Instantaneous Mortality Research Articles

Reconstructing populations dynamics: Mortality and recruitment of the southern geoduck Panopea abbreviata

In the development of management measures for sustainable fisheries, estimating the natural mortality rate and recruitment are fundamental. In northern Patagonia, Argentina, the southern geoduck, Panopea abbreviata, a long-lived clam that forms spatially disjunct subpopulations, supports an unregulated fishery. In this study, we estimate natural mortality. We studied the age structure of beds within the northern Patagonia gulfs, San Matías Gulf (SMG) and San Jose Gulf (SJG), and we estimated a time series for back-reconstructed recruitment to explore spatial coherence in relation to local oceanographic conditions and to elucidate its population dynamics.We constructed a cumulative frequency distribution of the age of dead shells collected and used the exponential and Weibull models to model mortality. Live geoducks were sampled from six populations between 2000 and 2006. Age-frequency distributions and mortality models were used to back-calculate the time series of recruitment for each population. The recruitment time series was analysed using continuous wavelet transform.The value of natural mortality estimated by the exponential model was 0.054 years−1, whereas those estimated by the Weibull model were α = 0.00085 years−1 and β = 2.1. For the latter, M values for cohorts were 0.01 for 10 years, 0.02 for 20 years, 0.04 for 30 years and 0.05 for 40 years. The Weibull model was observed to be the best fit to the data. The natural mortality rate of P. abbreviata estimated in this study was lower than that estimated in a previous work for populations from SMG.The back-calculated time series for recruitment demonstrated considerable yearly variation, suggesting that local conditions have an important role in recruitment regulation. At a decadal temporal scale, a clear increasing recruitment trend was evident over the last 20 years in all populations. Populations in SMG were settled >60 years ago. In contrast, no individuals older than 30 years were observed in the populations from SJG.P. abbreviata has several characteristics, such as longevity and low instantaneous natural mortality rate, which require attention in any resource planning. However, this species also has positive characteristics for fishery development, as historical recruitment trends indicate that populations are expanding and are part of a widely distributed metapopulation, suggesting that sustainable exploitation is possible.

Feeding deterrent effects of legume flours against two storage mites, Tyrophagus putrescentiae (Schrank) and Suidasia medanensis Oudemans (Acari:Acaridida)

Whole legume flour and its fractions possess a potential in controlling insect pests. Information concerning the activity of various legume flours as bioacaricides against storage mites is rare. Therefore, two kinds of legume flours were obtained from common faba bean (Vicia faba L.) and pea (Pisum sativum L.) seeds to evaluate their effects on growth and development time of two species of storage mites, Tyrophagus putrescentiae (Schrank) and Suidasia medanensis Oudemans via feeding test. The diet was dusted with legume flours at seven concentrations (0, 0.01, 0.1, 0.25, 0.5, 0.75 and 1%). After 21 days, the instantaneous rate of increase (ri) and mortality of both mite species were estimated. There was a significant decrease in (ri) values of both mite populations at concentrations higher than 0.1% of both legume flours. The concentration of 1% faba bean or pea flour was responsible for 100% mortality of T. putrescentiae and S. medanensis. Based on the LD50 and LD90values, pea flour was more toxic to T. putrescentiae and S. medanensis than faba bean flour. Moreover, T. putrescentiae was more sensitive than S. medanensis to legume flours. Development time of the two studied species was considerably prolonged by the addition of bean and pea flours. All tests were conducted under the optimal development conditions of storage mites. The results proved that both faba bean and pea flours possess potent acaricidal activity.

Toxic effect of lead on the fingerlings of Cirrhinus mrigala (Hamilton, 1822)

Pollution of water bodies caused by heavy metals such as lead is a major problem affecting aquatic fauna. The effect of lead on the fingerlings of fishes has not been widely investigated. The present study was undertaken to evaluate the impact of heavy metal lead on the fingerlings of the freshwater fish, Cirrhinus mrigala. Different concentrations of lead nitrate solutions, viz., 1 ppm, 10 ppm, 40 ppm, 100 ppm, 120 ppm, 160 ppm, 200 ppm, 240 ppm, 300 ppm, 400 ppm and 500 ppm were prepared. Ten fingerlings were introduced into each concentration. The mortality rate and the time of survival of fingerlings in the lead nitrate solution during next 96 hours were recorded. The mortality rate increased to a sudden plateau from 100 ppm to 200 ppm (from 10% to 100%) and total mortality was attained at 200 ppm. LC50 for the fingerlings was found to be 160 ppm. There was almost instantaneous mortality – absolute intolerance – of the fingerlings at 500 ppm. Our study results show that the fingerlings of Cirrhinus mrigala can survive the toxic effect of lead nitrate up to 40 ppm, without physiological stress.

Toxic effect of lead on the fingerlings of Cirrhinus mrigala (Hamilton, 1822)

Pollution of water bodies caused by heavy metals such as lead is a major problem affecting aquatic fauna. The effect of lead on the fingerlings of fishes has not been widely investigated. The present study was undertaken to evaluate the impact of heavy metal lead on the fingerlings of the freshwater fish, Cirrhinus mrigala. Different concentrations of lead nitrate solutions, viz., 1 ppm, 10 ppm, 40 ppm, 100 ppm, 120 ppm, 160 ppm, 200 ppm, 240 ppm, 300 ppm, 400 ppm and 500 ppm were prepared. Ten fingerlings were introduced into each concentration. The mortality rate and the time of survival of fingerlings in the lead nitrate solution during next 96 hours were recorded. The mortality rate increased to a sudden plateau from 100 ppm to 200 ppm (from 10% to 100%) and total mortality was attained at 200 ppm. LC50 for the fingerlings was found to be 160 ppm. There was almost instantaneous mortality – absolute intolerance – of the fingerlings at 500 ppm. Our study results show that the fingerlings of Cirrhinus mrigala can survive the toxic effect of lead nitrate up to 40 ppm, without physiological stress.

Assessment of natural mortality coefficients in fish stocks: a review

PDF HTML阅读 XML下载 导出引用 引用提醒 鱼类自然死亡系数评估研究进展 DOI: 作者: 作者单位: 1. 中国水产科学研究院南海水产研究所, 农业部外海渔业开发重点实验室, 广东省渔业生态环境重点实验室, 广东 广州 510300;2. 上海海洋大学 海洋科学学院, 上海 201306 作者简介: 耿平(1993-),男,硕士研究生,从事渔业资源评估研究.E-mail:bsg1030@live.com 通讯作者: 中图分类号: S931 基金项目: 国家自然科学基金项目（31602157）；农业部财政专项“南海北部近海渔业资源调查”项目（2014-2018）；公益性行业（农业）科研专项经费项目（201403008）. Assessment of natural mortality coefficients in fish stocks: a review Author: Affiliation: 1. Key Laboratory of Open-Sea Fishery Development, Ministry of Agriculture;Key Laboratory of Fishery Ecology and Environment, Guangdong Province;South China Sea Fisheries Research Institute, Chinese Academy of Fishery Sciences, Guangzhou 510300, China;2. College of Marine Sciences, Shanghai Ocean University, Shanghai 201306, China Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:自然死亡系数是渔业资源评估中不可或缺的重要参数，其准确度直接决定了资源评估结果的可靠性，进而影响渔业管理策略的制定。本文从生活史参数、标志回捕和年龄结构3个方面列举了国内外自然死亡系数的常用评估方法，讨论了相关方法的优缺点及影响因素，并以犬齿牙鲆（）和中国近海鱼类为例对比分析不同模型的计算结果。在此基础上，着重介绍了Pauly经验公式在中国近海主要经济鱼类自然死亡系数评估中的应用进展及存在问题。根据渔业资源调查和研究数据现状，认为现阶段使用Pauly经验公式评估中国近海经济鱼类自然死亡系数具有积极作用。 Abstract:Natural mortality coefficient () is a key parameter in fisheries stock assessment. Its accuracy directly determines the reliability of assessment results and also influences the establishment of fisheries management. Most mathematical models of fish stock dynamics incorporate , either directly or indirectly. Fishery scientists have explored accurate estimates of for a long time, in order to develop a more precise understanding of fish populations and to establish a more scientific basis for managing fisheries resources and sustainable development. The present study introduces and evaluates the most common models for estimating natural mortality coefficients for fish populations from three aspects, namely life-history parameters, tag-return, and age-structure. The first approach to estimate the instantaneous rate of natural mortality in fish stocks is based on the observation that is strongly correlated with life history parameters, such as maximum observed age, age at reproductive maturity, asymptotic fish length, and growth rate. The Pauly empirical equation, Gislason empirical equation, and Tanaka's maximum observed age's method are among the most commonly used methods for assessing inshore fisheries in China. By classifying tagging data, based on catch per unit effort, size at release, and the probability of tag loss, Chapman, Hampton, and Treble have each constructed their own models, and some scholars have combined these methods to develop a model that is superior to any of the individual models. The assessment results of using tag-return methods would have a high reliability, but the huge costs of investigation, lower credibility of recapture, and prior model assumptions contribute to poor generality. Considering that age is the potentially most important factor affecting estimates of , virtual population analysis (VPA) and cohort analysis (CA) are established using catch-at-age data. These methods could be used to reliably estimate fish stocks with long-term catch data. However, considering the incomplete and inaccurate statues of historical catch data in Chinese coastal fishes, the practicality of the VPA or CA models is relatively low. Meanwhile, taking and some coastal fish stocks as examples, this study compared estimation results through different methods and found that Pauly empirical equation is more reasonable to calculate . Then, this paper introduced the misapplications of Pauly empirical equation in inshore fisheries of China. The main misapplications were equation error, unit error and calculation mistake. According to the limited data and fishery exploitation status, we suggest that Pauly empirical equation has a positive meaning to assess the for major economic fish stocks in China. 参考文献 相似文献 引证文献

Relative importance of fishing and natural mortality for spotted seatrout (Cynoscion nebulosus) estimated from a tag-return model and corroborated with survey data

Abstract The spotted seatrout (Cynoscion nebulosus) is one of the most economically important sportfish in the U.S. South Atlantic and Gulf of Mexico, including at its northern distributional extent in North Carolina and Virginia. The recent stock assessment for this region used an assumed fixed rate of natural mortality (M), obtained from a general life-history relationship based on weight. However, biased estimates of fishing mortality (F) could result if the life-history proxy failed to capture either the magnitude or temporal variation in M. Data from the first comprehensive tag-return study of spotted seatrout in this region were used in a Bayesian statistical modeling framework to estimate F and M. Both laboratory and field studies, including high-reward and double tagging, were conducted to obtain estimates of auxiliary parameters (i.e., tag-reporting rate, tag loss, and tagging mortality) necessary for the tag-return model. There was no measured mortality associated with tagging, but reporting rate and loss of internal anchor tags limited returns in this study. From 2008 to 2012, tag-return model estimates of bimonthly instantaneous mortality rates ranged from 0.003 to 0.067 2-mo−1 for F and from 0.002 to 2.850 2-mo−1 for M. Annual estimates of F were much lower than M for the three years studied, and annual M-estimates were higher than those used for spotted seatrout in this region’s recent stock assessment. Bimonthly estimates of total mortality rate (Z) from tag-return data were similar to bimonthly estimates of Z from an independent analysis of concurrent gill net survey data, which corroborates the variability and magnitude of mortality estimates determined from tagging. A strong seasonal influence (i.e., winter severity) on annual loss of spotted seatrout was observed, suggesting that future assessments and management measures for this stock would be improved by explicitly accounting for temporal variation in M in models of fishery population dynamics.

Population dynamics of Atlantic seabob Xiphopenaeus kroyeri (Decapoda: Penaeidae) off the state of Sergipe, north-eastern Brazil

The aim of this study was to analyse the population dynamics of Xiphopenaeus kroyeri in Sergipe, Brazil. Four samples were collected monthly from shrimp trawlers based in the municipality of Pirambu from March 2015 to May 2016. Carapace length (CL), total length (TC), live weight (LW), sex and maturity stages were obtained for each specimen. A total of 13,035 individuals were analysed with an overall sex ratio of 1:1. However, this ratio favoured females in larger sizes, which reflects a reproductive strategy, as their larger size allows for larger gonads, higher fertility and production of more eggs. An inflexion point was observed in the relationship between total and carapace length, probably related to reproduction, as this occurred after first maturity. A reproduction peak was observed in August–September, which does not correspond to the closed season. The parameters estimated for a seasonally oscillating version of the von Bertalanffy growth function were CL∞ = 33 mm and K = 1.5 year−1 for females, and CL∞ = 31 mm and K = 1.7 year−1 for males (C = 0.6 and WP = 0.8 for both sexes). These estimates do not support the latitudinal rule in terms of larger sizes in higher latitudes, which may be associated to methodological differences, occurrence of more than one species along the South-western Atlantic coast, sampling bias, exploitation status and unbalanced availability of studies. The instantaneous total mortality rate was high and should be further investigated to allow for the definition of the exploitation status of seabobs in Sergipe.

Survival time of juvenile pen shell Atrina pectinata (Bivalvia: Pinnidae) in hyposaline water

Survival time of juvenile pen shell Atrina pectinata (shell length ≈ 34 mm) exposed to hyposaline water without sediments was investigated in laboratory experiments. The bivalves were individually maintained in rearing cups in which salinity was decreased either gradually (over 1–11 h to 12 salinities ranging from 0 to ca. 34 ppt) or rapidly (directly to 21 salinities) at 12 and 24 °C. When the environmental salinity was gradually decreased, survival time differed markedly between the bivalves exposed to: salinities ≤ 18.6 ppt (survival time < 20 h in general) vs. ≥ 21.1 ppt (> 83 h) at 24 °C; and between salinities ≤ 15.1 ppt (< 34 h) vs. ≥ 17.2 ppt (> 83 h) at 12 °C. When the environmental salinity was rapidly decreased, survival time, again, differed markedly between the bivalves exposed to: salinities ≤ 15.9 ppt (< 20 h in general) vs. ≥ 17.7 ppt (> 140 h) at 24 °C; and salinities ≤ 21.3 ppt (< 38 h in general) vs. ≥ 22.3 ppt (> 140 h) at 12 °C. Such sharp decreases in survival time due to reduced salinity led to the selected, statistical models that assume either a sharp exponential increase or stepwise hike in hazard (instantaneous mortality rate) according to salinity reduction. These data and models indicate that juvenile A. pectinata should not be kept at salinities < 21 ppt for periods > 1 day in environments without sediments.

Comparative larval growth and mortality of mesopelagic fishes and their predatory impact on zooplankton in the Kuroshio region

Larvae of mesopelagic fishes usually dominate in oceanic larval fish assemblages, but detailed investigations of their ecology are limited and thus preclude full assessment of the ecosystem structure and dynamics in oceanic waters. Here, we examined the growth and mortality of six taxa of numerically dominant mesopelagic fish larvae and their predatory impact on zooplankton in the Kuroshio region off southern Japan during late winter. The weight-specific growth coefficient (Gw) ranged from 0.077 (Sigmops gracilis) to 0.156d−1 (Vinciguerria nimbaria), and the instantaneous daily mortality coefficient (M) from 0.067 (S. gracilis) to 0.143d−1 (Myctophum asperum). The ratio Gw/M, an index of stage-specific survival of the larvae, was from 0.90 (Notoscopelus japonicus) to 1.24 (V. nimbaria), without a significant difference from a value of 1 in all species. Based on the reported relationship between Gw and ingestion rate of the larval fishes, the daily ration of each species was calculated to be 32–57% of body dry weight d−1. Mean and 95% confidence interval of food requirements of the six taxa of larvae was 1.41 ± 0.55mgCm−2d−1. Predatory impact of the mesopelagic fish larvae on the production rate of the available prey was estimated to be approximately 3.5–5.2%, implying that the larvae have a low level but consistent effect on zooplankton production in the oligotrophic Kuroshio region.

Age‐0 blue catfish habitat use and population demographics in the middle Mississippi River

AbstractThe demographics (e.g. hatch time, growth and mortality) and habitat (macrohabitat and mesohabitat) use of age‐0 blue catfish Ictalurus furcatus (Lesueur) were evaluated in the un‐impounded reach of the middle Mississippi River during 2003–2010. Each year, island complexes and adjacent main river habitats were trawled, and 7,373 age‐0 blue catfish (10–144 mm total length) were collected. Blue catfish hatch timing varied slightly across years and generally began in June and ended in August. Age‐0 blue catfish growth rates and instantaneous mortality rates differed among years. Catch rates of age‐0 blue catfish were highest in side channels and around islands, whereas main channel habitats were infrequently occupied. Regarding mesohabitat use, age‐0 blue catfish frequently occupied low velocity areas (i.e. 0.3–0.4 m/s) of shallow depth (i.e. 1–4 m) and sand substratum. This study has provided insight into age‐0 blue catfish population dynamics and has highlighted the importance of specific habitat characteristics in large rivers that may aid in recruitment of this species.

THE POPULATION DYNAMIC OF BANANA PRAWN (Penaeus merguiensis de Man) IN TANAH LAUT WATERS, SOUTH KALIMANTAN

Scientific advices on population dynamic of banana prawn (P. merguiensis de Man) are required as an input to support an apropriate fisheries management. This study aims to identify the population parameters of the banana prawn in Tanah Laut waters. The study was conducted in Tanah Laut based on monthly enumeration data (January to November 2016). Results has been shown that the length size of carapace at first maturity of banana prawn was 43.39 mm. Sex ratio of males and females was 1 : 0.8. The chi square test indicated that comparison of male and female of the banana prawn was significantly different. It means that there was not balance in number between males and females. The spawning season of banana prawn in Tanah Laut waters happened throughout year and reached the peak on November (south-east monsoon). The growth parameter of banana prawn was 1.05/year with maximum carapace length (Loo) of 55.0 mm. Instantaneous total mortality (Z) and natural mortality (M) were 6.05/year and 1.58/year, respectively. While fishing mortality (F) and exploitation rate (E) respectively were 4.47/year and 0.74/year respectively. The exploitation rate of banana prawn in Tanah Laut waters was high. Therefore, fishing effort of the banana prawn in that waters should be reduced to about 48 % for next coming year.

Age, growth, mortality and reproductive seasonality of jolthead porgy, Calamus bajonado, from Florida waters.

Ages of jolthead porgy (Calamus bajonado Schneider 1801) (n = 635) from Florida commercial and recreational fisheries from 2008–2016 were determined using sectioned sagittal otoliths. We determined, using edge-type analysis, that opaque zones were annular, forming March–June (peaking in April). Jolthead porgy ranged from 1–13 years, and the largest fish measured 680 mm TL (total length, mm). Body size relationships for jolthead porgy were TL = 1.09FL + 20.44 (n = 622, r2 = 0.99), FL = 0.90 TL –14.26 (n = 622, r2 = 0.99), and W = 1.1 × 10−5 TL3.06 (n = 577), where W is total weight (grams, g) and FL is fork length (mm). The von Bertalanffy growth equation for jolthead porgy was Lt = 737(1 − e−0.14(t+2.02)) (n = 635). Point estimate of natural mortality was M = 0.32, while age-specific estimates of M ranged from 0.58–0.17 y−1 for ages 1–13. Catch curve analysis estimated the instantaneous rate of total mortality Z = 0.70, while instantaneous rate of fishing mortality F was 0.38. Macroscopic staging of female gonads indicated the presence of hydrated oocytes from December–March, and GSI data indicates that peak spawning in females occurs during March. This study presents the first published findings of life history parameters for jolthead porgy from the Atlantic waters off the southeastern United States.

Length- and age-based demographics of exploited populations of stout whiting,Sillago robustaStead, 1908

This study assessed variability in the length and age compositions, longevity, length-at-age and rates of growth and mortality of the east Australian stout whiting Sillago robusta Stead, 1908 population harvested by demersal trawl fisheries. Sampling was done over 2 years and was spatially stratified across three depth strata between 11 and 90 m at two locations approximately 400 km apart. There were no consistent depth-related differences in length and age compositions, but the mean and median length and age of the population was greater at the lower latitude location. Age classes 2 and 3 years dominated samples in the north, and 1 and 2 years in the south. Observed longevity was 10 years in the north, and 6 years in the south. Mean length-at-age was not consistently different between sexes, years or locations, nor did the von Bertalanffy growth function differ significantly between sexes, even though females had a greater estimated L∞ (23.45 cm FL) compared to males (22.36 cm FL). Estimated natural mortality (M) ranged between 0.42 and 0.77, using age- and length-based methods. Age-based catch-curve analyses identified the instantaneous rate of total mortality (Z) to range between 1.48 and 2.70, with subsequent estimates of fishing mortality (F) ranging between 1.15 and 2.00, being greater than M. Exploitation rates (E) were greater than 0.7, indicating that S. robusta at the study locations was heavily fished. The data provided here can be used as a basis to evaluate future fishery- and climate-related changes in the population demographics of east Australian S. robusta.

Determining the growth and mortality parameters of longtail tuna (Thunnus tonggol Bleeker, 1851) using length frequency data in coastal waters of the northern Persian Gulf and Oman Sea, Iran

Longtail tuna (Thunnus tonggol) is one of the most economically important tuna species in Iranian waters of Persian Gulf and Oman Sea. Some population dynamics parameters of this species were investigated in coastal waters of the northern Persian Gulf and Oman Sea from January to December 2014. The fork length (FL) of all specimens ranged from 27 to 107 cm, and total weight (TW) was between 200 and 12,000 g. Among the length frequencies examined, specimens with fork length in the range of 62–65 cm were the dominant group. The equation of length–weight relationship was estimated as TW = 0.00003 × FL2.82 (R2 = 0.84) and isometric growth model was determined for longtail tuna in study area. The parameters of Von Bertalanffy growth function were obtained as: L∞ = 111.23 cm, k = 0.3 year−1 and t0 = −0.38 years and ϕ′ = 3.6. The annual instantaneous rate of total mortality (Z), natural mortality (M) and fishing mortality (F) was estimated to be 1.15, 0.43 and 0.72 year−1, respectively. The exploitation rate (E) was calculated as 0.63 indicating that longtail tuna was fully exploited in the study region.

Rate of natural mortality in the sea starArchaster angulatus(Echinodermata: Asteroidea)

The population size structure from a total of 876 individuals, together with published values of growth rate, maximum size and size at age were used to estimate an instantaneous rate of natural mortality (M) of 0.46–0.59 year−1in a population of the sea starArchaster angulatusfrom south-western Australia. Peak abundance (17%) of all animals sampled was 105–109 mm arm radius (means of 4.2–4.8 years of age) and only one per cent of sea stars are predicted to live beyond 8 years in the population studied. There are few comparable studies on sea stars but when compared with rates of natural mortality in other echinoderms (sea urchins),A. angulatusis intermediate among species which exhibit the extremes of life history strategies, that is, those which grow very rapidly and may live just two years or less and those with very slow growth rates and which may live for decades.

An integrated tagging model to estimate mortality rates of Albemarle Sound – Roanoke River striped bass

We developed an integrated tagging model to estimate mortality rates and run sizes of Albemarle Sound – Roanoke River striped bass (Morone saxatilis), including (i) a multistate component for telemetered fish with a high reward external tag; (ii) tag return components for fish with a low reward external or PIT tag; and (iii) catch-at-age data. Total annual instantaneous mortality was 1.08 for resident (458–899 mm total length, TL) and 0.45 for anadromous (≥900 mm TL) individuals. Annual instantaneous natural mortality was higher for resident (0.70) than for anadromous (0.21) fish due to high summer mortality in Albemarle Sound. Natural mortality for residents was substantially higher than currently assumed for stock assessment. Monthly fishing mortality from multiple sectors (including catch-and-release) corresponded to seasonal periods of legal harvest. Run size estimates were 499 000–715 000. Results and simulation suggest increasing sample size for the multistate component increases accuracy and precision of annual estimates and low reward tags are valuable for estimating monthly fishing mortality rates among sectors. Our results suggest that integrated tagging models can produce seasonal and annual mortality estimates needed for stock assessment and management.

Exploitation rates of two benthic resources across management regimes in central Chile: Evidence of illegal fishing in artisanal fisheries operating in open access areas.

There is an urgent need to quantify the impacts of artisanal fisheries and define management practices that allow for the recovery and conservation of exploited stocks. The extent of illegal catch is particularly critical as a driver of overexploitation in artisanal fisheries. However, the lack of data at proper spatial scales limits the evaluation of illegal fishing and effectiveness of management practices. We used a catch curve analysis to estimate total instantaneous mortality as a proxy of fishing pressure in the artisanal benthic fishery in central Chile. We compared the patterns of total mortality in fishing grounds under the well-studied territorial use rights for fisheries system (TURF) immersed in a landscape of open access areas (OAA; no access restriction), and from these patterns determined the extent of illegal fishing in open access areas focusing on the two most frequently extracted resources: locos (Concholepas concholepas) and keyhole limpets (Fissurella spp.). The beauty of this seascape is the presence of the no-take (NT) area of Las Cruces as control (no fishing), allowing us to estimate natural mortality. Loco exploitation is banned in OAAs. However, loco mortality in OAAs was 92% higher than in the NT, and 42% higher than in TURFs. Keyhole limpet mortality was similar between TURFs and the NT, but doubled in OAAs. We also found strong differences in mortality among fishing grounds with the same level of protection (i.e. TURFs), and over time. Our results highlight (a) the high level of illegal fishing that may occur in artisanal fisheries under traditional management regimes, and (b) that TURFs can be effective to reduce fishing mortality. However, large variability among TURFs suggests the need for a deeper understanding of the drivers of success of TURFs.

Age, growth parameters and fisheries indices for the lane snapper in the Abrolhos Bank, SW Atlantic

Otolith-based methods combined with catch lengths were used to produce three simple fishing indicators for assessing stock status of the lane snapper Lutjanus synagris in the Abrolhos Bank, central Brazilian coast. Fish were obtained during landings between May 2005 and June 2007. Marginal Increment Analyses combined with edge analysis on sectioned otoliths (n=303) confirmed annulus formation in an annual basis during June-October. Lane snapper were aged up to 18 years and the largest fish measured 56cm total length. Growth was not significantly different between sexes, and the von Bertalanffy growth equation was derived as Lt=56[1-e(−0.22(t−0.0))]. Highest cohort yield was achieved between 33.5–41.4cm (optimal length) at ages 4–6. Age at first maturity was 2.8 years, and generation length was 10 years. Instantaneous total mortality (Z) was 0.58year−1 and natural mortality rate (M) ranged from 0.17–0.36year−1. Overall indicators point out for the need to implement fish management, as 30% of catch are composed of immature individuals and 7–12% by mega-spawners. A slot limit for the lane snapper in Abrolhos Bank is proposed, with restrictions for individuals<24 and >50cm.

Growth and mortality of larval anchoveta Engraulis ringens, in northern Chile during winter and their relationship with coastal hydrographic conditions

AbstractLarval growth, age, growth effect and instantaneous mortality were estimated in anchoveta, Engraulis ringens, collected biweekly during the austral winter of 2014 in nearshore waters off Bay of Antofagasta (23°41′W–70°30′S), northern Chile. Through measuring standard length (SL) and sagitta microstructure analysis, it was estimated that the growth rate of E. ringens larvae decreased from June (0.85 mm day−1) to August (0.50 mm day−1). However, the water temperature was homogeneous during the sampling dates (14.6, 15.2, 14.4, and 14.6°C), suggesting that the decelerating larval growth was not linked to changes in sea temperature. Additionally, larvae with slow growth have larger otoliths compared with conspecifics with fast growth (growth effect). Larval mortality rates tended to decrease until the middle of July (0.18 per day) but increased to 0.25 per day in early August, which coincided with lower food availability (i.e., chlorophyll‐a, 2.7–5.6 mg m−3) and a high occurrence of smaller larvae (1.58–11.5 mm). Partial least squares analysis indicates low covariance between the biological and oceanographic variables (PLS: 11.71%), suggesting that other factors, such as parental effects, may explain the abrupt decrease in the larval growth rates.

Integrating demographic and environmental variables to calculate an egg production index for the Eastern Bering Sea snow crab (Chionoecetes opilio)

The complex life-history of the snow crab suggests that estimates of mature female biomass may not correlate proportionally with actual egg production. We calculate an egg production index (EPI) for the Eastern Bering Sea (EBS) snow crab using a simulation model that follows mature females from the molt-to-maturity through various reproductive stages (primiparous and multiparous) and reproductive cycles (annual and biennial). The model is parameterized with an estimate of annual instantaneous natural mortality, M, from a separate statistical model. The egg production model runs from 1980 to 2014, but the EPI is calculated only for 1985–2014 to be able to unambiguously assign mature females to the various component reproductive categories. Estimated M was 0.68yr−1 for 1980–2014. Linear regression of EPI lagged one year with stock assessment estimates of mature female biomass had an R2 of 0.78, but with a mean absolute percent error of 82% between observed and model predictions; mature female biomass is thus a variable and uneven predictor of egg production. On average, primiparous females contributed 46% to total annual egg production and multiparous females the remaining 54%. Multiparous females in an annual cycle made the largest contribution to the EPI, responsible for 50% of annual egg production. Sensitivity analysis showed that egg production increased by a factor of 1.75 on average when only annual spawning was assumed. Multiparous females were found to co-occur almost exclusively with larger older males, such as those targeted by the fishery; due to the large proportion of egg production from multiparous females, this co-occurrence pattern has potential fishery management implications. The EPI will allow for future recruitment and population dynamics studies to use a more accurate measure of EBS snow crab reproductive potential, especially when considering the effects of climate change and environmental variability. Further demographic research will help refine EPI estimates.