A temperature compensated von bertalanffy growth model for tagged red drum and black drum in Texas bays

Estimates of von Bertalanffy growth model (VBGM) parameters K and L_∞ were made for red drum (Sciaenops ocellatus), and black drum (Pogonias cromis), tagged and recaptured in Texas bays from November 1975 through June 1985. An annual temperature model was used to examine the growth model when periods of cold temperature were excluded. The best fit of the VBGM for red drum was based on time at large expressed in day-degrees with the coldest 60 days of the year excluded and yielded VBGM parameters estimates (± SE) of K = 0.422 (0.023) and L_∞ = 918 (21) mm. Black drum data were best fitted with time at large expressed in days with the coldest 120 days of the year excluded and yielded VBGM parameters of K = 0.219 (0.027) and L_∞ = 798 (42) mm. The exclusion of cold periods added to the body of evidence suggesting that scales and otoliths may be useful for ageing these species in the Gulf of Mexico. The source of the tag return (recreational fishermen, commercial fishermen, Texas Parks and Wildlife personnel) affected the parameter estimates. The pooled data, however, appeared to give the most reliable estimates.     

Preliminary recovery of coastal sharks in the south‐east United States

Relative abundance of many shark species in the Atlantic is assessed by compiling data from several independently conducted, but somewhat spatially limited surveys. Although these localized surveys annually sample the same populations, resulting trends in yearly indices often conflict with one another, thereby hindering interpretation of abundance patterns at broad spatial scales. We used delta‐lognormal generalized linear models (GLMs) to generate indices of abundance for seven Atlantic coastal shark species from six fishery‐independent surveys along the US east coast and Gulf of Mexico from 1975 to 2014. These indices were further analysed using dynamic factor analysis (DFA) to produce simplified, broad‐scale common trends in relative abundance over the entire sampled distribution. Effects of drivers including the North Atlantic Oscillation index, the Atlantic Multidecadal Oscillation index, annually averaged sea surface temperature and species landings were evaluated within the DFA model. The two decadal oscillations and species landings were shown to affect shark distribution along south‐east US coast. Estimated common trends of relative abundance for all large coastal shark species showed similar decreasing patterns into the early 1990s, periods of sustained low index values thereafter and recent indications of recovery. Small coastal shark species exhibited more regional variability in their estimated common trends, such that two common trends were required to adequately describe patterns in relative abundance throughout the Gulf of Mexico and Atlantic. Overall, all species’ (except the Gulf of Mexico blacknose shark) time series concluded with an increasing trend, suggestive of initial recovery from past exploitation.     

Observations on the natural history of the Gulf of Mexico sturgeon (Acipenser oxyrinchus de sotoi Vladykov 1955) in the Suwannee River, southeastern United States

From 1986 to 1994, we collected 3,098 Gulf of Mexico sturgeon (Acipenser oxyrinchus de sotoi) during their spring migration from the Gulf of Mexico to the Suwannee River, Florida. We estimated population size and described migratory and seasonal growth patterns of sturgeon in the Suwannee River, using data from tag returns, movement of ultrasonic-lagged fish and weight records. Population size estimates for 3.0- to 81.0-kg Gulf of Mexico sturgeon in the Suwannee River ranged from 1,504 to 3,066 fish. Sturgeon migrated from the Gulf of Mexico into the Suwannee River from mid-February to early May. Fish moved upstream and remained within a 2-km upstreamdownstream “home” area. These sites were closely associated with undenvater springs that discharge into the river. Sturgeon migrated downstream and into the Gulf of Mexico in October and November. In the Gulf of Mexico, ultrasonic-tagged fish were located in the Suwannee Sound area just north of Cedar Key, Florida. On an annual basis, fish gained an average of 20% of their body weight while in the Gulf of Mexico and lost about 12% of their weight during their stay in the Suwannee River. We observed movement of tagged sturgeon between the Suwannee and Apalachicola Rivers.     

Impacts of the nonlinear relationship between abundance and its index in a tuned virtual population analysis

The abundance index used in a tuned virtual population analysis (VPA) is usually assumed to be proportional to actual abundance. However, the actual abundance and abundance index do not always have a linear relationship. Such nonlinearity can cause biases in abundance estimates as well as retrospective biases arising from systematic differences in abundance estimates when more data are successively added. Severe retrospective biases can damage the reliability of stock assessments. In this study, we use an approach to estimate an additional parameter that controls the nonlinearity in a tuned VPA. A performance test using simulated data revealed that the tuned VPA was able to accurately estimate the nonlinearity parameter and thus yielded less biased abundance estimates and smaller retrospective biases. We also found that estimating the nonlinearity parameters was effective even under other model misspecification scenarios, such as disregarding historical increases in catchability and time-varying natural mortality. Moreover, we applied this approach to some Japanese fish stocks and evaluated its validity. We found that estimating the nonlinearity parameters in the tuned VPA enhances the reliability of fisheries stock assessments.     

Performance of deviance information criterion model selection in statistical catch-at-age analysis

Most stock assessments involve fitting alternative models and selecting among them to provide management advice. Incorrect model specification can lead to unreliable population and mortality estimates, and methods to decide among assessment models so as to obtain reliable estimates are needed. We used Monte Carlo simulations to assess whether using deviance information criterion (DIC) model selection and averaging resulted in improved accuracy of important management quantities from statistical catch-at-age models. We challenged DIC with three estimation models (that differed in how they estimated catchability) and three scenarios of data accuracy and time-varying catchability. DIC usually selected the structurally appropriate model, and point estimates from the best model or the model average were relatively unbiased in that the average deviation from the true value was near zero. The distributions of point estimates about true values from DIC-based model averaging and from the best model (lowest DIC) were similar, perhaps because all of the estimation models were quite similar to the data-generating models. DIC seems to provide a useful metric to compare evidence in favor of alternative assessment models. This study is one of the first to evaluate the performance of DIC in models where the purpose is to predict unobserved quantities.     

Natural mortality of Trachurus novaezelandiae and its size selection by purse seines off south‐eastern Australia

The natural mortality (M) and purse‐seine catchability and selectivity were estimated for yellowtail scad, Trachurus novaezelandiae, Richardson, a small inshore pelagic species harvested off south‐eastern Australia. Hazard functions were applied to two decades of data describing catches (mostly stable at a mean ± SE of 315 ± 14 t p.a.) and effort (declining from a maximum of 2,289 to 642 boat days between 1999/2000 and 2015/2016) and interdispersed (over 9 years) annual estimates of size at age (0+ to 18 years) to enable survival analysis. The data were best described by a model with eight parameters, including catchability (estimated at <0.1 × 10^?7 boat/day), M (0.22/year) and variable age‐specific selection up to 6 years with a 50% retention among 5‐year‐olds (larger than the estimated age at maturation). The low catchability implied very low fishing mortality by the purse‐seine fleet. Ongoing monitoring and applied gear‐based studies are required to validate purse‐seine catchability and selectivity, but the data nevertheless imply T. novaezelandiae could incur additional fishing effort and, in doing so, alleviate pressure on other regional small pelagics.     

Population dynamics and stock assessment of Wanshan Spring Decapterus maruadsi (T. & S.) in South China Sea

The general production model of Deriso-Schnute is modified to assess the stock of Wanshan Spring Decapterus maruadsi (T. & S.) in the South China Sea, using catch/effort data from 1960 to 1984. Limited data on age composition and growth were available and these were used to estimate growth parameters, the natural survival rate and proportions of fish recruiting at early ages. Stock-recruitment and catchability parameters were estimated by fitting the catch/effort data to the Deriso-Schnute model, using nonlinear parameter estimation. Equilibrium analysis for the fitted model suggests that the virginal stock was ∼63 600 tons, of which the maximum average yield is close to 17 900 tons and would be associated with an average biomass of ∼30 000 tons. To take this maximum would require approximately the present annual fishing capacity of 250 fishing boats, producing a 0.60 annual harvest rate. The present stock is at the lowest level on record; different recovery and management strategies were evaluated by computer simulations. Only ∼3 years would be needed for the stock to recover to optimum equilibrium biomass with no fishing, but it is suggested that a longer recovery period, under reduced fishing effort, would be preferable.     

Incorporating cannibalism into an age-structured model for the Chilean hake

We incorporated predation equations from the multispecies virtual population analysis model MSVPA into an age-structured model for the Chilean hake (Merluccius gayi gayi) to estimate cannibalism. Two models, model I with constant natural mortality and the MSM, were fitted to the total annual catch, spawning biomass from acoustic surveys and length composition data from fishery and acoustic surveys. Model I fitted the data better than MSM. The majority of the MSM estimates of adult population and spawning biomass were larger than the model I estimates; probably due to the choice of residual mortality M1. High estimates of predation mortality were observed for age-0 hake. In spite of a decreasing fishing mortality, the spawning biomass decreased in the last years. Preliminary MSM results suggest that this might be due to an increase in cannibalism. A sensitivity analysis suggested all response variables were not sensible to the “other food” parameter but sensible to M1 and the predator annual ration. MSM is a promising approach that introduces the predation mortality equations into a statistical framework, allowing the incorporation of the uncertainty in the estimation of the parameters and the use of standard statistical tools in a multispecies context. This approach will contribute to provide useful information on the indirect effects of fishing on non-target species to fisheries managers.     

Re‐evaluating the effect of wind on recruitment in Gulf of Maine Atlantic Cod (Gadus morhua) using an environmentally‐explicit stock recruitment model

A previous study documented a correlation between Atlantic Cod (Gadus morhua) recruitment in the Gulf of Maine and an annual index of the north component of May winds. This correlation was supported by modeling studies that indicated strong recruitment of Gulf of Maine Atlantic Cod results from high retention of spring‐spawned larvae in years when winds were predominately out of the north, which favor downwelling. We re‐evaluated this relationship using updated recruitment estimates and found that the correlation decreased between recruitment and wind. The original relationship was largely driven by two recruitment estimates, one of which (2005 year‐class) was highly uncertain because it was near the terminal year of the assessment. With additional data, the updated assessment estimated lower recruitment for the 2005 year‐class, which consequently lowered the correlation between recruitment and wind. We then investigated whether an environmentally‐explicit stock recruit function that incorporated an annual wind index was supported by either the original or updated assessment output. Although incorporation of the annual wind index produced a better fitting model, the uncertainty in the estimated parameters and the implied unexploited conditions were not appropriate for providing management advice. These results suggest the need for caution in the development of environmentally‐explicit stock recruitment relationships, in particular when basing relationships and hypotheses on recruitment estimates from the terminal years of stock assessment models. More broadly, this study highlights a number of sources of uncertainty that should be considered when analyzes are performed on the output of stock assessment models.     

A multispecies stock assessment of a pelagic coastal fishery of the south-west Gulf of Mexico

Abstract. Multispecies stock assessment based upon Schaefer's theory was applied to a coastal pelagic fishery (Spanish mackerel, Scomberomorus maculatus (Mitchill); king mackerel, S. cavalla (Cuvier) and the blue runner, Caranx fusus (Geoffroy-St Hilaire)), from the west central Gulf of Mexico. Linear and non-linear systems of equations were estimated by using a multiple stepwise regression technique. The values of interaction parameters show a clear competition between mackerels, and technological interdependences between the blue runner and mackerels, The maximum yield estimation was from 4000 to 5000 tonnes, obtained with 23 and 34 beach seines respectively, depending on the applied model. Two stages were observed from the statistical records; in the first the Spanish mackerel is the most important species while in the second the abundance of this species declines and the others remain at the same level. Significant interactions were found from the first data group.     

Maximum likelihood and Bayesian approaches to stock assessment when data are questionable

This study examines the use of age-structured maximum likelihood and Bayesian approaches for stock assessment of the Namibian monkfish, Lophius vomerinus, resource with questionable data, in which time series are short, abundance indices are variable, and research data conflict with commercial data. Bayesian approaches with both noninformative and informative priors are investigated to determine if they enhance estimation stability. Three data scenarios are assessed: commercial and research survey data, research survey data only, and commercial data only. Both statistical approaches show that resource abundance has decreased with exploitable biomass estimated at approximately 44% of pristine levels. The maximum likelihood and the Bayesian approach with noninformative priors result in similar estimates. As the abundance data contained little information pertaining to possible density dependence within the stock–recruit relationship, only a Bayesian approach with informative priors reduces uncertainty in the steepness parameter h. Estimated management quantities are sensitive both to the set of data sources and whether prior information was informative or not. The strengths of the Bayesian approach include the integration of prior information with uncertain data, the exploration of data conflicts, and the ability to show the uncertainty in estimates of management parameters. Its weakness is that estimation stability is dependent on the choice of priors, which alters some posterior distributions of management quantities.     

Dual-gear approach for calibrating electric fishing capture efficiency and abundance estimates

Abstract  Electric fishing depletion systematically underestimates fish abundance in streams. Electric fishing mark-recapture estimates are unbiased, but only when performed over several days to allow marked fish to recover from electric fishing. A mark-recapture procedure that can be performed in 1 day and produces unbiased population estimates is described. It involves minnow trapping, marking and releasing juvenile salmonids in a stop-netted reach, followed by electric fishing the reach 1 h after release of marked fish. Recapture of marked fish during electric fishing can form the basis of a dual-gear mark-recapture population estimate, or an unbiased estimate of electric fishing capture efficiency. The marking technique did not affect short-term catchability of the target species ( P  =   0.823), and provided unbiased estimates of capture efficiency (0.38–0.40) that were similar to those documented by other researchers. However, local validation to confirm equal catchability of marked and unmarked fish, as described in this study, is recommended.     

采样设计对估计矛尾虾虎鱼体长-体质量关系参数b的影响

鱼类体长-体重关系参数估计的准确与否影响进一步的渔业资源评估和管理。不同采样设计获得的生物学数据,对鱼类体长-体重关系参数b估计可能会有一定的影响。本文基于2013-2014年在黄河口水域调查获得的矛尾虾虎鱼(Chaemrichthys stigmatias)体长、体重数据,采用计算机模拟重抽样方法,选取相对估计误差和相对偏差两个指标,比较了不同采样设计对估计矛尾虾虎鱼体长-体重关系参数b的影响。结果表明,增加样本量可有效提高其体长-体重关系参数b的估计精度。不同季节数据对参数估计精度具有不同影响,应用多季节调查采样数据估计参数精度往往优于单季节采样。夏季数据对矛尾虾虎鱼体长-体重关系参数估计尤为重要。方案9(夏-冬季方案)在样本量达到540尾时,相对估计误差REE为2.08%,相对偏差RB的绝对值为0.71%,在相同样本量下该设计方案表现最好。在估计黄河口矛尾虾虎鱼等鱼类体长-体重关系参数时,应保证获得一定样本量的对参数估计具有较大影响的季节的生物学数据。     

Brown shrimp (Farfantepenaeus aztecus) density distribution in the Northern Gulf of Mexico: an approach using boosted regression trees

The estuarine‐dependent brown shrimp, Farfantepenaeus aztecus, is a significant commercial fishery and important species in the Gulf of Mexico (GOM) ecosystem as well as being a key component in energy transfer between benthic and pelagic food web systems. Because of the economical and ecological importance of brown shrimp, we developed a spatial population model to identify places of high shrimp density under a set of spatial, environmental and temporal variables in the Northern Gulf of Mexico (NGOM). We used fisheries‐independent data collected by the Southeast Area Monitoring and Assessment Program (SEAMAP) from 1992 to 2007 (summer and fall seasons). The relationship between the predictor variables and shrimp density was modeled using Boosted Regression Trees (BRT). Within the environmental variables included in the model, bottom type and depth of the water column were the most important predictors of shrimp density in the NGOM. Spatial predictions performed using the trained BRT model for summer and fall seasons showed a spatial segregation of shrimp density. During the summer, higher densities were predicted near the Texas and Louisiana coast and during the fall, higher densities were predicted further offshore. The model performed well and allowed successful prediction of brown shrimp hot spots in the NGOM. Model results allow fisheries managers to evaluate the potential impact from fisheries on the resource and to develop future fisheries management strategies, understand the biology of brown shrimp as well as assess the potential impacts of oil spills or climate change.     

基于Bootstrap的ELEFAN方法在评估方氏云鳚群体生长参数中的应用

渔业数据有限性是小型渔业资源评估所面临的常见问题。电子体长频率分析(electroniclengthfrequency analysis,ELEFAN)常用于年龄数据难以获取或缺失的渔业,但该方法的可靠性尚待检验。本研究根据2013―2018年春、秋季共11个航次的海州湾底拖网调查数据,分别使用传统的ELEFAN与结合Bootstrap的ELEFAN方法,比较了2013―2015年与2016―2018年两个时间段内海州湾方氏云鳚(Pholis fangi)群体von-Bertalanffy生长方程中参数之间的变化。结果显示,在海州湾海域,方氏云鳚的生长参数具有显著变化, 2013―2018年,群体的极限体长变小,生长速率加快,说明海州湾方氏云鳚群体近年来呈现小型化的趋势。相比传统的ELEFAN方法,结合Bootstrap的ELEFAN方法能够给出较为稳健的参数估计,受采样随机性的影响较小,可以较好地应用于数据缺乏的小型渔业中。本研究加深了对方氏云鳚种群动态的认识,并推动了基于体长频率的生长参数估算方法在数据有限资源评估中的应用。     

Catchability of Atlantic salmon at high water temperatures: Implications for river closure temperature thresholds to catch and release angling

Warming water temperatures, combined with increased mortality following catch and release, could have synergistic consequences if rivers remain open to catch and release at high water temperatures, and catchability of fish remains similar across water temperatures. Here archived data for Atlantic salmon, Salmo salar L., were used to (a) quantify the influence of water temperature on catchability and (b) refine estimates of absolute catch and release mortality to incorporate the relationship between temperature and catchability. A significant decline in the number of Atlantic salmon caught at warmer water temperatures was found after accounting for the effects of river water height, fishing effort, run duration and year-to-year differences in fish abundance. Overall, absolute catch and release mortalities were predicted to be infrequent at cool river temperatures. At river temperatures sometimes associated with fishing closures, mortality due to the catch and release ranged from 6% to 14%. Although post-release mortality increases with water temperature, it is somewhat compensated by the reduced catchability of Atlantic salmon. Thus, the catchability component of catch and release is an integral consideration when evaluating the effectiveness of river closure temperature thresholds when managing catch and release angling.     

种群模拟在渔业资源评估中的研究现状及展望

随着渔业资源评估理论、数理统计方法和计算机技术的进步, 资源评估模型朝着多样化和复杂化不断发展, 其中种群模拟技术是检测模型适用性和局限性的重要手段。该技术由种群仿真理念发展而来, 通过模拟“真实”种群的方式, 对资源评估结果和管理策略进行有效的评价和预测, 并凭借可结合海洋环境因子、鱼类洄游空间分布以及多鱼种渔业进行资源评估的特性, 已成为开发新资源的重要评估方法之一。为此, 本文对种群模拟的结构和发展过程进行了回顾, 对该技术的核心组成部分操作模型和常见的四类误差(过程误差、观测误差、模型结构误差和管理误差)展开分类讨论。此外, 本文还结合近年来迅速发展的数据缺乏和数据适中模型的特点, 根据实际应用案例对种群模拟的作用和使用前景进行梳理, 并就种群模拟技术发展中存在的主要问题和潜在解决办法提出分析和建议。     

Genetic diversity of immature Kemp's ridley (Lepidochelys kempii) sea turtles from the northern Gulf of Mexico

1. The Kemp’s ridley (Lepidochelys kempii) is the world’s most endangered sea turtle species. Predominately nesting at only one beach in Mexico, this species declined to an estimated 300 females in the mid-1980s. Conservation efforts in the United States and Mexico, including a head start programme in southern Texas in which hatchlings were reared in captivity for several months before being released into the wild, resulted in the recovery of this species.
2. Although genetic data have previously been used to assess the success of the head start programme and dispersal of individual adults, data on immature turtles sampled at foraging areas and adult females sampled at the main nesting beach in Mexico are lacking. Genetic characterization of immature individuals is important for understanding recruitment, survival, and population demography, while genetic data on individuals from Mexico are essential for understanding dispersal and overall genetic diversity in this species.
3. To address these gaps, mitochondrial DNA data were collected from 106 immature individuals sampled at four different foraging sites in the northern Gulf of Mexico and from 18 nesting females at the primary nesting beach in Mexico.
4. Two previously unknown mitochondrial DNA haplotypes were discovered among the immature individuals.
5. Except for these two new haplotypes, the genetic diversity of immature individuals in the northern Gulf of Mexico closely corresponds to that of adults sampled in Mexico, which suggests that much of the diversity within the nesting population can be found among immature animals dispersing to foraging grounds, including locations in the northern Gulf of Mexico.
6. Continued monitoring of the genetic variation of different life stages of this species across its distribution range will help assess the success of conservation programmes by ensuring the maintenance of genetic diversity and representation of this diversity across the species’ distribution range.

     

Potential distribution and population trends of the smalltail shark Carcharhinus porosus inferred from species distribution models and historical catch data

1. Updated distribution ranges are crucial for conservation status assessments. Comprehensive analyses combining published literature and available data on historical catches and species distribution models (SDMs) are effective tools that could improve the prediction of more realistic scenarios for some species, especially those with limited information available and facing multiple threats.
2. The present study aimed at generating an updated distribution for the smalltail shark Carcharhinus porosus, one of the most threatened and understudied shark species of the western Atlantic Ocean. Estimates of the key areas for this species conservation based on the SDMs, and trends in catch probabilities throughout its distribution range are provided.
3. Four algorithms (BIOCLIM, Domain, Mahalanobis, and Maximum Entropy) were used to model the distribution of C. porosus and calculate its habitat suitability based on marine environmental variables. To assess historical catch probability trends, we built a generalized linear model from published and grey literature data. This analysis was used to estimate catch probability as an indication of population trends.
4. SDMs suggest that the northern coast of South America (NCSA) harbours the most suitable habitats for C. porosus in the world, which was expected given its historically high catch rate in this region. In addition, there was a continuously declining catch probability trend starting in the 1970s. However, the decline was smaller for the NCSA as compared with the Gulf of Mexico and the eastern South America coast.
5. Results indicate that the NCSA should be considered the currently most important area in the world for this species conservation. Furthermore, the lack of data throughout Central and South American marine regions hampers the evaluation of extinction risk throughout its updated distribution. Thus, research in these areas is urgently required for a more comprehensive conservation status assessment.