White Hake Urophycis Tenuis Research Articles

Feeding Interactions between Fishes in a Coastal Ecosystem in the Southern Gulf of St. Lawrence, Atlantic Canada

AbstractDiet composition, diet similarity, and major predator–prey interactions between the 15 most abundant demersal and pelagic fishes (N = 12,163 stomachs) during the period 1999–2003 were described for Northumberland Strait, a semi‐enclosed, marine coastal ecosystem. Of the five pelagic species, Rainbow Smelt Osmerus mordax ate benthic prey (shrimps and polychaetes); Atlantic Herring Clupea harengus and American Shad Alosa sapidissima consumed small copepods and crab zoeae; and Atlantic Mackerel Scomber scombrus and Alewives Alosa pseudoharengus ate small copepods and moderate amounts of benthic prey and small fishes. Three demersal species were strongly piscivorous but with minimal diet overlap: Sea Ravens Hemitripterus americanus consumed small benthic fishes (especially flounders); Winter Skate Leucoraja ocellata consumed sand lances Ammodytes sp. and Rainbow Smelt; and White Hake Urophycis tenuis consumed Atlantic Herring and Atlantic Mackerel. Cluster analysis revealed seven feeding guilds, of which four contained a single species; consequently, the potential for compensation of predatory function was nonexistent for these guilds. The three multispecies guilds comprised consumers of (1) small copepods and crab zoeae; (2) small benthic invertebrates and polychaetes; and (3) shrimps and crabs. Based on diets, the principal route of energy transfer seemed to be the benthic–detrital pathway; however, confirmation requires representative abundance estimates for the various fishes. Moreover, abundances of many fish species have changed (i.e., most have decreased) since this study was completed, with unknown consequences for food web structure and functioning.

Feeding Interactions between Fishes in a Coastal Ecosystem in the Southern Gulf of St. Lawrence, Atlantic Canada

AbstractFor the period 1999–2003, diet composition, diet similarity, and major predator–prey interactions between the 15 most abundant demersal and pelagic fishes (N = 12,163 stomachs) were described for Northumberland Strait - a semienclosed, marine, coastal ecosystem. Of the five pelagic species, Rainbow Smelt Osmerus mordax ate benthic prey (shrimps and polychaetes), Atlantic Herring Clupea harengus and American Shad Alosa sapidissima consumed small copepods and crab zoea, and Atlantic Mackerel Scomber scombrus and Alewife A. pseudoharengus ate small copepods and moderate amounts of benthic prey and small fishes. Three demersal species were strongly piscivorous but with minimal diet overlap: Sea Raven Hemitripterus americanus consumed small benthic fishes (especially flounders); Winter Skate Leucoraja ocellatus consumed sand lance (Ammodytes sp.) and Rainbow Smelt; and White Hake Urophycis tenuis consumed Atlantic Herring and Atlantic Mackerel. Cluster analysis revealed seven feeding guilds of which fo...

Seabed Habitat Determines Fish and Macroinvertebrate Community Associations in a Subarctic Marine Coastal Nursery

AbstractFish exhibit habitat‐specific distributions in heterogeneous landscapes. Many sampling techniques are limited to specific seabed types and have limited utility in comparisons of fish abundance among multiple habitats. We measured the relative abundance and the composition of fish communities in four naturally occurring coastal marine seabed types (sand–pebble, cobble, bedrock, and eelgrass) and one anthropogenic habitat type (wharf) in Newman Sound, Newfoundland, Canada, by using baited video cameras. Fish and macroinvertebrate communities were significantly different among habitat types. Winter Flounder Pseudopleuronectes americanus, Atlantic Cod Gadus morhua, and Shorthorn Sculpin Myoxocephalus scorpius were significantly more abundant over sand–pebble substrate compared with bedrock and wharf sites. Cunners Tautogolabrus adspersus and Greenland Cod Gadus macrocephalus ogac were most abundant at wharf sites. Atlantic rock crabs Cancer irroratus and American lobsters Homarus americanus avoided sand–pebble seabeds, and American lobsters were almost exclusive to bedrock sites. Cunners, Winter Flounder, and Atlantic Cod were more abundant in summer, whereas Greenland Cod and Atlantic rock crabs were more abundant during autumn months. In paired comparisons of eelgrass habitats, the community sampled by two methods was different. Relative abundance estimates from baited video cameras matched beach seine estimates for abundant predatory species (e.g., Cunner, Greenland Cod, and Atlantic rock crab), but other species, including age‐0 Greenland Cod, Shorthorn Sculpin, and White Hake Urophycis tenuis, were better represented in beach seine samples. We demonstrated substrate preferences by common coastal marine fish and crab species, which have proven difficult to enumerate via active sampling techniques in the past. Our findings will facilitate comparative studies for these species among habitat components. For species that are well sampled by using baited video cameras, this technique will advance our ability to plan for their management in the nearshore.

Evaluating the potential for grey seal predation to explain elevated natural mortality in three fish species in the southern Gulf of St. Lawrence

Despite 2 decades of very low fishing levels, numerous NW Atlantic demersal fish stocks have failed to recover from collapsed states or are presently collapsing. In the southern Gulf of St. Lawrence, adult natural mortality (M) appears to be the demographic rate that most limits population productivity in at least 3 species: Atlantic cod Gadus morhua, white hake Urophycis tenuis and winter skate Leucoraja ocellata. The causes of elevated M are not well understood, though there is indirect evidence consistent with an effect of predation by grey seals Halichoerus grypus. However, direct evidence is lacking due to uncertainty in the seal diet. Consequently, Monte Carlo simulations were undertaken using data on the spatial overlap between the seals and the fishes and a seal food-consumption model, to estimate the plausibility that different seal-diet compositions could explain observed M levels. Under the simulation assumptions, we find that predation could explain up to 20 to 50% of M in adult white hake and cod even if these species comprise a small percentage of grey seal diets (<25%). If seals consume some of these fish only partially, by selectively feeding on soft tissues, a predation effect becomes more plausible. Preda- tion can also plausibly explain the observed elevated M in adult winter skate, even if they com- prise a negligible (<0.1%) percentage of the grey seal diet. Though the simulations deal with the factors that shape the potential for predation, a greater understanding of prey selection is required to conclude whether grey seals are actually adversely impacting these fish populations.

Ontogenetic Diet Comparison of Atlantic Cod and White Hake Occurring at Historically Low Population Abundances

AbstractAbundances of Atlantic cod Gadus morhua and white hake Urophycis tenuis have dropped to historically low levels in the southern Gulf of St. Lawrence. Stomach samples were collected during late summer 2001 and 2002 to compare ontogenetic diet patterns at a time when food presumably was not limiting. White hake had a narrow diet and showed an abrupt ontogenetic diet change: fish less than 35 cm total length (TL) consumed benthic invertebrates (sevenspine bay shrimp Crangon septemspinosa, gammarid amphipods, or polychaetes), while those at least 35 cm TL preyed mainly on Atlantic herring Clupea harengus. Atlantic cod had a broad diet initially dominated by benthic and pelagic invertebrates (Arctic argid Argis dentata, Aesop shrimp Pandalus montagui, Eualus spp., mysids, northern propeller clams Cyrtodaria siliqua, and polychaetes). Fish (mainly Atlantic herring, capelin Mallotus villosus, and small demersal species) were gradually incorporated into the Atlantic cod diet but did not comprise more than 50% of prey biomass until the cod reached a length of 50–60 cm TL. The incidence of cannibalism was low for both fishes. Diet overlap was low between all sizes of Atlantic cod and white hake but was high between adjacent size‐classes of Atlantic cod and for all size‐classes of white hake greater than 35 cm TL (where Atlantic herring comprised more than 70% of prey biomass).

Fractal measures of habitat structure: maximum densities of juvenile cod occur at intermediate eelgrass complexity

Habitat patchiness is known to alter the relation of a population to both its predators and its prey. We developed a biologically interpretable measure of habitat complexity to test whether juvenile fish density depends on degree of patchiness. In Newfoundland coastal waters, juvenile fish species, including Atlantic cod Gadus morhua, are associated with eelgrass Zostera marina. How- ever, the association of density with eelgrass cover is dependent upon site and the scale of analysis. We tested for non-monotonic relationships (with an intermediate optimum) between 5 spatial charac- teristics of eelgrass and density of 3 juvenile (Age-0) fish species: Atlantic cod, Greenland cod G. ogac, and white hake Urophycis tenuis. We used aerial photography to determine eelgrass perimeter and area measurements at multiple scales, fractal dimensions of perimeter (DP) and area (DA), and a measure that combines perimeter and area complexity at these scales (βP/A). Fish densities were esti- mated at each site using a seine net. We found parabolic relationships between βP/A and density for all 3 species, indicating highest fish densities at sites of intermediate patchiness and edge regularity. Furthermore, we determined that βP/A provided a less ambiguous estimate of spatial configuration than other measures. This intermediate maximum may reflect a trade-off, whereby eelgrass sites of intermediate spatial complexity provide juvenile fish with both optimal protective cover and oppor- tunity to feed. This pattern may apply to any species requiring open areas in which to forage as well as shelter to offset predation risk.

Structural and functional connectivity of marine fishes within a semi‐enclosed Newfoundland fjord

The interplay between structural connectivity (i.e. habitat continuity) and functional connectivity (i.e. dispersal probability) in marine fishes was examined in a coastal fjord (Holyrood Pond, Newfoundland, Canada) that is completely isolated from the North Atlantic Ocean for most of the year. Genetic differentiation was described in three species (rainbow smelt Osmerus mordax, white hake Urophycis tenuis and Atlantic cod Gadus morhua) with contrasting life histories using seven to 10 microsatellite loci and a protein-coding locus, PanI (G. morhua). Analysis of microsatellite differentiation indicated clear genetic differences between the fjord and coastal regions; however, the magnitude of difference was no more elevated than adjacent bays and was not enhanced by the fjord's isolation. Osmerus mordax was characterized by the highest structure overall with moderate differentiation between the fjord and St Mary's Bay (F(ST)c.0.047). In contrast, U. tenuis and G. morhua displayed weak differentiation (F(ST) < 0.01). Nonetheless, these populations did demonstrate high rates (< 75%) of Bayesian self-assignment. Furthermore, elevated differentiation was observed at the PanI locus in G. morhua between the fjord and other coastal locations. Interestingly, locus-specific genetic differentiation and expected heterozygosity were negatively associated in O. mordax, in contrast to the positive associations observed in U. tenuis and G. morhua. Gene flow in these species is apparently unencumbered by limited structural connectivity, yet the observed differentiation suggests that population structuring exists over small scales despite high dispersal potential.

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.

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.