In Elephant Butte Lake, New Mexico

EFFECTS OF COMMERCIAL FISHING ON THE POPULATION OF

SMALLMOUTH BUFFALO, Ictiobus bubalus (Rafinesque),

IN ELEPHANT BUTTE LAKE, NEW MEXICO

THOMAS MONROE MOODY, B.S.

A Thesis submitted to the Graduate School

in partial fulfillment of the requirements

for the Degree

Master of Science

Major Subject: Wildlife Science

New Mexico State University

Las Cruces, New Mexico

May 1970 "Effects of Commercial Fishing on the Population of Smallmouth

Buffalo, Ictiobus bubalus (Rafinesque), in Elephant Butte Lake,

New MeXico," a thesis prepared by Thomas Monroe Moody in partial fulfillment of the requirements for the degree Master of Science, has been approved and accepted by the following:

Dean of the Graduate School

Chairman of the Examining Committee

Date

Committee in charge:

Mr. Douglas B. Jester, Chairman

Dr. Charles A. Davis

Dr. A. L. Neumann

Dr. Ralph J. Raitt ACKNOWLEDGEMENTS

Financial support for this project came from the New Mexico

Department of Game and Fish, Commercial Fisheries Research and

Development Project 6-11-R, under contract with the Agricultural

Experiment Station, New Mexico State University, Project 4110-40.

I wish to express my personal gratitude to Mr. Douglas B.

Jester, Assistant Professor of Wildlife Science, New Mexico State

University, for guidance of the study and manuscript preparation.

Thanks go to Graduate Research Assistants Daryl E. Jennings,

Charlie Sanchez, Jr., Buddy L. Jensen, and James N. Hanson for

assistance with collection and analysis of data.

I am indebted to Mr. and Mrs. B. C. Sparkman for encourage-

ment and aid in collection of data.

Thanks are also due to Mr. Gene Bales and other members of

the New Mexico Department of Game and Fish for assistance in col-

lecting data and for use of equipment.

I am grateful to my parents and to my wife, Delpha, for their

encouragement and patience throughout the course of this study. VITA

November 7, 1946--Born in Santa Fe, New Mexico

1968--B.S., New Mexico State University, Las Cruces

1968-1970--Graduate Research Assistant, Department of Animal, Range, and Wildlife Science

PROFESSIONAL AND HONORARY SOCIETIES

Alpha Zeta

American Fisheries Society

American Institute of Biological Sciences

Blue Key

The Wildlife Society

111 '44 ABSTRACT

EFFECTS OF COMMERCIAL FISHING ON THE POPULATION OF

SMALLMOUTH BUFFALO, ictiobus bubalus (Rafinesque),

IN ELEPHANT BUTTE LAKE, NEW MEXICO

THOMAS MONROE MOODY, B.S.

Master of Science in Wildlife Science

New Mexico State University

Las Cruces, New Mexico, 1970

Professor Douglas B. Jester, Chairman

Studies were made on several parameters of the population of smallmouth buffalo in Elephant Butte Lake, New Mexico. Results are compared with similar studies made prior to April, 1968, to deter- mine influences caused by commercial removal of 95,640 fish weighing 383,639 pounds in six years.

Population estimates made by use of the Schnabel Method, decline in the commercial catch, catch rates in experimental gill nets, changes in condition of fish, and decreases in relative density and biomass, all indicate that the buffalo population has

iv •

been reduced. Comparison of age-growth studies, length-frequencies,

weight-frequencies, and length-weight relationships shows increases

in growth rates and improved condition resulting from reduction in

intraspecific competition.

Data on fecundity and reproduction indicate that the population

of smallmouth buffalo could expand rapidly if fishing pressure were

reduced or removed. It is recommended that commercial fishing be

continued to maintain the population at current or lower levels for

purposes of enhancing sport fisheries.

Secondly, continued commercial fishing will result in utiliza-

tion of this resource which would not otherwise be used. 1

TABLE OF CONTENTS

TITLE PAGE ....

ACKNOWLEDGEMENTS

VITA .... iii

ABSTRACT ..... iv

TABLE OF CONTENTS ..... vi

LIST OF TABLES .... vii

LIST OF FIGURES ..... ix

INTRODUCTION ...... 1

ELEPHANT BUTTE LAKE ...... 3

METHODS AND MATERIALS ...... 7

FINDINGS AND DISCUSSION ...... 9

Density and Biomass ...... 9

Number and Weight per Net-Unit ...... 9

Commercial Catch ..... 11

Length-Frequency ..... 12

Weight-Frequency ..... 13

Condition ..... 13

Length-Weight Relationship ..... 14

Age-Growth ..... 14

Population Estimates ..... 20

Reproduction and Fecundity ..... 22

SUMMARY ...... 26

LITERATURE CITED ..... 28

VI '

LIST OF TABLES

TABLE Page

1. Relative density and biomass, rank, and fish exceeding smallmouth buffalo in Elephant Butte Lake, New Mexico, June, 1964, through March, 1970 ...... 10

2. Number,and weight of smallmouth buffalo caught per net-unit in Elephant Butte Lake, New Mexico, from 1964-65 through 1969-70 ...... 11

3. Number of days fished, total number and weight of fish caught, daily means, and mean weight of buffalo harvested from Elephant Butte Lake, New Mexico, 1963 through 1969 ...... 12

4. Percent of buffalo included in length ranges taken from Elephant Butte Lake, New Mexico, 1967-68 through 1969-70 ...... 12

5. Percent of buffalo included in weight ranges taken from Elephant Butte Lake, New Mexico, in 1968-69 and 1969-70 ...... 13

6. Coefficient of Condition (Kt') of all buffalo taken from Elephant Butte Lake, New Mexico, 1964-65 through 1969-70 ...... 14

7. 'Weights of smallmouth buffalo at various lengths, derived from length-weight relationships of fish from Elephant Butte Lake, New Mexico, 1964-68 through 1969-70 ...... 14

8. Calculated mean lengths, weights, and increments of growth of 90 smallmouth buffalo from Elephant Butte Lake, New Mexico, April, 1969, through March, 1970 . 18

9. Grand mean lengths, weights, and increments of growth of buffalo compared with data found by Patterson ...... (1968) 19

10. Population estimates of smallmouth buffalo in Elephant Butte Lake, New Mexico, August, 1964, through March, 1970. Determined by use of the...... Schnabel Method 21

VII LIST OF TABLES (continued)

TABLE Page

11. Age, length, and weight of females, weight of ovaries, number of eggs produced per .female, and mean number of eggs from buffalo taken during spawning season, from Elephant Butte Lake, New ...... Mexico, 1969 25

VIII

LIST OF FIGURES

FIGURE Page

1. Locality and map of Elephant Butte Lake, New Mexico, showing shoreline at maximum storage capacity and approximate shoreline at average storage volume during this study ......

2. Surface and outlet temperatures and water storage values in Elephant Butte Reservoir for 1960 through 19 5

3. Body-scale regression of 90 smallmouth buffalo from Elephant Butte Lake ...... 17

IX EFFECTS OF COMMERCIAL FISHING ON THE POPULATION OF

SMALLMOUTH BUFFALO, Ictiobus bubalus (Rafinesque),

IN ELEPHANT BUTTE LAKE, NEW MEXICO

INTRODUCTION

The smallmouth buffalo, Ictiobus bubalus (Rafinesque), is classified by Blair et al. (1957) as follows:

Superclass Pisces

Class Teleostomi

Subclass Actinopterygii

Order Cypriniformes

Family Catostomidae

Genus Ictiobus

Species Ictiobus bubalus (Rafinesque)

Moore (in Blair et al. 1957) describes range 0C -the species as western Hudson Bay to the Ohio River drainage and south through the gulf states and northeastern Mexico. The species is found only in the lower Pecos and Rio Grande drainages in New Mexico.

It has not been recorded north of Elephant Butte Lake in the Rio

Grande drainage (Koster 1957).

Smallmouth buffalo are common in Elephant Butte Lake. They are one of three major "rough fish" species present. Rough fish are defined as species which compete with sport or "game" fish for space or food but contribute nothing to sport fisheries.

Reduction of numbers of smallmouth buffalo is one of the primary 2

objectives of the management plan proposed for Elephant Butte Lake by Jester (1963) and currently in operation.

Buffalo are palatable and acceptable to the market as a food fish. This allowed the plan to provide for establishment of a commercial fishery to remove buffalo from Elephant Butte Lake.

Mr. B. C. Sparkman, a commercial fisherman under permit from the

New Mexico Department of Game and Fish, started harvesting and mar- keting buffalo from the lake in August, 1963.

By the end of December, 1969, he had removed 95,640 fish weighing 383,639 pounds. Fish removal of this magnitude has significantly reduced the buffalo population, changed several growth parameters, and affected the ecology of the entire fish community in the lake. The portion of the research represented in this thesis deals with changes in parameters of the buffalo population.

Commercial exploitation of buffalo is shown here to be an effective means of reducing buffalo populations. At the same time, it allows for utilization of a human food resource that would otherwise be wasted. ELEPHANT BUTTE LAKE

Elephant Butte Lake is a large, warmwater reservoir. It is operated by the United States Bureau of Reclamation for purposes of irrigation storage and generation of electric power. The con- crete dam impounding the lake was completed in 1916. It is located on the main stream of the Rio Grande five miles northeast of Truth or Consequences, Sierra County, New Mexico (Fig. 1).

Capacity of the lake is approximately 2,000,000 acre feet with a maximum surface area of about 38,000 acres. Water storage is typically much less than this with rapid and pronounced fluctua- tions. Storage varied from approximately 180,000 to 600,000 acre feet during the period of July, 1964, through March, 1970.

Depth varied from 70,to 95 feet at the dam. It becomes con- sistently shallower upstream with maximum depths varying from 15 to 35 feet in the upstream third of the lake.

Patterson (1968) classified Elephant Butte Lake as marginally oliogotrophic in terms of productivity. It is a Temperate Lake of the II Order (Forel Classification modified by Whipple, from Welch

1952). It is classified after Hutchinson and Leffler (1956) as

Dimictic. Persistent winds and silt-laden density currents prevent formation of a thermocline. Temperature gradients occur during all seasons of the year. Homogeneous temperatures usually occur throughout the lake once each spring and fall. Summer temperatures vary up to 85°F at the surface and 70°F at the bottom. Winter surface temperatures range from 32°F to 45°F and bottom temperatures vary between 40°F and 42°F (Fig. 2). 4

THE NARROWS

ELEPHANT BUTTE LAKE

MONTICELLO CANYON

LACK BLUFFS

—KETTLE ROCK CANYON TOP

LONG POINT

McRae CANYON

ELEPHANT ELEPHANT BUTTE BUTTE DAM

Figure 1. Locality and map of Elephant Butte Lake, New Mexico, showing shoreline at maximum storage capacity and approximate shoreline at average storage volume during this study. 85 80 Surf ace 75 Temperature — 70

65 ' 60 55 . Outlet — 55 — Temperature 45

60 55 -

50 45 " 40 Water Storage 10,000) 35

(x 30 25 20 - 15 10 Acre-feet 5 1 I 1 1 i 1 1 I I 1 1 I 1 1 1 1 1 'J A'S `06 5 JIF ,1.1 A MIJ 'J 'S'O'N'D J F 1.0A M‘J J A VON DJF M A M .1 S O FIMIAT161 .7 J lAtS 0 ODljlpim IA m J JIA S 0 1: 1960 1961 1962 1963 1964 1965 85 80 75 Surface Temperature — 70 — 65 — 60 Outlet — 55— 55 Temperature 45 —45—

60 55 50 43 40 35 10,000) 30 25 20 15

Acre-feet(* 10 5 1 '1.1IJ PA S O'N DJ F MA M J 13 'A'S 10 TN' D'J FT M'A 'M 'J 1 J rS 1966 1967 1968 1969 1970 1971

Figure 2. Surface and outlet temperatures and water storage values in Elephant Butte Reservoir for 1960 through 19_. 6

The most abundant bottom material is a sand and gravel mixture.

Silt is also abundant. Bedrock, boulders, rubble, and organic

detritus occur as bottom deposits in limited areas. The upstream

third of the lake remains quite turbid because of heavy silt

deposits and wind action.

Water chemistry has remained relatively stable since 1964

(Jester et al. 1969, Moody et al. 1969).

Elephant Butte Lake provides adequate habitat for smallmouth

buffalo but their growth is generally slower here than has been

found in several other waters (Patterson 1968). METHODS AND MATERIALS

Fish were taken from April, 1968, through March, 1970, in experimental gill nets, 125 feet long by 10 feet deep, with equal panels of 2, 3, 4, 5, and 6-inch-stretch mesh. Fish taken prior to April, 1968, were obtained by comparable methods (Patterson

1968, Jester et al. 1969).

Total lengths of fish were measured in millimeters and weights in ounces. Scale samples were taken from an area below the origin of the dorsal fin above the lateral line. Fish which were not destroyed for other purposes were marked with monel jaw tags or nylon darts. Ovaries were removed intact and preserved for analysis in the laboratory.

All data were recordea on field forms and later analyzed in the laboratory.

A sample consisting of 695 fish was taken from April, 1968, through March, 1970. Age-growth, length-frequency, weight-frequency,

Coefficient of Condition, and length-weight relationships found in this study are compared with those found in earlier studies (Patter- son 1968, Jester et al. 1969).

Relative density and biomass of buffalo were calculated as percent of number and percent of weight of fish caught in experimental gill nets.

Number and weight of buffalo caught per net-unit were calculated to provide catch data independent of changes in other fish populations. One net-unit is 25 feet of net set for 24 hours. This amount 8

of net was selected to conform to the length of each mesh size in experimental nets. Twenty-four hours was selected to allow for variations in diurnal activity of fishes.

Population estimates were made by use of the Schnabel Method

(Ricker 1958) on the basis of cumulative mark-and-recapture data.

Observations of behavior, state of reproductive development of netted fish, and fecundity estimates comprised the data on buffalo reproduction.

Age-growth studies were made from scales, by use of the Lee

Method (Lagler 1956). Scales were examined on a Van Oosten-

Deason-Jobes (1934) scale projector.

Data on commercial catches were obtained from monthly Commer- cial Catch Reports prepared.by Mr. B. C. Sparkman for the New

Mexico Department of Game and Fish. FINDINGS AND DISCUSSION

Density and Biomass

Relative density of smallmouth buffalo in experimental gill net catches decreased from 13.9 percent of total number, the third most numerous nettable fish in 1964-65, to 2.7 percent of number, or seventh in density in 1969-70 (Table 1). Relative biomass has decreased from first, at 36.2 percent of total weight in 1964-65, to fourth, at 12.6 percent of weight in 1969-70 (Table 1). Trends in density and biomass indicate a decreasing buffalo population.

However, these trends are relative to catch rates of other fish and may vary with changes in other populations.

Number and Weight per Net-Unit

Trends in buffalo population, independent of changes in other populations, are revealed by changes in catch rates per unit of effort. Twenty-five feet of experimental gill net set for 24 hours is one net-unit. Catch rates per net-unit may be calculated by knowing the total feet of net set and total number and weight of buffalo caught in these nets. Number of buffalo caught has decreased from 0.40 per net-unit in 1964-65 to 0.29 in 1969-70. Weight of buffalo per net-unit has also shown a decreasing trend (Table 2).

These independent catch rate data lend credence to the decreasing buffalo population indicated by relative density and biomass. Table 1. Relative density and biomass, rank, and fish exceeding smallmouth buffalo in Elephant Butte Lake, New Mexico, June, 1964, through March, 1970.

Parameter 1964-65 1965-66 1966-67 1967-68 1968-69 1969-70

Percent number 13.9 9.3 7.0 5.2 3.1 2.7 Rank 3 2 4 5 8 7 Exceeded by Gizzard shad Gizzard shad Gizzard shad Gizzard shad Gizzard shad Gizzard shad River River River River River carpsucker carpsucker carpsucker carpsucker carpsucker Walleye Walleye Channel White bass catfish Channel White bass Carp catfish Walleye Channel catfish Carp Longear sunfish Longear sunfish Percent weight 36.2 36.6 • 22.5 16.7 9.9 12.6 Rarik 1 1 2 3 4 4 Exceeded by Walleye Walleye River River carpsucker carpsucker River Walleye Gizzard shad carpsucker Gizzard shad Walleye 11

Table 2. Number and weight of smailmouth buffalo caught per net- unit in Elephant Butte Lake, New Mexico, from 1964-65 through 1969-70. Weight in ounces.

Parameter 1964-65 1965-66 1966-67 1967-68 1968-69 1969-70

Number 0.40 0.52 0.23 0.46 0.24 0.29

Iti ght 11.4 , 19.3 10.9 18.1 8.5 . 10.8

Commercial Catch

A declining buffalo population is also indicated by decreasing commercial catches per unit of effort. Mr. Sparkman does not keep records of numbers of nets set daily, but personal communication indicates that the number is relatively constant throughout the year. Consequently, number and weight of buffalo caught per day may be used as a reliable measure of commercial catch per unit of effort.

The commercial catch has decreased from means of 169 buffalo weighing 766 pounds per day in 1963 to 33 fish weighing 119 pounds per day in 1969 (Table 3). The mean catch failed to decrease from the previous year only in 1966. In 1965, Mr. Sparkman was able to fish only in January, February, March, two days in April, and ten days in September. He did not fish at the peak of spawning season or in early fall, the times of year when he obtains the largest catches.

Mean weights of fish in the commercial catch have declined significantly because larger fish are constantly being harvested

(Table 3). 12

Table 3. Number of days fished, total number and weight of fish caught, daily means, and mean weight of buffalo harvested from Elephant Butte Lake, New Mexico, 1963 through 1969. Weights in pounds.

Mean Mean Mean Days Total Total Number Weight Weight Year Fished Number Weight per Day per Day of Fish

1963 113 19,147 86,504 169 766 .4.5 1964 168 13,695 57,715 82 344 4.2 1965 77 4,490 20,440 58 265 4.6 1966 303 27,151 103,127 90 340 3.8 1967 191 10,855 40,514 57 212 3.7 1968 271 12,036 45,226 44 167 3.8 1969 253 8,266 30,113 33 119 3.6

Grand: Totals 1,376 95,640 383,639 Means 70 279 4.0

Length-Frequency

Comparison of length-frequency distributions of buffalo in

annual samples shows that larger fish are being cropped, leaving proportionally more fish of smaller size in the lake. In 1967-68,

80 percent of the buffalo sampled were 400 to 549 millimeters long

(Jester et al. 1969). In 1968-69, 87 percent were 300 to 499 millimeters in length. In 1969-70, 88 percent of the buffalo caught were 300 to 499 millimeters long (Table 4).

Table 4. Percent of buffalo included in length ranges taken from Elephant Butte Lake, New Mexico, from 1967-68 through 1969-70. Lengths in mm.

Year Length 200-249 250-299 300-349 350-399 400-449 450-499 500-549 550+ 1967-68 4.3 6.7 7.6 1.3 26.5 41.8 11.6 0.1 1968-69 0.3 2.1 19.3 15.4 13.0 39.6 9.9 0.6 1969-70 0.0 0.9 7.2 27.8 24.8 27.8 10.5 0.9 13

Weight-Frequency

Comparisons of weight-frequency distributions of buffalo taken in experimental gill nets during 1968-69 and 1969-70 also reveal a proportionally smaller population of larger fish. In 1968-69, 55 percent of the buffalo included in the sample weighed more than 40 ounces, which is the approximate minimum weight acceptable for mar- keting. In 1969-70, only 43 percent of the buffalo weighed more than 40 ounces (Table 5).

Table 5. Percent of buffalo included in weight ranges taken from Elephant Butte Lake, New Mexico, in 1968-69 and 1969-70. Weights in ounces.

Weight 1-10 11-20 21-30 31-40 41-50 51-60 61-70 71-80 81-90 91+

1968-69 2.1 19.2 14.3 9.6 23.9 20.0 7.0 2.3 0.3 0.6 1969-70 1.0 6.9 22.2 27.1 15.0 15.0 7.2 3.9 1.0 0.7

Condition

Hile (1936, in Lagler 1956) established Coefficients of Con- dition as a measure of relative robustness of fishes. Condition is often used as an indication of environmental suitability for a species. It follows that.an improvement in the environment, in this case population reduction by commercial exploitation, should increase the Coefficients of Condition of fish in the population

(Cooper and Benson 1951).

Coefficients of Condition of buffalo taken in samples varied from year to year, but show an increasing trend (Table 6). This trend indicates that the buffalo population has been reduced. 14

Table 6. Coefficient of Condition (Ktl) of all buffalo taken from Elephant Butte Lake, New Mexico, 1964-65 through 1969-70.

Year 64-65 65-66 66-67 67-68 68-69 69-70 1.42 Ktl 1.37 1.44 1.43 1.45 1.41

Length-Weight Relationship

Length-weight relationships (LeCren 1951) were calculated for buffalo sampled in 1968-69 and 1969-70. They show that fish 200 to 500 millimeters in length are heavier than fish in the same length range sampled in 1964-68 (Table 7). These data indicate that smaller fish are gaining weight faster because of decreased intraspecific competition as a result of the indicated reduction in the population.

Table 7. Weights of smallmouth buffalo, at various lengths, derived from length-weight relationships of fish from Elephant Butte Lake, New Mexico, 1964-68 through 1969-70. Lengths in millimeters and weights in ounces.

Length

- ZAJU SOD" 500 130, Year Weight

1964-68 2.7 11.2 30.1 64.9 121.6 206.6 1968-69 3.8 13.2 32.3 64.7 114.0 184.1 1969-70 3.7 13.0 31.6 62.8 110.0 177.0

Age-Growth

Growth history of a fish population is best reviewed with an age-growth study. This involves obtaining scales, lengths, and weights from fish in the population, establishing validity of the scale method for determining age, correlating body-lengths and scale-lengths, and calculating age-growth by use of the Lee (1920)

Method (described by Lagler 1956). An age-growth study of smallmouth buffalo from Elephant Butte Lake was reported by Patterson

(1968). A comparative review of buffalo growth was done on a sample of 90 fish taken from April, 1969, through March, 1970.

Validity of annuli for aging smallmouth buffalo has been established by Martin et al. (1964), Walburg and Nelson (1966), and Patterson (1968). Validity in this study was demonstrated by agreement of back-calculated lengths of different age groups of fish and by close correlation of body-scale regression.

Body-scale regression was determined by plotting mean total lengths of fish against mean total lengths of anterior scale radii, of buffalo grouped into 10 millimeter intervals of total length.

The linear regression formula was applied to the linear relationship revealed by the plots. L and S were substituted for X and Y, respectively, so that the regression line was correlated with the data, thus:

L = a bS when

L = mean total length of fish in the group

S = mean total length of anterior scale radius in the group

a and b are empirical constants 16

The calculated body-scale regression was: L = 4.50 + 1.15 (S) with a Coefficient of Correlation (r) of 0.99 (Fig. 3). Thus, scale length was demonstrated to be proportional to body length.

This proportionality allowed use of the Lee Method for calcula- tion of length of fish at formation of each annulus. This method involved the formula:

Sn (Lt - a) + 8 S t when

Ln = total length of fish at •any annulus

Sn = length of scale radius at corresponding annulus

L total length of fish at capture t = S length of anterior scale radius at capture t = a = empirical constant from body-scale regression

Calculated mean lengths of each age group, grand mean lengths and increments, grand mean weights determined from length-weight relationship, and mean weight increments are shown in Table 8.

Comparative data from Patterson (1968) and differences are shown in Table 9.

These comparisons show that growth rates in the population have increased since 1966-67. Buffalo attain similar lengths one to three years younger than they did at that time. After the first year, similar weights are attained one to three years earlier.

Martin et al. (1964) and Patterson (1968) reported that buffalo 400 millimeters long were the smallest size vulnerable to Anterior Radius ofProjected Scale(mm) 400 600 700 500 300 200 100 Figure 3. L = 4.49587+ =

100 a +bS Elephant ButteLake. Lody-scale Total LengthofFish(mm) 200 1.34787 regressionof90 S 300 400 smallmouth 500 buffalofrom 600 17 Table 8. Calculated mean lengths, weights, and increments of growth of 90 smallmouth buffalo from Elephant Butte Lake, New Mexico, April, 1969, through March, 1970. Lengths in millimeters and weights in ounces.

Mean Length at Mean End of Year Year Age No. of Total Mean Class Group Fish Length Weight 1 2 3 4 5 6 7 8 9 10 11 1967 II 3 278 11.3 98 159 1966 III 27 350 21.0 88 194 264 1965 IV 18 405 34.7 96 195 275 341 1964 V 17 467 53.8 100 184 258 329 410 1963 VI 11 488 59.2 109 192 262 321 374 439 1962 VII 6 517 64.0 99 191 239 305 371 421 478 1961 VIII 4 513 68.0 73 135 191 251 313 368 431 477 1960 IX 2 504 59.5 60 138 200 255 310 356 381 427 473 1959 X 0 1958 , XI 2 743 144.0 156 243 301 366 421 462 507 540 587 629 687 Number of fish 90 90 87 60 42 25 14 8 4 2 2 Grand mean lengths 96 188 259 322 382 419 455 480 530 629 687 Mean length increments 96 92 71 63 60 37 36 25 50 99 58 Mean weights 0.3 3.1 8.3 16.2 27.4 36.4 47.0 55.4 75.1 127.3 167.1 Mean weight increments 0.3 2.8 5.2 7.9 11.2 9.0 10.6 8.4 19.7 52.2 39.8 Table 9. Grand mean lengths, mean weights, and increments of growth of buffalo, compared with data found by Patterson (1968). Fish from Elephant Butte Lake, New Mexico. Lengths in millimeters and weights in ounces.

Age Length Weight Group Measure Patterson This Study Change Patterson This Study Change I Grand mean 83 96 + 13 0.4 0.3 - 0.1 Increment 83 96 + 13 0.4 0.3 - 0.1 II Grand mean 126 188 + 62 1.1 3.1 + 2.4 Increment 43 92 + 49 0.7 2.8 + 2.1 III Grand mean 181 259 + 78 2.7 8.3 + 5.6 Increment 55 71 + 16 1.6 5.2 + 5.7 IV Grand mean 235 322 + 87 6.1 16.2 + 10.1 Increment 55 63 + 8 3.4 7.9 + 4.5 V Grand mean 284 382 + 98 10.9 27.4 + 16.5 Increment 49 60 + 11 4.8 11.2 + 6.4 VI Grand mean 326 419 + 93 16.7 36.4 + 19.7 Increment 42 37 - 5 5.8 9.0 + 3.2 VII Grand mean 361 455 + 94 22.9 47.0 + 24.1 Increment 35 36 + 1 6.2 10.6 + 4.4 VIII Grand mean 388 480 + 92 28.6 55.4 + 26.8 Increment 27 25 - 2 5.7 8.4 + 2.7 IX Grand mean 413 530 +117 34.6 75.1 + 40.5 Increment 25 50 + 25 6.0 19.7 + 13.7 X Grand mean 434 629 +195 40.4 127.3 + 86.9 Increment 21 99 + 78 5.8 52.2 + 46.8 XI Grand mean 446 687 +241 50.4 167.1 +116.7 Increment 12 58 + 46 3.4 39.8 + 36.4

•.0 six-inch-stretch-mesh gill nets, the type of commercial fishing

gear used in Elephant Butte Lake. Patterson (op. cit.) found that

this minimum size was not attained by all buffalo in one age group until the eighth year. This study indicates that all buffalo older than five years are susceptible to commercial fishing gear now being utilized. Buffalo are presently susceptible to harvest

two years younger than they were in 1966-67. Sixty-four percent of the population, as indicated by length-frequency, is now susceptible to commercial fishing, compared to 54 percent, calculated

from Patterson'sage-growth study, in 1966-67.

Growth rates determined by this study amply demonstrate that smallmouth buffalo in Elephant Butte Lake have faster growth rates

now than in 1966-67 indicating a smaller population with less intraspecific competition.

Population Estimates

Numbered monel jaw tags and nylon dart tags were placed on

1,854 smallmouth buffalo from June, 1964, through March, 1969.

Tags have been recovered from 126 of a total catch of 63,114 buffalo taken in experimental and commercial nets in that period of time. Returns were insufficient to allow population estimates, made by use of the Schnabel Method (Ricker 1958), to stabilize each year. Therefore, recruitment and mortality during the five year period undoubtedly influenced numerical accuracy of the estimates. Consequently, relatively crude, long-term estimates are used (Moody et al. 1969). 21

The mean population for the entire five year period was

571,600 buffalo of sufficient size to be caught in experimental or commercial nets (Table 10). This mean included the population in 1964-65 and 1965-66 when exploitation had just begun and in

1966 through 1969 after population reduction was in progress

(Moody et al. 1969).

Table 10. Population estimates of smallmouth buffalo in Elephant Butte Lake, New Mexico, August, 1964, through March, 1969. Determined by use of the Schnabel Method (Ricker 1958).

Years of Mean Number Change from Estimate of Buffalo Previous Mean

1964-69 571,600

1966-68 ' 461,000 -110,600

1967-69 413,500 - 47,500

Total reduction -158,100

Total commercial catch 87,000

Reduction not directly attributed to commercial harvest 71,100

The mean of estimates for the 1966-67 and 1967-68 sampling years was 461,000 buffalo, or 110,600 fewer than indicated by the five year mean. The mean of estimates for 1967-68 and 1968-69 was 413,500 fish, or 47,500 fewer than the previous two year mean

(Moody et al. 1969). 22

Prior to 1969 the total commercial catch numbered 87,374 buffalo while the population estimates indicated a decline of

158,100 fish. Therefore, the total decline in the population

cannot be attributed directly to commercial harvest. Additional reduction may be attributed to reduced reproduction resulting

from heavy exploitation of buffalo when they are concentrated

in spawning areas. During 1968 and 1969, 45.7 percent of the

total commercial catch for the two years was taken during spawn-

ing seasons in spawning concentration sites. Large numbers of ripe females are taken, resulting in removal of both the individual fish and their entire reproductive potential for the year and the future (Moody et al. 1969).

A portion of the reduction of reproductive potential may also be attributed to differential removal of larger fish during both spawning season and the remainder of the year. As shown below,

larger fish produce more eggs than do smaller fish. Hence, removal of larger fish results in eliminating a large portion of

the reproductive potential of the population.

Reproduction and Fecundity

Observations of behavior and examination of fish caught in gill nets allowed conclusions concerning reproduction of smallmouth buffalo. Heard (1955), after Canfield (1922), reported that

Ictiobus usually spawn in March and April at water temperatures of about 600F. Moody et al. (1969) found that buffalo in Elephant

Butte Lake began spawning in late April, 1968, at 68°F and reached

the peak of spawning activity in mid-June, at 76°F. Production of milt was found in a few males throughout the year. Frequency of individuals with milt increased sharply in March, 1969, at 47°F to

50°F. Some females began releasing eggs in late March, at 56°F.

Nearly all females contained well developed eggs at this time. The peak of spawning activity occurred during the first week of May, at

64°F to 65°F.

Heard (1955) reported deposition of eggs by Ictiobus over aquatic plants or inundated terrestrial vegetation. Canfield (1922),

Yeager (1936), Walker and Frank (1952) and Heard (op. cit.), all reported that buffalo spawning is associated with a spring runoff or rise in water level. Volume of water stored in Elephant Butte

Lake declined from 390,000 acre feet on March 1, 1968, to 190,000 acre feet on May 15, followed by an increase to 216,000 acre feet by June 15 (Fig. 2). Spawning began in late April while water level was falling. The peak of spawning activity occurred in mid-

June, corresponding with rising water levels.

During 1969, water levels increased from January 1 through

March 1. This corresponds to the earlier incidence of reproductive activity noted in that year (Moody et al. 1969). Peak spawning activity occurred within a month of the time of maximum water storage. At this time, the commercial fisherman found concentra- tions of spawning buffalo at the upstream end of the lake in recently-flooded shoreline vegetation at depths of four to eight 11 feet. Gill net sampling indicated that buffalo spawn in all areas 24

of the lake at depths of approximately 10 to 20 feet. All bottom types are utilized (Moody et al. 1969).

During the peak of spawning activity in 1969, ovaries from female buffalo were collected for fecundity estimates. Number of eggs produced by each female was determined by weighing each ovary in grams; dissecting a sample of eggs from anterior, median, and posterior thirds of the ovary; weighing the composite sample from each ovary; counting the eggs in the sample; and determining total number of eggs in the ovary by expansion of numbers of eggs in samples. The range of numbers of eggs was 79,300 to 323,252 with a mean of 197,371 per female (Table 11).

Although the smallmouth buffalo population in Elephant Butte

Lake has been reduced, these estimates of fecundity demonstrate that the possibility of an increase in the population is very real.

At the current low level of intraspecific competition, young buffalo probably survive at a high rate. Growth rate has been shown to be relatively fast. Therefore, without constant decimating pressure on the population, buffalo could achieve their former status as a management problem in Elephant Butte Lake in a relatively short time. 25

Table 11. Age, length, and weight of females, weight of ovaries, number of eggs produced per female, and mean number of eggs from buffalo taken during spawning season, from Elephant Butte Lake, New Mexico, 1969.

Age Fish Ovaries Number Mean Number Group Length Weight Weight of Eggs of Eggs for Age-Group (ozs.) (gms.)

IV 430 70 76.0 79,300 79,300

V 471 53 113.9 94,547 V 472 58 278.5 227,862 V 484 70 242.5 205,915 V 491 64 261.5 231,080 179,141 V 495 59 141.9 98,726 V 499 61 259.3 206,745 V 508 65 240.0 189,116

VI 453 52 255.1 207,646 VI 473 60 183.9 128,247 VI 476 52 179.1 149,661 189,566 VI 482 66 260.7 218,701 VI 493 64 '256.8 222,476 VI 501 67 261.8 210,667 - 460 32 250.3 207,976

VII 513 64 310.7 280,079 301,666 VII 554 90 396.1 323,252

VIII 496 64 281.0 258,238 234,765 VIII 520 73 246.9 211,292

IX 482 57 223.5 195,893 195,893

Mean 197,371 1.1 SUMMARY

From August, 1963, through December, 1969, 95,640 smallmouth buffalo weighing 383,639 pounds were removed from Elephant Butte

Lake by commercial harvest. An additional 71,100 buffalo have been removed by mortality and reduction of reproductive potential of the population.

The buffalo population 1-1. s declined from third in relative density and first in relative biomass among fish populations in the lake during 1964-65 to seventh in density and fourth in biomass during 1969-70. This change is very significant in improving ecology of the lake as a means of sport fish management, by pro- ducing a relative increase of game fish from 22.3 percent of total weight in 1964-65 to 33.7 percent in 1969-70. Actual benefit to game fish exceeds these relative figures. Catches of gizzard shad, the forage fish used almost exclusively by predatory species in

Elephant Butte Lake, have increased from 6.2 percent of total weight of fish caught in 1964-65 to 20.1 percent of weight in

1969-70. Catches of number have remained relatively stable. The larger catches of weight of gizzard shad resulted from a faster rate of growth being attained because of decreased intraspecific competition. As the shad population became subject to increased predation, its numbers were decreased, providing less competition.

In 1964-65 and 1965-66, virtually no shad were large enough to be caught in meshes larger than two-inch-stretch in experimental gill nets. As the population declined and achieved the more rapid rate 27

of growth, individual fish became larger. Currently, shad are caught in all of the two- and three-inch mesh and many are caught in four-inch mesh. This accounts for the seemingly large increase in biomass of shad in the catches, while the population has actually declined. Therefore, the large apparent but unreal increase in relative biomass of shad tends to dampen out increases in relative biomass of game fish.

Reduction of the buffalo population resulted in less intraspecific competition. Consequently, growth rates of the population have increased. All fish attain harvestable size (=t 400 mm) in

Age Group VI rather than in Age Group VIII as found by Patterson

(1968). The larger fish are being harvested, leaving proportionally more fish of smaller size in the lake.

Although the population has been reduced, smallmouth buffalo could again become a management problem in Elephant Butte Lake if control were eliminated. Therefore, it is recommended that commercial fishing be continued. ••• • •

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