Understanding the Key Contributors to Smooth Dogfish Trends in Abundance in New Jersey and Delaware Waters

The smooth dogfish, Mustelus canis, is a small coastal shark landed in a number of U.S. commercial fisheries. This study focused on the cause for the decrease in smooth dogfish catches during the NOAA shark survey in Delaware Bay. Another species, the sandbar shark, Carcharhinus plumbeus, showed an increasing trend during the same timeframe. To investigate these trends, we used NOAA survey data, along with trawl survey data from Delaware and New Jersey Divisions of Fish and Wildlife. Analyses indicated smooth dogfish catches are negatively correlated with temperature and larger sandbar catches within the bay. The sandbar is a more robust shark and may be outcompeting the smooth dogfish for the baited hooks. There is some habitat partitioning between the two species since small sandbar sharks use the shallow waters of the bay, whereas smooth dogfish tend to use the deeper cooler waters. The larger juvenile sandbars are widespread throughout the bay and would more likely interact with smooth dogfish. Regression analysis shows a significant positive trend in bottom water temperature across years during June. Smooth dogfish are a cooler water species that migrate into and out of the bay earlier than sandbar sharks. In response to increases in sandbars and water temperatures, smooth dogfish may be migrating out of the bay sooner. Adult smooth dogfish use the bay for mating and pupping in the spring. Juvenile smooth dogfish also return in the spring, but without the need to mate or pup they may migrate out sooner as temperatures rise.