Length Frequency Distributions Research Articles

FISHERIES AND BIOLOGICAL INFORMATION OF BOTTLENOSE WEDGEFISH (Rhynchobatus australiae) IN PULAU KAMBING FISH LANDING PORT TERENGGANU

Rhynchobatus australiae is a species of wedgefish that is vulnerable to overfishing due to their life history characteristics This study aimed to determine the fisheries and biological information of R. australiae in Terengganu waters. A total of 26 fish were collected over a 3-month period in Pulau Kambing Fish Landing Port, Terengganu and analysed for abundance, length frequency distribution, LWRs, and growth parameters. Results showed that the abundance of R. australiae in Terengganu was higher compared to the estimation made in other locations, with a CPUE of 49.05 kg/haul and 9.15 kg/day. The LWRs for males, females, and pooled sexes were a = 0.0057 and b = 2.9404, a = 0.0018, b = 3.2078, and a = 0.0029, b = 3.0979, respectively. The von Bertalanffy Growth parameters for male, female, and pooled sexes of R. australiae were k = 0.035, L∞ = 332.825, t0 = -4.495, k = 1.005, L∞ = 43.161, t0 = -2.99, and k = 0.089, L∞=222.412, t0=-2.565, respectively. Males R. australiae exhibiting a higher average length than females. This study was limited in terms of the time span covered and the sample size, which may have introduced variability in the results and may not be representative of the larger fish population. However, the results of this study may serve as preliminary data for the fish population dynamics of R. australiae in Terengganu waters and could be used to guide future research. Future study with a longer time span and a larger, more diverse sample size are needed to estimate the abundance and size of R. australiae more accurately in this region.

Pertumbuhan Ikan Tongkol Abu-Abu (Thunnus tonggol Bleeker, 1851) yang Tertangkap di Perairan Selat Bali

Longtail Tuna (Thunnus tonggol) in the waters of the Bali Strait is a by-catch fish, so that information on this fish resource was still very lacking and its management of longtail tuna was often neglected. The aimed of this study is to predict the signs of the unsustainability of longtail tuna resources based on growth aspects which include the distribution of length frequency, estimation of age groups, growth patterns and growth parameters. Data collection was carried out from December 2018 to February 2019. The growth pattern estimated by relationship of length and weight, cohort was identified using an analytical model based on the FISAT program (FAO I-CLARM Stock Assessment Tools) and growth parameters were analyzed using the Von Bertalanffy growth model. It can be seen that, the catch is dominated by the size of the fish that have matured gonads or adults (69% females and 73% males). The growth pattern of female and male of longtail tuna is negative allometric (length growth is more dominant than weight). So it can be assumed that there is an inconvenience in environmental conditions and competition in fighting for food and space in the waters of the Bali Strait.Longtail tuna had asymptotic length values of 784.71 mm (female) and 738.04 mm (male) with growth coefficients of 0.13 (female) and 0.18 (male). The growth performance inteprated as quite high when compared to other waters in Indonesia.

When the Trawl Ban Is a Good Option: Opportunities to Restore Fish Biomass and Size Structure in a Mediterranean Fisheries Restricted Area

This paper reports the results of a 15-year trawl ban imposed in 1990 in the Gulf of Castellammare (GCAST: NW Sicily, central Mediterranean Sea) and its effects on the biomass and size structure of demersal finfish and shellfish and on the proportion of different commercial categories of fish. Data were collected by experimental trawl surveys conducted in the GCAST and in two trawled areas before and after 1990. The biomass of the total assemblage and of a number of selected species was significantly higher in the GCAST after the ban. Highly commercial species had the largest increase in the same gulf after the ban, particularly at the depths used by artisanal fishermen. The results from size-based indicators were not as clear-cut as those from biomass though. Although the length frequency distributions obtained in the GCAST were significantly different from the other gulfs, in several cases, the values of the size indicators were higher in the trawled gulfs. Our results suggest that, at the temporal and spatial scale adopted, trawl bans may drive full biomass recovery but only partial size structure recovery of the fish populations subject to trawl exclusion, at least in the Mediterranean. The trawl ban in the Gulf of Castellammare provides an example of an effective ecosystem-based fisheries management tool that offers the potential for fish stock rebuilding and for the economic sustainability of artisanal, small-scale fisheries.

Some biological aspects of Mediterranean mud shrimp, Upogebia pusilla (Petagna, 1792) in the Boka Kotorska Bay, Southeastern Adriatic Sea

Biological aspects (length frequency distribution, length-weight ratio, sex ratio, allometric growth, Fulton?s condition factor) of Upogebia pusilla were studied in Tivat Saline (Tivatska solila), Boka Kotorska Bay in 2019. A total of 1,415 individuals were collected. The total length of all studied individuals ranged from 27 to 55 mm (8 and 20 mm CL), while the total weights ranged from 0.29 to 2.56 g (the total length of males ranged from 27 to 51 mm, non-ovigerous and ovigerous females ranged from 27 to 51 mm and 30 to 55 mm, respectively; the weights ranged from 0.29 to 2.52 g, 0.34 to 2.52 g and 0.47 to 2.56 g for males, non-ovigerous and ovoid females, respectively). The overall female:male ratio was 1.2:1. Ovigerous females were recorded from April (74.3%) to June (23.8%), with a peak in May (91.4% of all females). Males dominated in July (66.4%). The relationship between CL and W was negatively allometric in both males and females and in all sampled individuals. Fulton?s condition factor was higher only in females during the breeding season, while there were no significant differences between males and females during the rest of the year. Since this species is mainly used as live bait for commercial and sports fishermen, the results of this study would be useful for the sustainable management of this species.

Assessment of size structures, length-weight models and condition factors of Eleotridae (Pisces: Perciformes: Gobiodei) from the coastal waters of Benin (West Africa)

The Eleotridae is one of the fish family widely distributed in the Benin coastal waters where the species constitute an important component of artisanal fisheries. The current study evaluates length frequency distributions, length-weight models and condition factors of Eleotrid fishes in order to assess their wellbeing in the degrading coastal waters of Benin. Fish samplings were made during eighteen (18) consecutive months and morphometric data were recorded and analyzed using SPSS computer software. Larger Eleotrids were Eleotris vittata, E. senegalensis, E. daganensis and Bostrychus africanus while Dormitator lebretonis, the most abundant species displayed small sizes (standard length) ranging between 1.2 - 11.30 cm. Overall, all the species showed unimodal size distributions except Eleotris daganensis that exhibited a bimodal size distribution in Lake Nokoué. Length-weight models showed allometric growth with slopes b ranging between 2.4725 and 3.7296 along with significant correlation coefficients (r) varying between 0.7695 and 0.9965. Condition factors (K) varied significantly across the four (4) coastal waters and ranged between 0.79 (Dormitator lebretonis) and 3.60 (Eleotris daganensis). The sustainable exploitation of Eleotrid fishes in the Benin coastal waters requires a holistic approach of ecosystem management including ecological follow-up, habitat restauration and species valorization.

Age and growth of Pomatomus saltatrix in the south-western Pacific Ocean (eastern Australia), with a global comparison

Context Pomatomus saltatrix is one of few globally distributed pelagic mesopredators that is exploited heavily throughout its range. Despite the implementation of management strategies, the south-western Pacific Ocean (eastern Australian) population has few published estimates of the key life-history parameters including growth. Aims To estimate the age and growth of P. saltatrix in the south-western Pacific and compare these with the age and growth in other populations. Methods Age estimates were made using whole otolith readings and an age–length key was used with a length frequency distribution to estimate the age structure of the population. Eight different growth models were compared within a Bayesian framework for both juvenile and overall growth. Key results The Schnute growth equation provided the best fit for overall growth and yielded parameter values of a = −0.15, b = 2.56, Size-at-age 1 = 24.38-cm fork length (FL) and Size-at-age 4 = 47.36 cm FL. Conclusions P. saltatrix in the south-western Pacific has a growth rate similar to that in other populations of P. saltatrix. Implications Despite its geographically and genetically distinct populations, P. saltatrix demonstrates a generally consistent life-history strategy of fast growth and high mortality, except for the north-western Atlantic population, which has lower mortality.

A comparison of growth of a vulnerable species, common carp, Cyprinus carpio (Actinopteri: Cyprinidae), from two different reservoir types in the same river basin

Context The mechanisms underlying regional differences in growth parameters of common carp, Cyprinus carpio Linnaeus, 1758 (Actinopteri: Cyprinidae), are not yet fully understood, because comparisons among them have been made post hoc. Aims To simultaneously compare growth of common carp between sexes and between regions: Demirköprü Reservoir (DR) and Marmara Lake (ML), which have different structures (lowland type vs highland type) and are proximate to each other in the same river basin (Gediz River Basin). Methods Length-frequency distributions, length–weight relationships and three growth models (von Bertalanffy growth function (VBGF), Gompertz growth function (GGF) and Robertson growth function (RGF)) were used for both sexes and all individuals in reservoirs. Key results As none of the best-fitting models used among these growth models clearly suggested a ‘clear winner’ (Akaike’s weight (wi) > 0.9), the model-averaged multi-model inference (MMI) was used for the first time for common carp. Conclusions Asymptotic length obtained from MMI for all individuals in ML (lowland type) was statistically higher than that in DR (highland type) (P < 0.05). Implications Based on the maximum observed length and the mean L∞ obtained from MMI, the common carp population in the DR can be considered threatened by overfishing.

Small-scale differences in blue cod length distribution, growth, and trophic ecology in New Zealand

Growth and reproduction in marine fish populations can be strongly influenced by local habitat quality and nutritional resources. Habitat degradation can alter prey composition and availability, and, consequently, trophic position and dietary niche breadth of marine fish. In the present study, we compared length-frequency distributions, growth, stomach contents, and isotopic values (δ13C and δ15N) of blue cod Parapercis colias subpopulations from biogenic reef habitats and habitats that were more strongly influenced by shellfish dredges and fine sediment in New Zealand. Blue cod inhabiting more degraded regions were significantly smaller and relied on different prey items than blue cod from biogenic reef habitats. Results indicated that the isotopic niche areas of blue cod occupying degraded habitats were smaller than those of blue cod inhabiting relatively undisturbed biogenic reefs. Isotope mixing models demonstrated that blue cod from one of the biogenic reef regions relied predominantly on suspended particulate organic matter, while blue cod from the other biogenic and degraded regions primarily relied on macroalgae as their organic matter source. Dietary niche overlap was likely higher for blue cod from degraded habitats, with potential consequences for growth and reproduction. Blue cod inhabiting biogenic reefs showed a high degree of individual specialisation. The present study demonstrated that differences in length distribution, growth, and trophic ecology among blue cod subpopulations coincided with differences in habitat degradation. Ecosystem-based management solutions can help regenerate high-quality biogenic habitats while reducing fisheries mortality within these critical habitats.

Biometric evaluation of Gangetic pool barb Puntius sophore (Hamilton, 1822) from the River Ganga, Bihar, India

The Gangetic pool barb Puntius sophore (Hamilton, 1822) is widely distributed in the freshwater ecosystems of the Indian subcontinent and it is reasonably well-priced due to its nutritional value. A study was conducted to assess the morphometry, length-frequency distribution (LFD), length-weight relationship (LWR), condition factor (CF) and sex ratio of P. sophore collected from the Digha GhatPatipul in Patna, between March 2019 and February 2020. Fifteen morphometric characters and nine meristic counts of 137 specimens were examined for biometric evaluation and 982 samples (1.56-22.09 g TW, 51.06-115.11 mm TL) were analysed for LFD, LWR and CF, respectively. LFD revealed that 28.49% of the males sampled were in the 75-80 mm length class, while 15.94% of the total females sampled were in the 70-75 mm length class. In morphometric analysis, significant correlations were found across the variables and the highest correlation was observed between total length and standard length (r>0.981). LWR exponent value showed positive allometric growth patterns for male, female, and combined sexes, respectively. Condition factor showed no significant variation between the sexes and the observed average values were 1.06 and 1.24 for males and females, respectively (p<0.05). Analysis of the sex ratio showed that females outnumbered males from the 85-90 mm length group onwards and no male specimens were found beyond the 105-110 mm length group.Keywords: Condition factor, Length-weight relationship, Morphometry, P. sophore, Sex ratio

Control Copepod Abundances and Kilka Catch by Invasive Predator Mnemiopsis leidyi A. Agassiz, 1868 in the Southern Caspian Sea

The Caspian Sea has a variety of species and groups of aquatic animals, e.g., plankton and fishes that are exploited, unfortunately in the past decade, this sea has entered and expelled of some non-indigenous species such as ctenophore Mnemiopsis leidyi, Copepods Acartia tonsa, Balanidae Balanus improvisus and Mullets Lisa saliens have caused major changes in the Sea. One of the species got common in the coastal waters is M. leidyi with the highest biomass in summer at the temperature of 25-30 °C, and the highest abundance was observed in autumn while the minimum density was in winter of 8-10 °C. The ctenophore distribution of length frequency indicated that while 83% of the population consists of larval and immature organisms, only less than 17% belonged to the adult group in the costal waters of the Caspian. The largest size of the jelly was 70 mm long in the southern Caspian Sea in September 2002. Based on the jelly food consumption, the Nauplius, copepodites and adults of Acartia tonsa consisted 66% and bivalves was 13% in the Caspian. Therefore, it seems the reduction of the comb jelly compared to its early year's invasion was due to the reduction of edible zooplankton especially A. tonsa in the southern of the Caspian Sea. During 2001-2013, Kilka catches amount was decreased to ~15000 kg from 95000 kg in 1996 with the changes of Clupeidae species composition of Clupeonella engrauliformis to C. cultriventris caspia.

Length frequency distribution, growth, and condition factor of the endemic cyprinid fish Poropuntius tawarensis, in Lake Laut Tawar, Central Aceh, Indonesia

The Poropuntius tawarensis fish is an endemic fish of the family Cyprinidae found in Laut Tawar Lake, and has been listed on the Red List. This study aims to reveal the frequency of length distribution, growth patterns and condition factors of the fish in the lake as basic information for conservation. The study was conducted from January to May 2022 in the Laut Tawar Lake of Central Aceh. Sampling was conducted at four sampling sites based on representative activities on the lake. The location of the study was determined based on differences in environmental characteristics, namely Station 1 (Teluk One-One), Station 2 (Bewang), Station 3 (Gegarang) and Station 4 (Kebayakan). The results showed that the fish at Bewang Station was relatively higher in terms of the frequency of the length distribution. The growth pattern of male and female fish was negative allometric (b<3).The condition factor of the three stations was relatively the same ranging from 0.94 to 1.39, but it was different from the one-one station with a condition factor of 0.01.The value of the condition factor that can be obtained had insignificant differences every month, namely 1.12±0.38 (January), 1.00±0.49 (February), 0.93±0.55 (March), 0.85±0.59 (April), and 1.17±0.32 (May).

Phenotypic divergence and biometric indices of silond catfish, Silonia silondia (Hamilton 1822) populations inhabiting the coastal rivers of Bangladesh

To observe phenotypic differentiation among populations of Silond catfish, Silonia silondia (Hamilton 1822), a multilinear approach was used. A sum of 180 samples from three coastal rivers (Meghna, Payra, and Kirtankhola) of the Bangladesh coast were scooped up to comprehend whether distinct populations of S. silondia could be separated from one another due to adaptive divergence. The findings of this study reflect the first attempt to determine the stock structure, morphological characters, length-frequency distributions, length-length relationships, length-weight relationships, condition factors, relative weight, and form factor of S. silondia in the coastal rivers of Bangladesh. Important discrepancies between the means of the three populations were revealed using univariate and multivariate analysis of variance (p < 0.01). In principal component analysis, the first and second principal components described 83.546% and 4.302% of the total variation, respectively. The step-wise discriminant function analysis revealed two variables that separated the populations significantly. Besides, a dendrogram based on Euclidean distances accurately separated the populations. In a one-way analysis of variance study, nineteen out of twenty-one morphometric characters showed significant variation (p < 0.01)among three populations. The length parameters based on the length-length relationships of each sample were found to be highly significant (p < 0.01). The length-weight relationships exhibited that the b value fluctuated from 2.796 (Kirtankhola) to 3.498 (Meghna). The Fulton's condition factor was estimated in the current study for this species with an average value ranging from 1.12 to 1.35. The calculated form factor values of this species were 0.0016, 0.0054, and 0.0110 for Meghna, Payra, and Kirtankhola river, respectively. Therefore, this study will expectantly inform fisheries taxonomists about the species' current stock structure, intraspecific phenotypic divergences, and aid in its management and conservation in similar ecosystems in Bangladesh and around the world.

Life history and population structure of the Antarctic icefish, Pagetopsis maculata (Notothenioidei, Channichthyidae) from the Weddell Sea

The life history traits of many large-sized and commercial Antarctic icefishes are reasonably well known, except for smaller species such as Pagetopsis maculata Barsukov and Permitin, 1958. Therefore, we provide, for the first-time, data on growth and reproductive biology of this species based on a representative sample collected in the Weddell Sea during summer. Individual age and gonad stage of development were assessed by sagittal otolith readings and histological analysis of gonads respectively. The sampled population had an equal sex ratio and was composed of adult specimens spread over a wide size range. Both sexes exhibited isometric body growth and comparable condition factors. The estimated life span and growth parameters were similar between sexes, although females attained a larger asymptotic size than males, consistent with the length-frequency distributions. Typically, the reproductive investment of females, based on the gonadosomatic index, was larger than in males, although they both attained sexual maturity at a similar size. Most individuals were at an advanced stage of gonad maturity, indicating imminent spawning in late summer-early autumn. Compared to other icefish species with different geographical distributions, maximum sizes and lifestyles, P. maculata had the lowest growth performance and reproductive investment, primarily because of its smaller body size.

Ice fishing reveals size structure but not abundance of Eurasian perch in small boreal lakes

AbstractManagement of inland recreational fisheries would benefit from stock abundance and size structure data. Feasibly standardised angling methods such as ice fishing could produce representative catch‐per‐unit‐effort (CPUE) information on the abundance of different‐sized fish in small lakes. Here, we first used standard Nordic multimesh gillnets to obtain number‐per‐unit‐effort (NPUE), biomass‐per‐unit‐effort (BPUE) and size structure data on Eurasian perch (Perca fluviatilis) stocks in 11 small boreal lakes in summer. Second, the same lakes were ice‐fished by voluntary anglers using a pre‐defined, loosely standardised protocol to obtain angling‐based NPUE, BPUE, and length frequency distributions. Effects of environmental variables such as water oxygen concentration and light penetration on angling catch rates were controlled statistically. Neither perch Nordic gillnet NPUE nor BPUE corresponded to ice‐fishing CPUEs. However, the length distribution of the catch did not differ between methods. Our results imply that traditional ice fishing applying natural baits is relatively unselective for fish size and could produce valid length‐based indicators for management purposes while angling CPUE was poorly related to Nordic gillnet CPUE.

PENANGKAPAN TUNA MADIDIHANG (THUNNUS ALBACARES) DENGAN PANCING ULUR OLEH NELAYAN KECAMATAN AMAHAI KABUPATEN MALUKU TENGAH

One of the fishery commodities with high economic value is tuna, where in the Maluku region in 2021, tuna production will be 35.56% (BPS, 2022). Tuna is caught using handlines which are classified as small-scale fisheries. The existence of tuna that changes over time causes fishermen to experience uncertainty in finding suitable fishing areas. Temperature is an important indicator in the distribution and abundance of tuna. This study aims to determine the composition of the hand line catch and to analyze the temperature distribution based on the area of ​​the hand line fishing operation in Central Maluku Regency. The research was conducted in the waters with the method used is a survey method by following fishing trips and using GPS satellite-based Spot Trace to track vessel movement activities during fishing operations. Descriptive data analysis was used to determine the composition of fisherman catches and used SeaWiFS Data Analysis System (SEADAS) 7.3.1 and Surfer 12 to analyze the distribution of water temperatures at fishing locations. The results showed that yellowfin tuna (Thunnus albacares) dominated the catch by 70.30%, bigeye tuna (Thunnus obesus) by 20.19% and skipjack tuna (Katsuwonus pelamis) by 0.52%. The frequency distribution of yellowfin tuna length ranges from 23-171 cmFL where during 2019 it was dominated by sizes &lt;100 cmFL as much as 82.42%. The SST range in January is 290C-310C, optimal fishing is at 29.80C-30.40C, April is in the range of 30.20C-31.70C, optimal fishing is at 30.90C-31.30C, in May is in the range of 27.40C-31,40C the optimal catch is in the temperature range of 27.80C -30.80C, in June is 27.40C -280C the optimal catch is in the temperature range 27.60C-27.850C, in September 27.40C-29.50C the optimal catch is at a temperature range of 27, 80C -28.50C, and in December the range of 29.40C-31.50C is optimal for catching at a temperature range of 30.40C -31.20C

Estimation of population structure, growth and condition of Parastromateus niger in the Bay of Bengal

Black pomfret (Parastromateus niger) is one of the major commercial species of pomfret fishery in Bangladesh. This study illustrates the population structure (Length Frequency Distribution, LFD), relationship between length and weight (LWR), relationships between length and length (LLRs), Fulton’s condition factor (KF) and relative weight (WR) of P. niger in the Bay of Bengal (BoB). A total of 225 P. niger were collected from the four locations during January to December 2020. LFD analysis indicates three length classes 21-27 cm, 30-32 cm and 35-37 cm, respectively. This species showed isometric growth pattern (b = 2.981) that indicates that the size and weight increases proportionally and the surrounding habitat provides favourable environment for the growth. LWR between TL and BW were highly correlated (r² = 0.951). LLRs also showed significant correlation between TL and SL (r² = 0.845) and TL and FL (r² = 0.861). The mean value of KF was found as 1.60 which indicates that the BoB provides healthy environment for this species. The mean value of WR (101.09) indicates that the relationship between prey and predator was in balanced condition. This study suggests optimum catchable length for P. niger at 27 cm. Therefore, these findings could provide important information to design effective conservation and management planning for this species.

Estimation of life history parameters for river catfish Eutropiichthys vacha: insights from multi-models for sustainable management

The river catfish, Eutropiichthys vacha is a vital protein source for rural communities and has high commercial value, but understanding its life history and management strategies reveals major inadequacies and ambiguities in the riverine ecosystems. Consequently, this study employs multi-models to analyze the life history parameters of E. vacha in the Ganges River (northwestern Bangladesh) from January to December, 2020. The total length (TL) and body weight (BW) of 362 individuals (male = 170, female = 192) were measured by a measuring board and a digital weighing balance, respectively. The overall sex ratio (male: female) was 1.0: 1.13 and did not oscillate statistically from the standard 1:1 ratio (p > 0.05). The TL varied from 6.7–19.2 cm for males and 6.3–19.0 cm for females. The length-frequency distributions (LFDs) revealed females outnumbered in 8.0–9.99 cm TL whereas males in 7.0–7.99 cm TL. The slope (b) of the length-weight relationship (TL vs. BW) for both sexes (b = 2.87) was substantially lower than isometry, specifying negative allometric growth pattern for E. vacha. Sex-specific relative (KR) and Fulton’s (KF) condition analysis revealed better state of well-being of males than females. Only KF exhibited significant correlation with both BW and TL, hence making it ideal condition for predicting the fitness of E. vacha in this river. Moreover, the relative weight (WR) suggests an imbalanced habitat for females with higher abundance of predators but suitable for males. The form factor (a3.0) was 0.0062 and 0.0065, whereas the size at first maturity (Lm) and mean natural mortality (MW) were 11.38 and 11.27 cm TL and 1.29 and 1.28 year−1 for the respective sexes. Besides, the calculated mean optimum catchable length (Lopt) was 13.58 and 13.09 cm TL for each sex. These findings will be crucial for further studies and to recommend appropriate strategy for the sustainable management of E. vacha in the Ganges River and adjacent watersheds.

Spatial and temporal analysis (2009–2020) of the biological parameters, abundance and distribution of Trachurus mediterraneus (Steindachner, 1868) in the Western Mediterranean

Trachurus mediterraneus is captured as by catch by the fishing fleet in the Spanish Mediterranean and usually landed as the global category of Trachurus spp., consequently there is a prominent lack of biological data on this species. The knowledge of the spatial and temporal evolution of its distribution, abundance and main biological parameters is essential to achieve a proper management and sustainable exploitation. Data collected in the MEDiterranean International Acoustic Survey (MEDIAS) 2009–2020 time series, carried out in July, has been analyzed to determine the evolution of the main ecological aspects of T. mediterraneus in two GFCM management units: Northern Spain (GSA06) and Northern Alboran Sea (GSA01). The results suggest a possible neritic distribution of T. mediterraneus, mainly concentrated at depths less than 60 m in GSA01 and up to 105 m in GSA06, as well as the existence of significant differences in abundance and length frequency distributions among GSAs. Furthermore, preliminary results regarding T. mediterraneus age and growth seemed to indicate a faster growth during the first two years in GSA01 than in GSA06. In both areas, potential changes in the life history traits of this species were evidenced, with a decreasing trend in the size at first maturity and condition factor over the years. Finally, five persistent distribution areas were located along the study area, highlighting Málaga Bay as a possible recruitment ground. The relevance of this study lies in the growing need for robust and current biological data of intermediate species in the marine food web and it contributes to the global purpose of achieving an integrated management of fishery resources.

Krill biomass estimation: Sampling and measurement variability

Krill are the subject of growing commercial fisheries and therefore fisheries management is necessary to ensure long-term sustainability. Krill catch limits, set by Commission for the Conservation of Antarctic Marine Living Resources, are based on absolute krill biomass, estimated from acoustic-trawl surveys. In this work, we develop a method for determining an error budget for acoustic-trawl surveys of krill which includes sampling and measurement variability. We use our error budget method to examine the sensitivity of biomass estimates to parameters in acoustic target strength (TS) models, length frequency distribution and length to wetmass relationships derived from net data. We determined that the average coefficient of variation (CV) of estimated biomass was 17.7% and the average CV due from scaling acoustic observations to biomass density was 5.3%. We found that a large proportion of the variability of biomass estimates is due to the krill orientation distribution, a parameter in the TS model. Orientation distributions with narrow standard deviations were found to emphasise the results of nulls in the TS to length relationship, which has to potential to lead to biologically implausible results.

Estimating growth from length frequency distribution: comparison of ELEFAN and Bayesian approaches for red endeavour prawns (Metapenaeus ensis)

Abstract Using length frequency distribution data (LFD) is cost-effective for estimating somatic growth in fish or invertebrates as length data are relatively easy to obtain. The recently developed R packages TropFishR and fishboot extend classic ELEFAN (Electronic LEngth Frequency ANalysis) programs and include more powerful optimization procedures and a bootstrap method for estimating uncertainties. Yet, the fundamental functions require users to provide search conditions (e.g. upper and lower limits for each parameter, length-class size, number of length-classes for the calculation of moving average), which can significantly affect the results. In this paper, we compare the ELEFAN approach with a Bayesian approach in analysing LFD, employing both standard and seasonal von Bertalanffy growth functions. We apply both approaches to a commercially valuable but poorly studied red endeavour prawn (Metapenaeus ensis) harvested in Australia's Northern Prawn Fishery. Sensitivity tests on ELEFAN confirm that any change in search settings would affect the results. Simulation studies on Bayesian growth models show that Linf and K can be accurately obtained even with modal progression of only one year-class and using non-informative priors. However, age information, including the theoretical age at length zero (t0), is difficult to estimate and requires LFD from multiple age classes and informative priors. The Bayesian models yield mean parameters of: Linf = 36.56 mm (carapace length), K = 2.74 yr–1, and t0 = -0.02 yr for the males, and Linf = 51.81 mm, K = 1.94 yr–1, and t0 = -0.02 yr for the females. Seasonal oscillation models fit the LFD better, but the improvement is small and the estimated season-related parameters have large variances.