Population Dynamics of Common Nearshore Forage Fishes in the Delaware Inland Bays, USA

In the Mid-Atlantic, four species of forage fish, Menidia menidia (Atlantic Silverside), Fundulus heteroclitus (Mummichog), Fundulus majalis (Striped Killifish), and Cyprinodon variegatus (Sheepshead Minnow), account for a large proportion of fish abundance in estuarine environments and are important food sources for state and federally managed predatory species. The population dynamics of these species are poorly understood, and factors affecting their populations are largely unclear or unknown. Seine samples were collected in the Delaware Inland Bays over 9 years (2011–2019), with indices and trends in abundance, as well as climatic and biotic drivers of population changes investigated at both combined estuary and individual bay scales. Average interannual decreases in abundance for all four species at the combined estuary scale ranged between 31.9 and 69.2%, while increases ranged between 65.9 and 178.6%, indicating the extreme variability these species show between years. Standardized models of abundance demonstrated long-term declines in abundance for Mummichog and Sheepshead Minnow at both the combined estuary and individual bay scales. Spring discharge affected Mummichog and Sheepshead Minnow abundance, and Sheepshead Minnow showed a strong negative correlation with Summer Flounder abundance. These data quantify the variability in abundance for an important portion of the forage base in Mid-Atlantic estuaries and should be considered as fisheries management shifts away from single-species approaches and recognizes the forage needs of managed species. Results indicate that even commonly encountered species can consistently vary through time and emphasize the need to examine other important but poorly studied forage species.