Research Article
Calibrating virtual population analysis for fisheries stock assessment
- Yong Chen, Yan Jiao, Chi-Lu Sun, Xinjun Chen
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- Published online by Cambridge University Press:
- 11 June 2008, pp. 89-97
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Virtual population analysis (VPA) is often used for assessing freshwater and marine fisheries resources. One important component in VPA is to calibrate abundance estimates with a time series of abundance indices. One of the commonly used calibration processes usually includes simultaneous estimation of cohort sizes across all ages and years. This reduces the flexibility of the model in accounting for age- and year-effects, in particular in the presence of an age-specific curvilinear relationship between abundance index and stock abundance. In this study, we compared this simultaneous method tuning approach with a stepwise approach which calibrates abundance age by age in tuning VPA. The simulation study suggests that the stepwise procedure tends to perform better with no obvious retrospective errors in the estimated stock biomass compared with the simultaneous method which tends to have large positive retrospective errors. In applying the stepwise procedure and simultaneous method to a cod fishery data set, we found large differences in the stock sizes estimated for the most recent year using these two methods, with the current stock size estimated using the stepwise method being substantially smaller than that estimated with the simultaneous method. Considering the likelihood of the presence of curvilinear relationship between abundance index and stock abundance, we conclude that the stepwise method yields more reliable results, and is less risk-prone in using VPA for fisheries stock assessment.
Assessment and bioeconomic analysis of the Majorca (NW Mediterranean) trammel net fishery
- Gorka Merino, Beatriz Morales-Nin, Francesc Maynou, Antoni Maria Grau
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- 11 June 2008, pp. 99-107
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Trammel net is the main fishing gear used by artisanal fishers in Majorca Island (NW Mediterranean), and is representative of Mediterranean small-scale fisheries using static gear. The use of static gears close to the coast, where seasonal variability and spatial heterogeneity are high, promotes the diversification of fishing practices or metiers. We analyze the seasonal dynamics of the nets used, target species (red and black scorpionfish, red mullet and cuttlefish) exploitation patterns and the socio-economic conditions under which this fishery takes place, based on General Fisheries Directorate daily sale records (2002–2006). Additional personal socioeconomic interviews allowed the characterization of the trammel net fishery, its fishing behaviour, cost structure and conflicts. Catch and effort data and market surveys are used to evaluate the level of exploitation of the target species and allowed describing Majorca trammel net fishery as an activity based on a sustainable resource. The main target species were found to be near their maximum sustainable yield both by means of a surplus production model (with parameters estimated by CEDA-Catch Effort Data Analysis, software) and an age structured assessment model based on yield-per-recruit analysis. Management actions currently debated by local administration and fishers focus on improving fishers' economic situation, rather than on protecting a threatened resource. One of the management actions proposed is a one day effort reduction, which was analyzed here with the help of a bioeconomic simulation model. A 15-year (2005–2020) simulation allows providing advice to local managers to focus on the commercialization aspects, in order to obtain a higher value to the fish production, rather than expecting to obtain higher profits only by a reduction of the offer.
Mesoscale exploitation of a major tuna concentration in the Indian Ocean
- Alain Fonteneau, Vincent Lucas, Emilie Tewkai, Alicia Delgado, Hervé Demarcq
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- Published online by Cambridge University Press:
- 10 June 2008, pp. 109-121
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The paper analyzes the daily catch, fishing effort and fish size data of the purse seine fleet fishing in the western Indian Ocean in February 2005, when a major concentration of tuna occurred and was heavily exploited by this surface fishery. This tuna concentration event occurred over a period of just 12 days, in an area of about 3500 square nautical miles located to the west of the Seychelles. This small stratum produced a total catch of 22 000 t, corresponding to 6.5% of the total fishing mortality of all adult yellowfin (Thunnus albacares) in the entire Indian Ocean in 2005. Sets were made mainly on free schools and the catch mainly composed of large yellowfin tuna. The average CPUE and the average catch per set were very large, 65 t and 85 t per fishing day, respectively. This “event” took place in a precise area where a high concentration of chlorophyll had been localized 18 days before. The subsequent concentration of tuna schools probably arose due to the high densities of their prey feeding on this large phytoplankton biomass. This phytoplankton bloom was observed at the edge of an anticyclonic eddy, but its origin and its high density cannot be fully explained by available environmental data. The adult yellowfin were probably at a reproductive stage and actively feeding on the local food chain generated by the phytoplankton bloom. Such an event is extreme, but typical of tuna purse seine fisheries where fleets often search for such tuna patches. These events play an important role in tuna fisheries due to the increase in fishing effort and fishing efficiency of purses seiners, both of which increase their impact on the resource. The fine scale study of such events and their improved integration into tuna stock assessments is recommended.
Spatial distribution of Cubiceps pauciradiatus (Perciformes: Nomeidae) in the tropical Indian Ocean and its importance in the diet of large pelagic fishes
- Michel Potier, Evgeny Romanov, Yves Cherel, Richard Sabatié, Veniamin Zamorov, Frédéric Ménard
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- 10 June 2008, pp. 123-134
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The bigeye cigarfish (Cubiceps pauciradiatus) is a small pelagic nomeid of the tropical world ocean, often recovered in the stomach contents of top predators such as tunas, billfishes and marine mammals. In the Indian Ocean, a few studies have investigated the biology and the ecology of this species that is one of the most abundant fish of the intermediate trophic levels. In this paper, we investigated the spatial distribution of C. pauciradiatus in the Indian Ocean using pelagic trawl catches carried out between 20°N and 45°S, and the importance of bigeye cigarfish in the diet of 9 piscivorous fishes sampled by different fishing gears in the western part of the Indian Ocean. The highest densities were observed along the eastern coast of Africa and in the Arabian Sea (87 000 individuals per square nautical mile) during the South-West Monsoon and in the eastern part of the Seychelles archipelago (62 200 ind. square nmi) during the North-East Monsoon. Small sized bigeye cigarfish (20–80 mm SL) was a regular and abundant prey (20 to 200 ind. per stomach) for schooling predators exploited by purse seine fishery such as large yellowfin and bigeye tunas chasing prey near the sea surface. Large sized bigeye cigarfish (61–150 mm SL) occurred in small numbers (3 to 20 ind. per stomach) in the stomach contents of swordfish and of large yellowfin and bigeye tunas caught by longline sets at great depths. Large concentrations of bigeye cigarfish occurred in zones of high productivity, and that species constituted seasonally a strong link in the transfer of energy from low to high trophic levels in this part of the Indian Ocean.
Reducing discards in a demersal purse-seine fishery
- Jorge M.S. Gonçalves, Luis Bentes, Pedro Monteiro, Rui Coelho, Margarida Corado, Karim Erzini
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- 29 April 2008, pp. 135-144
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Fisheries bycatches and discards constitute a significant problem in many fisheries worldwide. Unlike the pelagic purse-seine, the demersal purse seine usually targets high commercial value demersal species such as sea breams (e.g., Diplodus spp., Pagellus spp., Sparusaurata) and the European sea bass (Dicentrarchuslabrax), while discards consist mainly of pelagic species and juveniles of the above mentioned species. In order to evaluate the efficiency of a selectivity device in reducing bycatch and consequently of discards in a demersal purse seine fishery, experimental deployments were carried out. The bycatch reducing device (BRD) consisted in the use of a panel of diamond-shaped mesh netting of 70 mm stretched mesh in the posterior part of the purse seine. Data from 61 experimental fishing trials allowed the evaluation of discards, with Scomberjaponicus, Boops boops, Sardina pilchardus, Diplodus bellottii and Belone belone being the main discarded species. The mean discard ratio per set was 0.49 (± 0.30 standard deviation). The causes for discarding were also identified, with low commercial value being the most important reason. The results of the trials with BRD, were promising, with an average of 49% (± 24%) of the fish escaping per set, especially from those species that are most discarded. Overall, the use of this method for reducing discards can be considered positive for the following reasons: there is no need for structural modification of the fishing gear, the BRD is easy to deploy, and it is efficient in terms of species, sizes and quantities of fish that manage to escape. It therefore has significant benefits for the demersal purse seine fishery and possibly for other “métiers” as well.
Do recent age structures and historical catches of mulloway, Argyrosomus japonicus (Sciaenidae), reflect freshwater inflows in the remnant estuary of the Murray River, South Australia?
- Greg J. Ferguson, Tim M. Ward, Michael C. Geddes
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- 27 June 2008, pp. 145-152
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Patterns of annual freshwater flows in the Murray River and recruitment of mulloway, Argyrosomus japonicus (Scianidae) were reviewed in terms of recent age structures and historical catches and CPUE. Age distributions from the nearshore marine fishery were dominated by the 1993 age class which comprised 35% and 41% of 2001 and 2002 catches, respectively. In 1993 annual freshwater inflow was 2.4 times the 25 year average. Freshwater inflow explained 28% and 35% of the variability in year class strength in the nearshore marine fishery in 2001 and 2002, respectively. Over 80% of the current South Australian commercial catch of mulloway comprises juveniles taken from the remnant estuary of the Murray River. Our results suggest that recent low levels of recruitment in South Australia's fisheries for A. japonicus may reflect low fresh water inflows since 1993. Since 2000, southern Australia has experienced the worst drought in recorded history and management strategies for this fishery must take into account effects of both environmental factors and fishing mortality on this vulnerable sciaenid population. We suggest that the population of A. japonicus located about the Murray River system is estuarine dependent, that the estuary provides important refuge for juveniles, and that strong year classes, or their absence, may be related to freshwater inflow to this environment. We also suggest that age distributions of this apex predator may provide an indicator of environmental health for the Murray River estuary.
Age and growth of brown meagre Sciaena umbra (Sciaenidae) in the Adriatic Sea
- Mario La Mesa, Sabrina Colella, Gianfranco Giannetti, Enrico Arneri
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- 10 June 2008, pp. 153-161
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Age and growth of the brown meagre Sciaena umbra (Sciaenidae) collected (n = 532) in the north-western Adriatic Sea was studied by means of transverse otolith sections. The maximum age estimated was 19 and 16 years for males and females, respectively. The length at age estimated for each sex indicated that females attain a larger size and grow slightly faster than males. Both marginal increment analysis and edge analysis confirmed that annuli are formed once a year, with opaque zones laid down in summer (June-July). Age readings were very precise, with a percentage agreement of 98% between readers and low values of the index of average percent error (0.9%) and coefficient of variation (1.3%). Von Bertalanffy growth function was fitted to age-length data, and growth parameters were estimated for males (L∞ = 44.9 cm; k = 0.27,t0 = −2.17 years) and females (L∞ = 47.2 cm; k = 0.28, t0 = -1.82 years). In both sexes of brown meagre, growth rate was high until they attain 2–3 years of age, i.e. at sexual maturity. Most of catches were obtained in late summer-early autumn. On the basis of present data, the sampled population of brown meagre mostly consisted of small fish younger than three years of age (about 90%). In addition, landings of this species in recent years largely decreased. As reported elsewhere in north-western Mediterranean, brown meagre stock in the Adriatic Sea showed clear signs of depletion, thus specific management measures for this species are urgently required.
Relationship between locomotor activity, environmental factors, and timing of the spawning migration in the European eel, Anguilla anguilla
- Caroline M.F. Durif, Francois Travade, Jacques Rives, Pierre Elie, Claude Gosset
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- 27 June 2008, pp. 163-170
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At the onset of sexual maturation, European eels Anguilla anguilla exhibit high locomotor activity which may correspond to migratory restlessness. We measured activity of captive eels and determined whether it correlated with downstream runs of silver eels as well as changes in environmental factors. Groups of eels at different stages of the silvering process (yellow to silver stage) were tagged and placed in separate tanks supplied with either river or tap water. Activity was measured by means of a flat-board antenna placed vertically in the middle of the tank at the surface of the water. Wild migrating silver eels were caught in the nearby river. Activity of eels in the river water tanks increased 1 to 2 days before downstream migrating eels were caught in the trap, and concurrently with a rise in turbidity and a decrease in conductivity. Activity of eels in the tap water tank showed a different pattern, which did not correspond to downstream runs. A peak in activity corresponded to a drop in tap water pH. It is concluded that eels do show periods of high locomotor activity at the onset of migration and this could be used to predict downstream migration. Movements are triggered by changes in water composition (as opposed to changes in discharge, atmospheric pressure and lunar cycle) measured using turbidity and/or conductivity as proxies. If eels are able to detect such small changes in water conductivity (80 µS cm−1), they may use it to find their way to the estuary.
Diet-morphology relationship in a fish assemblage from a medium-sized river of French Guiana: the effect of species taxonomic proximity
- Bernard de Mérona, Bernard Hugueny, Francisco Leonardo Tejerina-Garro, Emmanuelle Gautheret
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- 27 June 2008, pp. 171-184
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We investigated the global relationship between diet and morphology for 42 fish species from a medium-sized river in French Guiana and checked the influence of the species taxonomic proximity on the implication of individual morphological traits in that relation. The 42 species were classified in eight trophic guilds based on analysis of more than 4000 stomach contents. Taxonomic proximity between species was accounted for by an autoregressive model applied to original data of diet and morphology. Original and taxonomic-free data were then submitted to a Canonical Correspondence Analysis in order to detect the relationship between diet and morphology. We compared the results obtained by analyzing the original data and the corrected data. The results confirm the existence of a significant global relationship between diet and morphology. However, morphological traits responsible for that relation were different when considering the taxonomic-free data. Particularly the well known relationship between gut length and detritivory was not observed on the taxonomic free analysis. It is concluded that controlling for phylogeny is essential to the detection of relationships between diet and morphology. It is also concluded that, despite the robustness of some relationships between morphology and diet, many diets cannot be inferred by a ecomorphological approach.
Combined effects of water quality and stocking density on welfare and growth of rainbow trout (Oncorhynchus mykiss)
- Jeannine Person-Le Ruyet, Laurent Labbé, Nicolas Le Bayon, Armelle Sévère, Annick Le Roux, Hervé Le Delliou, Loic Quéméner
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- 29 April 2008, pp. 185-195
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An 84-day experiment assessed the combined effects of two fresh water quality levels (H: 1.71 ± 0.15 mg O2l−1 and 0.28 ± 0.01 mg l−1 total ammonia nitrogen (T-AN), L: 5.15 ± 0.07 mg O2l−1 and 0.54 ± 0.01 mg T-AN l−1) and 3 stabilized stocking densities: 24.8 ± 0.2, 74.2 ± 0.5 and 120.0 ± 0.9 kg m−3) on rainbow trout. Fish were fed using demand feeders with rewards proportional to stocking density. Mass increase was significantly affected by water quality and stocking density, being highest in H water and the lowest at 120 kg m−3. There was no significant difference in final weight between 25 and 74 kg m−3, but at 120 kg m−3 it was 27% and 19% lower in H and L water respectively than at 25 kg m−3. Feed intake (FI) from day 0–85 was significantly affected by water quality, 1.5% in H compared to 1.1–1.0 in L, but there were no significant differences in apparent feed conversion (AFC). FI was not significantly affected by stocking density but AFC was impaired, it increased with stocking density. Marked changes in fish morphology and composition were related to water quality: Condition K factor and fillet fat content were significantly higher in H than in L groups. Dorsal and pectoral fin condition was affected by stocking density and water quality: fins were significantly longer and less eroded in L groups and at low stocking density. Physiological measures were within the usual ranges, but differed between treatments. Changes in plasma osmolarity, hydromineral balance (Na+) and acid base balance (HCO3–) showed that fish were more affected by water quality than by stocking density. There was no sign of acute stress in acclimated fish as cortisol and glycemia were similar under all experimental conditions. This study highlights the importance of water quality and feeding conditions when considering the effects of stocking density on fish welfare.
Competition for food in the larvae of two marine molluscs, Crepidula fornicata and Crassostrea gigas
- Michel Blanchard, Jan A. Pechenik, Emilie Giudicelli, Jean-Paul Connan, René Robert
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- 29 April 2008, pp. 197-205
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The degree to which larvae of the invasive American slipper limpet (Crepidula fornicata) and the Japanese oyster (Crassostrea gigas) may compete for food was examined during 2003 in the laboratory. Larval microalgae uptake, growth and mortality were compared for larvae fed each of six species of unicellular algae, ranging in length from 2 to 10 µm. Tested diets included the two flagellates Tetraselmis chui (Prasinophyceae) and Isochrysis affinis galbana (T-ISO, Haptophyceae), one member of the Chlorophyceae (Nannochloris atomus), and three diatom species (Chaetoceros calcitrans forma pumilum, Chaetoceros gracilis, Skeletonema marinoï). We found that the limpet larvae ingested phytoplankton over a wider range of cell sizes and ate at higher rates on each diet than did the oyster larvae. For example, oyster larvae consumed 2216 cells h−1 of N. atomus, while limpet larvae consumed the same phytoplankton cells at approximately twice that rate, 5159 cells h−1, on the same diet. Larvae of both species grew more quickly on a mixture of flagellates than on any of the diatom alone (12 versus 7 µm d−1 for oyster larvae and 41 versus 28 µm d−1 for limpet larvae). Our results suggest that in the Bay of Mount Saint-Michel (France, Western Channel), where larvae of both species co-exist in the summer, intensive grazing by limpet larvae can potentially deplete phytoplankton concentrations to cause competition with oyster larvae, particularly for smaller sized phytoplankton species.
Characteristics of stripped and testicular Northern pike (Esox lucius) sperm: spermatozoa motility and velocity
- Martin Hulak, Marek Rodina, Otomar Linhart
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- 29 April 2008, pp. 207-212
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The effects of osmolality and accidental urine contamination on spermatozoa velocity and motility were studied, combined with an examination of the biological characteristics of stripped and testicular sperm. Analysis of Northern pike sperm showed higher ionic concentrations of Na+ (123 ± 9 mM), Cl- (127 ± 7 mM), and K+ (35 ± 5 mM) in the seminal fluid of testicular sperm (TS), than in that of stripped sperm (SS): Na+ (116 ± 9 mM), Cl− (116 ± 7 mM) and K+ (25 ± 4 mM). Highest osmolality of seminal fluid was observed in TS with a value of 358 ± 77 mOsmol kg−1 compared with 273 ± 21 mOsmol kg−1 for SS and 68 ± 36 mOsmol kg−1 for urine. A significantly higher spermatozoa concentration was observed in TS (34 ± 5 × 109 ml−1) than in SS (23 ± 4 × 109 ml−1). Spermatozoa concentration per male and per kg body weight was 22 ± 17 × 109 for TS and 18 ± 2 × 109 for SS, respectively. Both TS and SS showed significantly higher spermatozoa velocities and motilities after dilution in urine than after dillusion in distilled water during the activity period. In conclusion, the results obtained from the present study provide information on northern pike sperm physiology that be used to improve sperm management efficiency for this species.
Field study of metal concentrations and biomarker responses in the neogastropod, Murex trunculus, from Bizerta Lagoon (Tunisia)
- Samia Gharbi-Bouraoui, Mauricette Gnassia-Barelli, Michèle Roméo, Mohamed Dellali, Patricia Aïssa
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- 27 June 2008, pp. 213-220
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This study aims to evaluate the health status of Bizerta lagoon using a sentinel species, the Neogastropod Murex trunculus. Trace metal concentrations (Cd, Cu and Zn) in the foot and digestive gland, and biomarkers such as acetylcholinesterase (AChE), catalase (CAT) and glutathione transferase (GST) activities in the digestive gland, were determined in samples collected at four sites at different periods of the year. One site, in the North of the lagoon, is influenced by urban and industrial waste waters. Another, to the south, is located at the outfall of Ichkeul Lake. A third site is one that may be impacted by eutrophication processes, and the last, in the center of lagoon, is considered as less polluted. Temperature and salinity were simultaneously measured during the mollusc samplings. They varied greatly, from 13.5 °C and 30 psu in February to much higher values in summer-autumn: 30.7 °C and 37 psu. Metal concentrations were always higher in the digestive gland than in the foot. In the digestive gland, the lowest Cd and Cu concentrations were found in the center of the lagoon (mean ± standard deviation: 9.35 ± 0.78 µg Cd g−1 and 84.5 ± 15.3 µg Cu g−1) and no significant Zn variations were noted (682 ± 38 µg g−1) between sites. Metal concentrations in both types of tissue were higher in winter than in summer. AChE varied significantly among sites with high activities for individuals in the center of lagoon (15.4 ± 0.3 nmol min−1 mg-1 protein), whereas GST were low (12.2 ± 0.8 nmol min−1 mg−1 protein); CAT activities were low in this site 8.7 ± 0.5 µmol min-1 mg-1 protein. Season also had an influence on biomarkers, with low AChE in winter and rather low CAT and GST in summer. Principal component analysis showed that the center of lagoon can be considered as a reference site, whereas high chemical and biochemical responses were found in M. trunculus from other sites; particularly at the site which may be subject to eutrophication.
Book Review
Book Notices
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- Published online by Cambridge University Press:
- 27 June 2008, pp. 221-222
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