Agriculture - - Contents - >BY DR. RAFAEL D. GUER­RERO III

LAKE LANAO is our coun­try’s sec­ond largest lake, lo­cated in Lanao del Sur, Mindanao. It has a sur­face area of 35,700 hectares, a lake sur­face el­e­va­tion of 702 me­ters above sea level and av­er­age depth of 60.3 me­ters. The lake is one of the 17 an­cient lakes of the world and is be­lieved to be mil­lions of years old.

There used to be 18 species of en­demic fishes (cyprinids) in the lake that con­trib­uted much to its fish­eries pro­duc­tion and the liveli­hoods of Maranao fish­er­folk de­pen­dent on it. In a re­cent field sur­vey of Armi Tor­res, a Ph.D. stu­dent of the Univer­sity of the Philip­pines Los Baňos’ School of En­vi­ron­men­tal Science and Man­age­ment, only one species of the en­demic carp-like fishes was found and pos­si­bly two other species could still be ex­ist­ing.

In a mar­ket sur­vey con­ducted by Domi­ciano Vil­laluz in 1963-64, the cyprinids of the Lake Lanao con­sti­tuted 49.4% of the 991,120 kg of fishes caught fol­lowed by the white goby ( Glos­so­go­b­ius giu­rus) and Mozam­bique tilapia ( Tilapia mossam­bica) with 6.4% (127,750 kg), and 5.5% (109,500 kg), re­spec­tively. The tilapia (an ex­otic fish) was de­lib­er­ately stocked in the lake for fish­eries en­hance­ment while the white goby (a na­tive fish not found in the lake) is be­lieved to have been in­ad­ver­tently stocked with it in the early 1960s.

Prof. Pete Es­cud­ero of the Mindanao State Univer­sity’s Col­lege of Fish­eries in Marawi City found the fish land­ings of the fish­er­folk in the lake in 1976-77 to con­sist of 448,207 kg (55.7%) of cyprinids, 73,633 kg (9.1%) of Nile tilapia ( Tilapia niloti­cus), and 90,315 kg (11.2%) of white goby.

By 1990-91, the fish land­ing sur­vey of Prof. Es­cud­ero showed that the cyprinids only rep­re­sented 9% of the catch with 22,442 kg while the share of the Nile tilapia was 28.3% with 71,056 kg and that of the white goby was 0.92% with 2,308 kg. A shock­ing find­ing of the study was that 31.6% of the catch con­sisted of the eleotrid, Giu­rus mar­gar­i­tacea, another in­ad­ver­tently in­tro­duced fish in Lake Lanao.

The eleotrid, known to the Maranaos as “kat­u­long,” is a vo­ra­cious feeder that preys on the eggs, lar­vae and young of the cyprinids that in­habit the shal­low ar­eas of the lake with veg­e­ta­tion. How it was in­tro­duced in the lake is not ex­actly known. It is thought that it came along ac­ci­den­tally with the

Nile tilapia fin­ger­lings stocked in the lake from the Kitcharao fish hatch­ery in Suri­gao del Norte of the Bureau of Fish­eries and Aquatic Re­sources which is be­side Lake Mainit where the eleotrid is also found.

A sur­vey of the fishes landed in three out of the 19 mu­nic­i­pal­i­ties sur­round­ing Lake Lanao in 2008 by G. Is­mail and co-re­searchers showed that the catch quan­ti­ties for two cyprinid species, Bar­bodes tumba and Bar­bodes lin­dog, were only 7.02 kg (0.04% of to­tal catch) and 1.76% (0.01%), re­spec­tively, while those for the catch of the eleotrid and Nile tilapia were 67% and 26% of the to­tal catch, re­spec­tively.

One rea­son for the pro­lif­er­a­tion of the in­tro­duced eleotrid in Lake Lanao could be the lack of a preda­tor for it like the eu­ry­ha­line eel, An­guilla celebe­sen­sis, which mi­grates to the sea from the lake through the Agus River, the main out­let of the lake. The eel is found in Lake Mainit and its loss in Lake Lanao could be due to the changes made in the Agus River for the hy­dro­elec­tric fa­cil­i­ties of the Na­tional Power Cor­po­ra­tion that may have pre­vented the fish from swim­ming into the lake. Can the re­main­ing cyprinid in Lake Lanao still be saved?

In the sur­vey of Armi Tor­res in 2016-2017, only the Bar­bodes tumba was found in the river trib­u­taries of the lake. Two other species, Bar­bodes lin­dog and Bar­bodes sir­ang, were not found and were re­garded as pos­si­bly ex­tinct.

Prof. Es­cud­ero re­ported on the suc­cess­ful breed­ing through in­duced spawn­ing of the Bar­bodes tumba and Bar­bodes sir­ang in Marawi City in 1990. How­ever, no fol­low-up on this was done. If the fishes were bred in cap­tiv­ity and kept out of the lake to avoid pre­da­tion by the eleotrid, they would be in abun­dance to­day.

Another con­ser­va­tion strat­egy for the re­main­ing cyprinid ( Bar­bodes tumba) is to trans­fer it to a nat­u­ral wa­ter body like a small moun­tain lake that does not have the eleotrid or other preda­ceous species. This was done by Dr. Vic­tor Soli­man of the Bi­col Univer­sity’s Col­lege of Fish­eries in Tabaco, Al­bay who trans­ferred the “sinara­pan” ( Mys­tichthys lu­zo­nen­sis), an en­demic fish in Lake Buhi in Ca­marines Sur to Lake Mana­pao, where it is now thriv­ing.

A view of Lake Lanao. (In­set) Bar­bodes tumba, the re­main­ing en­demic cyprinid in Lake Lanao.

The white goby (A) and eleotrid (B).

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