A Review of Freshwater Inflows Data and Related Information regarding the
Rio Grande Estuary
February 2004
Little information appears to currently exist regarding the inflows needed to
sustain the Lower Rio Grande Valley estuarine ecosystem or its economic value. A small
body of research conducted along other parts of the Texas coast has generated estimates
of certain economic values associated with estuarine ecosystems. Although a significant
amount of research has been undertaken to determine the amounts of necessary inflows
needed to sustain estuarine ecosystems in many of Texas’ bays, estimates of such inflow
requirement for the Rio Grande estuary do not yet exist. Results of a study that compares
fish populations in the Gulf with and without freshwater inflows are currently being
analyzed. The Rio Grande estuary remains particularly difficult and complex to
characterize, in part because of its binational nature. Within this context, we characterize
the limited data that does exist and have contacted various experts to ensure the
completeness of our collection.
Raw data concerning the amount of inflows into the Valley is relatively complete.
The International Boundary and Water Commission (IBWC) maintains a series of gauges
that monitor the streamflow at multiple points along the Rio Grande. The furthest
downstream real-time gauge along the Rio Grande is gauge 08-4750.00, near
Brownsville. However, without the latest electronic meters and sophisticated data
processing, it is not possible to accurately monitor flows further downstream as the Rio
Grande becomes tidal after this point. In addition to monitoring streamflow, the IBWC
keeps reservoir storage statistics on Falcon and Amistad reservoirs located upstream on
the Rio Grande.
Historically, periodic flooding would affect the entire delta, adding freshwater
inflows to the Laguna Madre and the various manmade and natural floodways. However,
since the building of the Falcon dam, the flooding has become more of a theoretical than
an actual event.
In response to House Bill 2 (1985), Senate Bill 683 (1987), Senate Bill 1 (1997),
and other legislative directives, the Texas Water Development Board (TWDB) and the
Texas Parks & Wildlife Department (TPWD) jointly maintain a data collection and
analytical study program focused on determining the effects of and needs for freshwater
inflows to the state's bays and estuaries. A schedule announced in 1998 provided for the
study through 2006 of all of the Texas estuaries, minor bay systems, river estuaries, and
coastal preserves. Currently, estimates of freshwater inflow needs are available for all of
Texas’ major bays and estuaries. The South Bay Coastal Preserve and the Rio Grande
Estuary are classified as a minor estuary in this research program.
1
The study of the South Bay Coastal Preserve and Rio Grande Estuary was
originally scheduled to be completed in August 2003.1 Researchers from the TWDB and
TPWD have carried out some aspects of this study, but completion has been delayed, due
to the binational nature of the ecosystem, and the challenges of obtaining sufficient data
in the binational context.2 The methodology to determine the necessary inflows into the
estuarine ecosystem, specific to estuaries along the Texas coast – as well as for estuaries
throughout the world, appears in the journal Estuaries and will be discussed more
thoroughly in our next section of work. The methodology is not specifically applied to
the Rio Grande estuary.
Using baseline data collected from 1992-1997, and comparison data during the
river-mouth closure of 2001, the TPWD has collected fish population numbers using
trawls and bag seines in the Rio Grande. Comparing the two periods of time should
demonstrate the affect of river closure on fish populations and on the ecosystem. While
these results will be analyzed during 2004, some preliminary results are available.3 In
general, fish and shrimp populations dropped with the river mouth closure, and blue crab
populations rose. Fish populations included both fish that are forage for larger species,
and fish that are gamefish, such as Snook. Snook populations in the region were
dramatically affected, as this species requires the use of this estuary for the early stages of
life; Snook is also an important gamefish in the Laguna Madre and Gulf, with the Rio
Grande Estuary being one of the northernmost estuaries that it will breed in.
Additionally, with the closure of the river, fish that use the estuary as one of the few
regional locations with lower saline contents, such as Red Drum, Spotted Sea Trout,
White Shrimp, Blue Crab, Striped Mullet, and Gulf Menhaden were affected as well. Of
the species, Blue Crabs were the only species that seemed to benefit from the river mouth
closure – possibly due to the exclusion of predators from the estuary.4
Another study, commissioned by the TWDB, investigated the effects of reducing
freshwater inflows to the South Bay / Rio Grande Estuary. The study noted that due to
reduced flows, the forming of a sandbar caused the salinity to become much lower, and
the ecosystem to become much more representative of a freshwater lake ecosystem than
an estuary.5
In addition to the existing information regarding freshwater inflows data
ecological freshwater requirements, some information also exists concerning the
economic value of bay and estuarine ecosystems along the Texas coast. A July 2003
publication of the State of the Bays estimated that the Texas coastal estuaries as whole
generated roughly $2 billion annually from recreational fishing alone. Commercial
1
Texas Parks and Wildlife. Texas Bays and Estuaries.
http://hyper20.twdb.state.tx.us/data/bays_estuaries/sitelist.html
2
Personal communication with Brock, David Brock, January 5, 2004.
3
Personal communication with Randy Blankinship, January 22, 2004.
4
Personal communication with Randy Blankinship, January 29, 2004.
5
Montagna, Paul. “Effect of Freshwater Inflow on MacroBenthos Productivity in Minor Bay and River
Dominated Estuaries. TWDB Contract 2003-483-471. Technical Report # 03/03.
2
fisheries averaged another $266 million annually.6 Travel to coastal-based destinations
accounts for about 30% of travel in Texas, translating into $10 billion in economic
benefits each year. Much of these benefits are dependant on healthy estuaries.7
The Texas Water Resources Institute (TWRI), in the May 2001 study “Impacts of
Recreational and Commercial Fishing and Coastal Resource-Based Tourism on Regional
and State Economies”, also yielded important data regarding the economic value of
Texas’ estuaries.8 Their study area covered the six TWDB defined individual Texas bay
and estuaries, including the Sabine-Neches estuary, the Trinity-San Jacinto estuary, the
Lavaca-Tres Palacios estuary, the Guadalupe Estuary, the Nueces-Mission-Aransas
estuary, and the Laguna Madre estuary. Separate analyses were conducted for each
estuary to estimate direct and total economic impacts of the recreation-related and
commercial fishing sectors. In the TWDB definition of estuaries, some counties are
included in more than one estuary. Thus, a summary analysis was conducted separately
to avoid double counting and estimate aggregate impacts. The summary analysis, for the
entire Texas Gulf Coast, calculated that the direct impact of total recreation on the Gulf
Coast was $867 million in 1995.9 Additionally, commercial fishing in the bays
contributed another $37 million, and total commercial fishing added $175 million. It is
estimated that bay and estuary recreation-related sectors sales to final demand stimulated
total regional business sales of about $1.6 billion, personal income of $651 million, value
added of $999 million, and around 32,168 jobs in the Texas Gulf Coast region. Impacts
of commercial fishing in the bay contributed $57 million in total output, $17 million in
personal income, $40 million in value-added, and 1,190 jobs. The impact for all of Texas
was generally slightly higher, and commercial fishing in the Gulf had an additional
impact as well.
However, little information appears to exist specific to the value of the Rio
Grande estuarine ecosystem. According to the TPWD, no commercial fisheries exist on
the Texas side of the estuary, within the boundary of the river. However, commercial
finfish, crabs, oysters, and shrimp fisheries exist on the Mexican side of the estuary, and
their value is unknown.10 The gulf, however, is home to large shrimping fleets, but data
that exists does not pinpoint the exact location of the catches. Recreational fishing data
and other travel cost data specific for the Rio Grande estuary does not appear to be
compiled. In the TWRI 2001 study, the Rio Grande estuary data were aggregated into
the Laguna Madre data – as data were obtained by county data, as opposed to specific
estuaries, making it especially difficult to isolate individual estuary values.11 The Laguna
Madre had direct expenditures of $222 million for recreation in 1995 for a total economic
6
McKinney, Larry. “Why Bays Matter.” Texas Parks and Wildlife: The State of the Bays 2003. 24.
McKinney, Larry. “Why Bays Matter.” Texas Parks and Wildlife: The State of the Bays 2003. 24.
8
Jones, Lonnie. “Impcts of Recreational and Commercial Fishing and Coastal Resource-Based Tourism on
Regional and State Economies.”
9
Jones, Lonnie. “Impcts of Recreational and Commercial Fishing and Coastal Resource-Based Tourism on
Regional and State Economies.”
10
Personal communication with David Buzan, December 19, 2003.
11
Personal communication with Lonnie Jones, January 16, 2004.
7
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impact of $388 million, $153 million in personal income, $243 million in value-added,
and 8,938 jobs. Additionally, commercial fishing in the bay resulted in $1 million in
direct expenditures for a total economic impact of $2 million, and an additional $1
million in gulf fishing for an impact of an additional $2 million. In general, fishing
contributed a total economic impact of $93 million to the region’s economy, and $100
million to the state’s.12 The study designers noted that the greatest limitation encountered
was the overall lack of data regarding bay and estuary related tourism as well as
recreation visitation and expenditures along the coast. They noted that primary data
regarding estuary-related nature tourism and recreational activities should be obtained by
surveying recreational and commercial anglers and tourists.13
The Harvest Monitoring Program, run by the TPWD, conducts a creel survey,
which seeks capture recreational fishing data throughout the coast. Conducted by the
TPWD, recreational anglers are interviewed concerning the species, size, and location of
their catches. Single fishermen and party boats are both interviewed and data is compiled
separately. The survey is designed to determine the recreational fishing pressure in each
of the sub-bays. However, because of the nature of the creel survey data, its use to
analyze recreational fishing activity specific to individual estuaries faces a number of
challenges, and to our knowledge, an analysis of this data specific to the Rio Grande
Estuary has not been undertaken. Nonetheless, with GIS techniques, it may be possible
to use data from the creel survey to pinpoint regional recreational fishing specific to the
Rio Grande Estuary.
Outside of the rivermouth, a “good number” of people frequent the Port Isabel
Artificial reef, about four miles offshore of the Rio Grande and about one-half mile north
of the Mexican Border. This fishing hotspot is likely affected by freshwater inflows.
Tarpon anglers may also frequent the surf zone just off of the Rio Grande. A wade-bank
survey, last conducted in 1991 may provide more pinpointed data regarding the catches
along the beaches and jetties nearby the Lower Rio Grande.14 This data may allow for a
better understanding of the size and scope of recreational fishing in the area.
Overall, the hydrological data regarding inflows to the Rio Grande Estuary is
complete, with real-time data spanning the last several decades. With knowledge that no
commercial fisheries exist on the U.S. side of the border, data still needs to be compiled
regarding recreation and recreational fishing, as this data is incomplete and is not very
focused. It is also unclear how to address recreational and commercial fishing that take
place in the gulf, as opposed to within the boundary of the river. Surveys that have
included the Rio Grande estuary as a larger part of the coast or of the Laguna Madre
system can provide some insight into the value of the ecosystem. The Harvest
Monitoring Program may yield additional insight into the recreational fishing experience
12
Jones, Lonnie. “Impcts of Recreational and Commercial Fishing and Coastal Resource-Based Tourism
on Regional and State Economies.”
13
Jones, Lonnie. “Impcts of Recreational and Commercial Fishing and Coastal Resource-Based Tourism
on Regional and State Economies.”
14
Personal Communication with Mark Fisher March 9, 2004.
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in the estuary, and other travel cost surveys might be able to identify the economic usevalues of the estuary. A wade-bank survey, last conducted in 1991 may provide more
pinpointed data regarding the catches nearby the Lower Rio Grande Estuary from data
that was collected on the beaches and jetties nearby the estuary.15 A non-use value has
never been identified and that too can be determined through surveys.
15
Personal Communication with Mark Fisher March 9, 2004.
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