Coastal Fisheries Research

The Coastal Fisheries Division of the Texas Parks and Wildlife Department operates a research facility located midway on the Texas Coast at Palacios. The office is known as the Perry R. Bass Marine Fisheries Research Station in honor of the Parks and Wildlife Chairman Emeritus and longtime benefactor, Perry Bass. There are currently four biologists and three technicians at the station that conduct life history and genetic research on marine organisms to answer questions that the Division's long-term monitoring programs aren't designed to study. Specialized information on fish life history and genetics is often needed to make appropriate fisheries management decisions, and the PRB staff is often tasked with providing that information.

The Life History group at PRB studies age and growth and reproductive biology of marine fish; and participates in special studies with other Coastal Fisheries biologists. Information on fish size at age, spawning habits, relative and total fecundity, and age at reproductive maturity is determined at the station.

Projects investigating the distribution of a species or life stage, such as juvenile tarpon or gravid spotted seatrout, are also conducted by PRB staff. The information generated through these studies can help answer management questions and allows the TPWD to make appropriate fisheries management decisions.

The PRB Genetics staff investigates genetic variation and stock structure and relatedness of a marine population or species. The different genetic analyses conducted are designed to answer questions about the amount of genetic variation within a species, how that variation is partitioned by location or time, and if hybridization or inbreeding is occurring. Genetic variation studies can help with understanding stock structure, or how a species or population is organized genetically. For example, you may have multiple stocks sharing the same feeding areas; but each group may use different spawning areas, making them genetically different groups. It is also important to understand how genetically diverse organisms are; genetic diversity reflects the capacity of a species to adapt and cope with changing conditions. Maintaining genetic diversity is important because without sufficient genetic variation a species may not be able to adapt to changing conditions and may cease to exist. Species of concern such as Atlantic salmon or yellow grouper often exhibit low genetic diversity while other, more abundant, species like striped mullet and Gulf menhaden exhibit high levels of variation.

PRB staff typically base research projects on samples and specimens that are collected from the eight bay systems along the Texas coast. Coastal Fisheries management staff located at field stations in each of the eight bay systems along the coast collect the samples during the course of their routine monitoring activities. Fish otoliths, which are a bony structure in the skull, and whole fish are collected for life history studies; while pieces of fin tissue are collected and preserved for genetic studies. Samples are delivered to PRB where they are catalogued and stored until sufficient numbers are collected to allow efficient processing.

Fish otoliths are embedded in epoxy resin and thin-sectioned to reveal internal rings which are counted, much like rings in a tree, to determine age of the individual. A metallurgical saw is used to make the thin sections which are approximately 0.35 mm or 0.015 inches thick. The Coastal Conservation Association (CCA) recently purchased and donated a state-of-the-art metallurgical saw to the research station, which reduced the time required to section an otolith to 20-30 seconds. The otolith section is processed using a computerized image analysis system which takes measurements from the center of the otolith to each age ring, or annuli; and to the otolith margin. These measurements are analyzed using an age assignment computer program which calculates age of individual fish based on the date of capture, number of annuli, the marginal increment and the seasonality of spawning and annulus formation for the particular species. Age data is used to calculate growth curves and age-length keys, assign fish to appropriate age classes, and is combined with reproductive data to determine age at maturity.

Genetic sample processing starts with DNA isolation. A piece of preserved fin tissue is placed in a tube with some chemicals, incubated overnight, more chemicals are added and the mixture is centrifuged to concentrate the DNA. A PCR (polymerase chain reaction) machine is used to make copies of the DNA fragments that will be analyzed. The amplified DNA fragments are labeled for either genotyping (DNA fingerprinting) or sequencing and are processed using a DNA sequencer. Several different sequences are examined for existing genetic differences; hopefully informative fragments are located without having to survey too many fragments. Sequencer data are then analyzed using different programs, some of which examine genetic relatedness, while others group samples by criteria such as age class or location.

The primary application of genetic analysis for Coastal Fisheries has been the examination of population structure. Most species studied have exhibited population structure that can be described as isolation by distance. This means that as the geographic distance between areas where samples are collected increases, so does the genetic difference between fish. Like results from the life history studies, genetic study results are used to enhance the information available for managing marine resources in Texas.

The PRB Fisheries Research Station is an integral component of the multifaceted ecosystem based fisheries management approach employed by Coastal Fisheries Division. Look for life history and genetics studies results in a future article.