Yield- and biomass-per-recruit analysis for rotational fisheries, with an application to the Atlantic sea scallop (Placopecten magellanicus)

A general model for yield-per-recruit analysis of rotational (periodic) fisheries is developed and applied to the sea scallop (Placopecten magellanicus) fishery of the northwest Atlantic. Rotational fishing slightly increases both yield- and biomass-per-recruit for sea scallops at FMAX. These quantities decline less quickly when fishing mortality is increased beyond FMAX than when fishing is at a constant rate. The improvement in biomass-per-recruit appears to be nearly independent of the selectivity pattern but increased size-at-entry can reduce or eliminate the yield-per-recruit advantage of rotation. Area closures and rotational fishing can cause difficulties with the use of standard spatially averaged fishing mortality metrics and reference points. The concept of temporally averaged fishing mortality is introduced as one that is more appropriate for sedentary resources when fishing mortality varies in time and space.

On the strength of the California Current: a record from the southern Baja California margin [abstract]

EXTRACT (SEE PDF FOR FULL ABSTRACT): To characterize the strength of the flow of the California Current, we searched in the southern Baja California continental margin, the southernmost site affected by its relatively cool and less saline waters.

Estimation of maximum sustainable yield (MSY) of hilsa (Tenualosa ilisha Ham.) in the Meghna river of Bangladesh

MSY per recruit of Tenualosa ilisha in the Meghna river was predicted as 112 g per recruit at the F(msy)=0.6/yr and at T(c)=0.6/yr. But Y/R=95 g per recruit was obtained at the existing fishing level, F=1.14/yr and at T(c)=0.6/yr. Existing F level was nearly double than the F(msy) level. Fishing pressure should be reduced immediately from F=1.14/yr to F(msy)=0.6/yr. F(msy)=1.14/yr was the same at first capture, T(c)=1.0, 1.2 and 1.4/yr, and MSY could be obtained as 142 g, 162 g and 176 g per recruit respectively. It is easier to change the first capture age (Tc) rather than changing off level. So, hilsa fishery manager may adopt F(msy)=1.14/yr while age at first capture must be increased from T(c)=0.6/yr (3 cm size group) to T(c)=1.4/yr (25 cm size group), by which 1.8 times production could be increased than the present production. MSY also possible to obtain as 201 g and 210 g per recruit at F(msy)=2.0/yr and 4.0/yr at T(c)=1.7/yr and 1.9/yr respectively. Under both the situations, hilsa production could be increased 2 times than the present production. To obtain the MSY=210 g per recruit the fishing level could be increased up to F=4.0/yr at T(c)=1.9/yr (34 cm size group). Economic point of view, hilsa fishery managers may choose to obtain the economic MSY as 201 g per recruit at F(msy)=2.0/yr and T(c)=1.7yr (31 cm size group) in the Meghna river of Bangladesh.

Growth, mortality and yield-per-recruit of Copadichromis likomae (Cichlidae) in Lake Niassa, Mozambique

Analysis of the length-frequency data on Copadichromis likomae (Cichlidae) from Lake Niassa, Mozambique, suggests an asymptotic length of SL∞=14 cm associated with a K value of 0.93 yearˉ¹. Total and natural mortalities were estimated as 3.2 yearˉ¹ and 1.9 yearˉ¹, respectively. Yield-per-recruit analysis suggests that E=0.36 in this fishery.

Growth and yield of GIFT (Oreochromis niloticus) and Thai silver barb (Barbodes gonionotus Bleeker) in rice fields and their effects on the yield of rice

(GIFT) (Oreochromis niloticus) and Silver barb (Barbodes gonionotus) in rice fields and their effects on the yield of rice was carried out in nine experimental rice plots. Three treatments viz., treatment-1 with 0. niloticus (T1), treatment-2 with B. gonionotus (T2) and treatment- 3 was kept as control (T3, without fish) were used in this study. Fertilizers such as, Urea (178 kg ha-1), T.S.P (125 kg ha-1) and M.P. (67 kg ha-1) were applied in each treatment. The fishes were stocked @ 6250 ha·1 and the experiment was continued for a period of 107 days. The values of water quality parameters such as, water temperature, dissolved oxygen, pH and chlorophyll-a were found within suitable level. Between the two species, higher specific growth rate was recorded in 0. niloticus than that of B. gonionotus. But B. gonionotus showed much higher survival (72%) than that of 0. niloticus (35%). Similar to survival, higher production (244 kg ha-1) and income (Tk. 6399 ha-1) were recorded in B. gonionotus than those of 0. niloticus (142.8 kg ha'1 and Tk. 2137 ha-1). Significant differences (pyield of rice grain and straw were observed between the treatments with fish and without fish.

Growth performance, recovery rate and fish yield of GIFT strain at various water depths under rice-fish culture systems

Effect of water depth on recovery rate, growth performance and fish yield of GIFT in the rice-fish production systems was studies in experimental plots of 123 m2 with a pond refuge of I meter deep which covered 10% of the total land area. Mortality rate of fish was very low ranging from 0.81-1.63%. However, at harvest, recovery rate ranged from 76.69-82.93% with the highest recovery at 11-15 em of water depth. Significantly the highest absolute growth (99.97) and specific growth rate (2.42%) were found at 21-25 cm water depth. The same treatment also produced significantly higher fish yield (909.76 kg/ha) although statistically similar to the fish yield (862.60 kg/ha) obtained at ll-15 em of water depth. Results also suggested that higher water depth can produce bigger fish but no significant effects of water depth was found on fish yield in the treatments 11-15 cm and 21-25 cm water depths of this experiment.

Studies on the influence of moisture and specific gravity on the strength properties of mango wood (Mangifera indica)

Influence of moisture and specific gravity on the strength of mango wood is discussed. The co-efficient of correlation between specific gravity and breaking strength was found to be non-significant. The relation of strength and moisture was found to be highly significant. The mean strength values indicated a reduction in strength when the moisture increased from 8.5 to 18.8%. However no appreciable difference in strength values could be observed when moisture increased above 37%. The strength-moisture relationship is a straight line, passing approximately through the fibre saturation point. By using the exponential formula, the breaking strength corresponding to any moisture level between zero and fibre saturation can be determined.

A study on the average yield of different species pf prawns used for freezing and canning

The paper deals with the average yield of four spp of prawns viz. Metapenaeus dobsoni, Metapenaeus affinis, Parapenaeopsis stylifera and Penaeus indicus on conversion to peeled and deveined (PD), cooked and peeled (CP) and head less shell on (HL) forms in the different months of a year and the likely variations observed in the average yield.

Tensile strength properties of polyethylene netting twines under exposure to out-door and artificial UV radiation

Photodegradation of three types of polyethylene twines namely, polyethylene fibrillated tape twine, polyethylene flat tape twine and polyethylene monofilament twines were studied by exposing them to sunlight and artificial UV radiation. The percentage residual strength varied in the samples, the monofilament with the highest residual strength followed by fibrillated tape twine and flat tape twine. A plot of the difference between the breaking strengths of the fibrillated tape twine and the mono filament twines against any given period of exposure exhibited a linear relationship

Morphometric measurements as an index for estimating yield of meat in shell fishes, 2. Mussel (Perna viridis) and clam (villorita cyprinoides)

Observations (76 nos) on height-length and whole weight-meat weight relations of mussels (Perna viridis), both wild and cultured were made. From the length of mussel the height can be worked out by the equations (logarithmic scale), 1. y = 0.360+0.988 x for wild; 2. y = 0.334+1.011 x for cultured, where x is the length (cm) and y is the height (cms). So also to any height the corresponding meat weight can be obtained by the regression equation. log w=-0.8178+1.9769 log H for wild variety (1) log w=-1.3049+2.8385 log H for culture-variety (2) where w is the meat weight (g) and H is the height (cm) of the mussel. Fourteen observations on size weight measurements of dams were made. The yield varied from 8.9 to 13%. The length-height relationship worked out for clams (Villorita sp) is y=0.485+1.005 x for length x and height y.

Morphometric measurements as an index for estimating yield of meat of shell fishes, 1. Crab (Scylla serrata) Forskal

Sixty one observations on length-breadth and whole weight-meat weight relations of India crab (Scylla serrata) were made. From the length of crab (cm) the whole weight (gm) can be computed by the equation: log W=-0.1708+2.3341 log L. Similarly for any given length (cm) the meat weight (gm) can be found by the relation, log w=-1.5745+3.0148 log L.