scholarly journals Density-dependent distribution of Atlantic cod (Gadus morhua) into deep waters on the Faroe Plateau

2009 ◽  
Vol 67 (1) ◽  
pp. 102-110 ◽  
Author(s):  
Petur Steingrund ◽  
Lise H. Ofstad
Keyword(s):  
Deep Water ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
Food Utilization ◽  
Total Biomass ◽  
Strongly Correlated ◽  
Catch Per Unit Effort ◽  
Density Dependent ◽  
Natural Production ◽  
Deep Waters

Abstract Steingrund, P., and Ofstad, L. H. 2010. Density-dependent distribution of Atlantic cod (Gadus morhua) into deep waters on the Faroe Plateau. – ICES Journal of Marine Science, 67: 102–110. The natural production of cod on the Faroe Plateau depends on the spatial overlap between cod and their prey. However, cod tend to be distributed shallower than the bulk of their prey fish, such as Norway pout and blue whiting. We used commercial and survey catch per unit effort (cpue) data to investigate the distribution of cod in the deep water (150–400 m) on the Faroe Plateau. Cod often move to deep water when they are 4 or 5 years old. The extent of this habitat shift was positively correlated with the total biomass of 3- or 4-year-old cod on the Faroe Plateau, whereas prey densities in the shallow and deep areas, respectively, seemed to have much less influence. Hence, year classes that were a year older than strong year classes were distributed deeper than normal, and vice versa. The cpue in deep water for all ages pooled was strongly correlated with the age 3–6 biomass of cod on the entire Faroe Plateau. These findings are discussed in relation to food utilization and management.

Depth-dependent variation in condition and length-at-age of Atlantic cod (Gadus morhua) in the southern Gulf of St. Lawrence

2002 ◽  
Vol 59 (9) ◽  
pp. 1451-1459 ◽  
Author(s):  
G A Chouinard ◽  
D P Swain
Keyword(s):  
Deep Water ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
High Abundance ◽  
Shallow Waters ◽  
Depth Range ◽  
Deep Waters ◽  
Feeding Grounds

We describe depth-dependent variation in the condition and length-at-age of southern Gulf of St. Lawrence cod (Gadus morhua) on their feeding grounds in September 1971–2000. Bathymetric variation in condition appears to be linked to abundance. In periods of low abundance, condition was relatively uniform over shallow and intermediate depths (<100–125 m). During periods of high abundance, condition was highest in the shallowest waters and declined steadily as depth increased to 100 m. In all periods, condition was low in deep water. Bathymetric trends in length-at-age contrasted with those in condition. Length-at-age was high in the deep waters where condition was low. Length-at-age also tended to increase from minimum values at intermediate depths to high values in shallow waters. This tendency was most striking in the 1990s, a period when condition was uniform over this depth range. We discuss the ecological, bioenergetic, and sampling implications of these patterns.

scholarly journals Environmental DNA concentrations are correlated with regional biomass of Atlantic cod in oceanic waters

2019 ◽  
Vol 2 (1) ◽  
Author(s):  
Ian Salter ◽  
Mourits Joensen ◽  
Regin Kristiansen ◽  
Petur Steingrund ◽  
Poul Vestergaard
Keyword(s):  
Gadus Morhua ◽  
Atlantic Cod ◽  
Environmental Dna ◽  
Sampling Effort ◽  
Trawl Survey ◽  
Catch Per Unit Effort ◽  
Fish Stocks ◽  
Powerful Approach ◽  
Commercially Important ◽  
Positive Correlations

AbstractEnvironmental DNA (eDNA) has emerged as a powerful approach for studying marine fisheries and has the potential to negate some of the drawbacks of trawl surveys. However, successful applications in oceanic waters have to date been largely focused on qualitative descriptions of species inventories. Here we conducted a quantitative eDNA survey of Atlantic cod (Gadus morhua) in oceanic waters and compared it with results obtained from a standardized demersal trawl survey. Detection of eDNA originating from Atlantic cod was highly concordant (80%) with trawl catches. We observed significantly positive correlations between the regional integrals of Atlantic cod biomass (kg) and eDNA quantities (copies) (R2 = 0.79, P = 0.003) and between sampling effort-normalised Catch Per Unit Effort (kg hr−1) and eDNA concentrations (copies L−1) (R2 = 0.71, P = 0.008). These findings extend the potential application of environmental DNA to regional biomass assessments of commercially important fish stocks in the ocean.

The influence of forage fish abundance on the aggregation of Gulf of Maine Atlantic cod (Gadus morhua) and their catchability in the fishery

2014 ◽  
Vol 71 (9) ◽  
pp. 1349-1362 ◽  
Author(s):  
David E. Richardson ◽  
Michael C. Palmer ◽  
Brian E. Smith
Keyword(s):  
Gadus Morhua ◽  
Gulf Of Maine ◽  
Atlantic Cod ◽  
Distribution Patterns ◽  
Fish Populations ◽  
Dependent Data ◽  
Forage Fish ◽  
Catch Per Unit Effort ◽  
Sand Lance ◽  
Unit Effort

Shifts in the distribution and aggregation patterns of exploited fish populations can affect the behavior and success of fishermen and can complicate the interpretation of fisheries-dependent data. Starting in 2006, coinciding with an increase in sand lance (Ammodytes spp.) abundance, Gulf of Maine Atlantic cod (Gadus morhua) concentrated on Stellwagen Bank, a small (405 km2) underwater plateau located in the southwestern portion of the larger (52 461 km2) stock area. The cod fishery in turn concentrated on Stellwagen Bank. Specifically, the proportion of Gulf of Maine cod landings caught in a single 10-minute square area (260 km2) encompassing the tip of Stellwagen Bank increased from 12% in 2005 to 45% in 2010. An increase in landings per unit effort in the fishery coincided with the concentration of the fleet on Stellwagen Bank. Overall, both fisheries-independent and fisheries-dependent data indicate that an increase in sand lance abundance resulted in cod aggregating in a small and predictable area where they were easily caught by the fishery. More broadly, this work illustrates how changes in the distribution patterns of fish and fisherman can decouple trends in abundance and fisheries catch per unit effort.

scholarly journals Increased natural mortality at low abundance can generate an Allee effect in a marine fish

2014 ◽  
Vol 1 (2) ◽  
pp. 140075 ◽  
Author(s):  
Anna Kuparinen ◽  
Jeffrey A. Hutchings
Keyword(s):  
Population Dynamics ◽  
Population Growth ◽  
Density Dependence ◽  
Gadus Morhua ◽  
Allee Effect ◽  
Population Regulation ◽  
Atlantic Cod ◽  
Adult Mortality ◽  
Natural Mortality ◽  
Density Dependent

Negative density-dependent regulation of population dynamics promotes population growth at low abundance and is therefore vital for recovery following depletion. Inversely, any process that reduces the compensatory density-dependence of population growth can negatively affect recovery. Here, we show that increased adult mortality at low abundance can reverse compensatory population dynamics into its opposite—a demographic Allee effect. Northwest Atlantic cod ( Gadus morhua ) stocks collapsed dramatically in the early 1990s and have since shown little sign of recovery. Many experienced dramatic increases in natural mortality, ostensibly attributable in some populations to increased predation by seals. Our findings show that increased natural mortality of a magnitude observed for overfished cod stocks has been more than sufficient to fundamentally alter the dynamics of density-dependent population regulation. The demographic Allee effect generated by these changes can slow down or even impede the recovery of depleted populations even in the absence of fishing.

Structure and functioning of the eastern Scotian Shelf ecosystem before and after the collapse of groundfish stocks in the early 1990s

2005 ◽  
Vol 62 (7) ◽  
pp. 1453-1473 ◽  
Author(s):  
Alida Bundy
Keyword(s):  
Gadus Morhua ◽  
Atlantic Cod ◽  
Trophic Levels ◽  
Total Biomass ◽  
Scotian Shelf ◽  
Mass Balance Models ◽  
Key Species ◽  
Before And After ◽  
Species Groups ◽  
System Properties

The fishery-induced collapse of the Atlantic cod (Gadus morhua) stock on the eastern Scotian Shelf has altered the species composition of this ecosystem. Ecopath mass-balance models of the ecosystem before and after the collapse were developed to explore how the structure, function, and key species of the ecosystem had changed. For the first time, an analysis of uncertainty was conducted to examine the effects of the uncertainty on model estimates. A comparison of the two Ecopath models indicated that although total productivity and total biomass of the ecosystem remained similar, there were changes in predator structure, trophic structure, and energy flow, many of which were robust to uncertainty. Biomass has significantly increased at trophic levels 3 and 4, and the composition of these trophic levels has changed as a result of the mean increase in trophic level of many species-groups. Piscivory has increased, presumably because of the high abundance of small pelagic fish, and the ratio of pelagic feeders to demersal feeders has increased from 0.3 to 3.0. Thus, the ecosystem has changed from a demersal-feeder-dominated system to a pelagic-feeder-dominated system. Although uncertainty remains concerning some model estimates, the ecosystem has been profoundly altered and exhibits classic symptoms of "fishing down the food web". However, overall system properties were generally conserved.

scholarly journals Reproductive investment in Atlantic cod populations off Newfoundland: Contrasting trends between males and females

FACETS ◽  
2017 ◽  
Vol 2 (2) ◽  
pp. 660-681 ◽  
Author(s):  
Loïc Baulier ◽  
M. Joanne Morgan ◽  
George R. Lilly ◽  
Ulf Dieckmann ◽  
Mikko Heino
Keyword(s):  
Life History Theory ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
Temporal Trends ◽  
Reproductive Investment ◽  
Male Reproductive Success ◽  
Density Dependent ◽  
Theoretical Predictions ◽  
Two Populations

Life history theory predicts selection for higher reproductive investment in response to increased mortality among mature individuals. We tested this prediction over the period from 1978 to 2013 for three populations of Atlantic cod ( Gadus morhua) off Newfoundland. These populations were heavily fished for a long period. We considered changes in standardized gonad weight as a proxy for changes in gonadal investment. We accounted for the allometry between gonad and body weight, individual body condition, water temperature, and potential spatial and density-dependent effects. Males display significant temporal trends in gonadal investment in all populations; in agreement with theoretical predictions, these trends show increased gonadal investments during the earlier part of the time series when mortality was high, with the trends leveling off or reversing after the later imposition of fishing moratoria. In contrast, females display patterns that are less consistent and expected; significant trends are detected only when accounting for density-dependent effects, with females in two populations unexpectedly showing a long-term decline in gonadal investment. Our results support the hypothesis that fisheries-induced evolution has occurred in gonadal investment in males, but not in females, and suggest that gonadal investment is more important for male reproductive success than expected in this lekking species.

Estimating and testing non-additivity in fishing mortality: implications for detecting a fisheries collapse

2002 ◽  
Vol 59 (4) ◽  
pp. 597-601 ◽  
Author(s):  
Ransom A Myers ◽  
Terrance J Quinn II
Keyword(s):  
Population Model ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
Fishing Mortality ◽  
Catch Per Unit Effort ◽  
Structured Population Model ◽  
Structured Population ◽  
Powerful Approach ◽  
Age Structured ◽  
Age Structured Model

Common in many fisheries collapses is a disproportionate increase in fishing mortality at younger ages. One mechanism by which this increase could occur is sufficient depletion of the population at older ages due to strong overfishing, which leads to targeting of younger fish. Thus, it is essential for assessments to estimate and test for a change in selectivity in the fishery. We introduce a simple and powerful approach based upon Tukey's one degree of freedom test for non-additivity. This approach can be applied within any statistical age-structured population model that estimates selectivity. We illustrate the approach with data from Atlantic cod (Gadus morhua) from St. Pierre Bank, Canada. The results show significant non-additivity in fishing mortality that translates into an increase in selectivity on younger ages when fishing mortality is high. This approach also can be applied to the output of an age-structured model that assumes catch-at-age is known without error or to any survey or catch-per-unit-effort data for which estimates of abundance are made by year and age. We believe that this approach should be routinely applied in assessments, particularly when overfishing has led to depletion of the overall population or to truncation of the age structure.

Distribution–abundance relationships for North Sea Atlantic cod (Gadus morhua): observation versus theory

2005 ◽  
Vol 62 (9) ◽  
pp. 2001-2009 ◽  
Author(s):  
Julia L Blanchard ◽  
Craig Mills ◽  
Simon Jennings ◽  
Clive J Fox ◽  
Brian D Rackham ◽  
...  
Keyword(s):  
Habitat Selection ◽  
North Sea ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
Ideal Free Distribution ◽  
Density Dependent ◽  
The North ◽  
The North Sea ◽  
Density Dependent Habitat Selection ◽  
Ideal Free

Density-dependent habitat selection has implications for fisheries management and for the recovery of depleted fish populations. According to ideal free distribution theory, populations contract into areas of highest habitat suitability as their abundance decreases. This can increase their vulnerability to fishing and predation. We detected density-dependent habitat selection by juvenile Atlantic cod (Gadus morhua) (ages 1 and 2) in the North Sea and compared the observed distribution–abundance relationships with those predicted from a model based on ideal free distribution theory and knowledge of optimal temperatures for growth, where temperature was used as a measure of suitability. As predicted by the model, in years when stock size was low, the catches were largely confined to regions with near-optimal bottom temperatures. Conversely, when population size was high, catches were spread across a larger area including regions with suboptimal temperatures. The spatial extent of optimal habitat appears to have decreased from 1977 to 2002, reflecting a gradual warming of the North Sea. The combined negative effects of increased temperature on recruitment rates and the reduced availability of optimal habitat may have increased the vulnerability of the cod population to fishing mortality.

Regulation of infrapopulations of Cryptocotyle lingua on cod

Parasitology ◽  
1997 ◽  
Vol 114 (2) ◽  
pp. 145-150 ◽  
Author(s):  
D. A. LYSNE ◽  
W. HEMMINGSEN ◽  
A. SKORPING
Keyword(s):  
Gadus Morhua ◽  
Atlantic Cod ◽  
Host Responses ◽  
Density Dependent ◽  
Naturally Occurring ◽  
Infection Dynamics ◽  
Host Mortality ◽  
The Relationship

To study the infection dynamics of metacercariae of the digenean Cryptocotyle lingua, wild living Atlantic cod, Gadus morhua, were caged for 18 months close to the shore. Here they were exposed to naturally occurring transmission stages of the parasite. First, both the abundance and the variance to mean ratio of metacercariae increased, but during the second half of the study the abundance levelled out, and the variance to mean ratio showed a significant decrease. Host mortality was negligible throughout the study. Based on the relationship between pigment spots and metacercariae observed by skin digestion, there was no indication of density-dependent parasite mortality. We conclude that the infrapopulations of metacercariae on the caged cod probably were regulated by density-dependent host responses acting against the cercariae.

scholarly journals Atlantic cod (Gadus morhua) feeding over deep water in the high Arctic

Polar Biology ◽  
2017 ◽  
Vol 40 (10) ◽  
pp. 2105-2111 ◽  
Author(s):  
Randi B. Ingvaldsen ◽  
Harald Gjøsæter ◽  
Egil Ona ◽  
Kathrine Michalsen
Keyword(s):  
Deep Water ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
High Arctic
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