Red Hake Research Articles

What bycatch tells us about the diet of harbor and gray seals and overlap with commercial fishermen

Northwest Atlantic harbor (Phoca vitulina vitulina) and gray (Halichoerus grypus atlantica) seal populations are recovering from early to mid-20th century exploitation, increasing their biological interactions and bycatch in Northeastern US commercial fisheries. We evaluated the seals’ diet composition and compared their prey to commercial catches to assess trophic overlap and potential competition with commercial fisherman target catches. We obtained 148 harbor and 178 gray seal stomach samples from bycatch events that occurred between 2004 and 2018. We learned from the hard part remains that the majority of seals bycaught are young-of-the-year (≤12 months old) that consume a wide breadth of prey across three trophic groups. There was a general dichotomy in extrinsic factors associated with seal diet in which 45% trophic niche separation was explained by non-overlapping harbor and gray seal phenology and pup haul-out locations that are adjacent to active fishing areas. Prey size estimated from fish otoliths and squid beaks recovered from stomach contents showed that gray seals consumed larger prey than harbor seals and prey sizes from both seals showed limited overlap with prey sizes caught by commercial gillnet fishermen. The most important prey to both seals included large (>20 cm) and small (≤20 cm) silver hake (Merluccius bilinearis), (≤40 cm) red hake (Urophycis chuss), gulf stream flounder (Citharichthys arctifrons), medium (21–40 cm) white hake (Urophycis tenuis), and (<50 cm) Atlantic cod (Gadus morhua). Important prey to harbor seals that did not overlap with gray seals were Acadian redfish (Sebastes fasciatus), Atlantic herring (Clupea harengus), longfin (Doryteuthis pealeii), and shortfin squid (Illex illecebrosus). They contrasted with prey important to gray seals that did not overlap with harbor seals: yellowtail flounder (Limanda ferruginea), sand lance (Ammodytes spp.), Urophycis spp., and fourspot flounder (Hippoglossina oblonga). Despite the potential bias associated with opportunistic bycatch sampling, this study demonstrates the importance and value of utilizing carcasses retained from bycatch events, is complimentary to newer methodologies (i.e., DNA meta-barcoding), and fills data gaps in our understanding of the role recovering harbor and gray seal populations have on Northeastern US regional food webs.

What the Hakes? Correlating Environmental Factors with Hake Abundance in the Gulf of Maine

According to the latest estimates, the Gulf of Maine is currently warming faster than 99% of the world’s oceans. As a result, this region has become an ideal location for research into the effects that warming has on the historical fisheries that make up this ocean basin. Both white hake (Urophycis tenuis) and red hake (Urophycis chuss) are common Gulf of Maine groundfish species, distributed both inshore and offshore. While these two species are closely related phycid hakes, white hake stocks are recognized in the Gulf of Maine as rebuilding, while red hake are above target biomass levels. As a species commonly found throughout the Gulf of Maine that prefers cooler waters (4–12°C), we hypothesize the effects of climate change might influence stock behavior, such as changes in species distribution. We used generalized additive models (GAMs) to describe the relationship between hake abundance and environmental conditions using bottom temperature, bottom salinity, depth, and catch data contributed by the Maine Department of Marine Resources during their Maine – New Hampshire Inshore Trawl Surveys of the last 22 years (2000 – 2021). Our results reveal species-specific preferences for bottom temperature (white hake ~9 to ~13℃, red hake < 12℃) and depth (white hake ~55 to ~100m, red hake > ~65m), with no significant correlation to bottom salinity. Spatially over time, white hake abundance displayed a gradual center of gravity northward, while red hake rapidly increased inshore. Overall, these results highlight species-specific density changes in inshore distribution, consistent with previous studies, with considerable implications on future management strategies in this region.

The Role of Fishery‐Independent Bottom Trawl Surveys in Providing Regional and Temporal Context to Offshore Wind Farm Monitoring Studies

AbstractBottom trawl surveys are commonly used to examine potential effects on fishes and invertebrates from offshore wind (OSW) farms in Europe and in the northeastern United States. Because OSW surveys typically occur over a limited spatial footprint, comparison of OSW monitoring results to long‐term fishery‐independent surveys may provide a regional and temporal context for OSW data sets. We compared results of the Block Island Wind Farm (BIWF) bottom trawl survey (2013–2019) to three fishery‐independent bottom trawl surveys (Northeast Area Monitoring and Assessment Program, Northeast Fisheries Science Center, and Rhode Island Department of Environmental Management [RIDEM]) using catch rates of 12 federally managed species. We evaluated temporal trends in annual residual catches for each species calculated within each survey as the difference between the mean annual biomass per trawl and the long‐term mean. Regional consistency in relative catches was apparent for species exhibiting synchronous interannual variability among surveys (Black Sea Bass Centropristis striata, Scup Stenotomus chrysops, Summer Flounder Paralichthys dentatus, and Winter Flounder Pseudopleuronectes americanus) or a decreasing trend in residual catch rates across the 7‐year study period (Little Skate Leucoraja erinacea, longfin inshore squid Doryteuthis pealeii, and Winter Skate L. ocellata). For other species, catches among surveys were asynchronous (Atlantic Herring Clupea harengus, Butterfish Peprilus triacanthus, and Windowpane Scophthalmus aquosus) or anomalous catches in a single year affected the results (Red Hake Urophycis chuss and Silver Hake Merluccius bilinearis). Monitoring of BIWF occurred during a period with lower‐than‐average historical catches in a 32‐year RIDEM data set for Atlantic Herring, Butterfish, Little Skate, longfin inshore squid, Red Hake, Silver Hake, and Winter Flounder and higher‐than‐average catches for Black Sea Bass, Scup, and Summer Flounder. There was no evidence that variation in catches near BIWF differed from regional trends in a way consistent with a detrimental impact of OSW farm operation. The regional context provided from multiple bottom trawl surveys varies by species and thus may be limited for interpreting OSW monitoring results.

Annual Residency Patterns and Diet of Phoca vitulina concolor (Western Atlantic Harbor Seal) in a Southern New Jersey Estuary

From 1996 to 2011, researchers observed Phoca vitulina concolor (Western Atlantic Harbor Seal) on regional overwintering grounds in the Great Bay–Mullica River estuary in southern New Jersey. Over this 15-y time series, 299 observations were completed, with maximum local abundance increasing from 100 individuals in 1996 to 160 individuals in 2011. Our study did not document the presence of Atlantic Harbor Seal pups. In addition, we analyzed 142 scat samples, resulting in 1419 sagittal fish otoliths recovered and identified. Dominant recovered otoliths were as follows: 48% Phycidae (Urophycis regia [Spotted Hake]/Urophycis chuss [Red Hake]; 25% Clupeidae (Clupea harengus [Atlantic Herring], Alosa sapidissima [American Shad], Brevoortia tyrannus [Atlantic Menhaden], A. pseudoharengus [Alewife], and A. aestivalis [Blueback Herring]); 13% Ammodytidae (Ammodytes americanus/A. dubius [sandlance]); 6% Pseudopleuronectes americanus (Winter Flounder); and 4% Scophthalmus aquosus (Windowpane Flounder). Average back-calculated prey lengths across all prey groups (min–max = 5–41 cm, average = 19.75 cm) indicated that Western Atlantic Harbor Seals might utilize both estuarine and ocean environments for foraging. This temperate estuary currently represents the southern limit of routine Western Atlantic Harbor Seal occupancy in the Northeast. As such, our results are valuable in monitoring future changes in habitat use potentially resulting from climate change.

Evaluating a large-mesh belly window to reduce bycatch in silver hake (Merluccius bilinearis) trawls

Small-mesh trawls targeting silver hake (Merluccius bilinearis) in Northeastern USA are managed as exemptions to the northeast multispecies management plan. These exemptions require that the catch of regulated groundfish species is less than 5% of the total catch weight for small-mesh gears targeting silver hake. At present, only a raised footrope trawl (RFT) or drop-chain-only trawl (DOT) (in New England, it is specifically called “sweepless trawl”) in conjunction with a Nordmøre-style grid can be used to land silver hake with small mesh off the coast of Maine. The historical Maine silver hake fishing grounds have a very rugged bathymetry that makes the use of these modified groundgears difficult, if not impossible. This study tested a trawl with and without a large-mesh belly window (LMBW) using a traditional rockhopper footrope for 58 tows and reduced the bycatch of red hake (Urophycis chuss) and aggregated bycatch. There was no significant difference in the predicted mean catch of silver hake between trawls (although the LMBW trawl had a 13.50% reduction). Additionally, there was no difference in catch for commercial-size silver hake (>20cm) between the two trawls. Both video and length analysis determined that small silver hake were caught less frequently by the LMBW trawl. These results indicate that a small-mesh trawl employing a LMBW can effectively be used to commercially target silver hake off Maine (USA), replace the requirement of a RFT or DOT, and maintain the less than 5% regulated groundfish requirement.

Variation in wind and piscivorous predator fields affecting the survival of Atlantic salmon, Salmo salar, in the Gulf of Maine

Abstract Observations relevant to the North American stock complex of Atlantic salmon, Salmo salar L., suggest that marine mortality is influenced by variation in predation pressure affecting post‐smolts during the first months at sea. This hypothesis was tested for Gulf of Maine (GOM) stocks by examining wind pseudostress and the distribution of piscivorous predator fields potentially affecting post‐smolts. Marine survival has declined over recent decades with a change in the direction of spring winds, which is likely extending the migration of post‐smolts by favouring routes using the western GOM. In addition to changes in spring wind patterns, higher spring sea surface temperatures have been associated with shifting distributions of a range of fish species. The abundance of several pelagic piscivores, which based on their feeding habits may predate on salmon post‐smolts, has increased in the areas that serve as migration corridors for post‐smolts. In particular, populations of silver hake, Merluccius bilinearis (Mitchell), red hake, Urophycis chuss (Walbaum), and spiny dogfish, Squalus acanthias L., increased in size in the portion of the GOM used by post‐smolts. Climate variation and shifting predator distributions in the GOM are consistent with the predator hypothesis of recruitment control suggested for the stock complex.

Rope Grid: A new grid design to further reduce finfish bycatch in the Gulf of Maine pink shrimp fishery

The pink shrimp ( Pandalus borealis) is an important commercial species for the Gulf of Maine inshore fleet with annual landings exceeding 5500 metric tons in 2010. Due to the small codend meshes used in the trawl, bycatch of juvenile finfish has been an issue. The adoption of the Nordmøre Grid since the early 1990s has significantly reduced finfish bycatch in the fishery, but a small portion of juvenile fish continues to be caught and discarded. To further reduce finfish bycatch, flume tank tests and sea trials were carried out on a radically modified Nordmøre-style grid. The new design cut away two-thirds of the netting surrounding a traditional Nordmøre Grid, and replaced the netting with four ropes, hence called “Rope Grid”. A trouser trawl with two identical codends was used for sea trials on board F/V “North Star”, a 14 m shrimp trawler, comparing the codend equipped with the new Rope Grid to the codend with a regular Nordmøre Grid. Four major bycatch species with mean catch rates greater than 0.4 kg h −1 were silver hake ( Merluccius bilinearis), red hake ( Urophycis chuss), American plaice ( Hippoglossoides platessoides) and witch flounder ( Glyptocephalus cynoglossus). The results indicate that the new Rope Grid significantly reduced all four major bycatch species by 36–50% ( P < 0.001) with no significant reduction on the targeted pink shrimp (105 kg h −1 vs. 102 kg h −1, P > 0.1) or the size of the shrimp (number of shrimps in 1 kg, RNG: 109.3 ± 1.96; ROPE: 110.0 ± 1.70; P = 0.62). The reduction of finfish bycatch was length related for all four major species with an increased rate of escape for larger fish from the Rope Grid. The Rope Grid was practical to handle and easy to modify, and has potential for adoption in this fishery as well as possible application in other shrimp and prawn fisheries around the world.

Changes in Red Hake (Urophycis chuss) Muscle Induced by Different Freezing Strategies

The effect of single and double freezing at −20°C on fresh and aged red hake with two different holding times of the thawed fillets between the first and second freezing treatments was determined. In addition, twice-frozen fresh red hake was treated with two antioxidation systems to assess their effectiveness in reducing lipid oxidation. Fresh, untreated red hake at 0 time was used for comparison. Significant dimethylamine (DMA) production occurred with all frozen samples, and the differences were not marked after 7-month storage. With a storage time of 3 months, however, there were differences between the treatments in both the fresh and aged samples with the once-frozen sample producing the least DMA, the twice-frozen sample with the 24-h holding time between freezings the most, and the twice-frozen sample with a 6-h holding time between freezings giving intermediate values. All samples showed a greater than 50% loss in protein solubility as determined by lithium chloride extraction after 3 months of storage, and the protein solubility declined further when samples were tested at 7 months. Samples with the best (once-frozen fresh) and worst (twice-frozen with 24-h holding time between freezings of 5-day aged muscle) treatments had the highest thiobarbituric acid-reactive substances (TBARS) values. Both antioxidant treatments were effective in reducing TBARS development.

Long-term shifts in the species composition of a coastal fish community

To study decadal shifts in a coastal nekton community, we analyzed data on 25 fish and invertebrate species collected from 1959 to 2005 by the University of Rhode Island, Graduate School of Oceanography (Narragansett, Rhode Island, USA). This weekly trawl survey samples two locations: inside Narragansett Bay and in Rhode Island Sound. Over four decades, the community has shifted progressively from vertebrates to invertebrates and, especially since 1980, from benthic to pelagic species. Demersal species that declined include winter flounder ( Pseudopleuronectes americanus ), silver hake ( Merluccius bilinearis ), and red hake ( Urophycis chuss ); meanwhile warm-water fish (butterfish, Peprilus triacanthus ; scup, Stenotomus chrysops ) and invertebrates (lobster, crab, squid) increased with time. Total numbers reached a maximum in the 1990s, while mean body size decreased. Taxonomic diversity increased over time, as the community shifted from fish to invertebrates of several phyla. The shifts in species composition correlate most strongly with spring–summer sea surface temperature, which increased 1.6 °C over the 47-year time series. Species composition was also correlated with the winter North Atlantic Oscillation index and chlorophyll concentration, which has declined since the 1970s. Triggered primarily by rising temperatures, these decadal changes have altered the trophic structure of the nekton community, resulting in a shift from benthic to pelagic consumers.

Evaluation of Various Infused Cryoprotective Ingredients for Their Freeze–Thaw Stabilizing and Texture Improving Properties in Frozen Red Hake Muscle

Various cryoprotective ingredients were evaluated for their freeze-thaw stabilizing and texture improving properties during 6-mo frozen storage when red hake (Urophycis chuss) fillets were injected with sorbitol-sodium tripolyphosphate (STPP) (40% to 60% : 3%), 1.5% alginate, or 0.75% alginate with soy protein isolate (SPI)-sorbitol-STPP (5% to 10% : 40% : 3%). Injection of 10% SPI, 1.5% alginate, or 0.75% alginate-5% SPI effectively improved water binding and retarded the freeze-induced texture changes when drip and cooking loss, centrifugal expressible moisture, protein extractability, SDS-PAGE profile, and Instron and sensory texture were assessed. The sorbitol and STPP combination was not as effective as alginate and SPI. Freeze-susceptible whitefish can be injected with proper cryoprotective ingredients for improved frozen storability.

Use of submerged aquatic vegetation as habitat by young-of-the-year epibenthic fishes in shallow Maine nearshore waters

Epibenthic fishes were collected with daytime beam trawl tows ( n = 1713) in three shallow (<10 m) habitats of submerged aquatic vegetation (SAV), Zostera marina (eelgrass), Laminaria longicruris (kelp), Phyllophora sp. (algae), and unvegetated sandy/mud areas. We divided the Maine coast into three broad zones based upon geological features and sampled over five consecutive years; during April–November 2000 in the mid coast, in 2001 and 2002 along the south coast and in 2003 and 2004 along the eastern Maine coast. We quantified habitat use by eight economically important fish species ( Gadus morhua, Microgadus tomcod, Pollachius virens, Urophycis chuss, Urophycis tenuis, Osmerus mordax, Tautogolabrus adspersus, and Pseudopleuronectes americanus) and 10 other common epibenthic species ( n = 18 571). We identified the physical and biological variables most important in discriminating between habitats with and without individual fish species. Logistic regression models based on nearshore habitat characteristics were developed to predict the distribution of these species along the three zones representing broad geological regions of the Maine coast. Logistic regression models correctly classified individual fish species 58.7–97.1% of the time based on the temporal and physical habitat variables (month, temperature, salinity, and depth) and the presence–absence of submerged aquatic vegetation ( Zostera, Laminaria, or Phyllophora). Overall fish presence and economically important fish presence were correctly classified 61.1–79.8% and 66.0–73.6% of the time, respectively. The Maine shallow water fish community was composed primarily of young-of-the-year and juvenile fishes with all habitats functioning as facultative nursery areas. Presence of most fish species was positively associated with Zostera, Laminaria, and to a lesser extent, Phyllophora. This study provides direct evidence of shallow waters of the Gulf of Maine as critical facultative nursery habitat for juvenile G. morhua, M. tomcod, P. virens, U. tenuis, U. chuss, T. adspersus, O. mordax and P. americanus, and many ecologically important species.

Associations between Surficial Sediments and Groundfish Distributions in the Gulf of Maine–Georges Bank Region

AbstractThe delineation of essential fish habitat is an important element of contemporary fisheries management. Although local‐scale species–habitat relationships have been established for some managed species, we lack an understanding of these associations at the synoptic spatial scales on which fish populations and their associated fisheries operate. Interest in habitat delineations has been elevated further by an increased awareness of ongoing habitat degradation caused by mobile fishing gears and by the advancement of spatial management tools. Here we examine the associations between surficial sediment grain size and groundfish distributions in the Gulf of Maine–Georges Bank region. The mean abundances for 58 demersal fish species were determined for a spatial cell grid (185.2 km2 per cell), which was subsequently joined to a spatially referenced sediment database in a geographical information systems environment. Multivariate statistical methods were then used to examine how fish distribution and abundance varied with substrate grain size. Of the 58 species examined, 12 were consistently associated with particular substrate types. Atlantic cod Gadus morhua, longhorn sculpin Myoxocephalus octodecemspinosus, sea raven Hemitripterus americanus, and winter flounder Pseudopleuronectes americanus were consistently abundant in large‐grained substrate types, whereas white hake Urophycis tenuis, goosefish Lophius americanus, red hake U. chuss, silver hake Merluccius bilinearis, witch flounder Glyptocephalus cynoglossus, and American plaice Hippoglossoides platessoides were consistently abundant in fine‐grained substrates. Little skate Leucoraja erinacea was most abundant in sediments of intermediate grain size. Although broadly distributed, spring dogfish Squalus acanthias consistently distinguished assemblages in fine‐grained sediments. Given that we were able to detect even weak associations and that these relationships were consistent with local‐scale studies, we recommend using these relationships to further refine essential fish habitat and that they be given more weight in this and similar temperate ecosystems.

Characterisation and standardisation of a red shrimp &lt;i&gt;Aristeus antennatus&lt;/i&gt;, (Risso, 1816) fishery off the Alicante gulf (SE Spain)

SUMMARY: The red shrimp (Aristeus antennatus) is a target species of a deep trawl fishery in the Gulf of Alicante. This paper describes the fishery by following the activity of this trawl fleet between 1992 and 1999. Principal Components Analysis (PCA) of specific catch compositions identified five main components that explained 92% of the variability, and the catches were grouped into three main species: red shrimp, hake and blue whiting. Hierarchical Clustering Grouping of the percentage species catch composition allowed the fleet to be considered as two main groups, according to monthly landings and by differentiating the origin of the catches (slope or shelf). The species composition of the catch and the red shrimp catch rates (CPUE) differed between the two fleet groups. The application of Generalised Linear Modelling (GLM) to the CPUE series gave consistent indices of abundance. The fleet group, year and season had significant effects on shrimp catch rates, with the fleet group being the most important, and these models explained up to 62% of the total deviance. The abundance indices showed little variation from 1992, although 1994 had the highest value and 1997-1998 the lowest. Comparison with survey indices showed similar trends, while mean uncorrected CPUE differed. Monthly variations of shrimp indices showed a lower abundance in summer, which was attributed to the reproductive patterns of the species. As a result, the use of some fleet grouping techniques is recommended before standardising CPUEs to obtain trends or to calibrate assessment in a fishery.

Nursery use of shallow habitats by epibenthic fishes in Maine nearshore waters

Species richness and abundance of epibenthic fishes were quantified with daytime beam trawl tows in shallow water habitats during April–November 2000 of three mid-coast Maine estuaries: Casco Bay, Muscongus Bay and the Weskeag River. Five shallow (<10 m) habitats were sampled, Zostera marina, Laminaria longicruris, Phyllophora sp., Microciona prolifera and unvegetated sandy areas. Thirty-two species of fishes were collected. Species richness per tow was greater in Casco Bay followed by the Weskeag River and Muscongus Bay. Catch per unit effort (CPUE) of fishes was greater in Casco Bay than in the Weskeag River or Muscongus Bay. Species richness and faunal abundances were positively associated with vegetation, particularly Zostera, at all sampling locations. CPUEs of fishes were higher in Zostera primarily due to the abundance of Gasterosteus aculeatus, Apeltes quadracus, Pungitius pungitius, Myoxocephalus aenaeus, and Cylcopterus lumpus. The fish community of mid-coast estuaries was dominated by young-of-the-year (YOY) and juvenile fishes and all of the habitat types function as nursery areas. Twelve species (38%) of commercial and recreational importance were collected in the three estuaries, but the percentage was higher in Casco Bay (44%) and the Weskeag River (46%). These species included Anguilla rostrata, Clupea harengus, Gadus morhua, Microgadus tomcod, Pollachius virens, Urophycis chuss, Urophycis regia, Urophycis tenuis, Osmerus mordax, Macrozoarces americanus, Tautogolabrus adspersus, and Pleuronectes americanus. Four species, G. morhua, M. tomcod, P. virens, and U. tenuis were more common in spring than summer or autumn. P. americanus was most abundant in summer followed by spring and autumn. This study documents the importance of shallow estuarine areas in Maine as nurseries for these species.

Physicochemical Properties of Frozen Red Hake (Urophycis chuss) Mince as Affected by Cryoprotective Ingredients

ABSTRACT: Effects of alginate, iota‐carrageenan, soy protein concentrate (SPC), sodium tripolyphosphate (STPP), and sorbitol on physicochemical and sensory properties of red hake mince stored at −20 °C for 17 wk were investigated. The addition of 0.4% alginate, 4% sorbitol, and 0.3% STPP kept the mince from hardening and improved its dispersibility during mixing. This is believed to be a result of reduced protein denaturation as evidenced by higher levels of water, salt, SDS‐soluble proteins, and higher free sulfhydryl contents than the untreated control mince, which hardened with compact texture and exhibited considerable syneresis. Alginate appears to be responsible for preventing muscle fiber interaction through electrostatic repulsion and chelating Ca2+, thus improving dispersibility. Sorbitol and STPP with or without SPC and iota‐carrageenan did not improve the dispersibility.

Testes morphology and reproductive aspects of male Brazilian codling (Urophycis brasiliensis Kaup 1858)

Testes morphology and reproductive aspects of male Brazilian codling (Urophycis brasiliensis Kaup 1858)

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.

Evaluation of the quality of frozen minced red hake: use of fourier transform near-infrared spectroscopy.

The quality of frozen minced red hake was assessed by FTNIR spectroscopy in transmission mode. The region 1530-1866 nm was best correlated to dimethylamine (DMA) concentration, which is an accepted quality index for frozen gadoid fish. Partial least-squares (PLS) analysis showed that this technique predicts the DMA content sufficiently well for quality assurance (SD/SEP > 3). The PLS calibration was equally successful when five narrow spectral regions were chosen instead of the continuous spectrum, indicating that a cheap filter instrument may be developed for industrial use.

Production of seafood flavor from red hake (Urophycis chuss) by enzymatic hydrolysis.

Protein hydrolysates were prepared as a natural flavor stock from the red hake (Urophycis chuss) headed-gutted (H&G) mince and frame mince using commercial enzymes, Flavourzyme and Savorase, at the natural pH of fish (6.8) and the water/fish ratio of 2:5. The addition of 1.5% NaCl and 0.4% STPP improved the flavor quality of the hydrolysate by masking bitterness and off-flavor. A 6 h hydrolysis of H&G mince with Flavourzyme yielded a hydrolysate of the highest acceptability. Hydrolysis increased the concentration of most free amino acids except Arg and His. Leu, Lys, and Arg were predominant free amino acids in the hydrolysates, whereas Leu and Arg were major ones in the cooking juice. The concentration of Glu responsible for umami taste was increased by 6-9 times upon hydrolysis. Hydrolysates contained higher percentages of free amino acids giving both umami and sweet tastes than did cooking juice.

Evaluation of the Quality of Frozen Minced Red Hake: Use of Fourier Transform Infrared Spectroscopy

The suitability of FTIR spectroscopy for evaluating changes in the quality of frozen minced red hake was studied. The spectral data between 1600 and 890 cm-1 were correlated with the chemically determined dimethylamine (DMA) content of the fish using chemometric techniques. This spectral region contains all of the DMA and trimethylamine oxide (TMAO) absorbance bands. Discriminant analysis of the data results in a 90% success of distinguishing fresh from frozen fish and classifying frozen hake into three quality categories. The RPD value of 4 shows that the PLS model predicts the DMA content of the frozen fish well enough for quality assessment. Keywords: Fish quality; FTIR; hake; dimethylamine; discriminant analysis; PLS