PRELIMINARY STUDY OF THE FISHERY IN LAGUNA SALADA, BAJA CALIFORNIA
1. CHARACTERISTICS OF THE LAGUNA SALADA
3. ECONOMIC ASPECT
1. CHARACTERISTICS OF THE LAGUNA SALADA
1.1 LOCATION AND DESCRIPTION
Laguna Salada is located in the municipality of Mexicali, Baja California, between 32û33'00" and 32û33'50" latitude north, and 115û22'00" and 115û47'00" longitude west of the Meridian of Greenwich. It is bordered to the north by Cerro del Centinela, to the southeast by the Sierra de las Pintas, to the east by the Sierras Cucapa and El Mayor, and to the west by the Sierra de Juárez (Figure 1).
The climate for this area of Mexico, according to Koppen's classification (1948) and later modified by Garcia (1973), is as follow: BW(h')hW(e)*, meaning dry heat with cool winter and rain during summer and winter months. The average precipitation is 5mm/yr and the average evaporation is 170mm/yr. The temperatures range from 12ûC to 49ûC (Perez, 1981).
This region has northwest-southeast winds from December through April, and southeast-northeast winds from June through October. The months of May and November are usually calm. The maximum wind velocity recorded in this region was 170 km/hr.
The surrounding vegetation it is typical of arid and semiarid environments. Most plants can be categorized as xerophyte shrubs.
Laguna Salada is an enclosed basin that is part of the delta of the Colorado River. It extends from Cerro El Centinela, through the Sierras de Juárez and Cucapa, to the zone of inundation of the Colorado River to the southeast of the Sierra El Mayor, where there is a passage through the deposits of the Colorado River (com.pers. Ing. Eduardo Paredes). This dry zone was occasionally flooded by extremely high tides from the Gulf of California before the construction of Highway Number 5, linking Mexicali and Tijuana. It was not until 1974 that this area started to receive water supplied by the discharge drains located in the district of irrigation number 14 (the drains are: the discharge drain at the Hardy River, the drain Plan de Ayala, and the south Collector drain), passing through the supplying canal which connects the Colorado River and Laguna Salada. The construction of the supplying canal started in September 1973, and became operational in February 1974. It was approximately 37.5 km long, 25 m wide, with an average depth of 2.5 to 3 m, the original flow rate was 6.24 m3/seconds.
Very hot: average annual temperature of 22ûC, the average temperature for the colder months being 18ûC
Precipitation during summertime
Semi-warm with cool winters, the average annual temperature being between 22ûC and 18ûC, the average temperature for the colder months being 18ûC
Precipitation during the summer, but with percentages of rain during winter 10.2 with respect to the annual precipitation rate
Extreme weather, fluctuations between 7ûC and 14ûC
At the beginning of 1979, the United States of America sent excess water from the Colorado River to Mexico, which led the Secretary of Agriculture and Hydraulic Resources to initiate a series of constructions in order to prevent the flooding of agricultural fields bordering the river, especially those in the irrigation district. These constructions deviated the excess water to the supplying canal &endash; Canal Alimentador-, which in turn increased the volume of water discharged in the Laguna. The widening of the canal was started in May 1974, with the intend to increase the discharge flow rate to 25 m3/seconds and to decrease the length to 35 km. The operation was finished in January 1980. As the control structure was no longer in use due to increased water levels, the supplying canal had a maximum flow rate of 60 m3/seconds.
Presently, the Laguna Salada has an inundated area of 40,700 hectares, with a volume of 730 .106 m3 . The depth of the lake ranges from 20 cm for the shallowest areas and 4 m for the deepest ones.
The average evaporation is 2,420.63 mm/year (Table 1), representing an average evaporated volume of 13,967.79 m3/hectare/year. A continuous inflow of water to the lake is necessary to counterbalance the losses due to evaporation and infiltration. This has been possible up to now by the input of excess water kept in the irrigation district.
With a discharge of 6 m3 /second, it is possible to maintain an inundated area of 7,604 hectares during the month of June, with a maximum of 31,984 hectares for December (Table II).
In general, the Laguna Salada is a shallow body of water, with a variable total volume depending upon the water inflow from the Colorado River. The temperatures are usually high although December, January and February are sensibly cooler; the oxygenation levels are variable within the watershed; as far as the other physical and chemical characteristics are concerned, they are relatively stable in the lake and its surroundings (Tables III, IV, V, VI and VII). The benthic sediments are rather muddy and the bottom topography displays irregularities.
There are basically two species dominating the vegetation: Tamarix petandra, and the cattail Typha latifolia, an emergent hydrophyte characteristic of the flanks of fresh water rivers and basins.
A zonation pattern can be observed for the two species. Tamarix sp. is located on the sides of the supplying canal and the Laguna, while Typha sp. is mostly abundant around the ramifications of the supplying and into the basin at shallow depths, extending to the northeast away from the main basin, where is forms dense thickets. This distribution pattern corresponds to a depth gradient.
Seven families of fish and two families of crustaceans have been caught in the supplying canal and from the lake. If the poecilidae Poecilia velifera obtained from another study is included, then a total of 13 species have been identified from the Laguna and its tributaries (Table VIII).
None of the species of freshwater fish are endogenous of the Colorado River in the Mexicali valley, but were introduced from California, U.S.A. As there were no ecological barriers, populations settled and reproduced in the Colorado River and its tributaries in this region.
The presence of marine species within the Laguna is due to the fact that the Colorado River originally flowed into the sea. However, this situation has changed as there is no longer any permanent connection between the river and the sea. The Colorado River was connected to the sea between 1979 and February 1981. During that time, squids, mullets and chiros swam upstream the river and colonized Laguna Salada, where the environmental conditions were adequate for their establishment.
Presently, there is no connection between the Colorado River and the sea, preventing the squids from completing their biological cycle. With regards to the mullets, it is probable that they are able to spawn and recruit in freshwater, as they have been observed in the valley of Mexicali since 1967. It can be speculated that there is a continuous recruitment of mullets within the lake, and that the juveniles are not coming from the sea.
2.1 COMMERCIAL FISHERY
Commercial fishing is carried out in the Laguna basin as well as in the supplying canal. Boats approximately 3 meters in length, made of wood or fiber glass, and with a maximum speed of 40 km/h are used. Nets are more readily used in the supplying canal than in the lake, and 17 gillnets were counted once, some made of several 60-meter long nets connected together, extending along the cattail borders or across the canal, thus preventing the passage of other boats.
Within the Laguna, the nets are arranged in the shallow zones.
The fishing methods are usually similar in the lake and supplying canal, although there may be some differences based upon the targeted species (Figure 2). In general, the nets are made of mono- and polyfilaments of nylon polyamide (P.A.). These nets vary in dimensions, mesh size, material and diameter of the filaments used. Of the observed nets, the mesh sizes were 3, 3 1/4, 5 1/4, and 61/4 inches.
The species that are of commercial value are: mullet, catfish, carpe, tilapia and squid, and there is some demand for "chiros"
2.2 SCIENTIFIC FISHERY
The fishing methods used during this investigation were: a gillnet 60-meter long with a mesh size of 3 1/4 inches, and trawlnet with a diameter of 320 centimeters.
The gillnet was used twice (Figure 1): once on a nocturnal run in the supplying canal (run A), and once on a duirnal run in the lake (run C). During the first run, six squids and approximately 100 kg of "chiros" were caught. On the second run, the nets were left in the water for two hours. The fish caught were mostly mullets, carps and tilapia. These results were compared with the catch of a commercial run to obtain a yield in 500m/12hrs (Table IX). The results of two other commercial courses performed within the lake are shown (Table IX).
A total of 18 runs were done in the canal and in lake using trawlnets having a mesh size of 1 1/4, 1 1/2 and 1 3/4 inch. The catch consisted mostly of tilapia (Figures 3 and 4).
2.3 BIOLOGICAL INFORMATION
The species caught for commercial purposes and the ones caught during this investigation are non-endegenous of the Colorado River. They were all introduced from North America, either from fresh water or marine environments.
The species for which some information is available are the following.
This species was caught only during this investigation. The gillnet was placed in the supplying canal (station A). A total of six adults were caught, all with immature gonads. As no juveniles were caught, it is unlikely that this species reproduces within the canal or the lake. As these invertebrates can live for up to one and a half year, it is possible that the specimens caught arrived in the canal when the Colorado River and the gulf were last in contact.
This euryhaline species has been caught in important quantities, especially in the Laguna basin, as it is less abundant in the supplying canal. As the fishing effort is considerable in the canal and as this species is at the base of the fishery, it is therefore possible that the fish caught were migrating from within the basin. None of the fish caught had mature gonads or showed the signs of a recent spawning activities. As the only stages present were I and II, it is probable that the mullets spawn in the Laguna during the months of January and February. Furthermore, a wide range of sizes was caught (Figures 5 and 6). Mullets and squids are the most valuable from an economical perspective, hence more data must be obtained before taking administrative decisions that could jeopardize the health of these fishery resources.
There are three very abundant species of tilapia, present in all trophic levels. They are commercially fished within the Laguna and the canal. This group has probably the greatest likelihood to dominate the fishery because: it can sustain salinities up to 53.5ppm, it has a high reproductive rate, and is believed to be omnivorous, although it should be noted that it can feed on squid larvae when they invade coastal waters.
The species of this group are abundant in the basin of the Laguna and in the supplying canal. A large range of sizes have been caught in both commercial and scientific fisheries. As this taxon predominantly includes fresh water species, it is assumed that they are able to reproduce normally in the Laguna, although none of the specimens caught had either mature gonads or showed signs of recent spawning activity.
This eurhyaline species was reported to have been introduced from the Colorado River (Miller, 1958). It was captured in important quantities in the supplying canal during the experimental sampling (Table IX, station A). However it cannot be concluded that it is restricted to the canal based upon the absence of capture from the Laguna basin. There is no commercial demand for this species, despite its abundance.
The species in this family is carnivorous and is found in freshwater. It is ideal for sport fishing, and has a low conversion index. It is commercially fished due to its demand on the market. When the level of the Laguna decreases, its reproduction will be impeded as it build nests in areas near the surface.
There are probably more than one species of catfish in the Laguna, although it was not confirmed during this study. Nevertheless, it probably reproduces in the basin based upon its abundance and range of sizes caught, especially in the supplying canal.
This foraging species is abundant in both the lake and the canal. Along with the blue-gilled tilapia (Lepomis macrochirus), it is preyed upon by the largemouth bass.
2.4 FISHERY MANAGEMENT
The resources sustaining the fishery of Laguna Salada are difficult to evaluate for several reasons. Some are directly related to the characteristics of the Laguna, such as the changes of water inflow, which in turn lead to fluctuations in the acreage of inundated surface and in the physicochemical components of the system.
Other difficulties are biological. For example, there is probably an important migration of fish difficult to quantify between the water basin, the canal and the Gulf of California whenever a connection is created. In addition to these difficulties, it is necessary to mention the variation in the fishing effort, due to fluctuations amongst stations. These fluctuations are more or less related to the water inflows and to administrative decisions such are restrictions.
On the other hand, accurate catch data are not available as the total catch probably includes data obtained from Rio Hardy and San Felipe.
Models can be used to estimate the densities of the present resources. However, these models depend upon catch and effort data and assume that the fish stock is proportional to the total biomass of adult fish Therefore, as the fishing effort increases, the adult densities gradually change. It is clear that as the fishing effort constantly increases, the fish are caught before reaching sexual maturity. Thus in theory, their reproduction should decrease to zero.
The populations of the Laguna have not reached a point of rapid changes due to reasons inherent to the lake. Rapid changes would have been triggered by the absence of water inflow -even though there is no connection to the Gulf presently- or by pollution due to sewage or industrial runoffs.
On the other hand, the fishing effort has increased and is difficult to quantify as it is basically unregulated. It was observed during this study that the number of registered fishing vessels was lower than the number of vessels fishing in the basin and the canal. Moreover, this study was not exhaustive and only a percentage of the total inundated area was surveyed. Not only is it necessary to quantify the total fishing effort, but also the fishing effort within stations and to obtain information concerning the dominant species of fish captured.
3. ECONOMIC ASPECT
Based upon the observations and interviews gathered during this investigation, as well as the data obtained from the Office of Computer Analysis and Statistics of the Fishery Department, three fishing groups are officially recognized. Two are official agencies fishing on a big scale, and the other is the Unit of Fishery Production of the local community of Cucapa. Other groups were not included as there are no reliable records indicating the source of the species commercialized in the Mexicali Valley, Baja California.
The information gathered based solely upon the officially recognized fishing vessels and their influence on the catches and the revenues generated, is subjected to future corrections. Table 10 is a list of the official fisheries, including the number of boats and type of equipment used, the number of fishermen and dependents employees. The number of fishing vessels belonging to these groups is actually higher than the number of registered vessels, at least based upon the information that was obtained during the study.
Tables 11 and 12 show the catches recorded by the Office of Fishery in Mexicali, Baja California, for the 5 most economically important species for 1981. The value of the catches based upon the wholesale prices are shown in table 13.
The evaluation and management of the fishing resources of Laguna Salada as mentioned previously depend upon various activities. These activities permit to anticipate the changes of the fish populations under the pressure of a commercial fishery.
The estimation of the fishing effort necessary in order to predict the variations observed in the resources under the fishing pressure. However, this evaluation is difficult to quantify because of the lack of employees and regulations. Nonetheless, a possible solution to overcome this problem is to carry out aerial surveys over the basin to obtain the number of nets per hectares, and to survey the canal with boats to determine the number of nets per kilometers, which would be similar to the method of this study. To be effective, these censuses would have to be carried out at least four times a year, and ideally on a monthly or bimonthly basis. These survey would not require more than two employees.
As the total catches are underestimated and difficult to correct based on the data from the Office of Fishery of Mexicali, a proposed solution is to record the content of the nets in the different zones (basin, canal and cattail areas) and to assess in parallel the fishing effort. The data hence obtained could be extrapolated to obtain an estimate of the total catch for each commercial species.
At the same time, biological surveys (gonad studies and sizes) should be carried out to understand the reproductive cycle of various species. This would allow to verify whether the mullets reproduce within the basin for example. These researches could be done with the help and support of the "Investigations Histologic" program of the Center for Fishery Investigations of Sauzal de Rodriguez, Baja California.
The squid fishery is anticipated to diminish due to the absence of connection with the gulf, and an import of larvae would not advisable because of the predation pressure exerted by the tilapia population. Larvae could only be introduced in enclosed areas such as the ones of Yurimuri.
In the same manner, studies can be initiated to determine the viability of mullet culture, since it is possible that the hypothesis that they reproduce in the lake is false. Techniques for inducing spawning in mullet adapted to freshwater are already well developed, and it would only be necessary to adapt them to the technical conditions for the region.
With respect to the current fishery, it is recommended that this be carried out further toward the interior of the lake, since as we have already mentioned, the effort is very high in the canal. Also the placing of nets from one bank to the other of the canal should be avoided as we have no knowledge of movements of species between the canal and the main portion of the lake.
Finally, all the fisheries biology considerations that we have mentioned should be conditioned on an in depth study of the presence of contaminants in Laguna Salada and in the species fished there. We must not forget that we are dealing with a closed basin, one with a high evaporation rate and which is fed by waters from a well-developed agricultural zone that uses large quantities of pesticides, herbicides and insecticides, as well as a great number of fertilizers. It will be important to know the destination and exact quantities of fish harvested from Laguna Salada.
This commission has been successful in large part thanks to cooperation of members of Cucapá Production Unit and of Oceanographers Norbert Castro C. and Benito Nava C. of the National Native Peoples Institute.
We thank, as well, Engineer José Trejo of the Office of Studies and Project of the Secretary of Agriculture and Water Resources, for having provided technical data on Laguna Salada and its feeder canal.
FIG. No. 1. Map of Laguna Salada (Enlarged)
Fig. 3. Enlarged
Fig. 4. Enlarged
Fig. 5. Enlarged
Fig. 6. Enlarged
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