Fishing Mortality Coefficient Research Articles

Population dynamics of the prawn Metapenaeus dobsoni (Miers) exploited in the trawl fishery along the Southwest Coast of India

Study of the dynamics of the exploited stock of Metapenaeus dobsoni indicates that for an age at first capture ( t c) of 1.5 years the fishery generates a steadily increasing yield up to about 17 000 tons for an annual effort ( f) of 2500 trawlers per day (tpd), equivalent to 537.5 × 10 3 boat-days (bd), at which the annual fishing mortality coefficient ( F) is 2.50 and the annual exploitation ratio ( E) is 0.52. Beyond this level of exploitation, the rate of increase in yield is negligible. The potential yield per recruit ( Y′) is estimated to be 1.12 g (for the natural mortality coefficient M = 2.303, E = 1, F ∞ = 4772 tpd or 1026 × 10 3 bd and the optimum age of exploitation t y = 1.06 years). The biologically optimum yield (i.e. the MSY) is 18 000 tons (Kerala = 15.2 × 10 3 tons, Karnataka = 2.1 × 10 3 tons and Goa = 1.1 × 10 3 tons) for an effort ( f MSY) of 2702 tpd, equivalent to 580.9 × 10 3 bd (Kerala = 1535 tpd = 330.0 × 10 3 bd, Karnataka = 676 tpd = 145.3 × 10 3 bd and Goa = 491 tpd = 105.6 × 10 3 bd) for an average 215 fishing days a year, at which E is 0.54 and F is 2.70. The average yield of 17.4 × 10 3 tons from 1976 to 1984 is marginally less than the MSY, whereas the average annual effort for this period (f = 2760 tpd or 59.3 × 10 3 bd, F = 2.76 and E = 0.53) is marginally higher than the f MSY. Although the current (1983–1985) yield (17.7 × 10 3 tons) remained much the same as the average annual yield for 1976–1984, the current effort has increased substantially to 3500 tpd, equivalent to 752.5 × 10 3 bd ( F = 3.5, E = 0.61) much beyond the f MSY.

Growth, mortality and potential yield of bonga, Ethmalosa fimbriata (Bowdich 1825) of Nigerian inshore waters

The distribution of and fisheries for bonga, Ethmalosa fimbriata (Clupeidae), in Nigerian inshore waters east of the Niger delta are discussed. Data on length frequency collected between 1973 and 1982 are analysed to obtain the von Bertalanffy's growth parameters ( L ∞=30 cm, K=0.43 and T 0=−0.20) which are then used to estimate the instantaneous total ( Z), natural ( M) and fishing ( F) mortality coefficients. Catch-per-effort statistics (1973–1982) allow for a simple graphical treatment of Schaefer's logistic model from which the maximum sustainable yield ( Y max=30 075 t year −1) is derived for the stock of bonga in this part of the Nigerian coast. Considering the level of mean catch (25 030 t year −1), which is very close to the optimum level of yield ( Y ec) and the mean value of the exploitation ratio ( F Z =0.57 ), it is concluded that the stock of E. fimbriata of the inshore waters east of the Niger delta is being fished at about its Y ec. Although this is the desirable level of exploitation if profit is to be maximized, this fishery might be allowed to expand beyond Y ec to contribute to the solution of an important socio-economic problem, namely, reduction of unemployment, but fishing at Y max should be avoided to prevent the collapse of the stock.

期間毎の標識再捕データに基づく死亡係数の推定について

The aim of this article is to consider a method for estimating fishing and natural mortality coefficients, denoted by F and M, respectively. It is assumed that the length of the life of atagged fish is distributed as an exponential distribution with mean (F+M)-1. When the sample is grouped and is censored at a certain time, and the group intervals are unequal in length, the problems of estimation of the parameters from tag recoveries are discussed. Using the recovery data of young red sea bream Pagrus major in the Seto Inland Sea, two numerical examples are given. The goodness of fit of the theoretical model to sample data is also demonstrated.

Incorporating Mortality from Catch and Release into Yield-per-Recruit Analyses of Minimum-Size Limits

We evaluated the effect on yield per recruit of mortality from catch and release of fish smaller than a legal minimum length. Catch-and-release mortality reduces the potential effectiveness of minimum size limits for increasing yield per recruit by an amount that depends on the fishing mortality coefficient, the minimum size limit, and the probability that undersized fish survive if released. For a given probability of survival, catch-and-release mortality has its greatest influence when fishing mortality and the minimum size limit are large, because these factors determine the number of undersized fish that are caught and released. As the survival probability declines, minimum size limits become less effective for increasing yield per recruit because greater numbers of undersized fish die and cannot contribute to future catches. With low survival probabilities, minimum size limits may actually reduce yield per recruit. We calculated yield per recruit for red snapper (Lutjanus campechanus) in the Gulf of Mexico for minimum size limit ranging from 254 to 635 mm total length, survival probabilities ranging from 0.20 to 1.00, and several natural (M) and fishing mortality coefficients. A recently implemented 330-mm minimum size limit is predicted to increase yield per recruit as long as the survival probability exceeds 50% if M = 0.25; the survival probability must exceed 60% if M = 0.35.

The surf clam beam trawl fishery and its biological management in Sendai Bay.

Parameters of the Sakhalin surf clam Spisula sachalinensis stock in Sendai Bay were estimated by analyzing the fishery data to examine the management of fishery. The fishing has been greatly influenced by the fluctuation in recruitment, since the age structure has skewed to younger side, The average fishing mortality coefficient F and natural mortality coefficient M during 1980-84 were 0.6358±0.2735, and 0.5323±0, 0915, respectively. The catchability coefficient q was 3.164×10-5. Since the natural mortality coefficient is high, we can expect higher yield per recruit from higher F and lower age of first capture. The most important problem in the management of the stock recruited intermittently by the strong year class, however, is to secure the minimum level of stock which could produce a lat of progeny if the circumstances might become favorable. Since it might be difficult to predict the recruitment from the stock-recruitment relationship, two models were proposed to follow successive stock density. Optimum fishing mortality coefficient is presumed to be between 0.5 and 0.6, which would be able to hold the stock at a level enough to produce recruits under deteriorated conditions.

Estimation of fishing mortality coefficient from tag recoveries in a finite period with a few closed seasons.

Estimation of fishing mortality coefficient from tag recoveries in a finite period with a few closed seasons.

Dominancy of the immigration-emigration coefficient over other coefficients on a short time-scale.

Analyzing echo-sounding and experimental fishing data, Ohkawa and Misu have estimated the daily abundance of the Japanese anchovy Engraulis japonica in Yuya Bay. Using data of the abundance and commercial catch, and assuming the natural mortality coefficient, M. to be 5×10-8 s-1, this paper estimates magnitudes of the fishing mortality coefficient, F, and the immigration-emigration coefficient, I, for one or two days. Plots of |I| estimated by this and other papels vs. the time-scale, T, adopted in the respective papers show a relation, |1|=0.1/T to √10/T; due partly to offsets of positive and negative values of I for long T. Usually, both of Gi and M<10-7 s-1 where Gi is the individual growth coefficient; F<3×10-7 s-1. When T is shorter than five days or so, I should dominate over them.

Area of Distribution, Movements, Age Composition and Mortality Rates of the Australian Salmon Population in Tasmania, Victoria and New South Wales

Two subspecies of the Australian salmon, a perciform fish, occur in eastern Australian waters. The western subspecies, Arripis trutta esper (Whitley), is found only in Tasmania and Victoria. In Tasmanian waters fish do not occur above an age of 2+ years. In Victoria about 300 000 fish (180 tonnes) of an age range from of to 5+ years are caught annually. The younger age groups are found in sheltered areas, and the older age groups along the open coastline, especially in western Victoria. Returns of tags from fish thought to be of the western subspecies indicate that movement towards Western Australia takes place via western Victoria and South Australia, rather than by a direct seawards movement. For the eastern subspecies, Arripis trutta marginata (Cuvier &amp; Valenciennes), young fish from 0+ to 2+ years are found predominantly in Tasmania and Victoria, and older fish from 4+ years in New South Wales. Recaptures of tagged fish indicate that there is a continual movement at all stages of the life cycle from Tasmania to Victoria and then to New South Wales. Fish within New South Wales also show evidence of a movement southwards, which probably occurs only once, to the eastern Bass Strait area. Fish older than 5+ years move increasingly northwards in New South Wales waters. For the eastern subspecies estimates of M, the instantaneous annual natural mortality coefficient, range from 0.5 to 1.0, and estimates of F, the instantaneous annual fishing mortality coefficient, range from 0.3 to 0.7. It is suggested that in the present eastern subspecies fishery greater yields should result from increasing the fishing pressure up to about twice the present value.

Relation Between Yield and Fishing Mortality for Ricker’s Yield Equation

A method is presented that can be applied to examine the relation between yield and magnitude of fishing mortality for Ricker’s dynamic pool yield equation. The magnitude of fishing mortality is measured by the norm of the vector of interval specific instantaneous fishing mortality coefficients. The method is applied to a bluegill sunfish (Lepomis macrochirus) population.

東シナ海におけるマアジ資源の研究-I

In the case of assessment of fish resources, it is essential to know natural and fishing mortality coefficients of the fish resources under consideration. In 1958, the virgin resource of the jack mackerel, Trachurus japonicus (TEMMINCK et SCHLEGEL), was found in the mid-region of the East China Sea, and has been intensely exploited since 1959 (Fig. 2). In consequence the yield of the fish from the East China Sea has markedly been increasing, but recently this trend has stopped and the catch remains on the same level (Fig. 1). In the present paper is shown: (1) the corrected fishing effort (X) in terms of the number of fishing days of the purse seine of one-boat-operation type of 50-100 tons (Table 1). (2) the total mortality coefficient of the fish in each of the recent years which is acquired on the basis of the age composition of the fish caught in one day's operation by purse seine of one-boat-operation type in the East China Sea during the period from 1957 to 1963 (Tables 2 and 3). According to WIDRIG (1954), if a series of pairs of values of fishing effort (X) and total mortality coefficient (Z) is known, equation (3) gives a linear relation between them, as shown in Fig. 3. By application of the method, estimates of natural mortality coefficient (M) and catchability coefficent (q) are obtained at a high level of 0.994 and 0.03154 per 1, 000 fishing days, respectively. The 95% confidence limits for M and q are 0.055-1.933 and -0.00491-0.07797, respectively. The estimate of M aforementioned is greater than that of F, and also correspondent to 1.32 K (“K” represents growth rate in BERTALANFFY's growth equation). Judging from the various facts, the estimate of M in the present paper seems to give an indication of its order of magnitude. The high level of M shows one of the characteristics of the jack mackerel fisheries in the East China Sea.

On Estimating Mortality Coefficients in Exploited Fish Populations, Given Two Censuses

Abstract Biologists frequently assume that the number of individuals in a “discrete” population follows an exponential relationship with respect to time, at least over the latter part of the life of the members. Such a discrete population may be, for example, a year class of a particular species of fish in a particular body of water. In an exploited population some individuals die from natural causes, and others are harvested. To estimate the extent of natural mortality a common assumption is that total, natural, and fishing mortality coefficients are all constant over the period of study. The present paper differs in that it assumes that only the natural mortality coefficient is constant throughout the period. It assumes that the fishing mortality coefficient is zero when no harvesting occurs, finite and constant when harvests are made over an extended period, and almost infinitely large when large harvests are made in short periods.