Marine mammals in the Dutch Caribbean

DUTCH CARIBBEAN – The Caribbean waters are home to 36 species of marine mammals, but surprisingly little is known about the lives of these intelligent and social creatures.

A humpback whale feeding at the Stellwagen Bank National Marine Sanctuary. - Photo credit: Kai Wulf

Highly dependent on large, intact and healthy underwater ecosystems, marine mammals are sensitive to human-based pressures such as overfishing, land-based pollution and even cruise tourism (cruise ship collisions with whales is not uncommon).

1 Extralimital: ranges in the Atlantic – eastern central; Atlantic – northeast; Atlantic – northwest. 2 Possible southern Caribbean range. 3 River/Coastal dolphin – mainly in the Amazon region, South America

One species of marine mammal, the Caribbean Monk Seal,  suffered from overfishing of their food source (reef fish and invertebrates such as lobsters and octopuses) and habitat loss through coastal development. Those threats combined with large-scale hunting of the seals pushed the species to a population collapse and extinction in the 1950s.

Bottlenose and spinner dolphins travel in social groups and communicate with each other by a complex system of squeaks and whistles. They track their prey through the use of echolocation just like bats, their cavern dwelling mammalian relatives. Dolphins make up to 1,000 clicking noises per second. These sounds travel underwater until they encounter objects, then bounce back to their dolphin senders, revealing the location, size, shape, and movement of their target.

To prevent other marine mammals from going extinct, conservation efforts are crucial. The establishment of marine protected areas of the Dutch Caribbean, most recently on Saba Bank and in St. Maarten are significant steps in safeguarding habitat and ecosystems for our marine mammals. Several nations, including the USA, the Dominican Republic and France, have established marine mammal sanctuaries in Caribbean waters. The Netherlands will now follow suit with the establishment of a marine mammal sanctuary in the Dutch Caribbean by December 2012.

The recently established ‘Man of War Shoal’ marine protected area in St. Maarten is an important hotspot for marine mammals. A survey conducted by the St. Maarten Nature Foundation counted 41 Humpback Whales, numerous Sperm Whales, 21 Bottlenose Dolphins and 15 Spinner Dolphins in the period February – June 2012. The survey contributes to closing the knowledge gap as it increased the understanding of migration routes, feeding behavior and occurrence in general of marine mammals in the Dutch Caribbean. Video of marine mammals in St. Maarten.

Sperm whales emit a series of clicking sounds that may be used for communication or for echolocation. They are best known for their huge head, which makes up to one third of their body and contains a brain that weighs up to 9kg. Such massive bodies need a lot of food, around one ton per day. They eat squid and fish and dive on average a 1000m deep in search for their food. On these dives sperm whales have to hold their breath for 60 to 90 minutes. In the deep channel between the Saba Bank and St. Maarten numerous sperm whales were recorded and it is yet to be determined if these waters are on a frequented sperm whale migration path.

The waters around St. Maarten and Saba have proven to be important breeding areas for marine mammals. This was one of the reasons the conservation efforts for the Saba Bank and the Man of War Shoal Park were vigorously driven and finally succeeded in 2010. In October 2010 a decree was passed that prohibits anchoring of tankers and other big ships on the Saba Bank, the third largest submerged atoll in the world. This makes the Saba Bank the fifth largest marine protected area in the wider Caribbean.

A similar success was the establishment of the Man of War Shoal Marine Park in St. Maarten in late December 2010, the first protected area of St. Maarten. The area is of fundamental ecological, economic and cultural value as a home and migratory stop over for over 100 endangered and protected species. It is an area with a relatively healthy population of marine mammals including migratory whales and dolphins; numerous species of shark, sea turtles and fish species. As marine mammals travel at great speed and migrate to and from the Caribbean swimming also through Dutch Caribbean waters, the Dutch Government will establish a Marine Mammal Sanctuary before the end of this year.

Humpback whales frequent the warmer waters of the Caribbean during their breeding season from December to June before they migrate to their northern feeding grounds in the summer. Humpback whales feed on tiny shrimp-like krill, plankton and small fish that they stir up at the bottom of the sea, chase to the surface where they eat them. Humpbacks are powerful swimmers as they use their massive tail fin called fluke to propel themselves through the water and out of it. It is unclear if these leaps from the water are a way of cleansing their skin or if whales do it for fun. Scientists are also still determining the meaning of the humpback whales’ songs, which can be heard at great distances. These magic songs are most likely a way of communication with others and to attract potential mates. Humpback Whales frequent the warmer waters of the Caribbean during their breeding season from December to June before they migrate to their northern feeding grounds in the summer. Humpback Whales feed on tiny shrimp-like krill, plankton and small fish that they stir up at the bottom of the sea, chase to the surface where they eat them. Humpbacks are powerful swimmers as they use their massive tail fin called fluke to propel themselves through the water and out of it. It is unclear if these leaps from the water are a way of cleansing their skin or if whales do it for fun. Scientists are also still determining the meaning of the Humpback Whales’ songs, which can be heard at great distances. These magic songs are most likely a way of communication with others and to attract potential mates.

In a meeting representatives from the Netherlands, France, the US, and the Dominican Republic discussed how they could collaborate on the conservation of marine mammals. In all of these countries except the Netherlands marine mammal sanctuaries already exist. Some of these sanctuaries are working together with so-called sister sanctuary agreements. The French Agoa Sanctuary and the Dutch Caribbean islands are working together on surveys for marine mammals. The joint survey work will be continued in October and start in Aruba, Bonaire and Curaçao and continue through the arc of Eastern Caribbean islands via the French islands to the Dutch Windward Islands (SSS). In addition, a regional network of acoustic underwater listening posts has been set up. They record songs and other sounds produced by marine mammals but also document underwater noise generated by humans such as ships, jet skis and speedboats in order to assess the impact of these noises on the mammals.

reaching humpback whale at Stellwagen National Marine Sanctuary. Photo credit - Kai Wulf

Expertise is being exchanged to build capacity by mutual participation in joint work, standardization of methods and sharing of marine mammal data. One example of knowledge sharing was the participation of Kai Wulf, Managing Director of the Saba Conservation Foundation in a research trip at the Stellwagen Bank National Marine Sanctuary (SBNMS).

The Stellwagen Bank off the coast of Boston (USA) has been a marine sanctuary for decades and the research on humpback whales spans a time of over 30 years. This year the research cruise focused on observing the feeding behavior of humpback whales and study the animals’ techniques of utilizing the food resources within the sanctuary at day and night to discover potential variations. The research cruise followed the whales and tagged them with a radio tag. The process of tagging requires high expertise from the whole crew. Besides a skilled crew, the vessel was also equipped with advanced technology for data gathering, which was logged into the system on the ship.

Wulf has been inspired by his participation on board the research vessel and says that he returned with many lessons learned on how to monitor and research these mammals at the Saba Bank and the marine mammal sanctuary. He hopes that the ongoing relationship with the French Agoa will continue and the two sanctuaries will become sister sanctuaries of Stellwagen in order to further understanding for marine mammals and help protect them.

 

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