■ig. 2. Relationship In the Mexican (eastern Pacltlc) tuna fleet betweeen SST
and the proportion of aeta with tuna.
also found that, apart from the common dolphin (Delphinus
delphis), other species were sighted mostly at 27-28'C
irrespective of area or season. Stenella attenuata and the
spinner dolphin Stenella Iongirostris, havebeen encountered
mainly off southern Mexico, where the relatively deep
20 *C isotherm indicates a large surface lens of warm
water. The warmest surface waters in the Eastern Tropical
Pacific normally occur in this area (Λu and Perryman
1985).
Results and Discussions
The correlation between monthly mean SST and the
proportion of dolphin sets was significant (P<0.01) for
the time period considered here, i.e., 1985-1990 (Fig. 2).
Dividing the time series into individual years leaves the
correlation still significant (P<0.05), except for the 1987,
an El NiAo year when these variables had
opposite trends during February-June and
November.
The data presented here suggest that the
tuna-dolphin association depends on the
gradient and depth of the thermocline, and
that SST is a good indicator of this situation.
References
Anon. 1983. Annual Report 1982. Inter-Ain. Trop. Tuna
Comm., La Jolla, California, 294 p.
Au, D.W.K., W.L Perrymanand W.F. Perrin. 1979. DolpWn
distribution and the relationship to environmental
features in the eastern tropical Pacific. NOAA SWFC
Admin. Rep. No. LJ-79-43,59 p.
Au, D.W.K. and W.L. Perryman. 1985. Dolphin habitats in the eastern
tropical Padfic. Fish. BuU. 83(4):623-643.
Blackburn, M. 1965. Oceanography and the ecology of tunas. Oceanogr.
Mar. Biol. Ann. Rev. 3:299-322.
Nakamura, H. 1969. Tuna distribution and migration. Rshing News
B∞ks, Farnham, Surrey, 76 p.
Perrin, W.F., G.J. Walker, F.M. Ralston and D.W.K. Au. 1983. Distribution
of four dolphins (Stendla spp. and Delphinus delphis) in the eastern
tropical Pacific with an annotated catalog of data sources. U.S. Dep.
Commer., NOAA Tech. Memo. MNFS-SWFC-38,65 p.
Ortega-Garda, S. 1989. Anilisis y nonnalizaciôn de la flota atunera
mexicana de cerco y vara que opera en d Padfico Oriental. Instituto
PoUtécnico Nadonal, México. 103 p. MJSc. thesis.
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V.M. GθMEZ∙MuflOZisfromCentroTnterdireiplinariodeCienciar
Marinar, Apartado Postal 592, La Paz, Baja California Sur, Mexico
2300.
Population Parameters of Sardinella Species in the Coastal
Waters of Dar es Salaam, Tanzania
E.D.S. MAKWAIA
L.B. NHWANI
Abstract
Population parameters of Sardinelle spedes from the artisanal purse
seine and ring net fisheries of the Dar es Salaam area, Tanzania, were
investigated based on length-frequency data, analyzed with FAO's
LFSA and ICLARM's Compleat ELEFAN packages. The results for S.
gΛbosa and S. albella were Laa = 18.6 cm and K = 1.8 year1, respectivdy,
L_ = 16.8 cm and K = 1.15 year1. Preliminary estimates on mortaUHes
and exploitation rates are also presented.
Introduction
Small pelagic fishes are the main target of the light-
assisted purse seine and ring net fishery off Dar es
Salaam, Tanzania. The important spedes caught are the
goldstripe Sardinella(Sardinellagibbosfl), the white sardinella
(Sardinella albella) and the spotted sardinella (Amblygaster
sirm), which form more than 60% of the catches (Nhwani
and Makwaia 1988). The small pelagic fishes caught
along the coast of Tanzania were increased from 5,4001
or 11.6% of the total marine catch in 1977 to 9,200 t or
19.8% of the catch in 1986. Although these catches are
quite modest compared to the estimated potential yield
Ofbetween 20,0001 (FAO 1979) and 40,0001 (Iversen et al.
1984), the doubling of catch within ten years indicates the
increasing intensity of fishing on these species. Since the
estimates of potential yield are not very precise, also in
view of the year to year fluctuations in recruitment
JANUARY 1M2
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