Diel foraging cycles and interactions among juvenile Atlantic cod (Gadus morhua) at a nearshore site in Newfoundland

1998 ◽  
Vol 55 (6) ◽  
pp. 1307-1316 ◽  
Author(s):  
Scott M Grant ◽  
Joseph A Brown
Keyword(s):  
Resource Use ◽  
Zostera Marina ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
Prey Size ◽  
Foraging Activity ◽  
Daily Ration ◽  
Behavioural Responses ◽  
In The Wild ◽  
Activity Cycles

In coastal Newfoundland, age 0 Atlantic cod (Gadus morhua) settle in shallow, nearshore regions occupied by older conspecifics. Although intercohort cannibalism is common, little is known of the behavioural responses that limit interactions among juvenile cohorts in the wild. We examined the day-night differences in catch and diet of age 0 and age 1 cod to delineate peak foraging activity and resource use in eelgrass (Zostera marina) habitat. Cod exhibited a size-related shift (age 0 to age 1) from feeding predominantly on zooplankton by day to benthos at night. Intercohort cannibalism occurred when age 1 cod were approximately three times larger than their prey. Concentrations of age 0 cod foraged in the water column during the day, ceased feeding at night, and appeared to disperse to the bottom. Seasonally decreasing daylength and prey size contributed to a decline in daily ration, yet age 0 cod still maintained a strict diurnal foraging cycle. The nocturnal decrease in feeding coincided with an increase in the catch of older conspecifics (age 2 and age 3) and increased foraging activity of age 1 cod, suggesting that avoidance of older conspecifics is an important factor influencing the diel foraging and activity cycles of age 0 cod.

scholarly journals Atlantic Cod ( Gadus morhua ) benefits from the availability of seagrass ( Zostera marina ) nursery habitat

2014 ◽  
Vol 2 ◽  
pp. 367-377 ◽  
Author(s):  
Richard J. Lilley ◽  
Richard K.F. Unsworth
Keyword(s):  
Zostera Marina ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
Nursery Habitat

scholarly journals Catch-and-release of Atlantic cod (Gadus morhua): post-release behaviour of acoustically pretagged fish in a natural marine environment

2015 ◽  
Vol 72 (2) ◽  
pp. 252-261 ◽  
Author(s):  
Keno Ferter ◽  
Klaas Hartmann ◽  
Alf Ring Kleiven ◽  
Even Moland ◽  
Esben Moland Olsen
Keyword(s):  
Large Scale ◽  
Gadus Morhua ◽  
Sublethal Effects ◽  
Atlantic Cod ◽  
Small Scale ◽  
Marine Environments ◽  
Vertical Movements ◽  
Catch And Release ◽  
Diel Vertical Migrations ◽  
In The Wild

Studying the sublethal effects of catch-and-release (C&R) is challenging, as there are several potential sources of bias. For example, if behavioural alterations immediately after the release event are to be studied, separation of tagging effects from actual C&R effects is required, which is a challenge in the wild, particularly in marine environments. To investigate the effects of C&R on Atlantic cod (Gadus morhua) in their natural environment, 80 cod were caught in fyke nets, fitted with acoustic transmitters, and released. After recovery from tagging and handling for at least 14 days, nine individuals were recaptured and released at least once during experimental angling, following best release practice. All cod survived the C&R event and did not show any large-scale behavioural changes (i.e., changes in diel vertical migrations). However, analysis of small-scale vertical movements showed that three individuals underwent short-term alterations (e.g., reduced or increased swimming activity). This study showed that pretagging fish with acoustic transmitters before experimental angling is an option when investigating fish behaviour immediately after the release event in marine environments. Moreover, release guidelines for cod should be developed, as cod can recover quickly if caught in shallow waters (<20 m) and properly handled and released.

scholarly journals Evolutionary response to size-selective mortality in an exploited fish population

2007 ◽  
Vol 274 (1613) ◽  
pp. 1015-1022 ◽  
Author(s):  
Douglas P Swain ◽  
Alan F Sinclair ◽  
J Mark Hanson
Keyword(s):  
Gadus Morhua ◽  
Atlantic Cod ◽  
Fish Population ◽  
Fish Populations ◽  
Selective Mortality ◽  
Genetic Changes ◽  
Evolutionary Response ◽  
In The Wild ◽  
Size At Age ◽  
Change In Mean

Many collapsed fish populations have failed to recover after a decade or more with little fishing. This may reflect evolutionary change in response to the highly selective mortality imposed by fisheries. Recent experimental work has demonstrated a rapid genetic change in growth rate in response to size-selective harvesting of laboratory fish populations. Here, we use a 30-year time-series of back-calculated lengths-at-age to test for a genetic response to size-selective mortality in the wild in a heavily exploited population of Atlantic cod ( Gadus morhua ). Controlling for the effects of density- and temperature-dependent growth, the change in mean length of 4-year-old cod between offspring and their parental cohorts was positively correlated with the estimated selection differential experienced by the parental cohorts between this age and spawning. This result supports the hypothesis that there have been genetic changes in growth in this population in response to size-selective fishing. Such changes may account for the continued small size-at-age in this population despite good conditions for growth and little fishing for over a decade. This study highlights the need for management regimes that take into account the evolutionary consequences of fishing.

Interpopulation differences in growth rates and food conversion efficiencies of young Grand Banks and Gulf of Maine Atlantic cod (Gadus morhua)

2000 ◽  
Vol 57 (11) ◽  
pp. 2223-2229 ◽  
Author(s):  
Craig F Purchase ◽  
Joseph A Brown
Keyword(s):  
Growth Rates ◽  
Gadus Morhua ◽  
Gulf Of Maine ◽  
Atlantic Cod ◽  
Larval Fish ◽  
Food Conversion ◽  
Life History Variation ◽  
Grand Banks ◽  
In The Wild ◽  
Conversion Efficiencies

Geographically separated Atlantic cod (Gadus morhua) stocks in the northwest Atlantic exhibit life history variation and have been shown to differ genetically. The genetic and environmental contributions to phenotypic differences, however, have not yet been measured. We used common environment experiments to evaluate the importance of temperature on the observed growth variation between Grand Banks (GB) and Gulf of Maine (GOM) cod stocks. Larvae from the GB grew faster than GOM larvae at both 7 and 12°C. Growth rates of juveniles were not different, but GB juveniles had higher food conversion efficiencies than those from the GOM (at both ambient and warm temperatures). The results indicate that faster growth of GOM cod in the wild is not due to a higher genetic capacity for growth rate in GOM than in GB fish. The findings give evidence of genetically based phenotypic variation, which is in agreement with molecular studies on population differentiation in cod, and support the theory of countergradient variation in growth rates of larval fish.

Overwintering of Adult Northern Atlantic Cod (Gadus morhua) in Cold Inshore Waters as Evidenced by Plasma Antifreeze Glycoprotein Levels

1994 ◽  
Vol 51 (12) ◽  
pp. 2834-2842 ◽  
Author(s):  
Sally V. Goddard ◽  
J. S. Wroblewski ◽  
C. T. Taggart ◽  
K. A. Howse ◽  
W. L. Bailey ◽  
...  
Keyword(s):  
Gadus Morhua ◽  
Atlantic Cod ◽  
Antifreeze Glycoproteins ◽  
Cold Temperatures ◽  
Antifreeze Glycoprotein ◽  
Trap Fishery ◽  
In The Wild ◽  
History Of ◽  
Inshore Waters ◽  
Trinity Bay

Adult Atlantic cod (Gadus morhua) are known to produce antifreeze glycoproteins in response to cold temperatures. Our laboratory studies demonstrated that blood plasma levels in adult cod were positively correlated with the number of days they spent in subzero water. Between April 1991 and June 1993, we monitored concentrations of antifreeze glycoproteins in the plasma of late juvenile and adult cod in Trinity Bay, Newfoundland, and used the results to estimate how long cod had been exposed to low water temperatures. A consideration of these data in conjunction with detailed temperature profiles of the area taken over the course of the study allowed us to deduce the distribution of cod in relation to the temperature field. This study provides evidence that (1) blood antifreeze glycoprotein levels can be used to deduce the recent thermal history of cod in the wild and (2) after their inshore summer feeding period, considerable numbers of adult cod overwintered inshore in Trinity Bay in subzero water, producing antifreeze glycoproteins as temperatures fell below 0 °C. From May onwards, "cold-adapted" cod moved into warming surface waters, where they became available to an early inshore trap fishery.

scholarly journals Behavioural responses to pressure changes in cultured Atlantic cod (Gadus morhua): Defining practical limits for submerging and lifting sea-cages

Aquaculture ◽  
2010 ◽  
Vol 308 (3-4) ◽  
pp. 106-115 ◽  
Author(s):  
Øyvind J. Korsøen ◽  
Tim Dempster ◽  
Jan Erik Fosseidengen ◽  
Anders Fernö ◽  
Einar Heegaard ◽  
...  
Keyword(s):  
Gadus Morhua ◽  
Atlantic Cod ◽  
Behavioural Responses ◽  
Pressure Changes

scholarly journals Predation on hatchery-reared lobsters released in the wild

2000 ◽  
Vol 57 (9) ◽  
pp. 1794-1803 ◽  
Author(s):  
Gro I van der Meeren
Keyword(s):  
Gadus Morhua ◽  
Carapace Length ◽  
Atlantic Cod ◽  
Fish Predation ◽  
Rocky Substratum ◽  
Cancer Pagurus ◽  
Shorthorn Sculpin ◽  
In The Wild ◽  
Myoxocephalus Scorpius ◽  
Labrus Bergylta

Predation on hatchery-reared lobsters (Homarus gammarus) in the wild was studied in order to identify predators in southwestern Norway on rocky and sandy substrates in winter and summer. Lobsters of 12-15 mm carapace length were tagged with magnetic microtags. About 51 000 juvenile lobsters were released on 10 occasions at three locations. Predator samplings were by trammel nets, eel traps, and videorecordings during the 24 h immediately following the releases. In summer, loss to predators occurred on both rocky and sandy substrates. The loss was lower in winter when lobsters were found as prey in predators caught on sand. The risk of fish predation was highest in the first hours after release, when the lobsters were out of shelter. The wrasses Labrus bergylta and Labrus mixtus were the major predators of lobsters, while Atlantic cod (Gadus morhua), shorthorn sculpin (Myoxocephalus scorpius), and crab (Cancer pagurus) were mainly winter predators. Winter predators were never as abundant as summer predators. To minimise predatory loss of reared and costly lobsters, they should be released onto rocky substratum in winter. Due to the damage to the predated lobsters, it was not possible to correlate survival against lobster size.

Biochemical correlates of growth and condition in juvenile Atlantic cod (Gadus morhua) from Newfoundland

1998 ◽  
Vol 55 (7) ◽  
pp. 1591-1598 ◽  
Author(s):  
Patrice Couture ◽  
Jean-Denis Dutil ◽  
Helga Guderley
Keyword(s):  
Growth Rate ◽  
Water Content ◽  
Gadus Morhua ◽  
Citrate Synthase ◽  
Atlantic Cod ◽  
Nucleoside Diphosphate Kinase ◽  
Multiple Regression Model ◽  
Hepatosomatic Index ◽  
In The Wild ◽  
Muscle Water

The aim of this study was to examine how the biochemical composition of tissues varied with growth rate and condition in juvenile Atlantic cod (Gadus morhua) caught in the wild and kept in captivity. The hepatosomatic index, brain water content, and muscle sarcoplasmic protein content as well as the activities of phosphofructokinase, lactate dehydrogenase, nucleoside diphosphate kinase, and citrate synthase in the muscle, nucleoside diphosphate kinase and citrate synthase in the intestine, and cytochrome c oxidase and citrate synthase in the brain increased with growth rate or condition factor. Conversely, liver and muscle water contents were lower in fish with a higher growth rate. A multiple regression model that included the hepatosomatic index, water content of muscle and brain, and citrate synthase activity in the intestine explained 79.7% of the variability of growth in mass under our conditions. A similar model, using liver water content instead of muscle water content, explained 82.5% of the variability of growth in length. These easy to measure variables may be used in fisheries management to estimate the growth rate of fish in the wild.

Effect of foraging activity on the shoal structure of cod (Gadus morhua)

1995 ◽  
Vol 52 (11) ◽  
pp. 2377-2387 ◽  
Author(s):  
E. M. DeBlois ◽  
G. A. Rose
Keyword(s):  
Gadus Morhua ◽  
Critical Level ◽  
Atlantic Cod ◽  
Horizontal Displacement ◽  
Foraging Activity ◽  
Laboratory Findings ◽  
Acoustic Methods ◽  
Theoretical Predictions ◽  
Shrimp Density ◽  
The Relationship

Acoustic methods used to quantify the shoaling dynamics of Atlantic cod (Gadus morhua) during their shoreward migration across the northeast Newfoundland shelf (spring 1992) showed that shoal structure and horizontal displacement were associated with the density distribution of small pelagic scatterers, for example, shrimp (Pandalus borealis). Cod speeds (to 20 km/d) were lower after encounters with shrimp (4–7 km/d). The relationship between several characteristics of the cod shoal (density, vertical spread, height off the bottom) and shrimp density was dome shaped. Internal shoal densities declined and shoal spread and height increased until shrimp densities surpassed a critical level. Above this threshold, these trends were reversed. The vertical spread of the cod shoal matched that of shrimp up to, but not beyond, a shrimp spread of 85 m. At this observed maximum in the expansion of the shoal, fish were eight body lengths apart. At all times during our survey, cod stayed within the warmer waters (> 2 °C) found at depths greater than 250 m. Our results are the first field verification of theoretical predictions and laboratory findings that shoals expand and contract in response to foraging activity and demonstrate the potential importance of cod aggregation dynamics to interpretations of trawl data.

scholarly journals Barents Sea cod (Gadus morhua) diet composition: long-term interannual, seasonal, and ontogenetic patterns

2019 ◽  
Vol 76 (6) ◽  
pp. 1641-1652 ◽  
Author(s):  
Rebecca E Holt ◽  
Bjarte Bogstad ◽  
Joël M Durant ◽  
Andrey V Dolgov ◽  
Geir Ottersen
Keyword(s):  
Gadus Morhua ◽  
Trophic Ecology ◽  
Barents Sea ◽  
Atlantic Cod ◽  
Prey Size ◽  
Ecosystem Dynamics ◽  
Polar Cod ◽  
Important Species ◽  
Predator Prey ◽  
The North

Abstract Atlantic cod (Gadus morhua) is an ecologically and commercially important species in the North-Atlantic region. Cod is a top predator and information on its trophic ecology is integral for understanding predator–prey relationships and food-web dynamics. We present an analysis of the trophic patterns of Barents Sea (BS) cod using a unique 33-year time-series of stomach-content data from 1984 to 2016. We assessed patterns in diet (prey) composition across years, between seasons, as well as ontogenetic trends in diet, including predator–prey size relationships. Ontogenetic shifts in diet were observed, with fish becoming more important prey with increasing cod size. A very early onset of piscivory was found in &lt;20 cm cod. Cannibalism was found in cod &gt; 20 cm and increased with size. Juvenile cod exhibit a tendency towards consuming prey up to 33% of their body length, whereas larger cod feed on all prey sizes, resulting in asymmetric predator–prey size distributions. Diet varied significantly during 1984–2016, consistent with changes in both prey, cod abundance, and distribution. Seasonal differences were observed; capelin dominated the winter diet, whereas cod, polar cod, and other fish species were prevalent in summer/autumn months. This work represents an important step towards understanding trophic linkages that determine BS ecosystem dynamics.

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