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stat.isti:cal program that gr:ElduCeS= p~pulatia~ estiarat_es based on <br />capture probabilities, generated fry- cagturel~removal studies . The <br />capture .probabilities ~~.. g.e~erat.ed fir.. eaEh species . <br />Baclo~raters were classified. into s:x.. subtypes based on tMe <br />perceived difficulty in.seinz:ng, ranging from easy (1} to hard {6) <br />(_Tab1e 1). There are two basic difficulties .encountered in <br />backwater sampling. One in~alves our samg~,ing effectiveness ~n <br />areas: with. deep mud; or ether difficult substrates; and the. other <br />our ability to. representatively sale habitats very large in' area <br />and~or water.. depth. Factors ta.consic~:in..sampling efficiency are: <br />Mud. dept3z .and consistenc~r,. Iarger- cohhYe~boulcter sutxstrat~s, <br />debris, water. depth and tumidity.,. size. of. fish, and size of tie <br />backwater. <br />Ai I o.f _ the hahitate tested ~._ i:n the . fires-n rive-rr. _ ~i.ac~ mud ~ s and <br />substrates.. In the s~rri~g of_ 199.,.. sampl~g efficiency was tested <br />on the Colorado River_ near NFoab. to. explcne:. alternati~re substrates, <br />such a~ cablil~e. Also., the blocked. se~ctorrs- were electroshock~ed <br />after aTI seining was e~gleted ta. c~ture. any remai~ng fish. <br />Ta~rle i . Sampling e~ffici~"cp- hack~zat~- sgbtppe~s ~l~ar3s-ri~~d by <br />rnerce_ived difficulty in se~~}r,c~_ <br />1 ~ ss~all ( <=l~?~ F fi r~ substrate ~ <= 10 cam; -mud) <br />2 small, mud depth > laem <br />~ loge (>100m~~~ shalloc~ ~<_ 1r.}~_ mud depth <_~ 1C~em <br />4 large, deep (>_ l') .' .mud depth <:- -IOcm <br />5 La-rc~e, deeP~r- . `~ d~p~t~ ~ ~:~cm <br />~ size- -and mud: c~egth variable, cvbrFle or weed: substrate <br />~es~~s <br />~~~ S <br />For all sampling_ occaszons_,. the initial catch .rates (CgUE~j in <br />fish/10Q~2 were extremely Qar~.able. S~,ig~tt differences. ih .:OPIIE~. wexe <br />observed dependent ou. the-. d~rectox~ of: seine hauls, ~,rh~ere bask <br />