Instantaneous Mortality Coefficient Research Articles

Growth, mortality and hatch-date distributions of striped sea bream Lithognathus mormyrus inhabiting the Çanakkale Strait, Turkey

This paper studies age, growth and hatch date distributions of young of the year striped sea bream Lithognathus mormyrus from Canakkale near shores by using a beach seine during September 2006–December 2007. Using otolith microstructure analysis, a total of 416 specimens ranging from 20 to 103 mm LT were aged and found to be between 30 and 307 days old. Average growth rates were estimated to 0.325 mm d−1. The juvenile instantaneous mortality coefficient was found to be 0.0219, which corresponds to a daily mortality of 2.16%. The hatching period of the striped sea bream was determined to occur between April and January, with relatively higher hatching frequency in August.

Distribution, growth and mortality of larval jack mackerel Trachurus japonicus in the southern East China Sea in relation to oceanographic conditions

Distribution, growth and mortality of jack mackerel Trachurus japonicus larvae <10 mm standard length (SL) were investigated in relation to habitat conditions in the southern East China Sea (ECS) in 2005, 2007 and 2009. In all the years, the center of larval distribution shifted northeastward with growth, indicating northeastward entrainment by the Kuroshio branch current. In 2005, the mean habitat temperature of the larvae was ∼2°C lower than the other two years. Mean density of the major prey item Paracalanus spp. in the larval habitat varied interannually, with the highest and lowest values in 2007 and 2005, respectively. The mean absolute growth rate and weight-specific instantaneous growth coefficient (Gw) were highest in 2007 (0.30 mm d−1 and 0.217 d−1, respectively) and lowest in 2005 (0.19 mm d−1 and 0.120 d−1, respectively), corresponding with the habitat temperature and food availability. There was no significant interannual difference in the daily instantaneous mortality coefficient (Z) which ranged from 0.107 d−1 in 2009 to 0.136 d−1 in 2007. The ratio Gw/Z, an index of stage-specific larval survival, was highest (1.60) in 2007 and lowest (1.02) in 2005. The lowest Gw/Z in 2005 corresponded with the lowest recruitment of the juveniles (mainly 50–75 mm SL) in the ECS in 2005. However, Gw/Z in 2007 and 2009 did not clearly correspond with recruitment levels, suggesting that a high Gw/Z is a necessary, but may not be a sufficient, criterion of a strong year-class.

Selective mortality of larval Japanese seabass in Ariake Bay, Japan

This article describes the growth, mortality, and selection patterns in early larval stage of Japanese seabass Lateolabrax japonicus in Ariake Bay, Kyushu, Japan. Japanese seabass larvae were collected from the spawning ground in December 2007, and juveniles were collected from the nursery ground in March 2008. Otoliths were analyzed to produce back-calculated daily records of size-at-age and growth rate. Back-calculated growth rates and sizes were compared between larvae and juveniles to determine whether selective mortality occurred. A weight-specific growth coefficient (G) and instantaneous mortality coefficient (M) were computed, and the recruitment potential was evaluated from the ratio of M:G. Selection for fast-growing and bigger larvae was evident during the 5–14 days after hatching (DAH). Selective mortality acted to preferentially remove fish that were slow growing and/or relatively small members of the cohort at least during the period examined. Trends in the growth rate differences between larvae and juveniles suggested that the selection process continued beyond 14 DAH although the exact duration over which selective mortality occurred was unknown. Survivors of Japanese seabass exhibited traits consistent with all aspects of the ‘growth–mortality’ hypothesis: faster growth, larger size-at-age, and shorter larval stage duration (LSD), i.e., larvae with faster growth, bigger size-at-age and a shorter LSD selectively survived the larval period. Larvae had higher M (0.323) than G (0.159), resulting in the M:G ratio of >1.0 (M:G = 2.031), suggesting that the larval cohort was rapidly losing biomass. Future studies should look to determine the duration over which selective mortality occurs and the timing of transition between M and G (M = G) and accumulation of cohort biomass.

Life History, Ecology, and Long‐term Demographics of Queenfish

AbstractQueenfish Seriphus politus were collected at coastal power plants from San Clemente to Ventura, California. Power functions best described relations between otolith length, width, or weight and either standard length (SL) or total body weight. The length–weight relationship was described by the following equation: weight = 10−5 × SL3.09. Individuals were aged to 12 years by using sagittal otolith sections. Females grew at a significantly faster rate than males. Both sexes reached 50% maturity by 100 mm SL, or shortly after age 1. The total annual instantaneous mortality coefficient was estimated at 0.42. Catalina Harbor (on the windward side of Santa Catalina Island) and Ventura were the most populous sites based on gill‐net catch per unit effort from 1995 to 2006. Juvenile and adult queenfish populations have declined since 1980 in a significant relationship with nearshore plankton biomass. Larval queenfish densities recorded in King Harbor (Redondo Beach) have declined since 1987. Long‐term recruitment estimates indicated peak recruitment prior to 1976, with three subsequent downward baseline shifts.

Latitudinal variation in the recruitment dynamics of small pelagic fishes in the western North Pacific

The subarctic Oyashio Current flows south-westward and the subtropical Kuroshio Current flows north-eastward in the western North Pacific, converging in the waters off northern Japan to form the Kuroshio-Oyashio transition region. Some small pelagic fishes inhabit the subarctic or subtropical waters, and others seasonally migrate north and south across the major ocean fronts. Environmental conditions in the subarctic and transition waters are variable, whereas in the subtropical Kuroshio waters conditions are relatively stable. Latitudinally different environmental conditions may affect vital parameters and recruitment variability of small pelagic fishes inhabiting the various waters. Pacific saury Cololabis saira migrate seasonally from the Kuroshio to Oyashio waters and spawn in the transition waters in autumn and spring and in the Kuroshio waters in winter. During 1990–1999, the coefficients of variation (CVs) of daily growth rates (G) and instantaneous mortality coefficients (M) were large for larvae and juveniles spawned in the northern transition waters, but relatively small for those from the southern Kuroshio waters. The Pacific stock of chub mackerel Scomber japonicus spawns in the Kuroshio waters in spring and early summer and migrates to the subarctic Oyashio waters in summer for feeding, whereas the Tsushima Warm Current stock spawns in the East China Sea in spring and fish remain in the subtropical warm waters throughout their lifetime. The Pacific stock had CVs > 100% for the fish aged 0–5 during 1970–2002. In contrast, the Tsushima Warm Current stock had CVs of 34–40% during 1973–2002. Pacific herring Clupea pallasii, which inhabits subarctic waters, had CVs of 118–178% for the fish aged 3–8 y during 1910–1954. Japanese sardine Sardinops melanostictus, which spawn in the subtropical Kuroshio waters and migrate to the subarctic Oyashio waters in summer for feeding, had CVs > 120% for the fish aged 0–4 during 1976–2003. Contrasting with these subarctic Oyashio associated species, subtropical round herring Etrumeus teres had a CV of 26% over the total catch during 1976–2003. For these small pelagic fishes, latitudinal variation in early life parameters and recruitment was evident at the levels of cohorts ( C. saira), stocks ( S. japonicus), and species (Clupeidae). Large variations were observed in the subarctic Oyashio and the Oyashio-affected transition waters, whereas relatively stable results were recorded for the subtropical Kuroshio and its branch, the Tsushima Warm Current. Because the cohorts of Pacific saury and stocks of chub mackerel are not genetically distinct, it is likely that the large variability in the northern waters was environmentally induced in these species. The differences in CVs among clupeids are probably the result of differences in specific reproductive strategies and the environmental characteristics of the waters inhabited by the different species.

Sustainable harvest of two large predatory catfish in the Cuiabá river basin, northern Pantanal, Brazil

Fishery is an important economic activity in the Pantanal. Among the regions species, the Pimelodidae catfish stands out as an important part of the annual catch. This study assesses the structure, exploitation and stock management of Hemisorubim platyrhynchos and Sorubim cf. lima, the sixth and seventh largest Pimelodidae of the Pantanal. The analysis is based on fish caught by commercial fishing in the Cuiabá river and landed at the "Antônio Moysés Nadaf" Market in the Cuiabá city, Mato Grosso state, Brazil. The findings indicate that commercial fishing activities target several fish cohorts and that usually only individuals above mean length at first maturation are caught. Estimates of the instantaneous mortality coefficient show that the current fishing mortality is low. Simulations of relative yield-per-recruit model demonstrate that the current yield of two species could be greater if the fishery effort were increased, indicating that the stocks are underexploited. However, an increase in current fishery efforts should be viewed with caution, since the stock-recruitment relationship for the species is unknown. The results indicate that the current harvest of two species in the Cuiabá River Basin is sustainable.

Simultaneous estimation of instantaneous mortality coefficients and rate of effective survivors to number of released fish using multiple sets of tagging experiments

A method is proposed for estimating two instantaneous mortality coefficients, and rate of effective survivors to number of tagged fish released, using exact times at liberty from multiple sets of tagging experiments. Effective survivors are defined here by the product of survivors immediately after releasing and reporting rate of recaptures. A least-squares method was applied to estimate the parameters using statistical models expressing the numbers of effective survivors, which were calculated by a principle similar to virtual population analysis. In order to investigate the statistical performance of the method, simulation trials using operating models were carried out. The method was applied to data of tagging experiments for alfonsino Beryx splendens from 1957 to 1969, off Kanagawa Prefecture. In most of the results of simulation trials, the method yielded estimates of natural mortality coefficient of which expected values were within ±12% of true values. Estimates of natural mortality coefficient, fishing coefficient and the rate of effective survivors for alfonsino are 0.57 (per year, 95% confidence limits [CL] 0.40–0.69), 0.094 (per year, 0.03–0.25) and 0.39 (0.12–1.00), respectively. Modifications for the generalization of the method and notes on its applications are discussed.

Aspects of the biology of the Atlantic Midshipman, Porichthys porosissimus (Teleostei, Batrachoididae): an important by-catch species of shrimp trawling off southern Brazil

Trawl fishing for pink shrimp (Farfantepenaeus brasiliensis and F. paulensis) catches large quantities of by-catch fish, discarded due to their having no commercial va)ue. As these species have rarely been studied, the impact of fisheries on these populations is not known. This contribution studies the biology of a species of no commercial value, the Atlantic midshipman Porichthys porosissimus. The last haul /Tom a commercial trawler, operating on the northern coast of São Paulo State and the southern coast of Rio de Janeiro State, was preserved (/Tom being discarded) and identified at the species leveI. It was observed that this fishery affects the juvenile population which is intluenced by the seasonal variation of the water masses. Growth parameters were estimated: L∞ = 37.0 cm, K = 0.285 year-1. Instantaneous mortality coefficients were estimated: 2=2.14, M=0.63, F= 1.51, S= 11.8 and E=0.71. Considering the intensive activity of the shrimp trawl tleet operating in this area, the deleterious action of trawling is considered as of high impact. The stock management measures applied for pink shrimp are without effect regarding P. porosissimus. which has its spawning period before the closed season and its recruitment peak after it. The results show overfishing and the need to apply measures to reduce trawling action, such as adequate policies, introduction of selectivity devices and the creation of exclusion zones for trawl fishing.

Modelling of unexploited and exploited populations of eels, Anguilla anguilla (L.), in the Thames Estuary

Eels were fyke‐netted in different zones of the Thames Estuary at various times of year and subsamples sexed, aged and stomachcontentsexamined. Instantaneous mortality coefficients (Z) were calculated for each 3 cm length class for eels &gt; 30 cm and used to construct a compartmental model to assess effects of natural and fishing mortality and migration on different life stages of males and females. Growth rates were good and fishing mortality effects low and masked by effects of emigration/immigration (and, possibly, local migrations). Density‐dependent mortality appeared to be having minor effects. Males dominate freshwater sites, females the more saline zone and possible implications of food availability and density are discussed. It is concluded the stock is not being over‐exploited but that elver recruitment is relatively low. Means of increasing exploitation are discussed, as are ways of increasing production of females to enhance elver recruitment to the Thames and other European rivers.

Utilization of detritus by the copepod, Acartia tonsa1

Ingestion, survivorship, and growth experiments were conducted with the marine calanoid copepod, Acartia tonsa, various concentrations of the diatom, Thalassiosira weissflogii, and detritus derived from the macrophyte, Thalassia testudinum. Copepod ingestion rates of detritus increased with detritus concentration from &lt;50 to &gt; 1,700 µg C·liter−1.Copepod survival in detritus suspensions was significantly greater than in filtered seawater controls. The instantaneous mortality coefficient, z, of A. tonsa was a linear (negative) function of the diatom concentration (r2 = 0.7831). When T. weissflogii suspensions were supplemented with detritus (1,000 µg C·liter−1), the copepod instantaneous mortality rate decreased (0.3002–0.1362 in 50 µg C liter−1 T. weissflogii; 0.1345–0.0406 in 200 µg C·liter−1 T. weissflogii). The growth rate of A. tonsa was a linear function of diatom concentration (r2 = 0.8816). When the diatom suspensions were supplemented with T. testudinum detritus, the growth rate of the copepod increased.Thalassiosira weissflogii contained 12 × the protein, 8 × the fatty acids, and a greater amount and diversity of amino acids and polyunsaturated fatty acids per unit dry weight than T. testudinum detritus. Although A. tonsa could not grow from egg to adult on a detrital diet, T. testudinum detritus did supplement algal diets to increase copepod production rates.

Mortality and production in natural, artificially-seeded and experimental populations of Anadara granosa (Bivalvia: Arcidae)

Declines in density of one natural, three artificially-seeded and eight experimental populations of Anadara granosa were monitored over periods ranging from seven to twelve months. For three of four large populations the decline in density has been adequately described by a model of the form N t=N 0·e zt where N t is density at time t, N o is initial density and z is the instantaneous mortality coefficient. The mean value of the latter was found to be-1.88·yr-1 with 95% confidence limits-1.54 to-2.25. The data obtained from the experimental populations demonstrated that mortality is unaffected by initial densities upto 2,500·m-2, but increases as shore elevation decreases due at least partly to greater access by predators at the lower levels.The data on mortality rates have been combined with previously-published information on growth rates in order to arrive at estimates of production. At one of the artificially-seeded sites the 95% confidence limits of estimates of mean production are 24 and 62 g dry tissue·m-2·yr-1 with an average value of 42 g·m-2·yr-1. Examination of the effects of shore elevation on production revealed that the latter is greatest at the uppermost shore level studied because down-shore increases in growth rate are more than offset by increases in mortality. Production per individual has been shown to decrease with increasing density. This latter fact has been used to estimate the maximum possible production which, for one site 250 cm above chart datum, lies between 49 and 72 g·m-2·yr-1 (95% confidence intervals). It has been demonstrated that for one of the culture sites variation about an estimate of mean mortality rate does not contribute as much to the variation of the final estimate of production as does the variation about the estimates of the mean values of the constants in a growth equation.As far as possible production of Anadara granosa has been compared with values reported for other marine and estuarine bivalve molluscs and it is concluded that A. granosa may be considered moderately to highly productive.

Estimating mortality from growth parameters and a size distribution when recruitment is periodic1

A size distribution of organisms is determined by growth and survivorship functions together with variability in recruitment. If recruitment is seasonal and constant from year to year, then the instantaneous mortality coefficient, Z, is equal to ln{[1 ‒ C]/ [1 ‒ C·exp(K)]} where C = {S∞ ‒1/n ‒ X̄}/ {S∞‒1/n b·exp[K(1 ‒ t)]}, X̄ is mean size of individuals in the population at time t since recruitment of the year, and other parameters are from the Richards function. Examples are presented for a simulated population and for a population of the sea urchin diadema setosum, which has an annual mortality of 25% and an average lifespan of about 3.5 years.

Culture, Feeding, and Growth of Alewives Hatched in the Laboratory

Abstract Alewives (Alosa pseudoharengus) were reared from the egg to the early juvenile life stage. The major obstacle to rearing alewives from the egg — providing an acceptable food that facilitates first feeding — was overcome by presenting a mixture of wild Zooplankton to the larvae twice daily, beginning on the day of hatching. Initial feeding by larvae held at 20°C was observed 2 days after hatching, when the yolk was nearly absorbed. Comparison of stomach contents and the wild Zooplankton composition suggested that the diet of larvae during the first 15 days of life shifted with changes in the availability of food but remained within a fairly narrow range of food sizes. Larvae hatched at a mean total length of 3.8 mm and grew at an average rate of 0.62 mm per day, to a mean of 35.5 mm after 50 days. At 50 days most fish had transformed into juveniles. The daily instantaneous mortality coefficient was 0.018. About half of the mortality occurred during the first 13 days after hatching.

Growth and Survival of Haddock (Melanogrammus aeglefinus) Larvae in Relation to Planktonic Prey Concentration

When newly hatched haddock (Melanogrammus aeglefinus) larvae were fed zooplankters at nominal rates of 0.5, 1.0, and 3.0/ml in the laboratory at 7 C, they grew at similar rates. After 6 wk, they averaged 8.7, 10.0, and 11.2 mm in standard length and 810, 1300, and 1728 μg in dry weight, and had condition factors of 1.25, 1.22, and 1.32. When fed at 0.1 and 0.01 plankters/ml, all larvae died in 3 and 2 wk; at 0.5-3.0 plankters/ml, daily instantaneous mortality coefficients were 0.06–0.02 during 6 wk. Larvae began feeding 2 days after hatching, and the point of no return after they were deprived of food was 6 days after hatching, yolk absorption being completed on day 6 or 7. All larvae deprived of food until 8 and 10 days after hatching, although initiating feeding, did not survive another 4 days. Prey concentration also influenced delayed feeding with greater percentages of larvae able to initiate feeding at higher plankton levels on the point-of-no-return day.

Mortalidade da pescada-foguete, Macrodon ancylodon

The instantaneous mortality coefficient (F + M) of the commercial weakfish, Macrodon ancylodon (Bloch, 1801) caught by trawls along southern Brazilian coast (from latitude 28oS to 34oS), was computed by means of the annual catch variation (in number) by age per fishing effort from March 1961 to December 1964. The instantaneous mortality coefficient mean values for female and male was respectivelly 1.31 and 1.53. One year old recruits appear in the landings and the mesh selectivity operates on fish up to three years old. Three-year old class predominates in the landings.