J. Fish Biol. (1973) 5, 429-440

The Sulmo guirdneri (Rich.) fishery of

G. V. EVERETT* Universidud Te'cnica del Altipluno, Puno,

(Received 25 February 1972)

Rainbow trout were introduced to Lake Titicaca in 1942. A conimercial trout canning operation started in 1961 but terminated in 1970. Data for this study were collected in 1966 and 1967, with the object of examining the life history, biology, and commercial fishery of Titicaca rainbow trout. Trout were caught commercially and experimentally by gillnets in different parts of the lake. Lake Titicaca lies across the border of Peru and at 3212 m above sea level. The physico-chemical characteristics of the lake appear ideal for self-sustaining populations of rainbow trout. Growth was constant throughout the year, and was good in relation to growth rates of rainbow trout in other parts of the world. Spawning took place in the tributaries in the winter. Recruitment to the fishery occurs in 7.62 cm stretch mesh gillnets at about 27 cm fork length. The total annual commercial catch increased to 500 metric tons in 1965 before subse- quently decreasing. The simplest explanation for the decline in total catch would be the increase in fishing mortality due to increased fishing effort, although it is possible that the decline in water level has had some effect. It appeared possible that the lake could sustain an annual catch of about 350 tons.

I. INTRODUCTION Lake Titicaca lies on an inland drainage plateau which extends across the borders of Peru and Bolivia (Fig. 1). The lake is up to 176 km long, 66 km wide, 3212 m above sea level, and located between the latitudes of 68" 37' and 70" 02'W and longitudes 15" 14' and 16" 35's. Waters of Lago Pequeiio, Pun0 Bay, and the northern part of the lake are less than 20 m deep, but the deepest part of the main lake is 281 m. Four main rivers are tributaries of the lake. The River Ramis has the greatest flow (up to 200m3/sec in February and March) followed in flow rate by the Rivers llave, Escoma, and Coata. The total catchment area is 60 800 km2 and the water surface is 7600 km2. Mean flow of the only outlet, the River Desaguadero, is 20 m3/sec. Evaporation accounts for 95 of the water that leaves the lake. Water level in 1963 was the highest since 1933. Since 1963 the lake level has receded (Table I). Gilson (1964) has described the physical, chemical, and biological characteristics of the lake. Monheiin (1956) has described the hydrology of the lake and its basin. Average annual rainfall is 584 mm with 73 "/o falling in December through March. Monthly mean air temperatures are least in June (5.5"C) and greatest in November (9-S°C), the annual average being (74°C) (Table 11). Lake temperature fluctuates around 12°C (Table 111) and tributary temperatures vary from 4 to 20°C. Waters are slightly alkaline (pH 8) and are high in ionic solutes (788 ppm). Oxygen concentra- tions fluctuate between 4.5 and 5.0 ppm in surface waters of the lake. *Present address: Hunting Technical Services, Borehamwood, Hertfordshire, England. 429 430 G. V. EVERETT

71' 70'

15O

16' 16'

PERU

17O 17'

0 80 -krn -.-. International boundary I I 71' 70' 69' FIG.1. Topography of Lake Titicaca.

The catfish rivulatus Valenciennes lives in the lake and its tributaries. All other endemic fish belong to the cyprinid genus Orestias, the largest species of which-0. pentlandi (Val)-reaches about 25 cm fork length. The freshwater pejerrey Basilichthys bonariensis (Girard) (family Atherinidae) escaped into the lake in 1956 and by 1967 was abundant in all parts. The lake trout Sahelinus namaycush (Walb), the brown trout Salmo trutta (L.), and the eastern brook trout Salvelinus fontinalis (Mitchill) were also introduced to the area, but only the brown trout is now common, in the River Ilave. The rainbow trout Salmo gairdneri (Rich.) was brought to the Titicaca region in 1942, and by 1950 was abundant throughout the lake and its tributaries. A cannery opened at Chucuito, Peru, in 1961 and four other canneries have since operated on THE RAINBOW TROUT FISHERY OF LAKE TITICACA 43 I

TABLEI. Variation in the water level of Lake Titicaca from the Peruvian Corporation, Arequipa, Peru)

Lowest level Highest level A br> Year cm below cm below or above zero gauge* Month zero gauge Month

1951 -145 January - 66 March 1952 -150 December - 71 March 1953 -151 January - 79 April 1954 -129 January -2 May 1955 - 60 January f 36 April 1956 - 94 December -I- 21 February 1957 -141 December - 64 March 1958 -141 December - 63 April 1959 - 147 December - 76 April 1960 - 76 November - 22 April 1961 - 71 January - 15 May 1962 - 47 January + 57 April 1963 -5 January +I20 April 1964 -2 December + 86 April 1965 - 34 November +44 April 1966 - 83 December -1 March 1967 -129 December - 49 March 1968 -119 January - 51 April 1969 -155 December - 60 April 1970 -163 December - 90 April

*Zero gauge, 3212 m above sea level.

TABLE11. Air temperatures at Pun0 (data from the Meteorological Service, Lima), 1950 to 1965

Mean Mean Monthly Month maximum minimum mean I“c> (“C) (“C)

January 15.3 3.5 8.2 February 15.0 3.8 8.5 March 14.9 3.9 8.4 April 15.0 2.2 8.1 May 14.0 -0.4 6-4 June 13.5 -2.1 5.5 July 13.8 -2.3 6.1 August 14.5 - 1.8 6.7 September 15.0 -0.5 8.0 October 16.6 2.0 9.0 November 16.2 4.8 9.8 December 15.9 3.4 9.6 Mean 15.0 1.4 7.8 432 G. V. EVERETT

TABLE111. Seasonal temperature of lake water (Monheim, 1956)

Late Annual Summer Winter winter range (“a (“C) (“C) (“C) Mean 13.3 12.9 11.8 1.5 Maximum 15.0 14.8 12.5 2.2 Minimum 11.7 10.5 11.0 1.2 Diurnal range 3.3 4.3 1.5 the lake shore. By 1970 a scarcity of trout had led to closure of all the trout canneries. This paper presents the results of an investigation into the life history, biology, and commercial fishery of rainbow trout in Lake Titicaca.

IT. METHODS AND MATERIALS Data were collected from September, 1965, through December 1967. The Chucuito trout hatchery, Puno, Peru, served as centre for the study programme. Rainbow trout were exam- ined from commercial catches in the areas of Huancane, Juli, and Pusi, and from nets set non-commercially in Pun0 Bay at Chucuito and in the lake tributaries. The Huancane area comprised points located within 15 km radius of the mouth of the River Ramis. Pusi is 30 km to the west of the Ramis mouth. The Juli area referred to fishing locations along the western side of the lake. Catches of fishermen in Lago Pcquefio, near Yunguyo, were inspected each month but no trout were caught. Each fishermman set gillnets overnight within 3 km distance of the shore. The nets were of 7.62, 10.15, 12.70 and 15-24cm stretch mesh, and hung by the half to 100 m length and 3 m depth. At the landing location every fifth trout loaded on a vehicle collecting trout for the canneries was examined. This examination took place at least three times per month at each location. No commercial fishing occurred in the closed seasons of June through mid-August in 1965, 1966 and 1967. Data on the monthly commercial catch per unit effort at each loca- tion in 1961 through 1967 were supplied by the cannery manager at Chucuito. The unit of effort at a fishing location was taken as one journey to that location by a cannery vehicle collecting trout. This was the only unit of effort continually recorded since canning opera- tions started, and it is believed to be a reasonably reliable index of fishing effort. Gillnets were set in Puno Bay at Chucuito for ten nights each month from February, 1966 through December, 1967. The nets were 100 m long and 3 m deep, when hung by the half, and made from multifilament twine size 9 and 12. The nets were set at right angles to the shore in water 3 to 4 m deep. Nets of stretch mesh 7.62 and 10.15 cm were set regularly but others of 4.44, 5.08, 6.35, 12-70and 15-24cm were set at less regular intervals. The 4.44 and 5.08 cm nets caught less than 12 rainbow trout throughout the study. A beach seine of 20 m length, 4 m deep (when hung) with 1.90 cm stretch mesh was used for seining the Rivers Ramis, Ilave, and Coata. Sampled trout were weighed whole and gutted, and measured at fork length to the nearest 4 cm below. Individuals of more than 20 cm were sexed. The gut was cut at the oesophagus just posterior to the pectoral girdle, and all viscera removed. Gonads were weighed, and stomach contents analysed. Eggs were hardened in formalin before counting. Scales and otoliths were examined unsuccessfully for growth marks which might be annuli.

111. RESULTS 1. BIOLOGY Two size groups were apparent in the monthly length frequency distributions of trout in Pun0 Bay at Chucuito (Fig. 2). Recruits entered the fishery in February THE RAINBOW TROUT FISHERY OF LAKE TITICACA 433

Huoncane'oreo and Pusi - Chucuito Jonuary 20 - Jonuary 10-- 20 10 Februory 10 - March 30E20 rtl

April t March 40.i n

20 10

20 10 m 10

I0

November 10 -,,,, n c December 10

r-l nn I I I I I 20 30 40 50 60 70 Length (crn) FIG.2. Length frequency distribution of rainbow trout caught non-commercially at Chucuito in Puno Bay (1966 and 1967 pooled data), and commercially in the Huancank area and at Pusi (August 1966 through May, 1967). Petersen curves have been fitted to the size groups apparent in data from the Huancanb area and Pusi. through May and showed monthly increments in length before leaving the area after March of the following year. Recruitment to the fishery in the Huancank area occurred in May. It is possible that fish of a size normally recruited in 7.62 cm gillnets would have been available in February but at this time the Huancant fishermen were known to be using nets of 10.15 cm and larger mesh so that the smaller fish would not be 434 G. V. EVERETT caught. Trout of less than 10 cm length were caught in dipnets from the river bank at the mouth of the River Ramis after the first heavy rains in December. Trout of length 20 cm were taken with hook and line in the same location during June and July. Trout of 3 to 4 cm length were first caught by seine net in the rivers in October. Less than 12 trout of over 27 cm length were taken from the rivers. Abundance and mean fork length of size groups in the HuancanO area and at Pusi were assessed by analysis of the length frequency distribution aided by the use of probability paper (Cassie, 1954). The monthly mean length of size groups at Chucuito and Huancant were then related to time, and the von Bertalanffy growth equation, adapted for application to growth of fish (FAO, 1969), described growth of rainbow trout in the lake as L - 82.42~(1 -e-0.095(t-0.061)) t- (1) where L, is the fork length in cm, 82.42 is the asymptotic length of the fish in cm, 0.095 is the rate at which the length reaches the asymptote, and 0-061 is to. The length interval, t, was 3 months. Based on the above calculations, the length of trout in the lake, when related to age in years, was Age 23456 Length (cm) 38.2 52.8 61.6 68.2 73.2 Growth rate in the rivers could not be adequately assessed directly from the avail- able data, but it is believed reasonable to assume that hatching of most eggs occurred by September, and that most downriver migration had occurred by April, one and a half years later. On this assumption it would appear that river growth (at 1.54 cm/ month) was higher than growth rate during the first year in the lake (1.38 cm/month). Lengths and weights were recorded of 952 rainbow trout, caught from all parts of the lake during the year. The regression line describing the logarithmic length total weight relationship was log W = 3.21 log L - 2.16 (2) and the logarithmic length gutted weight relationship was log W = 3.08 log L-2.00 (3) where W is the weight in g and L is the fork length in cm. Analysis of the variation in length weight relationship by month was not attempted, and initial analysis of variation between sexes indicated that the difference was negligible. Trout from all parts of the lake were sexed throughout the year. Male numbers decreased to a minimum in the 50 through 59cm range length before becoming predominant above the 75 cm mark (Fig. 3). In January over 60 % of all fish caught at the mouth of the River Ramis were males which inferred that males moved up- stream before females. The gonad weight as a percentage of gutted body weight in females increased from March (5%) to a maximum approaching 16% in June in anticipation of the spawning season which peaked in June and July. Male gonad weight was higher in males than females in January through March and reached a maximum 9% of gutted body weight in April (Fig. 4). Numerous males of around 17 cm and females of around 25 cm length were observed spawning in the rivers in June and July. THE RAINBOW TROUT FISHERY OF LAKE TITICACA 435

20 - - 1111111111111

FIG.3. Percentage number of males in the total monthly catch from all parts of the lake, by 5 cm length group.

11 I. I I 11.1 I I I JFMAMJJASOND FIG.4. Gonad weight as a percentage of the gutted body weight.

Few fish carried less than 2000 or more than 8000 eggs. The logarithmic relation- ship between number of eggs and length (Fig, 5) for 65 trout was log N = 2.041 log L+0.098 (4) where N is number of eggs, and L is length in cm. Viscera weight, as percentage of gutted body weight, was related to time of year, length and location of capture. In the trout from Chucuito Bay the viscera weight remained fairly constant throughout the year at 7 %. In the Huancant area the weight rarely increased above 7% and decreased to 2% in June through August. The per- centage viscera weight did not increase as trout length increased. The predominant food was the fish Orestias but pejerrey was also eaten. Vegetation was frequently present, and insects were found in the stomachs of trout up to 60 cm in length, but no trout of any size were found.

2. GILLNETT SELECTION CURVES The length frequency distribution of trout caught in each mesh size approximated a normal curve (Fig. 6). The normal curve for the 7.62 cm mesh was steeper than for larger meshes. The ' tail ' at the upper limit of mesh size curves was due to entangle- ment of large fish. The mean length of trout retention (length) caught in each mesh size (Table IV) indicated that size of trout sampled was a fair representation of size of available trout. 436 G. V. EVERETT

Log L FIG.5. Log number of eggs plotted against log length of trout (cm).

0- Length (crn) FIG.6. Length frequency distribution of rainbow trout caught in gillnets of different mesh size.

TABLEIV. Mean retention length for gillnets of different mesh size

Mean Number of Mesh size retention length observations (cm) (cm)

7.62 33.0 413 10.15 43.3 152 12.70 54.0 80 15.24 63.4 74 THE RAINBOW TROUT FISHERY OF LAKE TITICACA 437

3. COMMERCIAL FISHERY Total fishing effort increased annually from 1961 through 1967. Total annual catch on the lake increased until 1965 and then decreased. In 1965 410 metric tons were caught in Peru and 90 tons were caught in Bolivia. Catch has been plotted against effort in the manner of Schaefer (1954) and a curve has been fitted by eye to the relationship for the total Peruvian catch and effort, and to the data obtained from the Chucuito cannery (Fig. 7). Stocks have notably decreased in abundance in recent years.

t I i I I I I I I I I I 1000 2000 3000 4000 5000

Effort (number of collection journeys/year) FIG.7. Annual catch related to annual effort, for both the Peruvian fishery and the Chucuito cannery. Schaefer’s curve has been fitted by eye. Effort is taken as the number of journeys in a year to fishing locations by cannery vehicles collecting trout.

More detailed evidence of the decrease in stock abundance was indicated by the information on catch per unit effort for 1961 through 1967 at HuancanC and Pusi (Fig. 8). Catch per unit effort in 1961 through 1963 at HuancanC was low, in relation to 1964 through 1966, due to oversupply of trout to the Chucuito cannery. Trout tended to be more abundant at Pusi in September through November than in other months, and at this time the trout were scarce in the HuancanC area. It is possible that many trout feed in the Pusi area and move to the HuancanC area near spawning time. Catches in the Huancane area were normally higher than in other areas of Lake Titicaca, and greatest monthly catch corresponded with times of greatest river dis- charge in February and March (Table V).

IV. DISCUSSION Chucuito, and possibly Pusi, appear to be nursery areas where food is plentiful and into which the trout move for approximately one year after downstream migration. The main upstream migration occurs from January through August with a peak in March. Most spawners are believed to be 2) and 34 years and migrating upstieam 438 G. V. EVERETT

Year FIG.8. Mean catch per unit effort in the Huancanb area and at Pusi.

TABLEV. Total monthly discharge of the River Ramis, and commercial catch at the river mouth (Huancank area) (The Direccion de Irrigacion, Lima, supplied the discharge information) 1964 1965 Discharge Catch Month (million (metric Discharge Catch ma) tons)

January 206 199 313 6.7 February 310 24.6 563 19.6 March 487 26.1 732 31.3 April 305 25.6 369 26.4 May 141 14.0 142 8.5 June 54 62 July 46 51 August 42 8.2 41 4.3 September 33 5.7 32 6.6 October 27 3.2 29 3-8 November 29 1a7 42 3.2 December 92 1.6 152 5.0 1966 1967 January 227 13.6 131 4.1 February 377 20.6 172 12.5 March 371 38.6 462 14.7 April 114 19.9 134 5.8 May 64 13-6 62 6.0 June 45 30 July 33 26 August 26 3.2 22 1.3 September 17 4.0 21 1-1 October 35 1-5 N/A 0.4 November 68 0.5 N/A 0.0 December 216 0.8 N/A N/A

N/A = Data not available. THE RAINBOW TROUT FISHERY OF LAKE TITICACA 439 for the first time. The majority of spawners are around 45 cm in length. It is difficult to assess when spent rainbow trout move downstream but it is tentatively suggested as July through September. It seems reasonable to assume that redds are laid in gravels of the middle reaches of the rivers in June through August. By mid-September most fry would have emerged. With the beginning of the rainy season in December some fry of 8 to 10 cm are carried downstream to the lake. The main downstream migration is believed to occur the following year in February through April when the trout would be 14 years, and around 27 cm in length. Normally the fish would be recruits to the fishery, and liable to capture in 7.62 cm gillnets. The recruits to the HuancanC fishery in August through September are believed to comprise 2-year-old trout in addition to the fast growers of fry carried downstream the previous December. Growth of trout was constant throughout the year, and compared favourably with growth rates of rainbow trout in New Zealand (Fish, 1963), England (Worthing- ton, 1940), and North America (McAfee, 1966). The physico-chemical conditions of Titicaca water are similar to those summarized by MacCrimmon (1971) as optimal for growth and self-sustaining populations of rainbow trout. The absence of cannibalism may be due to the abundant supply of forage fish (Urestias species) and the relative absence of juvenile trout from the lake. Gilson (1964) calculated the area between isobaths 0 and 50 m in the main basin as 99 000 ha. It is perhaps unlikely that rainbow trout inhabit areas of more than 25 m depth. Hence the lake area possibly inhabited by rainbow trout is 54 000 ha in Pun0 Bay and 44 500 ha in the main basin. The annual yield would therefore vary from 2.03 ka/ha (at 200 tons annual catch) to 4.06 kg/ha (at 400 tons annual catch). The decline in water level since 1963 may have led to decrease in food supply and a consequent decline in abundance of the rainbow trout stock. It would appear reasonable to believe that the greatest influence on decline in stock density has been the considerable increase in fishing effort. The decline in annual commercial catch from 500 to below 200 tons has led to a decrease in earnings for fishermen, and for persons originally engaged in fish canning. However the Schaefer curve indicates that if the fishery is well managed the annual sustainable yield could approach 350 tons. Management of the fishery should initially aim at stock rehabilitation. It was impossible to introduce a system of effort restriction based on the index of effort used in this study, because canning operations have ceased and, if recommenced, are unlikely to follow previous procedures. It is suggested that an index of effort, based on a unit such as nets, boats, or fisher- men, be continuously recorded in future. Initially it is proposed that management be dependent on catch restriction methods. The catch restriction would be implemeiited by a system of closed areas, mesh size restriction, and closed fishing areas. Restricted areas should extend for a radius of approximately 3 km from the mouths of the four main rivers, preferably in view of landmarks obvious to fishermen. In these restricted areas no nets of less than 10.15 cm stretch mesh should be permitted, and throughout the year fishing would be limited to one week of open fishing followed by two weeks of closed fishing. No fishing of pejerrey and other fish should be permitted in these areas, except during open fishing periods and in nets of mesh size greater than 10.15 cm. The times of open fishing would operate on a rota basis between areas, thus permitting a modest commercial exploitation. Gillnets of all mesh sizes would be permitted outside the restricted areas ; allowing capture of available trout, pejerrey and Orestias 440 G. V. EVERETT species. The principal feature of the catch restriction system is thus the prevention of unlimited fishing at river entrances, where the trout are particularly susceptible to capture during the spawning migration. No netting of any description should be allowed in the rivers, although it is believed impractical to attempt to restrict line fishing or limit the size of fish which might be caught. Following rehabilitation of the stock to yield about 350 tons/year the management procedure could be varied to allow for fluctuations in fishing mortality and recruitment strength. It would seem unreason- able to expect the rainbow trout stock to support the requirements of more than one cannery although, additionally, the stock could form the basis of a valuable sport fishery.

I am indebted to A. C. Burd of the Fisheries Laboratory, Lowestoft, for assistance in implementation of the programme and analysis of the data. The study was financed by the Universidad Tecnica del Altiplano and CORPUNO of Puno, the Fishery Service of the Ministry of Agriculture, Lima, and by the United Nations Association of London.

References Cassie, R. M. (1954). Some uses of probability paper in the analysis of size frequency distri- butions. Aust. J. mar. Freshwat. Res., 5, 513-522. FA0 (1969). Manual of Methods for F;sh Stock Assessment, J. A. Gulland. Part 1, Fish population analysis. FA0 manuals in fisheries science (4), Rome. Fish, G. R. (1963). Limnological conditions and growth of trout in three lakes near Rotorua. Proc. N.Z. ecol. Soc., 10, 1-7. Gilson, H. C. (1964). Lake Titicaca. Verh. int. Verein. theor. angerv. Limnol., 15, 112-127. MacCrimmon, H. R. (1971). World distlibution of rainbow trout (Salmo gairdneri). J. Fish. Res. Bcl Can., 28, 663-704. McAfee, W. (1966). Rainbow Trout. In Inland Fisheries Management. (Ed. Calhoun, A.), pp. 191-215. California: Department of Fish and Game. Monheim, F. (1956). Beitrage zur Klimatologie und Hydiologie des Titicacabeckens. Heidelb. geogr. Arb. No. 1. Schaefer, M. B. (1954). Some aspects of the dynamics of populations important to the management of commercial marine fisheries. Bull. Inter-Am. trop. Tuna Comm., 1, 2&56. Worthington, E. B. (1940). Rainbows, a report on attempts to acclimatize rainbow trout in Britain. Salm. Trout Mag. 100, 241-260.