Vessel Catch Research Articles

The Atlantic surfclam fishery and offshore wind energy development: 1. Model development and verification

Abstract Competing pressures imposed by climate-related warming and offshore development have created a need for quantitative approaches that anticipate fisheries responses to these challenges. This study used a spatially explicit, ecological-economic agent-based model integrating dynamics associated with Atlantic surfclam stock biology, decision-making behavior of fishing vessel captains, and fishing fleet behavior to simulate stock biomass, and fishing vessel catch, effort and landings. Simulations were implemented using contemporary Atlantic surfclam stock distributions and characteristics of the surfclam fishing fleet. Simulated distribution of fishable surfclam biomass was determined by a spatially varying mortality rate, fishing by the fleet was controlled by captain decisions based on previous knowledge, information sharing, and the ability to search and find fishing grounds. Quantitative and qualitative evaluation of simulation results showed that this modeling approach sufficiently represents Atlantic surfclam fishery dynamics. A fishing simulation showed that the captain's decision-making and stock knowledge, and the distribution of fishing grounds relative to home ports controlled the landed catch. The approach used herein serves as the basis for future studies examining response of the Atlantic surfclam fishery to a nexus of simultaneous, complex natural and anthropogenic pressures, and provides a framework for similar models for other resources facing similar pressures.

Characterizing Industrial and Artisanal Fishing Vessel Catch Composition Using Environmental DNA and Satellite-Based Tracking Data.

The decline in wild-caught fisheries paired with increasing global seafood demand is pushing the need for seafood sustainability to the forefront of national and regional priorities. Validation of species identity is a crucial early step, yet conventional monitoring and surveillance tools are limited in their effectiveness because they are extremely time-consuming and require expertise in fish identification. DNA barcoding methods are a versatile tool for the genetic monitoring of wildlife products; however, they are also limited by requiring individual tissue samples from target specimens which may not always be possible given the speed and scale of seafood operations. To circumvent the need to individually sample organisms, we pilot an approach that uses forensic environmental DNA (eDNA) metabarcoding to profile fish species composition from the meltwater in fish holds on industrial and artisanal fishing vessels in Ecuador. Fish identified genetically as present were compared to target species reported by each vessel’s crew. Additionally, we contrasted the geographic range of identified species against the satellite-based fishing route data of industrial vessels to determine if identified species could be reasonably expected in the catch.

Profitability, Capacity and Productivity Trends in an Evolving Rights Based Fishery: The Norwegian Purse Seine Fishery

Regulators in many countries have adopted individual quotas as a means of dealing with the open access problem inherent in fisheries. The Norwegian Purse Seine fishery has evolved over the last 40 years from an open access fishery to a Rights Based management system with individual vessel catch quotas assigned to all major fish species. Regulations do allow for merging vessel quota. The purpose of this paper is to employ an index approach to decompose vessel revenues and costs by factor components. The index approach can measure the importance of prices, output and regulatory changes impacting productivity and provides insight into changes in a mature IVQ fishery. The current study uses a large individual vessel data set for the period 1994–2013. Results show that over time output prices have been the main drivers associated with increased revenues. We correlate output prices with an evolving IVQ fishery, and changes in harvest and demand conditions. Ongoing capital investment, not offset by increased harvest, has seen productivity decline in the early periods of the study but some recovery towards the end of the period.

Strategic investments in catch capacity and quotas: How costly is a mismatch for a firm?

Despite improved fisheries management, overcapacity is still a major issue in fisheries worldwide. This study investigates the economic effect of a mismatch between catch capacity and quota holdings on the economic performance of fishing boats operating in a system of Individual Fishing Quota (IFQ) system. Based on the data of 71 fishing vessels, which constitute the entire fleet of Norwegian seagoing purse seiners, an ordinal least squares model is applied by including the vessel's catch capacity, quota holding, and return on invested capital (ROIC) along with several control variables. The estimated results suggest that the key factor affecting ROIC is overcapacity. Specifically, when the relative ratio of capacity and quota holding increases by 1%, a vessel's ROIC decreases by 0.692%. This finding indicates that the overcapacity problem in the Norwegian seagoing purse seine fleet still exists even more than a decade after an IFQ regime was introduced. The paper concludes by discussing implications of the findings.

DAMPAK KEBERADAAN KAPAL PENYAMBANG TERHADAP PERTUMBUHAN KAWASAN EKONOMI PERIKANAN DI PELABUHAN PERIKANAN MUARA KINTAP KABUPATEN TANAH LAUT

Kintap coastal area is one of the areas that developed as a coastal fishery production. Area-based coastal fisheries as Kintap Muara district is consisting of the main activities of fishing activity in the form of Fish Landing Base (PPI) with a variety of amenities. Coastal areas in the village of Muara Kintap pattern fisheries are people who are known to pattern middlemen (Indonesian : penyambang) and developed since 2003. Study was conducted to see how the existence determines penyambang ships for fishing communities and the fishing estuary fishing port Kintap with : identifying the impact of fishing communities penyambang vessel catch and fishing port Muara Kintap; analyze business profits as penyambang ship; formulate strategy development as a fishing port economic zone fisheries. Technique uses qualitative and quantitative methods with a descriptive approach.The existence of the ship penyambang was a positive impact on fishermen catch. Fishermen catch will work more effectively and provide capital as a form of business development, while for the Port of Muara Kintap, penyambang ship has negatif impact on the port becauses penyambang ship can not be loading and unloading in the port. So that data from the catches of fishermen willnot be sould to penyambang as data the basis for determining the policy is difficult to know and retribution for PAD port no. Average profit businesses penyambang vessel during fishing season is Rp. 2.773.611,00 per month while the crew (ABK) get Rp.1.386.806, 00 per month and crew still above the local minimum wage (UMR) South Kalimantan Province of Rp. 1.337.500.00. Fishing harbor in the village of Muara Kintap, Tanah Laut District as district fisheries economy still needs a better development strategy so that the presence of the ship penyambang can contribute to Improved Income (PAD) Kintap Estuary Fishery Port.

A Bayesian state-space model to estimate population biomass with catch and limited survey data: application to the thornback ray (Raja clavata) in the Bay of Biscay

The thornback ray (Raja clavata ) in the Bay of Biscay is presumed to have declined during the 20th Century. To evaluate this decline and estimate biomass trajectories, a hypothetical catch time series was created for the period 1903–2013. A Bayesian state-space biomass production model with a Schaefer production function was fitted to the hypothetical catch time series and to a shorter research vessel Catch Per Unit Eeffort (CPUE) time series (1973–2013, with missing years). A censored likelihood made it possible to obtain biomass estimates without a CPUE time series or only with an estimate of biomass depletion. A simulation-estimation approach showed a high sensitivity of results to the prior for the intrinsic growth rate. The model provided biomass trajectories which corroborated and quantified the decline of the Bay of Biscay population. The estimated biomass corresponding to the maximum sustainable yield, B MSY , was 32 000 tonnes, which is 17 times higher than the estimated biomass in 2014. The biomass estimates obtained without a CPUE time series were highly uncertain. Adding a current biomass depletion observation improved precision, though the biomass time trend was sensitive to this value. Results should be interpreted carefully as several assumptions were necessary to create the long catch time series and to define informative priors, notably for the intrinsic growth rate. Despite this, the results confirm the depleted state of the thornback ray in the Bay of Biscay with the estimated biomass in 2014 being around 3% of carrying capacity.

ICT SOLUTION TO MINIMIZE ILLEGAL, UNREPORTED AND UNREGULATED (IUU) FISHING

Marine environment is one of the natural ecosystem which is been affected by the unscrupulous human activities. Lots of efforts are taken to preserve and maintain the balance of the aquatic resources by responsible bodies. European Union convention on the law of the sea has a great impact on avoiding the IUU fishing activities of the countries with large scaled fisheries industry. Fishing grounds should be harvested with caution otherwise whole could be endanger in extinction while harvesting the whole school of fish. There the fishermen are responsible for releasing under-weight fishes and the other fish types which are prohibited to be caught.
 With the technology all the manual works has been eased and heightened in accuracy wise. Albeit the advantages are there, the main drawback is that they are being expensive. Localizing those products and requirement adding has been the major gap which has limited those commercial products being popularized in the countries with native languages. In this paper we have discussed a novel approach for fishing vessel tracking and catch reporting which minimizes above drawbacks.

Candidate biological and economic target reference points for the south Pacific albacore longline fishery

The south Pacific albacore tuna (Thunnus alalunga) stock is predicted to remain above the adopted limit reference point under recent increased catch levels. However, vessel catch rates are predicted fall and economic conditions worsen, which is of particular concern for those smaller-scale fleets within Pacific island countries and territories that rely on this stock for income and employment. We examine candidate target reference points that might achieve wider management objectives integrating across multiple plausible states of nature using a deterministic bio-economic model, and potential implications of those targets for the stock and fisheries through stochastic stock projections. Maximum sustainable yield (MSY), the ‘default’ reference point within the Western and Central Pacific Fisheries Commission, implied a relatively low stock size and more than a 1-in-3 chance of the stock falling below the limit reference point. Minimum target levels, defined by the permissible level of risk (5–20%) of falling below the limit reference point, implied larger stock sizes than at MSY, but a halving in longline catch rates that would lead to increased social and economic hardship. These results suggest that economic, rather than biological, requirements will provide the standards for an albacore target reference point. However, achieving maximum economic yield (MEY) implied severe reductions in effort, likely incompatible with objectives for employment within the local fishery sector or the level of vessel licensing revenue. Sub-optimal but improved economic performance levels examined, such as a 10% revenue margin over economic costs, or revenues equal to the economic costs, could be obtained with less severe reductions in effort. Identifying an acceptable target reference point compatible with fishery objectives, and ways to transition from recent fishing levels to those targets, is urgently needed to ensure fleets remain viable.

An experimental setup for autonomous operation of surface vessels in rough seas

SUMMARYA small-scale experimental setup for autonomous target tracking of a surface vessel in the presence of obstacles is presented. The experiments are performed in simulated rough seas through wave, current, and wind generation in a small indoor pool. Absolute position of the agent and the target as well as the obstacle size and position are provided through an overhead camera by detecting color light emitting diodes installed on all objects. Ordinary differential equations with stable limit-cycle solutions are used to define transitional trajectories around obstacles based on the camera data. A sliding mode control law is implemented for real-time tracking control which is capable of rejecting large disturbances from the generated waves and wind. The sliding mode control signals are sent to wireless receivers on the autonomous vessel where a proportional integral speed controller maintains the commanded speed. A special scaling method is presented to show that the environmental forces are similar to those of moderate through high sea states. Several experiments are presented where the autonomous vessel catches and follows a target boat moving in arbitrary trajectories in both the presence and absence of obstacles.

Management of and Economic Returns from Selected Fisheries in the Nordic Countries

There is potential to increase the economic returns in many fisheries by improving fisheries management. In this article, maximum and estimated current resource rents are analyzed using a standardized methodology for five case studies of fisheries with different management regimes: individual quotas (Norway), individual transferable quotas (Iceland), co-management (Denmark), vessel catch limits (Sweden), and tradable days-at-sea regulation (Faroe Islands). The Danish co-managed fishery had the highest estimated current rent, corresponding to 51% of landing value compared to a maximum rent of 62%. The Danish case was followed by the Icelandic ITQ fishery (estimated current 30%, maximum 66%), Faroese tradable days-at-sea (current 28%, maximum 55%), Swedish vessel catch limits (current 3%, maximum 74%), and Norwegian individual quotas (estimated current −22%, maximum 43%). Fishery characteristics other than management might influence the estimated resource rent, and the results are discussed in relation to biological sustainability. The method used across fisheries and countries for the estimation of the current economic rent, based on standardized opportunity costs of labor and capital, exaggerates the current positive rent for the ITQ fishery and the negative rent for the individual quota fishery.

Catch Density: A New Approach to Shifting Baselines, Stock Assessment, and Ecosystem-Based Management

Since 1995, researchers have worked to incorporate historical perspectives into fisheries management. however, problems of scale and distribution, data incompatibilities, and strictures of standard stock assessment models have limited success so far. here we offer a new metric, catch density (CD = catch/area fished), as a simple way to examine fish concentration that standardizes historical and modern catch by geographical area fished. we present three case studies based on historical gulf of maine fisheries. The first compares five discrete datapoints of annual catch and CD for american shad from 1634 to 1999. Changes in fish habitat, fishing effort, and geographical area make direct comparison of catch alone misleading, but CD declined three orders of magnitude over four centuries. The second study compares discontinuous and continuous time series of yearly catch and CD for 18 species and two species groups from 1887 to 1945 and from 1989 to 2005. modern catch is aggregated over each stock's entire range; the historical area is the gulf of maine. in each case, historical context explains the results. overall catch is higher today, while CD was higher historically, likely reflecting expanded vessel range and catch per unit effort. finally, when catch, CD, and average trophic level are compared for functional groups over the same time periods, CD accurately reflects shifts in trophic level not seen in catch alone. CD standardizes catch across spatial and temporal scales, timeframes, and geographic distribution. By integrating fisheries history with fisheries science, it offers a new perspective, quickly obtained, that may aid in developing ecosystem-based management.

Optimal vessel size and output in the Australian northern prawn fishery: a restricted profit function approach*

Individual transferable quotas (ITQs) are to be introduced into Australia’s Northern Prawn fishery in the near future. Total allowable catches (TACs) are to be set with the objective of maximising economic efficiency in the fishery. Under ITQs, vessel owners have the ability to adjust their fishing activities to maximise profits and changes in fleet structure resulting from management changes need to be considered when determining TACs. A restricted profit function for the fishery was estimated to determine the optimal vessel characteristics and output levels as a guide to how the fleet may adjust under an ITQ system. Vessels were found to be currently close to their optimal size given average historic prices and current stock conditions. However, higher tiger prawn stocks are expected to result in the average size of vessels increasing, with rising fuel prices also likely to result in capital being substituted for fishing days. Optimal average vessel‐level catches of the main species are lower than current average vessel catches for a wide range of input and output prices. These changes in vessel characteristics and behaviour need to be incorporated in the derivation of the optimal TACs if economic efficiency objectives are to be achieved.

Improving the quality of information on Scottish anglerfish fisheries: making use of fishers' data

Abstract Dobby, H., Allan, L., Harding, M., Laurenson, C. H., and McLay, H. A. 2008. Improving the quality of information on Scottish anglerfish fisheries: making use of fishers’ data. – ICES Journal of Marine Science, 65: 1334–1345. In recent years, the International Council for the Exploration of the Sea (ICES) Working Group on the Assessment of Northern Shelf Demersal Stocks has been unable to provide an analytical assessment for anglerfish. One of the reasons for this has been the poor quality of the commercial catch-and-effort data, with ICES and the European Commission’s Scientific, Technical, and Economic Committee for Fisheries (STECF) stressing the need for reliable information on which to base estimates of stock status. In response, and following consultation with the fishing industry, an anglerfish tallybook project was implemented in Scotland as part of a long-term approach to providing better data. Tallybooks are completed on a haul-by-haul basis. Skippers record catches of anglerfish (by size category) and other species where possible, together with information on haul location, duration, and depth. Individual vessel catch rates are calculated and used to provide insights into temporal trends in the stock and the spatial distribution of the fishery. The history of the fishery and management advice are summarized, and an overview of the tallybook project is provided. Catch rates are analysed using a generalized additive modelling approach which incorporates seasonal, annual, spatial, and vessel-dependent effects. The results show increased catch rates between 2006 and 2007.

Use of commercial vessels in survey augmentation: the size-frequency distribution

The trend towards use of commercial vessels to enhance survey data requires assessment of the advantages and limitations of various options for their use. One application is to augment information on size-frequency distributions obtained in multispecies trawl surveys where stratum boundaries and sampling density are not optimal for all species. Analysis focused on ten recreationally and commercially important species: bluefish, butterfish, Loligo squid, weakfish, summer flounder, winter flounder, silver hake (whiting), black sea bass, striped bass, and scup (porgy). The commercial vessel took 59 tows in the sampled domain south of Long Island, New York and the survey vessel 18. Black sea bass, Loligo squid, and summer flounder demonstrated an onshore-offshore gradient such that smaller fish were caught disproportionately inshore and larger fish offshore. Butterfish, silver hake, and weakfish were characterized by a southwest-northeast gradient such that larger fish were caught disproportionately northeast of the southwestern-most sector. All sizes of scup, striped bass, and bluefish were caught predominately inshore. Winter flounder were caught predominately offshore. The commercial vessel was characterized by an increased frequency of large catches for most species. Consequently, patchiness was assayed to be higher by the commercial vessel in nearly all cases. The size-frequency distribution obtained by the survey vessel for six of the ten species, bluefish, butterfish, Loligo squid, summer flounder, weakfish, and silver hake, could not be obtained by chance from the size-frequency distribution obtained by the commercial vessel. The difference in sample density did not significantly influence the size-frequency distribution. Of the six species characterized by significant differences in size-frequency distribution between boats, all but one was patchy at the population level and all had one or more size classes so characterized. Although the variance-to-mean ratio was typically higher for the commercial vessel, five of the six cases that were otherwise were among the species for which the size-frequency distribution differed between the two vessels. Thus, the origin of the significant differences observed between vessels would appear to lie in the spatial pattern of the species as it interacts with the tendency for one vessel to obtain large catches more frequently for some size classes. One consequence of differential distribution and catchability is that more large fish were present in the commercial vessel catches than in the survey vessel catches in cases where the two vessels obtained different size-frequency distributions. Application of commercial vessels to the evaluation of size frequency hinges on understanding how to interpret differences among boats, gear, and sampling design. Here we show that key ingredients to this understanding are the degree of nonlinearity in catchability across a range of size classes, the interaction of varying spatial arrangements among size classes and the sampling design, and the interaction of varying spatial arrangements with differential catchability.

Survey augmentation using commercial vessels in the Mid-Atlantic Bight: Sampling density and relative catchability

Summary A series of side-by-side tows was conducted between a survey vessel and a commercial vessel in two seasons, spring and fall (autumn), to examine the use of commercial vessels to increase sampling density in trawl-based stock surveys. Both vessels caught more fish offshore in the spring. The commercial vessel caught more fish than the survey vessel in both seasons. Catches of nearly all species were contagiously distributed in the spring. Most were contagiously distributed in the fall; however, somewhat more species were characterized by random or even distributions. The variance-to-mean ratio was consistently higher for most species for commercial vessel catches, regardless of season. As both vessels sampled in the same region at the same time, the increased predilection for the survey vessel to assess the distribution pattern as less patchy than the commercial vessel must accrue from some difference in sampling dynamics rather than variation in species distribution. A simulated decrease in sampling effort from 59 to 30 or 15 hauls increased the variance-to-mean ratio. Reduced sampling effort increased the tendency for occasional large catches to vary the estimate of domain biomass. The sampling program included an onshore–offshore gradient in station density. Domain biomass was considerably underestimated with reduced station density for six species characterized by large catches offshore in that portion of the survey domain characterized by low station density. In this study, a factor of two variation in domain biomass became more likely in 40% of species when sampling effort was reduced to 15 hauls from 59. A factor of two in biomass may distinguish a sustainable fishery from one in which a species is overfished. As survey sampling effort in this area was 18 hauls, increasing sample number by inclusion of commercial vessel tows would be advantageous. A regression between paired tows failed to adequately predict catches of one vessel from catches of the other. Standardization of vessel catches by the ratio-of-mean catches provided a more realistic comparison because large catches accounted for a significant fraction of domain biomass; however, a single conversion coefficient between boats could not be used for both sampling periods. The underlying impediment in developing a general conversion factor between the two vessels seems to be rooted in the differential in variance-to-mean ratios of the catches; this differential exists despite sampling of the same distribution of fish.

Changes in the North Sea fish community: evidence of indirect effects of fishing?

Abstract We investigate changes in the North Sea fish community with particular reference to possible indirect effects of fishing, mediated through the ecosystem. In the past, long-term changes in the slope of size spectra of research vessel catches have been related to changes in fishing effort, but such changes may simply reflect the cumulative, direct effects of fishing through selective removal of large individuals. If there is resilience in a fish community towards fishing, we may expect increases in specific components, for instance as a consequence of an associated reduction in predation and/or competition. We show on the basis of three long-term trawl surveys that abundance of small fish (all species) as well as abundance of demersal species with a low maximum length (Lmax) have steadily and significantly increased in absolute numbers over large parts of the North Sea during the last 30 years. Taking average fishing mortality of assessed commercial species as an index of exploitation rate of the fish community, it appears that fishing effort reached its maximum in the mid-1980s and has declined slightly since. If the observed changes in the community are caused by indirect effects of fishing, there must be a considerable delay in response time, because the observed changes generally proceed up to recent years, although both size and Lmax spectra suggest some levelling off, or even recovery in one of the surveys. Indeed, significant correlations between all community metrics and exploitation rate were obtained only if time lags ≥6 years were introduced.

Inverse regional responses to climate change and fishing intensity by the recreational rockfish (Sebastes spp.) fishery in California

The interactive effects of ocean climate and fishing pressure on nearshore rockfishes (Sebastes spp.) were examined using historical commercial passenger fishing vessel catch records from California. Principal component analysis was used to characterize the dominant patterns in catch per unit effort (CPUE) over time (1957–1999) and space (10′ latitude × 10′ longitude blocks). Ocean climate explained 60% of the variation in CPUE and revealed opposite responses in northern and southern California. In warm El Niño years, CPUE was 4.2 times higher in the north and 1.8 times lower in the south. CPUE responded similarly to low-frequency climate shifts by increasing in the north and decreasing in the south after 1976–1977. Four geographic regions responded as discrete units to environmental forcing and fishing intensity: North, Central, South, and Channel Islands. Over time, annual fish landings declined sharply in the South, with fishing effort remaining stationary and high relative to that in the other regions. In the North, landings and fishing effort remained tightly coupled, with effort an order of magnitude lower than in the South. These findings support a management strategy for nearshore rockfishes in California based on regional responses to ocean climate and fishing intensity.

An Ichthyophonus hoferi epizootic in herring in the North Sea, the Skagerrak, the Kattegat and the Baltic Sea

DAO Diseases of Aquatic Organisms Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials DAO 28:191-199 (1997) - doi:10.3354/dao028191 An Ichthyophonus hoferi epizootic in herring in the North Sea, the Skagerrak, the Kattegat and the Baltic Sea Mellergaard S, Spanggaard B An epizootic caused by the internal parasite Ichthyophonus hoferi in herring Clupea harengus was recorded from 1991 to 1993 in the waters around Denmark. A surveillance programme from research vessels and commercial fishing boats was conducted in the North Sea, Skagerrak, Kattegat and Baltic Sea. A total of 15769 hearts of adult herring were examined macroscopically for evidence of infection. The prevalence of the infection in this period decreased from 10.6 to 2.0% in the North Sea, from 8.0 to 5.6% in the Skagerrak, from 12.0 to 1.1% in the Kattegat and from 4.5 to 0.4% in the Baltic Sea. Prevalence rates in research vessel catches were significantly higher (by 1.8 times) than in commercial fishing boat catches. The results show a high degree of temporal and spatial variation of the prevalence of I. hoferi. Infected fish were found to be significantly longer than unaffected fish in the North Sea and the Skagerrak. The majority of the infected fish belonged to the age groups 2+, 3+ and 4+ except in the commercial catches from the North Sea where most of the affected fish belonged to the age groups 5+, 6+ and 7+. Annual mortality in the different areas, based on the observed prevalences was roughly estimated at 12.8 to 36% in 1991, decreasing to a few percent in 1993. The spawning stock biomass of North Sea herring was reduced by 50% during the period 1990 to 1995. This reduction may have been due to a combination of increased fishing intensity and the general effect of the I. hoferi epizootic. Ichthyophonus hoferi · Epizootic · Herring · North Sea · Skagerrak · Kattegat · Baltic Sea Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in DAO Vol. 28, No. 3. Publication date: March 27, 1997 Print ISSN:0177-5103; Online ISSN:1616-1580 Copyright © 1997 Inter-Research.

Skipjack pole-and-line operations in east Indonesia: A comparative analysis of catch performance

There is a wide geographical spread of skipjack pole-and-line fishing bases in east Indonesia. The article identifies and analyses the relative importance of several interactive factors on pole-and-line vessel catch performance, including the effects of the vessel (eg its size, horse power and age), baitfish (its availability and abundance), the crew (number and skill), season, weather, use of Fish Aggregating Devices (FADs), geographical location of the fishing ground, and ‘fleet congestion’. The importance of FADs in improving catch performance is particularly highlighted. Partly from this comparative analysis, it is postulated that the resident stock in this area is supplemented by large seasonal migrations of skipjack from the western tropical Pacific stock. As the bulk of this migration passes through the waters north of Irian Jaya, this region must offer some of the best fishing opportunities, and hence will have the highest priority for the future development of skipjack pole-and-line and purse seine bases in Indonesia.

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

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.