Movement Dynamics in a Fishery: Application of the Ideal Free Distribution to Spatial Allocation of Effort

Many traditional analyses of fisheries data assume that there is a negligible effect of alternative fish stocks on the spatial distribution of fishing effort and that the amount of local effort does not influence catchability. There is growing evidence that contradicts these assumptions. Because of the potential biases that these erroneous assumptions may cause in the interpretation of catch-per-unit-effort (CPUE) statistics, it is important to determine the factors governing the spatial distribution of effort in a fishery. We used data on the Hecate Strait, British Columbia, Canada, trawl fishery to test hypotheses about spatial allocation of effort and interaction among fishing vessels. The ideal free distribution of Fretwell and Lucas (1970. Acta Biotheor. 19: 16–36) was the foundation for deriving these tests. We found evidence for competition among vessels, although we could not distinguish whether the mechanism was interference or exploitation competition. As well, CPUE was generally equalized among the areas fished, as predicted by the ideal free distribution, because of movement of boats among areas. Thus, area-specific CPUE would not be a reliable index of relative abundance of fish in different areas; relative fishing effort may be better.

Download Full-text

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

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/f97-206 ◽

1998 ◽

Vol 55 (1) ◽

pp. 37-46 ◽

Cited By ~ 64

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.

Download Full-text

Spatial distribution of catch and effort in a fishery for snow crab (Chionoecetes opilio): tests of predictions of the ideal free distribution

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/f03-076 ◽

2003 ◽

Vol 60 (8) ◽

pp. 897-909 ◽

Cited By ~ 57

Author(s):

Douglas P Swain ◽

Elmer J Wade

Keyword(s):

Spatial Distribution ◽

Resource Distribution ◽

Ideal Free Distribution ◽

Snow Crab ◽

Catch Per Unit Effort ◽

Chionoecetes Opilio ◽

Free Distribution ◽

Crab Abundance ◽

Ideal Free ◽

The Ideal

The ideal free distribution (IFD), a hypothesis from behavioural ecology, predicts that fishery effort should map resource distribution better than catch-per-unit-effort (CPUE) when interference competition occurs in the fishery. We tested this prediction using data from the fishery and annual research survey for snow crab (Chionoecetes opilio) in the southern Gulf of St. Lawrence. Effort was positively correlated with the local abundance of crabs in all years. Correlations between CPUE and local crab abundance were also positive in some years, but negative in others. In the latter cases, CPUE and effort were also negatively correlated, suggesting intense competition in the fishery. In most years, CPUE tended to be equalized among areas compared with the distributions of effort and local crab abundance, as predicted by the IFD. In most years, differences in spatial distribution were more significant between CPUE and crab abundance than between effort and crab abundance. Although effort was the more reliable indicator of resource distribution, even it provided a distorted view of this distribution, as predicted given expected violations of IFD assumptions. For example, effort tended to be higher than expected on fishing grounds near home ports and lower than expected on distant grounds.

Download Full-text

Advancing the application of the ideal free distribution to spatial models of fishing effort: the isodar approach

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/f2012-091 ◽

2012 ◽

Vol 69 (10) ◽

pp. 1610-1620 ◽

Cited By ~ 19

Author(s):

D.M. Gillis ◽

A. van der Lee

Keyword(s):

Behavioral Ecology ◽

Interference Competition ◽

Ideal Free Distribution ◽

Spatial Dynamics ◽

Spatial Models ◽

Fishing Effort ◽

Model Parameters ◽

Free Distribution ◽

Ideal Free ◽

The Ideal

The ideal free distribution (IFD) of behavioral ecology has been used in the study of the distribution of fishing effort since the 1990s. Concurrently, evolutionary perspectives on forager distributions have led to the development of theoretical curves of equal fitness, named isodars, to test IFD hypotheses. We develop isodars, based upon catch rates and unknown costs, to quantify regularity in the distribution of fishing effort among alternative areas. Our analyses indicate that these isodars provide significantly better predictions than a simple IFD without costs. Autocorrelation in the catch and effort data necessitates the use of generalized linear least squares when estimating model parameters. Differences in costs that are proportional to effort are more clearly identified in the model than nonlinear effects, which may arise from extreme interference competition. The isodar approach provides a new tool for examining the spatial dynamics of catch and effort data. It improves the accuracy of predictions and provides new parameters related to costs and vessel interactions that can be applied to rapidly identify situations where effort dynamics have changed.

Download Full-text

Predicting Spatial Distribution of Foragers over Large Resource Landscapes: A Modeling Analysis of the Ideal Free Distribution

Oikos ◽

10.2307/3546022 ◽

1997 ◽

Vol 79 (2) ◽

pp. 376 ◽

Cited By ~ 39

Author(s):

Jeffrey A. Tyler ◽

William W. Hargrove

Keyword(s):

Spatial Distribution ◽

Ideal Free Distribution ◽

Free Distribution ◽

Modeling Analysis ◽

Ideal Free ◽

The Ideal

Download Full-text

Variation in the Competitive Abilities of Fishermen and its Influence on the Spatial Distribution of the British Columbia Salmon Troll Fleet

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/f90-129 ◽

1990 ◽

Vol 47 (6) ◽

pp. 1116-1121 ◽

Cited By ~ 37

Author(s):

M. V. Abrahams ◽

M. C. Healey

Keyword(s):

British Columbia ◽

Ideal Free Distribution ◽

Fishing Effort ◽

Catch Rate ◽

Fish Distribution ◽

Fish Stocks ◽

Fishing Vessels ◽

Catch Rates ◽

Ideal Free ◽

The Ideal

We estimated the catch rates of individual fishing vessels within the British Columbia salmon troll fleet from the data of a 7-yr log book program. Catch rates varied considerably among vessels. A portion of the variation could be attributed to environmental variation. However, there were also significant differences in competitive ability among vessels. The top ranked vessels had a catch rate 3.6 times that of the lowest ranked vessels. Top ranked vessels distributed their fishing effort among more fishing areas than bottom ranked vessels, but were also more successful at catching fish when fishing in the same areas as bottom ranked vessels. This information, through an application of the ideal free distribution theory, can be used to develop a model that will describe the expected relationship between vessel distribution, vessel catch rate, and fish distribution, potentially allowing vessel distributions to be used as a tool for assessing fish stocks.

Download Full-text