Impacts of Hurricanes on Sabine Coastal Fisheries and Associated Habitats
Terry Stelly, Sabine Lake Ecosystem Biologist
Sabine anglers fishing inshore of the Gulf of Mexico are usually concerned with the weather, where to go and what to fish with. Anglers last summer and fall dealt with several weather events that make decisions on the other two issues easier. They were dodging one tropical storm (Cindy) and three hurricanes that reached category 5 (Katrina, Rita, and Wilma). Outside the devastation these storms left in their path, some relief for species of open Gulf waters was observable. For example, during the summer in the northern Gulf of Mexico, bottom waters usually experience low dissolved oxygen levels caused by excess nutrients flowing into the Gulf from the Mississippi River. However, by mid to late summer 2005, the dissolved oxygen deficit was reduced as tropical storms and hurricanes churned Gulf waters -- adding more oxygen to the waters.
This change in the oxygen deficit is reflected in Figure 1. Four observations based on Figure 1 are note worthy: 1) average dissolved oxygen levels are highest in May 2005 (7.0 mg/l); 2) by June they reached their summer low (2.5 mg/l); 3) Tropical Storm Cindy disrupted the dead zone's dissolved oxygen deficit by mixing the northern Gulf; and 4) Hurricanes Katrina and Rita continued to provide mixing for the northern Gulf preventing the return of the dissolved oxygen deficit. The data show that as oxygen reaches 4-5 mg/l, the percent-saturation remains above 50%. In general, 5.0 mg/l dissolved oxygen is often thought of as a minimum for supporting the needs of many life forms.
Gulf trawl samples also provide some insight into how dissolved oxygen may have affected vertebrates and invertebrates abundance. The very popular table food white shrimp, started 2005 with catch rates above the 20-yr average (Figure 2). Then, a second high level of dissolved oxygen occurred in July after the Tropical Storm Cindy, accompanied by a slight increase in white shrimp catch rates. The big surprise came in December with the closing data from 2005 with a record catch rate of 770 white shrimp/hour. On the vertebrate side, Atlantic croaker Gulf trawl catch rates were erratic throughout 2005, bouncing on either side of its 20-year average. Finally, two months after Rita, December's catch rate hit a 20-year record of 103 croaker/hour (Figure 3).
As hurricanes mixed waters in the oxygen deficient Gulf waters, increasing the dissolved oxygen, Sabine Lake's inshore conditions appeared to change for the worse. Hurricane Rita hit western Louisiana coastline at Johnson Bayou and Holly Beach pushing a 15-20 ft storm surge, while Sabine Pass on Texas northeastern coast received a much smaller 9 ft storm surge. Farther inshore tidal height reached a maximum of nearly 4 ft above mean sea level at Port Arthur and Sabine Pass. The most northern of the three measuring stations located at the Rainbow Bridge over the Neches River recorded the lowest tidal rise at just over 3 ft. The nearly 10 ft storm surge hitting Sabine Pass severely damaged the tide gage located there limiting its tidal record. Property owners on the Sabine Lake side of Pleasure Island's southern end sustained wind and water damage, reporting water marks up to 8-9 ft above sea level.
Hurricane Rita spilled saltwater and pushed uprooted vegetation (trees included) into the Sabine Lake estuary, placing a higher-than-normal organic load on surrounding water bodies. Because of this, dissolved oxygen levels plummeted drastically a short time after the storm in both the Sabine and Neches rivers, reaching well below 1.0 mg/l for days. Within the first week after the storm, aerial and ground surveys conducted by TPWD Coastal Habitat staff documented massive numbers of dead juvenile fishes along both rivers, presumably due in large part to the low oxygen levels.
A preliminary survey of public use of Sabine Lake resources through boat counts at system access points (ramps and marina slips) was conducted within two weeks of the storm surge. During that second week, only 5 boats were determined to be in use and 7 during the following week. By October's end 102 boats were out fishing which is about one-third of those seen in 2004. This was in contrast to June through August with counts at or above those of 2004.
Surveys to monitor angler landings and resource use at boat access points resumed October 14th. Creel surveys conducted between May 15 and November 20, 2005 showed decreases in sport angler numbers, fishing effort (number anglers X trip length) and total fish landed. Specifically, spotted seatrout, red drum, and southern flounder decreased in numbers. Even after adjustments for samples lost during the storms are made, these reduced trends will probably be sustained.
Gill net collections to evaluate species size and abundance resumed in the 4th week after the storms when the dissolved oxygen deficit was present. It took 5 weeks after Rita made landfall before oxygen saturation returned to normal. Surprisingly, the oxygen deficit appeared to have little effect on the 2005 fall gill net catch rates, since Atlantic croaker, red drum, southern flounder, and spotted seatrout catches stayed above their 20-year averages. However, if compared to only the 2004 catch rates, Atlantic croaker were lower, southern flounder and spotted seatrout stayed near the same, while only red drum rates increased.
Sport anglers should start getting their fishing gear ready for the coming season. The fish are there even as another storm season begins.
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