Southern Scotian Shelf Research Articles

Life-stage-dependent supergene haplotype frequencies and metapopulation neutral genetic patterns of Atlantic cod, Gadus morhua, from Canada's Northern cod stock region and adjacent areas.

Among highly migratory fish species, nursery areas occupied by juveniles often differ from adult habitats. To better understand the spatial dynamics of Canada's Northern cod stock, juveniles caught off the east coast of Newfoundland and Labrador were compared to adults from the same region as well as individuals from other areas in Atlantic Canada using double-digest restriction site-associated DNA sequencing-derived single nucleotide polymorphisms. A reduced proportion of homozygotes with a chromosomal inversion located in linkage group 1 (LG1) was detected between juvenile and adult samples in the Northern cod stock region, potentially indicating age-dependent habitat use or ontogenetic selection for attributes associated with the many genes located in LG1. No selectively neutral genetic differences were found between samples from the Northern cod stock; nevertheless, significant differences were found between some of these samples and cod collected from St. Pierre Bank, Bay of Fundy, Browns Bank and the southern Scotian Shelf. Clustering analysis of variants at neutral loci provided evidence for three major genetic units: (a) the Newfoundland Atlantic Coast, (b) eastern and southern Gulf of St. Lawrence and Burgeo Bank and (c) the Bay of Fundy, Browns Bank and southern Scotian Shelf. Both adaptive and neutral population structure within the Northern cod stock should be considered by managers to promote demographic rebuilding of the stock.

Spatiotemporal bycatch analysis of the Atlantic halibut (Hippoglossus hippoglossus) longline fishery survey indicates hotspots for species of conservation concern

The Atlantic halibut (Hippoglossus hippoglossus) longline fishery is the second most valuable groundfish fishery in Atlantic Canada and received Marine Stewardship Council certification in 2013. The bottom longline fishery accounts for most halibut landings but incidentally catches nontargeted species (bycatch). Since 1998, Fisheries and Oceans Canada and the halibut fishing industry performed annual longline surveys across the Scotian Shelf and Southern Grand Banks stock management area to monitor halibut abundance, and at‐sea observers also recorded bycatch information. We examined the species composition and proportion of the survey bycatch and analyzed temporal and spatial trends in standardized weight of (a) halibut catch, (b) total bycatch, and (c) bycatch of species of conservation concern. From 1998 to 2016, 70% of the total catch by weight and 85% by number of individuals were bycatch. Over 100 identified species of finfish, sharks, skates, benthic invertebrates, marine mammals, and seabirds were caught as bycatch in the survey. This included four species listed under the Species at Risk Act (Northern wolffish, Anarhichas denticulatus; spotted wolffish, A. minor; Atlantic wolffish, A. lupus; Atlantic cod, Gadus morhua), and another 14 species awaiting a listing decision based on assessments by the Committee on the Status of Endangered Wildlife in Canada. Generally, the standardized weight of halibut and barndoor skate (Dipturus laevis) increased over time, while Atlantic cod, spiny dogfish (Squalus acanthias), white hake (Urophycis tenuis), and thorny skate (Amblyraja radiata) decreased. Spatial patterns indicated high bycatch levels on the southern Scotian Shelf and southern edge of the Southern Grand Banks, with hotspots for certain species of conservation concern. Our results identify temporal trends in threatened species and areas where they are susceptible to the Atlantic halibut longline fishery which can inform recovery strategies, bycatch levels and spatial zoning in fisheries management and marine conservation.

Recessional moraines on the southern Scotian Shelf of Atlantic Canada

Recessional moraines are end moraines deposited during a temporary but significant pause in the final retreat of a glacier or ice sheet. Curvilinear, sub-parallel ridges of sediment on the southern Scotian Shelf are interpreted as recessional moraines formed in proximity to the grounding line of the southeastern extent of the Laurentide Ice Sheet; collectively they are termed the Scotian Shelf end moraine complex (e.g. King 1969; King & Fader 1986). Mapping of the distribution of moraines on the Scotian Shelf provides a basis for the interpretation of the advance and retreat of the Laurentide Ice Sheet during the Last Glacial Maximum (Courtney 1993; Stea et al. 1998; Shaw et al. 2006, 2014). The seismostratigraphy of the recessional moraines and overlying postglacial deposits enables shelf-wide correlation of glacial and deglacial events. The southern Scotian Shelf is 130–190 km wide and consists of a series of banks and basins (Fig. 1a). Roseway Basin is flanked by Browns Bank to the SW and Roseway Bank to the NE; the basin itself is subdivided into two sub-basins by a ridge (the most prominent of the Roseway Basin Moraines, Fig. 1a). To the NE of Roseway Bank is the LaHave Basin. Water depths range from <100 m on the banks to almost 300 m …

De Geer moraines on German Bank, southern Scotian Shelf of Atlantic Canada

Numerous regularly spaced, parallel, linear to curvilinear ridges of sediment are recognized to form at or close to the grounding lines of water-terminating glaciers (Linden & Moller 2005). These ice-flow transverse ridges, sometimes known as De Geer moraines (De Geer 1889), have modest heights and widths and variable lengths. De Geer's original description of Swedish moraines with these characteristics invoked an annual cycle. Present use of ‘De Geer moraine’ refers to closely spaced subaqueous moraine ridges which may or may not be annual. The distribution and pattern of ubiquitous De Geer moraines on German Bank provide insight into the direction and timing of regional deglaciation of the southern Scotian Shelf (Todd et al. 2007). Across a bathymetric range of over 100 m, southern German Bank is mantled by swarms of ridges; each ridge displays a quasi-linear or curved line in planform (Fig. 1). In topographic depressions, the ridges are subdued in relief or are absent (Fig. 1a). The strike of the ridge crests is generally WSW–ENE. Individual ridges can be traced horizontally from short segments of a few hundred metres up to almost 10 km. …

Surficial geology and benthic habitat of the German Bank seabed, Scotian Shelf, Canada

To provide the scientific context for management of a newly opened scallop fishing ground, surficial geology and benthic habitats were mapped on German Bank on the southern Scotian Shelf off Atlantic Canada. To provide a seamless regional dataset, multibeam sonar surveys covered 5320 km 2 of the bank in water depths of 30–250 m and provided 5 m horizontal resolution bathymetry and backscatter strength. Geoscience data included high-resolution geophysical profiles (seismic reflection and sidescan sonar) and seabed sediment samples. Geological interpretation revealed that bedrock is exposed at the seafloor on much of German Bank and is overlain in places by glacial and postglacial sediment. Biological data included seafloor video transects and photographs from which 127 taxa of visible megabenthos were identified. Trawl bycatch data were obtained from government annual research surveys. Statistical analysis of these two datasets and a suite of oceanographic environmental variables demonstrated that significantly different fauna exist on bedrock, glacial sediment and postglacial sediment.

Assessment of the population structure of western North Atlantic right whales (Eubalaena glacialis) based on sighting and mtDNA data

Photoidentifications and 11 years of sighting data revealed that only two-thirds of the western North Atlantic right whale (Eubalaena glacialis) reproductive females took their calves to the Bay of Fundy, the only known summer nursery. Study of cow–calf pairs further indicated that female, and to a lesser extent male, calves were philopatric with respect to this nursery. To further examine population structure, mtDNA composite restriction morphs were determined for 150 animals (47% of the population). Using 11 restriction enzymes, three composite mtDNA morphs were identified. One morph was not found among reproductive females that brought all of their calves to the Bay of Fundy. In contrast, all three morphs were present, in the same relative frequencies, among males that were seen in the Bay of Fundy and those that were not. These findings support the hypothesis that this population may be divided into two subgroups, which are defined by their use of the Fundy nursery, and that males are generally less philopatric than females. Animals from both subgroups were seen on the southern Scotian shelf, where most right whale courtship behavior was observed. Hence, although segregated by nursery areas, the western North Atlantic right whales probably represent a single breeding population.

Planktonic Sea Scallop Larvae (Placopecten magellanicus) in the Georges Bank Region: Broadscale Distribution in Relation to Physical Oceanography

During autumn surveys for sea scallop larvae (Placopecten magellanicus) from 1985 to 1987, the mean abundance of sea scallop larvae on the northeast part of Georges Bank (1201–20080∙m−2) was much greater than on the southern Scotian Shelf (5–240∙m−2). Few larvae were collected between these two areas, and exchange between Georges Bank and the Scotian Shelf appears very limited. Transects across the northern flank in 1988 revealed peaks in larval abundance when on-bank temperature stratification was high. Relative larval abundance on the transects was positively related to the speed of the along-front current, suggesting physical convergence of larvae. The on-bank retention of scallop larvae on Georges Bank appears to be due to physical processes alone, since scallop larvae undertake only limited diel vertical migration. Larval exhange among adult scallop aggregations on Georges Bank (the northeast peak, the southeast part, and the South Channel) is probable, but evidence from this study is limited. The autumn production of late-stage larvae on the northern flank and northeast peak of Georges Bank is estimated to range from 120 to 1500∙m−2, which is 10–100 times greater than the density of scallops aged 1–2 yr.

Erythrocyte micronuclei in winter flounder (Pseudopleuronectes americanus): Results of field surveys during 1980?1988 from Virginia to Nova Scotia and in Long Island Sound

Erythrocyte micronuclei (MN) frequencies of 280 winter flounder (Pseudopleuronectes americanus) from Chesapeake Bay to the southern Scotian Shelf including Long Island Sound were measured. The MN data were combined with data previously reported for 224 flounder and the combined data sets were analyzed. Incidences of MN were elevated sixfold in flounder from the New York Bight Apex as compared to frequencies for fish from the inshore Gulf of Maine and Block Island Sound, and twice those found in Georges Bank and Long Island Sound flounder. Inshore New Jersey fish had higher MN frequencies than those from inshore Gulf Of Maine and Block Island Sound. The occurrence of MN in flounder from inshore Virginia was higher than in flounder from inshore Gulf of Maine and Block Island Sound. The large subset of stations from Long Island Sound indicated higher frequencies of MN in flounder from Hempstead and Shoreham as compared to most other sites in the Sound. There was no significant difference in the frequency of MN between males and females, but males had significantly more MN than sexually immature flounder. Flounder over the entire sampling area had increased levels of MN during the fall months of the year. This is probably influenced by the maternal cycle of gonadal maturation.

BOOK REVIEWS

Book Reviwed in this article:SCALLOP AND QUEEN FISHERIES IN THE BRITISH ISLES, Edited by James MasonEVOLUTIONARY ECOLOGY OF NEOTROPICAL FRESHWATER FISHES, edited by Thomas M. ZaretGUIDE TO THE EARLY STAGES OF MARINE FISHES OCCURRING IN THE WESTERN NORTH ATLANTIC OCEAN, CAPE HATTERAS TO THE SOUTHERN SCOTIAN SHELF. Edited by Michael P. FahayFISH PATHOGENS AND ENVIRONMENT IN EUROPEAN POLYCULTURE, edited by J. OlahPERIPHYTON OF FRESHWATER ECOSYSTEMS. (Developments in Hydrobiology 17) Edited by R. G. WetzelTILAPIINE FISHES OF THE GENERA SAROTHERODON, OREOCHROMIS and DANAKILIA. by Ethelwynn Trewavas

Vertebral and Dorsal Fin-ray Numbers in Atlantic Wolffish (Anarhichas lupus) of the Northwest Atlantic

From collections of Atlantic wolffish in the Northwest Atlantic (West Greenland to the Scotian Shelf) during 1950-67, mean vertebral counts increased gradually from the colder northern to the warmer southern areas (74.19 off Labrador to 75.29 on the southern Scotian Shelf). This is the reverse of the usual pattern in other fishes of the region with pelagic eggs. The pattern for mean dorsal fin-ray counts was similar, but the area coverage and sample sizes were less extensive and the differences were less significant than in the vertebral data. The overall ranges in counts were 72-78 for vertebrae and 71-77 for dorsal fin-rays. Dorsal fin-ray and vertebral numbers were moderately well correlated in a limited number of specimens.

Guide to the Early Stages of Marine Fishes Occurring in the Western North Atlantic Ocean, Cape Hatteras to the Southern Scotian Shelf

Guide to the Early Stages of Marine Fishes Occurring in the Western North Atlantic Ocean, Cape Hatteras to the Southern Scotian Shelf

Guide to the Early Stages of Marine Fishes Occurring in the Western North Atlantic Ocean, Cape Hatteras to the Southern Scotian Shelf

Guide to the Early Stages of Marine Fishes Occurring in the Western North Atlantic Ocean, Cape Hatteras to the Southern Scotian Shelf