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Hernan Aubert 1 and 0. Eugene Maughan 1
Abstract.-There is some evidence that C. gnidia historically occurred in the estuary of La Cruz. However, C. gnidia has not occurred in any numbers in that estuary for at least thirty years and current habitat conditions do not appear suited to this species.
Resumen.-Hay alguna evidencia que C. gnidia ocurrio historicamente en el estuario de La Cruz. Sin embargo, C. gnidia no ha ocurrido en numeros altos en el estuario por lo menos de treinta anos y condiciones del habitat actual no parecen ser adecuados para esta especie.
INTRODUCTION
Clams are abundant along the coasts of Mexico and are highly prized food items (Manzi & Castagna 1989). One of the most sought after species of clams along the western coast of Mexico is Chione gnidia (Broderip &
Sowerby). In spite of the demand for this species, little has been published about its' distribution or basic ecology (Aquilera & Mathews 1974,
Baqueiro & Masso 1983). C. gnidia is harvested in large numbers from the estuary of Huivuilai, 100 km southwest of Ciudad Obregon, Sonora,
Mexico. The species may have also once occurred in harvestable numbers in the estuary of La Cruz further north (Martinez 1986). Martinez (1986) suggested the possible reintroduction or culture of this species in the estuary of La Cruz, in an effort to reestablish this fishery.
We undertook an evaluation of the feasability of reintroduction of C.
gnidia to the estuary of La Cruz. We also compared the habitats occupied by C. gnidia in the estuary of Huivuilai with those available in the estuary of La Cruz.
1 Biological Resources Division of U. S. Geological Survey, Arizona Cooperative Fish and
Wildlife, Research Unit School of Renewable Natural Resources, The University of Arizona
Tucson, Arizona 85721
269 USDA Forest Service Proceedings RMRS-P-5. 1998

DESCRIPTION OFTHE
STUDY AREA U.S.A.
The estuary of La Cruz is located about 100 km southwest of Hermosillo,
Sonora (figure 1). It is about 52 square km in area. The nearest town
(1500 inhabitants) is Kino
V~.ejo about 1 km west of the estuary. Water enters and leaves the estuary through a single 300 meter opening.
The estuary of Huivuilai is located about 100 km southwest of Ciudad
Obregon (figure 2). The estuary is formed by the mainland on the west and
Huivuilai island on the east.
Water enters and leaves the
§. ...... .
BAHIA KINO
Figure 1. Map of Kino Bay. Region I composed of fine and coarse sand and II sand mud mixtures. A) location of C.I.C.T.U.S. research station. estuary (also called Paradon
Bay) through a 500 meter wide opening at either end of Huivuilai island.
The villages (combined population about 2500) of Paredon Colorado and
El Paredoncito are located along the coastal side of the estuary. A nonfunctional bridge between the mainland and the island has three 150 meter openings through which water can flow.
MATERIAL AND METHODS
We surveyed transects across the estuary of La Cruz and the estuary of
Huivuilui to determine the macrohabitats present and the presence or absence and density (rare, common, abundant) of C. gnidia in each habitat.
Simultaneously, we surveyed the families that have historically fished for clams in the estuaries of La Cruz and Huivuilui to define the oral traditions concerning the occurrence and harvest of C. gnidia from each location. We determined the availability of "optimal habitats" (those where C. gnidia was abundant) in both estuaries.
270 USDA Forest Service Proceedings RMRS-P-5. 1998

N
6
Oelle .... ~:.... ~-
.. ::~~
..
• ..
~. u.s.A.
RESULTS
Figure 2. Map of Huivuilai coast. I) Northern estuary, II) Eastern coast of Huivuilai
Island, Ill) Southern estuary, IV) Bay's coastal region, and V) Central Fringe.
There are only two types of macrohabitats in the estuary of La Cruz. Along the shore north from Punta
Santa Cruz there is a narrow band of sediments composed of a mixture of mud and sand. The sediment in the rest of the estuary is nutrient rich anaerobic mud.
There are five distinct macrohabitats in the estuary of Huivuilui. Habitat 1 has sediments composed of nutrient rich anaerobic mud comparable to those in the estuary of La Cruz. Several species of clams inhabit these areas but C. gnidia is rare. Habitat 2 is an area of predominantly sandy substrates with a few areas of mud and gravel. C. californiensis (Broderip) is the primary clam present; C. gnidia is rare. Habitat 3 is geographically seperated from Habitat 1 but is similar physically and biologically. Habitat 4 is a shallow intertidal area that has a substrate of mostly mud and mud/ sand. Few clams are present.
Habitat five is the largest (5 square kilometers surface area) and has a highly aerobic mud substrate with little aquatic vegetation. C. gnidia is abundant; an individual fisher can harvest about 600 clams per day.
Oral Traditions Concerning the Occurrence and Harvest of C. gnidia from the Estuary of La Cruz and the Estuary of Huivuilui
About six families are traditionally involved in seasonal clam harvest from the estuary of La Cruz. No one surveyed ever remembered a time when C. gnidia had been either abundant or commercially harvested from this area. Conversly, C. gnidia is regularly harvested from the estuary of
Huivuilui. Daily harvest averages about 600 clams per individual, and between 10 and 15 individuals harvest clams each day. This rate of harvest has continued for at least the last 30 years.
USDA Forest Service Proceedings RMRS-P-5. 1998 271

DISCUSSION
Although C. gnidia may have once been present within the estuary of La
Cruz, there is no recent evidence that the species has ever been abundant.
The oral traditions of the local fishers suggest that the species has not been present in the estuary in any numbers for at least the last thirty years. In addition the habitats currently available in the estuary of La Cruz are not suitable for this species; highly aerated mud substrates with little aquatic vegetation are absent. Attempts to culture or to augment the population of
C. gnidia within the estuary of La Cruz do not appear feasible given their current low numbers and the absence of suitable habitat. ·
ACKNOWLEDGMENTS
The University of Sonora provided logistic support. Francisco Ornelas and Ernesto Meza Vega helped with data collection and manuscript preparation. Reviewers were Charles Ziebell and William J. Matter.
LITERATURE CITED
Aquilera, F.& P. Mathews. 1984. Un estudio poblacional de almeja ladera
(Chione sp.) del Golfo de Santa Clara. V Congreso Nacional de
Oceanografia, Mexico, D. F.
Baqueiro, C. E. &
J.
A. Masso. 1983. Variaciones poblacionales y reproduccion de dos poblaciones de almeja ronosa Chione undetella bajo diferentes regimenes de pesca enla Bahia de La Paz B. C., Ciencia
Pesquera. Mexico. 3.
Manzi, J. J. & M. Castagna. 1989. Clam mariculture in North America.
Developments in Aquaculture and Fisheries Science 19. 461 pp.
Martinez, L. 1986. Estudio bioecologico de dos especies de almeja sometidas a sobre explotacion en el estero de La Cruz, Sonora. Cictus.
Informe tecnico. Hermosillo, Sonora, Mexico.
272 USDA Forest Service Proceedings RMRS-P-5. 1998