Approaches to assessing stocks of Loligo gahi around the Falkland Islands

Agnew, David J.; Baranowski, R.; Beddington, J. R.; Clers, Sophie des; Nolan, Conor P.

doi:10.1016/s0165-7836(98)00083-6

Cited by 56 publications

(60 citation statements)

References 15 publications

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“…Genetic studies using allozymes (Carvalho and Pitcher 1989) and microsatellite DNA (Shaw et al 2004) have found that seasonal cohorts and geographic groupings of L. gahi around the Falkland Islands represent a single, genetically homogeneous population. However, the existence of spawning peaks (one in autumn and the other one in spring) is consistent among years (Agnew et al 1998), as is the location of spawning grounds both to the north and to the south of the islands (Arkhipkin et al 2000). The results of the present study revealed that spring-and autumn-spawned cohorts have specific elemental signatures in statoliths that are significantly different at every maturity stage.…”

Section: Discussionsupporting

confidence: 83%

Spatial and temporal variation in elemental signatures of statoliths from the Patagonian longfin squid (Loligo gahi)

Arkhipkin¹,

Campana²,

Fitzgerald³

et al. 2004

Can. J. Fish. Aquat. Sci.

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Abstract:We quantified elemental signatures in statoliths of 718 Patagonian longfin squid (Loligo gahi) collected in the vicinity of the Falkland Islands (southwest Atlantic) and at sites on the Patagonian Shelf and coastal Peru. All squid were assigned to a spawning cohort by size, spawning condition, and back-calculated spawning date based on daily increments in statoliths. The remaining statolith was then analyzed for six elemental ratios (Mg/Ca, Mn/Ca, Sr/Ca, Cd/Ca, Ba/Ca, and Pb/Ca) using high-resolution inductively coupled plasma mass spectrometry (ICP-MS). Elemental concentrations in the statoliths were broadly similar to other biogenic aragonites. Differences in Sr/Ca ratios in statoliths among geographic locations were generally consistent with a negative correlation between Sr/Ca and temperature. Variations in statolith Cd/Ca and Ba/Ca values confirmed that during winter months, the squid were foraging deeper in the water column. Both Mg/Ca and Mn/Ca ratios in statoliths decreased with squid size, probably corresponding to a decrease in the contribution of the organic component of the statolith. Elemental signatures in the statoliths of L. gahi varied significantly geographically and between spring-and autumn-spawned cohorts, which must therefore have spent significant portions of their life histories in different environments. Résumé : Nous avons quantifié les signatures d'éléments dans les statolithes de 718 calmars patagons (Loligo gahi)récoltés dans les environs des îles Falkland (Atlantique sud) et à certains sites sur la plate-forme patagonienne et la côte du Pérou. Tous les calmars ont été assignés à une cohorte de fraye d'après leur taille, leur état reproductif et leur date de fraye déterminée par rétrocalcul à partir des couches de croissance journalière sur les statolithes. Nous avons déterminé six rapports d'éléments dans le second statolithe, soit Mg/Ca, Mn/Ca, Sr/Ca, Cd/Ca, Ba/Ca et Pb/Ca, après une analyse par spectrométrie de masse à source de plasma à couplage inductif (ICP-MS) de haute résolution. Les concentrations d'éléments dans les statolithes sont grossièrement semblables à celles des autres aragonites d'origine biologique. Les différences de Sr/Ca dans les statolithes provenant des diverses localités géographiques s'accordent en général avec la corrélation négative qui existe entre Sr/Ca et la température. Les variations de Cd/Ca et de Ba/Ca dans les statolithes confirment que durant les mois d'hiver les calmars recherchent leur nourriture à de plus grandes profondeurs dans la colonne d'eau. Les rapports Mg/Ca et Mn/Ca déclinent tous les deux à mesure que le calmar grandit, ce qui correspond probablement à une diminution de la contribution de la composante organique du statolithe. Les signatures des éléments des statolithes de L. gahi varient de façon significative en fonction du site géographique, ainsi qu'entre les cohortes pondues au printemps et à l'automne, qui doivent alors avoir passé une partie significative de leur temps dans des environnements différents.[Traduit par l...

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Section: Discussionsupporting

confidence: 83%

Spatial and temporal variation in elemental signatures of statoliths from the Patagonian longfin squid (Loligo gahi)

Arkhipkin¹,

Campana²,

Fitzgerald³

et al. 2004

Can. J. Fish. Aquat. Sci.

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“…In this approach, information obtained from fishing vessels is applied in real time to determine at what point the fishery should be closed, thus regulating the catch. Real-time management is presently utilized in some squid fisheries (Agnew et al, 1998;Basson et al, 1996;Rosenberg et al, 1990;Morales-Bojórquez et al, 2001), but has not yet been implemented in any U.S. squid fishery. A key issue is the development of an approach to measure catch per unit effort (CPUE) during the course of the season without distributing an uneconomical number of observers within the fleet.…”

Section: Introductionmentioning

confidence: 99%

Evaluation of Real-time Catch and Effort Reporting in the U.S. Ilex illecebrosus Fishery

Powell¹,

Bonner²,

Mann³

et al. 2003

J. Northw. Atl. Fish. Sci.

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The Illex illecebrosus fishery in the northwestern Atlantic Ocean is a trawl-based fishery. Illex illecebrosus normally lives less than one year, thus managing the fishery using a standard stock assessment approach is difficult. Real-time management is an attractive option. The purpose of this study was to investigate the validity and utility of data reported by commercial vessels for application in real-time management in the I. illecebrosus fishery. The assessment includes evaluating the frequency of erroneous reports, identifying the best measures of effort for catch per unit effort (CPUE) analysis, and examining the influence of vessel type and vessel behavior on subsequent analyses of trends in catch and effort.Incomplete reports occurred 24% of the time in the commercial data. Misreported times and positions occurred less than 1% of the time. Searching time was not discriminated consistently. Searching times and distances were recovered from the more accurately-reported data on tow times and tow positions. Tow duration was more accurately estimated from Captains' reports than tow distance. True distances were underestimated by 1020% using the position of net deployment and retrieval to measure tow distance because tows did not follow a straightline path. Effort could be estimated based on tow distance or tow duration. Duration was the most accurate effort term. Searches between tows did not improve subsequent catch. Similarly, overnight transits, arguably a type of searching behavior, did not improve the subsequent day's catch. Thus, vessels, on the average, would have improved trip economics by not searching. Because of the apparent absence of a positive effect of searching and the lower accuracy of searching time and searching distance in comparison to tow-based metrics, particularly tow duration, addition of searching time or searching distance to effort did not materially improve the measurement of CPUE.RSW (refrigerated seawater) trawlers search much less often than freezer trawlers. As a consequence of lower catch and longer duration tows, the CPUE for RSW trawlers is distinctly lower than for freezer trawlers. Catch per tow was higher by more than a factor of two for larger vessels. As a consequence of the higher catch and longer tows, CPUE was significantly higher also for the larger vessels. Managing the I. illecebrosus fishery using an industry-based reporting scheme would require information from freezer and RSW trawlers and specified vessel size categories.

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“…Such high variations seem to be inherent to cephalopod stock modelling using DMs, as they have been observed in most studies published till date (e.g. Agnew et al, 1998;Royer et al, 2002Royer et al, , 2006Young et al, 2004). In the English Channel, for example, the initial population size of squid ranged between 49.000 and 6.000.000 individuals (M = 0.2) and the recruitment numbers at the beginning of the depletion period ranged between about 1.000.000 and 2.100.000 individuals.…”

Section: Discussionmentioning

confidence: 85%

“…In such valuable fisheries, real-time assessments using depletion methods might be useful and have already been applied in the squid fishery from the Falkland Islands (Agnew et al, 1998;Arkhipkin et al, 2013). The assessment and management system used in this area makes it one of the best-managed squid fisheries in the world, with effective cooperation between scientists, managers and stakeholders to assure sustainable, longterm resource exploitation (Arkhipkin et al, 2013).…”

Section: Discussionmentioning

confidence: 99%

“…The assessment and management system used in this area makes it one of the best-managed squid fisheries in the world, with effective cooperation between scientists, managers and stakeholders to assure sustainable, longterm resource exploitation (Arkhipkin et al, 2013). The Falkland Islands squid fishery is managed using a combination of effort control (a limited number of vessels are licensed to fish during each of two open seasons), a recruitment biomass survey before each commercial season and an in-season assessment of the state of the stock in relation to biological reference points, such as minimum levels of spawning stock biomass (Agnew et al, 1998;Arkhipkin et al, 2013). The stock size is then monitored in real time using DM assessments, and the fishery may be closed early to preserve a target escapement (Agnew et al, 2002).…”

Section: Discussionmentioning

confidence: 99%

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The use of Depletion Methods to assess Mediterranean cephalopod stocks under the current EU Data Collection Framework

et al. 2015

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Fuelled by the increasing importance of cephalopod fisheries in Europe, scientists and stakeholders have demanded their assessment and management. However, little has been done to improve the data collection under the EU Data Collection Framework (DCF) in order to analyse cephalopod populations. While the DCF allows member states to design flexible national sampling programmes, it establishes the minimum data requirements (MDR) each state is obliged to fulfil. This study was performed to investigate whether such MDR currently set by the DCF allow the application of depletion models (DMs) to assess European cephalopod stocks. Squid and cuttlefish fisheries from the western Mediterranean were used as a case study. This study sheds doubt on the suitability of the MDR to properly assess and manage cephalopod stocks by means of DMs. Owing to the high plasticity of life-history traits in cephalopod populations, biological parameters should be estimated during the actual depletion period of the fished stocks, rather than performing triennial sampling as established by the DCF. In order to accurately track the depletion event, the rapid growth rates of cephalopods implies that their populations should be monitored at shorter time scales (ideally weekly or biweekly) instead of quarterly as specified by the DCF. These measures would not require additional resources of the ongoing DCF but a redistribution of sampling efforts during the depletion period. Such changes in the sampling scheme could be designed and undertaken by the member states or directly integrated as requirements.

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Approaches to assessing stocks of Loligo gahi around the Falkland Islands

Cited by 56 publications

References 15 publications

Spatial and temporal variation in elemental signatures of statoliths from the Patagonian longfin squid (Loligo gahi)

Spatial and temporal variation in elemental signatures of statoliths from the Patagonian longfin squid (Loligo gahi)

Evaluation of Real-time Catch and Effort Reporting in the U.S. Ilex illecebrosus Fishery

The use of Depletion Methods to assess Mediterranean cephalopod stocks under the current EU Data Collection Framework

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