Shrimp Partial Harvesting Model: Decision Support System User Manual

Transcription

1 CTSA Publcaton No. 153 Shrmp Partal Harvestng Model: Decson Support System User Manual Lotus E. Kam, Run Yu, and PngSun Leung Department of Molecular Boscences and Boengneerng College of Tropcal Agrculture and Human Resources Unversty of Hawa` at Mānoa, Honolulu, USA Paul Benfang Department of Oceanography School of Ocean and Earth Scence and Technology Unversty of Hawa` at Mānoa, Honolulu, USA CENTER FOR TROPICAL AND SUBTROPICAL AQUACULTURE

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3 User Informaton & Program Requrements Ths Shrmp Partal Harvestng Model, often hereafter referred to as Model, ncludes worksheets to smplfy data entry and navgaton. Ths manual descrbes the data entry procedures, equatons unque to the Model, and a smplfed fnancal analyss. Users of the Model should have a general workng knowledge of Mcrosoft Excel. For a detaled descrpton of the program, ts functons and commands, consult a Mcrosoft Excel manual or one of the many books descrbng Mcrosoft Excel. Ths beta verson of the Model requres a Wndows PC or compatble that runs Mcrosoft Excel 2002, 2003, or Free space of 1MB s requred. Ths applcaton requres the Solver add-n avalable wth Mcrosoft Excel. Ths applcaton s not compatble wth the Premum verson of the Solver avalable through Frontlne Systems Inc. If you have nstalled the Premum Solver, you must unnstall the advanced verson of the add-n n order to use ths Model software. The provders are not responsble for conflcts between versons of the Solver and Mcrosoft Excel. Lmts of Lablty and Dsclamer of Warranty The authors of ths manual have used ther best efforts to prepare ths manual and the program t supports. The authors make no warranty of any knd, expressed or mpled, wth regard to these programs or the documentaton contaned heren. The authors shall not be held lable for ncdental or consequental damages n connecton wth, or arsng from, the furnshng, performance or use of the program. Shrmp Partal Harvestng Model: Decson Support System User Manual

4 Contact Please drect nqures regardng ths publcaton and assocated software to PngSun Leung through ether e-mal or regular mal usng the below contact nformaton: PngSun Leung Department of Molecular Boscences and Boengneerng Unversty of Hawa` at Mānoa 3050 Male Way, Glmore 111 Honolulu, HI 96822, USA Trademarks Mcrosoft and Excel are trademarks of the Mcrosoft Corporaton. Copyrght 2008 CTSA Publcaton No. 153

5 Acknowledgements Many people contrbuted to the development of ths Shrmp Partal Harvestng Model. The authors thank Mr. James N. Sweeney and Mr. Davd Godn of the former Ceatech USA Inc. for ther varous forms of support for and assstance wth the valdaton of ths Model. The Model and software development was made possble by the generous support of the Center for Tropcal and Subtropcal Aquaculture through grant nos and from the U.S. Department of Agrculture Cooperatve State Research, Educaton, and Extenson Servce. Shrmp Partal Harvestng Model: Decson Support System User Manual

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7 Shrmp Partal Harvestng Model Decson Support System User Manual 1. Introducton In tradtonal shrmp culture and other ntensve aquaculture systems, an entre crop can be harvested at one tme. However, snce growth and survval are densty-dependent, sngle-batch harvestng can lead to compettve pressures that lower ndvdual growth and ncrease mortaltes. In comparson to sngle-batch harvestng, a partal harvestng approach can enhance growth rates and total yeld, snce a reducton n total bomass reduces compettve pressure. In partal harvestng, a crop can be partally-harvested so that only a porton of the crop s extracted. Ths Shrmp Partal Harvestng Model was created to smulate the effects of partal harvestng and assst farm managers n decdng the most proftable harvestng schedule. Ths Shrmp Partal Harvestng Model, often hereafter referred to as Model, s a decson support system based on a network-flow approach. Ths Model determnes the optmal harvestng tmes that maxmze the overall net revenue based on bologcal and economc factors (e.g., survval, growth, and prce). Ths Model was mplemented n a spreadsheet form usng Mcrosoft Excel. The model requres the use of the Solver add-n. See Part B of the Appendx for nstructons on nstallng the standard Solver. Detals of the Model development also can be found n the Appendx. Clck Begn on the ntroducton screen to begn usng the Partal Harvestng Model (Fgure 1-1). Fgure 1-1. Vew of the ntroducton screen. 1

8 2. Man Menu The Man Menu of ths spreadsheet Model provdes access to worksheets to enter nformaton about farm operatons (Operatons), market prce and demand nformaton (Market Info), and boproducton technology performance (Boproducton). Use the Analyss button to determne the optmal harvestng strategy. Use the Results button to fnd the producton schedule and overall net revenue soluton for the most recent analyss. In compatble versons of Excel, a navgaton toolbar s located at the top of the screen. The navgaton toolbar provdes access to the worksheets, fle, vewng, and prntng optons. The navgaton toolbar s not avalable n Mcrosoft Offce Fgure 2-1. Vew of the Man Menu used for navgaton. 3. Operatons Informaton about farm operatons s needed to estmate the operatng expenses that a farm wll ncur. 2 CTSA Publcaton No. 153

9 The total pond area must be specfed n acres. The total pond area refers to the sze of a sngle pond. Multple ponds are not consdered n ths smplfed partal-harvestng model. Multple ponds ntroduce a more complex schedulng problem (Yu and Leung 2005). Key farm costs are requred, ncludng the expenses lsted as examples below: weekly mantenance cost ($/week), feed cost ($/lb), harvest cost ($/harvest), and seed cost ($/1000). Ths Model s desgned to determne f t s more advantageous to engage n multple small partal harvests n comparson to a sngle (or few) very large harvests. In order to nvestgate the benefts of the partal-harvest strategy, users must specfy the cost for a tradtonal full harvest and a partal harvest. Fgure 3-1. Vew of the nput screen for Operatons. In ths partal harvestng software, users specfy the maxmum sze of the partal harvest (partal harvest lmt) n lbs/harvest. The partal harvest lmt should be greater than 0 and ndcates the maxmum amount that can be harvested at the partal harvest cost ($/harvest). In Fgure 3-1, for example, the cost to harvest any amount over 1,000 lb. s $1,000. For harvests less than or equal to 1,000 lb., the cost s $250. Shrmp Partal Harvestng Model: Decson Support System User Manual 3

10 Specfy the seed sze n grams. The seed cost must be specfed n conventonal unts of dollars per thousand peces ($/1,000). The cost s converted nto $/lb based on the seed sze entered. Note: If there s no dstncton between a partal harvest and large harvest, the harvest cost should be the same. Do not leave ether of these cells blank. For large pond szes, t may make sense to ncrease the partal harvest lmt accordngly. 4. Market Informaton (Input) Informaton about the market sze and demand s needed to determne the potental revenue avalable to the farm enterprse. Fgure 4-1. Vew of the Market Informaton nput screen. 4 CTSA Publcaton No. 153

11 4.1. Market Sze (B1) Ths spreadsheet dvdes the market demand for shrmp products nto seven common count szes. Snce market szes are specfed as ranges correspondng to the number of shrmp per pound, a farmer can specfy hs target weght crtera. In partcular, a farmer may choose to meet the mnmum, average, maxmum, or other weght crtera correspondng to each range. In ths example, the farmer has chosen to meet the mnmum shrmp szes, whch are 9.07 g (40 50 count), g (41 45 count) and g (16 20 count). The mnmum settng s the most conservatve and recommended for most producton systems. Hgh crtera requre more effcent boproducton technologes. Ths Model wll not be able to provde a harvest soluton f boproducton technology (dscussed n Secton 5) cannot acheve the sze crtera specfed. Therefore, f you have dffculty runnng your model, you may want to revse your Market Sze nformaton. The count ranges are based on current market demand but can be customzed by a user. As llustrated n Fgure 4-2, a user can customze the range settngs by modfyng the maxmum count correspondng to each growout phase and the overall mnmum count (.e., the largest shrmp). The maxmum count of shrmp for each market range should be decreased for successve ranges. The length of a growout perod corresponds to shrmp sze and shrmp count. Specfcally, extendng the length of growout means ncreasng shrmp sze and reducng shrmp counts. Ths Model requres consecutve ranges such that the maxmum counts for each range decrease for later growout phases. Ths Model wll verfy whether szes are sequental before conductng analyss. A user can specfy target szes n the Other column. When selectng Other for crtera, weghts must be specfed for each range n the far rght column. These target weghts should fall between the mnmum and maxmum count szes for each sze range. The values n the Other column cells are only actve when the target weght crtera s set to Other from the drop down menu. Fgure 4-2. Specfyng target weght crtera and market sze range. Shrmp Partal Harvestng Model: Decson Support System User Manual 5

12 4.2. Market Demand The Target Sze (n grams) should reflect the weght correspondng to your target weght crtera. Enter the Mnmum Producton correspondng to each sze. If no producton s requred for a sze category, enter 0. In Fgure 4-5, no mnmum producton s requred. Enter the Maxmum Demand correspondng to each sze. If demand s unknown or not very large, type =MaxValue and the maxmum default value wll appear. Fgure 4-3. Default Mnmum Producton and Maxmum Demand (Partal Harvest Scenaro). Farms may be requred to fulfll a mnmum producton level f they have contracts wth shrmp wholesalers. If a mnmum level of producton s requred, the Mnmum Producton amount must reflect the requred producton for each sze. Fgure 4-4 llustrates the case where a farm s requred to produce a mnmum volume of 5,000 lb. of count and 14,000 lb count shrmp. For the sngle-batch harvest scenaro, the Mnmum Producton for all product szes should be set to 0. The Maxmum Demand should also be equal to 0 for all growout szes except for the fnal harvest sze (see Fgure 4-5). The mnmum producton requred must be less than the carryng capacty. The Maxmum Demand for the fnal harvest (growout phase) cannot be equal to zero. Fgure 4-4. Specfyng a producton requrement (Partal Harvest Scenaro wth Producton Requrement). Fgure 4-5. Sngle-batch harvest scenaro (baselne scenaro). 6 CTSA Publcaton No. 153

13 5. Boproducton (Input) In order to measure the fnancal performance of a shrmp farm, nformaton about boproducton technology s needed. Recommended boproducton performance data s avalable n the Boproducton worksheet. Values are based on data collected from a commercal shrmp farm n Hawa`, whch operated 40 one-acre ntensve shrmp ponds (Yu, Leung, and Benfang 2007). Growth and mortalty nformaton s based on tradtonal sngle-batch harvest practces. Fgure 5-1. Vew of nput screen for Boproducton Technology. Boproducton performance values may be changed based on your farm s producton specfcatons: Indcate the carryng capacty for your pond (kg/m 2 ). The carryng capacty s assumed to be the same for all phases and s based on the value you specfy. Provde the ntal stockng densty for the frst growout perod n shrmp per square meter (.e., frst row n the current densty column). Estmate the densty for subsequent phases based on your pond performance. These densty estmates should be based on sngle-batch harvest practces. Estmate the weekly growth rate (g/week) for each growout phase. Provde the current survval rate for each phase (% survval). Shrmp Partal Harvestng Model: Decson Support System User Manual 7

14 Enter the maxmum growth rate for each phase (g/week). Current growth rates should always be less than maxmum growth rates. Enter the feed rate as a percentage of pond bomass. The worksheet also provdes a summary about the growth curve, tme requred to reach market weght, and growth lmts based on the producton technology specfed. Fgure 5-2. Boproducton growth and lmt summary. 6. Analyss To run a partal harvest analyss based on your nput, clck the Analyss button. Some valdaton has been bult nto ths Model. Ths worksheet verfes that entered values are consstent or acceptable wthn the workbook. Ths program wll verfy that the followng constrants are met: Count szes should decrease for subsequent phases. Maxmum growth s less than the growth lmt for each phase. Please be patent as the analyss runs through a sequence of sx dfferent algorthm settngs. If your analyss s successful, you wll be drected to a summary report. The optmal soluton s compared to the sngle-batch harvestng soluton n ths report. 8 CTSA Publcaton No. 153

15 Fgure 6-1. Begnnng the analyss. Note: If the program s not able to run successfully based on your nput, a partal-harvest soluton wll not be gven. You wll receve a message that requests revson of your nputs. Shrmp Partal Harvestng Model: Decson Support System User Manual 9

16 7. Results Results nclude summary nformaton about boproducton performance (D1), market summary (D2), revenue and expenses (D3), and net revenue (D4). Fgure 7-1. Results spreadsheet Boproducton Performance Informaton about Boproducton Performance ncludes ntal densty, duraton of each phase, weekly growth rates, harvest weght, and harvest schedule. The optmal partal harvestng soluton for a scenaro wth no producton requrement and unlmted demand s ndcated n Fgure 7-2. Accordng to these results, the stockng densty should be shrmp/m 2 wth harvests after 7.4 weeks (1,000 lb. of count shrmp), 9.0 weeks (1,000 lb. of count shrmp), 14.9 weeks (102 lb. of count shrmp), and 20.6 weeks (14,738 lb. of count shrmp). The total weght harvested by the end of the 20.6 weeks s 16,840 lb. of shrmp Market Demand In the Market secton, the mnmum demand (requred producton) and maxmum demand values entered earler by a user n the Boproducton sheet nput are dsplayed. These demand ranges ndcate market constrants mposed on the farm. The count ranges used n ths analyss are also dsplayed for reference. Ths market nformaton s llustrated n Fgure CTSA Publcaton No. 153

17 Fgure 7-2. Boproducton performance and market nformaton Revenue and Expenses Operatng costs, proft from sales (revenue operatng costs), and harvest costs are lsted n the results worksheet (D3). Proft from sales (revenue producton costs) s calculated for each growout phase (Fgure 7-2) Net Revenue Summary The Net Revenue Summary provdes nformaton on revenue from sales, expenses (operatng costs and harvest costs), and net revenue for each growout phase. The Pond Summary s based on user-entered nformaton on operatons, boproducton, and market. The partal harvest soluton s always compared to the sngle-batch, full-harvest optmal soluton. In the example above (Fgure 7-3), the partal harvest soluton s expected to generate an overall net revenue of $58,119 n comparson to the sngle-batch harvest of $57,239 at 19.9 weeks. Therefore, the partal harvest method s expected to ncrease overall net revenue by $880. Fgure 7-3. Partal harvest result compared to snglebatch baselne scenaro. Shrmp Partal Harvestng Model: Decson Support System User Manual 11

18 7.5. Producton Requrement Example The followng example (Fgure 7-4) llustrates the mpact of market constrants on the partal harvest soluton. In contractual busness relatonshps, a farm may be requred to produce a mnmum level of producton for a certan market sze of shrmp. Gven these constrants, a producer s forced to harvest a mnmum volume of product at specfc tmes durng the growout perod. In ths producton requrement (PR) example, the farm s requred to produce 5,000 lb. of count shrmp and 14,000 lb. of count shrmp. The market demand nputs for ths scenaro are entered as llustrated earler n Fgure 4 4. Note: Whenever changes are made to nput values, the analyss must be run n order to determne the harvest schedule based on the new nformaton. Usng the Shrmp Partal Harvestng Model on ths example produces the followng analyss. Optmal stockng s anmals per square meter. Shrmp should be harvested as follows: 5,000 lb. at 10.7 weeks (36 40 count), 102 lb. at 18.0 weeks (21 25 count) and 14,738 lb. at 23.7 weeks (16 20 count). The result of ths producton schedule s overall net revenue of $53,317 and a total harvest of 19,840 lb. These producton requrements, then, result n a loss of $3,921 n comparson to the tradtonal sngle-batch harvest method. In comparson to the optmal partal harvest soluton wth no producton requrement exhbted n Fgure 7-3, the projected loss s $4,801 (= $58,119 - $53,317). Ths example llustrates the case where a farmer s dsadvantaged by a wholesalng contract that mposes producton requrements. Fgure 7-4. Partal harvest result for requred producton compared to the sngle-batch baselne scenaro. 12 CTSA Publcaton No. 153

19 8. References R. Yu and P.S. Leung Optmal harvestng strateges for a mult-pond and mult-cycle shrmp operaton: a practcal network model. Mathematcs and Computers n Smulaton 68(4): R. Yu, P.S. Leung, and P. Benfang Modelng partal harvestng n ntensve shrmp culture: a network-flow approach. European Journal of Operatonal Research. do: /j. ejor APPENDIX A. The Mathematcal Model Suppose a shrmp producton cycle s comprsed of N growout phases. Let H and P s denote the amount of shrmp harvested at the th growout phase n kg and ts assocated shrmp prce ($/kg), N N N Ps H - (C f+c m)- HC =1 =1 =1 s.t. HC =0, f H =0 HC =C h, f H > 0 H H H max mn (1) respectvely. The overall net revenue from ths producton cycle can be estmated as follows: where C f, C m, HC are feed cost, mantenance cost, and harvest cost occurrng n the th growout phase, respectvely. Only a quas-fxed harvest cost, C h, s consdered n the present model. In other words, f the producer decdes to do a harvest, t wll result n a fxed expendture; H max and harvest. C h. H mn are the maxmum and mnmum amount of shrmp that can be extracted by the th Let D and B denote the densty of shrmp stock (e.g., kg/m 2 ) at the begnnng and end of the th growout phase, respectvely. Defne V as the total area (or volume) of the water body of the growout faclty (e.g., m 2 ). Assume there s no restockng between two successve growout phases. The amount of shrmp that s extracted by the th harvest at the end of the th growout phase, +1, then can be estmated as H =VB -VD,.e., the dfference between the bomass at the end of the th growout phase and that at the begnnng of the +1 th growout phase. Snce all the shrmp wll be harvested at the end of the growout cycle, t mples producer s to maxmze overall net revenue. H N N H =VB. Assume the objectve of the Shrmp Partal Harvestng Model: Decson Support System User Manual 13

20 The partal harvestng problem can be expressed as follows: D N-1 +1 N N N N s f m + s f m N (2) =1 Max [P V (B -D )-C -C -HC ] P V B -C -C -HC Let W denote the target weght of shrmp n the th growout phase (e.g., g/shrmp). Defne N+1 0 D =0 and Ps = Cs, where C s s seed cost per unt (e.g., $/kg). Problem (2) then can be rewrtten as follows: D N -1 s s f m (3) =1 Max [V (P B -P D )-C -C -HC ] s.t. 0, f D >Dmax G =g(d )= G max, f D <Dmn Gmax -(Dmax -D )(G max -G current ) (Dmax -D current ), otherwse (4) 0, f D >Dmax S =s(d )= Smax, f D <Dcurrent (Dmax -D )(Scurrent -S mn ) (Dmax -D current )+S mn, otherwse (5) W B = W DS -1 (6) V (D +B ) W -W C =P 2 G -1 f f FR (7) W -W G -1 m m C =P H V (B -D ) H +1 max mn (8) (9) +1 0, f V(B -D )=0 HC = C h, otherwse (10) P = C, D =0, (11) 0 N+1 s s 14 CTSA Publcaton No. 153

21 where G and S are the growth (e.g., g/week) and survval rates (%) of shrmp n the th growout phase and equatons (4) and (5) are the correspondng densty-dependent growth and survval functons used to estmate the mpacts of densty on growth and survval. As llustrated n Fgures 1 and 2, D max s the densty at the carryng capacty (e.g., kg/m 2 ), the current practce, and G max and ts assocated mnmum possble densty. Smlarly, Dcurrent s the densty under D mn are the maxmum possble growth (e.g., g/week) and S current s the survval rate under the current densty level ( D current ) and S m n s the survval rate at the carryng capacty ( D max ). Equaton (6) defnes that the densty at the end of the th growout phase ( B ) s the product of the densty at the begnnng of the th growout phase ( D ), the assocated survval rate ( S ), and the rate of ncreased shrmp weght ( W ). Equaton (7) estmates total feed costs n the th growout phase, where P - 1 f W and FR are, respectvely, feed cost per unt (e.g., $/kg) and average feedng rate n terms of percentage of the prevalng bomass. Equaton (8) calculates total mantenance costs, where Pm s mantenance cost per unt (e.g., $/week). Equaton (9) specfes the maxmum and mnmum possble amount of shrmp that can be harvested by the th harvest. Equaton (10) s the quas-fxed harvest cost functon. Fgure A-1. Densty-dependent growth. Note: D max denotes the densty at the carryng capacty (e.g., kg/m 2 ); D current and G current denote the densty (e.g., kg/m 2 ) and growth (e.g., g/week) under the current practce; G max and D denote the mn maxmum possble growth (e.g., g/week) and assocated mnmum possble densty (e.g., kg/m 2 ). Shrmp Partal Harvestng Model: Decson Support System User Manual 15

22 Fgure A-2. Densty-dependent survval. Note: D max denotes the densty at the carryng capacty (e.g., kg/m 2 ), D current and S current denote the densty (e.g., kg/m 2 ) and survval rate (%) under the current practce, and S mn denotes the survval rate (%) at carryng capacty. 16 CTSA Publcaton No. 153

23 B. Installng the Solver The Frontlne Solver s requred n order to run ths Shrmp Partal Harvestng Model. If the Solver add-n has already been actvated n your Mcrosoft Excel software, t wll appear n your Tools drop-down menu. Fgure B-1. Solver appears n the Tools menu of Excel. Shrmp Partal Harvestng Model: Decson Support System User Manual 17

24 B.1. Solver s not located n the Tools menu If the Solver s not located n the Tools menu, the followng steps wll assst you n loadng the Solver add-n. 1) Start Excel and clck on Tools on the menu. Then clck on Add-ns... 2) A box should appear wth a lst of add-ns. If there s no checkbox for Solver Add-n, go to B.2. on the next page. 3) Check the checkbox for the Solver add-n 4) Clck OK. 5) The Solver should now be lsted on the Tools menu n Excel (see Fgure B-1). Fgure B-2. Select the Solver add-n. 18 CTSA Publcaton No. 153

25 B.2. Solver s not located n the lst of avalable add-ns. If the Solver s not located n your lst of add-ns, you wll need your Mcrosoft Offce CD-ROM. The followng steps wll assst you n nstallng the Solver add-n. 1) Insert the Mcrosoft CD-ROM. If the CD does not run the setup program automatcally, open My Computer, locate and double-clck the setup.exe fle on the CD. 2) Clck the Add or Remove Features button. 3) In the graphc that then appears, clck the lttle plus sgn next to Mcrosoft Excel for Wndows. Ths opens up the outlne under that box. 4) Clck the plus sgn next to Add-ns n order to expand the lst. The Solver should be lsted n the expanded lst of add-ins. 5) Clck on Solver and choose Run from My Computer, so that the box s whte, wth no yellow 1. Ths pcture llustrates how t should look when you re done. 6) Then clck Update Now to proceed wth the nstallaton. Dependng on your verson of Mcrosoft Offce, your screen may be dfferent, but ths procedure wll be smlar. 7) Go to step B.1 on the prevous page. Fgure B-3. Installng the Excel Solver add-n. Shrmp Partal Harvestng Model: Decson Support System User Manual 19

26 C. Macros used n the Model Ths Shrmp Partal Harvestng Model contans macros and executable VBA scrpt. Macros must be enabled n order to use ths Model. When openng ths Model n Mcrosoft Excel, the followng warnng about macros may appear: C.1. Enablng macros Clck on the Enable Macros optons n order for ths Model to run properly. Fgure C-1. Enable Macros dalog box. If you open the fle and the Enable Macros dalog box does not appear, please change your securty settngs n Excel (see C.2. on the next page). 20 CTSA Publcaton No. 153

27 C.2. Changng your securty settngs 1) From the Excel Tools Menu, select Macro > Securty. Fgure C-2. Changng Macro Securty settngs. Shrmp Partal Harvestng Model: Decson Support System User Manual 21

28 2) In the Dalog box, select Medum securty 3) Press OK. 4) Close the fle, and then open t agan. You should see the Enable Macros dalog box (Fgure C-1) Fgure C-3. Changng the macro securty level. 22 CTSA Publcaton No. 153

29 For more nformaton, please contact the Center for Tropcal and Subtropcal Aquaculture Oceanc Insttute Kalanana`ole Hwy. Wamanalo, HI Tel: (808) Fax: (808) Unversty of Hawa` 3050 Male Way, Glmore 124 Honolulu, HI Tel: (808) Fax: (808)