We're Not Alone!

Norman Boyd | San Antonio Bay Ecosystem Leader
We're Not Alone!

One of the characteristics of fishing that makes it so challenging is that you can't usually see your quarry. Our knowledge of what is swimming beneath our boats, or around our ankles, is limited to what we have caught or what we have learned from other sources. How many species of fish, shrimp, crabs, or other critters live in Texas bays? Which are the most abundant species? The actual number of different inhabitants in Texas bays would be difficult to come up with. However, the abundance of many species is measured routinely by the Texas Parks & Wildlife Department, Coastal Fisheries Division (TPWD-CF) monitoring program on a monthly basis. In fact, that is one of the primary goals of the program, to monitor trends in relative abundance of finfishes and shellfishes along the Texas coast.

This program has been ongoing for over 35 years and consists of using several different fishing gears to capture animals for identification and enumeration. Most species are caught in one or more of 3 different fishing gears by TPWD-CF: shoreline seine, Otter Trawl (shrimp trawl), or gill nets. Seines are used to catch small animals living along the shoreline. Trawls are used to catch small to medium-size animals living away from the shore in open water. Gill nets are used to catch larger animals living within 600 feet of the shore. Seines and trawls are active fishing gears in that they are actively pulled through the water to catch animals. Gill nets are passive fishing gears in that they are deployed along the shoreline and not moved until they are retrieved; animals must move into and entangle themselves in the gill net to be caught. The action of deploying a gear, retrieving it, and recording the catch is called a sample. Used together, these fishing gears allow scientists to better understand the population trends of many of the species living in Texas bays.

Each gear catches an assemblage of species characteristic of the habitat in which the gear is used. There is some overlap between the gears with regards to the species they catch; however, sizes of individuals are typically different between gears. The information presented here was collected in 2014 and consists of 2,160 seine samples which caught 229 different species, 1,680 trawl samples that caught 226 different species, and 780 gill net samples with 126 different species caught. All samples were collected in Texas bays between the Louisiana border and the Mexican border.

What makes a species numerous or common? For this story, numerous means those species which made up a large portion of the total 2014 catch for any of the 3 fishing gears used. A species can be numerous and not be caught in a large number of samples. Common means those species which were caught in a large number of the samples for any gear. A species can be common but not be caught in large numbers in any gear. Some species were numerous and/or common in more than one gear.

The catch data for trawls and seines does not include some organisms, such as plants, algae, oysters, colonial organisms, and organisms for which the number caught is estimated. For gill nets, total catch includes only fish, blue crabs, lesser blue crabs, and stone crabs. Some of the species, such as ctenophores, bryozoans, and corals, were excluded because their numbers could not accurately be determined. These species occasionally occurred in very large numbers. No fish were excluded from the data, even though one species, Gulf Menhaden, occasionally is caught in large numbers.

So, just which species living in Texas bays are most abundant and which are most common? Table 1 contains the most numerous and most common species caught in gill nets. Table 2 contains the most numerous and most common species caught in trawls. Table 3 contains the most numerous and most common species caught in seines.

Care must be taken when inferring anything from scientific data, and this data is no different. It is necessary to look at the catch of the 3 gears separately because the many species in Texas bays have very different susceptibilities to each gear. Also, we cannot assume that because species X was caught in larger numbers than species Y, that there are more of species X in our bays. Each species has a different susceptibility to each fishing gear. In this format, these tables serve primarily to demonstrate some of the diversity of marine life in Texas bays that is not obvious to the casual observer.

As you peruse the tables you will see that a few species made the most numerous and most common lists for all 3 gears. This is a good indication that these species are important ecological components in Texas estuaries, and that their populations are important for the wellbeing of the estuary. Also note that Gulf menhaden was the most numerous species in seine samples, but was present in only 17% of the samples. This is because some species, when young, inhabit shoreline habitats in large numbers and are vulnerable to seines. As they quickly grow they move to deeper habitats. Gulf menhaden are a perfect example of this phenomenon. Over 107,000 juvenile menhaden were caught in one Sabin Lake seine sample in May 2014. See if you can spot other anomalies in this routine sampling data.