Galveston Bay Dolphin Research Program Activities
October – December 2021
Galveston Bay Foundation and the Environmental Institute of Houston (University of Houston at Clear Lake) are pleased to share the latest Galveston Bay Dolphin Research Program (GDRP) quarterly newsletter. Thank you for your interest in our research!
A Splashy Overview
The research crew completed four days of field work this quarter, and achieved good survey coverage of both upper and lower Galveston Bay. Although since inception of the GDRP we have focused primarily on surveying western upper Galveston Bay, we are now aiming to cover areas of lower Bay more consistently. During the surveys this quarter, the boat crew completed a total of 32hrs of observation covering 304 kilometers. Approximately 300 dolphins were sighted in 45 groups throughout the Bay.
We are thrilled to announce that our study “Salinity and water temperature as predictors of bottlenose dolphin (Tursiops truncatus) encounter rates in upper Galveston Bay, Texas” was published in November in the journal Frontiers in Marine Science. Our main objectives in this study were to 1) evaluate if dolphins are found year-round in our primary study area in UGB and 2) investigate the effects of water temperature and salinity on dolphin presence in UGB. Dolphin presence was measured using “encounter rates” that are equivalent to the number of dolphins sighted (dolphins) per linear kilometer surveyed (km). Using multiple regression analyses, a statistical tool that identifies relationships between variables, we evaluated if and how water temperature and salinity predicted dolphin encounter rates.
The results of the study showed that dolphins are present in UGB year-round but many leave during the cooler months. Every year, dolphin encounter rates will increase in UGB after the water has warmed to about 23°C (73°F – typically in May) and will remain high throughout the summer. However, if there is a drop in salinity, usually due to heavy precipitation and flooding, many dolphins will leave UGB regardless of the time of year and water temperature. In conclusion, water temperature and salinity are both very important factors in determining dolphin presence in UGB, and low salinity will supersede temperature.
With these findings, we have scientific support to answer a question that we are asked often: “When can I see dolphins in upper Galveston Bay?” Unless heavy precipitation occurs and lowers salinity, June through September are the months of the year when you are most likely to see dolphins in UGB. But, you may be lucky enough to see them any time!
Now that we have completed this study, we are eager to learn more about where dolphins go during the cooler months and during periods of low salinity. It is the primary reason that we want to survey more areas of the Bay, as we suspect that many dolphins hang out in lower Bay during the winter. Please consider making a donation to support our surveys. You will help us answer important remaining questions about where these dolphins live throughout the year.
While passing the Texas City Dike during a survey on November 29, the team observed a group of dolphins swimming near several fishermen. Dolphins may hang out near fishers because they are attracted to bait and unwanted catch, and they may want to take advantage of an “easy” meal. While fisher-dolphin interactions are common, they can have important negative consequences, such as dolphins becoming entangled in fishing line. Fishers should reel in lines if dolphins are near and always recycle fishing line. Please always remember to follow dolphin safe fishing tips and tell your fishing buddies about these guidelines!
Have you every wondered what dolphin poop looks like? …Wonder no more! Our researchers were “lucky” enough to capture this shot. Although it is an unsightly sight and an unpopular topic, marine mammal feces can be important. It can be a food source for fishes and contribute to the transfer of nutrients within and between ecosytems.
The content of this section is available to current members of our Dolphin Society. To become a member and receive updates on our individual dolphins, please adopt or name one of our dolphins. Adoption kits are a fun and unique gift! All funds go directly to the Galveston Bay Dolphin Research Program.
We want to extend a huge THANK YOU to all of you that adopted a dolphin during the holiday season. Our dolphin adoption holiday campaign is our most important annual fundraiser, and your generous donations made it a success. We are also very grateful for the two namings that took place at the end of 2021.
Sir Swimsalot (#297) was generously named by the Bowen and Brewster families.
Angelique (#39) was generously named by Madeleine and Raul Montes.
What YOU want to Know…
“Do bottlenose dolphins kill sharks?”
Large sharks, such as tiger sharks (Galeocerdo cuvier) and bull sharks (Carcharhinus leucas), are apex predators that prey on bottlenose dolphins. Bottlenose dolphins do not feed on these large sharks. However, if they are threatened by a shark, dolphins may defend themselves and this can result in serious injury to the shark. Sharks typically target small, injured and/or sick dolphins, and other dolphins may step up and fight off the shark as a group.
In some bays, encounters between sharks and dolphins are very common. In Shark Bay, Australia, for example, nearly 75% of adult dolphins have shark bite scars. Predation risk from sharks can influence dolphin behavior and can affect dolphin distribution and habitat use. Although we have not yet studied these interactions in Galveston Bay, several dolphins in the GDRP catalog have scars consistent with shark attacks.
If you have a question regarding the GDRP, Galveston Bay dolphins, or dolphin biology, please submit your question using the button below. We select questions to answer from your submissions. We look forward to knowing what YOU want to know!
All activities are conducted under a NMFS Scientific Research Permit.
Galveston Bay Foundation
1725 Highway 146
Kemah, TX 77565
Environmental Institute of Houston
University of Houston at Clear Lake
2700 Bay Area Blvd.
Houston, TX, 77058