Striped Searobin Diet
By Maggie Heinichen, Graduate student, University of Rhode Island Graduate School of Oceanography
Striped searobin (Prionotus evolans) may not be a fish that you think about often, unless these voracious feeders happen to be stealing your bait. However, this species has been at the forefront of the minds of researchers at the University of Rhode Island’s Graduate School of Oceanography (URI GSO) and College of Environment and Life Sciences (CELS) who recently finalized work on striped searobin diet to better understand their role in the Narragansett Bay food web. These researchers were developing a food web model of Narragansett Bay that could be used to test hypothesis of how different factors, such as fishing, human behavior, or temperature could impact the Bay in the future. This model requires diet data for the major fish species of the Bay. Despite high searobin abundance, investigators at URI noticed that data on striped searobin diet either did not exist or was too old to yield conclusive results. Without high quality diet data, it is difficult to predict how this ever-increasing species could be impacting Narragansett Bay.Generally, scientists have been focused on species of greater recreational or economic importance like summer flounder or striped bass. However, striped searobin have become one of the major players of Narragansett Bay. Since the 1970s, the population has exploded due to rising water temperatures, and this fish species is now the seventh most abundant species caught by the University of Rhode Island’s weekly fish trawl. Not only are there more searobins, but they’re also staying in the Bay longer than they used to. Searobins come into the Bay in the late spring or early summer to spawn. As their population has grown, their residence in the Bay has continued to expand into fall and early winter after spawning. Previous laboratory studies have shown that striped searobins can prey on juvenile stages of winter flounder. Therefore, investigators are more intently examining the predation from striped searobin on valuable species in the Bay. With the help of a Roger Williams University undergraduate in Summer 2019 and funding through an EPSCoR grant with the Rhode Island Consortium for Coastal Ecology Assessment Innovation & Modeling (RI C-AIM), these URI scientists collected 293 searobins from Narragansett Bay from May through November. Stomach contents were examined, weighed, and analyzed for trends in diet across searobin length, month of capture, and Bay region (lower-, mid-, or upper-Bay). So what do striped searobin eat? Anything they can fit in their mouth. Researchers found all types of prey in the searobin stomachs, from tiny shrimps and small bivalves to larger crabs, mantis shrimp, and fish. Diet varied by length, month, and region, though there were not obvious patterns in all cases. Larger searobins ate a wider assortment of fish and other, larger prey. More small mysid shrimp were found in the diets of upper-Bay searobins, and greater weights of fish and crabs were found in the diets of searobins caught at the end of the sampling season.The investigators have concluded that striped searobin are generalist omnivores that adapt their diet to their surroundings and are, therefore, highly connected to the rest of the Narragansett Bay food web. These predators essentially act like little vacuums sucking up any prey they can find on the seafloor. Unfortunately, data on the spatial distribution of these small prey creatures are scant and represent a research topic to explore in the future. The most interesting result was the discovery of nine different species of commercial or recreational importance in searobin stomachs. You may not think of summer flounder as a prey species for smaller benthic fish, but Narragansett Bay is an important nursery habitat for many fish and invertebrate species. Throughout the year, various fish, squid, and crustaceans come into the Bay to spawn, and the newly hatched juveniles stay in the Bay for a few months to grow. For a long time, these young fish were protected from predation to some degree by growing during a time of year, predominantly early spring, late fall, and winter, when the predators including striped searobin were offshore or in Rhode Island Sound. However, striped searobin, now present in the Bay at the same time, find juvenile cod, black sea bass, winter flounder, and other commercially important species to be the perfect bite sized snack. While some predation in nursery habitats is normal, if there are too many predators or if there is a particularly weak year class of prey, this predation could have significant impacts on later recruitment to the fishery. As the Bay continues to warm, the searobin could expand their residence time further, potentially overlapping with the spawning periods of other valuable species such as Atlantic menhaden or tautog. The striped searobin population continues to grow in Narragansett Bay, likely due to the ample food and hospitable environment. Their numbers can easily increase since they are not a regularly fished species. While searobin are often overlooked and underutilized, they’re eating a lot of fish that Rhode Islanders do care about. So maybe the next time you catch a good sized searobin you should try it! They may not be as appetizing as fluke or bass, but researchers at URI can say from experience that they’re a decent fish for eating. In particular, their skinny fillets work perfectly for some delicious summer spicy fish tacos!