Changing Sea Surface Temperature and Atlantic Menhaden (Brevoortia tyrannus) abundance and its effect on the abundance of the Atlantic Bottlenose Dolphin (Tursiops truncatus) and Humpback Whale (Megaptera novaeangliae) in Cape May, New Jersey
As the fall progresses in Cape May New Jersey the sea surface temperatures in the waters surrounding the southern tip of New Jersey begin to drop steadily. Beginning at around 70 degrees in September and dropping to around 40 degrees in December. Many fish species are year round residents in the area and are not affected by this drop in temperature. However there is one species of fish that cannot sustain itself in the colder waters of winter and must migrate in order to survive and that fish is the Atlantic Menhaden. Atlantic Menhaden (Brevoortia tyrannus) is a schooling species of fish that is distributed from the Maritime Provinces of Canada to the east coast of Florida. Atlantic Menhaden (Brevoortia tyrannus) lives in estuaries, coastal embayments, and shelf coast habitats, where is is one of the most abundant species (Lozano 2012). As larval, Atlantic Menhaden (Brevoortia tyrannus) feed primarily on zooplankton. As they begin to grow, juveniles form gill rakers which allow them to filter feed. Adult Menhaden (Brevoortia tyrannus) filter feed on small particles such as phytoplankton (Lynch 2007). Adult Atlantic Menhaden (Brevoortia tyrannus) migrate seasonally along the eastern coast of the United States, moving northward in the spring and southward in the fall (Lozano 2012).
The two main marine mammals that are found in the area around Cape May, New Jersey is the Atlantic Bottlenose Dolphin (Tursiops truncatus), and the Humpback whale (Megaptera novaeangliae). These two marine mammals feed primarily on Atlantic Menhaden (Brevoortia tyrannus) while in the waters around Cape May. Atlantic Bottlenose Dolphins (Tursiops truncatus) fall under the category of cetacean. Cetaceans are high trophic level marine predators that have their movement and habitat preferences related to that of their prey. Small cetaceans such as Atlantic Bottlenose dolphins (Tursiops truncatus) seasonally move inshore or offshore along regionally scaled coastlines (Henderson 2014). Cape May, New Jersey, and the southern portion on New Jersey, is a nursery location for Atlantic Bottlenose Dolphin (Tursiops truncatus) to raise their young. Mother Atlantic Bottlenose Dolphin (Tursiops truncatus) care for their offspring for the first three to four years of their life (Hill 2007). Atlantic Bottlenose Dolphin (Tursiops truncatus) use the shallow water around Cape May, New Jersey as a nursery site to raise their young, and are able to use the Atlantic Menhaden (Brevoortia tyrannus) as a main food source for their young.
Humpback Whales (Megaptera novaeangliae) falls under the category of Baleen Whale, which means it has baleen plates in its mouth instead of teeth. All Baleen Species including the Humpback Whale (Megaptera novaeangliae) feed by swallowing both water and prey into their mouth and then filtering the prey from the water by pushing it through keratinized baleen plates that hang from the rostrum of the whale (Goldbogen 2013). This allows baleen whales to feed on large quantities of prey at once, and is considered one most energy efficient feeding methods in the animal kingdom (Goldbogen 2013). Humpback whales (Megaptera novaeangliae) spend the majority of the summer in the Gulf of St. Lawrence in the North Atlantic, and can also be found in the Gulf of Maine, Eastern Canada and Western Greenland. While in the Gulf of St. Lawrence Humpbacks feed on a variety of zooplankton and various species of schooling fish (Ramp 2015). The Gulf of Maine Population of Humpback Whales (Megaptera novaeangliae) breed in the West Indies during the winter months (Ramp 2015).
- I will observe the abundance of Atlantic Menhaden (Brevoortia tyrannus) and its effect on the abundance of Atlantic Bottlenose Dolphin (Tursiops truncatus) and Humpback Whale (Megaptera novaeangliae).
- I will observe the changing sea surface temperatures, and its effect on the abundance of Atlantic Menhaden (Brevoortia tyrannus).
For this project I have developed a scale to determine the abundance of menhaden during a sighting of either bottlenose dolphin or humpback whale. When arriving upon a sighting the first two pieces of data that are recorded is the species that is being viewed and the geographic coordinates of the sighting. Then after recording the species an estimation is made of the amount of Bottlenose Dolphin (Tursiops truncatus), and Humpback Whale (Megaptera novaeangliae) that is in the sighting. Often times when sighting a group of bottlenose dolphin there will be between 20 and 30 individuals. Once determining the size of the group the water temperature of the area is collected using a sensor on the boat. After all of these factors are determined the next piece of data that is focused on is the menhaden scale. There are two factors that are taken into account when recording the menhaden scale data the first is the abundance of menhaden on the surface. Menhaden when in the presence of a predator will often push towards the surface, and can be easily seen as a dark cloud moving through the water. Based on the size of the cloud and the amount in the area and estimation between one and ten is made. Then I look towards the depthfinder on the boat to determine the amount of menhaden that may be under the surface of the water, this is also an estimation between one and ten.
Through this research I expect to see a positive correlation between the size of the group of marine mammals present in a sighting and the abundance of atlantic menhaden in the area. I also expect to see a negative correlation between sea surface temperature and abundance of Atlantic Menhaden, and marine mammals during a sighting. I also expect to see an increase in the size of the groups of Atlantic Bottlenose dolphin (Tursiops truncates) as the temperature drops and other species of baitfish begin their migration south. Leaving menhaden as their main source of food in the region.
Endicott College, Intern at Cape May Whale Watch and Research Center
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