Age Composition Of Catches Research Articles

Fisheries and biological characteristics and state of stocks of the main commercial fish species in Beloye Lake

The current composition of the ichthyofauna and the importance for fisheries of the main fish species in Beloye Lake (Vologda Region) is described in the article based on research materials from 2018 – 2022. The biological features and commercial use of twelve most valuable fish species are summarized as result of the composition of industrial and research catches studies. The size and age composition of catches, the age of puberty, the timing and conditions of spawning, and the feeding patterns of fishes were studied. The influence of net fishing gear with different mesh spacing on commercial fish populations and the magnitude of nets fishing productivity (fishing effort) were studied for the first time. The role of the most important fish species for industrial fisheries in Beloye Lake was assessed.

Using Common Age Units to Communicate the Relative Catch of Red Snapper in Recreational, Commercial, and Shrimp Fisheries in the Gulf of Mexico

AbstractThe natural mortality rates and fecundity of Red Snapper Lutjanus campechanus vary substantially by age, so the age composition of catch is an important consideration when quantifying the relative effects of catch on the Red Snapper population across different fisheries. For example, the shrimp fishery catches many (but younger) Red Snapper, whereas directed commercial and recreational fisheries catch fewer (but older) individuals. We propose a simple approach for comparing catch across sectors. Fish that are caught can be scaled to a common age by multiplying or dividing by natural mortality rates so that the catch data can then be reported in “common age units.” Applying this approach to the catch data from the 2018 Red Snapper stock assessment, we showed that the shrimp‐trawl bycatch typically accounts for <10% of the relative catch, the commercial sectors account for ~32%, and the recreational sectors are responsible for ~59%. We believe that the effective management of Red Snapper requires regulation and oversight of each fishery that is proportional to its effect on the population. Given the apparently large influence of recreational fisheries on Red Snapper populations, recent management changes that delegate state‐by‐state control over important aspects of the recreational fishery (Amendment 50) should be accompanied by efforts to improve the understanding of this sector's interactions with Red Snapper.

Investigation of age composition and growth of cod Gadus morhua morhua of the Barents Sea in connection with the estimation of its stocks state

The age composition of catches and growth of the cod Gadus morhua morhua in the Barents Sea were investigated on the materials, collected in 2002–2006 in comparison with the data for the previous fishing periods. Analysis of data on the age composition indicated that the range of age groups had not changed since the beginning of the past century; however, a part of the younger age groups in the catches increased. The likeness of the cod sizes in the present period with those of the individuals of the same age caught in 1949–1980 and the significant decrease of the sizes as compared with those observed in 1981–1993 are observed. It is possible to suppose that the present decrease of indices of cod growth is connected with an increase of its numbers. A selective effect of the trawl fishery withdrawing in the first place the quick-growing individuals can be another factor that determined the decrease of body sizes of the fishes of the same age.

Using continuation-ratio logits to analyze the variation of the age composition of fish catches

Major sources of information for the estimation of the size of the fish stocks and the rate of their exploitation are samples from which the age composition of catches may be determined. However, the age composition in the catches often varies as a result of several factors. Stratification of the sampling is desirable, because it leads to better estimates of the age composition, and the corresponding variances and covariances. The analysis is impeded by the fact that the response is ordered categorical. This paper introduces an easily applicable method to analyze such data. The method combines continuation-ratio logits and the theory for generalized linear mixed models. Continuation-ratio logits are designed for ordered multinomial response and have the feature that the associated log-likelihood splits into separate terms for each category levels. Thus, generalized linear mixed models can be applied separately to each level of the logits. The method is illustrated by the analysis of age-composition data collected from the Danish sandeel fishery in the North Sea in 1993. The significance of possible sources of variation is evaluated, and formulae for estimating the proportions of each age group and their variance-covariance matrix are derived.

The 1996 Flatfish Symposium; a summary report

A summary report of the 1996 Flatfish Symposium is presented. Three topics of the Symposium are discussed: taxonomy and systematics, recruitment processes, and management issues. It is strongly recommended that a taxonomic advisory committee should be formed that will facilitate the transfer of information between different scientific disciplines focused on increasing our knowledge about flatfishes. Recruitment variation in flatfish appears to be dominated by density-independent factors operating at a local scale on the eggs and larvae. Variability in hydrodynamic circulation is suggested to be an important factor. Density-dependent processes are likely to be restricted to the smaller size classes which are not affected by fishing. The debate on the species range hypothesis is continuing. The patterns in latitudinal variation observed in fish did not correspond with the expectations. However, the species range hypothesis could neither be accepted nor rejected, because other sources of variation such as water temperature, sampling strategy, age composition of catches, inshore–offshore gradients and shifts in species ranges are biasing and maybe overruling the patterns in recruitment. Evaluations of the management of different flatfish stocks stressed the importance of the interactions between management measures and flatfish population structures. This field should be strengthened in the future.

Catchability for the Main Fishing Methods in the Cuban Fishery of the Spiny Lobster Panulirus Argus (Latreille, 1804), and Implications for Management (Decapoda, Palinuridea)

The fishing period for the lobster Panulirus argus (Latreille, 1804) in Cuba usually starts in June, after a closed season from March to May. Between June and September (beginning of the fishing period), 88% of the catch is obtained by the use of the artificial shelters (pesqueros) in the Gulf of Batabano, while from October to February, a mass migration occurs and 70% of the catch is obtained using traps joined by nets (jaulones). The application of analytical methods based on size and age composition of catches, like cohort analysis and catch curve analysis, allowed to calculate fishing mortality rates, catchabilities and the selection curves of the fishing gears operated during both seasons (beginning and migration) for the period 1982-1993. It was found that the variation in fishing mortality rate at the beginning of the period is significantly related to the number of pesqueros checked and the catchability is higher for the 3 and 4 year old lobsters, with a length at first capture of 24.19 cm (total length). For the season of mass migration, fishing mortality is related to the number of jaulones checked and the catchability is higher for the age groups 4 and 5, while the length at first capture is 25.54 cm (total length). Taking into account that jaulon catchability is 2.33 times pesquero catchability, the optimum allocation of the fishing effort was assessed through a predictive age-based model.

日本近海におけるブリの資源生態に関する研究‐Ｉ ブリ来遊量の長期傾向

The yearly changes in catches of the yellowtail Seriola quinqueradiata in the coastal waters of Japan are analyzed. The results obtained are as follows: 1) Long-term trends of fish catches from 1947 to 1986 show different patterns among regions. 2) From the age-composition of catch in each region, older fish were more often caught in the southern regions than in the northern regions of Japan, while the reverse was the case with younger fish. 3) The migration of adult fish into the waters of Japan has been decreasing since the mid-1960's, sharply in the northern regions and gradually in the southern regions. 4) However, the recruitment of young 0-1 year-old fish has remained nearly constant since 1970 along the coast of the Sea of Japan. These results suggest that the distributional/migrational range of adult fish has been in a process of reduction and restriction to the southern regions since the mid-1960s, due to the decrease in its stock size, and that an unexploited spawning stock exists near the East China Sea and reproduces most of the young fish migrating into the Sea of Japan.

Variations in the age composition of catch of anchovy (Engraulis mordax) and alternatives for the management of the resource

The structure of the northern anchovy population before the disturbance caused by “El Niño” in 1982-1983 is analyzed. 20,205 age data originated from biological sampling of the commercial catches in Baja California throughout the 1978-1982 period were processed, and the results are presented here. The year classes responsible for the catch in 1979-1981 are identified. It is established that the one year old group has been the main catch generator. The age composition variability is described and a situation of capture of young individuals is observed. It is suggested to limit the capture of individuals younger than one year with the purpose of allowing a higher biomass incorporation by the growth process. The year class and recruitment concepts as well as their relation to vulnerability and social behavior processes are discussed.

Growth and age structure of alfonsino(Beryx splendens)from the lower east coast, North Island, New Zealand

Abstract Commercial landings of alfonsino (Beryx splendens Lowe, 1834) from the Palliser Bank, Tuaheni High, and Paoanui Ridge were sampled to describe growth and determine the age composition of catches. The study indicated that one opaque and one hyaline zone were formed annually in sagittal otoliths, the hyaline zone being deposited in late autumn. Fish were probably about 10 months old when the otolith nucleus was fully formed. The length‐weight equations for males and females differed and both changed throughout the year in parallel with the spawning cycle. Size‐selective mortality did not occur on the Palliser Bank. Females were significantly larger at any given age than males on all grounds examined, but growth of males and females appeared consistent between grounds. Growth was slower than in Japanese waters and the Atlantic. Age structure varied between grounds, but was reasonably constant over time on the Palliser Bank. Full recruitment to the commercial fishery occurred at age 5 on the Palliser...

The Effect of Parameter Uncertainties in an Age–Length Relationship upon Estimating the Age Composition of Catches

A simple, but frequently applied, procedure for decomposing fish length frequencies into age-classes is considered. This decomposition consists of converting fish lengths into ages using an age–length relationship. A method for assessing the effect of parameter uncertainties in this relationship upon estimates of the age composition of catches is presented. It is assumed that the parameter uncertainties can be described by probability distributions. Our aim is to determine probability distributions of age composition estimates resulting from these uncertainties. This is done using a stochastic sensitivity analysis technique involving Monte Carlo simulations and/or a first-order theory if such a theory is valid in the case under consideration. The method is illustrated by its application to data from the southern bluefin tuna (Thunnus maccoyii) fishery. It is found that simulated (Monte Carlo) catch estimates for age-classes 3 (fish at age 2–3 yr) to 13 (fish at age 12–13 yr) are normally distributed. The coefficients of variation of these estimates are less than 12%. Simulated catch estimates for age-classes 1, 2, and 14–20 deviate considerably from normality and their ranges bounded by the 2.5 and 97.5 percentiles are extremely wide; they include values different by up to 810% from the best deterministic catch estimates.Key words: catch, age composition, uncertainties, sensitivity analysis, Monte Carlo simulations, southern bluefin tuna