Cane River sourc 

 (Altitude 650 m) 



'Rowlands 



• • • Locations 

 of sampling 

 stations 



Caribbean Sea 



FIGURE 1.— Map of study area and its location in Cane River, 



Jamaica. 



To sample, the legs were forced into the substrate 

 and the net flaps pinned around by stones. The 

 collecting net was attached to the frame, and its bot- 

 tom side held firmly down by the operator's feet. All 

 stones within the sample area were then removed and 

 the shrimps swept into the collecting net by the 

 current. 



During a 20-mo period (February 1973-September 

 1974), 10 samples, randomly chosen, were taken 

 monthly at each of 15 stations along the length of the 

 river. Areas of the stream bed which were devoid of 

 stones were not sampled since they were known to be 

 without shrimps (Hunte 1976). Samples were taken 

 during the day when the shrimps are inactive and 

 hide under stones. 



Each specimen of M. faustinum was sexed, and its 



total length measured (from the tip of the rostrum to 

 the tip of the telson) to the nearest 0.5 mm for adults 

 and 0.1 mm for juveniles. Specimens subsampled 

 from each month's catch were weighed to the nearest 

 10 mg for adults and the nearest 1 mg for juveniles. 

 Growth and mortality were estimated from monthly 

 length-frequency histograms. 



The catch of fishermen was sampled opportunis- 

 tically throughout the period of sampling in the river. 

 On each occasion the shrimps in the catch were 

 measured and the resulting length-frequency dis- 

 tribution converted to a catch curve using the age- 

 length relationship. 



Yield per recruit (Y/R) for various levels of fishing 

 mortality (F) was estimated for males and females 

 combined by the method of Thompson and Bell 

 (Ricker 1975), using an APL algorithm (Rivard 

 1980). The parameters required for the input are b, 

 age of the youngest age-group fished; m, age of the 

 oldest age-group fished; w i3 weight (g) at age i\ r„ the 

 partial recruitment to fishing mortality at age i; and 

 M, the instantaneous rate of natural mortality. Then 



Y/R= i wMF ^ 1 ~ e ~ Zi) . 



where F i = r, F, Z { = F, + M, and N, = N M <T z i-i. 

 The sequence of iV, for each age-group in the fishery 

 is calculated assuming N b = 1. 



The partial recruitment to fishery mortality (r ( ) is 

 the proportion of the fishing mortality which can be 

 allocated to age-group i. These values increase 

 throughout recruitment to a maxium of 1 for fully re- 

 cruited age-groups. In this study r, was estimated as 

 the ratio of the proportions of age- group i in the catch 

 and population survey, standardized to a maximum 

 of 1 by dividing each ratio by the largest one (Win- 

 ters 1978). 



The number of eggs produced per female recruit (E/ 

 R) was estimated for various levels of fishing 

 mortality. 



E/R= Z E t N, 



where a is the age of first maturity for females and E t 

 is the number of eggs per female at age i. For postre- 

 cruits (i > b), N l were as defined above for the esti- 

 mation of Y/R. For prerecruits (i < b), N, were 

 backcalculated assuming iV fc — 1, and Z — M. The 

 number of eggs per female at each age was deter- 

 mined from the fecundity-length and age-length 

 relationships. 



655 



