Goodness Gracious, Great Balls of Baitfish

What’s the first thing that comes to mind when you think of Texas’ coastal fisheries? For many anglers, dreams of catching beautiful Speckled Trout and Redfish spring forward. However, biologists of the Coastal Fisheries Division of Texas Parks and Wildlife think of how to maintain healthy populations of recreationally and economically important species so that they can be enjoyed by everyone. While directly monitoring gamefish populations is essential for good management, it is just as important to keep an eye on the catch rate trends of the key forage species that feed our favorite predatory fishes.

Studies conducted on the diets and feeding habits of important predatory species, such as Red Drum (Scienops ocellatus) and Spotted Seatrout (Cynocion nebulosus), have found that Atlantic Croaker (Micropogonias undulatus), Gulf Menhaden (Brevoortia patronus), and White Shrimp (Litopenaeus setiferus) are a few of the key forage species available in the Galveston Bay ecosystem. This article focuses on six years of catch per unit effort (CPUE) data collected for these three forage species in Galveston Bay using bay trawls. CPUE is calculated by dividing the number of individuals of a species caught by the amount of time spent or distance covered while using a specific gear type (typically calculated as catch per hour for bay trawls). Bay trawls collect everything from small invertebrates and juvenile fish to large adult fish in the open water of the bays. It is important to note that sampling was not completed in April and May of 2020 due to COVID-19.

In the past seven years, the Texas coast has been impacted by two notable natural disasters. In August of 2017, Hurricane Harvey made landfall and brought an enormous amount of rainfall to Texas bays. Data from 2017 show catch rates of croaker and menhaden were less than half of what they were in 2016, though menhaden catch rates are seemingly unrelated to Hurricane Harvey due to lower CPUE catches earlier in the year before the hurricane occurred. It is  possible that the low salinities caused by a massive inundation of freshwater triggered fish to take refuge in abnormal areas that were not being sampled by bay trawls, though we have no way of tracking this. Croaker catch rates continued to decline after Harvey throughout the remainder of 2017. Both species saw a quick rebound, with catch rates increasing again in 2018. While catch rates did drop for White Shrimp in 2017 as well, this was also seemingly unrelated to Harvey, as there was an increase in catch rates from June-November 2017.

In early 2021, the Texas coast was shocked by Winter Storm Uri. The multiple-day freeze event had major impacts on many types of wildlife, including birds, sea turtles, and both game fish and non-game fish. While the lower coast was more heavily impacted than the upper coast, Galveston Bay saw its share of mortalities from the low temperatures. While collecting bay trawl samples on February 20^th, TPWD biologists recorded water temperatures as low as 5.4 degrees Celsius (41.7 degrees Fahrenheit). Like Hurricane Harvey, Winter Storm Uri had a varying effect on the aforementioned forage species.  Contrary to the minimal effect Harvey had on White Shrimp, the freeze hit this species quite hard, likely due to the species having a sensitivity to cold temperatures. However, White Shrimp are prolific and short-lived, so the catch rates bounced back in 2022. Gulf Menhaden also saw a slight dip in numbers in 2021, this is potentially due to juvenile menhaden having a lower tolerance to cold temperatures.  More eye-catching is that the negative trend continued into 2022. On the other end of the spectrum, Atlantic Croaker (Figure 1) saw an increase in catch rates in 2021. This species is a winter spawner that moves offshore to spawn, so the bulk of the mature population were likely protected in deeper, warmer offshore waters during the freeze. Juvenile croaker and the portion of mature croaker that did not migrate to spawn likely saw very little mortality due to their extreme tolerance to cold temperatures. It is possible that Atlantic Croaker’s resilience to this freeze event and a sudden lack of competition from species that experienced larger mortalities have given croaker a chance to increase their numbers in recent years, as data shows catch rates have continued to rise.

Data from 2023 has not been included in these graphics due to the sampling season being incomplete at the time of writing this article, however, preliminary bay trawl numbers for Atlantic Croaker continue to show an extremely positive trend in 2023. After displaying a negative trend in catch rates in 2022, Gulf Menhaden populations suffered from multiple mass mortality events in the Galveston Bay – Freeport area during 2023. These species are relatively short lived and highly prolific. This allows them to bounce back quickly after natural disasters if the conditions take a favorable turn. With the interannual variability that is commonly observed in the catch rates for these species, it is important to look at long-term data trends when assessing their populations.

It is no secret that the Galveston Bay ecosystem is ever-changing. Forage species can be affected in countless ways, from natural disasters to natural predation to harvest by humans for bait or consumption. Though these species may be easily overlooked at times, they are a crucial part of the Galveston Bay system and a valuable food source for many of the game fish anglers love to catch in Texas’ delicately balanced bays.