Catchability and the spatial distribution of fishing vessels

2003 ◽  
Vol 60 (3) ◽  
pp. 259-268 ◽  
Author(s):  
Are Salthaug ◽  
Sondre Aanes
Keyword(s):  
Gadus Morhua ◽  
Fish Stock ◽  
Melanogrammus Aeglefinus ◽  
Catch Per Unit Effort ◽  
Spatial Concentration ◽  
Commercial Catch ◽  
Fish Stocks ◽  
Fishing Vessels ◽  
The Relationship ◽  
Stock Abundance

A central problem when using commercial catch per unit effort (CPUE) as an index of fish stock abundance is that fishing vessels search for concentrations of fish. For a given stock abundance, CPUE may become high if the vessels succeed in finding patches of fish and low if the vessels distribute their catching operations more randomly. In this work, the relationship between catchability and two measures of the degree of spatial concentration of a trawl fleet (the fleet's spatial extent and the fleet's degree of spatial patchiness) is investigated for four different fish stocks. The catchability of northeast Arctic cod (Gadus morhua) is strongly related to the fleet's degree of spatial concentration, but the relationship is weaker for northeast Arctic haddock (Melanogrammus aeglefinus), and no relationships appear for two saithe (Pollachius virens) stocks. Our findings suggest that adjusting CPUE with a measure of the fleet's average degree of concentration relates CPUE more strongly with abundance for migratory stocks.

The relationship among catch, fishing effort, and measures of fish stock abundance: implications in the Adriatic Sea

2015 ◽  
Vol 72 (3) ◽  
pp. 410-421
Author(s):  
Luca Mulazzani ◽  
Rosa Manrique ◽  
Giovanna Trevisan ◽  
Corrado Piccinetti ◽  
Giulio Malorgio
Keyword(s):  
Adriatic Sea ◽  
Fishing Effort ◽  
Fish Stock ◽  
Catch Per Unit Effort ◽  
Management Decisions ◽  
Heterogeneous Distribution ◽  
Unit Effort ◽  
Space Data ◽  
The Relationship ◽  
Stock Abundance

Relationships among catch, fishing effort, and measures of fish stock abundance have several implications for fisheries research. In this context, spatial and seasonal aspects are of significant importance for management decisions, especially when effort regulation schemes are used. In this paper, the multispecies trawl fishery in the Northern and Central Adriatic Sea was investigated, taking into account the heterogeneous distribution of fish stocks. Two approaches are presented depending on the availability (or not) of fishery-independent indices of stock abundance. The empirical results indicate that (i) aggregation and targeting behaviours affect catches by modifying the relationship between abundance and catch per unit effort and (ii) these relationships are not homogenous across space. Data from the Adriatic Sea is still insufficient to guarantee reliable estimations. However, these preliminary results call into question management decisions being made on the basis of catch per unit effort. Furthermore, the high heterogeneity between the northern and central areas of the sea basin calls for the adoption of spatially explicit management systems.

Do dietary changes of Australasian gannets (Morus serrator) reflect variability in pelagic fish stocks?

2004 ◽  
Vol 31 (4) ◽  
pp. 383 ◽  
Author(s):  
Ashley Bunce
Keyword(s):  
Fisheries Management ◽  
Prey Species ◽  
Relative Proportion ◽  
Pelagic Fish ◽  
Commercial Catch ◽  
Fish Stocks ◽  
Important Prey ◽  
Morus Serrator ◽  
The Relationship ◽  
Stock Abundance

The relationship between changes in the diet of Australasian gannets (Morus serrator) and commercial fisheries landings was investigated. The contribution of pilchard (Sardinops sagax) to the diet of gannets was significantly related to the commercial catch of that species, suggesting that changes in the relative proportion of pilchard in the diet of gannets may be a useful index of pilchard abundance and availability. Equivalent relationships, however, were not found for other common prey species in the gannet diet. It is considered that the abundance of important prey items in the gannet diet, such as pilchards, and commercial landings are proportional to stock abundance. The implications of this relationship for fisheries management are examined.

Interaction Between Stock Area, Stock Abundance, and Catchability Coefficient

1985 ◽  
Vol 42 (5) ◽  
pp. 989-998 ◽  
Author(s):  
G. H. Winters ◽  
J. P. Wheeler
Keyword(s):  
Stock Assessment ◽  
Population Decline ◽  
Clupea Harengus ◽  
Atlantic Herring ◽  
Population Abundance ◽  
Commercial Catch ◽  
Standard Manner ◽  
Clupea Harengus Harengus ◽  
The Relationship ◽  
Stock Abundance

The relationship between commercial catch-rates and population density upon which many stock assessment models depend assumes that stock area (A) is constant and independent of population abundance. Starting from a theoretical demonstration that the catchability coefficient (q) is inversely proportional to A, we establish the empirical basis of this relationship through comparisons of q and A of various Northwest Atlantic herring (Clupea harengus harengus) stocks and, in more detail, for Fortune Bay herring. For these stocks the relationship was of the form q = cA−b. For Atlantic herring stocks, levels of b were in excess of 0.80. In Fortune Bay herring, reductions in abundance were accompanied by proportional reductions in A, which in turn was inversely correlated with changes in q. School size, measured as catch per set, also declined as population levels declined but the change was not proportional. Published findings indicate that pelagic stocks in particular, and fish stocks in general, exhibit a common response of reductions in A with interactive increases in the q during periods of rapid population decline. We conclude that the conventional assumption of a constant stock area is usually violated due to the systematic interaction between A and population abundance which is reflected in an inverse relationship between stock abundance and q. Calibration of sequential population models should therefore be restricted to research vessel data collected in a standard manner and covering the distributional area of the stock.

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.

Implications of interference among fishing vessels and the ideal free distribution to the interpretation of CPUE

1998 ◽  
Vol 55 (1) ◽  
pp. 37-46 ◽  
Author(s):  
D M Gillis ◽  
R M Peterman
Keyword(s):  
Ideal Free Distribution ◽  
Fishing Effort ◽  
Catch Per Unit Effort ◽  
Free Distribution ◽  
Fishing Vessels ◽  
Factor Interactions ◽  
The Relationship ◽  
Index Of Abundance ◽  
Ideal Free ◽  
The Ideal

Despite recognized biases, catch per unit effort (CPUE) statistics remain widely used for the estimation of fish abundance. Previous workers have shown that CPUE can be a misleading index of abundance due to fish behavior, the nominal effort units used, and increases through time in efficiency of fishing (catchability). We examine the theoretical implications of a different factor, interactions among fishing vessels, for the relationship between abundance and CPUE. Our model simulates a fishery that occurs in several adjacent fishing grounds. The spatial distribution of catch and effort is based on a simplification of the Baranov catch equation, the relationship between fishing efficiency and local fishing effort (interference), and the assumptions of the ideal free distribution. Our results indicate that (i) even low levels of interference among fishing vessels can cause a breakdown in the correlation between CPUE and local abundance and (ii) the influence of interference on this relationship is dependent on the correlation of abundances among adjacent areas. Our model suggests an alternative index of abundance, based on the proportion of fishing effort on a ground, that would be appropriate for cases where interference occurs among fishing gear.

How reliable are the abundance indices derived from commercial catch–effort standardization?

2009 ◽  
Vol 66 (7) ◽  
pp. 1169-1178 ◽  
Author(s):  
Yimin Ye ◽  
Darren Dennis
Keyword(s):  
Generalized Linear Model ◽  
Observation Error ◽  
Potential Bias ◽  
Catch Per Unit Effort ◽  
Rock Lobster ◽  
Commercial Catch ◽  
Abundance Indices ◽  
Catch Rates ◽  
Power Component ◽  
Stock Abundance

Commercial catch-per-unit-effort (CPUE) data are often standardized to construct indices of stock abundance. The value of such standardization lies in the improvement in the proportionality between the derived index and true abundance. Using the Torres Strait rock lobster ( Panulirus ornatus ) fishery in Australia as an example, we first standardized the commercial CPUE data using a generalized linear model (GLM) and then fitted observation error models to the resulting abundance indices and independent abundance data (as estimated by research diver surveys) to examine the proportionality. While the GLM standardization greatly improved proportionality in comparison with the nonstandardized commercial catch rates, it could produce biased results if the model did not explicitly incorporate variables that had caused changes in fishing efficiency. As most catch–effort standardizations do not model the fishing power component simultaneously, this result may serve as a warning to the potential bias in stock abundance indices extracted from GLMs that are underfitted.

scholarly journals Detecting regime shifts in fish stock dynamics

2015 ◽  
Vol 72 (11) ◽  
pp. 1619-1628 ◽  
Author(s):  
Tommi Perälä ◽  
Anna Kuparinen
Keyword(s):  
Gadus Morhua ◽  
Atlantic Cod ◽  
Stock Assessment ◽  
Detection Algorithm ◽  
Regime Shifts ◽  
Change Point Detection ◽  
Fish Stock ◽  
Fish Stocks ◽  
Data Generating Process ◽  
Change In Mean

Environmental factors such as water temperature, salinity, and the abundance of zooplankton can have major effects on certain fish stocks’ ability to produce juveniles and, thus, stock renewal ability. This variability in stock productivity manifests itself as different productivity regimes. Here, we detect productivity regime shifts by analyzing recruit-per-spawner time series with Bayesian online change point detection algorithm. The algorithm infers the time since the last regime shift (change in mean or variance or both) as well as the parameters of the data-generating process for the current regime sequentially. We demonstrate the algorithm’s performance using simulated recruitment data from an individual-based model and further apply the algorithm to stock assessment estimates for four Atlantic cod (Gadus morhua) stocks obtained from RAM legacy database. Our analysis shows that the algorithm performs well when the variability between the regimes is high enough compared with the variability within the regimes. The algorithm found several productivity regimes for all four cod stocks, and the findings suggest that the stocks are currently in low productivity regimes, which have started during the 1990s and 2000s.

scholarly journals Cod catches taken by the German recreational fishery in the western Baltic Sea, 2005–2010: implications for stock assessment and management

2012 ◽  
Vol 69 (10) ◽  
pp. 1769-1780 ◽  
Author(s):  
Harry V. Strehlow ◽  
Norbert Schultz ◽  
Christopher Zimmermann ◽  
Cornelius Hammer
Keyword(s):  
Baltic Sea ◽  
Gadus Morhua ◽  
Stock Assessment ◽  
Mail Survey ◽  
Fishing Effort ◽  
Commercial Fishery ◽  
Catch Per Unit Effort ◽  
Yearly Variation ◽  
Fish Stocks ◽  
Recreational Fishery

Abstract Strehlow, H. V., Schultz, N., Zimmermann, C., and Hammer, C. 2012. Cod catches taken by the German recreational fishery in the western Baltic Sea, 2005–2010: implications for stock assessment and management. – ICES Journal of Marine Science, 69: 1769–1780. Next to the commercial fishery, the recreational fishery plays an important role in the removal of biomass from fish stocks. In this study, we present estimates of German recreational cod (Gadus morhua) catches in the western Baltic Sea between 2005 and 2010. Fishing effort was estimated using a stratified mail survey and annual sales of fishing licences. Catch per unit effort was estimated by stratified random sampling of access points and interviews about completed trips. Length distributions of cod catches were acquired by sampling recreational cod catches from charter boats and data from community fishing events. Estimates of the total cod biomass removed by the recreational fishery fluctuated between 2159 t in 2009 and 4127 t in 2005. Annual recreational fishery cod harvests accounted for a significant share of the total landings, with a yearly variation from 34 to 70% of the German commercial cod landings from the western Baltic Sea. The majority of recreational fishery cod catches were taken from private boats and charter vessels. Because of the amount and specifically the variability of the recreational catches, they are important for the assessment and management of the resource and, therefore, need to be surveyed annually.

scholarly journals Implementing ecosystem-based fisheries management: from single-species to integrated ecosystem assessment and advice for Baltic Sea fish stocks

2013 ◽  
Vol 71 (5) ◽  
pp. 1187-1197 ◽  
Author(s):  
Christian Möllmann ◽  
Martin Lindegren ◽  
Thorsten Blenckner ◽  
Lena Bergström ◽  
Michele Casini ◽  
...  
Keyword(s):  
Baltic Sea ◽  
Fisheries Management ◽  
Gadus Morhua ◽  
Single Species ◽  
Clupea Harengus ◽  
Fish Stock ◽  
Fish Stocks ◽  
The Baltic ◽  
Ecosystem Based Fisheries Management ◽  
Sea Fish

Abstract Theory behind ecosystem-based management (EBM) and ecosystem-based fisheries management (EBFM) is now well developed. However, the implementation of EBFM exemplified by fisheries management in Europe is still largely based on single-species assessments and ignores the wider ecosystem context and impact. The reason for the lack or slow implementation of EBM and specifically EBFM is a lack of a coherent strategy. Such a strategy is offered by recently developed integrated ecosystem assessments (IEAs), a formal synthesis tool to quantitatively analyse information on relevant natural and socio-economic factors, in relation to specified management objectives. Here, we focus on implementing the IEA approach for Baltic Sea fish stocks. We combine both tactical and strategic management aspects into a single strategy that supports the present Baltic Sea fish stock advice, conducted by the International Council for the Exploration of the Sea (ICES). We first review the state of the art in the development of IEA within the current management framework. We then outline and discuss an approach that integrates fish stock advice and IEAs for the Baltic Sea. We intentionally focus on the central Baltic Sea and its three major fish stocks cod (Gadus morhua), herring (Clupea harengus), and sprat (Sprattus sprattus), but emphasize that our approach may be applied to other parts and stocks of the Baltic, as well as other ocean areas.

Is catch proportional to nominal effort? Conceptual, fleet dynamic, and statistical considerations in catch standardization

2019 ◽  
Vol 76 (12) ◽  
pp. 2332-2342
Author(s):  
M. Aljafary ◽  
D.M. Gillis ◽  
P. Comeau
Keyword(s):  
Mixed Model ◽  
Linear Mixed Model ◽  
Meta Analysis ◽  
Melanogrammus Aeglefinus ◽  
Catch Per Unit Effort ◽  
Apparent Relationship ◽  
Proportional Relationship ◽  
Disaggregated Data ◽  
The Relationship ◽  
Haddock Melanogrammus Aeglefinus

Often, catch-per-unit-effort (CPUE) standardizations are used to reflect fish abundance. This implies that catch is directly proportional to effort. We examine this using 78 reported catch and effort series in a meta-analysis, correcting for errors-in-variables in the relationship. Though proportionality in the apparent relationship is the average, there is significant variation among fisheries. We then examine the Scotian Shelf haddock (Melanogrammus aeglefinus) fishery in detail. We used a generalized linear mixed model (GLMM) predicting catch-per-set, accounting for annual and within-year variation in fish, fleet activity, aggregation, and vessel locations and differences. In individual trawls, the catch was less than expected from a proportional relationship with effort. The GLMM revealed both interference and facilitation among vessels as well as autocorrelation among sets. The greatest impact on coefficient estimates was seen by allowing the effort coefficient to vary. Temporal aggregation made the catch–effort relationship appear more proportional. We recommend that fisheries researchers standardize catch explicitly, rather than CPUE, and use disaggregated data to more closely match the underlying relationships in the fisheries being examined.

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