TPWD 1968 F-6-R-15 #1172: Job Completion Report: Appraisal of Various Mesh Sizes in Taking Fishes at Lake Corpus Christi, Texas, Project F-6-R-15, Job D-3

JOB COMPLETION REPORT AS required by FEDERAL AID IN FISHERIES RESTORATIONACT -TEXAS Federel Aid PrOject No. F-6~15 FISHERIES INVESTIGATIONS - REGION 5-3 Job No. D-3 (3rd of 4 segments) Appraisal of various Mesh' Sizes in Taking Fishes at Lake CorpuS_Christi, TeXas Project Leader: JOhn C. BarrOn- J. R. Singleton . Executive_Director Parks and-Wildlife Department; Austin, Texas Marion Toole I Eugene A..Walker D—J Coordinator Director, Wildlife Services October 17, 1968 ABSTRACT Uniform mesh gill nets varying from 1 to 4 inches square mesh were set monthly at three locations in Lake Corpus Christi. These data were collected and transposed to punched cards for computer analyses. Tentative analysis utilizing the negative binomial distribution provided information on the net mesh sizes to which various fish species were vulner— able. A detailed example analysis with freshwater drum showed that mesh size introduced the greatest variability into the catch distribution, followed closely by location. Except for blue catfish, few game fish were taken in 3-inch and larger mesh. 1 JOB COMPLETION REPORT «int? Oi Texas Praject No. F—6-15 Name: Fisheries Investigations — Region S-B ' Ens No. D-3 ' Title: Appraisal of Various Mesh Sizes in Taking Fishes -_ ivriod Covered: January 12 1967 to December 31, 1967 . _ magnetive: To determine the relation between mesh size of gill nets and species .nnnnsition of the catch. Transduresz Monthly netting was conducted at Lake Corpus Christi. The nets used “at? uniform mesh gill nets 100 feet long and of the following bar measures: is“, 2—, 2%-, 3-, 3%-, and 4-inches. The nets were set parallel to each ~:hnr approximately fifty yards apart. A random design was.used_to deter- w‘aa set and run order so that fishing time variation would be minimized. -1raa stations were established and each mesh size set at each location every varib; A total of 252 settings were made. Station No. 1 was immediately are rhe dam; Station No. 2 was at Miller's Island, about five miles above Jan: and Station No. 3 in Ramirena Creek, about 11 miles above the dam. “or each fish taken, the following data were recorded: Species Net mesh size Date collected Station location Body depth (not measured over curvature) Total length Standard length Weight Fishing time (number of minutes net remained in water) Mean water temperature (average of set and run values) Water turbidity (Secchi disc) Mean station depth (average of inner, mid, and outer depth readings) NHOkOOOwcjmebwmr-J All data were recorded in the field; and upon return to headquarters were typed, checked for accuracy, and mailed to the Data Processing Section at the Austin Headquarters to be transferred to punched cards. This procedure was in preparation for future analysis by electronic data processing equipment. Results: There is substantial.literature on the subject of fishing gear and gear selectivity, and the mathematics are sometimes formidable. Beverton and Holt (1957) have-covered the subject extensively in their book, although most of their examples deal with marine species and their equations usually presuppose a knowledge of age of the specimen. Since the purpOse of this study was not to determine the fishing power or efficiency of gill nets, but instead to determine the composition of their catches (with particular emphasis on game fishes), a simple approach seemed justifiable. Moyle and Lound (1960), Lambou (1963), and numerous other investigators have demonstrated that the negative binomial distri— bution will yield an appropriate unit for comparing catches of the number of fishes of specific species. The negative binomial is a contagious distribution; contagion being used in the sense that if an individual of a species is found in a given area then the probability that a similar individual will be in the same area is increased and implies that fishes are not distributed at random. The negative binomial distribution concerns the number of times a specific number of individuals of a species is taken in a series of samples. The shape of the curve is usually positively skewed indicating that more individual observations occur below the mean than do above it. Generally the zero class (no fish of the species in question taken in a sample) has the greatest frequency. The distribution is described by three parameters: the mean, m; the variance, v; and the coefficient of contagion, K. Com— putation of the first two is common knowledge, and the latter can be approximated by: K = m Obviously, m = v since division by zero is undefined; therefore, if v = m then the distribution in question cannot be fitted to the negative binomial. The mean, too, is never larger than the variance in the negative binomial- This distribution has the advantage in that transformations are available which tend toward the normal distribution. Moyle and Lound demonstrated that the transformation yi = log (Xi + %K) is more applicable than the easier to use yi =N/ xi'+ %? These transformations are of primary importance if analysis of variance is contemplated. Table 1 ' Catch Distribution of the Freshwater Drum Fitted to the Negative Binomial Distribution Number of Calculated Observed _ Fish ner Net Fre-uenc (F) Fre-uenc .1 OH \00 NH Table 2 Analysis of Variance of the Catch Distribution of Freshwater Drum Source of Variation Mesh sizes : ' 32.358169 Months 2' ' . ' 1.679618 Locations ' - 20.580390 Months x location ' ' . ; 1.789221 Months x mesh sizes . ; .I : 0.487310 Locations x mesh sizes ' 5 4.401644 .Second order interaction _ ; 1 0.824874 ?Tota1 * Significant at the 0.5% level. Table 3 Catch Distribution Per Mesh Size for Several Species Mesh _ Number of fish uer net Secies (in) W Alligator gar ' Longnose gar Spotted gar - Gizzard shad f Smallmouth buffalo *Denotes an infinite or negative reciprocal. Table 4 Catch Distribution Per Mesh Size for Several Species Mesh } ' Number of fish er as: Species 3 (in.) 3 4 Channel catfish ' Blue catfish I Flathead catfish White bass *Denotes an infinite or negative reciprocal. Table 5 Catch Distribution Per Mesh Size for Several Species 1/K 5+ 2 1 Number of fish per net _ _ 3 4 _ 0 . Mesh S-ecies (..) 6.47 29 1... Largemouth bass 31 1/2 36 36 36 172 36 36 1/2 122334 35 Warmouth 36 .. 11.1.1.9 ill... 5.1.11... '1'... 1!... 00 00 00 000000 000000 000000 100000 . Bluegill 1000 0000 1000 ' Redear sunfish 00 0 2221 14/011. 352/... 'White crappie *Denotes an infinite or negative reciprocal. Table 6 . Catch Distribution Per Mesh Size for Several Species . Mesh ' ' Number of fiSh per net _ T- 7". S-ecies _ . , (ins); _ _O_ _ 1.. _m£m__fl 3 infimmn__§:n..iw .x Black crappie 1 23 8 2 0 2 1 ' 1% 10 4 4 6 2 10 2 29 6 0 1 0 0 2% 36 0 0 0 0 0 3 35 l 0 0 0 0 3% 36 0 0 0 0 0 6 36 0 .9... 0 0 19...... . Freshwater drum_ ' I 20 5 4 1 2 4 ' 5 2 3 5 0 21 8 8 4 2 1 13 22 4 4 3 1 2 26 6 2 1 0 1 31 5 0 0 0 0 36 .2 I 0 ._ 0 _. 0 9.___ i *Denotes an infinite or negative reciprocal.