Northwest Atlantic Fisheries Center

St. John's, Canada

Northwest Atlantic Fisheries Center

St. John's, Canada
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Invasive species have been associated with significant negative impacts in their introduced range often outcompeting native species, yet the long-term evolutionary dynamics of biological invasions are not well understood. Hybridization, either among waves of invasion or between native and introduced populations, could alter the ecological and evolutionary impacts of invasions yet has rarely been studied in marine invasive species. The European green crab (Carcinus maenas) invaded eastern North America twice from northern and southern locations in its native range. Here we examine the frequency of hybridization among these two distinct invasions at locations from New Jersey, USA to Newfoundland, Canada using restriction-site-associated DNA sequencing (RAD-seq), microsatellite loci and cytochrome c oxidase subunit I mitochondrial DNA (mtDNA) sequences. We used Bayesian clustering and hybrid assignment analyses to investigate hybridization between the northern and southern populations. Of the samples analyzed, six locations contained at least one hybrid individual, while two locations were characterized by extensive hybridization, with 95% of individuals collected from Placentia Bay, Newfoundland being hybrids (mostly F2) and 90% of individuals from Kejimkujik, Nova Scotia being classified as hybrids, mostly backcrosses to the northern ecotype. The presence of both F2 hybrids and backcrossed individuals suggests that these hybrids are viable and introgression is occurring between invasions. Our results provide insight into the demographic and evolutionary consequences of hybridization between independent invasions, and will inform the management of green crabs in eastern North America.Heredity advance online publication, 19 April 2017; doi:10.1038/hdy.2017.22. © 2017 Macmillan Publishers Limited, part of Springer Nature.

Dalpadado P.,Norwegian Institute of Marine Research | Mowbray F.,Northwest Atlantic Fisheries Center
Progress in Oceanography | Year: 2013

Four years of capelin (Mallotus villosus) diet data were examined from each of two ecosystems where capelin are an important forage species, the NW Atlantic off Newfoundland and the Barents Sea. Trophic studies from the two areas showed that, the Total Fullness Index (TFI), which reflects the diet weight, was significantly lower in capelin off Newfoundland compared to the Barents Sea, suggestive of poorer feeding conditions for Newfoundland capelin during the study period. In both regions, the copepod, Calanus finmarchicus dominated the diet of smaller capelin (<12. cm) comprising over half of their stomach content. However, there was a major difference in the diet of larger capelin. In the Barents Sea, a pronounced shift in the diet from copepods to krill, mostly Thysanoessa inermis, was observed in larger capelin (>12. cm), with krill being the largest contributor to the diet weight. In contrast, off Newfoundland, copepods remained the most important prey in larger capelin. In both ecosystems arctic amphipods, mostly dominated by Themisto libellula, contributed a small amount to the diet of larger capelin but were nearly absent in the diet of smaller fish. Findings for Newfoundland waters contradict past studies where krill (T. raschii) seems to have been a major component in the diet, especially for mature capelin. In both systems diurnal patterns in TFI indicated that daytime feeding was more successful. In general, a short efficient food chain (phytoplankton via Calanus or herbivorous krill to capelin) was observed in both regions. The extent of consumption of carnivorous zooplankton such as hyperiid amphipods may lengthen the trophic levels and thus reduce efficiency of energy transfer. © 2013 Elsevier Ltd.

Rice J.C.,Northwest Atlantic Fisheries Center | Garcia S.M.,FAO Fisheries Management Division
ICES Journal of Marine Science | Year: 2011

This paper reviews global projections to 2050 for human population growth and food production, both assuming constant climate and taking account of climate-related changes in growing conditions. It also reviews statistics on nutritional protein requirements, as well as how those requirements are met by fish on a regional basis. To meet projected food requirements, the production of fish has to increase by ∼50 from current levels. The paper also summarizes the main pressures on marine biodiversity that are expected to result from the impacts of changing climate on marine ecosystems, as well as the management measures and policy actions promoted to address those pressures. It highlights that most of the actions being proposed to address pressures on marine biodiversity are totally incompatible with the actions considered necessary to meet future food security needs, particularly in less developed parts of the world. The paper does not propose a solution to these conflicting pulls on policies for conservation and sustainable use. Rather, it emphasizes that there is a need for the two communities of experts and policy-makers to collaborate in finding a single compatible suite of policies and management measures, to allow coherent action on these crucial and difficult problems. © 2011 International Council for the Exploration of the Sea.

Cobb D.G.,Northwest Atlantic Fisheries Center | Galloway T.D.,University of Manitoba | Flannagan J.F.,Northwest Atlantic Fisheries Center
Canadian Journal of Fisheries and Aquatic Sciences | Year: 2015

Effects of discharge/substrate stability relationships on the abundance, diversity, and distribution of aquatic insects were studied from 1986 to 1988 in three reaches of a small stream in the Manitoba escarpment. Substrate stability (percentage of streambed paving material at incipient motion) ranged from 80 to 20% at bankfull discharge. Eleven taxa of mayflies, 15 taxa of caddisflies, and 10 taxa of stoneflies were collected. All but a few taxa were present at all stations. Benthic insect densities were negatively correlated with increasing discharge and substrate particle movement at all stations. Regression models describing insect density in terms of substrate stability usually accounted for more variation than models describing density in terms of discharge. Insect density decreased up to 94% at the most unstable stream reach following summer and autumn spates when 8 and 12%, respectively, of the streambed paving material was at incipient motion wheres no reduction occurred in a stable riffle constructed nearby. Most insect species were highly resilient; densities and diversities returned to prespate levels during periods of low flow. Temporal and spatial aspects of substrate stability should be considered in stream insect studies, particularly in relation to disturbance. De 1986 à 1988, on a étudié les incidences des relations entre ledébitet la stabilite du substrát dans trois tronçons d'un petit cours d'eau de l'escarpement du Manitoba sur I'abondance, la diversité et la repartition des insectes aquatiques. La stabilite du substrát (soit le pourcentage de matériaux recouvrant le lit du cours d'eau en début de mouvement) variait de 80 à 20% au cours du débit à plein bord. On a recueilli 11 taxons d'éphémères, 15 „ taxons de phryganes et 10 taxons de perles; tous étaient présents, sauf quelques-uns, à toutes les stations. La densité des insectes benthiques était en corrélation négative avec un plus grand débit et un plus grand dépla- cement des particules du substrát à toutes les stations. Les modèles de régression décrivant la densité des insectes en termes de la stabilite du substrát tenaient généralement compte dune plus grande variation que les modèles décrivant la densité en termes de débit. La densité des insectes a montré une baisse allant jusqu'á 94% dans les tronçons les plus instables aprés les erues dété et dautomne, lorsque 8 et 12% respectivement des matériaux recouvrant le lit du cours d'eau commençaient à se déplacer, tandis qu'aucune baisse du genre n'a été notée dans un radier stable voisin. Laplupartdes espèces d insectes se sontfacilement adaptéesàces conditions; ainsi, leur densité et leur diversité se sont rapidement rétablies au niveau pré-crue au cours des périodes de faible débit. On devrait done tenir compte des aspects temporaux et spatiaux de la stabilité du substrát lors d'études sur les insectes peuplant au cours d'eau, en particulier en ce qui a trait aux perturbations. © 2015, National Research Council of Canada. All rights reserved.

Abbott C.L.,Northwest Atlantic Fisheries Center
Current Biology | Year: 2014

DNA-based methods continue to unveil the diversity and evolutionary origins of life on Earth. 'Next generation' methods have just solved a long-standing puzzle by uncovering previously unseen yet globally distributed diversity within a lineage of amitochondriate parasites affecting commercially exploited aquatic hosts. This discovery will impact both pure and applied research fields. © 2014 Elsevier Ltd.

Hamoutene D.,Northwest Atlantic Fisheries Center
ICES Journal of Marine Science | Year: 2014

This study is a description of sediment sulphide levels and redox potential associated with different values of bacterial mats (Beggiatoa) coverage at stations in deep Subarctic finfish sites. Beggiatoa was not observed at reference stations and significant differences were found between geochemical parameters before aquaculture and at-harvest. Beggiatoa coverage should be considered in the light of other evidence gathered through video imaging such as benthic diversity and the presence of other visual indicators and not used as strict regulatory thresholds. © 2014 International Council for the Exploration of the Sea. All rights reserved.

Rice J.,Northwest Atlantic Fisheries Center
Fish and Fisheries | Year: 2011

The four general components of an ecosystem approach to fisheries (EAF) are reviewedIn taking account of environment forcing in stock dynamics, arguments are presented that effects of environmental forcing on growth, maturation and natural mortality are often more important to management than effects on recruitmentIn holding fisheries accountable for the ecosystem effects of fishing, it is argued that direct effects of fishing are generally known and can be managedHowever, interactions among fisheries and between fisheries and other sectors pose difficult challenges to equitable decisions in managing these impacts, and many traditional incentives function differently in EAF than in target-stock managementAchieving inclusiveness in decision-making and stewardship is also made more complex in EAF, because of the much larger number of interests with a legitimate role in decision-makingAs a result, integrated management (IM) becomes a necessary component of EAF, although EAF and IM are not interchangeable conceptsThe treatment of all four components of an EAF considers the need for a balanced and stable outcome on all three dimensions of sustainability - ecological, economic and socialIt also highlights that different participant groups in governance display different risk tolerances for misses (not taking conservation action when needed) and false alarms (restraining access to social or economic benefits when little ecological benefit results)These differences in tolerances for different kinds of management errors often complicate decision-making an EAF setting and raise transaction costs greatly. © 2011.

Thomson R.E.,Northwest Atlantic Fisheries Center | Krassovski M.V.,Northwest Atlantic Fisheries Center
Journal of Geophysical Research: Oceans | Year: 2010

The California Undercurrent is known to transport relatively warm, high-salinity, nutrient-rich water from the equatorial Pacific to Vancouver Island along the western continental slope of North America. This transport helps maintain the high productivity of the eastern boundary California Current system. In this study, we use several decades of water property survey data for the coasts of Oregon, Washington, British Columbia, and Alaska to show that equatorial Pacific water carried poleward by the undercurrent can eventually reach the Aleutian Islands, roughly 11,000 km from the source region. Long-term current meter records confirm the undercurrent as far north as Vancouver Island, where the current is found to be weakest in spring but then to strengthen through the summer and fall before merging with the wind-forced, poleward flowing Davidson Current in winter. The core depth of the equatorial water increases from 150 m 25 m off northwest Washington (near the northern end of the western North America coastal upwelling domain) to 225 m ± 25 m off southeast Alaska (near the southern end of the Gulf of Alaska coastal downwelling domain). Copyright 2010 by the American Geophysical Union.

Melvin G.D.,Northwest Atlantic Fisheries Center
ICES Journal of Marine Science | Year: 2016

Field studies to investigate the survey capability of a 500-kHz multibeam sonar to monitor and quantify Atlantic bluefin tuna were undertaken at several fishing locations (commercial and recreational) off Prince Edward Island and at a grow-out pen in Nova Scotia. The results demonstrate that individual bluefin can be detected, enumerated, and tracked acoustically within the swathe of the sonar. Bluefin were observed individually, and in groups ranging from 2 to 16 fish. Schooling tuna, assumed to be foraging, were observed moving in a soldier formation. Estimates of in situ swimming speeds (0.5-11.0 m s-1) were made by tracking individual fish within the swathe. The mean interspatial distance between fish when swimming in a group of two or more tuna was estimated to be 8.94 m with a range of 2.68-22.63 m. Groups of up to 48 bluefin were observed aggregating around active herring gillnet vessels. Dorsal aspect target strength estimates of bluefin, obtained from an accompanying 120-kHz echosounder (Simrad EK60), ranged from -33 to -14 dB for fish from 220 to 313 cm (size estimated from commercial catches). Sonar detection ranges were dependent upon sea state and water depth. In rough seas, the surface layer became too turbulent, and air bubble attenuation too high, to consistently separate reverberation from fish-like targets. In shallow water (20-30 m), a range setting of >50 m could not be utilized due to seabed reflections. In water depths >50-60 m, a tilt angle of 7.5o below the horizontal allowed the sonar's range of up to 150 m to be utilized with minimal reverberation from the surface and seabed. The results indicate there is potential for using a 500-kHz multibeam sonar in fishery-independent surveys to monitor and to quantify bluefin in shallow water (<100 m). © 2016 International Council for the Exploration of the Sea. All rights reserved.

Pepin P.,Northwest Atlantic Fisheries Center
Deep-Sea Research Part I: Oceanographic Research Papers | Year: 2013

This study evaluated the distribution of major calanoid copepods in the western Labrador Sea in relation to that of the myctophid Benthosema glaciale, and investigated patterns of prey composition and feeding periodicity by the latter to assess the potential impact of mesopelagic fish on copepod populations that reside in the deep ocean. Hydroacoustic surveys indicated that B. glaciale and the deep-scattering layer are widely distributed throughout the region with limited evidence of patchiness, with an average abundance of 6 fish m-2 and biomass of 9.3gm-2. There was clear evidence of diurnal variations in feeding activity that was achieved through vertical migration from several hundred meters depths to the surface layer. B. glaciale fed principally on calanoid copepods, with prey size dependent on the length of the fish but the relative variability in prey size was independent of predator length. Average rations were generally less than 1% of body weight per day, and the patterns of diurnal vertical migration by myctophids suggest that individuals fed once every two days rather than daily. The estimated mortality caused by B. glaciale on the calanoid populations, which considers most sources of uncertainty, ranged from 0.002 to 1.8% d-1, with the mid-point of these estimates being ~0.15% d-1, which is well below the estimated mortality rates of 10-20% d-1 based on vertical life tables. From observations from this and other ecosystems, understanding and contrasting the drivers of population dynamics and productivity of calanoid copepods in different deep basins of the North Atlantic will likely require a more comprehensive characterization of the plankton and pelagic and oceanic fish faunas of the epipelagic and mesopelagic zones and their trophic relationships and interactions. © 2013.

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