Length Frequency Data Research Articles

Integrating size-structured assessment and bioeconomic management advice in Australia's northern prawn fishery

Abstract Punt, A. E., Deng, R. A., Dichmont, C. M., Kompas, T., Venables, W. N., Zhou, S., Pascoe, S., Hutton, T., Kenyon, R., van der Velde, T., and Kienzle, M. 2010. Integrating size-structured assessment and bioeconomic management advice in Australia's northern prawn fishery. – ICES Journal of Marine Science, 67: 1785–1801. Three species in Australia's northern prawn fishery (Penaeus semisulcatus, P. esculentus, and Metapenaeus endeavouri) are assessed using a size-structured population model that operates on a weekly time-step. The parameters of this multispecies population model are estimated using data on catches, catch rates, length frequency data from surveys and the fishery, and tag release–recapture data. The model allows for the technical interaction among the three species. The results from the multispecies stock assessment are used to calculate the time-series of catches and levels of fishing effort that maximize net present value. The bioeconomic model takes into account costs which are proportional to catches and those which are proportional to fishing effort, as well as fixed costs. The sensitivity of the results is examined by changing the assumptions regarding the values for the economic parameters of the bioeconomic model as well as those on which the assessment are based. The results suggest that fishing effort needs to be reduced in the short term to achieve economic goals, although most stocks are estimated currently to be above the stock size corresponding to maximum sustainable yield. Short-term catches and effort levels are sensitive to model assumptions, and in particular, to trends in prices and costs.

Exploring the population dynamics of winter skate (Leucoraja ocellata) in the Georges Bank region using a statistical catch-at-age model incorporating length, migration, and recruitment process errors

Winter skate ( Leucoraja ocellata ) of all length classes increased dramatically in abundance on Georges Bank in the 1980s following the decline of many groundfish species. We present a full population model of winter skate to better understand the population dynamics of the species and elucidate the mechanisms underlying their increase in abundance in the 1980s. Specifically, we developed four statistical catch-at-age models incorporating length-frequency data with the following model structures: (i) observation error only (base model R1); (ii) observation and recruitment process errors (model R2); (iii) adult migration modeled as a random walk in adult mortality (model R3); and (iv) observation and recruitment process errors and adult migration (model R4). Akaike’s information criterion values indicated that models R3 and R4, which both included adult migration, were the most parsimonious models. This finding strongly suggests that the winter skate population increase on Georges Bank in the 1980s was not solely a result of increases in recruitment but likely involved adult migration (i.e., it is an open population). Finally, recent predicted fishing mortalities exceeded FMSY for all models.

Population structure and stock assessment of Hoplias malabaricus (Characiformes: Erythrinidae) caught by artisanal fishermen in river-reservoir transition area in Brazil

Hoplias malabaricus is a viable economic alternative for artisanal fishermen who used to live on the banks of rivers that now are dammed in Brazil. In order to preserve the species' natural stock, the main objectives of this study were to obtain bio-ecological information on this species reproduction, feeding dynamics and the description of the extent of its exploitation in river-reservoir transition area in Brazil. This way, from January to December 2005, different fishery catches were made with gill nets by artisanal fishermen, and a total of 426 individual H. malabaricus were obtained and sampled. From each specimen, the following biometric and biological data were analyzed: standard length, total weight, stomach contents, reproductive data such as sex, weight and gonadal maturation stage; with these data we estimated sex ratio, reproduction period and feeding habits. To assess growth parameters and infer on the degree of exploitation, the standard length frequency data were analysed using the FISAT (ELEFAN I) computer program. Data revealed a sex ratio of 0.8:1 (M:F), that reproduction occurs all year around, being more intense during spring and summer; it also showed that H. malabaricus is piscivorous. The growth parameters and mortality were estimated at: L(infinity) = 35.18 cm, k = 0.32 year, longevity = 9.3 years, Z = 1.25 years, M = 0.63 year and F = 0.62 year. The weight-length relationship was: In Wt = -3.1663+2.7456 In Lp. The yield-per-recruit analysis produced the following values: E = 0.496, E(max) = 0.916, E0.1 = 0.701 and E0.5 = 0.378. Overall, our data suggest that the stock of H. malabaricus is not yet overfished in the studied area.

Photo-based approach as an alternative method for collection of albacore ( Thunnus alalunga) length frequency from longline vessels

Length frequency data are essential to the stock assessments of albacore ( Thunnus alalunga) which has been either fully- or over-exploited in many regions of the world. To obtain ‘visible’ and verifiable length data, a photo-based length measurement approach was previously developed in which fishers take photos of fish adjacent to a plastic calibration board with colored squares using ordinary digital camera technology. Here we assess the feasibility of implementing the photo-based approach using direct comparisons with measured lengths from observer programs. Data from the Taiwanese longline albacore fishery are used to assess the utility of the photo approach in terms of accuracy (with considerations of on-board photographing and at-land length estimation) and cost (comparing with port-sampling and observer programs). Results indicate potentially significant cost savings compared with the other two programs, with acceptable levels of estimation error.

Breeding seasonality and population dynamics of the catfish Schilbe mystus (Schilbeidae) in the Cross River, Nigeria

Twelve consecutive months length frequency data (N = 6999) and FiSAT software were used in the study of the dynamics of exploited population the catfish Schilbe mystus in the Cross River Nigeria. Variation in monthly mean gonadosmtic index showed two peaks, March and September and this indicates that the species spawned twice in a year. Fitting the seasonalized von Bertalantffy growth function to our length frequency data gave the following growth parameters: L∞ = 38 cm, k = 0.33 y-1, C = 0.42 and WP = 0.96. The seasonalized length converted catch curve procedure gave the instantaneous total mortality coefficient Z = 2.97 y-1, the instantaneous natural mortality coefficient M = 0.81 Y-1, the instantaneous fishing mortality coefficient F = 2.16 y-1 and the current exploitation rate E = 0.73. This high value of E points to the high fishing pressure on the stock. The analysis of probability of capture of each length class showed that the length at first capture Lc 28.67cm. The predicted maximum exploitation rate of Emax = 0.59. This stock was deemed overexploited because E>Emax. Relative yield isopleths were used to demonstrate the response of relative yield per recruit of the fish to variation Lc and E. Suitable management procedure must be instituted to avoid the collapse of the fishery.Keywords: Breeding, population dynamics, Schilbe mystus Cross River estuary.

Growth parameters and mortality rates of Liza klunzingeri in the Iranian waters of the Persian Gulf and Oman Sea, using Length Frequency Data

The aim of the present study was to investigate the population dynamics of Liza klunzingeri , in Hormouzgan province waters located in northern coasts of the Persian Gulf and Oman Sea. This study was carried out from October 2007 to September 2008. samples were collected from commercial stake traps. The relationship between weight and fork length was found to be W= 0.0214 F.L 2.8233 suggesting that Liza klunzingeri shows isometric growth. Lengthbased stock assessment using the FiSAT software package showed an asymptotic length (L �) of 20.3cm FL and growth coefficient of 0.6.yr -1 . These results gave a growth performance index (o) of 2.39. The total mortality coefficient was estimated to be 2.31, a natural mortality of 1.09 and fishing mortality of 1.22. The estimated total mortality which, in relative terms, is considered average (2.31.yr -1 ), coupled with the currently observed exploitation rate of 0.52 for L. klunzingeri , estimated from the mortality rates, suggested that the species is moderately exploited.

Artisanal Fishery of the Exploited Population of Macrobrachium vollenhovenii Herklot 1857 (Crustacea; Palaemonidae) in the Asu River, Southeast Nigeria

River prawn in Nigeria sustains viable commercial fisheries, which, however, are poorly studied. In this study we evaluated the migrant prawn fishery in the Asu River and the relevance of length-frequency data to the estimation of Macrobrachium vollenhovenii population dynamics using the data collected monthly from January 2007 to December 2008. The length-frequency data were analysed using the FAO-ICLARM stock assessment tool. Over 80% of captured prawns were M. vollenhovenii with peak catches attained in July. Growth parameters of L∞ = 23.65 cm, K = 1.14 year-1 and (t0) = -1.45, were estimated. The estimated longevity of 2.10 years and the growth performance index (Φ') of 2.80 compared favourably with the available information on the species, authenticating reliability of our results. The instantaneous rate of total mortality estimated from the length-converted catch curve was 6.47 years-1. Natural and fishing mortality were 2.14 years-1 and 4.33 years-1 respectively, which yielded the exploitation rate...

Population size structure indices and growth standards forSalmo (trutta) truttaLinnaeus, 1758 in Central Italy

The purpose of this study was to provide reference data on the growth and population structure of brown trout Salmo (trutta ) trutta Linnaeus, in Central Italy. Standards for growth (percentiles and a standard growth model) were developed from the von Bertalanffy growth model by using length-at-age data obtained from 122 sampling sites in the River Tiber basin. Length-frequency indices provide a numeric estimation for deviations of the population structure from a balanced population. We adapted the traditional North American Relative Stock Density (RSD) and Proportional Stock Density (PSD) indices to brown trout populations in Central Italy by means of two methods. In the first method, the benchmarks of length categories were established by using percentages applied to the largest individual in the dataset. In the second method, asymptotic length and size at maturity were used to define the length categories for index calculation. Both methods were tested on length-frequency data from 263 sampling sites in the River Tiber basin. The results showed that the PSD calculated by the first method provided a better insight into the population structures of brown trout.These results provide tools that will help ichthyologists and fish managers to compare the growth and population structure of brown trout throughout Central Italy.

A Likelihood-Based Model of Fish Growth With Multiple Length Frequency Data

A Likelihood-Based Model of Fish Growth With Multiple Length Frequency Data

Exploratory analysis of spatial–temporal patterns in length–frequency data: An example of distributional regression trees

Understanding the spatial–temporal distributions of fish populations is important for their assessment and management. Given the complex structure often present in fisheries length–frequency samples, there is a need for flexible statistical techniques to explore patterns with these types of data. We present a multivariate regression tree method for binned frequencies that uses the Kullback–Leibler divergence to measure node heterogeneity. To illustrate this approach, we apply the method to length–frequency data for yellowfin tuna caught in the purse-seine fishery of the eastern Pacific Ocean.

Length-weight and length-length relationships of three endemic butterflyfish species (Chaetodontidae) from coral reefs of the Northwestern Hawaiian Islands, USA

Summary Length–weight and length–length relationships are presented for three species of butterflyfish endemic to the Hawaiian Islands and Johnston Atoll. From specimens collected within the Papahānaumokuākea Marine National Monument (PMNM), the weight–length relationships were determined for Chaetodon fremblii as W = 0.029SL3.17, Chaetodon miliaris as W = 0.042 SL3.00, and Chaetodon multicinctus as W = 0.029SL3.19 where weight, W, is reported in grams and standard length, SL, in centimeters. Length-frequency data and equations to calculate total length from standard length are also presented.

Population dynamics of the Giant African River prawn <i>Macrobrachium vollenhovenii</i> Herklots 1857 (Crustacea, Palaemonidae) in the Cross River Estuary, Nigeria

Growth, mortality, recruitment, yield-per-recruit and present rate of exploitation of the African river prawn Macrobrachium vollenhovenii were studied in the Cross River Estuary, Nigeria. The research was based on length-frequency data collected between January 1997 and June 1998, and FAO-ICLARM Software (FiSAT) routine runs. Growth parameters obtained from the seasonalized von Bertalanffy growth function were L‡ 213.63 and 198.99 mm, K = 1.24/year and 1.24/year; C = 0.95 and 0.95; WP = 0.6 and 0.45, for M. vollenovenii males and females, respectively. Using the seasonalized length-converted catch curves, the instantaneous rate of total mortality Z was estimated as 3.93/year and 6.85/year for males and females. Natural mortality M, fishing mortality F, and exploitation rate E of both sexes were 2.21/year and 2.27/year, 1.72/year and 4.58/year, and 0.44 and 0.67, respectively. The length at first capture Lc estimated from the probability of capture routine was 44.25 mm and 73.41 mm for males and females. One recruitment peak was observed for males, and two of unequal strength for females. Length-weight relationship gave ebf values of 3.483 and 3.329 for males and females, respectively. The relative yield-per-recruit analysis predicted maximum exploitation rates (Emax) of 0.42 and 0.47 as against current exploitation rates of 0.44 and 0.67 for males and females and suggest that only female M. vollenhovenii are being over-exploited. Hence, it is proposed that fishing on females during the reproductive season is reduced, and that the return of egg-bearing females into the waters is enforced.

Using length-frequency data to elucidate the population dynamics ofArgulus foliaceus(Crustacea: Branchiura)

This study uses a novel method for discriminating cohorts and investigating the population dynamics of the parasitic crustacean, Argulus foliaceus. Analysis of parasite length-frequency data was carried out in order to elucidate the timings and drivers behind the parasite's life cycle. Up to 6 cohorts of the parasite emerge through the course of 1 year in still-water trout fisheries in England. Recruitment ceases over the winter months; however, 3 cohorts of the parasite over-winter, 2 as eggs and 1 as a hatched stage. The technique, when used in conjunction with temperature data, also allowed for the reliable prediction of growth rates and provided estimates of egg incubation times and the length of hatching periods. These data showed that growth rates increased exponentially between the observed temperatures of 4 to 22 degrees C. The method allowed for the time taken from hatching to egg laying under field conditions to be predicted and produced estimates that were validated against independent laboratory studies on the growth of the parasite.

Difficulties associated with modeling growth in the Atlantic angel shark ( Squatina dumeril)

Several methods were used in an attempt to develop an age and growth model for the Atlantic angel shark ( Squatina dumeril). Band counts from vertebral sections, which were fit to the traditional von Bertalanffy growth equation, the Gompertz growth equation, and the two-parameter von Bertalanffy growth equation, did not produce realistic parameter estimates. Additionally, a length-based Bayesian model was applied to fishery-independent length–frequency data, and a full Bayesian model was fitted to length-at-age data to estimate parameters for von Bertalanffy growth equation. Both the length-based and full Bayesian models failed to converge; the length–frequency data showed high bimodality unrelated to season, year, or other factors, and band counts were not predictable by length. Vertebral band counts were not valid for ageing Atlantic angel sharks, and length-based methods, which require normally distributed length–frequencies, were not appropriate for this data set. This study represents the first attempt at modeling age and growth for this species and provides research guidelines for future research initiatives.

Growth and mortality of the fish Citharichthys xanthostigma (Pleuronectiformes: Paralichthyidae) off the Western coast of Baja California, México

Longfin sanddab (Citharichthys xanthostigma) represents a very important fishery resource in Southern and Baja California but are not very well known. The purpose of this study is to provide information on the growth and mortality of longfin sanddab population in the Mexican Pacific Ocean at Baja California, México. Data on growth were obtained for longfin sanddab collected with otter trawls during six cruises off the Western coast of Baja California. A total of 1017 longfin sanddab were caught over the sampling period, and from 860 specimens, the male to female ratio was 1:1.8. The relationship between total weight (W) and standard length (SL) is described: W=0.00000743 SL(3.196) for females and W=0.00000764 SL(3.193) for males. Age groups were estimated from length frequency data, and von Bertalanffy annual growth parameters for all fish data combined were the following: L infinity=289.2 mm SL, k=0.20, t0=-0.73; for males, they were L infinity=265.9 mm SL, k=0.21, t0=-0.68, and for females, L infinity=293.6 mm SL, k=0.23, t0=-0.35. Longfin sanddab caught during this study reached a maximum age of 10 years, and at that age, males attained smaller sizes than females. The age groups had a total mortality (Z) rate of 0.82 year(-1), a fishing mortality (F) of 0.52 year(-1), and a natural mortality (M) of 0.3 year(-1). Although the longfin sanddab is not a target species of commercial fisheries, it suffers high mortality as part of the bycatch in the shrimp fishery.

Recruitment Pattern Of <i>Macrobrachium vollenhovenii</i> In The Lagos – Lekki Lagoon System, Nigeria

Recruitment pattern of Macrobrachium vollenhovenii in the Lagos – Lekki Lagoon System was estimated from a time series length-frequency data of two years (April 2002 – May 2004). The annual recruitment pattern was estimate through back-projection, along a trajectory defined by the von Bertalanffy Growth Formula (VBGF) of the restructured data onto the time axis. M. vollenhovenii from the Lagos Lagoon exhibited two peaks of unequal pulse strength. The peaks of the smaller sized prawn for M. vollenhovenii were noted in September to November and in February. The recruitment pattern exhibited, revealed that for sustainability of this resource exploitation should be avoided in the months of September to November and also in February, as this would allow the young recruits to grow and reproduce thereby ensuring resource sustainability. Keywords : Recruitment Pattern, Pulse Strength, Macrobrachium vollenhovenii , Resource Sustainability, Lagos – Lekki Lagoon System. The Zoologist Vol. 6 2008: pp. 55-60

Systematic Errors in Length Frequency Data and their Effect on Age‐Structured Stock Assessment Models and Management

AbstractLength frequency data are a central component of many statistical age‐structured models, which are used widely to conduct fisheries stock assessments and produce estimates of stock status for management. However, these data can be biased due to systematic errors during the sampling process. This study examined how bias in length frequency data affected stock status estimates from an age‐structured assessment model and subsequent prescribed management actions. A simulation approach was used to test the effect of two different scenarios of bias on assessment results. Populations were simulated based on life history parameters for three different serranid species in the southeastern United States and followed a trajectory that increased and then decreased over time. From these simulated populations, fishery‐dependent length frequency data were generated and then altered to represent different types of systematic sampling error. Data that were biased towards larger fish had a considerable effect on the age‐structured assessment model, producing more‐optimistic estimates of stock status, which tended to support management actions that would not adequately protect stocks from overfishing. This may be particularly problematic for longer‐lived species and for stocks that have been depleted well below their original population size. Stock status estimates were much less affected by data that contained a higher frequency of small fish, although this type of biased length frequency information could support unnecessarily stringent management actions in the most extreme cases. The results of this study suggest that error and possible bias in length frequency data should be thoroughly considered when selecting an appropriate modeling approach for fisheries stock assessment.

Age Composition, Growth, and Density‐Dependent Mortality in Juvenile Red Snapper Estimated from Observer Data from the Gulf of Mexico Penaeid Shrimp Fishery

AbstractBeginning in May 1998, the National Marine Fisheries Service has required that bycatch reduction devices be installed in penaeid shrimp trawl gear in the Gulf of Mexico. Changes in observer protocols were introduced, one of which was that all of the red snapper Lutjanus campechanus collected would be enumerated and measured when possible. This change has yielded catch and length information from the Gulf of Mexico shrimp fishery. To date, however, an integrated approach to determining the age composition, growth, and mortality of juvenile red snapper has not been attempted. To address this problem, we constructed a length‐based, age‐structured model to objectively estimate the growth and mortality parameters and age composition of the shrimp trawl bycatch of red snapper in the western Gulf of Mexico from 81 monthly length frequency data sets (a total of 239,521 fish were measured) from July 1999 to February 2007. Our modeling strategy was to make simple and straightforward representations of the deviations in growth from the mean trend, partial recruitment, density‐dependent mortality, and population dynamics. Bayesian parameter estimation was accomplished by calculating the mode of the posterior distribution. Important findings of this paper include (1) the shrimp trawl bycatch during the first and third trimesters is dominated (86–87%) by age‐0 fish, (2) the growth patterns of age‐0 and age‐1 red snapper suggest that the fish form an opaque annulus in winter months, (3) the natural mortality of age‐0 fish appears to be about double (a minimum 70% increase) the value used in the last stock assessment, and (4) the evidence for density‐dependent juvenile mortality is overwhelming. Inclusion of these findings in the red snapper stock assessment has the potential to substantially alter management practices.

Life History Aspects of the Black Madtom, Noturus funebris (Siluriformes: Ictaluridae), in the Cahaba River Drainage, Central Alabama, USA

ABSTRACT The black madtom (Noturus funebris) is a diminutive catfish (maximum standard length 124 mm) found throughout the southeastern United States. Life history aspects of N. funebris were examined using 298 specimens from Blue Girth Creek, a sand-bottomed second-order tributary to the Cahaba River in Bibb County, Alabama, collected in 1987–1988. Noturus funebris was associated with undercut banks, root masses, and woody debris. The youngest reproductive female was 3 years old. Noturus funebris produces many eggs (mean = 109 ova per female) compared to other species within the subgenus Schilbeodes; however, relative fecundity (oocytes per g body weight) indicated a lower relative position in the subgenus. Analysis of gonads and presence of young-of-the-year indicated a spawning season from late June to August. One nest of N. funebris was collected in July 1988 in a glass bottle with 70 eggs. Sex ratio was nearly 1:1. In summer 2005, placement of 30 clay flowerpots as in-stream artificial nesting cavities yielded no additional nests, which suggested a preference for smaller, closed cavities. Analysis of stomach contents indicated a similar diet to other Noturus species, which consisted mainly of decapods and larvae of dipterans, mayflies, and caddisflies. Odonates made up the higher percent of diet volume in winter, crayfish in the spring, and plant material in the summer. Length-frequency data indicated four size (age) classes, with most individuals in the age 0+ and other classes containing similar proportions of individuals. A potential age-4 class consisted of three individuals greater than 108 mm SL.

The impact of water level fluctuations on the year class strength of roach: Implications for fish stock management

Water level fluctuations in a drinking water reservoir (Saidenbach Reservoir, Saxony, Germany) and length–frequency data of roach ( Rutilus rutilus) derived from gillnet catches were studied over a period of eight succeeding years and subsequently analysed with respect to level change and cohort establishment. The results indicate a strong impact of water level on the year class strength of roach. Constantly high water level with large areas of inundated plants led to a very strong roach year class. Conversely, decreasing water level shortly after the spawning period was found to result in a total loss of the new roach year class. Any other possible factors influencing year class strength of roach (such as food, temperature, winter duration) may only play a role if the water level after spawning remained relatively stable. Consequently, water quantity management in reservoirs can be used as a biomanipulation tool to reduce the planktivorous fish stock and to improve water quality, which should be an interesting option especially in drinking water reservoirs.