Fisheries for small pelagic species: an empirical approach to management targets

Summary Long-term management targets based on MSY, F_max or F_0.1 are inappropriate for small pelagic fish because of the possibility of stock collapse owing to a stock-recruit relationship at low biomasses. Better reference points such as F_med and F_high that take account of stock and recruit data cannot be used in developing fishery situations because they are too demanding of data. A simple model was fitted to medium-term (about 10 year) periods in exploited small pelagic fisheries, relating change in stock biomass to exploitation rate. Data from 28 stocks and 11 species were used. The fitted model was used to estimate likelihood of stock decrease at different exploitation rates. The pelagic stocks included in the model appeared to be in equilibrium for an exploitation rate F/Z=0.4, which may be used as a guideline for the appropriate exploitation of pelagic stocks.     

Life‐history constraints on maximum population growth for loggerhead turtles in the northwest Atlantic

Conservation planning for protected species often relies on estimates of life‐history parameters. A commonly used parameter is the instantaneous maximum population growth rate (r_max) that can be used to limit removals and design recovery targets. Estimation of r_max can be challenging because of limited availability of species‐ and population‐specific data and life‐history information. We applied a method proposed by Neil and Lebreton, originally developed for birds, to loggerhead turtles. The method uses age‐at‐first‐reproduction and adult survival to estimate r_max. We used a variety of datasets and matrix population models to confirm an allometric assumption required by the method, and to generate estimates of age‐at‐first‐reproduction and adult survival. A meta‐analysis was applied to parameters from reported growth curves, which were then combined with the size distribution of neophyte nesters to derive estimates of age‐at‐first‐reproduction. Adult survival rates were obtained from an existing matrix population model. Monte Carlo simulation was then used to combine the estimates of the allometric coefficients, age‐at‐first‐reproduction, and adult survival to obtain a probability distribution of approximate r_max values. Estimated annual maximum population growth rates averaged 0.024, with a mode of 0.017 and a 95% highest density interval of 0.006–0.047. These estimates were similar to values reported by others using different methods and captured the variability in positive, annual change estimates across nesting beach sites for the northwest Atlantic loggerhead population. The use of life‐history parameters has a long history in wildlife and fisheries management and conservation planning. Our estimates of r_max, while having some biases and uncertainty, encompassed values presently used in recovery planning for loggerhead turtles and offer additional information for the management of endangered and threatened species.     

The use and abuse of genetic marker‐based estimates of relatedness and inbreeding

Genetic marker‐based estimators remain a popular tool for measuring relatedness (r_xy) and inbreeding (F) coefficients at both the population and individual level. The performance of these estimators fluctuates with the number and variability of markers available, and the relatedness composition and demographic history of a population. Several methods are available to evaluate the reliability of the estimates of r_xy and F, some of which are implemented in the program COANCESTRY. I used the simulation module in COANCESTRY since assess the performance of marker‐based estimators of r_xy and F in a species with very low genetic diversity, New Zealand's little spotted kiwi (Apteryx owenii). I also conducted a review of published papers that have used COANCESTRY as its release to assess whether and how the reliability of the estimates of r_xy and F produced by genetic markers are being measured and reported in published studies. My simulation results show that even when the correlation between true (simulated) and estimated r_xy or F is relatively high (Pearson's r = 0.66–0.72 and 0.81–0.85, respectively) the imprecision of the estimates renders them highly unreliable on an individual basis. The literature review demonstrates that the majority of studies do not report the reliability of marker‐based estimates of r_xy and F. There is currently no standard practice for selecting the best estimator for a given data set or reporting an estimator's performance. This could lead to experimental results being interpreted out of context and render the robustness of conclusions based on measures of r_xy and F debatable.     

Demographics of Lagocephalus inermis in the Arabian Sea unveils complex conservation challenges

The first assessment of the demographics of Lagocephalus inermis, a species associated with pufferfish bites and fishing down the food web in the Arabian Sea, south-west coast of India, was performed based on length structured population dynamics of 1601 individuals caught in commercial fisheries. Analysis revealed that the current level of exploitation is 90% of the predicted exploitation producing maximum relative yield per recruit (E_max), suggesting high levels of exploitation with potential for significant negative consequences for trophic cascades.     

Population biology and status of exploitation of introduced garfish Belone belone euxini (Günther, 1866) in the Black Sea

The garfish Belone belone euxini (Günther, 1866) is a commercially important pelagic fish species in Sinop artisanal fishery, which is showing a decreasing trend in catch results. As a basis for fisheries management a sampling program was carried out between October 2000 and September 2001 along the Turkish coast of the Black Sea, to study the population structure, growth, and reproduction cycle of garfish in the area, and to achieve a rough estimate of exploitation. The length–weight relationship and von Bertalanffy growth parameters were estimated as W = 0.00076 L^3.137, L_∞ = 74.64 cm, K = 0.13 year^?1, t_o = ?3.67, respectively. First sexual maturity was estimated at age 2 and at a total length of 38.8 cm for females. The spawning period was from May to September. The total fecundity–length relationship was estimated as F = 0.0041 L^4.1086 (r² = 0.92). Mortality rates were Z = 1.24 year^?1, M = 0.23 year^?1and F = 1.01 year^?1 for total, natural, and fishing mortality, respectively. The exploitation ratio E = 0.81 indicates that the population is heavily exploited.     

Effects of variable maternal temperature on offspring development and reproduction of Rhopalosiphum padi,a serious global pest of wheat

1. Global warming is occurring at an unprecedented rate. Information about how variable temperature affects insect life-history traits is still scarce. 2. The current study first evaluated the effects of two variable-temperature treatments [high-temperature-variation (HT) treatments and mild-temperature-variation (MT) treatments] on the life-history traits of a maternal generation (F₀) of Rhopalosiphum padi, a serious global pest, using a constant normal-temperature (NT) treatment as a control. Following this, the life-history traits of the offspring generation (F₁) under the NT, MT and HT scenarios were analysed. 3. The total developmental duration of the aphid F₀ generation was significantly shortened by MT treatments, while it was significantly increased by HT treatments. Adult longevity and the fecundity of F₀ were significantly decreased by HT treatments compared with those in the MT and NT treatments, whereas no significant difference was found between the latter two treatments. The HT treatments applied to the F₀ generation significantly prolonged the total developmental duration of the F₁ generation. The offspring adult longevity was not affected by the mothers' temperature experience. The offspring fecundity was significantly increased when the F₀ generation experienced MT treatments. The intrinsic rate of increase (r_m) was significantly decreased when the F₀ generation experienced an HT scenario. However, the MT scenario experienced by the F₀ generation did not significantly affect the r_m of their offspring. 4. The results will provide new insights into the effects of variable maternal temperature on the individual development and population dynamics of offspring under a global warming scenario.     

Intrinsic rate of natural increase in Neotropical forest mammals: relationship to phylogeny and diet

Summary The relationship of diet and phylogeny to the intrinsic rate of population increase (r _max) was examined in a sample of 39 mammalian species that live in Neotropical forests. Diets of species did not predict their r _max, contrary to published predictions based on associations between basal metabolic rate and diet and between basal metabolic rate and r _max. Phylogeny did however, apparently because life history characteristics and susceptibility to predation vary predictably with phylogeny and with one another.     

A MULTISPECIES APPROACH TO THE ANALYSIS OF GENE FLOW IN MARINE SHORE FISHES

Ten species of marine shore fishes with a wide range of life-history strategies were collected from four areas in southern California, U.S.A., and Baja California, Mexico, and examined for patterns of genetic differentiation. Multilocus D and F_ST values (based on 32–42 presumptive gene loci in each species) were both negatively correlated with estimated dispersal capability. These results were robust to variations in the number and type of loci used in the analysis and are compatible with the hypothesis that levels of genetic differentiation in these shore fishes are determined primarily by gene flow and genetic drift. There is no a priori reason to expect the observed correlation to result from natural selection or historical factors. The findings thus suggest that populations of these shore fishes are in at least a quasi-equilibrium with respect to migration, mutation, and genetic drift. Present data were also used to compare estimates of mN_e obtained by three different methods. Estimates based on F_ST values calculated by the methods of Nei and Chesser (F_ST(N)) and Weir and Cockerham (F_ST(W)) were highly correlated, but F_ST(N) ≤ F_ST(W) for every species, leading to generally higher mN_e estimates for Nei and Chesser's method. Estimates of mN_e based on the frequency of private alleles (Slatkin, 1985a) were not as strongly correlated with dispersal capability as were F_ST and D values. A low incidence of private alleles in many species may be responsible for this relatively weak correlation and may limit the general usefulness of Slatkin's method. In spite of their sensitivity to natural selection, F_ST and D may be better indicators of relative gene flow levels for high gene flow species.     

Reproduction, growth, mortality and yield of Tilapia mariae Boulenger 1899 (Cichlidae) in a Nigerian rainforest wetland stream

The biology and fisheries of Tilapia mariae, the only tilapiine cichlid fish in the Iba Oku (Uyo, Nigeria) wetland stream was studied. There were more females than males in the population. The smallest sexually mature female fish was 11.0 cm total length (TL) while the size at 50% maturity was 17.1 cm TL. Absolute fecundity (F_e) ranged from 953 to 3200 eggs and was positively correlated with TL. The fish bred year‐round with peaks in November, March–April and July–September. The seasonalized von Bertalanffy growth function (VBGF) was fitted to the 12 consecutive months length–frequency data (n = 2439) to obtain a VBGF with the following parameters: L∞ (asymptotic length) = 30.4 cm TL, K (growth coefficient) = 0.4 year^?1, C (amplitude of growth oscillation) =0.4, and WP (winter point) = 0.9. The seasonalized length‐converted catch curve method gave Z (instantaneous total mortality coefficient) as 1.75 year^?1, M (instantaneous natural mortality coefficient) was 0.99 year^?1 while F (instantaneous fishing mortality coefficient) was 0.76 year^?1 and E (=F/Z the current exploitation rate) was 0.43. Length at first capture (Lc) was 17.7 cm TL. The fish was recruited to the fishery year‐round with two pulses. From the Beverton and Holt relative yield per recruit analysis via the selection ogive procedure, E_max (predicted maximum exploitation rate) was 0.54. The stock was not overexploited, since E < E_max. This study also showed that the fish is an r‐selected species with a few K‐selected traits.     

Linking seed dispersal and genetic structure of trees: a biogeographical approach

Aim Natural and human‐induced differences in frugivore assemblages can influence the seed dispersal distances of trees. An important issue in seed dispersal systems is to understand whether differences in seed dispersal distances also affect the genetic structure of mature trees. One possible approach to test for a relationship between seed dispersal and the genetic structure of mature trees is to compare the genetic structure of two closely related tree species between two biogeographical regions that differ in frugivore assemblages and seed dispersal distances. Previous studies on two Commiphora species revealed that Commiphora guillauminii in Madagascar has a much lower seed dispersal distance than Commiphora harveyi in South Africa. We tested whether the lower seed dispersal distance might have caused decreased gene flow, resulting in a stronger genetic structure in Madagascar than in South Africa. Location Madagascar and South Africa. Methods Using amplified fragment length polymorphism markers we investigated the genetic structure of 134 trees in Madagascar and 158 trees in South Africa at a local and a regional spatial scale. Results In concordance with our hypothesis, kinship analysis suggests that gene flow was restricted mostly to 3 km in Madagascar and to 30 km in South Africa. At the local spatial scale, the genetic differentiation among groups of trees within sample sites was marginally significantly higher in Madagascar (F_ST = 0.069) than in South Africa (F_ST = 0.021). However, at a regional spatial scale genetic differentiation was lower in Madagascar (F_ST = 0.053) than in South Africa (F_ST = 0.163). Main conclusions Our results show that lower seed dispersal distances of trees were linked to higher genetic differentiation of trees only at a local spatial scale. This suggests that seed dispersal affects the genetic population structure of trees at a local, but not at a regional, spatial scale.     

Marker‐based estimates of relatedness and inbreeding coefficients: an assessment of current methods

Inbreeding (F) of and relatedness (r) between individuals are now routinely calculated from marker data in studies in the fields of quantitative genetics, conservation genetics, forensics, evolution and ecology. Although definable in terms of either correlation coefficient or probability of identity by descent (IBD) relative to a reference, they are better interpreted as correlations in marker‐based analyses because the reference in practice is frequently the current sample or population whose F and r are being estimated. In such situations, negative estimates have a biological meaning, a substantial proportion of the estimates are expected to be negative, and the average estimates are close to zero for r and equivalent to F_IS for F. I show that although current r estimators were developed from the IBD‐based concept of relatedness, some of them conform to the correlation‐based concept of relatedness and some do not. The latter estimators can be modified, however, so that they estimate r as a correlation coefficient. I also show that F and r estimates can be misleading and become biased and marker dependent when a sample containing a high proportion of highly inbred and/or closely related individuals is used as reference. In analyses depending on the comparison between r (or F) estimates and a priori values expected under ideal conditions (e.g. for identifying genealogical relationship), the estimators should be used with caution.     

Assessing Allowable Take of Migratory Birds

ABSTRACT Legal removal of migratory birds from the wild occurs for several reasons, including subsistence, sport harvest, damage control, and the pet trade. We argue that harvest theory provides the basis for assessing the impact of authorized take, advance a simplified rendering of harvest theory known as potential biological removal as a useful starting point for assessing take, and demonstrate this approach with a case study of depredation control of black vultures (Coragyps atratus) in Virginia, USA. Based on data from the North American Breeding Bird Survey and other sources, we estimated that the black vulture population in Virginia was 91,190 (95% credible interval = 44,520-212,100) in 2006. Using a simple population model and available estimates of life-history parameters, we estimated the intrinsic rate of growth (r_max) to be in the range 7–14%, with 10.6% a plausible point estimate. For a take program to seek an equilibrium population size on the conservative side of the yield curve, the rate of take needs to be less than that which achieves a maximum sustained yield (0.5 × r_max). Based on the point estimate for r_max and using the lower 60% credible interval for population size to account for uncertainty, these conditions would be met if the take of black vultures in Virginia in 2006 was <3,533 birds. Based on regular monitoring data, allowable harvest should be adjusted annually to reflect changes in population size. To initiate discussion about how this assessment framework could be related to the laws and regulations that govern authorization of such take, we suggest that the Migratory Bird Treaty Act requires only that take of native migratory birds be sustainable in the long-term, that is, sustained harvest rate should be <r_max. Further, the ratio of desired harvest rate to 0.5 X r_max may be a useful metric for ascertaining the applicability of specific requirements of the National Environmental Protection Act.     

Length–weight relationships of 12 marine fish species from the Pacific coast of Guatemala associated with small-scale fisheries

The length–weight relationships (LWRs) were estimated for 12 fish species. The species were collected monthly from the commercial catch of small-scale fisheries using gillnets (mesh size 7.6–15.2 cm, length 200–1,000 m, 6–48 hr of operation during the day) and longlines (surface and bottom, 300 hooks, sardine bait, operation during the day) in the period October 2017 to July 2018 along the Pacific coast of Guatemala. Most values for the parameter (b) of the length-weight equations were within the commonly expected range (2.50–3.50) except for two species: Bagre pinnimaculatus (2.22) and Menticirrhus panamensis (3.56). All values for the coefficient of determination (r²) were above .95 and thus the estimates can be considered reliable. Besides novel LWRs we provide for some species estimates which include a new TLmax not yet involved of any LWR studies.     

Reduced Global Genetic Differentiation of Exploited Marine Fish Species

Knowledge on genetic structure is key to understand species connectivity patterns and to define the spatiotemporal scales over which conservation management plans should be designed and implemented. The distribution of genetic diversity (within and among populations) greatly influences species ability to cope and adapt to environmental changes, ultimately determining their long-term resilience to ecological disturbances. Yet, the drivers shaping connectivity and structure in marine fish populations remain elusive, as are the effects of fishing activities on genetic subdivision. To investigate these questions, we conducted a meta-analysis and compiled genetic differentiation data (F_ST/Φ_ST estimates) for more than 170 fish species from over 200 published studies globally distributed. We modeled the effects of multiple life-history traits, distance metrics, and methodological factors on observed population differentiation indices and specifically tested whether any signal arising from different exposure to fishing exploitation could be detected. Although the myriad of variables shaping genetic structure makes it challenging to isolate the influence of single drivers, results showed a significant correlation between commercial importance and genetic structure, with widespread lower population differentiation in commercially exploited species. Moreover, models indicate that variables commonly used as proxy for connectivity, such as larval pelagic duration, might be insufficient, and suggest that deep-sea species may disperse further. Overall, these results contribute to the growing body of knowledge on marine genetic connectivity and suggest a potential effect of commercial fisheries on the homogenization of genetic diversity, highlighting the need for additional research focused on dispersal ecology to ensure long-term sustainability of exploited marine species.     

Thirty‐eight single nucleotide polymorphism markers for high‐throughput genotyping of chum salmon

We characterize 38 single nucleotide polymorphism genotyping assays for chum salmon (Oncorhynchus keta), an important species for both commercial and subsistence fisheries in western Alaska. These assays are based on the 5′‐nuclease reaction and thus facilitate high‐throughput genotyping with minimal optimization time. Minor allele frequency differences (Δq) among collections were between 0.01 and 0.50 resulting in per locus F_ST estimates of 0.00–0.08 with an average of 0.03.     

ECOLOGICAL AND HISTORICAL ASSOCIATIONS OF GENE FLOW IN DARTERS (TELEOSTEI: PERCIDAE)

Life history should relate to gene flow (Nm) through its influence on dispersal and effective population size. Comparative studies designed to elucidate this relationship must contend with historical events that can yield misleading estimates of gene flow and statistical problems associated with inclusion of life-history traits correlated with phylogeny. We studied the relationships of life-history characters and gene flow in 15 species of darters, a monophyletic group of stream fishes. Populations of coexisting species were sampled in three geographic regions with different Pleistocene glaciation histories. Gene flow was estimated indirectly from allozymes using two methods, 8 and private alleles. Isolation-by-distance was also tested using regression of pairwise estimates of gene flow (M?) on distance. Theta and private-alleles methods produced congruent estimates of Nm, except in a study region hypothesized to have been historically fragmented and then united following Pleistocene glaciation. A relatively weak association between life-history traits and Nm (based on θ) was observed when species from the historically fragmented region were included in stepwise regression analysis, because Nm was low despite life-history differences among taxa in this region. Excluding observations from this region produced stronger associations between clutch size and Nm (r² = 0.57), and between female size, egg size, and Nm (r² = 0.95). Additional analyses that corrected for female body size and phylogenetic nonindependence agreed that darters with high fecundity and small eggs exhibited high gene flow, whereas darters with small clutches and large eggs had low gene flow. The latter combination of life-history traits primarily is exhibited in species from headwater habitats where parental investment presumably confers survivorship on offspring. Reduced gene flow and genetic divergence among demes appear to be evolutionary consequences of this strategy.     

Design and use of a simulation model to evaluate germplasm for antibiotic resistance to the greenhouse whitefly (Trialeurodes vaporariorum) and the sweetpotato whitefly (Bemisia tabaci)

SARAH (Software for theAssessment of antibioticResistance toAleyrodidae inHost plants) is a deterministic simulation model of whitefly population growth based on whitefly life-history components determined on individual plants. The life-history components recorded were oviposition rate, adult survival, pre-adult survival, developmental period, and sex ratio. The simulation model serves as a tool to combine these components and to obtain a single criterion for (antibiotic) resistance. The criterion used was the decrease in simulated intrinsic population growth rate, r _s , relative the r _s value determined on a susceptible control genotype. This model-based evaluation method was tested using the greenhouse whitefly,Trialeurodes vaporariorum Westwood, on tomato and the sweetpotato whitefly,Bemisia tabaci Gennadius, on tomato, eggplant, collard, and pepper. To study its consistency over time, the evaluation method was repeated six times forT. vaporariorum on a susceptible and a resistant tomato cultivar. Simulated intrinsic population growth rate was more consistent in indicating resistance than any of the individual life-history components. Of tenL. hirsutum accessions tested for resistance toT. vaporariorum, three exhibited r _s values that were significantly lower than those for the susceptible control. In addition, on these tenL. hirsutum accessions, a significant positive correlation was observed between r _s and sex ratio (# females/# males). Four host plant species (tomato, collard, eggplant, and pepper) were evaluated for resistance toB. tabaci. All life-history components and r _s values varied among host species, while a negative r _s value was observed forB. tabaci on pepper. A high correlation was found between results from a sensitivity analysis of SARAH and results from a sensitivity analysis of a validated whitefly population simulation model by Yanoet al. (1989a). Significant correlations were found for the relationships between oviposition rate, adult survival, or pre-adult survival and r _s , indicating that none of these life-history components can be omitted from the test procedure. This model-based evaluation method offers a standardized way to quantify levels of antibiotic resistance to whiteflies and will enhance efficiency in breeding programs.     

Accounting for wildlife life-history strategies when modeling stochastic density-dependent populations: A review

This article briefly reviews and provides discussion on the evidence for, and nature of, density-dependence patterns in r and K-selected species. In this review, I discuss how life-history strategies cause different nonlinear density-dependence patterns and I provide a simple modeling recommendation to incorporate nonlinear density dependence in population growth equations. Second, I discuss the importance of incorporation of environmental stochasticity and local extinction associated with nonlinear density dependence associated with life-history patterns through a novel modeling exercise. Last, I discuss the importance of considering how life-history nonlinear density dependence could affect optimal harvest yields. Though these topics are extensive, this review should spur wildlife biologists and managers to consider more inclusive population models that incorporate life-history strategies and stochasticity in their decision-making processes. © 2012 The Wildlife Society.     

Age, growth, maturity, mortality, and yield-per-recruit for annular sea bream (Diplodus annularis L.) from the eastern middle Adriatic Sea

The population dynamics parameters of Diplodus annularis from the eastern middle Adriatic Sea were studied. Total lengths of 1704 specimens ranging from 3.3 to 23.0 cm were obtained from commercial and fishery‐independent catches (2000–2002). The species spawns from April through the end of August, with a peak in May. Overall male to female ratio was 1.00 : 1.05. The species is a rudimentary hermaphrodite in the Adriatic Sea. Total lengths (TL) at 50% maturity were 9.0 cm for males and 10.0 cm for females. These estimated sizes were smaller than the minimum legal landing size (MLS = 15 cm) and greater than the actual minimum landing size (L_c = 7.1 cm) for the bottom trawl net. All specimens sampled were fully mature above 13 cm TL. The oldest individual was 13 years old. Length–weight relationship showed close to isometric growth (b = 3.073). Parameters of the von Bertalanffy growth equation were: L_∞ = 23.95 cm; K = 0.126 per year; t₀ = −1.664 year; r² = 0.896. The low value of total mortality (Z = 0.72) was a consequence of the relatively low rate of natural mortality (M = 0.39) and fishing mortality (F = 0.33). The exploitation ratio was E = 0.46. Estimated parameters and the relative yield‐per‐recruit analysis did not indicate any overexploitation of the species in the study area. However, the estimates include uncertainties and require further confirmation, especially of the natural mortality.