Effect of Changes in Recruitment Levels on Multispecies Long-term Predictions

1993 ◽  
Vol 50 (11) ◽  
pp. 2315-2322 ◽  
Author(s):  
Henrik Gislason
Keyword(s):  
Gadus Morhua ◽  
Atlantic Cod ◽  
Relative Increase ◽  
Clupea Harengus ◽  
Melanogrammus Aeglefinus ◽  
Fish Stocks ◽  
The North ◽  
Predation Mortality ◽  
Spawning Stock ◽  
Relative Change

A multispecies model (MSFOR) is used to predict the relative change in equilibrium yield and spawning stock biomass (SSB) of commercially important fish stocks in the North Sea resulting from a reduction in the fishing mortality generated by the roundfish fishery. Because predation mortality is a function of the abundance of prey and predators the results will depend on recruitment. Assuming recruitment to be independent of stock sizes the effect of changes in recruitment is studied by repeating the predictions at all possible combinations of ±50% changes in predator and prey recruitment levels. All of the predictions result in a relative increase in the SSB of Atlantic cod (Gadus morhua) and saithe (Pollachius virens) and in a relative decrease in the SSB of Atlantic herring (Clupea harengus) and Norway pout (Trisopterus esmarkii). In these cases the sign of the relative change is robust to recruitment changes. However, for haddock (Melanogrammus aeglefinus), sprat (Sprattus sprattus), and sandeel (Ammodytes marinus) the relative change in SSB is found to be either positive or negative depending on the level of recruitment. The predictions for haddock are highly sensitive to changes in the level of saithe recruitment.

Parasites as biological tags in marine fisheries research: European Atlantic waters

Parasitology ◽  
2014 ◽  
Vol 142 (1) ◽  
pp. 54-67 ◽  
Author(s):  
K. MACKENZIE ◽  
W. HEMMINGSEN
Keyword(s):  
Marine Mammals ◽  
Gadus Morhua ◽  
Clupea Harengus ◽  
Melanogrammus Aeglefinus ◽  
Ecological Group ◽  
The North ◽  
Recent Developments ◽  
Host Parasite ◽  
Mediterranean And Black Seas ◽  
Biological Tags

SUMMARYStudies of the use of parasites as biological tags for stock identification and to follow migrations of marine fish, mammals and invertebrates in European Atlantic waters are critically reviewed and evaluated. The region covered includes the North, Baltic, Barents and White Seas plus Icelandic waters, but excludes the Mediterranean and Black Seas. Each fish species or ecological group of species is treated separately. More parasite tag studies have been carried out on Atlantic herring Clupea harengus than on any other species, while cod Gadus morhua have also been the subject of many studies. Other species that have been the subjects of more than one study are: blue whiting Micromesistius poutassou, whiting Merlangius merlangus, haddock Melanogrammus aeglefinus, Norway pout Trisopterus esmarkii, horse mackerel Trachurus trachurus and mackerel Scomber scombrus. Other species are dealt with under the general headings redfishes, flatfish, tunas, anadromous fish, elasmobranchs, marine mammals and invertebrates. A final section highlights how parasites can be, and have been, misused as biological tags, and how this can be avoided. It also reviews recent developments in methodology and parasite genetics, considers the potential effects of climate change on the distributions of both hosts and parasites, and suggests host-parasite systems that should reward further research.

Fish Catches and Long-Term Tidal Cycles in Northwest Atlantic Fisheries: A Nonlinear Regression Approach

1987 ◽  
Vol 44 (11) ◽  
pp. 1890-1897 ◽  
Author(s):  
Paul Cabilio ◽  
David L. DeWolfe ◽  
Graham R. Daborn
Keyword(s):  
New England ◽  
Nonlinear Regression ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
Significant Negative Correlation ◽  
Clupea Harengus ◽  
Atlantic Menhaden ◽  
Melanogrammus Aeglefinus ◽  
Grand Banks

Selected long-term fisheries catch data from the New England – Fundy area and the Grand Banks were examined for concordance between changes in fish catches and the 18.6-yr nodal cycle of the tides using a nonlinear regression model. Significant positive correlations were found for Atlantic cod (Gadus morhua), haddock (Melanogrammus aeglefinus), alewife (Alosa pseudoharengus), Atlantic herring (Clupea harengus harengus), and scallop (Placopecten magellanicus), with lag times that are biologically appropriate for the time from hatching to recruitment into the fishery. A significant negative correlation with the nodal cycle was evident for Atlantic menhaden (Brevoortia tyrannus), for which this area constitutes the most northerly part of its range. Cod catches on the Grand Banks showed no correlation with the nodal cycle. It is suggested that the correlations between the nodal cycle and the changes in fish catches are caused by correlated changes either in sea surface temperature or in productivity resulting from changes in the degree of vertical mixing.

scholarly journals A sea change: Johan Hjort and the natural fluctuations in the fish stocks

2014 ◽  
Vol 71 (8) ◽  
pp. 1993-1999 ◽  
Author(s):  
Vera Schwach
Keyword(s):  
Gadus Morhua ◽  
Clupea Harengus ◽  
Marine Science ◽  
Population Thinking ◽  
Fish Stocks ◽  
Fish Biology ◽  
The North ◽  
Scientific Results ◽  
Mere Existence ◽  
Scientific Truth

Abstract That recruitment of juveniles to the stocks of fish is subject to natural variations is considered a scientific truth, if not a truism, in marine science. However, in 1914, when the zoologist Johan Hjort (1869–1948) published the notion, it meant a basic change in the understanding of the biology of the sea fish. A century later, his insight is a topic still at the centre of interest in fish biology. Hjort based his concept largely on investigations of herring (Clupea harengus) and cod (Gadus morhua) in the North Atlantic. He was the mastermind, but worked with a small group at the Directorate of Fisheries in Bergen, Norway, and in cooperation with the International Council for the Exploration of the Sea (ICES). The theory of natural fluctuations prompted an important step from migration thinking to population thinking, and gave the emerging fish biology and multidisciplinary marine science a theoretical basis. The article aims to explore the set of important facts and reasoned ideas intended to explain the causes for variations in year classes, and in this the fluctuations in the recruitment to the stocks. It argues that in addition to scientific factors, economic and political circumstances had an important say in the shaping of the understanding of stock fluctuations. The mere existence of a theory does not alone account for a breakthrough, and the article draws attention to the acceptance of scientific results.

scholarly journals Worldwide status and perspective on gadoid culture

2006 ◽  
Vol 63 (2) ◽  
pp. 194-197 ◽  
Author(s):  
Grethe Rosenlund ◽  
Magnus Skretting
Keyword(s):  
Gadus Morhua ◽  
Atlantic Cod ◽  
Health Management ◽  
Raw Materials ◽  
Life Cycles ◽  
Melanogrammus Aeglefinus ◽  
Farmed Salmon ◽  
The North ◽  
Cost Efficient ◽  
Market Needs

Abstract Currently, Atlantic cod (Gadus morhua) is the primary species being developed for commercial culture, with activities concentrated around the North Atlantic. In addition, closed life cycles have been established for haddock (Melanogrammus aeglefinus), pollock (Pollachius pollachius), and hake (Merluccius australis), but production of these species (in Canada, Spain, and Chile) is rather modest. In the short- to medium-term, Atlantic cod will be the dominant gadoid species in culture, and it is believed that production can reach levels similar to those of farmed salmon within the next 15–20 years. This development is possible because methods for year-round production of juveniles and significant hatchery capacity have been established. Also, there is a demand for farmed cod to fill the gap between increasing market needs and diminishing supply from fisheries. However, challenges must be met if cod farming is to reach its anticipated potential. Juvenile production must become more reliable in terms of survival and quality. For the on-growing phase, the supply of cost-efficient feeds produced from sustainable raw materials is of utmost importance. Consumer markets need to be developed with an emphasis on quality and food safety. Relatively little is known about health management for gadoid species.

scholarly journals Linking spawning ground extent to environmental factors — patterns and dispersal during the egg phase of four North Sea fishes

2018 ◽  
Vol 75 (3) ◽  
pp. 357-374 ◽  
Author(s):  
Hannes Höffle ◽  
Cindy J.G. Van Damme ◽  
Clive Fox ◽  
Stéphanie Lelièvre ◽  
Christophe Loots ◽  
...  
Keyword(s):  
North Sea ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
Early Stage ◽  
Distribution Patterns ◽  
Melanogrammus Aeglefinus ◽  
Spawning Grounds ◽  
The North ◽  
Generalized Additive Mixed Models ◽  
Additive Mixed Models

Previous studies have shown that four commercially important demersal species, namely Atlantic cod (Gadus morhua), haddock (Melanogrammus aeglefinus), whiting (Merlangius merlangus), and European plaice (Pleuronectes platessa), spawn in distinct areas across the North Sea. Based on two comprehensive ichthyoplankton surveys in 2004 and 2009, the present study uses generalized additive mixed models to delimit these spawning grounds using the distribution of recently spawned eggs, investigates their relationship to specific environmental conditions, and examines egg dispersal during their development. Results indicate that presence–absence of early stage eggs is more related to temporal and topographic variables, while egg densities are closely linked with hydrography. Egg distribution patterns were relatively consistent during development and only changed near hatching. Compared with historic observations, the location of the spawning grounds appeared stable on the broad scale but centres of egg abundance varied between the surveyed years. Potential effects of long-term climate change and anthropogenic short-term disturbances, such as seismic surveys, on fish reproduction are discussed, pointing out the demand for multispecies studies on these issues.

Discarding practices for commercial gadoids in the North Sea

1998 ◽  
Vol 55 (7) ◽  
pp. 1632-1644 ◽  
Author(s):  
Yorgos Stratoudakis ◽  
Robert J Fryer ◽  
Robin M Cook
Keyword(s):  
North Sea ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
Melanogrammus Aeglefinus ◽  
The North ◽  
The North Sea ◽  
Merlangius Merlangus ◽  
Using Data ◽  
Species Specific ◽  
Catch Composition

Understanding fishers' discarding behaviour, and anticipating their reactions to changes in the biological or regulatory characteristics of a fishery, are important for dealing with the problem of discarding. In this paper, we investigate the discarding of haddock (Melanogrammus aeglefinus), whiting (Merlangius merlangus), and Atlantic cod (Gadus morhua) in the North Sea, using data collected by scientific observers onboard Scottish demersal vessels. We describe discarding on each trip by species-specific discard curves and explore how these curves depend on biological and regulatory variables. There are large differences in the size of discarded fish between inshore and offshore areas, with offshore-operating vessels discarding larger fish (high-grading). Increases in legal landing size correspond to immediate increases in the size of discarded fish, particularly for haddock and cod in inshore areas. In general, discarding practices for haddock and cod are similar over time and consistent across gears, whereas decisions for the lesser valued whiting are more variable and can be affected by the catch composition.

Estimating the biomass of a mixed species complex using hydroacoustics and catch data from the Bay of Fundy and Scotian Shelf summer ecosystem survey

2020 ◽  
Vol 77 (7) ◽  
pp. 1101-1116
Author(s):  
Allan J. Debertin
Keyword(s):  
Species Composition ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
Clupea Harengus ◽  
Bottom Trawl ◽  
Melanogrammus Aeglefinus ◽  
Acoustic Data ◽  
Catch Data ◽  
Scatter Coefficient ◽  
Management Advice

An acoustic-based index of biomass was developed due to concerns that the existing bottom-trawl index for western component pollock (Pollachius virens) was inaccurate and imprecise. Acoustic data were recorded during annual summer ecosystem surveys. Pollock and other common groundfish could not be readily identified from echo-traces within echograms. Survey catch data were analyzed concurrently with acoustic data to estimate biomass from echo-integrals contributed by the six most commonly caught fish species: pollock, Atlantic cod (Gadus morhua), haddock (Melanogrammus aeglefinus), redfish (Sebastes fasciatus), Atlantic herring (Clupea harengus), and spiny dogfish (Squalus acanthias). A cluster analyses that used a Bayesian conditional probability classified homogeneous regions based on species composition. Species composition, nautical area scatter coefficient, and backscattering cross-section of fishes for regions were used to calculate the biomass of fishes. Acoustic indices were considered as appropriate as bottom-trawl indices for fisheries management advice because the bias and variance were similar between the indices when analyzed using repeated K-fold cross-validation.

Production Responses for Multi-species Fisheries

1981 ◽  
Vol 38 (11) ◽  
pp. 1393-1404 ◽  
Author(s):  
R. J. Agnello ◽  
L. G. Anderson
Keyword(s):  
New England ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
Clupea Harengus ◽  
Categorical Variables ◽  
Melanogrammus Aeglefinus ◽  
Target Species ◽  
Northwest Atlantic ◽  
Fisheries Economics ◽  
Log Linear

Production equations are estimated for five major species of fish harvested in the Northwest Atlantic including Atlantic cod (Gadus morhua), haddock (Melanogrammus aeglefinus), flounder (Pleuronectiformes), redfish (Sebastes marinus), and herring (Clupea harengus) using data collected by the International Commission for the Northeast Atlantic Fisheries from 1960 to 1974. A log-linear regression specification is used in which the relationship between catch of a vessel and several factors including days fished and vessel characteristics is estimated simultaneously. Vessel characteristics are represented as (0, 1) categorical variables, and include a variable indicating the target species designated by the caption. Various settings for the target species variables allow the estimated equation to represent either a by-catch or target catch equation. The production parameters estimated by the regressions are used to analyze the effects of current quotas set by the New England Fisheries Management Council. For some fleets we find a likelihood of idle capacity given the current quotas.Key words: fisheries economics, multi-species harvesting, Northwest Atlantic fisheries

Species-specific residence times in the aft part of a pelagic survey trawl: implications for inference of pre-capture spatial distribution using the Deep Vision system

2018 ◽  
Vol 75 (4) ◽  
pp. 1393-1404 ◽  
Author(s):  
Melanie J Underwood ◽  
Shale Rosen ◽  
Arill Engås ◽  
Terje Jørgensen ◽  
Anders Fernö
Keyword(s):  
Spatial Distribution ◽  
Residence Time ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
Vision System ◽  
Ground Truth ◽  
Clupea Harengus ◽  
Melanogrammus Aeglefinus ◽  
Camera System ◽  
Species Specific

Abstract In-trawl camera systems promise to improve the resolution of trawl sampling used to ground-truth the interpretation of acoustic survey data. In this study, the residence time of fish in front of the Deep Vision camera system, used to identify, measure and count fish inside the trawl, was analysed to determine the reliability of spatial distribution recorded by the system. Although Atlantic herring (Clupea harengus), haddock (Melanogrammus aeglefinus), and most Atlantic cod (Gadus morhua) moved quickly back through the aft part of the pelagic trawl, saithe (Pollachius virens) spent up to 4 min in front of the system. The residence time increased for saithe and cod when other individuals were present, and cod swimming in the low water flow close to the trawl netting spent longer there than cod at the centre of the trawl. Surprisingly, residence time was not related to the size of the fish, which may be explained by the collective behaviour of shoaling fish. Our findings suggest that while in-trawl images can be used to identify, measure and count most species, when sampling fast-swimming species such as saithe the position inferred from when they were imaged may not reflect the actual spatial distribution prior to capture.

An Analysis of Errors in Catch Projections for Canadian Atlantic Fish Stocks

1987 ◽  
Vol 44 (5) ◽  
pp. 967-981 ◽  
Author(s):  
Denis Rivard ◽  
Malcolm G. Foy
Keyword(s):  
Retrospective Analysis ◽  
Atlantic Cod ◽  
Age Groups ◽  
Clupea Harengus ◽  
Melanogrammus Aeglefinus ◽  
Fish Stocks ◽  
Stock Size ◽  
Input Variables ◽  
The Impact ◽  
Made In

Two techniques were used to identify and evaluate the components of error inherent in the catch projection method used in the assessment of Canadian Atlantic fish stocks. Firstly, a retrospective analysis was used to evaluate, for the projections made in 1979 and 1981, the impact of the actual error made in input variables such as catch-at-age, mean weight-at-age, recruitment, and stock size. Secondly, the variance of projections was estimated from the variance of input variables. From the retrospective analysis, the principal causes of error in catch projections were identified as the estimation of stock size, as well as the estimation and forecast of fishing mortalities for the projection years. The difference between actual catch and assumed catch for the first year of a 2-yr projection did not appear to be a major source of bias for catch projections. The coefficients of variation of the catch projected at F0.1 were estimated as follows: 15–20% for the projections of Atlantic cod (Gadus morhua) catches; 25–50% for those of haddock (Melanogrammus aeglefinus); 28% for those of pollock (Pollachius virens); 16% for those of redfish (Sebastes sp.); and 35–42% for those of herring (Clupea harengus). The uncertainties associated with abundance estimates for prerecruited age-groups and estimates of stock size emerged as key factors in the projections. Also important was the effect of uncertainties associated with the forecast of reference fishing mortalities (partial recruitment coefficients × F0.1) for the projection period, e.g. uncertainties resulting from changes in fish catchability, in fleet behavior, and in fishing patterns.

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