The recreational fishery in cabra corral reservoir (Argentina): A first comprehensive analysis
C. Baigún1, R. Bernal2, D. Barrientos2, L. Muñoz2, E. Barros2, and J. Sauad2
1 IIB-INTECH, Camino de Circunvalación Laguna, Km 6, 7120 Chascomús, Argentina,
2 Universidad Nacional de Salta, Salta.
Address correspondence to: Claudio Baigún. IIB-INTECH, Camino de Circunvalación Laguna, Km 6, (7120) Chascomús, ARGENTINA. E-mail: claudiobaigun@intech.gov.ar
Key words: Pejerrey; Cabra Corral reservoir; Catamarans; Recreational fishery
Cabra Corral reservoir is located in Salta Province
and is the largest man-made lake in northern Argentina.
As other reservoirs located in this area, it was stocked
with pejerrey (Odontesthes bonariensis) with excellent
results. The pejerrey is the most important and valuable
recreational fish in Argentinean warmwater lakes and
at present most of these reservoirs exhibit well developed
populations being inhabited also by other non game
fish species. Cabra Corral was considered as the most
important recreational fishery in Salta Province concentrating
86% of fishing activity (Volante et al., 1997).
Pejerrey fishery in this reservoir poses management
challenges. Fisheries information is still sparse and previous
studies focused only on pejerrey biological features
(Barros and Regidor, 2002; Barros et al., 2004).
There is a lack of reliable data related to number of anglers
using the reservoir, annual harvest and potential
yeld. Socio-economic analysis in the reservoir was initiated
by Volante et al. (1997), but did not consider fishery
economic value. In the last years managers have
been confronted with the possibility of developing a commercial fishery, without having assessed the current
status of the recreational fishery and reservoir fish
production to support both activities. The aim of this
study is to present a general perspective of the pejerrey
recreational fishery in Cabra Corral reservoir acquiring
relevant data as a first step for developing a sustainable
management framework.
Study Area and fishery characteristics
Cabra Corral reservoir is located in Salta Province and was formed on the Juramento River (Fig. 1). The reservoir is 1,037 m above mean sea level about 80 km from Salta city. It has a surface of 11,360 ha, with a maximum and mean depth of 90 m and 28 m respectively. Trophic status is rather mesotrophic with 360 mS/cm of conductivity, 16 mg/l of total phosphorous, 71 mg/ l of chlorophyll and 2.10 m of transparency (Quirós et al., 1988).
FIGURE 1. Geographic location of Cabra
Corral reservoir in Salta province.
Cabra Corral fishery is mainly based on rented and private catamarans and boats but anglers fish also from a long bridge that cross on the reservoir at its narrowest point. Fishing activity takes place mostly at night using light attractors. Such modality is almost unique from this site and is not allowed for other pejerrey fisheries across the country. Tournaments take place only during day hours. The fishery is partially regulated and no lures and baits restrictions are imposed. Creel limit comprises 40 fish per angler/day and no size limits. The southern area of the reservoir (Zapallar Bay) is considered as a closed area during spawning season in spring (Barros, 1999).
The recreational fishery performance
Proposing management measures implies first
knowing the recreational fishery performance in terms
of catch and efforts. We assessed fishing activity between
November 2003 and October 2004 by developing
monthly samplings of boat anglers (catamarans) and
on boat tournament anglers, considering potential differences
between weekend and weekdays strata and between
seasons (Malvestuto, 1994). Only 25% of available
weekends per month could be sampled thus a
correction factor to estimate angler number on weekdays
was applied. Catamaran samplings were considered
as complete fishing trips since catch and effort data
were obtained from complete surveys at the end of each
sampling night (Pollock et al., 1994).
In Cabra Corral we found that summer season comprised
40% of fishing effort and 43% of total catch.
Twenty three rented catamarans operated regularly in
the reservoir during weekends carrying 84% of anglers,
whereas 16% of them fish on private (and smaller) catamarans
and boats. Mean party size in catamarans was
estimated as 22 anglers per trip. CPUE was higher for
regular fishing trips than for tournaments. Since mean
fishing effort was almost 8 hours per angler, and mean
CPUE was 4 fish/angler/hour, this indicated that anglers
did not surpass the creel limit (40 fish), except
during spring when CPUE increased up to 8 fish/angler/
hour, probably due to pejerrey spawning behavior.
In turn CPUE for tournaments was rather small (1.06
fish/angler/hour ) which may reflect differences in day
and night catchability.
Length structure showed only small differences
between tournaments, catamaran anglers and experimental
gillnet captures from this and a previous survey
(Fig. 2). Most of caught fish were above 13 cm SL (15.6
cm TL) which corresponds to length at first maturity
(Barros et al., 2004), but a large proportion of fish were
well below to Lm50 . For example, catch mean length by
regular catamaran anglers, bridge tournament anglers
and catamaran tournament anglers were 21.4, 19.6 and
22.8 cm respectively. Catamaran and bridge tournament
anglers captured 47% and 75% of fish below such size, whereas 57% captured fish were bellow Lm50. Total estimated
harvest by catamaran fishing for the sample
period was 47.7 tons, representing 4.2 kg/ha, but additional
22.7 tons (2 kg/ha) can be estimated from recreational
bridge anglers.
FIGURE 2. Length frequency distribution of pejerrey sampled from A:bridge tournaments;
B: catamarans; C: catamaran torunaments; D: 2003-2004 experimental gillnets;
E: 1986 experimantal gillnes at Cabra Corral reservoir
Is the fishery overexploited?
Determining the exploitation level is an important
step in Cabra Corral reservoir. We estimated first potential
yield by using morphoedaphic index models and
other variables and then compared with angler harvest
(Cryer, 1996). However, direct application of such models
in subtropical environments such as Cabra Corral
would underestimate fish yield. Thus following Baigún
(2001) approach, Ryder's (1965) original model was
used but corrected by a climatic constant (k=3) derived
from Henderson et al. (1973, Fig. 6). We also applied
Schlesinger and Regier (1982) equation that incorporates
mean air temperature, Jenkins' (1982) model for
reservoir sport fish harvest and Jenkins and Morais approach
(1971) based on middle latitude reservoirs area.
We considered the MEI value as an aggregate yield estimates
for all species, being analogous to the maximum
sustainable yield (MSY) (Matuszek, 1978).
As a measure of exploitation level the relative yield
index (RYI) defined by Adams and Olver (1977) was
used. The RYI is the ratio between the observed catch
and the estimated potential yield (RYI=Yobs/Yest). Since
MSY cannot be considered as an advisable target level,
Yest was corrected by a factor of 0.75 for safety margin
(Ontario Ministry of Natural Resources, 1983), thus
being RYI= (Yobs/Yest) x 0.75.
Estimated yield ranged from 16.8 and 25.7 kg/ha,
averaging 20.8 kg/ha (Table 1). Since pejerrey comprises
60% of community structure mean potential yield represented
12.5 kg/ha or 142 annual tons. On the other
hand, total fish biomasss was estimated in Cabra Corral
as 35 kg/ha (Mosa and Regidor, 2003), which corrected
by pejerrey relative abundance represents 21 kg/
ha. Assuming that yield is 0.6 of fish production
(Gulland, 1970) a MSY of 13.86 kg/ha may be achieved.
However, since MSY has been questioned as a management
concept (Caddy and Mahon, 1996), a more conservative
approach was derived by using a 2/3 correction
factor for MSY. Such approach yield 80% of MSY
without overexploitation risks (Doubleday, 1976) and
represented 9.2 kg/ha. Since total estimated harvest by
the recreational fishery for the 2003-2004 period was
calculated as 6.7 kg/ha, RYI derived from empirical
models ranged from 45 to 66% but was 73% from
biomasss estimation (Table 1). Although pejerrey population
cannot be considered as overexploited (RYI≥1),
CPUE values have strongly fluctuated during last years
(Mosa and Regidor, 2003; Fig. 16) and abundance variation
coefficients over 50% represents an indicator of
heavy fishing (Ontario Ministry of Natural Resources, 1983). At present recreational fishery would exerting a
fishing effort that removes between 50% of potential
yield (based on empirical models) and 80% (from biomass
estimation)
TABLE 1. Estimated potential yield for pejerrey in Cabra Corral reservoir based on empirical models and biomasss estimation.MEI: morphoedphic index; TEMP: Mean air temperature.
How valuable is the fishery?
Information on fishery economic value was obtained
using the contingent valuation method (Azqueta
Oyarzun, 1994). Pejerrey anglers were willing to pay
US $16 per day more than their current expenses (US
$62) to continue fishing in the reservoir. Total estimated
expenditures derived from a fishing trip represented US
$1,490,000 per year exceeding in some cases the economic
impact for well known pejerrey in Pampean lakes.
Because average consumer surplus increased 26% over
current expenditures a total of US $384,000 can be estimated
as net economic value on annual basis.
Expenditures estimated from recreational fishery
is very important if compared with the US $3,600,000
value determined for all the Salta province fisheries
(Volante et al., 1997). The economic yield per hectare
is in between the estimated value for several pampean
lakes (e.g. Grosman and Peluso, 1998; Baigún and
Delfino, 2003). In Table 2 we summarize key estimated
parameters of the pejerrey fishery. Effort and catch data
per unit area should be considered with caution since
some lake areas are strongly preferred by anglers.
TABLE 2. Pejerrey main fisheries and economic characteristics estimated for Cabra
Corral reservoir (11/03 to 10/04). Data corresponds to catamaran anglers.
Management perspectives
Comparing these results with length-frequency data
from a past survey (1986) with similar experimental
gillnets (Baigún, unpublished), length structure appears
as have been shifted to smaller sizes. Lack of large fish
size could be considered as indicator of exploited fisheries
(Tripped, 1995).
However, Cabra Corral is a mesotrophic reservoir
with low proportion of macrozooplankton (Quirós et
al., 1988). Such feature may limit fish grow and accounted
for observed low condition as was reflected by
the relative weight index and the length-weight relationship
slope (2.78). Based on observed results we conclude
that pejerrey population structure appears as being
shifted to small and medium fish size of poor
condition, thus lowering fishery quality due to lack of
trophy sizes. High socioeconomic values challenge
managers to mantain sustainable management actions.
Such scenario may limit the development of a commercial
fishery due to fish size and catch pressure exerted
by the recreational fishery. Future research should be
directed to elucidate how limnological conditions (water
quality and plankton composition), biological features
(trophic niche, mortality rate, reproduction size,
etc) and fishery impact are interacting and regulating
pejerrey population in this reservoir.
Acknowledments
We want to acknowledge Lorena Bonavia, Lourdes Casasola, Simón Chihan and Fernando Franqui for assistance in the field. We are indebted to catamaran owners and anglers for their help and participation.
References
Adams GG, Olver CR (1977). Yield properties and structure of
boreal percid communities in Ontario. J Fish Res Bd Can, 34:
1613-1625.
Azqueta Oyarzun D (1994). Valoración económica de la calidad
ambiental. McGraw-Hill/Interamericana de España, Madrid.
Baigún C (2001). Ecología pesquera de lagos y embalses
patagónicos (Argentina). Tesis doctoral, Fac. Cs. Exactas y
Nat., Univ. de Buenos Aires.
Baigún C, Delfino R (2003). Assessment of social and economic
issues as management tools for summer pejerrey recreational
fisheries in pampean lakes (Argentina). J Lakes Reserv Manage,
19: 242-250.
Barros SE (1994). Temporada reproductiva y fecundidad del
pejerrey (Odontesthes bonariensis) en el embalse Cabra Corral
(Salta). Tesis profesional para la Licenciatura en Recursos
Naturales, UNSA.
Barros SE, Regidor H (2002). Reproduction in Odontesthes
bonariensis (Atherinidae: Pisces) from north-western Argentina.
J Appl Ichthyol, 18(1):27-28.
Barros SE, Regidor H, Iwaszkiw J (2004). Biología pesquera del
pejerrey Odontesthes bonariensis (Cuvier y Valenciennes 1835)
en el embalse Cabra Corral en el subtrópico de Argentina.
Revista Aquatic 20: 32-37. http://revistaaquatic.com/aquatic/
art.asp?t=p&c=159
Caddy JF, Mahon R (1996). Puntos de referencia para la ordenación
pesquera. FAO Doc. Téc. Pesca 347, Roma, 109 pp.
Cryer M (1996). Trout yield in Lake Taupo, New Zealand: angler's
eldorado or just another fishery? In: Stock assessment in inland
fisheries. I. G. Cowx, Ed. Fishing News Books, pp. 378-386.
Doubleday WG (1976), Environmental fluctuations and fisheries
management. ICNAF Selec Pap, 1: 141-150.
Grosman F, Peluso F (1998). La pesca deportiva en lagunas de la
Pampasia. Realidad Económica 133: 74-99.
Gulland JA (1970). The fish resources of the ocean. FAO Fish. Tech
Rep 97.
Henderson HF, Ryder RA, Kudhongania (1973). Assessing fishery
potentials of lakes and reservoirs. J Fish Res Board Can, 30:
2000-2009.
Jenkins RM (1982).The morphoedaphic index and reservoirs fish
production. Trans Amer Fish Soc, 111: 133-140.
Jenkins RM, Morais DI (1971). Reservoir sport fishing effort and
harvest in relation to environmental variables. Amer Fish Soc
Spec Publ, 8: 371-384.
Malvestuto S (1994). Sampling the recreational creel. In: Fisheries
Techniques, Murphy B and Willis DW, Eds. American Fisheries
Society, 2nd edition, Bethesda, Maryland.
Matuszek JE (1978). Empirical predictions of fish yields of large
North Amercian lakes. Trans Amer Fish Soc, 107: 385-396.
Mosa S, Regidor H (2003). AES Juramento S.A. Programa de
Monitoreo Cabra Corral-Peñas Blancas-El Tunal. Informe
Anual 2003.
Ontario Ministry of Natural Resources (1983). The identification
of overexploitation. Report of SPOF Working Group Number
15, 83 pp.
Pollock, KH, Jones C, Brown T (1994). Angler survey methods
and their application in fisheries management. Am Fish Soc
Spec Publ, 25.
Quirós R, Baigún C, Cuch S, Delfino R, De Nichilo A, Guerrero
C, Marinone M, Menu Marque S, Scapini M (1988).
Evaluación del rendimiento pesquero potencial de la República
Argentna. I. Datos. Informe Técnico Nro 7, Dpto. Aguas
Continentales, INIDEP.
Ryder RA (1965). A method for estimating the potential fish production
of north-temperate laes. Trans Amer Fish Soc, 94:
214-218.
Schlesinger D, Regier HA (1982). Climatic and morphoedaphic
indices of fish yields from antural lakes. Trans Amer Fish
Soc, 111: 141-150.
Tripped EA (1995). Age at maturity as a stress indicator in fisheries.
Bioscience 45(11): 759-770.
Volante JH, Garrido J, Sauad J, Picón Matorras M (1997). Análisis
de la pesca deportivo-recreacional en la Provincia de Salta.
Manejo de Fauna, Publ. Téc 8: 1-11.
Received on March 15, 2005.
Accepted on April 21, 2005.