), indicating that it is an α-lineage parvalbumin. This alligator parvalbumin isoform is unusual in that it has an atypically high Ca 2+ content (almost 3.0 mole of Ca 2+ per mole of protein) following purification, a fact supported by terbium fluorescence titration experiments. Preliminary comparative analysis of the highly purified alligator parvalbumin isoform (in the Ca 2-loaded state) by two-dimensional 1H-NMR (2D 1H TOCSY and 2D 1H NOESY) indicates that there is considerable similarity in structure between the alligator protein and a homologous protein obtained from the silver hake (a saltwater fish species).

Fish meal quality assessment for Atlantic salmon (Salmo salar L.) reared in sea water

Studies were conducted to investigate the quality of 16 fish meals for Atlantic salmon (Salmo salar L.) reared in sea water, and to assess in vitro and in vivo methods for the measurement of the quality of the protein in fish meals. The commercial fish meals tested were Canadian-produced (herring, groundfish, and mixed meals) and were of West Coast and East Coast origin; they included silver hake (Russian origin), two mackerel meals (Chilean) and Norwegian fish meal (Norse-LT94®). In addition, five herring meals were produced in the laboratory to assess the influence of processing conditions and freshness of the raw material on fish meal quality. The dilute-pepsin digestibility was the preferred in vitro assay to evaluate the protein quality of herring meals for Atlantic salmon, but this assay correlated poorly with the results from in vivo assays when other types of fish meals (menhaden, mackerel, silver hake, groundfish) were included.

An Age-Structured Bioeconomic Simulation of U.S. Silver Hake Fisheries

Abstract We present a bioeconomic simulation of the U.S. fisheries for silver hake Merluccius bilinearis, an abundant species distributed over the northwest Atlantic continental shelf and historically important to both U.S. and foreign fishing fleets. The model combines elements of agestructured population and harvest yield models with a two-equation price response model. The analysis evaluates biological benefits of interest to managers, such as future yields or rebuilding of parental stock, as well as future revenues and net present value of interest to harvesters. In one set of simulations, yield and revenue response surfaces were generated for varying levels of fishing mortality (F) and selection at age under constant annual recruitment. In another, a stochastic stock–recruitment function permitted assessment of yield and revenue trajectories over time given variable annual recruitment. Under equilibrium conditions, response surfaces for both total fishery yield and revenue are asymptotic with increas...

The Role of Targeted Species in Identification of Technological Interactions in Mid-Atlantic Bight Groundfish Fisheries

Data from commercial sea sampling programs are used to examine the relationship between target species sought and the species composition of resulting catches in the mixed species otter trawl fisheries in the Mid-Atlantic Bight. Correlations between species abundances were higher when data were aggregated over an entire trip rather than when tows were examined singly. Based on discriminant function analysis of a subset of the data, tows from trips targeting cod and summer flounder were relatively easily identified by their characteristic species mix, while tows from trips targeting silver hake and squid were more prone to misclassification. These results indicate that trips target species mixes rather than single species with incidental by-catch; and that the predictability of the species composition of those mixes depends on the target.

Growth of silver hake within the U.S. continental shelf ecosystem of the northwest Atlantic Ocean

Von Bertalanffy growth parameters were estimated for silver hake Merluccius bilinearis within four regions of the United States continental shelf ecosystem of the northwest Atlantic Ocean during 1975–1980, 1982–1987 and 1988–1992. Differences in silver hake growth were found between the Middle Atlantic and southern Georges Bank regions (P&lt;0–01) over all three time periods. Growth also differed between northern Georges Bank and the Gulf of Maine (P&lt;0–01) during 1975–1980 and 1982–1987, and significant differences between southern Georges Bank and northern Georges Bank were found only during 1982–1987. Silver hake in the Gulf of Maine exhibited larger asymptotic sizes, but attained their asymptotic size at slower rates (L00= 47 cm and K=0–33) in comparison to silver hake in the Middle Atlantic (L00= 43 cm and K=0–51), while growth parameter estimates for silver hake on Georges Bank were intermediate between these. Although significant differences in growth of silver hake between the various regions are consistent with separate stocks in the U.S. continental shelf ecosystem, the growth characteristics from the different regions are inconsistent with the presently assigned stock boundaries. (c) 1996 The Fisheries Society of the British Isles

Growth of silver hake within the U.S. continental shelf ecosystem of the northwest Atlantic Ocean

Von Bertalanffy growth parameters were estimated for silver hake Merluccius bilinearis within four regions of the United States continental shelf ecosystem of the northwest Atlantic Ocean during 1975–1980, 1982–1987 and 1988–1992. Differences in silver hake growth were found between the Middle Atlantic and southern Georges Bank regions (P<0–01) over all three time periods. Growth also differed between northern Georges Bank and the Gulf of Maine (P<0–01) during 1975–1980 and 1982–1987, and significant differences between southern Georges Bank and northern Georges Bank were found only during 1982–1987. Silver hake in the Gulf of Maine exhibited larger asymptotic sizes, but attained their asymptotic size at slower rates (L00= 47 cm and K=0–33) in comparison to silver hake in the Middle Atlantic (L00= 43 cm and K=0–51), while growth parameter estimates for silver hake on Georges Bank were intermediate between these. Although significant differences in growth of silver hake between the various regions are consistent with separate stocks in the U.S. continental shelf ecosystem, the growth characteristics from the different regions are inconsistent with the presently assigned stock boundaries. (c) 1996 The Fisheries Society of the British Isles