J. Fish Biol. (1973) 5, 429-440 The rainbow trout Sulmo guirdneri (Rich.) fishery of Lake Titicaca G. V. EVERETT* Universidud Te'cnica del Altipluno, Puno, Peru (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 Bolivia 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 Trichomycterus 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.