Diet overlap and prey selection through metamorphosis in Irish Sea cod (Gadus morhua), haddock (Melanogrammus aeglefinus), and whiting (Merlangius merlangus)

2008 ◽  
Vol 65 (7) ◽  
pp. 1297-1306 ◽  
Author(s):  
William Ll. Rowlands ◽  
Mark Dickey-Collas ◽  
Audrey J. Geffen ◽  
Richard D.M. Nash
Keyword(s):  
Gadus Morhua ◽  
Prey Selection ◽  
Stomach Contents ◽  
Irish Sea ◽  
Melanogrammus Aeglefinus ◽  
Prey Preferences ◽  
Merlangius Merlangus ◽  
The Irish Sea ◽  
Haddock Melanogrammus Aeglefinus ◽  
Calanus Species

Copepods in the genus Calanus are usually considered to be the preferred prey of gadoid larvae in many areas; however, in the Irish Sea, the abundances of these Calanus species are low and highly variable. We use this situation to test whether Calanus species are still actively selected by gadoid larvae in Calanus -poor environments. Diets of Irish Sea cod ( Gadus morhua ), haddock ( Melanogrammus aeglefinus ), and whiting ( Merlangius merlangus ) were studied from the yolk-sac stage to the juvenile stage. Prey from stomach contents were compared with in situ abundance via an index of prey preference. As expected, all larvae selected copepod nauplii at the onset of feeding. As the larvae developed, their prey preferences changed and varied with species. Cod and whiting showed a similar transition of prey species preference, with a clear preference for Calanus species after metamorphosis, even in this area of low abundance of these Calanus species. The diet composition of haddock differed from that of cod and whiting, as nauplii remained in their diet later into development and there was little preference for individual copepod species detected. The differences in prey selectivity suggested between these gadoids may be attributed to their population variability through the known variability of their preferred prey items.

scholarly journals The vertical separation of fish in the aft end of a demersal trawl

2009 ◽  
Vol 66 (4) ◽  
pp. 772-777 ◽  
Author(s):  
Ludvig Ahm Krag ◽  
René Holst ◽  
Niels Madsen
Keyword(s):  
Vertical Distribution ◽  
Gadus Morhua ◽  
Melanogrammus Aeglefinus ◽  
Multinomial Model ◽  
Vertical Separation ◽  
Commercially Important ◽  
Merlangius Merlangus ◽  
The Vertical Distribution ◽  
Haddock Melanogrammus Aeglefinus ◽  
Important Fish

Abstract Krag, L. A., Holst, R., and Madsen, N. 2009. The vertical separation of fish in the aft end of a demersal trawl. – ICES Journal of Marine Science, 66: 772–777. Two multi-compartment separator frames were used to study the vertical separation of some commercially important fish species in the aft end of a trawl, with the aim of separating cod (Gadus morhua) from other species. A non-linear multinomial model with random effects was used to analyse the data and to compare the performance of the two frames. The vertical distribution of cod in the aft end of the trawl was close to uniform, whereas haddock (Melanogrammus aeglefinus), whiting (Merlangius merlangus), plaice (Pleuronectes platessa), and lemon sole (Microstomus kitt) showed more uneven distributions. The use of guiding bars in the separator frame significantly (p < 0.05) increased the catch of cod, plaice, and lemon sole in the upper compartment. The vertical separation of cod was density-dependent; high densities of fish resulted in a more uniform distribution of cod. The species separations found differ from those reported from the studies of species separation in the region of the trawl mouth.

Is Juvenile Natural Mortality in Marine Demersal Fish Variable?

1993 ◽  
Vol 50 (8) ◽  
pp. 1591-1598 ◽  
Author(s):  
Ransom A. Myers ◽  
Noel G. Cadigan
Keyword(s):  
Interannual Variability ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
Demersal Fish ◽  
Independent Component ◽  
Melanogrammus Aeglefinus ◽  
Natural Mortality ◽  
Juvenile Mortality ◽  
Merlangius Merlangus ◽  
Haddock Melanogrammus Aeglefinus

We test the hypothesis that the interannual variability of the density-independent component of juvenile natural mortality is a major source of variability in abundance of marine demersal fish. Our tests use data on populations for which there are research surveys consisting of two simultaneous estimates of abundance of young juveniles soon after settlement and two more simultaneous estimates of the same cohort a year later. We applied our test to 14 populations of Atlantic cod (Gadus morhua), haddock (Melanogrammus aeglefinus), whiting (Merlangius merlangus), plaice (Pleuronectes platessa), and sole (Solea vulgaris). We conclude that, in all populations examined except North Sea sole, there was very little or no interannual variability in the density-independent component of juvenile mortality.

scholarly journals Selectivity and escapement behaviour of five commercial fishery species in standard square- and diamond-mesh codends

2010 ◽  
Vol 67 (8) ◽  
pp. 1721-1731 ◽  
Author(s):  
Rikke P. Frandsen ◽  
Niels Madsen ◽  
Ludvig A. Krag
Keyword(s):  
Gadus Morhua ◽  
Mesh Size ◽  
Melanogrammus Aeglefinus ◽  
Commercial Fishery ◽  
Preferred Direction ◽  
Commercial Species ◽  
Merlangius Merlangus ◽  
Cover Design ◽  
Fishery Species ◽  
Haddock Melanogrammus Aeglefinus

Abstract Frandsen, R. P., Madsen, N., and Krag, L. A. 2010. Selectivity and escapement behaviour of five commercial fishery species in standard square- and diamond-mesh codends. – ICES Journal of Marine Science, 67: 1721–1731. The Danish fishery for Nephrops (Nephrops norvegicus) is often conducted in a mixed-species setting, characterized by high rates of discards of several target species, including Nephrops and cod (Gadus morhua). Experiments were conducted to investigate and compare the selective properties of a standard 70 mm square-mesh codend (standard SMC) and a standard 90 mm diamond-mesh codend (standard DMC). Selectivity estimates for five commercial species are provided for both codends. The standard SMC yielded higher estimates of length at 50% retention/mesh size (hereafter SF) for Nephrops and roundfish than did the standard DMC, but no effect of codend type on SF was found for plaice (Pleuronectes platessa). Moreover, a novel codend cover design allowed assessment of the preferred direction of escapement in the codend. Whiting (Merlangius merlangus) and Nephrops showed pronounced, but opposite, vertical preference in the direction of escapement, with whiting escaping upwards and Nephrops downwards. A significant (p < 0.05) difference in the direction of escapement between the two codends was found for haddock (Melanogrammus aeglefinus) and whiting. Owing to the relatively small catches, the outcome is probably most applicable to Nephrops-directed fisheries under similar conditions, and caution should be taken not to extrapolate the results to other fisheries.

scholarly journals FLEXSELECT: counter-herding device to reduce bycatch in crustacean trawl fisheries

2018 ◽  
Vol 75 (6) ◽  
pp. 850-860 ◽  
Author(s):  
Valentina Melli ◽  
Junita D. Karlsen ◽  
Jordan P. Feekings ◽  
Bent Herrmann ◽  
Ludvig A. Krag
Keyword(s):  
Gadus Morhua ◽  
Melanogrammus Aeglefinus ◽  
Target Species ◽  
Merluccius Merluccius ◽  
Flexible Tool ◽  
Flatfish Species ◽  
Trawl Fishery ◽  
Merlangius Merlangus ◽  
Trawl Fisheries ◽  
Haddock Melanogrammus Aeglefinus

FLEXSELECT is a simple counter-herding device that aims at reducing the bycatch of fish by scaring them away from the trawl path without affecting the catches of the target species. FLEXSELECT was tested in the Norway lobster (Nephrops norvegicus) directed trawl fishery, as this includes bycatch of both roundfish and flatfish. Length-based data were collected for Nephrops, four roundfish species (cod (Gadus morhua), haddock (Melanogrammus aeglefinus), whiting (Merlangius merlangus), and hake (Merluccius merluccius)), and two flatfish species (plaice (Pleuronectes platessa) and lemon sole (Microstomus kitt)), and length-based catch comparisons were performed. No significant effect on the target species, Nephrops, was detected, whereas a reduction of 39% (CI: 29%–46%) was obtained for the overall number of fish. Catches of all the six fish species examined were significantly reduced by FLEXSELECT, with the efficiency varying considerably among species and over length classes. No significant diel differences were found for either roundfish or flatfish species. FLEXSELECT prevents bycatch species from interacting with the trawl, thus most likely enhancing their survival and fitness. Moreover, its fast attachment system makes FLEXSELECT a flexible tool, adaptable to different fisheries and catch goals.

scholarly journals Fishery discards in the Irish Sea exhibit temporal oscillations and trends reflecting underlying processes at an annual scale

2010 ◽  
Vol 68 (1) ◽  
pp. 221-227 ◽  
Author(s):  
Mafalda Viana ◽  
Norman Graham ◽  
James G. Wilson ◽  
Andrew L. Jackson
Keyword(s):  
Gadus Morhua ◽  
Temporal Dynamics ◽  
Stock Assessment ◽  
Irish Sea ◽  
Melanogrammus Aeglefinus ◽  
Annual Cycles ◽  
The Irish Sea ◽  
Fishery Discards ◽  
Annual Scale ◽  
Underlying Processes

Abstract Viana, M., Graham, N., Wilson, J. G., and Jackson, A. L. 2011. Fishery discards in the Irish Sea exhibit temporal oscillations and trends reflecting underlying processes at an annual scale. – ICES Journal of Marine Science, 68: 221–227. Non-inclusion of discard data in stock assessment can lead to underestimation of biomass and fishing mortality; this is of particular concern if there have been changes in discard practices over time. Although variability in space and time is a well-documented feature of discards, the temporal dynamics of the practice has received little detailed attention. The aim here is to characterize the temporal patterns of discarding practices in the Irish Sea (ICES Division VIIa) from 1994 to 2008. Trend and seasonality were explored in discards per unit effort (dpue) of haddock (Melanogrammus aeglefinus), whiting (Merlangius merlangus), and cod (Gadus morhua) through Bayesian harmonic regression (HREG) models. The HREG models reveal discarding of all three species in annual cycles, with a peak in the second quarter, perhaps reflecting species biology or fisher behaviour, or both. The dpue of cod cycled around a constant level throughout the observation period, but whiting and haddock dpue increased.

Quantification of species selectivity by using separating devices at different locations in two whitefish demersal trawls

2009 ◽  
Vol 66 (12) ◽  
pp. 2052-2061 ◽  
Author(s):  
René Holst ◽  
Richard S.T. Ferro ◽  
Ludvig Ahm Krag ◽  
Robert J. Kynoch ◽  
Niels Madsen
Keyword(s):  
Gadus Morhua ◽  
Quantitative Approach ◽  
Melanogrammus Aeglefinus ◽  
Fish Behaviour ◽  
Target Species ◽  
Size Selection ◽  
Species Selectivity ◽  
Vertical Distributions ◽  
Merlangius Merlangus ◽  
Haddock Melanogrammus Aeglefinus

This paper presents a quantitative approach to the study of fish behaviour in trawls with the aim of maintaining the catching efficiency of target species and reducing discards of unwanted bycatch. Differences in vertical distributions of species during passage through a trawl are used to sort the catch into separate compartments prior to size selection. It is demonstrated that behavioural differences may be utilized in separating species prior to size selection. Comparisons indicate that these patterns are consistent over replicate trials. Unlike cod (Gadus morhua), haddock (Melanogrammus aeglefinus), saithe (Pollachius virens), and whiting (Merlangius merlangus) do not change their vertical preference longitudinally in the trawl.

Stomach contents of bottlenose dolphins (Tursiops truncatus) in Scottish waters

2001 ◽  
Vol 81 (5) ◽  
pp. 873-878 ◽  
Author(s):  
M.B. Santos ◽  
G.J. Pierce ◽  
R.J. Reid ◽  
I.A.P. Patterson ◽  
H.M. Ross ◽  
...  
Keyword(s):  
Salmo Salar ◽  
Tursiops Truncatus ◽  
Gadus Morhua ◽  
Feeding Habits ◽  
Bottlenose Dolphins ◽  
Stomach Contents ◽  
Melanogrammus Aeglefinus ◽  
North East ◽  
Moray Firth ◽  
Merlangius Merlangus

Data on stomach contents of ten bottlenose dolphins (Tursiops truncatus) stranded and by-caught around Scotland (UK) between 1990 and 1999 are presented. Although the species is resident in the Moray Firth (north-east Scotland), little previous information exists on the feeding habits of the species in Scottish waters. Cod (Gadus morhua), saithe (Pollachius virens) and whiting (Merlangius merlangus) were found to be the main prey eaten although several other fish species were also found, including salmon (Salmo salar) and haddock (Melanogrammus aeglefinus), and also cephalopods.

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