Spotted Seatrout in the Lower Laguna Madre
A Regional Approach to Restoring a World Class Fishery
by Dr. Larry McKinney, Director Coastal Fisheries, TPWD, Austin
The spotted seatrout (SST) fishery of the Lower Laguna Madre (LLM) sustained by miles of remote and relatively untroubled seagrass meadows deserves its world class reputation. Texas Parks & Wildlife Department (TPWD) fishery monitoring data tells the tale. It was routine in the late-80's to mid-90's for gill net catch rates (one of the primary means by which TPWD assesses adult fish populations) in the LLM to be twice and on occasion three times that of any other Texas bay. That is not the case today and that is the reason TPWD fisheries managers are worried and looking for an answer.
The idea of establishing special bag and size limits for spotted seatrout in the Lower Laguna Madre is one of those possible answers. The idea has been the focus of a series of scoping meetings held by TPWD's Coastal Fisheries over the summer, fall and early winter of this year. The concept of a "regional management" approach that would set unique bag and/or size limits for SST in the LLM was proposed for consideration because of concern about declining populations there as populations in all other Texas bays have steadily increased. The idea would be a significant departure from the historic approach of keeping bag and size limits the same for a particular species coastwide in Texas. Statewide regulations certainly has simplicity for both law enforcement and ease of understanding by anglers as an advantage but is it flexible enough to meet today's management challenges? The short answer is no and the situation in the Lower Laguna Madre is an example of why a regional management approach deserves strong consideration by the TPWD Commission.
This is part one of a two part series on the SST in the LLM that will examine the rationale behind the proposal. Part I will focus on the fisheries science upon which the recommendation is based and will also explore environmental issues related to the proposal. Part II will focus on the implications of regional management, including socio-economic considerations and will outline the range of options being considered along with their pros and cons.
Part I: Regional Management of Spotted Seatrout in the LLM — The Science
The TPWD Coastal Fisheries monitoring program is widely acknowledged as the best of its kind in the world. A recent peer review by an independent panel of nationally recognized fisheries scientists reaffirmed that status. Its comprehensive nature and 30-year record makes it a powerful management tool. The outcome of management decisions based on this database over the years has proved effective and the result has been the restoration of a recreational fishery to levels not seen in decades. The monitoring program is robust enough to support a regional management approach and maintain the sound science base for decision-making that Texas anglers expect.
The case for a regional approach to managing SST in the LLM is a strong one based on three sets of data derived from the monitoring program: overall population trends; spawning stock biomass; and, fish mortality.
TPWD Coastal Fisheries routinely and systematically monitor population levels of sportfish by the use of gill nets in the spring and fall. This "fisheries independent" data is an objective means of collecting information on adult fish populations. It tells us what is present in the bays, both in size and abundance. When used in conjunction with our "fisheries dependent" methods such as creel surveys of individual anglers, which tells us what is being landed; we have a very powerful dataset of the overall state of a fishery.
The population trends for SST along the Texas coast have shown a remarkable recovery since the freezes of the mid to late 1980's. Galveston, Matagorda, and the Upper Laguna Madre (Figures 1, 2 and 3) illustrate the statewide trend seen in all bays except the LLM. Figure 4 shows the LLM trends overlaid on the statewide trend. The spotted seatrout fishery in the LLM has always been in a class by itself but there has been a steady decline in gill net catch rates since the mid-80's. Annual variations can sometime mask that trend but in the last several years the trends have literally been coming to a point, a point where for the first time ever SST populations in the LLM were lower that the statewide average.
Figure 1. Spring gill net catches of spotted seatrout for Galveston Bay, 1985 to 2006.
Figure 2. Spring gill net catches of spotted seatrout for Matagorda Bay, 1985 to 2006.
Figure 3. Spring gill net catches of spotted seatrout for Upper Laguna Madre, 1985 to 2006.
Figure 4. Spring gill net catches for spotted seatrout - statewide summary and Lower Laguna Madre, 1985 to 2006.
Spawning Stock Biomass
Spawning stock biomass (total weight of mature females within a given area) is a relatively straightforward means of assessing the reproductive output of a fish population. For SST those are mainly fish of two to five years of age and sixteen to twenty-four inches in length. Some younger fish can also contribute to spawning as fifty to seventy per cent of females are sexually mature at age one. Females typically produce from 250,000 to a 1,000,000 eggs per spawning event and may produce from 2.5 million to 25 million eggs in a season, with larger females producing more eggs than smaller individuals. Multiple spawning events within a protracted spawning season (SST spawn from April to September) is a typical reproductive strategy for a highly adaptive estuarine species. It is a strategy that helps assure the species takes full advantage of the available habitat's carrying capacity and buffers survival in the face of catastrophic events like freezes, red tides and even manmade disasters such as oil spills.
Another significant characteristic of SST life history in assessing the management mplications of spawning stock biomass is the fact that SST show great "site fidelity" to the bay system where they were born. In contrast to red drum which will school up in the fall and move offshore to form spawning aggregates, SST typically spawn within their home bays or passes immediately adjacent to them. Tagging studies have found an average movement of only ten miles for SST and about a third of tagged fish were recaptured near the tagging site. This adherence to specific bay systems is especially conducive to regional management approaches.
Because of these life history characteristics an assessment of spawning stock biomass can be an important indicator for management action. Figure 5 illustrates the disturbing trend in spawning stock biomass for LLM spotted seatrout. This data was generated as part of the recently completed stock assessment for SST in Texas, the first review since 2000. Because of their reproductive strategy we are not seeing any obvious impact of reduced spawning biomass at present. Recruitment into the LLM spotted seatrout population remains good overall, as indicated by bag seine data collected as part of our monitoring program. There are two concerns. If the decline in spawning stock biomass continues at the current pace we will reach a point where recruitment is adversely affected and recovering from that condition would require management actions of a dramatic nature, far more severe than any we are now contemplating. Secondly, and of immediate concern is the ability of SST to respond to catastrophic events in the LLM like a severe freeze. Spawning stock biomass relates directly to recovery time following such events. Every decrease in spawning stock biomass means a longer and more uncertain recovery of the population. The present spawning stock is significantly lower (about 50%) than in the mid-80's when the LLM was recovering from a series of severe freezes.
Figure 5. Spawning stock biomass of spotted seatrout Lower Laguna Madre, 1985 to 2005.
Both gill net and creel data allows a fishery biologist to assess size class distribution of a fish population, although creel data can be influenced by minimum or maximum length limits and also by angler preferences. This information can provide insight into fishery mortality and what is causing it. If fish of a particular length (i.e. age) disappear from the population and that can be related to a specific factor(s), it can help direct effective management action. In Figure 6, length frequency data for SST in the LLM was summarized for the period 1985 to 2001 and 2002 to 2005. Those periods were chosen because the last significant SST regulations were adopted in 2000 and that seemed an appropriate break point. One problem noted by such an analysis is with 18 inch and greater classes of SST. Beginning with that length class, fish have been disappearing more rapidly in recent years than in the previous sixteen year period. To a fisheries manager this is a classic indicator of increased mortality due to fishing pressure and regulatory action to alter bag and/or size limits can be an effective management tool to rebuild these larger size classes.
Figure 6. Length frequency distribution of spotted seatrout Lower Laguna Madre 1985 to 2005.
Regional Management of Spotted Seatrout in the LLM — The Ecosystem
The comment has been made that before we make any regulatory changes in the LLM we need to address environmental problems that may be affecting the fishery. The Coastal Fisheries Division of TPWD does use an ecosystem based management approach in meeting its fisheries responsibilities. If we cannot successfully answer environmental challenges the carrying capacity of the LLM will diminish. The practical and most immediate impact being that TPWD would be relegated only to a llocating a continually shrinking resource to our angling constituents through the use of bag and size limits. That is the only regulatory authority available to TPWD. However, it does not mean we are without tools to address ecosystem health.
The Lower Laguna Madre is a unique marine ecosystem, one of largest hypersaline lagoons in the world. The 185 square miles of seagrass meadows support a recreational fishery of world class reputation. Although it remains relatively isolated the impact of coastal development is more and more evident. Changing land use from ranching to intensive farming, coastal housing development, and wastewater discharges from municipal, industrial and aquaculture facilities challenge ecosystem health. TPWD has worked diligently with other state and federal resource agencies to address these issues over the 20+ years of my tenure at TPWD and we will continue to do so. In this arena TPWD has no regulatory authority to mandate actions that would directly benefit fisheries. That is the purview of other agencies like the TCEQ and GLO. Both of those agencies do give great weight to such concerns but they must balance other demands as well. TPWD remains a leader in addressing long term environmental concerns both here and all along the coast but we do so with two caveats. One, TPWD can only influence these broader regulatory processes within the authority granted by the Texas legislature and two, solutions to environmental issues of ecosystem scope can take years to effect. TPWD does its best to assure these efforts work in concert with our regulatory authority but we will never hesitate to act to address issues of concern where we can be effective. SST is one of those issues.
It is important to note that while there are significant and even unique environmental challenges the Lower Laguna Madre is today a healthy and productive marine ecosystem. The most direct indicator of that condition may be found in the very database that has generated concern about the condition of spotted seatrout in the system. Coastal Fisheries collects a broad range of information as part of the monitoring program. Gill nets are just one of many including bag seines, trawls, water quality and habitat data, as well as, angler (creel) surveys.
That data allows our biologists to analyze population trends for a variety of species. Taken together they give an indication of ecosystem health. Some species are more sensitive to environmental change than others but a significant change in water quality or some other factor that had ecosystem-wide impact would most likely be reflected by downward trends in many species. We do not see any such evidence in our data. There are some ecosystem level water quality / quantity issues about which we have concern and we are working to address them. There is no doubt that these concerns, if realized, can affect the long term health of the LLM and may be doing so at a level we cannot yet discriminate. However, none of these can be related to the SST issue at this time.
The LLM possesses a wide diversity of fish species. Changes in diversity can be a very strong indicator of ecosystem health. We have seen a total of 63 different fish species landed by anglers in the LLM over the past 5 years in our creel survey, and our gill nets have caught a total of 69 different finfish species during the same time period. Across the broad range of possible indicator species for which we have trend data some are up, some are down and for some we cannot tell. It is the normal condition one would expect for an otherwise healthy ecosystem
Water Circulation in the LLM
Red drum illustrates a key point about the overall health of the LLM, especially water circulation and presents a telling contrast to SST. Over the last several years the LLM has been a hot spot for anglers seeking red drum, with record numbers being caught. This trend should continue in the LLM as TPWD data indicate continued high numbers of red drum entering the fishery. Interestingly, the health of the red drum fishery sheds light on a concern about water circulation in the LLM and most particularly the impact of the diminished Mansfield channel. Adequate water exchange is a key element to ecosystem health in the LLM. Before the Intercoastal Waterway and manmade channels such as the one to Port Mansfield, much of the LLM was extremely hypersaline and did not support a sustained fishery. In contrast to much of the river-influenced Texas coast, inflows into the LLM can come in the form of seawater which was often less saline than that of the Laguna. Greater and more dependable water exchange has produced better fisheries. Red drum spawn offshore, in contrast to SST and adequate water exchange through passes is vital to success. The condition of the red drum fishery in the LLM indicates that water exchange, at least for ecosystem health needs, is adequate and not a limiting factor.
If Regional Management — What?
The analysis of existing data makes a strong case for management action(s) to reverse the downward trends in both overall population and especially spawning stock biomass of SST in the LLM. The question is what specific actions make the most sense. There are a number of options and all have their pros and cons. Part II will focus on those issues.